U.S. patent application number 15/029815 was filed with the patent office on 2016-08-25 for methods and systems for printing 3d object by inkjet.
This patent application is currently assigned to XJET LTD.. The applicant listed for this patent is XJET LTD.. Invention is credited to Axel BENICHOU, Yohai DAYAGI, Guy EYTAN, Hanan GOTHAIT, Oleg KODINETS, Eli KRITCHMAN, Lior LAVID, Wael SALALHA, Timofey SHMAL.
Application Number | 20160243619 15/029815 |
Document ID | / |
Family ID | 52827743 |
Filed Date | 2016-08-25 |
United States Patent
Application |
20160243619 |
Kind Code |
A1 |
GOTHAIT; Hanan ; et
al. |
August 25, 2016 |
METHODS AND SYSTEMS FOR PRINTING 3D OBJECT BY INKJET
Abstract
3D (three-dimensional) ink jet printing includes techniques for
evaporating a carrier liquid during printing while at least a
portion of dispersant remains in the printed layer; evaporating
dispersant in a first layer prior to sintering the first layer
and/or prior to printing a second layer; leveling an upper-layer of
a printed object using a horizontal roller; and printing layers of
an object, each layer with both object and support portions,
resulting in an object with support, in particular, support for
negative angles and molds.
Inventors: |
GOTHAIT; Hanan; (Rehovot,
IL) ; KRITCHMAN; Eli; (Tel Aviv, IL) ;
BENICHOU; Axel; (Givataylm, IL) ; SHMAL; Timofey;
(Holon, IL) ; EYTAN; Guy; (Kldron, IL) ;
SALALHA; Wael; (Beit Gan, IL) ; DAYAGI; Yohai;
(Hanegev, IL) ; KODINETS; Oleg; (Bat Yam, IL)
; LAVID; Lior; (Rishon Lezion, IL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
XJET LTD. |
Rehovot |
|
IL |
|
|
Assignee: |
XJET LTD.
Rehovot
IL
|
Family ID: |
52827743 |
Appl. No.: |
15/029815 |
Filed: |
October 17, 2014 |
PCT Filed: |
October 17, 2014 |
PCT NO: |
PCT/IB2014/065400 |
371 Date: |
April 15, 2016 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61891926 |
Oct 17, 2013 |
|
|
|
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B33Y 80/00 20141201;
B28B 1/001 20130101; B33Y 10/00 20141201; C09D 11/30 20130101; B33Y
30/00 20141201; A43D 2200/60 20130101; B29C 64/40 20170801; B22F
3/1055 20130101; B33Y 50/02 20141201; B28B 17/0081 20130101; B29C
64/112 20170801; B33Y 40/00 20141201; B22F 2003/1057 20130101; C09D
11/03 20130101; B29C 64/194 20170801; B22F 2003/1059 20130101; B33Y
70/00 20141201; C09D 11/033 20130101 |
International
Class: |
B22F 3/105 20060101
B22F003/105; B28B 17/00 20060101 B28B017/00; B28B 1/00 20060101
B28B001/00 |
Claims
1-62. (canceled)
63. A method for printing a three-dimensional object, the method
comprising: supplying ink to a printing head having a plurality of
nozzles, wherein the ink includes at least carrier liquid,
particles, and dispersant; dispensing the ink from the plurality of
nozzles to form a first layer; heating the first layer to a
temperature below the burn off temperature of the dispersant to
evaporate the carrier liquid; and repeatedly dispensing and heating
additional layers above the first layer until a three-dimensional
object is constructed.
64. The method of claim 63, wherein the ink includes metal
particles.
65. The method of claim 63, wherein the ink includes ceramic
particles.
66. The method of claim 63, wherein a size of the particles is
between about 5 nanometer and 10 micrometer.
67. The method of claim 63, wherein heating a previously dispensed
layer to evaporate the carrier liquid is done by at least one of:
an electromagnetic source, a warm tray, and hot air.
68. The method of claim 63, wherein the dispersant binds the
particles to each other after evaporation of the liquid
carrier.
69. The method of claim 63, further comprising: cooling a
previously dispensed layer before dispensing ink to form a new
layer on top the previously dispensed layer.
70. The method of claim 63 further comprising: using a leveling
apparatus to peel off between about 5% and 30% of material of a
previously dispensed layer.
71. The method of claim 70, further comprising: applying sucking
force via a pipe to prevent scattering of particle waste when the
leveling apparatus peels off material of the previously dispensed
layer.
72. The method of claim 63, further comprising: heating a
previously dispensed layer to or above the burn off temperature of
the dispersant to disintegrate at least a portion of the
dispersant.
73. The method of claim 72, wherein heating the previously
dispensed layer to disintegrate at least a portion of the
dispersant comprises heating via at least one of: a laser, a
focused linear laser beam, a scanned focused pencil laser beam,
focused light from a linear incandescent bulb, and focused light
from a gas discharge lamp bulb.
74. The method of claim 72, wherein disintegrating at least a
portion of the dispersant includes removing substantially all of
the dispersant from the three-dimensional object.
75. The method of claim 72, wherein disintegrating the at least a
portion of the dispersant comprises bringing the remaining
dispersant in the three-dimensional object to a final concentration
less than 0.1%.
76. An additive manufacturing system for printing a
three-dimensional object, the system comprising: a printing head
with a plurality of nozzles configured to dispense ink including at
least carrier liquid, particles, and dispersant to form a first
layer; an energy source configured to supply heat to the first
layer to a temperature below a burn off temperature of the
dispersant to evaporate the carrier liquid; and a processor
configured to instruct the printing head and the energy source to
repeatedly dispense and heat additional layers above the first
layer until a three-dimensional object is constructed.
77. The additive manufacturing system of claim 76, wherein the
processor is further configured to control the energy source in
order to maintain a temperature of the three-dimensional object
being printed in a pre-defined range of temperatures.
78. The additive manufacturing system of claim 76, further
including a thermal buffer between the heated first layer and the
plurality of nozzles.
79. The additive manufacturing system of claim 76, further
including a leveling apparatus configured to peel off material from
a previously dispensed layer.
80. The additive manufacturing system of claim 76, wherein the
energy source is further configured to supply heat to a previously
dispensed layer to or above the burn off temperature of the
dispersant to disintegrate at least a portion of the
dispersant.
81. The additive manufacturing system of claim 76, further
including an additional energy source configured to supply heat
above the burn off temperature of the dispersant to disintegrate at
least a portion of the dispersant.
82. A three-dimensional object, manufactured using an additive
manufacturing process comprising: supplying ink to a printing head
having a plurality of nozzles, wherein the ink includes at least
carrier liquid, particles, and dispersant; dispensing the ink from
the plurality of nozzles to form a first layer; heating the first
layer to a temperature below a burn off temperature of the
dispersant to evaporate the carrier liquid; and repeatedly
dispensing and heating additional layers above the first layer
until a three-dimensional object is constructed.
Description
FIELD OF THE INVENTION
[0001] The present invention generally relates to 3D
(three-dimensional) printing.
BACKGROUND OF THE INVENTION
[0002] The 3D (three-dimensional) printing market is maturing
rapidly (2014). 3D printing or additive manufacturing (AM) is any
of various processes for making a 3D object of almost any shape
from a 3D model or other electronic data source primarily through
additive processes in which successive layers of material are laid
down under computer control. A 3D printer is a type of industrial
robot.
[0003] Conventional processes include stereo lithography employing
UV lasers to cure photopolymers, inkjet printers utilizing UV lamps
to cure photopolymers, metal sintering (such as selective laser
sintering and direct metal laser sintering), plastic extrusion
technology, and deposition of liquid binder on powder.
[0004] 3D printing is used in applications such as product
development, data visualization, rapid prototyping, specialized
manufacturing, and production (job production, mass production, and
distributed manufacturing). Fields of use are many, including
architecture, construction (AEC), industrial design, automotive,
aerospace, military, engineering, dental and medical industries,
biotech (human tissue replacement), fashion, footwear, jewelry,
eyewear, education, geographic information systems, food, and many
other fields.
SUMMARY
[0005] According to the teachings of the present embodiment there
is provided a method for printing an object including the steps of:
[0006] (a) printing a first layer of at least one ink, each of the
at least one ink including: [0007] (i) a carrier having a carrier
boiling point temperature (T1); [0008] (ii) a dispersant having a
dispersant boiling point temperature (T2); and [0009] (iii)
particles having a particle sintering temperature (T3), [0010] (b)
while maintaining a temperature of the first layer (TL) in a
pre-defined range of temperatures, [0011] (c) wherein the
pre-defined range of temperatures is above a lower-bound ([T1]) of
the carrier boiling point temperature and below an upper-bound
([T2]) of the dispersant boiling point temperature
([T1]<TL<[T2]), thus evaporating the carrier while the
dispersant remains in the first layer.
[0012] According to the teachings of the present embodiment there
is provided a method for printing an object including the steps of:
[0013] (a) printing a first layer of at least one ink, each of the
at least one ink including: [0014] (i) a carrier having a carrier
boiling point temperature (T1); [0015] (ii) a dispersant having a
dispersant boiling point temperature (T2); and [0016] (iii)
particles having a particle sintering temperature (T3), [0017] (b)
evaporating at least a portion of the dispersant; and [0018] (c)
performing a subsequent operation selected from the group
consisting of: [0019] (i) at least partially sintering the first
layer; and [0020] (ii) repeating step (a) by printing a subsequent
layer of the at least one ink on the first layer.
[0021] In an optional embodiment, the printing is via at least one
printing head jetting the at least one ink. In another optional
embodiment, at least one of the printing heads is modulated
according to a content of the first layer.
[0022] In another optional embodiment, the carrier is a liquid, the
particles are a material used to construct the object and dispersed
in the carrier liquid, and the dispersant is dissolved in the
carrier liquid, adhere to the particles' surface, and inhibit
agglomeration of the particles to each other.
[0023] In another optional embodiment, further including a step of
evaporating the carrier prior to the step of evaporating at least a
portion of the dispersant. In another optional embodiment, the
dispersant binds the particles to each other after the carrier is
evaporated. In another optional embodiment, the dispersant inhibits
sintering of the particles to each other after the carrier is
evaporated. In another optional embodiment, the printing is
selective, printing to areas that are part of the first layer of
the object. In another optional embodiment, the object is printed
on a tray made of a thermal isolation material.
[0024] In another optional embodiment, a temperature of the upper
surface (TS) of the object is at least 4% higher than the carrier
boiling point temperature T1, thereby creating a porous structure
in the object's printed lattice. In another optional embodiment,
the lower-bound ([T1]) includes 20% less than the carrier boiling
point temperature (T1) in degrees Kelvin. In another optional
embodiment, the upper-bound ([T2]) is 20% more or less than the
dispersant boiling point temperature (T2) in degrees Kelvin.
[0025] In another optional embodiment, the step of maintaining is
via use of a source selected from the group consisting of: a heated
tray; an electro-magnetic (EM) radiation source above the object;
and a hot gas.
[0026] In another optional embodiment, the printing is selective,
printing to areas that are part of the first layer of the object
and the EM radiation source is non-selective, irradiating an entire
area on which the object is being printed.
[0027] In another optional embodiment, further including a step of:
evaporating at least a portion of the dispersant. In another
optional embodiment, further including a step of: at least
partially sintering the particles. In another optional embodiment,
further including a step of: printing a subsequent layer of the at
least one ink on the first layer of at least one ink.
[0028] In another optional embodiment, the step of evaporating the
dispersant is via use of an EM radiation source selected from the
group consisting of: a heating lamp; a laser; focused linear laser
beam; a scanned focused pencil laser beam; focused light from a
linear incandescent bulb; focused light from a gas discharge lamp
bulb; a flash light; an ultra-violet (UV) light source; a visible
light source; and an infrared (IR) light source.
[0029] In another optional embodiment, the printing is selective,
printing to areas that are part of the first layer of the object
and the EM radiation source is non-selective, irradiating an entire
area on which the object is being printed. In another optional
embodiment, the scanned laser beam is modulated according to a
content of the layer.
[0030] In another optional embodiment, at least two inks are
printed, each of the at least two inks including particles of
different types, and a local proportion of each of the at least two
inks is determined by the first layer's specification.
[0031] In another optional embodiment, the particles are selected
from a group consisting of: metal; metal oxides; metal carbides;
metal alloys; inorganic salts; polymeric particles; Polyolefin; and
poly (4-methyl 1-pentene).
[0032] In another optional embodiment, after the step of at least
partially sintering the object, then repeating step 2(a) by
printing a subsequent layer of the at least one ink on the first
layer. In another optional embodiment, a catalyst is added to the
first layer. In another optional embodiment, the catalyst is added
via a technique selected from the group consisting of: including
the catalyst in at least one of the inks; jetting the catalyst in
gaseous form from above the first layer; jetting the catalyst in
liquid form from above the first layer; spraying the catalyst in
gaseous form from above the first layer; and spraying the catalyst
in liquid form from above the first layer.
[0033] In another optional embodiment, the catalyst is selected
from the group consisting of: a halide compound; and a copper
chloride compound.
[0034] According to the teachings of the present embodiment there
is provided a system for printing an object including: at least one
printing head configured to print a first layer of at least one
ink, each of the at least one ink including: a carrier having a
carrier boiling point temperature (T1); a dispersant having a
dispersant boiling point temperature (T2); and particles having a
particle sintering temperature (T3), a controller configured to
maintain a temperature of the first layer (TL) in a pre-defined
range of temperatures, wherein the pre-defined range of
temperatures is above a lower-bound ([T1]) of the carrier boiling
point temperature and below an upper-bound ([T2]) of the dispersant
boiling point temperature ([T1]<TL<[T2]), thus evaporating
the carrier while the dispersant remains in the first layer.
[0035] According to the teachings of the present embodiment there
is provided a system for printing an object including: at least one
printing head configured to print a first layer of at least one
ink, each of the at least one ink including: a carrier having a
carrier boiling point temperature (T1); a dispersant having a
dispersant boiling point temperature (T2); and particles having a
particle sintering temperature (T3), a controller configured for:
evaporating at least a portion of the dispersant; and subsequent
operation selected from the group consisting of at least partially
sintering the first layer; and repeating step (a) by printing a
subsequent layer of the at least one ink on the first layer.
[0036] In an optional embodiment, at least one of the printing
heads is an ink-jet head configured to print the at least one ink
via jetting. In another optional embodiment, at least one of the
printing heads is modulated according to a content of the first
layer.
[0037] In another optional embodiment, the carrier is a liquid; the
particles are a material used to construct the object and dispersed
in the carrier liquid; and the dispersant is dissolved in the
carrier liquid, adhere to the particles' surface, and inhibit
agglomeration of the particles to each other.
[0038] In another optional embodiment, the printing is selective,
printing to areas that are part of the first layer of the object.
In another optional embodiment, the object is printed on a tray
made of a thermal isolation material. In another optional
embodiment, the lower-bound ([T1]) includes 20% less than the
carrier boiling point temperature (T1) in degrees Kelvin. In
another optional embodiment, the upper-bound ([T2]) is 20% more or
less than the dispersant boiling point temperature (T2) in degrees
Kelvin.
[0039] In another optional embodiment, the step of maintaining is
via use of a source selected from the group consisting of: a heated
tray; an electro-magnetic (EM) radiation source above the object;
and a hot gas.
[0040] In another optional embodiment, the printing is selective,
printing to areas that are part of the first layer of the object
and the EM radiation source is non-selective, irradiating an entire
area on which the object is being printed. In another optional
embodiment, the step of evaporating the dispersant is via use of an
EM radiation source selected from the group consisting of: a
heating lamp; laser; a focused linear laser beam; a scanned focused
pencil laser beam; focused light from a linear incandescent bulb;
focused light from a gas discharge lamp bulb; a flash light; an
ultra-violet (UV) light source; a visible light source; and an
infrared (IR) light source.
[0041] In another optional embodiment, including at least two
printing heads configured to print at least two inks, each of the
at least two inks including particles of different types, and a
local proportion of each of the at least two inks is determined by
the first layer's specification.
[0042] According to the teachings of the present embodiment there
is provided a method for printing an object including the steps of:
[0043] (a) printing a first layer of at least one ink; [0044] (b)
at least partially hardening the first layer; and [0045] (c)
leveling the first layer using a horizontal roller, the horizontal
roller having a rotation axis generally parallel to a plane of the
first layer.
[0046] In an optional embodiment, the horizontal roller is mounted
on a horizontal axis with respect to a plane of the first layer. In
another optional embodiment, the horizontal roller is selected from
the group consisting of: grinding roller having an abrasive
surface; a cutting roller having discrete blades; a cutting roller
having spiral blades; and a cutting roller having discrete blades
of steel and/or Tungsten Carbide.
[0047] In another optional embodiment, particle waste produced from
leveling is removed from the first layer via use of a technique
selected from the group consisting of: suction; and suction via a
pipe through a dust filter.
[0048] In another optional embodiment, the horizontal roller is
heated to a roller temperature higher than a layer temperature of
the first layer, using a heating source selected from the group
consisting of: a heat source external to the roller; a heat source
internal to the roller; and a static internal heat source. In
another optional embodiment, further including a step of: printing
a subsequent layer of at least one ink on the first layer.
[0049] According to the teachings of the present embodiment there
is provided a system for printing an object, the system including:
at least one printing head configured to print a first layer of at
least one ink; a horizontal roller having a rotation generally
perpendicular to a plane of the first layer; and a controller
configured for at least partially hardening the first layer; and
leveling the first layer using the horizontal roller.
[0050] In an optional embodiment, the horizontal roller is mounted
on a horizontal axis with respect to a plane of the first layer. In
another optional embodiment, the roller is selected from the group
consisting of: a grinding roller having an abrasive surface; a
cutting roller having discrete blades; a cutting roller having
spiral blades; and a cutting roller having discrete blades of steel
and Tungsten Carbide.
[0051] According to the teachings of the present embodiment there
is provided a method for printing an object with support, the
method including the steps of [0052] (a) printing an object portion
of a first layer using at least a first ink, the first ink
including: [0053] (i) a first carrier; and [0054] (ii) first
particles used to construct the object and dispersed in the first
carrier, [0055] (b) printing a support portion of the first layer
using at least a second ink, the second ink including: [0056] (i) a
second carrier; and [0057] (ii) second particles used to construct
the support and dispersed in the second carrier.
[0058] In an optional embodiment, the first and second carriers are
liquids.
[0059] In another optional embodiment, further including a step of
printing a subsequent layer including respective object and support
portions on the first layer.
[0060] In another optional embodiment, the second particles are
selected from a group consisting of miscible in water; at least
partially soluble in water; inorganic solid; organic; polymer;
particles having a hardness less than the hardness of the first
particles; salt; Metal oxides; Silica (SiO.sub.2); Calcium sulfate;
and tungsten carbide (WC).
[0061] In another optional embodiment, further including removing
the support using a technique on the object with support, the
technique selected from the group consisting of: firing; immersing
to dissolve the support; immersing in water to dissolve the
support; immersing in acid; sand blasting; and water jetting.
[0062] In another optional embodiment, the particles are selected
from a group consisting of: metal; metal oxides; metal carbides;
metal alloys; inorganic salts; polymeric particles; Polyolefin; and
poly (4-methyl 1-pentene).
[0063] According to the teachings of the present embodiment there
is provided a system for printing an object with support, the
system including: at least one printing head a controller
configured for: printing, via the at least one printing head, an
object portion of a first layer using at least a first ink, the
first ink including: a first carrier; and first particles used to
construct the object and dispersed in the first carrier, printing,
via the at least one printing head, a support portion of the first
layer using at least a second ink, the second ink including: a
second carrier; and second particles used to construct the support
and dispersed in the second carrier.
[0064] In an optional embodiment, the second carrier is the first
carrier. In another optional embodiment, the second particles are
other than the first particles. In another optional embodiment, the
printing a support portion is additionally with the first ink. In
another optional embodiment, the printing an object portion is via
at least a first printing head jetting the first ink and the
printing a support portion is via at least a second printing head
jetting the second ink. In another optional embodiment, at least
one of the printing heads is modulated according to a content of
the first layer.
[0065] According to the teachings of the present embodiment there
is provided a computer program that can be loaded onto a server
connected to a network, so that the server running the computer
program constitutes a controller in a system implementing any one
of the above system claims.
[0066] A computer-readable storage medium having embedded thereon
computer-readable code for printing an object, the
computer-readable code comprising program code for: [0067] (a)
printing a first layer of at least one ink, each of the at least
one ink including: [0068] (i) a carrier having a carrier boiling
point temperature (T1); [0069] (ii) a dispersant having a
dispersant boiling point temperature (T2); and [0070] (iii)
particles having a particle sintering temperature (T3), [0071] (b)
while maintaining a temperature of the first layer (TL) in a
pre-defined range of temperatures, [0072] (c) wherein the
pre-defined range of temperatures is above a lower-bound ([T1]) of
the carrier boiling point temperature and below an upper-bound
([T2]) of the dispersant boiling point temperature
([T1]<TL<[T2]), thus evaporating the carrier while the
dispersant remains in the first layer.
[0073] A computer-readable storage medium having embedded thereon
computer-readable code for printing an object, the
computer-readable code comprising program code for: [0074] (a)
printing a first layer of at least one ink, each of the at least
one ink including: [0075] (i) a carrier having a carrier boiling
point temperature (T1); [0076] (ii) a dispersant having a
dispersant boiling point temperature (T2); and [0077] (iii)
particles having a particle sintering temperature (T3), [0078] (b)
evaporating at least a portion of the dispersant; and [0079] (c)
performing a subsequent operation selected from the group
consisting of: [0080] (i) at least partially sintering the first
layer; and [0081] (ii) repeating step (a) by printing a subsequent
layer of the at least one ink on the first layer.
[0082] A computer-readable storage medium having embedded thereon
computer-readable code for printing an object, the
computer-readable code comprising program code for: [0083] (a)
printing a first layer of at least one ink; [0084] (b) at least
partially hardening the first layer; and [0085] (c) leveling the
first layer using a horizontal roller, the horizontal roller having
a rotation axis generally parallel to a plane of the first
layer.
[0086] A computer-readable storage medium having embedded thereon
computer-readable code for printing an object, the
computer-readable code comprising program code for: [0087] (a)
printing an object portion of a first layer using at least a first
ink, the first ink including: [0088] (i) a first carrier; and
[0089] (ii) first particles used to construct the object and
dispersed in the first carrier, [0090] (b) printing a support
portion of the first layer using at least a second ink, the second
ink including: [0091] (i) a second carrier; and [0092] (ii) second
particles used to construct the support and dispersed in the second
carrier.
BRIEF DESCRIPTION OF FIGURES
[0093] The embodiment is herein described, by way of example only,
with reference to the accompanying drawings, wherein:
[0094] FIG. 1 is a simplified diagram of 3D printing an individual
layer.
[0095] FIG. 2A is a simplified diagram of leveling apparatus.
[0096] FIG. 2B is a simplified diagram of leveling apparatus with
warming sources.
[0097] FIG. 3A is a simplified exemplary system for 3D
printing.
[0098] FIG. 3B is a diagram of a lamp as an exemplary radiation
source.
[0099] FIG. 3C is a diagram of a lamp as an exemplary radiation
source.
[0100] FIG. 4A is a simplified diagram of a system for removing
fumes during printing.
[0101] FIG. 5 is a simplified diagram of a system for removing
fumes during printing using an alternative radiation source.
[0102] FIG. 6A is a diagram of solid particles with small
edges.
[0103] FIG. 6B is a diagram of solid particles with bridged
sintering by smaller particles.
[0104] FIG. 7 is a diagram of partial sintering.
[0105] FIG. 8A is a diagram of dispensing catalyst material.
[0106] FIG. 9 is a diagram of using a liquid pump roller.
[0107] FIG. 10A is a diagram of objects built with different
materials.
[0108] FIG. 10B is a diagram of objects built with a mix of
materials.
[0109] FIG. 11A is a diagram of support when building a 3D
object.
[0110] FIG. 11B is a diagram of printing support portions and
object portions of layers.
[0111] FIG. 11C is a diagram of using reinforcing support
columns.
[0112] FIG. 12 is a diagram of an exemplary carousel machine for
production of 3D objects.
[0113] FIG. 13 is a high-level partial block diagram of an
exemplary system configured to implement a controller for the
present invention.
DETAILED DESCRIPTION
FIGS. 1 to 13
1. Overview
[0114] The principles and operation of the system and method
according to a present embodiment may be better understood with
reference to the drawings and the accompanying description. A
present invention is a system and method for 3D (three-dimensional)
printing by dispensing ink including particles of any chosen
material. Typically, the particles in the dispensed ink are micro
or nano particles. Either during the printing or following the
printing, the particles combine to each other (i.e. sinter) to form
solid or porous solid material. The system facilitates: [0115]
Building a 3D structure, [0116] Discharging the organic components,
[0117] Sintering the particles, [0118] Preventing deformation, and
[0119] Stable ink dispersion.
[0120] In the context of this document, the term "object" generally
refers to an item that a user desires to produce, in particular via
3D printing. In other words, the term "object" refers to an item to
be produced by the 3D printing process. During printing, the term
"object" can refer to an incomplete or partially generated
item.
[0121] In the context of this document, the terms "burn out" or
"burn off", "fire-off", or "firing-off" refer to evaporating or
disintegrating and evaporating a component of the ink.
[0122] In the context of this document, the mathematical sing for
power may appear as " ", e.g. cm 2 means centimeter square.
[0123] In the context of this document, the terms "printing liquid"
and "ink" refer in general to a material used for printing, and
includes, but is not limited to homogeneous and non-homogenous
materials, for example a carrier liquid containing a dissolved
material such as metal particles to be deposited via the printing
process.
[0124] In the context of this document, the term "dispersion"
generally refers to particles distributed and suspended in a liquid
or gas and/or distributed evenly throughout a medium.
[0125] In the context of this document, the term "pencil laser
beam" generally refers to a laser beam that can be focused to a
point, while "linear laser beam" refers to a laser beam that can be
focused to a line.
[0126] In the non-limiting examples used in this document,
generally the following notation is generally used to refer to
temperatures: [0127] T1 is boiling temperature of a carrier liquid.
[0128] T2 is organics (dispersant and additives) burn out
(fire-off, evaporation) temperature, often referred to as
"dispersant boiling point". [0129] T3 is particles' characteristic
temperature of sintering (depending on particles material and
size). [0130] TS is temperature of the upper surface of the object
on which the new layer is dispensed. In some embodiments, TS is
maintained substantially equal to the body temperature of the rest
of the object during printing. [0131] TL is temperature of the
layer currently being printed (also referred to in the context of
this document as the upper-layer, most recent layer, new layer, or
first layer). Note that the temperature of the new layer optionally
changes during printing of the new layer, as initially the new
layer gets the temperature of the upper surface on which the new
layer was dispensed (TS), and optionally later the temperature of
the new layer increases as a result of additional heat that is
applied to the new layer by auxiliary heat sources. Thus, TL is
defined as the maximum temporal temperature of the new layer
[0132] Although embodiments are described with regard to an inkjet
printing head, the described system and method is generally
applicable to liquid-ejection nozzles of a liquid-ejection
mechanism, such as nozzle dispensers. Liquid-ejection nozzles are
also referred to as dispensing heads.
2. 3D Inkjet Printing
[0133] A preferred embodiment is using inkjet printing heads for
dispensing ink. Another option is to use spray nozzles. Typically,
inkjet printing provides increased speed, finer object dimensions,
and increased quality of finished objects as compared to spray
nozzles. The inkjet heads normally dispense the ink layer-by-layer,
dispensing subsequent layers on previously dispensed layers.
Typically, each layer is hardened before dispensing the succeeding
layer. Preferably, the inkjet heads dispense each layer according
to the image content of that layer. Alternatively, the inkjet heads
"blindly" dispense the layer, and a hardening tool (e.g. a scanning
laser beam) hardens the layer according to the layer's specific
image content.
3. Ink
[0134] Generally, a printing system will include more than one type
of ink. Inks include object ink and support ink. Object ink is used
to produce the desired object, and support ink is used temporarily
during printing, for example to support "negative" tilted walls of
the object. In embodiments described in this document, inks
typically include the following ingredients:
[0135] a. Micro or Nano Particles.
[0136] The ink includes a dispersion of solid particles of any
required material, e.g. metals (iron, copper, silver, gold,
titanium etc.), metal oxides, oxides (SiO.sub.2, TiO.sub.2, BiO2
etc.), metal carbides, carbides (WC, Al4C3, TiC), metal alloys
(stainless steel, Titanium Ti64 etc.), inorganic salts, polymeric
particles, etc., in volatile carrier liquid. The particles are of
micro (0.5 to 50 micrometer size) or nano (5 to 500 nanometer size)
as required to maintain the required spatial resolution during
printing, maintain the required material character (after
sintering), or to satisfy limitations of a dispensing head. For
example, when the dispensing head is an inkjet array of nozzles,
including nozzles of 30=micrometer or micron) diameter, the
particle size should preferably be equal or smaller than 2.mu.. In
the context of this document, the term "particles" generally refers
to solid particles used to construct (print) the object and/or the
"bulk material" of the object. The use of the term particles will
be obvious from context.
[0137] b. Carrier Liquid.
[0138] The particles are dispersed in a carrier liquid, also
referred to as a "carrier" or "solvent". A dispersing agent (often
call dispersant) assist in dispersing the particles in the liquid.
According to one embodiment, the liquid should evaporate
immediately after printing so that the succeeding layer is
dispensed on solid material below. Hence, the temperature of an
upper layer of the object during printing should be comparable with
the boiling temperature of the carrier. In another embodiment, the
temperature of the upper printed layer is much higher than the
boiling temperature of the liquid carrier, encouraging thereby the
evaporation of other organic materials like dispersants or various
additives in the carrier. Conventional dispersants are readily
available, such as polymeric dispersants such as Disperbyk 180,
disperbyk 190, disperbyk 163, from Byk Chemie GMBH. Conventional
particle ink is readily available such as commercial SunTronic Jet
Silver U6503, from Sun Chemicals Ltd. (485 Berkshire Av, Slough,
UK).
[0139] c. Dissolved Material.
[0140] At least part of a solid material to be used to construct
(print) the object can be dissolved in the ink. For example, a
dispersion of silver (Ag) particles, which in addition to the Ag
particles includes a fraction of Ag organic compound dissolved in
the carrier liquid. After printing and during firing, the organic
portion of the Ag organic compound fires off, leaving the metal
silver atoms well spread. This conventional ink is readily
available such as Commercial DYAG100 Conductive Silver Printing
Ink, from Dyesol Inc. (USA), 2020 Fifth Street #638, Davis Calif.
95617.
[0141] d. Dispersing Agent.
[0142] In order to sustain particle dispersion, a dispersing agent
(also referred to as a dispersant) is used in the ink. Dispersants
are known in the industry, and are often a kind of polymeric
molecule. In general, the dispersing molecules (molecules of the
dispersant) adhere to the (solid) particle's surface (i.e. wrap the
particles) and inhibit agglomeration of the particles to each
other. When more than one solid particle species are dispersed in
the dispersion, using the same dispersant material for all solid
particle species is preferred so compatibility problems between
different dispersant materials are avoided. The dispersing agent
should also be able to dissolve in the carrier liquid so that a
stable dispersion can be formed.
[0143] In conventional printing, the dispersant remains in the
final object, typically at concentrations of about 10%. While
having dispersant as part of a final 3D product may be acceptable
for the construction of some objects, for other objects there is an
essential need to remove substantially all of the dispersant. For
example, to have the final concentration of dispersant be less than
0.1%. This is because: [0144] a. the dispersing material prevents
intimate touch of the particles with each other, and thereby
prevents full sintering, and [0145] b. the dispersing material
weakens the solidified 3D structure (for example, if the dispersant
agglomerates and remains as "islands" in the bulk material). [0146]
Hence, in some embodiments the dispersant must be removed before
final sintering.
4. Nozzle Scatter
[0147] Refer to FIG. 1, a simplified diagram of 3D printing an
individual layer. A printing head 100 is shown in a first position
100A when preparing to print a first layer 104 of the object, and
in a second position 100B when preparing to print a subsequent
layer of the object. The printing head 100 (e.g. inkjet head)
includes a nozzle array 102 that scans the layer 104 in an X
direction substantially perpendicular to the longitudinal axis Y of
the layer 104.
[0148] The jetted droplet volume of different individual nozzles
(of the nozzle array 102) may be slightly different from each other
individual nozzle (of the nozzle array 102) because of technology
deficiency of the head 100 construction. Moreover, a nozzle can
stop jetting as the nozzle can become clogged by aggregated ink
particles or because of other reasons. In order to maintain a flat
upper surface of the object being printed, and especially avoiding
deep vacant lines in the 3D printed object, the head 100 is shifted
along the Y-axis before every subsequent layer is printed. The
shift amount from layer to layer may be set random within a
predetermined shift range.
5. Leveling Apparatus
[0149] Due to many reasons, including different jetting power (i.e.
droplet volume) of the different nozzles, edge rounding due to
liquid surface tension of the ink at the edge of a layer, and other
known phenomena, the dispensed layer may not be perfectly flat (be
too rough), and the dispensed layer's edge may not be perfectly
sharp (be too rounded). Therefore, a leveling apparatus should be
incorporated to flatten (level) the upper layer and/or sharpen
(square off) one or more edges of the upper layer. In one
embodiment, the appropriate leveling apparatus includes a vertical
grinding roller or cutting (machining) roller. In a preferred
embodiment, the appropriate leveling apparatus includes a
horizontal (i.e. parallel to the printing surface) grinding roller
or cutting (machining) roller.
[0150] Refer now to FIG. 2A, a simplified diagram of leveling
apparatus and FIG. 3A, a simplified exemplary system for 3D
printing.
[0151] A 3D object 312 is typically constructed layer-by-layer on a
substrate or tray. The tray is typically heated, and a non-limiting
example of a heated tray 318 is generally used in this description.
As described above, the object is printed in the plane of the X-Y
axis, and a newly formed layer 310 (also referred to in the context
of this document as the upper-layer) is built along the Z-axis
during every printing pass. Ink 322 is supplied or contained in a
printing head 314. Optional cooling mask 316, windshield 324,
thermal partition 320 are used to protect the printing head 314
from the other printing equipment and/or vice versa. Optional
radiation source 308 and/or cooling fan 326 can be used to assist
with temperature control of the newly printed layer and/or 3D
object body 312. Optional leveling roller 302 can be used during
printing to smooth the surface of the newly formed layer 310 and/or
the top surface (outermost surface along the Z-axis) of the 3D
object body 312. An optional dust filter 306 can be used to suck
the dust output of leveling.
[0152] Leveling apparatus are also known in the field as "leveling
rollers" or simply "rollers". The leveling apparatus operates on a
newly formed layer 310 of a 3D object 312 after or as the layer
has/is being been printed (dispensed and solidified). The leveling
apparatus typically peels off between 5% and 30% of material of the
most recently printed layer's height. In other words, shaving the
top of the first layer (most recently printed layer). The roller
meets the ink after the carrier liquid ink has evaporated and the
layer is at least partially dry and solid. In some cases, solid
means "a piece of metal", i.e. well sintered particles. In other
cases, solid means a pile of particles adhered to each other by
organic material or by some initial sintering. The leveling roller
302 may be a grinding roller 202 including a metal cylinder 204
with an abrasive surface 206, for example coated with hard grinding
particles, e.g. WC (Tungsten carbide) or diamond "dust".
Alternatively, the leveling roller 302 may be a cutting roller 212
(also referred to in the context of this document as a "bladed"
roller) including a milling cutting tool 214 with sharp blades 216.
Smooth and knurled rollers 202 are known in the art, for example
smooth rollers as taught by Kritchman in U.S. Pat. No. 8,038,427
and knurled rollers as taught by Leyden in U.S. Pat. No. 6,660,209.
A smooth roller is typically used to meter a liquid layer of
material, and acts like a delicate shaving pump. A knurled roller,
typically adapted to meter soft wax surface, consists of a
multitude of relatively small knurls, or particles, as compared to
the size of the cylinder 204 and/or relative to the size of the
object to be ground. In contrast, a typical cutting roller 212
features discrete blades 216 that can be relatively large compared
to the size of the object to be ground. Neither smooth nor knurled
rollers can be adapted to level dry solid material for many
reasons. In addition, when using a grinding roller 202 (and also
smooth and knurled rollers), the grinding roller is substantially
constantly in contact with the object to be leveled. In contrast, a
cutting roller 212 is intermittently in contact with the object to
be ground--only when the edge of a blade 216 encounters the surface
to be leveled. Among the reasons that a knurled roller can be
adapted to level dry solid material, is the direction of force that
the vertical roller applies onto the shaped surface. When a
rotating blade touches the surface, the blade first cuts in by
applying horizontal force, and second lifts the cut chip up by
applying upward force. When a rotating knurl touches the surface,
the knurl first presses and pushes the material both downward and
forward by applying downward and horizontal force, and second
pushes the detached material up by applying forward and upward
force. The downward force may be harmful to delicate object
features, since the downward force will easily break the fragile
object features.
[0153] In general, when referring to axis and orientations of
rollers, reference is to the plane of printing, shown as the X-Y
axis in the accompanying figures. In conventional implementations,
vertical milling or smoothing tools, including multiple cutting
blades or grinding disk (e.g. including diamond dust surface), are
mounted to a vertical beam that is perpendicular to the plane of
printing/plane of the upper surface of the object, and rotates
about the beam. These vertical milling tools are used to level the
upper-layer (most recently printed and at least partially
solidified). The cutting or grinding surface of the vertical tools
is parallel to the plane of printing, but the rotation vector
points vertically upwards. In an innovative embodiment, the
leveling roller is mounted on a horizontal axis and rotates about a
horizontal axis (horizontal to the plane of the upper layer of the
object), thus providing a horizontal roller. The grinding surface
of a horizontal roller at the point of contact (touch) with the
material is generally also horizontal (parallel to the plane of
printing), but the rotation vector is horizontal (points
horizontally, perpendicular to the sweep direction X). The
horizontal roller rotates about a horizontal axis 220 relative to
the layer being ground. In other words, the outer surface of the
roller (or the blade's tip) moves horizontally at the point of
contact with the object's new layer. The horizontal roller can be a
grinding roller 202, or preferably, the horizontal roller allows
implementation with a cutting (bladed) roller 212. A feature of the
horizontal roller as compared to the vertical tools is the
feasibility to collect outcome dust (including shaved material).
While a vertical tool ejects the dust to all directions pointing
outward from the vertical axle (i.e. all around directions parallel
to the printing surface), a horizontal roller lifts the dust upward
in such manner that the dust can be more easily collected and
pumped out, such as via into a dust filter 306. In addition, the
vertical tool can be very sensitive to precise alignment, since the
vertical tool touches the printing surface all over the vertical
tool's horizontal surface. When the vertical axle deviates by an
angle of a from ideal verticality (towards X direction), the tool's
horizontal surface also deviates by the same angle of a from ideal
horizontality. In this case, the processed upper surface of the
object will not be flat in Y direction but rather having a banana
shape (lower in the middle). Quantitatively, if the radius of the
rotated blades or grinding surface is e.g. R=50 mm, the amount of
the banana effect will be .DELTA.Z=.alpha.*R (* means
multiplication, and a expressed in radians). Thus .alpha.=1
milliradian (i.e. .alpha.=0.06.degree., which is difficult to
achieve) results in .DELTA.Z=50 micron, which is hardly acceptable.
In comparison to this very sensitive alignment, a horizontal roller
touches the printing surface substantially only at a line, and
therefore there is no need to align a horizontal roller in the
X-axis direction. A substantial disadvantage of the grinding
surface in comparison to the cutting bladed roller/tool is that the
grinding surface is vulnerable to dust (shaved particles) sticking
to the diamond dust (of the grinding surface) and disturb thereby
proper grinding.
[0154] Experiments have shown that the smaller a chip that a blade
abrades from the object surface at a touch, the smaller will be the
tendency of fine details to break. In one implementation, the
cutting roller includes N blades and rotates at an F RPM
(revolution per minute), and the relative sweep velocity between
the roller and the object in X direction is V. For a given V, the
smallest chip is obtained when N and F are set to maximum values.
Experiments have also shown that using a spiral blade in comparison
to using a straight blade has also positive influence on preventing
harm to delicate details, since a spiral blade cuts only a
relatively small spot (as compared to a straight blade) in the
shaved surface at a time, while the spot's neighboring area holds
the spot from breaking. Successful results (no breakage) were
obtained with a horizontal roller including N=40, F=3500 RPM,
spiral blades (1 revolution per 150 mm roller length), V=100 mm/s
(roller diameter=25 mm). The roller material should be such that,
a. the blades can be highly sharpened, and b. the blades should
withstand the impact with the printed particles that the blades
shave. Both requirements dictate use of a hard material. Successful
results (no breakage and long blade life) were obtained with
cutting rollers made of, a. "high speed steel", and b. "Tungsten
Carbide" material (i.e. WC+Co).
[0155] For simplicity in this description, the orientation of a
horizontal roller is described as being perpendicular to the
direction of sweep during printing. However, one skilled in the art
will realize that the orientation does not have to be (can be other
than) strictly perpendicular and may be at an angle (non-zero) to
the sweep direction.
[0156] The rotation direction 222 of the cutting roller 212 vs. the
relative sweep direction between the roller and the object can be
either in the "cutting and lifting" direction (for example,
clockwise in FIG. 2A and FIG. 2B), or in the "dig and push"
direction (counter clockwise in FIG. 2A and FIG. 2B). The direction
of the relative object shift vs. roller during leveling (X-motion
of object and tray 300) is not definite (undefined/not
pre-defined), and can be different in different applications. Based
on this description, one skilled in the art will be able to
determined specific details, attributes of the printed material,
and other considerations of the printing machine for implementing a
specific application depending on the.
[0157] As discussed before, as a result of leveling (shaving) the
object via use of a roller (such as grinding or cutting rollers),
particle waste can be generated. The particle waste can include
shaved particles and/or dust of the solid particles from the
printing ink. Techniques to prevent the particle waste from being
scattered over the printing surface, and to remove the waste from
the roller blades, should be applied. The horizontal roller
facilitates implementation of techniques for preventing scattering
of particle waste, for example by adding a shield around the roller
(half-arch shield 303) and applying sucking force via pipe 304
during "rolling". The particle waste is sucked off the surface of
the object and the blades, optionally through a filter 306. [Eli:
Added half-arch shield 303 to FIG. 3A.]
[0158] The roller may be installed before or preferably after a
radiation source 308 such as incandescent or discharge lamp
(shown), coherent beam (laser), or ultra-violet (UV), visible, or
infrared (IR) radiation source, etc.
[0159] Refer now also to FIG. 2B, a simplified diagram of leveling
apparatus with warming sources. When the dried ink is sticky, the
ink particles may stick to the roller blades or grinding particles
and thereby disturb proper leveling. This might be a consequence of
insufficient drying of the ink or insufficient firing the organic
elements. To prevent this effect, the layer can be further dried by
elevating the layer temperature. This technique of elevating the
layer temperature might be unacceptable in some cases because of
other aspects of the printing process, e.g. deformation of the
printed object. Alternatively, the roller can be warmed to high
enough temperature in which the problem of stickiness of the ink is
avoided. In a non-limiting example, the roller may be set 100
degrees Celsius (.degree. C.) or even higher than the layer's
temperature. Warming the roller may be done by heating the roller's
outer surface by an external heat source (i.e. located outside the
roller) or by an inner heat source located in the roller. Inner
heat sources preferably include static (non-rotating) warming
element, such as a halogen lamp or a heat rode 230.
6. Mask
[0160] In the context of this document, a mask refers to a plate
that partially covers an orifice plate and has an opening to
facilitate printing from nozzles to a print area. Masks are also
referred to as "cooling masks" and can be used as a "thermal
buffer".
[0161] Since the printed object 312 is relatively hot (e.g.
230.degree. C.) as compared to room temperature (25.degree. C.), as
required during the formation of a layer and evaporating the
carrier liquid, the printing heads 314 (such as printing head 100)
that scan the upper layer in close vicinity (0.5-3 mm between the
printing head 314 and object 312) must be protected from the heat
and fumes emerging from the newly formed layer 310 (dispensed
layer). A cooling mask 316 maintained at a relatively low
temperature compared to the temperature of the object while being
printed (e.g. from 10 to 40.degree. C.) is installed as a buffer
between the printing head 314 and the printed object 312.
7. Heating Tools
[0162] In order to maintain printing accuracy, the printed object
should preferably be maintained substantially at uniform and
constant temperature throughout printing. The upper surface of the
object body, however, keeps losing heat to the surrounding
atmosphere during printing, and also supplies heat to the newly
dispensed layer, since the dispensed ink is usually colder than the
object, and since heat is consumed by the evaporation of the liquid
carrier of the new layer. If the heat source is only below the
object (for example, a heated tray 318), the heat constantly flows
up to the upper layer, and because of the heat-flow resistance of
the material, a temperature gradient is built, high temperature at
the bottom of the object and low at the upper surface of the object
(along the Z-axis). Preferably, the heat should also (or merely) be
supplied directly to the upper surface or layer. In addition, the
temperature of the upper layer should be the same during the
printing (though may be higher than the temperature of the bulk),
because drying and possibly evaporating the organics and partial
sintering occur in that layer, processes that strongly depend on
the layer temperature.
[0163] In the context of this document, the term "printing surface"
328 typically includes the most recently printed finished layer,
prior to printing of the current, newly formed layer 310. In other
words, the printing surface 328 is the upper surface or upper
layer, most recently previously printed along the Z-axis, and is
the surface upon which the newly formed layer 310 is printed. When
printing begins, the printing surface is the substrate, for example
the heated tray 318. However, after printing begins, the printing
surface is typically the upper surface of the object body, plus
supporting material, as appropriate.
[0164] In a first embodiment, heat is supplied to the upper surface
by an electromagnetic (EM) energy source through the surrounding
gas or vacuum. The EM energy source is one non-limiting example of
a radiation source 308. Typically, the radiation source 308 is
located above the upper layer/object being printed. The direct
heating by the EM source can assure constant temperature of the
upper layer. When direct heating of the upper layer is not applied,
the temperature of the tray 318 (on which the object is printed)
should be controlled higher and higher dependently on the interim
height of the object during printing, so as to keep the temperature
of the upper layer constant. An alternative supply of heat to the
upper surface is a stream of hot air blown on the upper printed
layer. The use of hot air is not only for increasing the
temperature of the upper layer but also, or rather for encouraging,
the evaporation of liquid carrier (and in some cases the dispersing
agent and other organic material) from the upper surface. A
combination of EM radiation, hot air, and warm tray (or any
combination thereof) can be used to maximize the heating and/or
evaporation performance.
[0165] The substrate's surface on which printing is accomplished
(for example, the tray 318) presents intimate touch with the object
and therefore should be at the same temperature of the object. If
the substrate (i.e. tray) is thermally conductive, e.g. made of
metal, warming the tray to the required object temperature can be
essential for producing correctly a desired object. Alternatively,
the tray may include thermally insulating material, e.g. wood,
plastic, or insulating ceramics. In this case, the substrate keeps
the object's temperature, while heating of the object is
accomplished by heat radiation from above.
[0166] When the object height is relatively small and the object's
material has high enough heat conductance, heating the object only
from the substrate side may be sufficient. In this context, "high
enough heat conductance" generally means that the temperature
gradient (which is given by the product of heat conductance per
length multiplied by the height Z) is small, e.g. smaller than 1%
of the object temperature during printing, measured in Celsius. For
example, if the heat conductance is comparable to that of fully
sintered metals (100 W/(Cm)), the condition on the temperature
gradient can be met up to a relatively small printing height of 10
mm. This, however, is not always the case. The object can be high,
e.g. higher than 10 mm in the current example, and can be made of
poor material heat conductance (e.g. 1 W/(Cm) and smaller).
Therefore heating from the upper side of the object is essential.
Heating from the upper side can be done in few different methods,
including heat conductance and convection by the air above the
object, flowing hot air from an air knife element on the upper
layer, EM energy source, etc. A preferred embodiment is the EM
energy source, as is described below.
[0167] 7.1. Radiation Source
[0168] As described above, the EM energy source is typically
positioned aside the printing head 314, and can be of a UV, visible
or IR radiation type.
[0169] Optionally, a radiation source 308 is installed after, or
preferably before, the leveling roller 302. The radiation source
308 can be used for one or more tasks, including: [0170] Heating
the upper layer of the object to maintain a constant temperature of
the upper layer, independent of the height of the layer above the
heated tray 318. [0171] Heating the upper new layer of the object
above the temperature of the printed surface (i.e. the former
layer) TS, and as a result: [0172] a. Assisting disintegration
and/or evaporation of the dispersant and other additives to the
ink. [0173] b. Assisting partial or full sintering. [0174] c.
Maintaining the 3D object 312 (whole body) at the same temperature
(except the temperature of the upper new layer that can be
temporarily higher), i.e. avoiding a temperature gradient along Z
direction (top to bottom of the object 312 as the object 312 is
being printed).
[0175] A special case is the UV radiation source. UV radiation has
the potential to disintegrate dispersing molecules that are
attached to the particles by breaking molecular connections. At the
same time, the UV also heats up the layer, assisting thereby the
evaporation of the dispersant material or the dispersant material's
fragments.
[0176] 7.2. Extra Heating of the New Layer
[0177] In one embodiment, assume the boiling temperature of a
carrier liquid is T1. The temperature of the upper surface is
preferably maintained at TS, which is substantially comparable to
or higher than T1 (e.g. higher than 0.8.times.T1 in Kelvin) so that
after jetting the ink, the temperature of the new layer (TL)
abruptly increases to TS, and carrier liquid evaporates
immediately. Generally, the temperature of the whole object during
printing can be maintained at TS as well.
[0178] In order to evaporate the dispersant material and other
organic additives, and optionally initiating at least partial
sintering between the building particles, higher temperature of the
upper (new) layer TL may be required. Substantial increase of the
temperature of printing surface TS above T1 (e.g. by 30.degree. C.)
is generally unacceptable, since the landing ink droplets on such a
hot surface would explode rather than attach to the surface, like
when water droplets land on a surface of 120.degree. C. (the
explosion effect can be exploited in a special embodiment which
will be described later). In this case, the rest of the object is
not required to maintain at such high temperature (TL), but just
maintain at a constant and uniform temperature TS.
[0179] When a newly formed first layer is dispensed, the layer is
typically exposed to air (the environment of the printing machine),
and thus organics in the ink have the chance to evaporate, prior to
this first layer being covered by a subsequent printed layer. Thus,
in one embodiment, the new layer is warmed to a higher temperature
TL than the boiling temperature of the carrier liquid Ti (e.g. if
T1=230.degree. C. the new layer can be warmed to 400.degree. C.),
even though the lower (previously jetted/previously printed) layers
stay at a relatively lower temperature TS (e.g. 230.degree.
C.).
[0180] Refer now to FIG. 3B, a diagram of a lamp as an exemplary
radiation source. As discussed above, heating the new layer can be
accomplished by a radiation source 308 typically from above the
object. If lower layers under the upper layer are at a lower
temperature than the upper layer, maximizing the heat irradiance
(i.e. irradiated power per surface area of the new layer) is
important in order to get an instant higher temperature of the
layer, before the heat dissipates to the preceding (previously
printed) layers by conduction or dissipates to the air above by
conduction and convection. Therefore, given a heating lamp 308A (as
radiation source 308), the lamp should be as close to the body 312
surface and reflector aperture as narrow as possible.
[0181] A lamp housing 332 typically includes a metal envelop
covered with an insulation material to prevent heating adjacent
elements. A polished aluminum reflector 334 is typically required
especially to protect the reflector and housing from overheating.
The polished aluminum reflector 334 typically reflects 97% of heat.
A transparent glass window 336 is typically high transparency (i.e.
small radiation absorbance is required especially to protect the
window from overheating). The window 336 is made of a material
appropriate for the specific application (e.g. Pyrex or quartz). An
aperture 338 (ex.: 9 mm) is used for a given radiation power. A
relatively small lamp's aperture assures high irradiation power
(i.e. high radiation power per unit area of the printed layer). A
small gap 340 between the heating lamp 308A (more specifically,
typically from the transparent window 336) to the upper layer of
the object body 312) assists in preventing the lamp radiation
illuminating large area of the layer at one time. However, focused
radiation enables much higher irradiance (FIG. 3C).
[0182] Refer to Table 1 and Table 2, below for exemplary
calculations showing that for most solid metals that are typically
used to construct a 3D object, thermal conduction is so high that
very intense radiation is required for warming the new layer to a
substantially higher temperature than that of the object (e.g.
Ir=1000 KW/cm 2 is required to obtain .DELTA.T=81C) [0183]
Temperature rise (.DELTA.T=TL-TS) of a new layer above the object's
temperature
TABLE-US-00001 [0183] TABLE 1 Example parameters Layer thickness 5
.mu. Light irradiation power (Ir) 0.1, 1, 10 KW/cm{circumflex over
( )}2 Radiation absorbance 0.7
TABLE-US-00002 TABLE 2 .DELTA.T Silver WC Plastic Air Ceramics
Thermal conductivity 430 84 0.2 0.04 0.5 to 5 Temperature rise
8E-03 4E-02 17.5 87.5 7 to 0.7 (Ir = 0.1 KW/cm{circumflex over (
)}2) Temperature rise 0.08 0.42 175 875 70 to 7 (Ir = 1
KW/cm{circumflex over ( )}2) Temperature rise 0.81 4.17 1750 8750
700 to 70 (Ir = 10 KW/cm{circumflex over ( )}2) Unit symbols: C.
means Celsius m means meter W means Watt .mu. means micron cm means
centimeter.
[0184] When a layer of metal is fully sintered just after being
dispensed, the layer's structure is continuously solid, and then
the relevant thermal conductivity is that cited for the metal (e.g.
430 W/(Cm for silver), and the temperature rise .DELTA.T is as
calculated in the table above (much less the 1.degree. C.).
[0185] However, when substantially no sintering occurs at the
printing stage, the layer's structure is like a pile of particles.
Measurements show that nearly only half the printed volume is
occupied by solid particles, while the rest is mostly air. Thus, in
each direction (X, Y, Z) only 80% of the layer is occupied by solid
particle (since 0.8.times.0.8.times.0.8.apprxeq.0.5), and the rest
of the volume of the non- or partially-sintered object is air.
Thus, every layer is equivalent to a layer that includes in height
of the layer 80% metal and 20% air. Since air conductivity (0.04
W/(Cm)) is substantially lower than metal conductivity (for example
WC: 84 W/(Cm)) the air layer portion dominants the conductivity of
the layer. Thus, when the irradiation power is 0.1 KW/cm 2, the
temperature rise in this case is the temperature rise of a
5.times.0.2.mu. air layer, i.e.
.DELTA.T=87.5.times.0.2=17.7.degree. C. (wherein 87.5 is taken from
the second row of Table 2).
[0186] All this holds with an irradiation of 0.1 KW/cm 2, which
represents an exemplary intense irradiation from a longitudinal
halogen lamp. If a focusing reflector (elliptic) is used, the
irradiation is more condensed by a factor of 10 (i.e. Ir=1 KW/cm
2), and then a similar calculation leads to
.DELTA.T=875.times.0.2=177.degree. C. (wherein 875 is taken from
the third row of Table 2).
[0187] Higher temperature rise .DELTA.T can be obtained at much
higher power density of the radiation, for example by a linear
laser beam which includes a focused line (typically Ir=6 KW/cm 2),
or by a scanning focused spot laser beam including a scanning spot
of irradiation (typically Ir=600 KW/cm 2), or by flash radiation
(wherein high power radiation is absorbed at very short time (see
typical example below)). These techniques are further described
below.
[0188] Operating a flash radiation source refers to a technique
where the radiation is transmitted in a very short time, e.g. 1 ms,
at high power, e.g. Ir=10 KW/cm 2. In this case, the temperature
rise of a non- or partially-sintered object would be
.DELTA.T=8750.times.0.2=1770.degree. C. (wherein 8750 is taken from
the fourth row of Table 2).
[0189] When printing thermal insulating material, e.g. oxides like
SiO2, TiO2 or other ceramic material, thermal conductivity is
typically between 0.5 to 5 W/(Cm) (see Table 2). If after warming
the upper layer, the upper layer does not become sintered (remains
un-sintered), the air layer portion conductivity is still lower
than oxide layer conductivity and the air dominants the
conductivity of the layer as in the case of metal particles. If the
layer becomes sintered (under the flash radiation), because of the
high irradiation power Ir and despite of the high thermal
conductivity, the temperature rise .DELTA.T of the layer will go up
to 70 to 700.degree. C. (see the fourth row of Table 2).
[0190] The above-described possibility to warm the new layer
significantly beyond the temperature of the former layers, enables
keeping the temperature of the printed object much lower than the
instant temperature required to burn off the organics or to sinter
the object. A fan (for example cooling fan 326) may be required to
lower the temperature back to a lower object temperature.
[0191] The upper surface of the body will dissipate to the
surrounding air roughly 3 W/cm 2 at a temperature of 400.degree. C.
Therefore the lamp above should supply this much power to the upper
layer in order to maintaining the object body's temperature
constant and even, and even larger power is required in order to
compensate for the material evaporation and sintering heat
consumption.
[0192] 7.3. Focused Radiation
[0193] As indicated above, focused radiation may be used to obtain
an instant temperature of the upper layer higher than the body
temperature. In conventional implementations, a layer of dry
particles is evenly spread on the preceding layer, and then focused
radiation (for example, a scanning focused point (i.e. spot) laser
beam) scans the layer and selectively solidifies the required
portion of the layer according to a layer map.
[0194] According to one embodiment, the particles used to construct
the current layer are not evenly spread (unevenly distributed) on
the preceding layer, but the particles (layer) is selectively
dispensed according to a layer map. This facilitates use of
non-selective radiation to create a newly formed layer only where
the particles have been selectively dispensed.
[0195] Refer now to FIG. 3C, a diagram of a lamp as an exemplary
radiation source. Embodiments can include one or more of the
following techniques:
[0196] a. Linear Lamp and Focusing Reflector
[0197] Refer now to FIG. 3C a diagram of radiation sources. A first
embodiment is a hot radiating lamp 350, including a linear bulb
(discussed above), including a linear radiating filament 352
enclosed a quartz transparent pipe 356, coupled with a focusing
reflective surface having elliptic transection 358, enclosed in a
transparent window 354 (for example, protective glass). The
filament is located in one focal point 360F1 of the elliptic
curvature, while the filament's hot image is obtained in the other
focal point 360F2, on the upper surface of the body being printed.
The width of the image can be comparable to the length of the
filament perimeter (but never smaller). In a practical example the
filament perimeter is equal to 1 mm, the width of the image of the
filament on the 3D upper surface is 3 mm, and the radiated power is
50 W/(cm length). Hence, the irradiation power obtained at the part
surface is 50/0.3=167 W/cm 2.
[0198] b. Focused Linear Coherent Beam
[0199] Refer again to FIG. 3C. A second embodiment includes a
linear coherent beam 370. An appropriate laser device 372 can be
obtained from, e.g. from Coherent Inc, Part No LIM-C-60. Such laser
has a focal plane, which is the plane of minimal waist. A typical
waist width is 50.mu.. A typical power of the laser is 20 W/cm.
Hence, the irradiation power is 4000 W/cm 2. At such power, heat
loss is much smaller than the input heat, and therefore the layer
temperature can substantially exceed the body's temperature. Before
the particles sinter to each other, the temperature rise of the
upper layer will get to .DELTA.T=1770.times.4/10=708.degree. C.,
wherein 1770.degree. C. is the temperature rise .DELTA.T of the
upper layer per irradiation power of 10 KW/cm 2 (due to the
isolation of air between the solid particles, see preceding
chapter), and 4/10 reflects the ratio between 4 and 10 KW/cm 2.
[0200] c. Scanning Focused Beam
[0201] A third embodiment includes a spot (point) coherent beam
with a scanning apparatus (e.g. rotating mirror polygon). Unlike
traditional 3D metal printing in which the beam is modulated on/off
according to the image of the layer, the beam in the current
embodiment can be "dumb" (although the beam can also be modulated
according to the image, at least for saving energy). This "dumb"
beam scans a line in the Y direction, while the object body moves
in X direction. A typical laser power is 500 W, and focal spot of
50.mu. diameter. Hence, the irradiation power is 500/0.005 2=2 10 4
KW/cm 2 (typically the difference between the area of a disk and a
square is ignored for this calculation). Such irradiation power can
warm the layer much above the sintering temperature of all metals
and ceramic material.
8. Getting Rid of Fumes
[0202] Refer now to FIG. 3A and FIG. 4A, a simplified diagram of a
system for removing fumes during printing and FIG. 5, a simplified
diagram of a system for removing fumes during printing using an
alternative radiation source. Typically, during inkjet printing of
a 3D object, a substantial amount of fumes emerges from the
dispensed and heated ink layer, including the carrier liquid and
possibly the dispersant. The fumes maybe harmful to the printer
parts since they can condense on relatively colder surfaces (as
compared to the temperature of the 3D object 312 during printing)
including surfaces such as electronic boards and parts. According
to an embodiment, the fumes are collected by sucking pipe(s) 404
providing sucking 414 located adjacent to the printing head 314
and/or near the spot where the layer is further heated by the
radiation source 308.
9. Sustaining the 3D Structure
[0203] In conventional technologies, glue is often added to the
particle ink (e.g. photo-polymer, thermo-plastic polymer etc). This
glue material assists sustaining the 3D structure during printing,
a time before subsequent hardening process (i.e. sintering) of the
entire object in a high temperature oven. For example, (in a
conventional process) a powder dispenser spreads solid (dry)
particles over the entire tray (tray on which the object is being
printed/constructed, such as heated tray 318), and a printing head
subsequently dispenses liquid glue on the particles spread
according to the desired content of the layer being printed. This
process repeats layer by layer until the printing finishes. Later,
the loose particles are removed, and the glued object is
transferred from the printer to an oven. In the oven, the object is
heated to a high temperature for accomplishing sintering. During
the sintering process a majority of the glue fires off, however
typically a portion of the glue remains. The remaining glue
interferes and/or interrupts sintering if the glue does not
completely evaporate in the oven. In addition, the presence of glue
in an object's structure may be undesirable, as described elsewhere
in this document.
[0204] A technique for avoiding problems with glue is to do
sintering during printing on a layer basis, and therefore glue is
not required. For example, a powder dispenser spreads particles
over the entire tray, and a subsequent focused laser beam scans the
spread particles according to the content of the layer. Every spot
that is illuminated by the beam heats up sufficiently to sinter the
powder at the illuminated location.
[0205] According to embodiments of the current invention, the
particle construction is sustained at least in part by: [0206] a.
During printing, the carrier liquid immediately evaporates, and the
particles attach to each other by the dispersant molecules that
surround each particle. In this case, the dispersant is chosen to
have not only the attribute of separating the particles from each
other in the ink dispersion, but also attaching to each other when
the carrier liquid (solvent) is removed. Using conventional terms,
the dispersant here plays the role of a binder. Often the
dispersant is a polymeric molecule that has good adhesion
properties. [0207] b. When the complete object is heated in an
oven, the dispersant molecules firstly evaporate and then initial
sintering takes place to hold the particles together until complete
sintering. [0208] c. Refer now to FIG. 6A a diagram of solid
particles with small edges. A well-known characteristic is that
small particles sinter at a relatively lower temperature than large
particles (e.g. 50 nm size WC particles sinter at 800.degree. C.
compared to 700 nm particles that sinter at 1400.degree. C.). In
this context, small is compared to large where the difference
between small and large is sufficient to result in an apparent
difference in sintering temperature for the desired application. In
cases where sintering starts at a much higher temperature than that
of the dispersant's evaporating, the solid particles 604 are
chosen, or made, not regular, i.e. irregular/including sharp edges
600, i.e. edges that are characterized by small round radii as
compared to the overall radius of the particle. Such edges have the
property of locally sintering 602 at a reduced temperature (as
compared to the higher sintering temperature for the bulk of the
particle) as much as particles made with such small radii have.
[0209] Refer now to and FIG. 6B a diagram of solid particles with
bridged sintering by smaller particles. In addition, the
preparation of the solid particles 610 can includes a fraction of
much smaller particles 612 than the average size of the main
(larger) particles (e.g. 50 nm size when the average size is 700
nm). These smaller particles will sinter at a lower temperature
(e.g. 800.degree. C. as compared to 1400.degree. C.), and partially
stick the large particles to each other by a "bridging" structure.
[0210] Thus, once the dispersant fires out, some initial sintering
takes place in the points of intimate touch between the sharp edges
of the large particles or due to the "bridging" effect by the small
particles between the large ones. Note that this partial sintering
is located in small points between the large particle, and
therefore the bulk structure remains porous so that the fired
dispersant can flow out of the material.
10. Getting Rid of Organic Material
[0211] The ink contains carrier liquid, dispersing material, and
possibly more than one additive that participate in perfecting
printing, all are often organic material. As described above, a
desired feature is to get rid of this organic material as soon as
possible, or at least before final sintering.
[0212] In one embodiment, the carrier liquid substantially
evaporates during the formation of the layer and thus the layer
becomes solid. This is accomplished at least in part by maintaining
a relatively high temperature of the body of the 3D object (or at
least the upper layers of the 3D object). In this case, the high
temperature is a temperature kept at a temperature comparable to
the boiling point of the liquid carrier or higher. In some
embodiments, the high temperature can be 20% more or less than the
boiling temperature of the carrier when the temperature is measured
in Kelvin.
[0213] In another embodiment, the temperature of the upper layer is
sufficiently high to also burn out other organic material(s),
particularly the dispersing material (dispersant), during the
formation of the upper layer. When a body (body of an object being
printed) is large (for example X, Y, Z dimensions=100 mm) this burn
off is normally necessary. If the organic material is not burned
off during printing, then the organic material remains during
printing, and during firing the organic material has difficulty
flowing to the outside of an already printed large object.
[0214] In another embodiment, the dispersant remains in the bulk
material during printing. In conventional terms, when the organic
material (which plays the role of a binder) remains in the printed
object, the object is referred to as a "green object". In this
case, after printing the object, but before firing the object, an
extra stage of initial heating is performed usually in an oven. In
this initial heating stage the organic material (whether
disintegrates or not) slowly flows out to the object's outer
surface, and evaporates. This initial heating is done before
elevating the firing temperature to a temperature where full
sintering occurs. A desirable feature is to prevent complete
sintering of the object particles during the stage of organics
extraction. This is desirable for reasons including: [0215] a. not
blocking the paths from which the organics flow out of the bulk
material, and [0216] b. not preserving the sponge-like lattice of
material that prevails before the organic material is
extracted.
[0217] Preventing complete sintering in the stage of organics
evaporation can be done by adjusting the particles' characteristic
temperature T3 of sintering (depending on particles material and
size) or by choosing the organics (dispersant and additives) with
appropriate burn out temperature T2, so that T3>T2.
11. Partial Sintering During Print
[0218] Partial sintering during printing can strengthen the newly
formed layer before leveling, or (as explained above) strengthen
the object before removing the object from the substrate, and/or
prior to firing the object (in an oven). In the context of this
document, the term "partial sintering" generally refers to
particles melting to each other only partially, that is at one or
more locations on the surface of each particle without the complete
surface of the particles contacting surrounding particle
surfaces.
[0219] In one embodiment, partial sintering of an object body is
obtained during printing of the object. Partial sintering can allow
subsequent firing and removing dispersant, even when firing of the
dispersant is done after completing printing the object, because
the open porous structure is still there.
[0220] In another embodiment, complete sintering of an object body
is obtained during printing of the object. Since the dispersant can
inhibit sintering, this method includes first evaporating the
dispersant during the layer formation at temperature T2, and
afterwards complete sintering takes place temperature T3, wherein
T3>T2.
[0221] Refer now to FIG. 7, a diagram of partial sintering. During
sintering objects typically contract since the particles move
closer to each other and fill voids in-between particles. In most
cases, this contraction of the object being sintered is substantial
(e.g. 20% in every dimension). Because the newly formed layer is
typically very thin (e.g. 5 micron before contraction) as compared
to the lateral dimension (X-Y) of the object (e.g 50 mm), the
friction of the newly formed layer with the former (previously)
printed and dried layer diminishes the contraction in X-Y plan, and
the vast contraction accomplished only in the bottom direction,
i.e. towards the preceding layer that has already sintered. Yet the
capillary force that acts to contract also in the layer plane (i.e.
in X, Y directions), which is balanced by the aforementioned
friction, introduces lateral contraction force in the layer. This
force repeatedly from layer to layer during complete sintering 702
may cause deformation in the nature of the object 712. On the other
hand, partial sintering 700 can be enough for holding the particles
together and yet not introducing too large contraction force in the
(newly formed) layer. Thus, partial sintering facilitates
maintaining a desired nature (shape) of the object during printing
710.
[0222] Sintering temperature should be considered carefully for
enabling partial sintering. At high enough temperature, the
particles melt to each other and form a nearly or fully solid
material (complete sintering). The required sintering temperature
substantially depends on the melting point of the particles'
material and the size of the particles. For example, the melting
point of silver is 960.degree. C.; 1 .mu.m (micrometer) silver
particles sinter at 800.degree. C., but 20 nm (nano-meter) silver
particles sinter at 200.degree. C. So in order to do partial
sintering of an object made of silver particles, if 1 um particles
are used, the newly formed layer can be warmed for example to
500.degree. C., a temperature in which the organics are fired off
and partial sintering replaces the organic material to hold the
object from being dismantled.
12. Complete (or Sufficient) Sintering at a Layer Level
[0223] The dispersant (and possibly other additives in the ink) can
interfere with the desired quality of sintering, and thus removing
these materials (the dispersant and possibly other additives) can
be important for obtaining sintering (but not necessarily
sufficient for obtaining sintering). For simplicity in the
following discussion, one skilled in the art will understand that
references to dispersant can also refer to possibly other
additives.
[0224] In contrast to printing at a moderate temperature (e.g.
230.degree. C.) and only later sintering the complete body in a
high temperature oven, the innovative technique of complete
sintering when printing a layer includes features such as: [0225]
a. Getting rid of dispersing molecules and additives just when the
upper layer (at a temperature T2) is in touch with the open air.
When evaporating the dispersant is done in an oven, the resultant
gases have difficulty defusing through the bulk material,
especially when part of the object can be at least partially
sintered. At this point note that the outer envelope of an object
in an oven sinters out before the bulk completely sinters. This is
mainly because that the heat flows in the oven from the outer
envelope towards the center of the object, and this must be
accompanied with a temperature gradient--higher temperature at the
envelope than in the bulk. So well before the bulk is sintered the
envelope sinters, and the gas cannot go out of the object. [0226]
b. Further heating the layer to a temperature T3, so as to
encouraging sintering, wherein contraction, which accompanies
sintering, takes place in the down (Z-axis) direction rather than
in lateral X-axis and Y-axis directions (as explained above).
Contraction in the Z-axis direction can be taken into account
before printing (a priori) and compensated for during preparation
of the digital description of the printed object. [0227] Note that
sintering at a layer level, not only presents an easy way to get
rid of the organics, but may also save the need of energy and time
consuming following firing in oven
[0228] Techniques and features of layer-by-layer dispersant removal
include the following:
[0229] a. Heat
[0230] Extra heating of the new layer by focused radiation or by a
high power flash light, e.g. both at Ir=5-10 KW/cm 2 can be used to
accomplish evaporating of the disturbing materials (such as
dispersant), and also heating the upper layer to as high
temperature as required for sintering the layer. At the layer
instant high temperature brought about by the intense radiation,
not only the carrier liquid is evaporated, but also the dispersant
evaporates or disintegrates and evaporates, and later full or
sufficient sintering takes place. Usually this technique is done by
dispensing the new layer on a moderately warm preceding layer, such
that the carrier liquid is evaporated before entering the extra
heating device, reducing thereby the required energy in the device
for evaporating both the carrier liquid and the dispersant, and
accomplishing sintering.
[0231] b. By Additional Catalyst
[0232] Printing a layer can be accompanied by dispensing catalyst
material, which accelerates sintering. A preferred embodiment
includes material that disintegrates the dispersant molecules, so
that they evaporate out or at least do not disturb sintering.
Furthermore, added heat can be used to evaporate out the
disintegrated molecules. The bare solid molecules left after
removing the dispersant spontaneously sinter at this stage to each
other, given that the temperature is high enough. For example, if
the solid particles are silver particles of 20 nanometer diameter,
a temperature as high as 200.degree. C. is sufficient for complete
sintering, given that the dispersant has removed. The catalyst can
be dispensed after or just before dispensing the model layer.
[0233] Refer now to FIG. 8A, a diagram of dispensing catalyst
material. Dispensing the catalyst 802 can be done by a catalyst
droplet jetting head 800 or by spray nozzle. The catalyst can be
dispensed selectively according to the object layer image, or
"blindly" on the entire reserved area for the object. The catalyst
can come in liquid form or gas. Optionally, the catalyst can be
dispensed by a roller that spreads the catalyst over or under the
new layer being printed. When the catalyst has the quality of
becoming aggressive (active) only at high temperature, the catalyst
can be included in the ink beforehand, and then heated with the
layer heating after printed, when activation is desired.
13. A Different Printing Technique
[0234] Refer now to FIG. 9, a diagram of using a liquid pump
roller. An alternative embodiment of printing, leveling, and
heating, includes printing layer by layer while the temperature of
the printed body is substantially smaller than the boiling
temperature of the carrier liquid (e.g. 150.degree. C. when the
boiling temperature of the carrier liquid is 230.degree. C.). After
printing a layer, the layer is flattened (leveled) by a liquid pump
roller (LPR) 900. An LPR is typically a smooth roller with an axis
parallel to Y-axis of the object, rotating in "reverse" (opposite
the relative X-axis motion of the object). Then the newly formed
layer 310 is irradiated by a high irradiation power beam (for
example laser 902) to at least evaporate the liquid and solidify
the layer (e.g. warming the layer to a temperature of 230.degree.
C. or higher). Later on, before dispensing the next layer, the
layer is cooled to the low object temperature (e.g. by a cooling
fan 326). The excess ink from the flattened layer attaches to the
rotating roller surface of the LPR 900, and is wiped by the roller
wiper (for example by metal wiping knife 904), and flows into a
collecting trough 906, from which the excess collected ink is
cycled back to an ink tank for re-delivery to the printing head 314
or pumped out to a waste tank.
14. Protecting the Jetting Head and the Jetted Droplets
[0235] Printing a hot 3D object body presents difficulties when
using an inkjet printing technique. The jetting nozzles are
positioned close to the printed layer, e.g. 1 mm apart. Thus, the
nozzles may heat up by the warm upper surface of the body being
printed, and the jetting quality injured. Techniques to prevent
nozzle heating may include a cooled shell (see FIG. 3A, cooling
mask 316) that behaves as a thermal buffer between the hot layer
and jetting nozzles. One such cooled shell is described in patent
International publication No WO2010/134072 A1 to Xjet Solar
Corporation.
[0236] Usually there is a desire to have the 3D body temperature
(including the upper surface) not high (relatively low), because
despite of the protecting mask, some heat still gets from the hot
body of the object to the nozzle plate of the head through a slit
in the mask through which the ink is jetted. Moreover, another
difficulty with printing on hot objects lies in the possible
"explosion" of the jetted droplets when touching the warm surface.
In this case, the term "explosion" refers to the carrier liquid
abruptly boiling rather than slowly evaporates.
[0237] An innovative solution is differentiation between the body
(object) temperature and the temperature of the new layer. This can
be accomplished by the following steps: [0238] a. heating up the
newly formed layer to a higher temperature than that of the body
immediately after the layer being dispensed (e.g. by a focused
radiation), and [0239] b. cooling the upper surface before
dispensing a new layer on the upper surface of the 3D body object.
Cooling can be done with the aid of a fan (see FIG. 3A cooling fan
326) or by dissipating the heat stored in the layer to the object
below and to the surrounding air.
15. Plural (Composite) Object Material
[0240] Refer now to FIG. 10A, a diagram of objects built with
different materials. Often the required object includes different
materials in different parts of the object. A special and important
case is when the bulk material 1006 of a first object 1002 should
be laminated (coated) with a coating material 1007 at an outer
surface of the first object 1002. Similarly, the bulk material 1006
of a second object 1004 can be laminated with a coating material
1007 at an outer surface of the second object 1004.
[0241] Refer now to FIG. 10B, a diagram of objects built with a mix
of materials. Requirements for a third object 1010 include a mix of
two or more materials required either over the entire object or
over part of the object. In the current diagram, third object 1010
includes a mix of a first material (material 1 1018) and a second
material (material 2 1020). When a section of the object 1012 is
enlarged 1014, the mix of materials can be seen in that each pixel
1016 is an alternating material.
[0242] One technique for printing an object with a mix of materials
in a given location of a layer can be done by dispensing one
material in certain pixels of the layer and another material in
other pixels.
[0243] In an alternate technique, one layer is printed by one
material and another layer by another material. A special case is
impregnation-like of a coating-like material 1008 at the outer
surface of an object (for example, second object 1004). The
impregnation-like can include a gradual decrease of the proportion
of impregnating material and bulk material as the distance from the
object surface increases.
[0244] A plurality of inks and ink heads can be used to
differentiate printing between object material and object support.
According to an embodiment, one ink can be used to build both the
object and support structures (layer by layer), while another ink
is dispensed only on the layer part that belongs to only one of the
object or support, introducing thereby a difference in a mechanical
attribute of both materials. This difference is used later when the
support is removed from the object. For example, a first ink
including Ag particles is used to print both object and support
portions of a layer. A second ink including Ag polymeric compound
material or particles dispensed only in the object portion of the
layer. When printing finishes, and after the printed complex has
been fired in an oven, a substantial difference is introduced
between both materials (the support of only Ag particles stays
un-sintered, while the object is sintered or at least formed of a
solid matrix of Ag in polymeric compound. This difference enables
removing the support from the object.
16. Printing the Object with a Mold
[0245] In one embodiment, a mold is printed together with an
object. A mold is any auxiliary body that is attached to the object
body 312 and can be removed from the object body. In the context of
this document, a mold can be considered support for the object, as
described below. The mold can be printed by a different ink than
the bulk in the same layer-by-layer printing. Printing an object
and a mold facilitates the object including particles that do not
adhere (are unattached or only lightly adhere) to each other until
the body is fired and sintered in an oven (at typically 600 to
1500.degree. C.). For this sake, the mold preferably includes
material that holds tight at a low temperature and disintegrates at
high temperature, or at least can be removed from the object. The
mold can also protect the object during printing. For example, the
mold protects the delicate edges of the object 312 from breaking
while the cutting roller 302 levels out the printed layer 310. Even
if the mold's material does not hold tighter (holds looser) than
the object's material, yet the mold protects the object's edges
while scarifying the mold's own edges through, for example, when
leveling the new layer or transporting the object after printing to
the firing oven. The mold can be thin (e.g. 0.5 mm thick), and can
get the shape of a skin around the object or part of the object.
Thus, the object (and simultaneously the mold) can be printed
embedded in a mold, expanding the range of materials and processed
available for creation of 3D objects.
[0246] An example of this technique is an object ink that includes
particles of high hardness (e.g. WC) wrapped with a dispersant. At
relatively low temperature (e.g. 200-400.degree. C.), the
dispersant behaves like a glue that holds the particles together.
At medium temperature (e.g. 400.degree. C.), however, the
dispersant evaporates and the 3D object may fall into a pile of
particles. If the object is surrounded with a material that
partially sinters at 400.degree. C. but melts or disintegrates and
evaporates at above 800.degree. C. (e.g. a mold ink including
polymeric particles that evaporate at 800.degree. C.), the mold
stays solid at and above a medium temperature, allowing evaporation
of the object's dispersant, until at higher temperature (e.g.
700.degree. C.) partial sintering of the object takes place.
17. Support
[0247] When an object is placed on a printing tray in an arbitrary
orientation, a positive or negative angle can be specified per
every spot on the object's surface, as follows: If an object
material is found just under the spot, the surface angle is
specified positive. Otherwise, the surface angle at that point is
specified negative (a negative angle or negative tilt of the
object). In other words, a negative angle is an area of an object
that while being built lacks a portion of the object immediately
beneath the area being printed.
[0248] Refer now to FIG. 11A, a diagram of support when building a
3D object. Supporting negative angles of the 3D object can be
critical for 3D printing. The support 1100 material should differ
from the object 312 material in a way that the support material can
be removed after printing or after following steps like sintering,
without deteriorating the object. The support may need to fulfill
many additional requirements, including being easy to remove,
hardly mixing with the model material at the touch interface line,
low cost, self-sustained, and compatible with the printing
technology (inkjet), etc.
[0249] Since printing is done by inkjet technology, the printer
typically includes at least two printing nozzle groups (often two
printing heads), one jetting object material, and one support
material. Each layer being printed may have zero, one, or multiple
portions of the layer that are desired in the final object,
referred to as "object portions" of the (current) layer. Similarly,
each layer may have zero, one, or multiple portions that are not
desired (undesirable) in the final object, referred to as "support
portions" of the (current) layer. The support portions are
generally used as support, molds, or other structures to assist
during production of the object, but are removed and/or lacking in
the final object. As described above, other techniques can be used
to print the object portion and support portion of the layer being
printed (for example, for the object portion using a first ink and
for the support portion using a combination of first and second
inks). In the context of this document, the object portion of the
layer being printed is sometimes referred to as the "object layer"
and similarly the support portion of the layer being printed is
sometimes referred to as the "support layer". In the context of
this document, references to support can also include reference to
the ink used to create the support (support ink) and to the portion
adjacent to the object (that either supports the object in the
gravitational sense, or surrounds the object for any purposed,
including to serve as a mold) (support portion). For simplicity,
the current description will use the current example of at least
two printing heads. Based on this description, one skilled in the
art will be able to apply the current methods to other
implementations.
[0250] Refer now to FIG. 11B, a diagram of printing support
portions and object portions of layers. A side view 1120 shows the
3D object 312 and support 1100 during printing. A corresponding top
view 1122 shows the upper layer. Each layer can include a support
layer adjacent to an object layer. In this case, the upper layer
includes a portion that is support layer 1102 (building support for
subsequent object layers), and a portion that is object layer 1104
(built on top of preceding object and/or support layers).
[0251] According to a first embodiment, the support includes
inorganic solid particles (e.g. high melting temperature particles
like oxide, carbides, nitrides, metals, e.g. Tungsten) or organic
particles (e.g. hard polymers) dispersed in a volatile carrier
liquid. The polymeric material should be hard because otherwise the
polymeric material can be difficult or not possible to grind (to
micro particle size). After printing a support layer, the liquid
carrier evaporates, leaving a solid laminate behind. When the
object printing is finished, the object is supported or even
wrapped by the support material. Considerations in choosing and
preparing the inks take care of establishing a substantial
difference in the adherence between the particles of the object
(cohesiveness) and of the support. This difference can show up just
after printing, or later after partial or complete firing. The
difference can be a result of a difference in the dispersant
attributes (e.g. different gluing characteristics between the solid
particles), or a difference in the sintering tendency of the solid
particles to each other. Typically, the support structure should be
softer or more brittle or more miscible in water or solvents then
the object, and therefore ready for being removed from the printed
object. An ideal support is such that during firing the support
disappears, e.g. by or disintegration and evaporation.
[0252] According to a second embodiment, the support includes solid
material dissolved in a volatile liquid. After the liquid
evaporation, a solid laminate is left behind to form a solid
support.
[0253] According to a third embodiment, the solid support material
after printing is soluble in a post treatment liquid. Thus, after
completing printing the 3D object and support, the object and
support can be immersed in the post treatment liquid such as water
or light acid, to remove the support by dissolution.
[0254] According to a fourth embodiment, the solid support material
is such that the solid support material evaporates or is burned
during the firing process. An example is dissolved wax in an
organic solvent, or dispersed particles of polymer in a dispersing
liquid. The solvent or dispersing liquid evaporates off layer by
layer during printing (at, for example, 200.degree. C.) and the wax
or polymer hardens. After printing, the object with the supporting
body is fired in an oven, preferably in vacuum. At 550.degree. C.,
(for example) the wax evaporates and disappears, and the same thing
with the polymer at 700.degree. C.
[0255] An example of the second and third embodiments is using salt
(e.g. NaCl--Sodium Chloride, also known as table salt) solution in
water. After the water evaporates, a solid support is left behind.
After completion of printing, the object can be immersed in water
and the salt is dissolved away.
[0256] Another example of support material is a dispersion of Zinc
oxide (ZnO) particles dispersed in a solvent with the presence of
an organic dispersant. After completion of printing and/or firing,
the dry ZnO particles can be removed by applying moderate force (in
this example we suppose that the ZnO particles do not sinter to
each other). Another option is immersing the object in strong acid
(e.g. HNO3) and the Zinc dissolved away
(ZnO+2HNO3=Zn(NO3)2+H2O).
[0257] An alternative of the former example is a mix of oxide
particles and dissolved salt in a carrier liquid. After printing
(when the support dries), the object and support are immersing in
water or acid liquid, the salt is dissolved by the liquid and the
oxide particles stay as a pile of loose dust.
[0258] Another example of support material is a dispersion of
Silica (SiO.sub.2). Silica is a readily available and relatively
inexpensive material. When the dispersion is dried, the remaining
silica particles are only loosely attach to each other even after
warming to 700.degree. C., and therefore the supporting body of
Silica can be removed from the object.
[0259] An example of such a Silica dispersion is Aerodisp G1220 by
EVONIK Industries, including SiO.sub.2 particle of an average
diameter of 12 nm, dispersed in ethylene glycol and Degbe
(Di-ethylene Glycol Butyl Ether) solvents.
[0260] Another example of support material is a dispersion of
Calcium sulfate. Calcium sulfate is common material used for many
applications such as gypsum board, plaster, and even as a food
additive. Calcium sulfate is an inorganic salt that is water
miscible, enabling removal of this support material by washing in
water after printing and/or firing. Calcium sulfate ink can be
prepared by the following steps: [0261] a. Solid Anhydrous Calcium
sulfate (CaSO4) is grinded in an agitator mill in Glycol Ether
solvent with a combination of ionic and acrylic dispersants to form
a stable dispersion that passes a 3 .mu.m mesh filtration. [0262]
b. The dispersion is further diluted by added Glycol Ether
according to the required solid content of the ink.
18. Reinforced Support and Pedestal
[0263] Refer now to FIG. 11C, a diagram of using reinforcing
support columns. A side view 1130 shows the 3D object 312 and
support columns 1110 during printing. A corresponding top view 1132
shows the upper layer. The view of the upper layer includes a
portion that is support 1114 (building support for subsequent
object layers), and a portion that is object layer 1104 (built on
top of object and/or support layers). In cases where the support
1100 material does not stick well to the tray 318 below or to the
object 312 above (and or below), reinforcement may be added,
preferably by adding columns 1110 of object material.
[0264] In cases in which the object is attached too strongly to the
tray, a pedestal 1112 including support can be added even under the
lower surface of the object. In the context of this document, the
pedestal can include all support layers (either reinforced or not)
that are lower than the lower object layer. The pedestal 1112 can
assist also obtaining proper and accurate Z-axis dimension of the
3D object. This is achieved at least in part by printing layers of
support-pedestal to such a height (in Z-axis direction) wherein the
leveling apparatus (such as roller 1116, similar to leveling roller
302) completely touches the pedestal 1112 and flattens the
pedestal. Subsequently, printing of object and supporting material
takes place on top of the leveled pedestal.
19. Complete (Final) Sintering in an Oven
[0265] After completion of printing, the object is typically placed
in an oven where the object is fired to the required temperature
until complete sintering occurs. This final (complete) sintering
stage can include the following steps: [0266] Initial warming to
burn out all organic material. [0267] Further warming to liquidize
inorganic additives (like Cobalt). [0268] Final warming to sinter
the particles in the liquid phase.
[0269] Part of the firing steps can include applying vacuum,
applying pressure, adding inert gas to prevent oxidation, and
adding other gases that may add desired molecular diffusion or
chemical reaction with the body, as described elsewhere in this
document.
20. High Throughput
[0270] Refer now to FIG. 12, a diagram of an exemplary carousel
machine for production of 3D objects. 3D printing is typically
characterized by low output because each object is typically
constructed from thousands of printed layers. A plurality of trays
1200 of a carousel production machine for 3D objects 1220 can be
used to increase the production throughput of 3D objects (such as
3D object 312)
[0271] According to an embodiment, a 3D production machine 1220
will preferably include a plurality of printing (preferably inkjet)
heads 1214 and a plurality of trays 1200 so as to enable production
of many objects in the same run by many printing (jetting) heads.
Multiple printing heads can be grouped into a group of printing
heads (1206A, 1206B, 1206C). Many and different parts (exemplary 3D
objects 1202) may be printed on each tray. Every object passes
multiple times (cycles) through the printing section (under the
printing heads), wherein each time adds one or a few layers. As
each object is typically constructed from thousands of printed
layers, typically thousands of cycles are necessary. In a case
where each cycle includes multiple printings from a plurality of
printing heads, the number of cycles can be reduced from thousands
to hundreds or less. Based on this description, one skilled in the
art will be able to determine how many heads and cycles and trays
1200 are necessary for constructing specific plurality of
objects.
[0272] The plurality of heads is arranged in the Y-axis direction
and are shifted in Y direction from each other so that respective
nozzles of the plurality of heads are staggered to fill completely
a layer's surface in one pass. More printing heads than required
for filling one layer can be used, e.g. to print more than one
layer in a pass. Heads for different building material can be
employed. For example, a first group of printing heads 1206A is
configured for printing a first material (material A) and a second
group of printing heads 1206B is configured for printing a second
material (material B). Heads for support material can be employed.
For example, a third group of printing heads 1206C configured for
printing support material. Optionally, a heat-radiating source 1208
(such as radiation source 308) from above the printed layers
follows the deposition of the layer(s) in a pass (i.e. a cycle).
Additionally and optionally, a leveling apparatus 1210 (for
example, leveling roller 302) can be included in the carousel's
cycle, typically after the printing heads.
[0273] When an object is finished printing, a robotic arm 1204 can
remove the completed tray 1200 from the carousel 1212 or remove
object(s) 1202 from a tray 1200, and send the object to further
production steps (e.g. firing) without stopping the carousel
rotation. Note that from layer to layer each tray shifts a little
lower in Z direction, so as the last printed layer is brought to
the height appropriate for the leveling apparatus to shave the
upper surface of the dried layer. In a preferred case where the
tray 1200 stays on the carousel 1212, when all parts from a tray
have been removed, the tray Z level (height) is controlled to an
initial position, and the machine would start printing a succeeding
group of parts.
[0274] An alternative implementation is to initially load a removal
plate 1216 on each tray 1200, on which the one or more objects 1202
are later printed. In this case, the tray 1200 is fixed to the
carousel and is referred to as a "chuck" which holds the removal
plate 1216. When all the objects 1202 on the plate 1216 are
printed, the robotic arm 1204 removes the removal plate 1216 and
sends the removal plate with the objects on the removal plate to a
follow-on stage, such as the firing stage. The removal plate may
include a thin metal plate, or, if a temperature higher than
typically 900.degree. C. is used in the firing stage, a carbon
plate. The plate may be held on the chuck by a vacuum force or by
holding "fingers" around the plate.
[0275] The portion of the carousel 1212 track under the printing
heads 1214 should preferably be straight. The heads should move in
Y-axis direction once a carousel cycle to perform "nozzle scatter".
As described elsewhere in this document, the trays 1200 are warmed
according to the required temperature during printing and the
printing heads 1214 are protected from the tray heat and fumes.
21. System Controller
[0276] FIG. 13 is a high-level partial block diagram of an
exemplary system 1300 configured to implement a controller for the
present invention. System (processing system) 1300 includes a
processor 1302 (one or more) and four exemplary memory devices: a
RAM 1304, a boot ROM 1306, a mass storage device (hard disk) 1308,
and a flash memory 1310, all communicating via a common bus 1312.
As is known in the art, processing and memory can include any
computer readable medium storing software and/or firmware and/or
any hardware element(s) including but not limited to field
programmable logic array (FPLA) element(s), hard-wired logic
element(s), field programmable gate array (FPGA) element(s), and
application-specific integrated circuit (ASIC) element(s). Any
instruction set architecture may be used in processor 1302
including but not limited to reduced instruction set computer
(RISC) architecture and/or complex instruction set computer (CISC)
architecture. A module (processing module) 1314 is shown on mass
storage 1308, but as will be obvious to one skilled in the art,
could be located on any of the memory devices.
[0277] Mass storage device 1308 is a non-limiting example of a
computer-readable storage medium bearing computer-readable code for
implementing the methods described herein. Other examples of such
computer-readable storage media include read-only memories such as
CDs bearing such code.
[0278] System 1300 may have an operating system stored on the
memory devices, the ROM may include boot code for the system, and
the processor may be configured for executing the boot code to load
the operating system to RAM 1304, executing the operating system to
copy computer-readable code to RAM 1304 and execute the code.
[0279] Network connection 1320 provides communications to and from
system 1300. Typically, a single network connection provides one or
more links, including virtual connections, to other devices on
local and/or remote networks. Alternatively, system 1300 can
include more than one network connection (not shown), each network
connection providing one or more links to other devices and/or
networks.
[0280] System 1300 can be implemented as a server or client
respectively connected through a network to a client or server.
Alternatively, system 1300 can be implemented as an embedded
controller.
Operation
First Embodiment
[0281] The principles and operation of a first embodiment may be
better understood with reference to the drawings and the
accompanying description. A present embodiment is a system and
method for printing an object. The system facilitates evaporating a
carrier liquid during printing while at least a portion of
dispersant remains in the printed layer.
[0282] While conventional implementations may heat an object body
after printing to evaporate the carrier, a feature of the current
embodiment is bringing or maintaining the temperature (TL) of the
(most recently/current) printed layer (upper surface of the body of
the object) near or above the boiling point of the carrier T1 (e.g.
above 0.7.times.T1 in Celsius) and simultaneously below the boiling
point of the dispersant. A result of this innovative feature is
that the carrier liquid evaporates as the ink is printing, in
contrast to conventional techniques of evaporating the carrier
after printing, while at least a portion of the dispersant remains
in the printed layer of the object. In some cases, the remaining
dispersant serves to bind the solid particles together after the
carrier liquid is evaporated. Alternatively, other materials can be
added to the ink to assist in binding of the solid particles
together after the carrier liquid evaporates.
[0283] One skilled in the art will realize that for a given object
(and associated ink, carrier liquid, dispersant, and other optional
components) there is a pre-defined (determined/calculated) range of
temperatures above a lower-bound ([T1]) of the carrier boiling
point temperature and below an upper-bound ([T2]) of the dispersant
boiling point temperature ([T1]<TL<[T2]), and wherein
bringing to, or maintaining a, temperature of the upper layer (TL)
in this pre-defined range of temperatures enables evaporating the
carrier while the dispersant remains in the current layer being
printed. In other words, in reality, the exact carrier boiling
point temperature Ti does not have to be used, but rather there is
a known range even below the carrier boiling point temperature T1
in which the carrier will evaporate. This range below the carrier
boiling point temperature Ti is referred to in this document as a
lower-bound ([T1]) of the carrier boiling point temperature.
Similarly, an exact dispersant boiling point temperature T2 does
not have to be used, but rather there is a known range around the
dispersant boiling point temperature T2 in which the dispersant
will not evaporate (remains liquid). This range around the
dispersant boiling point temperature T2 is referred to in this
document as an upper-bound ([T2]) of the dispersant boiling point
temperature. The lower-bound and upper-bound are typically 20% more
or less than the respective boiling point temperatures (typically
measured in degrees Kelvin). The lower-bound ([T1]) can be 20% less
than the carrier boiling point temperature (T1) typically measured
in degrees Kelvin. The upper-bound ([T2]) can be 20% more or less
than the dispersant boiling point temperature (T2) typically
measured in degrees Kelvin.
[0284] A first layer is printed on a printing surface of the
object. The object part of the first layer is printed with at least
one ink, typically from at least one corresponding inkjet printing
head. One or more of the printing heads, typically all of the
printing heads, can be modulated according to a content of the
first layer. Each of the at least one inks typically include a
carrier having a carrier boiling point temperature (T1), a
dispersant having a dispersant boiling point temperature (T2) and
particles having a particle sintering temperature (T3). When at
least two inks are printed, each of the at least two inks can
include particles of different types, and a local proportion of
each of the at last two inks is determined by the specification for
the layer being printed (first layer's specification). Typically,
the local proportion of each of the inks varies from one printed
layer to another printed layer, and from one point in a layer to
another point in the same layer. When the layer also includes a
support portion, the support is printed adjacent to the object
layer, as described below.
[0285] As described elsewhere in this document, the dispersant can
be chosen to additionally and/or alternatively bind the particles
to each other after the carrier is evaporated and/or inhibit
sintering of the particles to each other after the carrier is
evaporated.
[0286] A feature of inkjet printing is that the printing can be
selective, in other words, printing to areas that are part of each
layer being printed (such as the first layer of the object). Each
layer is typically printed based on a layer specification or layer
content (description) including information on what portion of the
current layer is the desired object. Optionally, the layer
specification can include information on areas of the current layer
not to be printed (to remain un-printed), to be printed with an
alternate ink (second ink, third ink, etc.), support areas, and/or
mold areas.
[0287] As described elsewhere in this document, bringing to or
maintaining a temperature of the upper layer (TL), evaporating of
the dispersant, and/or sintering can be achieved via techniques
such as use of a radiation source such as a heating lamp, an
electro-magnetic (EM) radiation source above the object, a
selective or non-selective laser, a focused linear laser beam, a
scanned laser beam, a scanned focused pencil laser beam, focused
light from a linear incandescent bulb, focused light from a gas
discharge lamp bulb, a flash light, an ultra-violet (UV) light
source, a visible light source, an infra-red (IR) light source, and
substrate (tray) temperature control. In a case where a scanned
laser beam is used, the beam can be modulated according to the
content of the layer (information on what portion of the current
layer is the desired object). The above-described techniques can be
used to evaporate the dispersant via temporarily increasing a
temperature of the first layer above a temperature of the
object.
[0288] In a case where printing is selective, printing to areas
that are part of the first layer of the object, then after
selective printing a non-selective laser can be used to irradiate
an entire area on which the object is being printed (for example,
using a line focused laser). This technique of selective printing
followed by non-selective use of a heating source, in particular
using a non-selective laser, can be used for heating the upper
surface or for firing-off (evaporating) dispersant. In contrast,
conventional techniques use non-selective printing (or simply
providing to the printing area an ink or other substance from which
to construct the 3D object) followed by a selective laser to sinter
desired portions of the object.
[0289] After evaporating the carrier, optionally the remaining
dispersant or a portion of the dispersant can be evaporated, and
then optionally the first (most recently printed) layer can be
sintered. Optionally, a subsequent layer can be printed on top of
the first layer after evaporating the carrier, after evaporating
dispersant, or after sintering (the printed layer). Typically, an
object is built from hundreds or thousands of printed layers, so
the method repeats by printing a subsequent layer (as a new "first
layer") on top of the previously printed (first) layer.
[0290] As described elsewhere in this document, a catalyst can be
added to the layer being printed (first layer). Catalysts can be
selected from compounds such as halides and copper chloride. The
catalyst can be added by a variety of techniques, for example:
[0291] including the catalyst in at least one of the inks; [0292]
jetting the catalyst in gaseous form from above the first layer;
[0293] jetting the catalyst in liquid form from above the first
layer; [0294] spraying the catalyst in gaseous form from above the
first layer; and [0295] spraying the catalyst in liquid form from
above the first layer.
[0296] The object is typically printed on a tray that is heated or
made of thermal isolation material.
[0297] In a case where the temperature of the upper surface TS is
kept above the carrier boiling temperature T1, (e.g. 30.degree. C.
higher than T1) the liquid carrier in the newly dispensed layer
abruptly boils (explodes like) when the ink lands on the upper
surface, creating a sponge like layer including open plenty tiny
inflations. This is because during the abrupt boiling, tiny
segments of the dispensed ink inflate (by the carrier gas) and
freeze (i.e. become dry), just before the gas makes an opening and
"flies" out. The resulting structure of the 3D object body is thus
porous. Creating a porous object body may be desirable to allow the
remaining dispersant to flow out of the structure of the object
during subsequent heating in an oven. Subsequent heating can be
used to remove (disintegrate and/or evaporate) remaining dispersant
and/or other ink components such as organic material.
Operation
Second Embodiment
[0298] The principles and operation of a second embodiment may be
better understood with reference to the drawings and the
accompanying description. A present embodiment is a system and
method for printing an object. The system facilitates evaporating
dispersant in a first layer prior to sintering the first layer
and/or prior to printing a second layer.
[0299] As described elsewhere in this document, conventional
implementations leave dispersant in a completed object, and after
printing the entire object then heat the entire object to fire-off
(evaporate) a portion of the dispersant. A feature of the current
embodiment is evaporating at least a portion of the dispersant
during printing. In general, a method for printing an object starts
with printing a first layer of at least one ink then evaporating at
least a portion of the dispersant, typically substantially all the
dispersant. After evaporating at least a portion of the dispersant,
a subsequent operation is performed. Subsequent operations include:
[0300] at least partially sintering the first layer, and [0301]
repeating printing a subsequent layer of the at least one ink on
the first layer.
[0302] Optionally, prior to evaporating at least a portion of the
dispersant, the carrier can be evaporated while the dispersant
remains in the first layer.
[0303] In general, the techniques and options discussed above, in
particular in reference to the first embodiment, can also be
implemented for this second embodiment.
Operation
Third Embodiment--FIGS. 2a to 3
[0304] The principles and operation of a third embodiment may be
better understood with reference to the drawings and the
accompanying description. A present embodiment is a system and
method for printing an object. The system facilitates leveling an
upper-layer of a printed object using a horizontal roller.
[0305] As described elsewhere in this document, printing can result
in an upper-layer (most recently printed/first layer) that is not
sufficiently flat (too rough) for subsequent processing. In this
case, leveling the top of the object is desired. Conventional
implementations use vertical milling or grinding disks rotating
about vertical beam, or smooth or knurled rollers. In the current
embodiment, an innovative horizontal roller is used. In an optional
embodiment, the horizontal roller is a cutting (bladed) roller.
[0306] Generally, a method for printing an object starts with
printing a first layer of at least one ink and then at least
partially hardening the first layer. Then the first layer is
leveled using an innovative horizontal roller. The horizontal
roller can include one or more blades (or alternatively a
cylindrical grinding surface) and rotation generally about an axis
parallel to a plane of the first layer (typically the Y-axis).
[0307] Additions, options, and alternatives for the current
embodiment are described in the above section "leveling apparatus".
After leveling and optionally: cleaning, further hardening,
evaporating at least a portion of the dispersant, and/or partial
sintering, if the object is not yet complete (incomplete) a
subsequent layer of at least one ink is printed on the first
layer.
Operation
Fourth Embodiment--FIGS. 10A to 11C
[0308] The principles and operation of a fourth embodiment may be
better understood with reference to the drawings and the
accompanying description. A present embodiment is a system and
method for printing an object with support. The system facilitates
repeatedly printing layers according to a map, each layer with
potentially both object and support portions, resulting in an
object with support. In particular, support for negative angles and
molds.
[0309] As described elsewhere in this document, techniques for
using support can facilitate using molds, support for negative
angles, using reinforced support, and pedestals.
[0310] The object portion of the layer is printed with object ink,
generally referred to as a first ink. Similarly, the support
portion of the object is printed with support ink, generally
referred to as a second ink.
[0311] Generally, a method for printing an object with support
starts with printing an object portion of a first layer using at
least a first ink, the first ink including: [0312] a first carrier;
and [0313] first particles used to construct the object and
dispersed in the first carrier.
[0314] A support portion of the first layer using at least a second
ink is printed prior to, simultaneously with, or after the object
portion is printed. The second ink includes: [0315] a second
carrier; and [0316] second particles used to construct the support
and dispersed in the second carrier.
[0317] Preferably, the second carrier is the first carrier.
Typically, the second particles are other than the first particles
and the carriers are liquids.
[0318] As described above, the support portion can be printed with
the second ink and additionally with the first ink. In other words,
typically printing both the object and support portions with the
first ink and then (or simultaneously) re-printing only the support
portions with the second ink.
[0319] In a preferred embodiment, printing is via at least a first
printing head, typically two or more printing heads, each printing
head jetting one type of ink and each printing head modulated
according to a content (object, support, and empty portions) of the
first layer.
[0320] After printing a first layer, if the object is not complete
(incomplete), a subsequent layer is printed on the first layer, the
subsequent layer including respective object and support portions
on the first layer.
[0321] The solid particles in the support ink can include particles
that are: miscible in water; at least partially soluble in water,
inorganic solid, organic, polymer, particles having a hardness less
than the hardness of the first particles, salt, metal oxides (e.g.
Zinc oxide), Silica (SiO.sub.2), Calcium sulfate, and tungsten
carbide (WC).
[0322] As discussed elsewhere in this document, the particles used
in the object and support portions depend on the specific
application, requirements, and object properties. Particles used
can include metal, metal oxides, metal carbides, metal alloys,
inorganic salts, polymeric particles, Polyolefin, and Polyolefin
poly (4-methyl 1-pentene).
[0323] When printing of the object with support is complete, the
support must be removed from the object either just after printing
or after subsequent processing in an oven. The support can be
removed from the object using various techniques, the specific
technique depending on the type of support. Techniques include
firing, immersing to dissolve the support, immersing in water to
dissolve the support, immersing in acid to dissolve the support,
immersing in a light acid, immersing in a strong acid, immersing in
HNO3, sand blasting, water jetting, etc.
[0324] It is foreseen that the described methods can be used in
other areas. For example, constructing objects that are generally
(informally) call two-dimensional (2D). Non-limiting examples
include flexible metal or composite antennas and biological
sensors. 2D objects may be composed of a single layer, or
relatively few layers. In these cases, the 2D object may have
similar requirements as construction of a 3D object. For example,
where an ink being used to print a 2D object includes a dispersant
for printing but the dispersant must be removed in the completed
object.
[0325] Note that the inks referred to in the current description
are commercially available conventional inks. It is foreseen that
alternative, additional, and new inks can be used with the current
invention.
[0326] The choices used to assist in the description of this
embodiment should not detract from the validity and utility of the
invention. It is foreseen that choices that are more general can be
used, depending on the application.
[0327] The use of simplified calculations to assist in the
description of this embodiment should not detract from the utility
and basic advantages of the invention.
[0328] Note that a variety of implementations for modules and
processing are possible, depending on the application. Modules are
preferably implemented in software, but can also be implemented in
hardware and firmware, on a single processor or distributed
processors, at one or more locations. The above-described module
functions can be combined and implemented as fewer modules or
separated into sub-functions and implemented as a larger number of
modules. Based on the above description, one skilled in the art
will be able to design an implementation for a specific
application.
[0329] Note that the above-described examples, numbers used, and
exemplary calculations are to assist in the description of this
embodiment. Inadvertent typographical errors, mathematical errors,
and/or the use of simplified calculations do not detract from the
utility and basic advantages of the invention.
[0330] To the extent that the appended claims have been drafted
without multiple dependencies, this has been done only to
accommodate formal requirements in jurisdictions that do not allow
such multiple dependencies. Note that all possible combinations of
features that would be implied by rendering the claims multiply
dependent are explicitly envisaged and should be considered part of
the invention.
[0331] It will be appreciated that the above descriptions are
intended only to serve as examples, and that many other embodiments
are possible within the scope of the present invention as defined
in the appended claims.
* * * * *