U.S. patent application number 16/490257 was filed with the patent office on 2020-03-05 for object made by additive manufacturing and method to produce said object.
The applicant listed for this patent is BOND HIGH PERFORMANCE 3D TECHNOLOGY B.V.. Invention is credited to Jan Teun BARTELDS, Adrianus BRUGGEMAN, Thomas Jonathan BRUGGEMAN, Klaas GROEN, Bouwe KUIPER, Koendert Hendrik KUIT, Kevin Hendrik Jozef VOSS, Martijn Johannes WOLBERS.
Application Number | 20200070404 16/490257 |
Document ID | / |
Family ID | 61274285 |
Filed Date | 2020-03-05 |
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United States Patent
Application |
20200070404 |
Kind Code |
A1 |
BRUGGEMAN; Thomas Jonathan ;
et al. |
March 5, 2020 |
OBJECT MADE BY ADDITIVE MANUFACTURING AND METHOD TO PRODUCE SAID
OBJECT
Abstract
A three-dimensional object created by Fused Deposition Modeling
(FDM) of a modeling material from polyaryletherketones (PAEK),
polyphenylsulfides, polyamide-imide, polyethersulfon,
polyetherimide, polysulfon, polyphenylsulfon, polycarbonates (PC),
polyacrylonitrile butadiene styrene) (ABS), polymethylmethacrylate
(PMMA), polyethyleneterephtalate (PET), polystryrene (PS),
acrylonitrilstyrene acrylate, polypropylene (PP), polylactic acid
(PLA), polyvinylalcohol (PVA), polyethylene (PE), polyoxymethylene,
polyurethane (PU), copolymers of polyvinylalcohol and
butenediolvinylalcohol and mixtures thereof, optionally filled with
inorganic or organic fillers, wherein the object has a porosity of
less than 5 vol %, as determined according to the porosity test
procedure `Porosity test`. The objects are leak tight and show
improved mechanical properties. FDM printing of PEEK generating
parts having high isotropy.
Inventors: |
BRUGGEMAN; Thomas Jonathan;
(Enschede, NL) ; BRUGGEMAN; Adrianus; (Enschede,
NL) ; KUIPER; Bouwe; (Enschede, NL) ;
BARTELDS; Jan Teun; (Enschede, NL) ; KUIT; Koendert
Hendrik; (Enschede, NL) ; GROEN; Klaas;
(Enschede, NL) ; WOLBERS; Martijn Johannes;
(Enschede, NL) ; VOSS; Kevin Hendrik Jozef;
(Enschede, NL) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
BOND HIGH PERFORMANCE 3D TECHNOLOGY B.V. |
Enschede |
|
NL |
|
|
Family ID: |
61274285 |
Appl. No.: |
16/490257 |
Filed: |
March 2, 2018 |
PCT Filed: |
March 2, 2018 |
PCT NO: |
PCT/EP2018/055169 |
371 Date: |
August 30, 2019 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B29C 64/118 20170801;
B29C 64/209 20170801; B29C 64/393 20170801; B33Y 30/00 20141201;
B33Y 50/02 20141201; G06F 30/00 20200101; B33Y 10/00 20141201; B29K
2101/12 20130101; B33Y 70/00 20141201; B41J 3/4073 20130101; B33Y
80/00 20141201 |
International
Class: |
B29C 64/118 20060101
B29C064/118; B33Y 10/00 20060101 B33Y010/00; B33Y 50/02 20060101
B33Y050/02; B33Y 70/00 20060101 B33Y070/00; B29C 64/393 20060101
B29C064/393 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 2, 2017 |
NL |
2018455 |
May 17, 2017 |
EP |
17171475.1 |
Claims
1. A three-dimensional object created by Fused Deposition Modeling
(FDM) of a modeling material from polyaryletherketones (PAEK),
polyphenylsulfides, polyamide-imide, polyethersulfon,
polyetherimide, polysulfon, polyphenylsulfon, polycarbonates (PC),
poly(acrylonitrile butadiene styrene) (ABS), polymethylmethacrylate
(PMMA), polyethyleneterephtalate (PET), polystryrene (PS),
acrylonitrilstyrene acrylate, polypropylene (PP), polylactic acid
(PLA), polyvinylalcohol (PVA), polyethylene (PE), polyoxymethylene,
polyurethane (PU), copolymers of polyvinylalcohol and
butenediolvinylalcohol and mixtures thereof, optionally filled with
inorganic or organic fillers, wherein the object has a porosity of
less than 5 vol %, as determined according to the porosity test
procedure `Porosity test` as defined in Paragraphs [0033] to
[0060].
2. The object according to claim 1, wherein the porosity is less
than 1 vol %.
3. The object according to claim 1, wherein the object has a leak
tightness below 10.times.10.sup.-6 mbarl/s, as determined by the
leak test procedure as defined in paragraphs [0061] to [0065].
4. The object according to claim 1, wherein an ultimate tensile
strength of a test piece measured in a Z-direction is at least 70%
of the ultimate tensile strength of the test piece measured in an
x-direction or a y-direction, wherein the ultimate tensile strength
is measured according to ISO 527-2:2012 SPECIMEN 5A.
5. The object according to claim 1, wherein object is prepared from
a thermoplastic composition using FDM, and wherein the
thermoplastic polymer is chosen from polyethylene, polypropylene,
ABS, polycarbonate and polyarylether ketones (PAEK) like for
example polyether ketone (PEK), polyethyer ethyer ketone (PEEK),
polyether ketone ketone (PEKK), polyether ether ketone ketone
(PEEKK) and polyether ether ketone ether ketone ketone (PEKEKK) and
combinations thereof.
6. The object according to claim 5, wherein the thermoplastic
polymer composition comprises at least 80 wt. % of a PAEK.
7. The object according to claim 5, wherein the thermoplastic
polymer composition comprises at least 80 wt. % of PEEK.
8. The object according to claim 6, wherein a test specimen of the
object having dimensions according to ISO 527-2:2012 SPECIMEN 5A
made from said polymer composition by said additive manufacturing
has an ultimate tensile stress according to ISO 527-2:2012 SPECIMEN
5A of at least 70 MPa.
9. The object according to claim 1, wherein the FDM is performed by
providing a layer in an X-Y plane having X-direction and
Y-direction and successively adding further layers on top of said
layer in Z-direction by depositing a modeling material onto
predetermined positions, wherein X-direction, Y-direction and
Z-direction are perpendicular to each other, wherein the depositing
step involves a. exerting a pressure on the modeling material to
feed the modeling material onto the predetermined positions; b.
determining a parameter indicative for the pressure exerted on the
modeling material and c. controlling the feeding depending on said
parameter.
10. The object according to claim 9, wherein providing of each of
the layers is performed by a. printing contour lines of the object
in the X-Y plane marking a primary area, b. filling a first part of
the primary area inside the contour lines of the object in the X, Y
plane, leaving open a second part in the primary area, c. filling
the second part by the depositing step.
11. The object according to claim 10, wherein filling of the first
part is performed by feeding the modeling material onto the
predetermined positions in a flow-controlled way.
12. An object created by Fused Deposition Modeling (FDM) from a
thermoplastic composition comprising at least 80 wt. % of a
polyarylether ketone (PAEK), wherein a test specimen of the object
having dimensions according to ISO 527-2:2012 SPECIMEN 5A made from
said polymer composition by said additive manufacturing has an
ultimate tensile stress according to ISO 527-2:2012 SPECIMEN 5A of
at least 70 MPa.
13. The object according to claim 12, wherein the FDM is performed
by providing a layer in an X-Y plane having X-direction and
Y-direction and successively adding further layers on top of said
layer in Z-direction by depositing a modeling material onto
predetermined positions, wherein X-direction, Y-direction and
Z-direction are perpendicular to each other, wherein the depositing
step involves a. exerting a pressure on the modeling material to
feed the modeling material onto the predetermined positions; b.
determining a parameter indicative for the pressure exerted on the
modeling material and c. controlling the feeding depending on said
parameter. and wherein providing of each of the layers is performed
by d. printing contour lines of the object in the X-Y plane marking
a primary area, e. filling a first part of the primary area inside
the contour lines of the object in the X, Y plane, leaving open a
second part in the primary area, f. filling the second part by the
depositing step.
14. The object according to claim 13, wherein the thermoplastic
composition comprises at least 90 wt. % PEEK.
15. A process for making an object according to claim 1, wherein
the process comprises the steps of: a. exerting a pressure on the
modeling material to feed the modeling material onto the
predetermined positions; b. determining a parameter indicative for
the pressure exerted on the modeling material and c. controlling
the feeding depending on said parameter. and wherein providing each
of the layers is performed by d. printing contour lines of the
object in the X-Y plane marking a primary area, e. filling a first
part of the primary area inside the contour lines of the object in
the X, Y plane, leaving open a second part in the primary area f.
filling the second part by the depositing step.
16. The object according to claim 3, wherein the porosity is less
than 0.5 vol %, and wherein the object has a leak tightness below
4.3.times.10.sup.-6 mbarl/s.
17. The object according to claim 16, wherein the porosity is less
than 0.2 vol %, wherein the object has a leak tightness between 0
and 3.times.10.sup.-6 mbarl/s.
18. The object according to claim 17, wherein the porosity is less
than 0.01 vol %.
19. The object according to claim 2, wherein an ultimate tensile
strength of a test piece measured in a Z-direction is at least 70%
of the ultimate tensile strength of the test piece measured in an
x-direction or a y-direction, wherein the ultimate tensile strength
is measured according to ISO 527-2:2012 SPECIMEN 5A; and wherein
wherein object is prepared from a thermoplastic composition using
FDM, and wherein the thermoplastic polymer is chosen from
polyethylene, polypropylene, ABS, polycarbonate and polyarylether
ketones (PAEK) like for example polyether ketone (PEK), polyethyer
ethyer ketone (PEEK), polyether ketone ketone (PEKK), polyether
ether ketone ketone (PEEKK) and polyether ether ketone ether ketone
ketone (PEKEKK) and combinations thereof.
20. The object according to claim 19, wherein the thermoplastic
polymer composition comprises at least 90 wt. % of a PAEK, or
wherein the thermoplastic polymer composition comprises at least 90
wt. % of a PEEK.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a three-dimensional object made by
additive manufacturing of a modeling material, like for example a
thermoplastic polymer composition.
BACKGROUND OF THE INVENTION
[0002] In additive manufacturing objects are formed by layering
modeling material in a controlled manner such that a desired
three-dimensional shaped object can be created. Very often for
additive manufacturing an additive manufacturing printer is used.
The printer has a two or three dimensionally moveable printhead
which dispenses the modeling material, while the printhead is moved
over previously deposited tracks of the modeling material. A
preferred examples of additive manufacturing is fused deposition
modeling (FDM).
[0003] The object to be printed can be placed on a base. The
printhead is movable in a three-dimensional space relative to the
object being modeled or printed or vice versa. In some cases, the
object is movable in one or more dimensions relative to the
printhead. Various combinations are possible for moving the object
on which the object is modeled relative to the printhead and vice
versa.
[0004] The motions of the printhead and optionally base are
controlled by a control system which controls a controllable
positioning system to which the printhead (and optionally base) is
attached. By means of software a pattern of tracks can be designed,
which pattern is used for moving the printhead and for depositing
the tracks.
[0005] The object is created on a base structure in a reference
location relative to the movable printhead. The modeling material
can be fused with previously formed tracks. The additive
manufacturing material can be fed in the printhead in the form of
for example filaments, granulate, rods, liquid or a suspension. The
printhead dispenses the modeling material from the printhead
through a nozzle and deposits it on the base in the form of tracks
forming a layer of tracks, or when a previous layer of the object
to be created has been deposited, on the object on previously
deposited tracks where it is allowed to solidify. The modeling
material can be thermally or chemically or otherwise fused with the
previously deposited tracks. The chemically modeling material can
be dispensed from the printhead and deposited on the previously
deposited tracks and cured to solidify immediately after the
deposition.
[0006] The relative motion of the base and object to the printhead
in tracks and simultaneous deposition of modeling material from the
printhead allow the fused deposition modeled object to grow with
each deposited track and gradually attains its desired shape.
[0007] In current material extrusion printers (including granulate
extruders, ram extruders and syringe extruders), the material is
deposited in a feed forward, flow-controlled way. The flow of the
modeling material is kept constant, depending on thickness of the
tracks to be deposited and the print speed. As part of the machine
calibration, the material flow is calibrated.
[0008] Moreover, the X-Y-Z positioning system which causes the
printhead to move over the previously deposited tracks of the
object being created must be calibrated in order to maintain
accurate dimensions of the object to be created and especially to
maintain a controlled thickness of the tracks being deposited.
[0009] When the calibration is correct, solid objects can be
printed accurately using flow control. When the gap between the
printhead nozzle and the previously deposited layer for example
increases due to lack of calibration, the flow of modeling material
can become too small to fill up the gap, thereby causing the
occurrence of spaces between the printed tracks, resulting in
cavities in the printed object. This is called under-extrusion.
[0010] On the other hand, when the gap between the printhead nozzle
and the previously deposited layers decreases due to lack of
calibration, the flow of modeling material can become too high for
the track being deposited, so too much material will be extruded.
This is called over-extrusion. Over-extrusion can also occur when
the track is laid between two previously deposited tracks and the
space there between is narrowing. This may result in excessive
forces between the object and the printhead and in a rough surface
of the object due to overflow of the modeling material. The
overflow of modeling material may lead to debris or residue on the
nozzle tip of the printhead which may come off the nozzle tip and
fuse with the object being printed and cause potential loss of the
object. Also, the print head smears over the object being printed,
causing a very rough top surface of the object and excessive forces
which ultimately cause the object from breaking loose from the
build plate.
[0011] Loss of calibration may also be caused by thermal expansion
while printing and subsequent shrinking after printing of thermally
fused material. When the thermal expansion and shrinking are
insufficiently compensated, the gap between nozzle and previously
deposited layers may not have constant dimensions. Likewise, also
dimensions in directions perpendicular to the deposition direction
by the printhead or nozzle may vary due to thermal effects. Another
cause of under- or over extrusion may lie in variation of the
modeling material feedstock dimensions. When for example filament
of modeling material is used, its diameter may vary causing
variations in the amount of modeling material deposited when
printing, giving cause to under-or over-extrusion when using
constant flow control of the modeling material being deposited.
[0012] When performing the calibration of the X-Y-Z system and of
the feeding means of the modeling material, the highest priority is
to prevent over-extrusion, since this will make the process
unreliable. Therefore, additive manufacturing (like fused
deposition modeling) extrusion printers usually have some degree of
under-extrusion causing formation of open spaces or cavities. As a
side effect, parts will not be leak-tight or pressure resistant and
the strength of the part will be sub-optimal.
[0013] Generally, the mechanical properties of an object prepared
by fused deposition modelling (FDM) of a modeling material (like
for example a thermoplastic polymer composition) are less favorable
than an object with the same dimensions made by injection molding.
In injection molding of a thermoplastic polymer composition, all
polymer chains have strong interactions due to the fluid state of
the polymer and will have ample time to entangle and solidify to
form a strong object. The mechanical properties of the object are
mainly determined by the polymer composition used to prepare the
object. In FDM, a new layer in a fluid state is provided onto an
existing layer which has already solidified. The polymer chains of
the new layer have a limited possibility to entangle with the
solidified material of the existing layer, and also bonding with
the existing layer will be limited. Accordingly, the adhesion
between the new layer and the existing layer is weaker than the
adhesion between the polymer chains within the same layer. This
results in an object having lower mechanical properties in the
Z-direction than in the X-direction and Y-direction.
[0014] US2014/0141166 describes an FDM process using a blend of 2
polyamides: the blend comprises at least one semi-crystalline
polyamide and one amorphous polyamide. The blends are being printed
in order to generate a dimensionally stable part. The parts are
conditioned with water after being printed. The conditioning
reduces the porosity of the parts, since the polyamides will absorb
water through the conditioning step and swell. the reduction of the
porosity is attributed to the very specific blend of two
polyamides. The US2014/0141166 mentions different comparative
materials that do not show this effect, like for example
poletherimide, ABS, virgin PA12 polyamide and carbon filled
PA12.
SUMMARY OF THE INVENTION
[0015] It is therefore an object of the invention to overcome the
above described problems and disadvantages.
[0016] According to one aspect, the invention provides a
three-dimensional object created by Fused Deposition Modeling (FDM)
from a material selected from polyaryletherketones (PAEK),
polyphenylsulfides, polyamide-imide, polyethersulfon,
polyetherimide, polysulfon, polyphenylsulfon, polycarbonates (PC),
poly(acrylonitrile butadiene styrene) (ABS), polymethylmethacrylate
(PMMA), polyethyleneterephtalate (PET), polystryrene (PS),
acrylonitrilstyrene acrylate, polypropylene (PP), polylactic acid
(PLA), polyvinylalcohol (PVA), polyethylene (PE), polyoxymethylene,
polyurethane (PU), copolymers of polyvinylalcohol and
butenediolvinylalcohol and mixtures thereof, optionally filled with
inorganic or organic fillers, having a porosity of less than 5 vol
%, as determined according to the porosity test procedure `porosity
test`.
[0017] Accordingly, the additive manufacturing according to the
invention is performed such that under-extrusion is avoided so that
the object has less volume of cavities, and a low porosity.
[0018] Preferably the porosity is less than 1 vol %, or less than
0.5 vol %, less than 0.2 vol %, or even less than 0.01 vol %.
[0019] Porosity is a measure for the presence of cavities inside an
object. Another indication for the presence (or preferably absence)
of cavities is a leak test. In the leak test, leakage of air is
measured through a sample of an object.
[0020] When an object has no cavities, the object will be leak
tight. Preferably, the object according to the invention has an air
leak tightness below 10.times.10.sup.-6 mbarl/s, preferably below
4.3.times.10.sup.-6 mbarl/s, more preferably between 0 and
3.times.10.sup.-6 mbarl/s, as determined by a leak test procedure
(see definition below).
[0021] FIG. 13 shows the typical structure of a sample according to
the invention (schematic).
[0022] FIG. 14 shows a typical structure of 3D printed object
according to the prior art (schematic).
[0023] Preferably, the three-dimensional object according to the
invention has a high isotropic strength, which means that the
mechanical properties (strain and ultimate strength) are similar in
all directions (X, Y, Z). Usually in FDM, the mechanical properties
in the Z direction are lower compared to the mechanical properties
in the X and Y direction. Herein the X and Y direction are parallel
to the build plate of the FDM apparatus, and the Z direction is
perpendicular to the build plate of the FDM apparatus.
[0024] Accordingly, the FDM process according to the invention is
preferably performed in such a way that when a test specimen having
dimensions according to ISO 527-2:2012 specimen 5A is made from
said modeling material by said FDM process, the ultimate tensile
strength of the test piece in the Z-direction is at least 70% of
the ultimate tensile strength of the test piece in the X-direction
or Y-direction, wherein the ultimate tensile strength is measured
according to ISO 527-2:2012 SPECIMEN 5A.
[0025] Preferably the ultimate strength in the Z direction is at
least 80%, more preferably 85% or 90% compared to the X or Y
direction of the testpiece.
[0026] The thermoplastic polymer composition may contain any
thermoplastic polymer which can be used for FDM. Preferred example
of modeling materials are selected from the group of
polyaryletherketones (PAEK), polyphenylsulfides, polyamide-imide,
polyethersulfon, polyetherimide, polysulfon, polyphenylsulfon,
polycarbonates (PC), poly(acrylonitrile butadiene styrene) (ABS),
polymethylmethacrylate (PMMA), polyethyleneterephtalate (PET),
polystryrene (PS), acrylonitrilstyrene acrylate, polypropylene
(PP), polylactic acid (PLA), polyvinylalcohol (PVA), polyethylene
(PE), polyoxymethylene, polyurethane (PU), copolymers of
polyvinylalcohol and butenediolvinylalcohol and mixtures therefore,
optionally filled with inorganic or organic fillers. Preferred
examples of the thermoplastic polymer are polyethylene,
polypropylene, ABS, polycarbonate, polyamide and polyarylether
ketones (PAEK) like for example polyether ketone (PEK), polyether
ether ketone (PEEK), polyether ketone ketone (PEKK), polyether
ether ketone ketone (PEEKK) and polyether ether ketone ether ketone
ketone (PEKEKK) and combinations thereof. Most preferably the
polymer is PEEK. The polymer composition may further comprise
additives and fillers as customary in the art.
[0027] In a preferred embodiment the thermoplastic polymer
composition comprises at least 80 wt. % of a PAEK, preferably at
least 90 wt. % of a PAEK. In a particularly preferred embodiment,
the thermoplastic polymer composition comprises at least 80 wt. %
of PEEK, preferably at least 90 wt. % of a PEEK, more preferably
PEEK.
[0028] Preferably, the thermoplastic polymer composition comprises
at least 80 wt. % of a PAEK, preferably PEEK, and a test piece
having dimensions according to ISO 527-2:2012 SPECIMEN 5A made from
said polymer composition by said additive manufacturing has an
ultimate tensile stress according to ISO 527-2:2012 SPECIMEN 5A in
any of the X, Y, Z directions (as defined above) of at least 50,
preferably at least 60, or 70, or 80 MPa.
[0029] Printing of PEEK is extremely difficult, due to the high
printing temperature, which is very close to the decomposition
temperature, and the high thermal expansion/shrinkage of PEEK. FDM
printing a part from PEEK giving an object having high mechanical
properties has not yet been reported in literature.
[0030] The invention also relates to an object created by FDM from
a thermoplastic composition comprising at least 80 wt. % of a
polyarylether keton (PAEK), wherein a test specimen of the object
having dimensions according to ISO 527-2:2012 SPECIMEN 5A made from
said polymer composition by said additive manufacturing has an
ultimate tensile stress according to ISO 527-2:2012 SPECIMEN 5A of
at least 70 MPa, preferably 80 MPa, more preferably 90 MPa.
[0031] The object is preferably obtained in a process wherein the
FDM is performed by providing a layer in an X-Y plane having
X-direction and Y-direction and successively adding further layers
on top of said layer in Z-direction by depositing a modeling
material onto predetermined positions, wherein X-direction,
Y-direction and Z-direction are perpendicular to each other,
wherein the depositing step involves [0032] a. exerting a pressure
on the modeling material to feed the modeling material onto the
predetermined positions; [0033] b. determining a parameter
indicative for the pressure exerted on the modeling material and
[0034] c. controlling the feeding depending on said parameter.
[0035] and wherein providing of each of the layers is performed by
[0036] d. printing contour lines of the object in the X-Y plane
marking a primary area, [0037] e. filling a first part of the
primary area inside the contour lines of the object in the X, Y
plane, leaving open a second part in the primary area, [0038] f.
filling the second part by the depositing step.
[0039] Testing Procedures
[0040] Porosity Test Procedure
[0041] Optical Setup
[0042] The optical setup consists of: [0043] A Basler acA1920-50 gm
digital monochrome camera with a 11.3 mm.times.7.1 mm sensor with
1920.times.1200 pixels [0044] An Edmund Optics 1.times., 40 mm WD
CompactTL.TM. telecentric lens 1.times. magnification and through
the lens illuminator port [0045] A Dolan-Jenner MI-150 Fiber Optic
Illuminator with a 150 W lamp with 3250K color temperature
configured to provide on-axis illumination [0046] A Thorlabs GN2/M
dual axis manual gonio stage with sample holder.
[0047] Sample Preparation
[0048] The sample shall contain an area of at least 15 mm.times.10
mm printed with 100% infill
[0049] The sample is potted in a puck to maintain flatness of the
surface during polishing.
[0050] The following potting material is used: [0051] 7 parts
Streuers Specifix-20, with 1 part Streuers Curing agent and the
samples is impregnated under vacuum.
[0052] The plane of the cross section is perpendicular to the
printing direction.
[0053] Both sides of the puck are grinded to make the planes
parallel and to make a cross section showing only the infilled
area.
[0054] The grinding and polishing procedure with the Struers
polisher and Struers consumables is: [0055] 80 grid: 150 seconds at
150 rpm and 20 N force [0056] 800 grid: 120 seconds at 150 rpm and
20 N force [0057] 1200 grid: 120 seconds at 150 rpm and 20 N force
[0058] 2000 grid: 120 seconds at 150 rpm and 20 N force [0059] 4000
grid: 120 seconds at 150 rpm and 20 N force [0060] 3 .mu.m diamond
paste: 180 seconds at 150 rpm and 25 N [0061] 5 minutes ultrasonic
cleaning [0062] 1 .mu.m diamond paste: 180 seconds at 150 rpm and
30 N [0063] 10 minutes ultrasonic cleaning [0064] Careful removal
of remnants of the polishing step to obtain a clean surface.
[0065] While grinding the grinding disc and sample area are flooded
with cold flowing water in order to prevent sample heating to
damage the surface texture.
[0066] The samples are grinded until the surface is smooth and
hardly any polishing scratches are visible under the
microscope.
[0067] Subsequently use polishing paste to remove remaining
scratches.
[0068] This polishing procedure is standard operation for a person
skilled in the art.
[0069] Imaging
[0070] Adjust both rotations of the manual rotating stage while
observing the camera image such that the polished surface is
exactly perpendicular to the optical axis of the optical system and
the illumination light is exactly reflected into the camera,
obtaining the highest brightness and contrast.
[0071] Adjust the shutter time of the camera such that: [0072] less
than 1% of the pixels are underexposed, i.e. have an intensity of
less than 1% of the dynamic range and [0073] less than 1% of the
pixels are overexposed, i.e. have an intensity of more than 99% of
the dynamic range
[0074] Images must be stored with full resolution and single
channel grey image without image compression.
[0075] A solid piece of printed material should be visible inside
the field of view, without the skin or the edge of the part being
visible in the image.
[0076] Ensure at least 10 and no more than 25 tracks are imaged to
the width of the image sensor.
[0077] Ensure at least 14 and no more than 40 layers are imaged to
the height of the image sensor.
[0078] If the structure of the printed tracks is too large or too
small to allow for this number of printed tracks or layers in the
field of view, use a lens with similar optical properties but
different magnification and scale the size of the sample
accordingly.
[0079] Image Post Processing
[0080] The following post procedure assumes that the cavities are
dark colored and the print material in between is bright. The
images are imported and processed as signed 16 bit integers. [0081]
1. Determine a variable R measured in pixels which is 1/10th of the
long short side of the image. [0082] 2. Create a copy of the image
and apply a median filter to the copy of the original image with a
square shaped structural element with width and height 2*R (or the
nearest odd integer value if this is required by the implementation
of the algorithm) [0083] 3. Subtract the filtered image from the
image from step 2 and add a value of 15 20 to each pixel in the
same step [0084] 4. Check if the resulting image is not clipped
according to the 1% criterion mentioned above. In case clipping
occurs, adjust the illumination and shutter time and repeat the
procedure [0085] 5. Convert the resulting image to a binary image,
converting each pixel with positive value to 1, and all other
pixels to 0 [0086] 6. Perform region erosion with a disk-shaped
structural element with a radius of 31.5 pixels [0087] 7. Perform
region dilation with a disk-shaped structural element with a radius
of 5.53.0 pixels [0088] 8. Perform region erosion with a
disk-shaped structural element with a radius of 31.5 pixels [0089]
9. Crop the resulting image, cropping off a band of width R from
each edge leaving a square portion as large as the height of the
original image [0090] 10. Determine the number of black pixels with
a pixel value of 0 [0091] 11. Determine the total number of pixels
[0092] 12. Calculate the porosity as the quotient of the number of
black pixels and the total number of pixels, expressed in
percent.
[0093] The source code for calculating the porosity is a Python
source code and is defined as:
TABLE-US-00001 Version of Python used: 3.6.4 (v3.6.4:d48eceb, Dec
19 2017, 06:54:40) [MSC v.190064 bit (AMD64)] Version of NumPy
used: 1.14.0 Version of openCV used: 3.4.0 import numpy as np
import cv2 import os import sys def VisionAlgorithm(image,
blurRadius=10, threshold=20, erodeRadius=1.5, dilateRadius=3.0): #
1) Determine blur radius height, width, depth = image.shape R =
round ( height / blurRadius ) # 2) Perform median blur blurred =
cv2.medianBlur(image, R*2+1) # 3) Convert to signed int to prevent
overflow when subtracting img16 = np.int16( image[;,;,1] )
blurred16 = np.int16( blurred[;,:,1] ) # 4) Subtract images and add
threshold difference = img16 - blurred16 + threshold # 5) Convert
to binary binary = difference < 0 binary = np.uint8(binary) # 6)
Erode X,Y = [np.arange(-2*(erodeRadius+1),2*(erodeRadius+1)+1)]*2
disk1 = np.uint8(X[:,None]**2 +Y**2 <= erodeRadius*erodeRadius)
erosion = cv2.erode(binary,disk1,iterations = 1) # 7) Dilate X,Y =
[np.arange(-2*(dilateRadius+1),2*(dilateRadius+1)+1)]*2 disk2 =
np.uint8(X[:,None]**2 + Y**2 <= dilateRadius*dilateRadius)
dilation = cv2.dilate(erosion,disk2,iterations = 1) # 8) Erode
again erosion2 = cv2.erode(dilation,disk1,iterations = 1) # 9) Only
use center square portion of the image leftMargin = int((width -
height)/2) cropped = erosion2[0:height,
leftMargin:leftMargin+height] # 10) Count black pixels blackPixels
= (cropped == 0) black = np.sum(blackPixels == 0) H, V =
blackPixels.shape porosity = 100*black/(H*V) # 11) Create blended
image to display the result center = image[0:height,
leftMargin:leftMargin+height] islands=np.zeros( (H,V,3), np.uint8)
islands[:,:,2]=255*(cropped > 0) blend =
cv2.addWeighted(center,0.7,islands,0.2,0) header=`porosity`
result=`{porosity}%`.format(porosity=porosity) # Return the header,
the results and the image back to the main program return (header,
result, blend) # MAIN PROGRAM # Determine a list of files to be
processed results=[ ] # Prepare a directory for storing result
files resultsDir=os.path.join(os.getcwd( ), `results`) if not
os.path.isdir(resultsDir): os.mkdir(resultsDir) for de in
os.scandir(os.path.join(os.getcwd( ),`samples`)): if de.name.lower(
).endswith(`png`): # Derive the file name sample, extension =
os.path.splitext(de.name) path = de.path # Open the image file
image = cv2.imread(path, cv2.IMREAD_UNCHANGED) # Have the image
processed by the vision algorithm header, result, blend =
VisionAlgorithm(innage) header=`samples\t`+header
result=samples`\t`+result # Store the blend of the image and the
voids as a result image sampleFile=`%s.png` % sample
resultfile=os.path.join(resultsDir, sampleFile)
cv2.imwrite(resultfile,blend) # Append the header to the results
list if required if len(results)==0: print(header)
results.append(header) # Append the results to the result list
print(result) results.append(result) results.append('')
results.append(`Version of Python used: %s` % sys.version)
results.append(`Version of NumPy used: %s` % np.version.version)
results.append(`Version of openCV used: %s` % cv2._version_) #
Write the results to file resultfile=os.path.join(resultsDir,
`results.txt`) open(resultfile, `w`).writelines([`%s\n` % s for s
in results])
[0094] Leak Test
[0095] For testing the leak tightness, test specimens A, B and C
are defined, each with a cuboid shape of 20 mm.times.20 mm.times.2
mm (see FIG. 9): [0096] test specimen type `A` is printed in the XY
plane of the printer [0097] test specimen type `B` is printed
perpendicular to the XY plane of the printer [0098] test specimen
type `C` is retrieved by sawing the specimen from a larger printed
object
[0099] The test is performed with the test setup according to FIG.
10. The test sample is placed horizontally in the test setup. Above
the test sample is water. Under the test sample is compressed air
with an air overpressure of 6 bar. Leaking of air or water past the
sample is prevented by O-rings with an inner diameter of 14 mm and
an outer diameter of 19 mm. The construction of the setup is such
that if the O-ring seal is imperfect, air will flow to the
environment and will not lead to false detection of a leak through
the sample.
[0100] While the sample is exposed to the test overpressure of 6
bar, the occurrence of air bubbles in the water is observed. If
over a period of 10 minutes no air bubbles larger than o1 mm are
observed, the sample is considered leak tight. The leak tightness
is preferably below 10.times.10.sup.-6 mbarl/s, more preferably
below 4.3.times.10.sup.-6 mbarl/s, most preferably between 0 and
3.times.10.sup.-6 mbarl/s. The leak tightness value in mbar*l/s
number can be calculated by estimating the total volume of the
(assumingly spherical) air bubbles, multiplying this by the
overpressure (6 bar) and dividing this by the test period (10
minutes). The diameter of the air bubbles can be measured with a
suitable, calibrated digital camera
[0101] Of each sample, 3 random samples are tested according to the
test method as described below. Thus, a total of 9 experiments are
carried out. The samples are considered leak tight if all 9 samples
pass the test.
[0102] Test specimen for mechanical testing.
[0103] For the determination of the mechanical properties of the
printed parts, test specimens `D`, `E` and `F` are defined. Each
test specimen has dimensions according to ISO 527-2:2012 specimen
5A (see also FIG. 11a).
[0104] A coordinate system is defined which is oriented relative to
the direction of printing (see FIG. 11b).
[0105] Test specimen type `D` is printed flat on the print bed,
with print tracks in the direction of the tensile bar, such that
the tensile strength in X-direction can be measured (FIG. 11c).
[0106] Test specimen type `E` is printed flat on the print bed,
with print tracks in the direction of the tensile bar, such that
the tensile strength in Y-direction can be measured (FIG. 11d).
[0107] For test specimens `D` and `E`, the printed tracks are
printed on top of each other (see FIG. 11e left). A `bricklaying
structure` is not allowed (FIG. 11e (right)).
[0108] Test specimen type `F` is printed upright with respect to
the print bed, such that the tensile strength in X-direction can be
measured (FIG. 11f).
[0109] The specimens are printed with a solid infill. If desired to
obtain optimal mechanical properties, thermal treatment is applied.
Specimens are printed with small overdimensions and milled down to
obtain the correct dimensions and fine surface roughness.
[0110] Of each specimen, three samples are printed. The mean value
of the mechanical properties is taken.
[0111] The process according to the invention can be performed with
different modeling materials. The most common modeling material to
be used is a thermoplastic polymer. Is it also possible to use
other modeling materials, like for example reactive liquids,
resins, filled materials like for example concrete, gypsum,
thermosetting materials, elastomers, liquid crystal polymers, 2K
polymers, polymer clay or binded ceramics.
[0112] The object according to the invention can be obtained by
fused deposition modelling (FDM) in which the depositing of a
modeling material (like for example a thermoplastic polymer
composition) onto the predetermined positions is controlled
according to the pressure exerted on the modeling material. More in
particular, depositing of the modeling material onto the
predetermined positions involves [0113] exerting a pressure on the
modeling material to feed the modeling material onto the
predetermined positions; [0114] determining a parameter indicative
for the pressure exerted on the modeling material and [0115]
controlling the feeding depending on said parameter.
[0116] In some embodiments, providing of each of the layers is
performed by [0117] printing contour lines of the object in the X-Y
plane marking a primary area, [0118] filling a first part of the
primary area inside the contour lines of the object in the X, Y
plane, leaving open a second part in the primary area [0119]
filling the second part by the depositing step.
[0120] In some embodiments, filling of the first part is performed
by feeding the modeling material (like for example the
thermoplastic polymer composition) onto the predetermined positions
in a flow-controlled way.
[0121] An example of an additive manufacturing system for creating
the three-dimensional object according to the invention comprises
an additive manufacturing printhead, wherein the printhead is
attached to positioning means spatially moving at least one of the
printhead and the object being printed relative to one another.
[0122] The printhead comprises a tubular feed member and a nozzle
arranged at one end of the tubular feed member, the nozzle having
an outlet for dispensing modeling material, and a nozzle tip, for
facing previously deposited tracks of modeling material on the
object to be created. The modeling material can be a thermoplastic
polymer composition.
[0123] The tubular feed member comprises a feed channel for feeding
the modeling material to the nozzle outlet.
[0124] The system further comprises modeling material feeding means
arranged at an end of the tubular feed member opposite of the
nozzle, wherein the modeling material feeding means are arranged
for exerting a pressure exerted on the modeling material within the
feed channel towards the nozzle.
[0125] The system further comprises pressure determining means for
determining a parameter indicative for a pressure exerted on the
modeling material.
[0126] The system further comprises a control system arranged for
controlling the modeling material feeding means based on the
determined parameter indicative for a pressure exerted on the
modeling material.
[0127] By controlling the pressure, it can be sensed by the control
system using the pressure determining means that the
under-extrusion occurs when for example the pressure drops below a
certain level. By increasing the pressure exerted on the modeling
material within the tubular feed member, this under-extrusion can
be compensated for. This may occur for example when a space between
previously deposited adjacent tracks is widening while depositing
the current track.
[0128] On the other hand, it can be sensed that over-extrusion
occurs when the parameter indicative of the pressure exerted on the
modeling material pressure increases above a certain level. By
decreasing the pressure exerted on the modeling material within the
tubular feed member, this over-extrusion can be compensated for.
This may occur for example when a space between previously
deposited adjacent tracks is narrowing. By controlling the pressure
of the modeling material, remaining spaces in the printed object
will be filled well, independent of the volume of the remaining
space. This will result in fusing of the track being deposited with
the previously deposited adjacent tracks, causing total infill of
cavities and improved bonding between adjacent tracks. Therefore,
parts will have optimal leak tightness and strength.
[0129] The track thickness, determined by the gap between nozzle
and previously deposited layer, is usually very small. This implies
that the pressure drop over this gap is large due to viscosity of
the modeling material. It requires only a distance in the order of
magnitude of a millimeter for the pressure drop from the level of
the pressure in or at the nozzle tip to reach ambient pressure. As
the distance to the nozzle becomes larger, the pressure drop over
the gap increases. When the pressure drop is equal to the
overpressure in the nozzle, the flow stops and the track does not
become wider. As the printhead moves over the object, this balances
out to become a stable track width
[0130] The main difference with flow controlled printing is that
width of the track being deposited balances out to a constant line
width while filling up all the gaps nicely, while flow based
printing would soon result in systematic under- or
over-extrusion.
[0131] By controlling the pressure exerted on the modeling
material, variations in the gap size between the nozzle and
previously deposited tracks are compensated for.
[0132] In an embodiment, the control system is arranged for
controlling the modeling material feeding means to maintain a
pressure exerted on the modeling material between a predetermined
minimum pressure value and a predetermined maximum pressure value.
This allows the pressure exerted on the modeling material to be
within a range ensuring that no over- or under-extrusion occurs,
regardless of imperfections of alignment or calibration of the
positioning means.
[0133] In an embodiment, the control system is arranged for
maintaining the parameter indicative for a pressure exerted on the
modeling material at a constant value. This further improves tracks
to be deposited between or adjacent previously deposited tracks to
be filled up fully without leaving open spaces, or cavities, while
preventing formation of debris and residue. Moreover, the constant
pressure reduces wear in the printhead and modeling material
feeding means.
[0134] In an embodiment, the modeling material feeding means
comprise a controllable drive and transmission means connected to
the drive for transferring a force generated by the drive to the
modeling material. The controllable drive allows the control system
to generate a controllable force which results in a pressure
exerted on the modeling material within the tubular feed means,
i.e. the feed channel and a pressure exerted on the modeling
material at the nozzle tip.
[0135] In an embodiment, the pressure determining means for
determining a parameter indicative for a pressure exerted on the
modeling material comprise pressure determining means for
determining the parameter indicative of the pressure exerted on the
modeling material within the feed channel. This allows for example
the parameter indicative for a pressure exerted on the modeling
material to be determined by the force exerted on the modeling
material by the controllable drive and the transmission means. The
thus determined parameter constitutes a measure indicative for the
pressure exerted on the modeling material within the feed
channel.
[0136] Depending on the modeling material, an appropriate drive and
force transmission means can be chosen. The controllable drive is
controllable by the control system. Forces at the nozzle tip and
torque within the drive and transmission system can be considered
indicative for a pressure exerted on the modeling material.
[0137] In an embodiment, the controllable drive comprises a rotary
drive, and the pressure determining means for determining the
parameter indicative of the pressure exerted on the modeling
material on the modeling material within the feed channel comprise
torque determining means for determining a torque exerted by the
rotary drive and/or transmission. This allows the parameter
indicative of the pressure exerted on the modeling material to be
derived from the torque exerted by at least one of the rotary drive
and the transmission.
[0138] In an embodiment, the controllable drive comprises an
electric motor, and wherein the torque determination means comprise
a motor current measuring means. This allows torque determination
without any further torque sensor.
[0139] In an embodiment, the modeling material feeding means
comprises a plunger for feeding modeling material into the modeling
material feeder. The plunger allows modeling material in the form
of rods to be fed into the tubular feed member.
[0140] The parameter indicative for a pressure exerted on the
modeling material within the feed channel is determined by the
pressure exerted on the modeling material by the plunger, and
wherein the pressure determining means for determining the
parameter indicative of the pressure exerted on the modeling
material within the feed channel comprise a force sensor, arranged
at the plunger for measuring the pressure exerted by the plunger on
the modeling material.
[0141] From the exerted force, the parameter indicative for the
pressure exerted on the modeling material within the feed channel
can be derived. This is an alternative way to measuring motor
current or torque from the drive system to easily determine the
parameter indicative for a pressure exerted on the modeling
material within the feed channel of the tubular feed member.
[0142] In an embodiment, the pressure determining means for
determining the parameter indicative of the pressure exerted on the
modeling material within the feed channel comprise a pressure
sensor connected to the feed channel of the tubular feed member,
Thus, the parameter indicative of the pressure exerted on the
modeling material within the feed channel can be determined
directly by the pressure sensor.
[0143] In an embodiment, the pressure determining means for
determining the parameter indicative of the pressure exerted on the
modeling material within the feed channel comprise a pressure
sensor connected to the feed channel at the nozzle. Thus, the
parameter indicative of the pressure exerted on the modeling
material within the feed channel can alternatively be directly
determined by the pressure sensor within the nozzle.
[0144] In an embodiment, the pressure sensor arranged at the nozzle
comprises a nozzle deformation sensor. This has an advantage that
the sensor does not need direct contact with the flow of modeling
material within the feed channel of the nozzle.
[0145] In an embodiment, the pressure determining means for
determining a parameter indicative of a pressure exerted on the
modeling material comprise pressure determining means for
determining a parameter indicative of a pressure exerted on the
modeling material within the track being deposited. This allows
direct measurement and control of the modeling material within the
track being deposited, thus ensuring smooth deposition of the
modeling material and optimal fusing with laterally previously
deposited tracks.
[0146] In an embodiment, the pressure determining means for
determining a parameter indicative of a pressure exerted on the
modeling material within the track being deposited comprise a
pressure sensor having a fluid channel at the nozzle tip for
measuring a pressure in the deposited modeling material at the
nozzle tip. The fluid channel at the nozzle tip allows measuring a
pressure in the deposited track outside the nozzle near the nozzle
outlet. This allows direct measurement of the pressure at the
nozzle tip, within the modeling material being deposited, ensuring
fast and accurate pressure measurement.
[0147] In an embodiment, the pressure determining means for
determining the parameter indicative of a pressure exerted on the
modeling material within the track being deposited comprise a force
sensor arranged between the printhead and the positioning means.
The force exerted by the printhead, i.e. nozzle tip, on the
modeling material of the track being deposited, can be measured by
measuring a counterforce at a different location in the mechanical
path from the printhead via the gantry and positioning system,
base, to the object to be created, which transmits the force
exerted by the printhead on the track being deposited. From the
determined force, the pressure exerted on the modeling material at
the tip can be derived.
[0148] In an embodiment, the force sensor is arranged at an
interconnection of the printhead and the positioning means. In this
case the force can be measured between the printhead and
positioning means, more specifically the gantry against which the
printhead is mounted.
[0149] In an embodiment, the pressure determining means for
determining the parameter indicative of a pressure exerted on the
modeling material within the track being deposited comprises a
force sensor arranged on a base of the positioning means, which is
arranged for receiving the object to be created. The object to be
created is located at the reference location. It can be mounted on
the base. A force on the build plate can be measured, or
alternatively a force between the build plate and positioning means
can be measured from which the parameter indicative of the pressure
can be derived.
[0150] The determined pressure can be compensated by the weight of
the object being printed. This weight can for example be determined
by the force sensor when the printhead is not active or withdrawn.
This can be performed in time intervals during the printing process
wherein the deposition of tracks is performed.
[0151] In an embodiment, the system further comprises modeling
material flow determining means. This allows determination of an
amount of modeling material used in depositing tracks. From the
modeling material flow and printing speed a thickness of the
deposited tracks can be determined.
[0152] In an embodiment the flow determining means comprise a
displacement sensor for determining displacement of the modeling
material feeding means, and wherein the control system is arranged
for determining the flow by determining a displacement per unit in
time. The modeling material feeding means push the modeling
material into the tubular feed member. By measuring a displacement
of the feeding means per time unit, a modeling material flow can be
determined from the displacement in time and a cross section area
of the tubular feeding member.
[0153] In an embodiment, the control system is arranged for
alternatively controlling a flow of the modeling material using the
determined modeling material flow, and controlling the pressure
exerted on the modeling material.
[0154] In an alternative embodiment, the flow determining means
comprise a flow sensor for determining flow of the modeling
material feeding means.
[0155] In an embodiment, the flow determining means comprise a
sensor for determining a rotation speed of the rotary drive. The
rotary drive drives the modeling material feeding means.
Displacement of the modeling material within the tubular feed
member is thereby linked to the rotary speed of the rotary drive.
Thus, from the rotary speed of the rotary drive the modeling
material flow in the tubular feeding member can be derived. This
has an advantage in that when an electric motor is utilized as
rotary drive, the rotary speed can easily be determined from
electric parameters associated with the driving of the motor. Thus,
no separate displacement sensor is required.
[0156] In an embodiment, the control system is arranged for
controlling the positioning means and the printhead for depositing
two first tracks using flow control, wherein the first two tracks
are spaced apart, and wherein the control system is arranged for
controlling the positioning means and the printhead for depositing
an intermediate track between the two first tracks while
controlling the pressure exerted on the modeling material. In this
scheme, the first tracks are deposited independent of previously
deposited tracks. Such tracks do not require a high filling grade
for preventing spaces and cavities, thus flow control can be used.
The intermediate second track to be deposited between the first two
tracks however require the high filling grade leaving no cavities.
Thus this third track can be deposited using pressure control.
[0157] In an embodiment, the tubular feed member is heatable by a
heating element arranged around at least a lower portion of the
tubular feed member adjacent to the nozzle. This allows heatable
modeling material to be processed by the fused deposition modelling
system. The modeling material is heated while it is pushed into the
tubular feed member. When the modeling material reaches the nozzle,
the modeling material is heated to its melting temperature. The
heating element can be dimensioned and controlled to reach the
required melting temperature.
[0158] In an embodiment, the nozzle is heatable by a heating
element arranged around or within the nozzle. This allows the
heating element of the tubular feed member to be adjusted to a
lower temperature preventing the modeling material to thermally
degrade as some materials can only be kept at a high temperature,
i,e, melt temperature for a limited time. Only in the last part of
the feed channel near the nozzle the modeling material is heated to
its melting temperature, thus adequate printing is provided while
the modeling material is maintained in good condition, i.e.
degradation is prevented.
[0159] An example of an additive manufacturing method for creating
the three-dimensional object according to the invention comprises
performing additive manufacturing using the system for additive
manufacturing as described above.
[0160] The method further comprises:
depositing a first track of modeling material, comprising
[0161] feeding the modeling material using the modeling material
feeding means;
[0162] determining a parameter indicative of a pressure exerted on
the modeling material;
[0163] controlling the modeling material feeding means depending on
the parameter indicative of the pressure exerted on the modeling
material.
In an embodiment, the controlling the modeling material feeding
means depending on the parameter indicative of the pressure exerted
on the modeling material comprises comparing the parameter
indicative of the pressure exerted on the modeling material with a
reference value, and wherein the controlling the modeling material
feeding means is based on a difference between the exerted pressure
and the reference value.
[0164] In an embodiment, the controlling the modeling material
feeding means depending on the pressure exerted on the modeling
material comprises maintaining the parameter indicative of the
pressure exerted on the modeling material between a previously
determined minimum pressure value and a previously determined
maximum pressure value.
[0165] In an embodiment, the controlling the modeling material
feeding means depending on the parameter indicative of the pressure
exerted on the modeling material comprises maintaining the
parameter indicative of the pressure exerted on the modeling
material at a previously determined constant value.
[0166] In an embodiment, wherein the step of depositing a first
track of modeling material comprises depositing the first track in
a space between a previously deposited second track of modeling
material, and a previously deposited third track of modeling
material, the third track being spaced apart from the second
track.
[0167] In an embodiment the determining a parameter indicative of a
pressure exerted on the modeling material comprises determining a
parameter indicative of a pressure exerted on the modeling material
within the feed channel of the tubular feed member and/or
nozzle.
[0168] In an alternative embodiment, the determining a parameter
indicative of a pressure exerted on the modeling material comprises
determining a parameter indicative of a pressure exerted on the
modeling material within the track being deposited.
BRIEF DESCRIPTION OF THE DRAWINGS
[0169] FIG. 1 a shows a diagram of a system for additive
manufacturing according to the state of the art.
[0170] FIG. 1b shows a block diagram of a control system for
controlling a system for additive manufacturing according to the
state of the art.
[0171] FIGS. 2a-2c show aspects of a system for additive
manufacturing according to the state of the art
[0172] FIGS. 3a-3b show aspects of a system for additive
manufacturing according to an embodiment of the invention.
[0173] FIG. 4a shows a diagram of a system for additive
manufacturing according to an embodiment of the invention.
[0174] FIG. 4b shows a block diagram of a control system for
controlling a system for additive manufacturing according to an
embodiment of the invention.
[0175] FIG. 5 shows a diagram of a system for additive
manufacturing according to an embodiment of the invention.
[0176] FIGS. 6a-6d show aspects of a system for additive
manufacturing according to an embodiment of the invention.
[0177] FIGS. 7a-7c show aspects of a system for additive
manufacturing according to an embodiment of the invention.
[0178] FIGS. 8a-8b show aspects of a system for additive
manufacturing according to an embodiment of the invention.
[0179] FIG. 9 shows test specimens A, B and C for the leak
test.
[0180] FIG. 10 shows the test set-up for the leak test.
[0181] FIG. 11a shows the ISO 527-2: 2012 specimen 5A.
[0182] FIG. 11b shows the coordinate system relative to the
direction of printing.
[0183] FIG. 11c shows the orientation of test specimen D.
[0184] FIG. 11d shows the orientation of test specimen E.
[0185] FIG. 11e shows ordering of layers in the Z direction.
[0186] FIG. 11f shows the orientation of test specimen F.
[0187] FIG. 12 shows porosity test data.
[0188] FIG. 13 shows a schematic image of a sample prepared
according to the process of the present invention.
[0189] FIG. 14 shows an image of a sample produced in a prior art
FDM process.
[0190] FIG. 15 shows a typical image of a sample according to the
invention (at step 5 of the image processing procedure).
[0191] FIG. 16 shows a detail of an image of a sample according to
the prior art (at step 5 of the image processing procedure).
DETAILED DESCRIPTION OF EMBODIMENTS OF THE PROCESS
[0192] In FIG. 1a a system for additive manufacturing 100 is shown
in a simplified form. The system 100 comprises a view step position
modeling printhead 121 attached via a connection 107 to a gantry
106, which gantry 106 is comprised in a X-Y-Z positioning system,
not shown in FIG. 1a, which allows the printhead 121 and object to
be printed to be moved relatively to one another while depositing
layers 110 of modeling material. The printhead 121 comprises a
tubular feed member 101, which acts as an extruder tube, and which
is arranged for feeding modeling material 108 from one end of the
tubular feed member 101 towards a nozzle 102 connected at the
opposite end of the tubular feed member 101. The tubular feed
member 101 can for example be made from a metal, such as stainless
steel.
[0193] The tubular feed member 101 and the nozzle 102 comprise a
feed channel 120a, 120b respectively. The feed channel 120b of the
nozzle 102 leads to the nozzle outlet 102a at the nozzle tip 102b.
During printing, the nozzle tip 102b is in contact with the
modeling material being deposited 110.
[0194] The modeling material 108 may include thermoplastic polymers
such as for example polylactic acid (PLA), acrylonitrile butadiene
styrene (ABS), polycarbonate (PC) and polyether ether ketone
(PEEK). These materials can be melted within the tubular feed
member 101 and dispensed from the printhead nozzle 102 in
subsequent tracks 109, 110, for forming an object to be
created.
[0195] The tubular feed member 101 and also the nozzle can be
provided with one or more heating elements, which can be arranged
around the tubular feed member 101, to heat and melt modeling
material feedstock in order to allow the printhead to deposit and
fuse modeling material in a molten state.
[0196] Other modeling materials can be deposited in thin tracks
109, 110 and optionally cured for example by exposure to
ultraviolet light, air, heat, or other curing agents.
[0197] The modeling material 108 is deposited on a base in a first
track, and on previously deposited tracks 109 in a successive
deposition operations conducted by the X-Y-Z positioning system.
The base can be a base plate, ground or any other structure
suitable for initiating the deposition of tracks and building and
carrying the object to be printed. The base can be fixed or
movable. In some cases, the base is movable in a horizontal X_Y
direction, whereas the printhead is movable in a vertical
Z-direction. In other cases, the base is movable in X-Y-Z
horizontal and vertical direction relative to the printhead. In
again other cases, the printhead is movable in X-Y-Z horizontal and
vertical direction relative to the base. In this description the
latter case is provided by way of example.
[0198] While the printhead 121 is moved over the previously
deposited tracks 109, a drive system comprising a drive 104, a
transmission 105a,105b for transmitting the rotary motion of the
drive 104 to a longitudinal motion of a plunger 103, which pushes
the modeling material within the feed channel 120a of the tubular
feed member 101 towards the nozzle 102. The rotation to translation
transmission 105,a, 105b, 103 can be a spindle transmission,
wherein the nut 105b is driven by the rotary drive 104. The
pressure exerted on the modeling material 108 by the rotation to
translation transmission can be derived from the determined torque
using the transfer ratio of the angular displacement of the motor
axle and the longitudinal displacement of the plunger 103 attached
to a spindle of the rotation to translation transmission 105a,
105b, 103. The rotary drive 104 can be a stepper motor which can be
controlled digitally to proceed a discreet number of steps in a
chosen direction. The rotary drive 104 can also be an electric
motor, DC or AC, or servomotor, which is controllable by voltage
and/or current supplied to the motor. In the latter case, an
encoder connected to the motor axle may provide position
information of the motor.
[0199] The plunger 103 can be provided with a displacement sensor
111, which can be arranged to measure a displacement X of the
plunger 103 relative to the tubular feed member 101. The state of
the art as depicted in FIG. 1a is shown as an example for example
feeding modeling material rods in the tubular feed member 101 to
the nozzle 102. In the art alternative examples of feeding modeling
material to the nozzle are available, such as feeding modeling
material filament into a tubular feed member 101 using for example
filament punch rollers, which can be driven by an electric motor.
The deposition of tracks 110 on top of previously deposited tracks
109 performed in similar ways using a X-Y-Z positioning system
whilst the modeling material filament is fed into the tubular feed
member 101.
[0200] The system 100 according to FIG. 1a, can be controlled by a
control system which is arranged to dispense additive manufacturing
material at a rate proportional to a required track thickness and
printing speed. In order to achieve this, a predetermined flow of
the modeling material 108 is to be achieved. The control system
controls the drive 104, and a displacement sensor 111 measures
displacement X of the plunger 103. The displacement of the plunger
103 per time unit provides the flow of the modeling material 108,
thereby allowing the control system to regulate the required amount
of dispensed modeling material 108 in track 110.
[0201] In FIG. 1b an example of a control system is shown wherein a
set value S for the required flow is provided to a subtraction unit
115, which is arranged to subtract the calculated displacement X
per time unit, thereby giving an error signal which can be supplied
to a regulator module 114 of the control system.
[0202] The regulator module 114 can be provided with an appropriate
transfer function H1, having a proportional, proportional and
integrating, or proportional integrating and differential control
function. The control system controls the drive 104 and
transmission unit 105,105a and the transmission of the spindle
transmission from the gear 105b to the plunger 103. The drive 104,
transmission 105a, 105b and associated transmission ratio of these
elements are symbolically depicted in block 113 of the example in
FIG. 1b. As descripted the displacement of the plunger 103 can be
obtained from a displacement sensor 111, however the skilled person
may find alternatives for establishing the displacement of the
plunger 103.
[0203] In FIG. 2a. additive manufacturing 100 is illustrated
according to the state of the art. A new track 110a of modeling
material 108 is deposited on previously deposited tracks 109. In an
ideal situation, the deposited tracks are continuously deposited.
There are no gaps between the previously deposited tracks and
tracks, neither in horizontal direction nor in vertical direction.
This can be achieved when the flow of modeling material is
accurately controlled relative to the required track thickness and
deposition speed of the printhead 121. The degree and tightness of
depositing modeling material 108 depends highly on calibration of
the system or printer.
[0204] In FIG. 2b, a common fault in flow controlled additive
manufacturing is shown called under-extrusion. In under-extrusion,
cavities or gaps 201 occur during the deposition of the modeling
material. A track 110b is shown which is incompletely dispensed
while printing on the printing on the previously deposed tracks.
Such gaps 201 may occur when the additive manufacturing system is
not properly calibrated. When performing the calibration, the aim
is normally to prevent over-extrusion, since this will make the
process unreliable. However, perfect calibration is not possible
due to random errors, therefore additive manufacturing systems or
printers usually have some degree of under extrusion. As a side
effect, parts will not be leak-tight or pressure resistant and the
strength of the part will be sub-optimal.
[0205] In FIG. 2c, over-extrusion is represented. In
over-extrusion, the flow of modeling material 108 into the
deposited layer 110c is too high. As a consequence, crests 202 of
modeling material 108 may occur, caused by the nozzle tip 102b
accumulating modeling material 108 and pushing excess modeling
material to the sides, transverse to the deposition or printing
direction.
[0206] In FIG. 3a, track 110d of modeling material is deposited
tight fitting between previously deposited tracks 109 independent
of the volume of the remaining space between these tracks.
Similarly, in FIG. 3a. the space between the previously deposited
tracks 109 is narrower than the tracks themselves.
[0207] In FIG. 3b, the deposited track 110e is broader than the
previously deposited tracks. This will result in total infill of
cavities and improved bonding to adjacent and lower print tracks.
Therefore, parts printed in this way will have optimal leak
tightness and strength, which can be achieved in a deposition
modeling system as described below.
[0208] In FIG. 4a a fused deposited modeling system 400 is shown
similar to FIG. 1a. A torque sensor 401 can be provided to measure
the torque exerted by the drive 104 and transmission 105a, 105b to
the plunger 103 and thereby to the modeling material 108. From the
measured torque, a pressure exerted on the modeling material 108 in
the tubular feed member 101 can be derived.
[0209] Alternatively, a pressure sensor may be attached to the
plunger 103. The pressure sensor is arranged for measuring the
pressure exerted by the plunger 103 to the modeling material 108.
The plunger pressure sensor can be attached to the tip of the
plunger 103 to measure the pressure exerted on the modeling
material directly. The plunger pressure sensor can also be a force
sensor attached to the point of engagement of the plunger 103 with
the drive 104 and/or transmission system 105a, 105b. Moreover, the
pressure sensor can be a strain gauge attached the plunger stem.
When a pressure or force is applied to the plunger 103, this
pressure or force is transferred to the modeling material 108. Due
to the applied pressure or force, the plunger stem will deform,
which can be measured by the strain gauge. The pressure exerted by
the plunger 103 on the modeling material 108 in a higher end of the
tubular feed member 101 eventually results in a pressure of the
modeling material within the nozzle 102.
[0210] In FIG. 4b, a control system is shown for performing
pressure controlled additive manufacturing with the system 400. As
an example, the torque sensor 401 can provide a measured torque of
the motor which drives the modeling material feed means which can
be used as the measured parameter PM indicative of the pressure
exerted on the modeling material 108 within the feed channel 120a,
120b of the tubular feed member 102. Alternatively, the motor
current can be used as parameter PM indicative of the pressure
exerted on the modeling material 108 within the feed channel 120a,
120b. The motor current is proportional to the torque delivered by
the motor to the transmission 105a, 105b to the plunger 103.
Moreover, the plunger pressure can be used as parameter PM
indicative of the pressure exerted on the modeling material
108.
[0211] The control system 412 can be arranged to compare the
measured parameter PM to a reference parameter value PR, by means
of a subtractor 403. The measured parameter PM is subtracted in the
subtractor 403 from the reference parameter value PR, which
difference is supplied to the regulation function module 402 having
a transfer function H2. The transfer function H2 can be
proportional (P), proportional and integrating (PI), or
proportional, integrating and differentiating (PID). The controller
provided with a regulation module 402 controls the drive system
113.
[0212] By controlling the motor current, pressure control on the
modeling material 108 within the tubular feed member 101 can be
achieved.
[0213] The reference parameter value or setpoint PR may vary
depending on printhead travel speed, gap size, temperature,
modeling material properties.
[0214] In FIG. 5 the system corresponding to the system of FIG. 4a
is shown having an alternative way for establishing the parameter
indicative of the pressure exerted on the modeling material 108. In
the system of FIG. 4a, the parameter is indicative of the pressure
exerted on the modeling material within the printhead 121, i.e. the
tubular feed member 101. In the system of FIG. 5, the parameter
indicative of the pressure exerted on the modeling material is
determined by the pressure exerted on the modeling material being
deposited in track 110 at the tip 102b of the nozzle 102. While
extruding by exerting a pressure on the modeling material 108 in
the printhead 121, a pressure at the nozzle tip 102b is caused
within the deposited layer 110, which results in an force which
pushes the nozzle tip 102b away from the previously deposited
tracks 109.
[0215] This force is propagated from the printhead 121 via the
gantry 106 and X-Y-Z positioning system 503 which is connected to
the base 504 whereupon the object to be modeled is placed.
Alternatively, the X-Y-Z-system and gantry may be connected to
ground. Thus, the object to be printed can be on ground which
serves as a base for the object to be printed. The force exerted on
the modeling material is then measurable between the object and the
ground.
[0216] The force is thus also being propagated between the gantry
106 and the printhead 121 and can for example be measured at the
connection 107. The connection 107 of the printhead 121 to the
gantry 106 of FIG. 4a can be formed by at least one resilient
connection member 502. A displacement sensor 501 can measure the
deformation of the resilient connection member 502 as a measure for
the force transmitted through the propagation path from the
printhead to the object to be created via the X-Y-Z system and
base, and thereby the pressure exerted on the feed in the deposited
track 110. Alternatively, measurement of the force can also be
achieved in a system according to FIG. 4a, wherein the connection
107 between the printhead 121 and gantry 106 is provided with a
load cell or strain gauge, which measure a pressure exerted by the
printhead 121 and the track 110 being deposited.
[0217] Moreover, the force exerted on the modeling material in the
layer 110 being deposited can be measured between the object and
the base 504, by for example using a weight scale, or pressure pad.
The force thus measured is indicative for the pressure exerted on
the modeling material within the layer being deposited.
[0218] As shown in FIGS. 6a-6d, alternatively to measuring the
pressure exerted on the modeling material within the printhead 121,
as described in relation to FIG. 4a, i.e. the torque of the drive
and transmission system or force at the plunger 103, a pressure
exerted on the modeling material 108 within the tubular feed member
101, i.e. the feed channel 120a can be measured directly, as shown
in FIG. 6a. The pressure measured by the pressure sensor 601 can be
used for controlling the drive 104 in order to obtain a pressure
suitable for printing the modeling material into the track 110 to
be deposited. An alternative placement of pressure sensor 602 is
shown in FIG. 6b, wherein the pressure sensor 602 is placed within
the nozzle 102 and wherein the pressure is sensed of the feed
channel 120b within the nozzle 102. An alternative for measuring
the pressure within the feed channel 120b is to measure deformation
of the nozzle around the feed channel 120b.
[0219] An alternative to measuring the pressure within the feed
channel 120a, 120b, is to have a pressure sensor 604 as shown in
FIG. 6d, which is arranged within the nozzle 102 and which is
fluidly connected to the nozzle tip 102. The pressure measured at
the nozzle tip 102b represents the pressure exerted on the modeling
material track 110. Thus, this way an alternative way to for
establishing a pressure exerted on the modeling material in track
110 is established relative to FIG. 5 is provided.
[0220] Pressure sensors suitable for use in an additive
manufacturing system as described above for measuring pressure
within the printhead 121, comprise membrane sensors which have a
deformable membrane. A liquid such as mercury may transfer the
pressure within the modeling material channel wherein pressure is
to be measured, i.e. the feed channel 120a, 120b, or at the nozzle
tip 102b to the membrane. The sensor itself may be of a type
including a thin film metal sensor, a conductor/strain gauge
related sensor, a piezo-electric sensor, magneto-resistive sensor,
laser interferometer sensor and sensor based on mechanical
displacement.
[0221] As shown in FIGS. 6a-6d, the track 110 can be deposited next
to a previously deposited track 109 using pressure control forming
a continuous track of deposited modeling material. The track 110
will by the pressure exerted on it via the nozzle orifice or nozzle
tip flow to the previously deposited track and fuse with the
previously deposited material. In FIGS. 7a-7c an alternative
strategy is shown for deposition of tracks of modeling material
using pressure control.
[0222] A first track 701 is deposited, using flow or pressure
control as shown in FIG. 7a. In FIG. 7b a second track 702 is shown
being deposited spaced apart from the first track 701. In FIG. 7c a
third track 703 is shown being printed between tracks 701 and 702
using pressure control. The modeling material 108 fills the open
space between the first track 701 and the second track 702 and
fuses with these previously deposited tracks, such that the tracks
701, 702-703 form a continuous layer without gaps or cavities.
[0223] In FIGS. 8a, 8b a refinement of the printing strategy is
shown, wherein a first stack of tracks 801 is deposited using flow
control. Adjacent tracks 802a, 802b having a more coarse deposition
profile can be deposited using pressure control as an infill.
[0224] The control system may comprise a programmable logic
controller (PLC), a microcontroller or processor having a memory
(RAM, ROM, EPROM, etc) comprising program instructions, which in
operation cause the processor to perform the controlling as
described.
[0225] The program instruction may comprise modules for calculating
pressures exerted on the modeling material 108 from these
indicative forces and torques as described. Moreover, losses due to
friction and other causes within the drive, transmission, modeling
material tubular feed member 101 and nozzle may be calculated and
used to compensate or correct the control loops 412 as
described.
[0226] The embodiments above are descripted as examples only.
Supplements and modifications can be made to these embodiments
without departing from the scope as defined set out in the claims
below.
REFERENCE NUMERALS
[0227] 100 Additive manufacturing system [0228] 101 Tubular feed
member [0229] 102 Nozzle [0230] 102a Nozzle outlet [0231] 102b
Nozzle tip [0232] 103 Piston [0233] 104 Drive [0234] 105a, 105b
Gear [0235] 106 Gantry [0236] 107 Connection bar [0237] 108
Modeling material [0238] 109 Previously deposited tracks [0239] 110
Deposited FDM track [0240] 110a New track of modeling material
[0241] 110b Incompletely dispensed track of modeling material
[0242] 110c Over-extruded track of modeling material [0243] 110d
Track of modeling material deposited in tight fitting [0244] 110e
Track of modeling material broader than the previously deposited
tracks [0245] 111 Displacement sensor [0246] 112 Displacement
control system [0247] 113 Drive system compensation [0248] 114 Flow
regulator module [0249] 120a, 120b Feed channel [0250] 121
Printhead [0251] 400 Additive manufacturing system for pressure
control within the printhead [0252] 401 Sensor for parameter
indicative of pressure within feed channel [0253] 402 Pressure
control module [0254] 403 Subtractor [0255] 412 Control system for
pressure control [0256] 500 Additive manufacturing system for
pressure control at nozzle tip [0257] 501 Displacement sensor
[0258] 502 Resilient member [0259] 503 XYZ positioning system
[0260] 601-604 Pressure sensor [0261] 605 First track [0262] 606
Third track [0263] 607 Second track [0264] 701 First track using
flow control [0265] 702 Second track using flow control [0266] 703
Third track using pressure control [0267] 801 First stack of tracks
[0268] 802a-802b Adjacent tracks [0269] `S` Flow setpoint [0270]
`X` Displacement per time unit [0271] PR Pressure setpoint [0272]
PM Measured parameter indicative of the pressure [0273] `H1` Flow
control transfer function [0274] `H2` Pressure control transfer
function
EXPERIMENTAL
[0275] Parts have been prepared according to the method of the
present invention, wherein the process comprises the steps of
[0276] a. exerting a pressure on the modeling material to feed the
modeling material onto the predetermined positions; [0277] b.
determining a parameter indicative for the pressure exerted on the
modeling material and [0278] c. controlling the feeding depending
on said parameter, and wherein providing each of the layers is
performed by [0279] d. printing contour lines of the object in the
X-Y plane marking a primary area, [0280] e. filling a first part of
the primary area inside the contour lines of the object in the X, Y
plane, leaving open a second part in the primary area [0281] f.
filling the second part by the depositing step.
[0282] Hereinafter, this process is called the BOND process.
[0283] Porosity
[0284] For the porosity test, test specimens printed of PEEK
material were printed according to the BOND process, were compared
to test specimens printed from Ultem 9085 with 100% infill on a
Stratasys Fortus 450mc printer. Microscopic samples were examined
and the images were processed according to the procedure `Porosity
test`. The results are shown in FIG. 12 and in the Table 1
below:
TABLE-US-00002 TABLE 1 Sample Material Porosity According to the
B01 PEEK 0.0% invention B02 PEEK 0.0% B03 PEEK 0.0% B04 PEEK 0.0%
B05 PEEK 0.033% B06 PEEK 0.006% B07 PEEK 0.017% According to the
S01 Ultem 13.3% prior art S02 Ultem 14.0% S03 Ultem 13.6% S04 Ultem
10.6% S05 Ultem 13.1% S06 Ultem 14.5% S07 Ultem 15.4% S08 Ultem
12.2% S09 Ultem 17.8% S10 Ultem 18.4% S11 Ultem 10.8% S12 Ultem
16.1 S13 Ultem 19.0
[0285] Leak Tests
[0286] Leak tests were carried out according to the leak test
experiment described above.
[0287] Different parts have been prepared from Ultem prepared on a
state of the art Stratasys Fortus 450 mc machine with different
thickness, varying from 1 to 2.5 mm. Also, parts have been prepared
from polycarbonate (prepared on the Stratasys machine) and ABS
(prepared on an Ultimaker machine, Parts have been taken from the
build plane of the part (XY direction).
[0288] 4 parts have been prepared with varying thickness from PEEK,
prepared according to the BOND process, which uses pressure
controlled printing as described above. Parts have been prepared
from the build plane (XY) and perpendicular to the build plane
(Z-direction).
[0289] The results are summarized in table 2.
TABLE-US-00003 TABLE 2 Machine brand Machine type Material Result
Stratasys Fortus 450 mc Ultem 9085 too many bubbles to estimate
flow Stratasys Fortus 450 mc PC too many bubbles to estimate flow
Ultimaker II ABS too many bubbles to estimate flow Bond
Experimental setup PEEK 450G below detection limit; no bubbles
[0290] In all samples prepared from Stratasys parts and Ultimaker
parts, bubbles were found, so much that the flow could not be
measured in the leak test. For all parts made according to the BOND
process, no bubbles could be observed, meaning that all parts were
leak tight.
[0291] Mechanical Properties.
[0292] 10 samples of PEEK were prepared according to the BOND
process and the critical strength in the Z direction (perpendicular
to the build plane) has been determined according to ISO
527-2:2012. Results are shown in Table 3.
TABLE-US-00004 TABLE 3 Stress at break Strain at break Sample [MPa]
[%] 1231 93.925 5.246 1234 95.829 5.174 892 102.326 9.105 889
89.496 6.157 888 92.603 5.858 901 101.338 6.889 914 104.186 7.604
912 101.036 6.833 908 100.115 6.616 905 100.864 7.787
[0293] 3 samples have been prepared from Ultem on a Stratasys
machine. Strength at break according to prior art has been
determined and is shown in
TABLE-US-00005 TABLE 4 Stratasys Ultem .SIGMA.X (M Pa) .SIGMA.Y (M
Pa) .SIGMA.Z (MPa) Sample 1 74.73 61.24 42.03 Sample 2 62.65 60.88
43.55 Sample 3 68.36 53.43 41.78 Average 68.6 58.5 42.5 Best 74.7
61.2 43.6
[0294] Testbars have been prepared with a FDM process on Ultimaker,
Stratasys equipment and the according to the BOND process. Parts
have been prepared from different thermoplastic materials and
properties have been determined as shown in Table 5.
TABLE-US-00006 TABLE 5 Manufacturer Ultimaker Stratasys Stratasys
Bond Technology FDM FDM FDM FDM Material ABS PC Ultem PEEK 1.
Porosity >10% >10% >10% <0.05% 2. Leak tight No no no
Yes 3. Lowest strength 30 MPa 35 MPa 43 MPa >89 MPa 4. Strength
isotropy 90% 61% 62% >90 5. Lowest strain 1.8% 2.8% 3.8% 5-9% 6.
Strain isotropy 34% 58% 70%
[0295] The data show that the Bond parts show no porosity and are
leak tight. The parts made in conventional machines are not
leaktight and show a lot of cavities due to under-extrusion.
[0296] The BOND process is capable of printing parts of more
demanding thermoplastic materials than the parts made on prior art
machines. PEEK is very difficult to use in an FDM process because
of the polymer characteristics and cannot be printed on an
Ultimaker or Stratasys machine.
* * * * *