U.S. patent application number 09/841871 was filed with the patent office on 2002-05-02 for multiple beams and nozzles to increase deposition rate.
Invention is credited to Keicher, David M., Miller, W. Doyle.
Application Number | 20020051853 09/841871 |
Document ID | / |
Family ID | 21746859 |
Filed Date | 2002-05-02 |
United States Patent
Application |
20020051853 |
Kind Code |
A1 |
Keicher, David M. ; et
al. |
May 2, 2002 |
Multiple beams and nozzles to increase deposition rate
Abstract
A method has been developed to exploit the desirable material
and process characteristics provided by a low powered laser
material deposition system, while overcoming the low material
deposition rate imposed by the same process. One application of
particular importance for this invention is direct fabrication of
functional, solid objects from a CAD solid model This method of
fabrication uses a software interpreter to electronically slice the
CAD model into thin horizontal layers that are subsequently used to
drive the deposition apparatus. The apparatus uses a single laser
beam to outline the features of the solid object and then uses a
series of equally spaced laser beams to quickly fill in the
featureless regions. Using the lower powered laser provides the
ability to create a part that is very accurate, with material
properties that meet or exceed that of a conventionally processed
and annealed specimen of similar composition. At the same time,
using the multiple laser beams to fill in the featureless areas
allows the fabrication process time to be significantly
reduced.
Inventors: |
Keicher, David M.;
(Albuquerque, NM) ; Miller, W. Doyle;
(Albuquerque, NM) |
Correspondence
Address: |
Anglin & Giaccherini
Post Office Box 1146
Carmel Valley
CA
93924
US
|
Family ID: |
21746859 |
Appl. No.: |
09/841871 |
Filed: |
April 24, 2001 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
09841871 |
Apr 24, 2001 |
|
|
|
09010673 |
Jan 22, 1998 |
|
|
|
5993554 |
|
|
|
|
Current U.S.
Class: |
427/596 ;
427/248.1 |
Current CPC
Class: |
B29C 64/40 20170801;
B29C 64/153 20170801; B23K 26/144 20151001 |
Class at
Publication: |
427/596 ;
427/248.1 |
International
Class: |
C23C 014/30 |
Claims
We claim:
1. A direct material deposition method comprising the steps of: a.
providing a powdered material that can be melted by a laser beam;
b. providing a laser nozzle assembly having multiple laser beams
coupled with said powdered material from a set of powder nozzles
directed to approximately the same location; c. positioning a
deposition substrate adjacent to the laser deposition head outlets;
d. melting said powdered material with said laser beam; and e.
providing relative motion between the laser deposition apparatus
and said deposition substrate.
2. The method of claim 1, wherein said powdered material is melted
with said laser beams, whereby the melted powdered material is
fused to a substrate to create a thin layer of material.
3. The method of claim 1, wherein said powdered material is
vaporized with said laser beams, whereby the vaporized powdered
material is deposited onto the substrate to create a thin layer of
material.
4. The method of claim 1, wherein said relative motion derives from
a CAD model.
5. The method of claim 4, wherein a single laser beam can be used
to outline features defining surfaces of an object under
construction.
6. The method of claim 4, wherein said multiple laser beams are
used to fill the featureless regions defining the surfaces of said
object.
7. The method of claim 1, wherein said laser beams are controlled
individually, whereby one or more of the beams may be modulated on
and off during any part of the deposition process to create one or
more line deposits simultaneously.
Description
[0001] This is a division of Ser. No. 09/010,673, Filed Jan. 22,
1998.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] This invention relates to the use of multiple beams and
nozzles in direct material deposition (DMD) processes in order to
increase the deposition rate without compromising material
properties or dimensional accuracy.
[0004] 2. Description of Prior Art
[0005] Direct material deposition processes allow complex
components to be efficiently fabricated in small lot sizes to meet
the stringent requirements of the rapidly changing manufacturing
environment. This process produces three-dimensional parts directly
from a computer aided design (CAD) solid model. U.S. Pat. No.
4,323,756 teaches that complex, net-shaped objects can be built by
sequential layer deposition of feedstock material in powder or wire
form, whereby the material is directed into a focused laser beam,
melted, and deposited onto a deposition substrate to generate solid
objects of varying three-dimensional complexity in a layer-wise
manner. Other prior art using this method includes "Using the Laser
Engineered Net Shaping (LENS.TM.) Process to Produce Complex
Components from a CAD Solid Model" by D. M. Keicher et al. in SPIE
Conference, San Jose, Calif., January 1997. This method of direct
material fabrication uses a single nozzle or powder delivery system
that introduces a converging stream of powdered material into the
laser beam at or near the beam's minimum diameter (i.e. focus or
focal plane). The stream is at an angle off-normal to a deposition
surface whereby uniform geometries of three-dimensional objects can
be produced by providing computer controlled motion of the
deposition surface relative to the laser beam. Experience has
shown, however, that this nozzle design does not provide uniform
flow independent of the translation direction. In addition, to
achieve goal material properties, the deposition rate is
sufficiently low, such that fabrication times required for even
intermediate volume objects (100 cubic inches) are prohibitive.
[0006] U.S. Pat. No. 5,043,548 discloses a laser plasma spraying
nozzle and method that permits high deposition rates and
efficiencies of finely divided particles of a wide range of feed
materials. This system uses powdered materials that are carried to
the interaction regions via a carrier gas and lasers to melt these
particles. However, this system relies solely on the use of a
plasma to melt the particles before they are ever introduced to the
deposition region. In fact, the carrier gas is often a mixture
which promotes ionization, and, as such, the formation of a plasma.
The plasma serves to melt the powder particles before they ever
come into contact with the deposition substrate. In addition, the
beam is diverging such that when it does impact the deposition
substrate, the beam irradiance is sufficiently low so that no
melting of the deposition substrate occurs. A great distance
between the focal point of the laser and the central portion of the
plasma is maintained to prevent the substrate from melting. This
distance, ranging from 1-6 inches, is a characteristic of this
apparatus. The materials are deposited in either a liquid or
gaseous state. This design provides a unique method for coating
parts; however, it has never been intended for fabrication of
multilayered parts. Due to the diverging nature of the powder
material, this plasma technique fails to provide the feature
definition necessary for fabricating complex, net-shaped
objects.
[0007] Another nozzle design is shown in U.S. Pat. No. 4,724,299.
This nozzle design requires the powder to be delivered from an
annular source that is coaxial with a single laser beam. This
design provides a uniform feed of powder to the cladding region, a
laser used as an energy source to melt the powder that is to be
deposited, and a powder distribution system. However, this system
requires that the powder distribution system be contained within
the nozzle assembly.
[0008] This nozzle design is very specific to the laser cladding
application. The term laser cladding is used specifically to imply
surface modification and not the direct fabrication method. More
importantly, the design relies on having an annular powder
distribution channel to deliver the powder to the deposition
region. The annular powder distribution region provides powder to
the focused laser beam from all directions and does not concentrate
the powder for a tightly focused powder stream. For a single laser
beam that is coaxial to the powder flow, this nozzle should work
well to provide a uniform layer; however, there is concern that the
powder distribution at the deposition surface is greatest at the
center of the deposition region, causing it to diminish radially
away from the center of the deposition spot. With this change in
powder volume uniformity, the inclusion of multiple beams will
certainly result in varying line size for parallel deposited
lines.
[0009] U.S. Pat No. 4,323,756 also covers the direct metal
deposition (DMD) process. This technique uses both wires and
powders as filler material. It also uses a single laser beam to
deposit the various materials. This patent teaches that the volume
of the feedstock material must be less than that of the melted
substrate material. However, this reduces the rate of deposition
and increases the time to produce parts. The requirement to limit
the volume of the feedstock material to be less than that of the
melted substrate material was driven by the desire to remove
impurities and obtain epitaxial growth. Instead of removing
impurities by continuously remelting the previously deposited
materials, impurities can be efficiently eliminated by performing
the deposition in a controlled atmosphere environment, such as a
glove box. Furthermore, expitaxial growth is not desired in most
three-dimensional parts, since it may result in anisotropic
material characteristics. For most general applications, uniform
material properties are desired that do not limit the feedstock
volume to be less than that of the deposition substrate melted
region.
[0010] The above single laser nozzle's side design lack the ability
to increase the deposition rate of powder without sacrificing vital
process conditions, including reduced residual stress, enhanced
material properties, process time, and good dimensional
repeatability, as well as feature definition. Also, this nozzle
design does not provide uniform flow independent of the translation
direction. Therefore, such nozzle designs are not suitable for mass
3-D net-shape production.
[0011] U.S. Pat. No. 5,578,227 contains similarities to the present
invention, such as the use of a positioning system to direct the
location of deposition, and the use of a laser to deposit the
feedstock material. However, this patent only uses a single laser
beam for the deposition process, which uses wire as the feedstock
material. This patent also claims that the laser causes the
feedstock material to bond to the previously deposited layer
without substantially altering the cross-section of the newly
deposited material. Such a continuous form of material would appear
to be prone to substantial problems of warpage and distortion of
the deposited layers due to an incomplete melting of the feedstock
material. For the powder deposition processes, the feedstock
material is completely consumed within the 3-D net shape, with the
powder's cross-section being substantially altered.
[0012] A need exists for improved material deposition nozzles for
the laser-assisted process.
Objects and Advantages
[0013] Accordingly, several objects and advantages of the present
invention are:
[0014] (a) to provide multiple beams and nozzles within a single
system which will increase the deposition rate without compromising
process conditions or time;
[0015] (b) to provide multiple beams and nozzles within a single
system which will increase the volume usage rate of feedstock;
[0016] (c) to provide multiple beams and nozzles within a single
system which will reduce residual stress within parts by using more
lower powered, finely focused laser beams in a single system;
[0017] (d) to provide multiple beams and nozzles within a single
system which will achieve good dimensional repeatability and
feature definition by using more lower powered, finely focused
laser beams in a single system;
[0018] (e) to provide multiple beams and nozzles within a single
system which can create uniform material properties in parts that
do not limit the feedstock volume to be less than that of the
deposition substrate melted region.
[0019] (f) to provide multiple beams and nozzles within a single
system which can form streams of particles that are partially or
completely melted and can then be consumed to become part of a
solid structure.
[0020] Further objects and advantages are to provide multiple beams
and nozzles within a single system that allow for the use of either
a single laser beam or any combination of laser beams during any
part of the process. The powder filler nozzles can be used in a
combination of one or more pairs, depending on the needs of the
design. Still further objects and advantages will become apparent
from a consideration of the ensuing description and drawings.
DRAWING FIGURES
[0021] FIG. 1 schematically illustrates the position of the present
invention within a material deposition system.
[0022] FIG. 2A shows a three-dimensional front view of the multi
beam apparatus without the manifold, and a substrate.
[0023] FIG. 2B is an enlarged front view of the powder nozzles.
[0024] FIG. 3 is a three-dimensional front view of the deposition
head and the deposition substrate.
[0025] FIG. 4A is three-dimensional close-up of the powder nozzles
and deposition substrate.
[0026] FIG. 4B is an enlarged side view of the powder nozzles.
[0027] FIG. 5 is a close-up frontal view of the multi beam fill
deposition approach, showing the two outline powder nozzles.
[0028] FIG. 6 is a three-dimensional front view of the multi beam
apparatus with the manifold.
[0029] FIG. 7A is a three-dimensional isometric bottom view of the
manifold system connected to the deposition head.
[0030] FIG. 7B is a three-dimensional isometric top view of the
manifold system connected to the deposition head.
1 Reference Numerals in Drawings 10a filler powder feeding 10b
outline powder feeding apparatus apparatus 12 laser 14 vertical
stage 15 focused laser spot 16 prescribed distance 17 spacing
between focused 18 focus plane laser spots 20 sealed chamber 22
convergence plane 24 fill region 26 orthogonal positioning stages
32 computer 34 software 36 deposition head 38 beam delivery fibers
40 divergent laser beams 42 collimating lens 44 collimated laser
beams 46 focusing lens 48a-h filler powder nozzles 48i-j outline
powder nozzles 49 powder convergence points 50 focused laser beams
51a-h stream of powder 52 powder 54 line deposits 56 interaction
zone 58 deposition substrate 60a external deposited feature 60b
internal deposited feature 62 manifold 64a filler powder inlet tube
64b outline powder inlet tube 66a-b filler powder separation 66c
outline powder channel separation channel 68a filler powder layer-
68b-e outline powder layer- connecting orifice connecting orifice
70a filler powder delivery tube 70b outline powder delivery tube 72
front view of powder 74 side view of powder nozzles nozzles
SUMMARY OF THE INVENTION
[0031] The present invention provides an apparatus for the use of
multi beams and nozzles in the deposition of materials to form
three-dimensional parts whereby the deposition rate increases. The
deposition head assembly consists of the following features: an
array of output powder nozzles for creating a converging flow of
powder to the deposition region, and a central orifice which allows
the multiple beams to be focused onto the deposition substrate. In
particular, the invention includes a manifold system designed into
the deposition head assembly that can use more than one laser beam
simultaneously for the deposition process.
[0032] The use of multiple beams and nozzles within a single system
allows an increase in the deposition rate without compromising the
process conditions or time. The present invention will increase the
volume of feedstock used in a given time. The use of more than one
laser beam allows for lower powered, finely focused laser beams to
be used in order to minimize residual stress within parts. This
characteristic also achieves good dimensional repeatability and
feature definition, while providing excellent material
properties.
[0033] The present invention also provides a means for using either
a single laser beam or any combination of laser beams during any
part of the process.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0034] A schematic of the preferred embodiment of this invention is
given in FIG. 1, showing the position of the invention within a
direct material deposition system. The system includes: a powder
feeding apparatus 10, to deliver a uniform flow of powder to the
deposition region; a laser 12, to cause heating and subsequent
melting of the powder feed particles; and a deposition head/heads
36. The system also includes a set of orthogonal positioning stages
26, which are computer driven to direct the location of deposition;
a vertical stage 14; a computer 32, on which software 34 is used to
slice the CAD solid models and generate a motion control program to
control deposition processing sequence based on CAD file data; and
a sealed chamber 20, to contain the powder particles during
processing and provide an inert environment.
[0035] Referring to FIGS. 2A and 2 B, the multi beam deposition
apparatus begins with four beam delivery fibers 38, that are
equally spaced apart at a prescribed distance 16, which are used to
transport the laser beams to the deposition apparatus. The beams
out of the fiber are divergent laser beams 40 and transmitted
through the spherically shaped collimating lens 42. The laser beams
then leave the collimating lens 42 as collimated laser beams 44
located above the deposition head 36. These collimated laser beams
44 are then transmitted through a second spherically shaped
focusing lens 46 to be focused onto the deposition substrate 58.
The focused laser beams 50 create a linear array of focused laser
spots 15 on the deposition substrate 58. The focus plane 18 of the
focused laser spots is located at/or near the deposition substrate,
which is also the same as the deposition substrate 58. This spacing
between the focused laser spots 17 is dictated by the prescribed
distance 16 between the beam delivery fibers 38 and the
magnification provided by the imaging system created by the
combination of the collimating lens 42 and the focusing lens
46.
[0036] For this configuration, the deposition head is conical in
shape. An array of powder nozzles 48 project from underneath the
deposition head 36. Streams of powder 51a-d exit from the powder
nozzles 48 and interact with the focused laser beams 50 to form
line deposits 54 on a deposition substrate 58.
[0037] FIG. 3 shows the relationship between the focused laser
beams 50, the powder 52, and the deposition substrate 58. The
focused laser beams 50 are shown both above and below the
deposition head 36. The powder 52 and focused laser beams 50 then
interact below the deposition head 36 in order to form features 60
on the deposition substrate and to deposit material in the region
between the features to form a uniform solid layer of material. For
this process, the internal deposited features 60b and external
deposited features 60 a on the deposition substrate 58 serve to
define the geometry of the component being fabricated as well as
provide boundaries for the fill region 24.
[0038] Referring to FIGS. 4A and 4B, the multi beam deposition
apparatus includes eight filler powder nozzles 48a-h and two
outline powder nozzles 48i-j, of which only one is shown 48i, that
project from the deposition head 36. Streams of powder 51a-h are
ejected from the powder nozzles 48a-h. The eight filler powder
nozzles 48a-h are positioned within the deposition head 36 such
that the stream of powder 51a-d from one filler powder nozzle 48a-d
intersects with the stream of powder 51e-h from a second filler
powder nozzle 48e-h from an opposing direction. In this fashion,
the streams of powder 51 from two of the eight powder filler
nozzles 48 interact to form a pair of filler powder nozzles whose
powder streams form a powder convergence point 49 on the deposition
substrate 58. The convergence plane 22, which cuts through the
intersection of the powder streams from the nozzles and is
orthogonal to the propagation direction of the laser beams, is
located at/or near the deposition plane, which parallels the top
surface of the orthogonal positioning stages 26, as shown in FIG.
1. From these eight filler powder nozzles 48a-h, four pairs of
filler powder nozzles interact to form four powder convergence
points 49. The powder convergence points 49 can be described as the
location where the area circumscribed by one powder nozzle overlays
the area circumscribed by the second powder nozzle forming one pair
of interacting powder nozzles. The four powder convergence points
form a linear pattern on the substrate and are separated by a
distance equal to the spacing of the focused laser spots 17, as
shown in FIG. 2B. These powder convergence points 49 are located so
that the elliptical pattern circumscribed by the powder convergence
point 49 is concentric with one of the focus laser spots 15.
[0039] All powder nozzles, regardless of whether they are outline
powder nozzles 48i-j or filler powder nozzles 48a-h, join the
focused laser beams 50 in the interaction zone 56. However, not all
types of powder nozzles are always working at the same time.
Outline powder nozzles 48i-j interact with one pair of the filler
powder nozzles 48a-h to provide powder that is used to form
external deposited features 60 a and internal deposited features
60b. Filler powder nozzles 48a-h then operate independently of the
outline powder nozzles 48i to provide streams of powder 51a-d that
form the uniform deposited solid material layer between the
boundaries created by various combinations of external deposited
features 60a and internal deposited features 60b. Each of the
focused laser beams 50 has independent on-off control to allow the
length of each of the layer fill lines to be varied independently.
This feature permits the solid material layers to be formed within
regions whose external deposited features 60 a or internal
deposited features 60b do not conform to the linear front or the
width of the deposition region formed by the linear array of
focused laser spots 15. Each of the line deposits 54 can be
sequenced on or off as the various line deposits intersect external
deposited features 60a or internal deposited features 60b, allowing
material to be deposited in desired regions only.
[0040] FIG. 5 shows a close-up frontal view of the multi beams and
nozzles in contrast to FIG. 4B. In this diagram, the outline powder
nozzles 48i-j are shown to be directed to interact with only one
pair of the filler powder nozzles 48a-h. This geometry allows
uniform deposition of the external deposited features and internal
deposited features independent of the direction of motion of the
deposition substrate 58 relative to the deposition head. The powder
to the outline nozzles 48i-j is directed at the deposition surface
only when the external deposited features and internal deposited
features are being formed. Otherwise, powder is not flowing from
the outline powder nozzles 48i-j.
[0041] FIG. 6 shows the multi beam deposition apparatus with a
manifold 62 and powder inlet tubes 64a-b. For this apparatus, the
powder is delivered to the deposition head 36 via a carrier gas.
This gas can be inert or reactive depending on the specific
application. Once the powder is entrained in the gas stream, it is
introduced into the deposition head 36 through the powder inlet
tubes 64a-b. The powder then exits the deposition head 36 through
the filler powder delivery tubes 70a and the outline powder
delivery tubes 70b, as shown in FIGS. 7A and 7B.
[0042] The internal structure of the manifold system 62 is shown in
FIGS. 7A and 7B. The powder is injected into the filler powder
inlet tube 64 a and enters into a manifold system 62 that separates
the powder into eight approximately equal parts. To separate the
powder into the eight approximately equal parts, two series of
separation channels 66a-b and an orifice 68a are used. The powder
first enters the deposition head 36 through the filler powder inlet
tube 64a and is separated into two approximately equal parts. One
half of the powder is then carried through the first filler powder
separation channel 66a. At the end of this filler powder separation
channel 66a, the powder is again separated into two approximately
equal parts and directed through the filler powder layer-connecting
orifice 68a. After passing through the orifice 68a, the powder is
directed down through the deposition head 36 to exit out of the
deposition head through the filler powder delivery tubes 70a and
finally out the filler powder nozzles. The path for the outline
powder is similar to that for the filler powder. A second powder
feed unit is used to meter the powder for the outline powder
nozzles. The powder used for the outline powder nozzles first
enters the deposition head 36 through the outline powder inlet tube
64b and is separated into two approximately equal parts. One half
of the powder is then carried through the outline powder separation
channel 66c. At the end of this channel 66c, the powder is directed
downward through a series of outline powder layer-connecting
orifices 68b-e, exiting the deposition head 36 through the outline
powder delivery tubes 70b, and finally out of the outline powder
nozzles, onto the top surface of the deposition substrate. The
powder flow rate from the second powder feed unit is metered to be
approximately equal to one fourth of the total quantity of powder
delivered to the filler powder nozzles. This method of powder
separation relies principally on the path lengths for each of the
nozzles to be approximately equal with an equal pressure drop at
each nozzle.
OPERATION OF THE PREFERRED EMBODIMENT
[0043] This invention can be explained in terms of the multiple
nozzle deposition apparatus and the multiple laser beam deposition
apparatus. The multiple nozzle deposition apparatus has been
developed for the application of powdered materials onto a
substrate to create a uniform fused layer in a desired pattern with
exceptional material properties, very good dimensional accuracy,
and at a rate that is practical for the direct fabrication of solid
objects. In the preferred embodiment, four beam delivery fibers 38
transmit approximately equally powered laser beams that become four
focused laser beams 50 that are used as heat sources to melt the
powder supplied to the deposition region, where it is fused to the
deposition substrate 58, as shown in FIGS. 2A, 2B, and 6. For this
invention, the number of focused laser beams 50 is not nearly as
important as the concept of using multiple beams to achieve
normally conflicting requirements of a high deposition rate coupled
with exceptional material properties and very good dimensional
accuracy. The trend among current research groups has been to focus
on using a single laser beam with increased power to achieve the
higher deposition rates. Although the high-powered laser beam does
allow these groups to achieve the high deposition rates, the
results reported for material properties and dimensional accuracy
are poor. Conversely, using a lower powered laser beam of several
hundred watts has allowed solid parts to be made with increased
material strength and ductility with very good accuracy. This is
the cornerstone on which this invention builds upon.
[0044] For the multiple beam deposition apparatus, one or more
powder feeding apparatus 10a-b are used to supply powdered
materials to the deposition head 36, as shown in FIG. 1. The
powdered material from these sources can be either gravity fed or,
preferably, carried to the deposition region via a carrier gas. The
carrier gas can be inert or reactive with the powder material. The
powder is entrained in a gas stream and brought into the multiple
beam deposition apparatus through either of the two powder inlet
tubes 64a-b, as shown in FIGS. 6, 7A, and 7B. The two different
powder feeding apparatus 10a-b supply powder for either the filler
powder nozzles 48a-h or the outline powder nozzles 48i-j. The
manifold 62 serves to separate the powder input to the deposition
apparatus into approximately equal parts for the deposition
process. For the filler powder, the powder enters the powder
separation manifold 62 through the filler powder inlet tube 64a and
is directed onto the wall of the powder passage. The collisions of
the powder with the passage wall along with the length of each
passage being approximately equivalent for each of the nozzles
serves to separate the powder into approximately equal parts for
the deposition process. After being separated into several parts,
the gas entrained powder material exits from the multiple beam
deposition apparatus from a series of nozzles located in the base
of the multiple beam deposition apparatus. In a similar fashion,
the powdered material from the second powder feeding apparatus 10b
is separated into two approximately equal parts and directed out of
the multiple beam deposition apparatus from the outline powder
nozzles 48i-j. The volume of powder output from the filler powder
nozzles and the outline powder nozzles is controlled to be
equivalent by monitoring the volumetric powder flow out of the two
powder feeding apparatus 10a-b.
[0045] Referring to FIGS. 4A and 4B, each of the filler powder
nozzles 48a-h is located within the multiple beam deposition
apparatus, such that the powder stream out of one filler powder
nozzle interacts with the powder stream from a second filler powder
nozzle to create a plane of convergence 22. This plane of
convergence 22 is similar to the focal plane of one of the focused
laser beams 50 from the multiple beam deposition apparatus.
Deposition of the powdered material occurs in a plane .+-.0.5
inches above or below this plane of convergence 22. Referring to
the multiple beam deposition apparatus in the description section,
each of the filler powder nozzles 48a-d interacts with only one
other filler powder nozzle 48e-h to create four pairs of filler
powder nozzles whose powder convergence planes are located at a
similar position from the multiple beam deposition apparatus. In a
similar fashion, the outline powder nozzles 48i-j are located
within the multiple beam deposition apparatus such that the powder
stream from each of these nozzles interacts to form a convergence
plane 22. This convergence plane 22 is located at a similar
distance from the deposition apparatus as is the convergence plane
formed by the filler powder nozzles 48a-h. It should be noted that
the convergence plane of the intersecting powder streams from the
outline powder nozzles is similar to that for the filler powder
nozzle pairs, and the convergence point of the intersecting powder
streams from the outline powder nozzles is co-located with the
convergence point created by the powder from one pair of filler
powder nozzles. During the outline process, the center pair of
filler powder nozzles interact with the outline nozzles to provide
uniform flow from all four directions, simulating a Cartesian
coordinate. The convergence plane created by the interacting
outline powder nozzles 48i-j forms the plane at/or near the plane
where the material deposition will occur.
[0046] In the convergence plane, each pair of the filler powder
nozzles 48a-h interacts to form an elliptical spot that has the
maximum powder density in its central region. One of the focused
laser beams is directed through this location of maximum powder
density such that the focused laser beam is centered within the
elliptical spot formed by the two powder nozzle streams. This is
similar for each of the filler powder nozzle pairs, each pair
having one laser beam. Each of the laser beams interacts with both
powdered materials and the deposition substrate 58 to cause the
powdered material to become molten and be fused/bonded to the
surface of the deposition substrate 58. The elliptical spot created
by the interacting outline powder nozzles 48i-j is located to be
coincident with the elliptical spot created by one set of the
filler powder nozzles and the focused laser beam that passes
through this spot. In this fashion, a single deposition head 36 can
be used to both outline features and then fill in the featureless
regions in an expeditious fashion. The powder flowing to the
outline powder nozzles 48i-j is only flowing to the deposition
region where feature outlining will occur. During the feature
outline deposition process, only the focused laser beam that
interacts with the filler powder nozzles aligned with the outline
powder nozzles is transmitted to the deposition surface. In this
fashion, the uniform fill layer thickness can be preserved and the
outline layer thickness can be made uniform to the fill layer
thickness by control of the traverse rate of the deposition
substrate 58 relative to the focused laser beam. Although the
embodiment described uses a single deposition head for the material
deposition application, this operation can also be performed using
multiple deposition heads 36 with one or more powder feeding
apparatus.
[0047] This invention can be used for material cladding, surface
modification, or other processes where the addition of a layer or
region of material is required. One application of particular
importance in using the multiple beam deposition apparatus involves
building a solid object from the powdered material one layer at a
time. This direct fabrication application will be used to describe
the general operation of the deposition system that incorporates
the multiple beam deposition apparatus. For the direct fabrication
application, a computer aided design (CAD) solid model of the
component to be fabricated is used. The CAD solid model, which
represents the component in its entirety, is first sectioned into
thin layers within the computer. This operation is generally
referred to as a slicing operation. Each of these layers represents
a cross-section of the component at a given distance away from the
base of the component, including a hatching pattern that defines
the regions to be filled during the deposition process. The
hatching pattern includes a series of equally spaced parallel lines
that are used to define the line deposition regions within the
areas to be filled.
[0048] Referring to FIGS. 2A and 2B, the deposition process is
similar to a printing process in which a thick printed layer is
deposited. The computer transforms the layer information into a
series of control commands for the deposition process. Typically,
the outline of the feature is deposited first using the outline
powder nozzles 48i-j and the filler powder nozzles 48a-h that
coincide. The deposition substrate 58 is located beneath the
multiple beam deposition apparatus and the outline process is
initiated by turning on the outlining beam and moving the part
relative to the beam to outline both the internal and external
features required for each layer. The outline layers can have a
varying thickness in comparison to the fill layers. Then the flow
of powder to the outline powder nozzles 48i-j is stopped and the
filling process occurs. The filler powder nozzles 48a-h interact
with the focused laser beams 50 to create lines that are equally
spaced apart such that an integer number of lines will exactly fill
the regions between the lines. The first series of lines is
deposited. Next, the substrate 58 is translated relative to the
deposition head 36 such that a second set of lines can be deposited
alongside the first set of lines. The operation continues until the
space between the first set of equally spaced parallel lines is
completely filled with material, creating a flat layer with a
uniform thickness. After this region is filled, the substrate 58 is
again translated relative to the deposition head 36 to begin to
fill the region adjacent to the first fill region. The fill process
is repeated until the space between the first set of equally spaced
parallel lines in the second region is filled, once again creating
a flat layer with a uniform thickness, which is also equal to the
thickness of a line deposit 54. This process is repeated across the
layer until the entire area requiring material has been filled.
Once this layer is deposited, the multiple beam deposition
apparatus is translated away from the deposition plane, a distance
equal to the thickness of the flat layer. This entire process is
repeated to deposit subsequent layers in a sequential manner, until
the finished object is completed.
[0049] It is also possible to have different scan patterns for
alternating layers, while maintaining the process time advantage of
multiple beams and nozzles. This is achieved by rotating the
orientation of the deposition surface relative to the deposition
head 36 about the axis, which is normal to the deposition surface.
For example, if a Cartesian coordinate system is used to define the
three-dimensional space above the substrate, where the deposition
substrate lies in the X,Y plane, then the rotation would occur
about the Z-axis. This is desired in some parts because it creates
a uniform heating within the part that results in uniform stress
throughout the part.
[0050] Independent control of the focused beams 50 transmitted to
the surface of the deposition substrate 58 allows each beam to be
modulated on and off independent of the other beams. During the
filling operation for each layer, each of the beams is turned on
and off as the deposition lines intersect the external deposited
feature 60a and internal deposited features 60b. In this fashion,
the filling process can be controlled to fill the areas where
material is required and leave void those areas that do not require
material. One alternative to leaving certain regions void is to
apply a second material which is sacrificial and used only as a
support structure material.
[0051] While this invention has been described as having a
preferred embodiment, it is understood that it is capable of
further modifications, uses and/or adaptations of the invention,
following in general the principle of the invention and including
such departures of the present disclosure as come within known or
customary practice in the art to which the invention pertains, and
as may be applied to the central features hereinbefore set forth,
and fall within the scope of the invention of the limits of the
appended claims.
* * * * *