U.S. patent application number 15/406467 was filed with the patent office on 2018-07-19 for additive manufacturing using a mobile build volume.
The applicant listed for this patent is GENERAL ELECTRIC COMPANY. Invention is credited to Zachary David FIELDMAN, Justin MAMRAK, MacKenzie Ryan REDDING.
Application Number | 20180200792 15/406467 |
Document ID | / |
Family ID | 62837366 |
Filed Date | 2018-07-19 |
United States Patent
Application |
20180200792 |
Kind Code |
A1 |
REDDING; MacKenzie Ryan ; et
al. |
July 19, 2018 |
ADDITIVE MANUFACTURING USING A MOBILE BUILD VOLUME
Abstract
The present disclosure generally relates to additive
manufacturing systems and methods on a large-scale format. One
aspect involves a build unit that can be moved around in three
dimensions by a positioning system, building separate portions of a
large object. The build unit has an energy directing device that
directs, e.g., laser or e-beam irradiation onto a powder layer. In
the case of laser irradiation, the build volume may have a gasflow
device that provides laminar gas flow to a laminar flow zone above
the layer of powder. This allows for efficient removal of the
smoke, condensates, and other impurities produced by irradiating
the powder (the "gas plume") without excessively disturbing the
powder layer. The build unit may also have a recoater that allows
it to selectively deposit particular quantities of powder in
specific locations over a work surface to build large, high
quality, high precision objects.
Inventors: |
REDDING; MacKenzie Ryan;
(Cincinnati, OH) ; FIELDMAN; Zachary David;
(Hamilton, OH) ; MAMRAK; Justin; (West Chester,
OH) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
GENERAL ELECTRIC COMPANY |
Schenectady |
NY |
US |
|
|
Family ID: |
62837366 |
Appl. No.: |
15/406467 |
Filed: |
January 13, 2017 |
Current U.S.
Class: |
1/1 |
Current CPC
Class: |
B23K 15/0086 20130101;
B23K 37/0235 20130101; B23K 15/002 20130101; B22F 3/1055 20130101;
B23K 26/14 20130101; B23K 2103/00 20180801; B23K 26/0876 20130101;
B23K 26/1437 20151001; B29C 64/153 20170801; B23K 2103/42 20180801;
B23K 26/127 20130101; B29C 64/371 20170801; Y02P 10/25 20151101;
B33Y 40/00 20141201; B33Y 30/00 20141201; B22F 2003/1056 20130101;
B23K 26/0006 20130101; B23K 2103/26 20180801; B23K 15/0093
20130101; B23K 26/082 20151001; B33Y 10/00 20141201; B23K 26/342
20151001 |
International
Class: |
B22F 3/105 20060101
B22F003/105; B33Y 10/00 20060101 B33Y010/00; B33Y 30/00 20060101
B33Y030/00; B33Y 50/02 20060101 B33Y050/02; B23K 15/00 20060101
B23K015/00; B23K 26/342 20060101 B23K026/342; B23K 26/08 20060101
B23K026/08; B23K 37/02 20060101 B23K037/02; B23K 26/14 20060101
B23K026/14 |
Claims
1. An additive manufacturing apparatus comprising: a build unit
comprising a laser irradiation directing device, a gasflow device
with inlet and outlet portions immediately adjacent to a work
surface and a laminar flow zone, the gasflow device adapted to
provide substantially laminar gas flow within two inches of, and
substantially parallel to, a work surface, and the laser
irradiation directing device during operation of the apparatus
directs a laser beam to pass through the laminar flow zone; and a
positioning system adapted to provide independent movement of the
build unit in at least two dimensions that are substantially
parallel to the work surface.
2. The apparatus of claim 1, wherein the positioning system is
adapted to provide independent movement of the build unit in at
least three dimensions.
3. The apparatus of claim 1, wherein the gasflow device is adapted
to provide a low oxygen environment around the work surface in a
region below the build unit.
4. The apparatus of claim 3, wherein the build unit includes a
reduced oxygen gas zone above the laminar flow zone.
5. The apparatus of claim 4, further comprising a containment zone
surrounding at least the build unit and positioning system.
6. The apparatus of claim 3, wherein the laser irradiation
directing device is within the build unit.
7. The apparatus of claim 1, wherein a fiber-optic cable extends
from a laser to the build unit.
8. The apparatus of claim 1, wherein the positioning system allows
for rotation of the build unit in the two dimensions that are
substantially parallel to the work surface.
9. The apparatus of claim 1, wherein the build unit further
comprises a powder delivery unit and a recoater arm.
10. The apparatus of claim 9, wherein the laser irradiation
directing device is within the build unit.
11. A method for making an object from powder comprising: (a)
moving a build unit over a build area of a work surface, the build
unit comprising a gasflow device with a laminar flow zone over the
build area, the gasflow device providing substantially laminar gas
flow within two inches of, and substantially parallel to, the work
surface; (b) irradiating at least a portion of the build area of
the work surface with a laser that passes through the laminar flow
zone to form a first fused layer; and (c) repeating at least steps
(a) through (b) to form the object.
12. The method of claim 11, further comprising a step (d) of moving
the build unit vertically away from the work surface.
13. The method of claim 12, further comprising repeating steps (a)
and (b) after step (d).
14. The method of claim 11, wherein the gasflow device provides a
low oxygen environment around the work surface in a region below
the build unit.
15. The method of claim 14, wherein the build unit includes a
reduced oxygen gas zone above the laminar flow zone.
16. The method of claim 15, further comprising a containment zone
surrounding at least the build unit and positioning system.
17. The method of claim 11, wherein the laser irradiation directing
device is within the build unit.
18. The method of claim 11, wherein the positioning system allows
for rotation of the build unit in the two dimensions that are
substantially parallel to the work surface.
19. The method of claim 11, wherein the build unit further
comprises a powder delivery unit and a recoater arm.
20. The method of claim 18, wherein build unit is rotated
90.degree. and moved in a direction perpendicular to the direction
of movement in step (a).
21. The method of claim 11, further comprising using a second build
unit to build at least a portion of a second object on the work
surface.
22. The method of claim 11, further comprising using a second build
unit to build at least a portion of the build envelope.
Description
INTRODUCTION
[0001] The present disclosure generally relates to methods and
systems adapted to perform additive manufacturing ("AM") processes,
for example by direct melt laser manufacturing ("DMLM"), on a
larger scale format.
CROSS REFERENCE TO RELATED APPLICATIONS
[0002] Reference is made to the following related applications
filed concurrently, the entirety of which are incorporated herein
by reference:
[0003] U.S. patent application Ser. No. ______, titled "Additive
Manufacturing Using a Mobile Scan Area," with attorney docket
number 037216.00060, and filed Jan. 13, 2017.
[0004] U.S. patent application Ser. No. ______, titled "Additive
Manufacturing Using a Dynamically Grown Wall," with attorney docket
number 037216.00061, and filed Jan. 13, 2017.
[0005] U.S. patent application Ser. No. ______, titled "Additive
Manufacturing Using a Selective Recoater," with attorney docket
number 037216.00062, and filed Jan. 13, 2017.
[0006] U.S. patent application Ser. No. ______, titled "Large Scale
Additive Machine," with attorney docket number 037216.00071, and
filed Jan. 13, 2017.
BACKGROUND
[0007] A description of a typical laser powder bed fusion process
is provided in German Patent No. DE 19649865, which is incorporated
herein by reference in its entirety. AM processes generally involve
the buildup of one or more materials to make a net or near net
shape (NNS) object, in contrast to subtractive manufacturing
methods. Though "additive manufacturing" is an industry standard
term (ASTM F2792), AM encompasses various manufacturing and
prototyping techniques known under a variety of names, including
freeform fabrication, 3D printing, rapid prototyping/tooling, etc.
AM techniques are capable of fabricating complex components from a
wide variety of materials. Generally, a freestanding object can be
fabricated from a computer aided design (CAD) model. A particular
type of AM process uses an irradiation emission directing device
that directs an energy beam, for example, an electron beam or a
laser beam, to sinter or melt a powder material, creating a solid
three-dimensional object in which particles of the powder material
are bonded together. Different material systems, for example,
engineering plastics, thermoplastic elastomers, metals, and
ceramics are in use. Laser sintering or melting is a notable AM
process for rapid fabrication of functional prototypes and tools.
Applications include direct manufacturing of complex workpieces,
patterns for investment casting, metal molds for injection molding
and die casting, and molds and cores for sand casting. Fabrication
of prototype objects to enhance communication and testing of
concepts during the design cycle are other common usages of AM
processes.
[0008] Selective laser sintering, direct laser sintering, selective
laser melting, and direct laser melting are common industry terms
used to refer to producing three-dimensional (3D) objects by using
a laser beam to sinter or melt a fine powder. For example, U.S.
Pat. No. 4,863,538 and U.S. Pat. No. 5,460,758, which are
incorporated herein by reference, describe conventional laser
sintering techniques. More accurately, sintering entails fusing
(agglomerating) particles of a powder at a temperature below the
melting point of the powder material, whereas melting entails fully
melting particles of a powder to form a solid homogeneous mass. The
physical processes associated with laser sintering or laser melting
include heat transfer to a powder material and then either
sintering or melting the powder material. Although the laser
sintering and melting processes can be applied to a broad range of
powder materials, the scientific and technical aspects of the
production route, for example, sintering or melting rate and the
effects of processing parameters on the microstructural evolution
during the layer manufacturing process have not been well
understood. This method of fabrication is accompanied by multiple
modes of heat, mass and momentum transfer, and chemical reactions
that make the process very complex.
[0009] FIG. 1 is schematic diagram showing a cross-sectional view
of an exemplary conventional system 100 for direct metal laser
sintering ("DMLS") or direct metal laser melting (DMLM). The
apparatus 100 builds objects, for example, the part 122, in a
layer-by-layer manner by sintering or melting a powder material
(not shown) using an energy beam 136 generated by a source 120,
which can be, for example, a laser for producing a laser beam, or a
filament that emits electrons when a current flows through it. The
powder to be melted by the energy beam is supplied by reservoir 126
and spread evenly over a powder bed 112 using a recoater arm 116
travelling in direction 134 to maintain the powder at a level 118
and remove excess powder material extending above the powder level
118 to waste container 128. The energy beam 136 sinters or melts a
cross sectional layer of the object being built under control of an
irradiation emission directing device, such as a galvo scanner 132.
The galvo scanner 132 may comprise, for example, a plurality of
movable mirrors or scanning lenses. The speed at which the laser is
scanned is a critical controllable process parameter, impacting how
long the laser power is applied to a particular spot. Typical laser
scan speeds are on the order of 10 to 100 millimeters per second.
The build platform 114 is lowered and another layer of powder is
spread over the powder bed and object being built, followed by
successive melting/sintering of the powder by the laser 120. The
powder layer is typically, for example, 10 to 100 microns. The
process is repeated until the part 122 is completely built up from
the melted/sintered powder material.
[0010] The laser 120 may be controlled by a computer system
including a processor and a memory. The computer system may
determine a scan pattern for each layer and control laser 120 to
irradiate the powder material according to the scan pattern. After
fabrication of the part 122 is complete, various post-processing
procedures may be applied to the part 122. Post processing
procedures include removal of excess powder by, for example,
blowing or vacuuming. Other post processing procedures include a
stress release process. Additionally, thermal and chemical post
processing procedures can be used to finish the part 122.
[0011] FIG. 2 shows a side view of an object 201 built in a
conventional powder bed 202, which could be for example a powder
bed as illustrated by element 112 of FIG. 1. Then as the build
platform 114 is lowered and successive layers of powder are built
up, the object 201 is formed in the bed 202. The walls 203 of the
powder bed 202 define the amount of powder needed to make a part.
The weight of the powder within the build environment is one
limitation on the size of parts being built in this type of
apparatus. The amount of powder needed to make a large part may
exceed the limits of the build platform 114 or make it difficult to
control the lowering of the build platform by precise steps which
is needed to make highly uniform additive layers in the object
being built.
[0012] In conventional powder bed systems, such as shown in FIG. 1,
the energy beam 136 must scan a relatively large angle
.theta..sub.1 when building a part large enough to occupy most of
the powder bed 118. This is because the angle .theta..sub.1 must
increase as the cross-sectional area of the object increases. In
general, when making these larger parts, the angle .theta..sub.1
becomes large at the periphery of the part. The energy density at
the point of contact between the laser and powder bed then varies
over the part. These differences in energy density affect the melt
pool at large angles relative to that obtained when the laser is
normal to the powder bed. These melt pool differences may result in
defects and loss of fidelity in these regions of the part being
built. These defects may result in inferior surface finishes on the
desired part.
[0013] Another problem that arises with prior art methods and
systems involves cooling the layer of powdered material and
removing smoke, condensates, and other impurities produced by
irradiating the powder (sometimes called the "gas plume") which can
contaminate the object and obscure the line of sight of the energy
beam. It is also important to cool and solidify the layer quickly
to avoid formation of deformations or other defects. For large
objects, i.e. objects with a largest dimension in the xy plane (for
conventional powder bed systems, the plane of the powder bed) of
400 to 450 mm, it is very difficult to provide consistent laminar
gas flow and efficient removal of unwanted gasses, particulates,
condensates, and other undesirable impurities and contaminants.
[0014] Another problem that arises in the prior art systems and
methods is the need to finely control the quantity and location of
powder deposited to avoid wasting powder, while also avoiding
contact of the powder with undesirable materials. Prior art methods
and systems deposit powder using blowing, sliding, or auger
mechanisms. These mechanisms utilize multiple moving parts that may
malfunction, or may be made of materials that are not suited to
contact with the powder due to concerns with contamination.
[0015] For example, EP 2191922 and EP 2202016 to Cersten et al.
discuss a powder application apparatus that dispenses powder using
rotating conveyor shafts with recesses for holding separate,
discrete amounts of powder. One problem encountered with these
systems is increased risk of powder contamination and failure of
the device.
[0016] Other attempts to overcome the limitations of conventional
powder bed systems have failed to address the problems associated
with scale-up of these machines. In some cases, attempts to provide
large format systems have introduced additional problems and
challenges in creating laser fused parts from powder. Prior systems
failed to provide uniform layer-wise powder distribution, effective
management of the gas plume, and good control of the laser energy
density over the part being produced.
[0017] For example, the concept of moving a laser within a build
area was explored in U.S. Application Publication No. 2004/0094728
to Herzog et al., the present inventors have noted this disclosure
does not address how powder might be distributed onto the part
being built. These techniques imply more traditional laser powder
deposition where powder is injected into a laser beam and melted
onto the object being built. Because there is no discussion of how
to achieve uniform layers or powder over the part being built, the
dimensional accuracy of such systems are very limited. Moreover,
because the build environment is large, achieving a suitable gas
environment near the laser melt pool would be difficult.
[0018] In another example, the concept of a large format system
whereby powder is deposited using a hopper is explored in U.S.
Patent Application Publication No. 2013/0101746 to Keremes et al.
Material 30 is deposited onto a part 40 being built using a
material applicator 28. Retaining walls 42 are utilized to allow
material 30 to build up as the part 40 is made. The system utilizes
a laser 18 placed in a stationary position near the top of the
build chamber. As the part 40 grows in size, the angle of the laser
beam 20 increases, particularly at the peripheral regions of the
part. In addition, because material 30 is deposited onto the part
40, the thickness of the material 30 deposited onto the part 40 is
difficult to control precisely.
[0019] International Application No. WO 2014/199149 titled
"Additive Manufacturing Apparatus and Method" to McMurtry et al.
("McMurtry") discusses utilizing multiple polygonal mirrors with a
localized gasflow device to build separate portions of an object in
a single dimension, i.e. along a line, and lowering the build
platform to provide another layer of powder. For large objects, it
is difficult to build a platform that can both stably hold
sufficient powder, and also be lowered by the precise layer
thickness required.
[0020] There remains a need for a large format powder manufacturing
system that overcomes the above-mentioned problems.
SUMMARY OF THE INVENTION
[0021] The present invention relates to an additive manufacturing
apparatus. In an embodiment, the apparatus comprises a build unit
with a powder dispenser and a recoater blade, an irradiation
emission directing device, and a positioning system, the
positioning system adapted to move the build unit in at least three
dimensions which may be, for example, x, y, and z coordinates,
during operation. The build unit may also be rotated in the x-y
plane. Advantageously, according to an embodiment of the present
invention the positioning system can move the build unit within a
volume that is at least ten times larger than the cube of the width
of the recoater blade. The build unit may also move the build unit
around an xy area that is at least ten times larger than the square
of the recoater blade width. The irradiation emission directing
device may be adapted to direct laser irradiation or e-beam
irradiation. For instance, the irradiation emission directing
device could be an optical mirror or lens, or it could be an
electromagnetic coil.
[0022] The build unit may further comprise a laminar gasflow zone
within a gasflow device adapted to provide substantially laminar
gas flow over a work surface. The gasflow device may also be
adapted to provide a reduced oxygen environment over the work
surface. During operation, if the gasflow device provides gas flow
over the work surface, then the irradiation emission directing
device is adapted to direct laser irradiation from a laser source.
The laser source may be within the build unit or outside the build
unit. If the laser source is within the build unit, for instance in
the case that a fiber optic cable extends from the laser to the
build unit, the fiber optic cable transports the laser irradiation
from the laser to the irradiation emission directing device (which
is within the build unit), then the build unit may further comprise
a second positioning system attached to the laser source, the
second positioning system adapted to move the laser source within
the build unit, independent of the motion of the build unit.
[0023] The present invention also relates to a method for
fabricating an object. In an embodiment, the method comprises (a)
moving a build unit to deposit a first layer of powder over at
least a first portion of a first build area, the build unit
comprising a powder dispenser and a recoater blade, (b) irradiating
at least part of the first layer of powder within the first build
area to form a first fused layer, (c) moving the build unit upward
in a direction substantially normal to the first layer of powder,
then (d) repeating to form the object. After step (b), but before
step (c), the method may further comprise at least the steps of
(a') moving the build unit to deposit a second layer of powder, the
second layer of powder abutting the first layer of powder; and (b')
irradiating at least part of the second layer of powder to form a
second fused layer. The irradiation may be laser irradiation or
e-beam irradiation. When there is a gasflow device providing
substantially laminar gas flow to a laminar gasflow zone over a
work surface, then the irradiation is laser irradiation.
[0024] The present invention also relates to an additive
manufacturing apparatus comprising a selective recoater. In an
embodiment, the apparatus comprises a powder dispenser, e.g. a
hopper, the powder dispenser comprising a powder storage area and
at least a first and second gate, the first gate operable by a
first actuator that allows opening and closing the first gate, the
second gate operable by a second actuator that allows opening and
closing the second gate, and each gate adapted to control the
dispensation of powder from the powder storage area onto a work
surface. The powder dispenser may have any number of powder gates,
for instance at least ten powder gates, or more preferably at least
twenty gates. Advantageously, the powder dispenser and each gate
may be made of the same material, for instance cobalt-chrome, which
may also be the material of the powder. Each actuator may be, for
example, either an electric actuator or a pneumatic actuator. The
selective recoater may be part of a build unit adapted to provide a
layer of powder over the work surface. The build unit may further
comprise an irradiation emission directing device, which may be
adapted to direct a laser irradiation, or it may be adapted to
direct e-beam irradiation. The build unit may further comprise a
gasflow device adapted to provide substantially laminar gas flow
over the layer of powder.
[0025] The present invention also relates to a method for
fabricating an object using a selective recoater. In an embodiment,
the method comprises (a) depositing powder onto a work surface from
a powder dispenser, the powder dispenser comprising a powder
storage area and at least a first and second gate, the first gate
operable by a first actuator that allows opening and closing the
first gate, the second gate operable by a second actuator that
allows opening and closing the second gate, and each gate adapted
to control the dispensation of powder from the powder storage area
onto the work surface; (b) irradiating at least part of the first
layer of powder to form a first fused layer; and (c) repeating at
least steps (a) through (b) to form the object. Each gate may be
attached to a spring mounted to the powder dispenser that opposes
the force of the actuator. The powder used may be a material
suitable for additive manufacturing, such as cobalt-chrome, and
each surface of the powder dispenser and gates that comes into
contact with the powder may be made from the same material. The
method may further comprise a step of opening the first gate while
leaving the second gate closed to selectively deposit powder onto
the work surface. The method may also involve irradiating at least
part of the first layer of powder to form a portion of a build
envelope, and opening the first gate to deposit powder within the
build envelope while closing the second gate to avoid depositing
powder outside the build envelope.
[0026] The present invention also relates to an additive
manufacturing apparatus comprising a mobile gasflow device. In an
embodiment, the apparatus comprises a laser emission directing
device, a build unit comprising a gasflow device adapted to provide
substantially laminar gas flow to a laminar gasflow zone within two
inches of, and substantially parallel to, a work surface, a
positioning system adapted to provide independent movement of the
build unit in at least two dimensions that are substantially
parallel to the work surface, the laser emission directing device
adapted to direct laser irradiation to a build area over the work
surface during operation of the apparatus. The positioning system
may be adapted to provide independent movement of the build unit in
at least three dimensions. The positioning system may also be
adapted to allow for rotation of the build unit in two dimensions
substantially parallel to the work surface. The gasflow device may
be adapted to maintain a laminar gasflow zone, to provide a low
oxygen environment around the work surface in a region below the
build unit. There may also be a reduced oxygen gas zone above the
laminar gasflow zone. Both gas zones may be contained within a
containment zone surrounding at least the build unit and
positioning system. The laser emission directing device may be
within the build unit, and the laser irradiation may be transported
from a laser to the laser emission directing device via a
fiber-optic cable. The build unit may further comprise a powder
delivery unit and a recoater arm.
[0027] The present invention also relates to a method for
fabricating an object using a gasflow device with a laminar flow
zone. In an embodiment, the method comprises (a) moving a build
unit over a build area of a work surface, the build unit comprising
a gasflow device around a laminar flow zone over the build area,
the gasflow device providing substantially laminar gas flow within
two inches of, and substantially parallel to, the work surface, (b)
irradiating at least a portion of the build area of the work
surface with a laser that passes through the laminar flow zone to
form a first fused layer; and (c) repeating at least steps (a)
through (b) to form the object. The method may further comprise a
step (d) of moving the build unit vertically away from the work
surface. Steps (a) and (b) may be repeated after step (d). The
build unit may be rotated 90.degree. and moved in a direction
perpendicular to the direction of movement in step (a).
[0028] The present invention also relates to an apparatus for
making an object from powder using a mobile scan area. In an
embodiment, the apparatus comprises a build unit with a powder
delivery unit, a recoater arm, a laser emission directing device,
and a gasflow device around a laminar flow zone, the gasflow device
adapted to provide substantially laminar gas flow within two inches
of, and substantially parallel to, a work surface, and a
positioning system adapted to provide independent movement of the
build unit in at least three dimensions. The apparatus may further
comprise a containment zone enclosing the build unit and
positioning system. The build unit may be at least partially
enclosed to form a low oxygen environment above the build area of
the work surface, i.e. around the path of the beam. The laser
emission directing device may be positioned within the build unit
at a height such that, when the apparatus is in operation, the
maximum angle of the laser beam relative to normal within the build
area is less than about 15.degree.. A fiber-optic cable may extend
from the laser to the build unit, and thus transport laser
irradiation from the laser to the laser emission directing device.
The laser emission directing device may have a laser positioning
unit that allows movement of the laser emission directing device
within the build unit, independent of the motion of the build unit.
The build unit may further comprise an x-y axis galvo adapted to
control the laser beam in x-y, and the laser positioning system may
be adapted to move the laser emission directing device in x, y,
and/or z. The positioning system may be adapted to allow rotation
of the build unit in the two dimensions that are substantially
parallel to the work surface.
[0029] The present invention also relates to a method for
fabricating an object using a mobile scan area. In an embodiment,
the method comprises (a) moving a build unit to deposit a first
layer of powder over at least a first portion of a first build
area, the build unit comprising a powder delivery unit, a recoater
arm, a laser emission directing device, and a gasflow device around
a laminar flow zone over a build area of a work surface, the
gasflow device providing substantially laminar gas flow within two
inches of, and substantially parallel to, the work surface; (b)
irradiating at least part of the first layer of powder within the
first build area to form a first fused layer; (c) moving the build
unit upward in a direction substantially normal to the first layer
of powder; and (d) repeating at least steps (a) through (c) to form
the object. Steps (a) and (b) may be repeated after step (d). The
laser emission directing device may be positioned within the build
unit at a height above the build area to provide a maximum angle
relative to normal within the build area of less than
15.degree..
[0030] The present invention also relates to a method for
fabricating an object using a recoater blade and a dynamically
grown build envelope. In an embodiment, the method comprises (a)
moving a recoater blade to form a first layer of powder over at
least a portion of a first build area, (b) irradiating at least
part of the first layer of powder within the first build area to
form a first fused layer, and (c) repeating steps (a) and (b) to
form the object, wherein a build envelope retains unfused powder
about the object and has a volume that is larger than the cube of
the recoater blade width. For instance, it may be ten times larger
than the cube of the recoater blade width. The method may further
comprise the steps (a') moving the recoater to form a second layer
of powder over at least a portion of a second build area and
adjacent the first layer of powder; and (b') irradiating at least
part of the second layer of powder within the second build area to
form a second fused layer. Steps (a') and (b') may be performed
after step (b) but before step (c). The method may further comprise
a step (d) of removing the build envelope and unfused powder within
an envelope area to reveal the object. The powder material may be
cobalt-chrome. The build envelope may be formed from powder fused
by irradiation. For example, the build envelope may be formed by
laser powder deposition. The second layer of powder may be
substantially even with the first layer of powder. The irradiation
may be conducted in a reduced oxygen environment, and may be laser
irradiation. The irradiation may also be e-beam irradiation. The
method may further comprise using a second build unit to build at
least a portion of a second object. The method may also comprise
using a second build unit to build at least a portion of the build
envelope.
[0031] The present invention also relates to a method for
fabricating an object using a build unit and a dynamically grown
build envelope. In an embodiment, the method comprises (a) moving a
build unit to deposit a first layer of powder over at least a first
portion of a first build area, the build unit comprising a powder
dispenser, a recoater blade, and a directed energy emission
directing device; (b) irradiating at least part of the first layer
of powder within the first build area to form a first fused layer
of the object; and (c) repeating steps (a) and (b) to form the
object, wherein a build envelope retains unfused powder. The method
may further comprise (a') moving the recoater to form a second
layer of powder over at least a portion of a second build area and
abutting the first layer of powder; and (b') irradiating at least
part of the second layer of powder within the second build area to
form a second fused layer. Steps (a') and (b') may be performed
after step (b) but before step (c). The method may further comprise
step (d) of removing the build envelope and unfused powder within
the envelope area to reveal the object. The powder material may be
cobalt-chrome. The build envelope may be formed from powder fused
by irradiation. For example, the build envelope may be formed by
laser powder deposition. The second layer of powder may be
substantially even with the first layer of powder. The irradiation
may be conducted in a reduced oxygen environment, and may be laser
irradiation. The irradiation may also be from an electron beam.
[0032] In general, any number of build units may be used in
parallel, i.e. substantially simultaneously, to build one or more
object(s) and/or build envelope(s), all on the same work
surface.
BRIEF DESCRIPTION OF THE FIGURES
[0033] FIG. 1 shows an exemplary prior art system for DMLM using a
powder bed.
[0034] FIG. 2 shows a conventional powder bed that is moved down as
the object is formed.
[0035] FIG. 3 shows a large scale additive manufacturing apparatus
according to an embodiment of the invention.
[0036] FIG. 4 shows a side view of a build unit according to an
embodiment of the invention.
[0037] FIG. 5 shows a side view of a build unit dispensing powder
according to an embodiment of the invention.
[0038] FIG. 6 shows a top view of a build unit according to an
embodiment of the invention.
[0039] FIG. 7 shows a top view of a recoater according to an
embodiment of the present invention.
[0040] FIG. 8 illustrates a large scale additive manufacturing
apparatus with two build units according to an embodiment of the
present invention.
[0041] FIGS. 9A-9C illustrate a system and process of building an
object according to an embodiment of the invention.
[0042] FIGS. 10A-10D illustrate a system and process of building an
object according to an embodiment of the invention.
[0043] FIG. 11 shows an object being built by two build units in
accordance with an embodiment of the invention.
[0044] FIG. 12 shows two objects being built by a single build unit
according to an embodiment of the invention.
DETAILED DESCRIPTION
[0045] This detailed description and accompanying figures
demonstrate some illustrative embodiments of the invention to aid
in understanding. The invention is not limited to the embodiments
illustrated in the figures, nor is it limited to the particular
embodiments described herein.
[0046] The present invention relates to an apparatus that can be
used to perform additive manufacturing, as well as methods for
utilizing the apparatus to additively manufacture objects. The
apparatus includes components that make it particularly useful for
making large additively manufactured objects. One aspect of the
present invention is a build unit. The build unit may be configured
to include several components necessary for making high precision,
large scale additively manufactured objects. These components may
include, for example, a recoater, a gasflow device with a gasflow
zone, and an irradiation emission directing device. An irradiation
emission directing device used in an embodiment of the present
invention may be, for example, an optical control unit for
directing a laser beam. An optical control unit may comprise, for
example, optical lenses, deflectors, mirrors, and/or beam
splitters. Advantageously, a telecentric lens may be used.
Alternatively, the irradiation emission directing device may be an
electronic control unit for directing an e-beam. The electronic
control unit may comprise, for example, deflector coils, focusing
coils, or similar elements. The build unit may be attached to a
positioning system (e.g. a gantry, delta robot, cable robot, robot
arm, belt drive, etc.) that allows three dimensional movement
throughout a build environment, as well as rotation of the build
unit in a way that allows coating of a thin powder layer in any
direction desired.
[0047] FIG. 3 shows an example of one embodiment of a large-scale
additive manufacturing apparatus 300 according to the present
invention. The apparatus 300 comprises a positioning system 301, a
build unit 302 comprising an irradiation emission directing device
303, a laminar gas flow zone 307, and a build plate (not shown in
this view) beneath an object being built 309. The maximum build
area is defined by the positioning system 301, instead of by a
powder bed as with conventional systems, and the build area for a
particular build can be confined to a build envelope 308 that may
be dynamically built up along with the object. The gantry 301 has
an x crossbeam 304 that moves the build unit 302 in the x
direction. There are two z crossbeams 305A and 305B that move the
build unit 302 and the x crossbeam 304 in the z direction. The x
cross beam 304 and the build unit 302 are attached by a mechanism
306 that moves the build unit 302 in the y direction. In this
illustration of one embodiment of the invention, the positioning
system 301 is a gantry, but the present invention is not limited to
using a gantry. In general, the positioning system used in the
present invention may be any multidimensional positioning system
such as a delta robot, cable robot, robot arm, etc. The irradiation
emission directing device 303 may be independently moved inside of
the build unit 302 by a second positioning system (not shown). The
atmospheric environment outside the build unit, i.e. the "build
environment," or "containment zone," is typically controlled such
that the oxygen content is reduced relative to typical ambient air,
and so that the environment is at reduced pressure.
[0048] There may also be an irradiation source that, in the case of
a laser source, originates the photons comprising the laser
irradiation that is directed by the irradiation emission directing
device. When the irradiation source is a laser source, then the
irradiation emission directing device may be, for example, a galvo
scanner, and the laser source may be located outside the build
environment. Under these circumstances, the laser irradiation may
be transported to the irradiation emission directing device by any
suitable means, for example, a fiber-optic cable. When the
irradiation source is an electron source, then the electron source
originates the electrons that comprise the e-beam that is directed
by the irradiation emission directing device. When the irradiation
source is an electron source, then the irradiation emission
directing device may be, for example, a deflecting coil. When a
large-scale additive manufacturing apparatus according to an
embodiment of the present invention is in operation, if the
irradiation emission directing devices directs a laser beam, then
generally it is advantageous to include a gasflow device providing
substantially laminar gas flow to a gasflow zone as illustrated in
FIG. 3, 307 and FIG. 4, 404. If an e-beam is desired, then no
gasflow is provided. An e-beam is a well-known source of
irradiation. For example, U.S. Pat. No. 7,713,454 to Larsson titled
"Arrangement and Method for Producing a Three-Dimensional Product"
("Larsson") discusses e-beam systems, and that patent is
incorporated herein by reference. When the source is an electron
source, then it is important to maintain sufficient vacuum in the
space through which the e-beam passes. Therefore, for an e-beam,
there is no gas flow across the gasflow zone (shown, for example at
FIG. 3, 307).
[0049] Another advantage of the present invention is that the
maximum angle of the beam may be a relatively small angle
.theta..sub.2 to build a large part, because (as illustrated in
FIG. 3) the build unit 302 can be moved to a new location to build
a new part of the object being formed 309. When the build unit is
stationary, the point on the powder that the energy beam touches
when .theta..sub.02 is 0 defines the center of a circle in the xy
plane (the direction of the beam when .theta..sub.2 is
approximately 0 defines the z direction), and the most distant
point from the center of the circle where the energy beam touches
the powder defines a point on the outer perimeter of the circle.
This circle defines the beam's scan area, which may be smaller than
the smallest cross sectional area of the object being formed (in
the same plane as the beam's scan area). There is no particular
upper limit on the size of the object relative to the beam's scan
area.
[0050] In some embodiments, the recoater used is a selective
recoater. One embodiment is illustrated in FIGS. 4 through 7.
[0051] FIG. 4 shows a build unit 400 comprising an irradiation
emission directing device 401, a gasflow device 403 with a
pressurized outlet portion 403A and a vacuum inlet portion 403B
providing gas flow to a gasflow zone 404, and a recoater 405. Above
the gasflow zone 404 there is an enclosure 418 containing an inert
environment 419. The recoater 405 has a hopper 406 comprising a
back plate 407 and a front plate 408. The recoater 405 also has at
least one actuating element 409, at least one gate plate 410, a
recoater blade 411, an actuator 412, and a recoater arm 413. The
recoater is mounted to a mounting plate 420. FIG. 4 also shows a
build envelope 414 that may be built by, for example, additive
manufacturing or Mig/Tig welding, an object being formed 415, and
powder 416 contained in the hopper 405 used to form the object 415.
In this particular embodiment, the actuator 412 activates the
actuating element 409 to pull the gate plate 410 away from the
front plate 408. In an embodiment, the actuator 412 may be, for
example, a pneumatic actuator, and the actuating element 409 may be
a bidirectional valve. In an embodiment, the actuator 412 may be,
for example, a voice coil, and the actuating element 409 may be a
spring. There is also a hopper gap 417 between the front plate 408
and the back plate 407 that allows powder to flow when a
corresponding gate plate is pulled away from the powder gate by an
actuating element. The powder 416, the back plate 407, the front
plate 408, and the gate plate 410 may all be the same material.
Alternatively, the back plate 407, the front plate 408, and the
gate plate 410 may all be the same material, and that material may
be one that is compatible with the powder material, such as
cobalt-chrome. In this particular illustration of one embodiment of
the present invention, the gas flow in the gasflow zone 404 flows
in the y direction, but it does not have to. The recoater blade 411
has a width in the x direction. The direction of the irradiation
emission beam when .theta..sub.2 is approximately 0 defines the z
direction in this view. The gas flow in the gasflow zone 404 may be
substantially laminar. The irradiation emission directing device
401 may be independently movable by a second positioning system
(not shown). This illustration shows the gate plate 410 in the
closed position.
[0052] FIG. 5 shows the build unit of FIG. 4, with the gate plate
410 in the open position (as shown by element 510) and actuating
element 509. Powder in the hopper is deposited to make fresh powder
layer 521, which is smoothed over by the recoater blade 511 to make
a substantially even powder layer 522. In some embodiments of the
present invention, the substantially even powder layer may be
irradiated at the same time that the build unit is moving, which
would allow for continuous operation of the build unit and thus
faster production of the object.
[0053] FIG. 6 shows a top down view of the build unit of FIG. 4.
For simplicity, the object and the walls are not shown here. The
build unit 600 has an irradiation emission directing device 601, an
attachment plate 602 attached to the gasflow device 603, hopper
606, and recoater arm 611. The gasflow device has a gas outlet
portion 603A and a gas inlet portion 603B. Within the gasflow
device 603 there is a gasflow zone 604. The gasflow device 603
provides laminar gas flow within the gasflow zone 604. There is
also a recoater 605 with a recoater arm 611, actuating elements
612A, 612B, and 612C, and gate plates 610A, 610B, and 610C. The
recoater 605 also has a hopper 606 with a back plate 607 and front
plate 608. In this particular illustration of one embodiment of the
present invention, the hopper is divided into three separate
compartments containing three different materials 609A, 609B, and
609C. There are also gas pipes 613A and 613B that feed gas out of
and into the gasflow device 603.
[0054] FIG. 7 shows a top down view of a recoater according to an
embodiment of the invention. In this particular illustration the
recoater has a hopper 700 with only a single compartment containing
a powder material 701. There are three gate plates 702A, 702B, and
702C that are controlled by three actuating elements 703A, 703B,
and 703C. There is also a recoater arm 704 and a wall 705. When the
recoater passes over a region that is within the wall, such as
indicated by 707, the corresponding gate plate 702C may be held
open to deposit powder in that region 707. When the recoater passes
over a region that is outside of the wall, such as the region
indicated as 708, the corresponding gate plate 702C is closed by
its corresponding actuating element 703C, to avoid depositing
powder outside the wall, which could potentially waste the powder.
Within the wall 705, the recoater is able to deposit discrete lines
of powder, such as indicated by 706. The recoater blade (not shown
in this view) smooths out the powder deposited.
[0055] Advantageously, a selective recoater according to an
embodiment of the present invention allows precise control of
powder deposition using powder deposition device (e.g. a hopper)
with independently controllable powder gates as illustrated, for
example, in FIG. 6, 606, 610A, 610B, and 610C and FIG. 7, 702A,
702B, and 702C. The powder gates are controlled by at least one
actuating element which may be, for instance, a bidirectional valve
or a spring (as illustrated, for example, in FIG. 4, 409. Each
powder gate can be opened and closed for particular periods of
time, in particular patterns, to finely control the location and
quantity of powder deposition (see, for example, FIG. 6). The
hopper may contain dividing walls so that it comprises multiple
chambers, each chamber corresponding to a powder gate, and each
chamber containing a particular powder material (see, for example,
FIG. 6, and 609A, 609B, and 609C). The powder materials in the
separate chambers may be the same, or they may be different.
Advantageously, each powder gate can be made relatively small so
that control over the powder deposition is as fine as possible.
Each powder gate has a width that may be, for example, no greater
than about 2 inches, or more preferably no greater than about 1/4
inch. In general, the smaller the powder gate, the greater the
powder deposition resolution, and there is no particular lower
limit on the width of the powder gate. The sum of the widths of all
powder gates may be smaller than the largest width of the object,
and there is no particular upper limit on the width of the object
relative to the sum of the widths of the power gates.
Advantageously, a simple on/off powder gate mechanism according to
an embodiment of the present invention is simpler and thus less
prone to malfunctioning. It also advantageously permits the powder
to come into contact with fewer parts, which reduces the
possibility of contamination. Advantageously, a recoater according
to an embodiment of the present invention can be used to build a
much larger object. For example, the largest xy cross sectional
area of the recoater may be smaller than the smallest xy cross
sectional area of the object, and there is no particular upper
limit on the size of the object relative to the recoater. Likewise,
the width of the recoater blade may smaller than the smallest width
of the object, and there is no particular upper limit on the width
of the object relative to the recoater blade. After the powder is
deposited, a recoater blade can be passed over the powder to create
a substantially even layer of powder with a particular thickness,
for example about 50 microns, or preferably about 30 microns, or
still more preferably about 20 microns. Another feature of some
embodiments of the present invention is a force feedback loop.
There can be a sensor on the selective recoater that detects the
force on the recoater blade. During the manufacturing process, if
there is a time when the expected force on the blade does not
substantially match the detected force, then control over the
powder gates may be modified to compensate for the difference. For
instance, if a thick layer of powder is to be provided, but the
blade experiences a relatively low force, this scenario may
indicate that the powder gates are clogged and thus dispensing
powder at a lower rate than normal. Under these circumstances, the
powder gates can be opened for a longer period of time to deposit
sufficient powder. On the other hand, if the blade experiences a
relatively high force, but the layer of powder provided is
relatively thin, this may indicate that the powder gates are not
being closed properly, even when the actuators are supposed to
close them. Under these circumstances, it may be advantageous to
pause the build cycle so that the system can be diagnosed and
repaired, so that the build may be continued without comprising
part quality. Another feature of some embodiments of the present
invention is a camera for monitoring the powder layer thickness.
Based on the powder layer thickness, the powder gates can be
controlled to add more or less powder.
[0056] In addition, an apparatus according to an embodiment of the
present invention may have a controlled low oxygen build
environment with two or more gas zones to facilitate a low oxygen
environment. The first gas zone is positioned immediately over the
work surface. The second gas zone may be positioned above the first
gas zone, and may be isolated from the larger build environment by
an enclosure. For example, in FIG. 4 element 404 constitutes the
first gas zone, element 419 constitutes the second gas zone
contained by the enclosure 418, and the environment around the
entire apparatus is the controlled low oxygen build environment. In
the embodiment illustrated in FIG. 4, the first gasflow zone 404 is
essentially the inner volume of the gasflow device 403, i.e. the
volume defined by the vertical (xz plane) surfaces of the inlet and
outlet portions (403A and 403B), and by extending imaginary
surfaces from the respective upper and lower edges of the inlet
portion to the upper and lower edges of the outlet portion in the
xy plane. When the irradiation emission directing device directs a
laser beam, then the gasflow device preferably provides
substantially laminar gas flow across the first gas zone. This
facilitates removal of the effluent plume caused by laser melting.
Accordingly, when a layer of powder is irradiated, smoke,
condensates, and other impurities flow into the first gasflow zone,
and are transferred away from the powder and the object being
formed by the laminar gas flow. The smoke, condensates, and other
impurities flow into the low-pressure gas outlet portion and are
eventually collected in a filter, such as a HEPA filter. By
maintaining laminar flow, the aforementioned smoke, condensates and
other impurities can be efficiently removed while also rapidly
cooling melt pool(s) created by the laser, without disturbing the
powder layer, resulting in higher quality parts with improved
metallurgical characteristics. In an aspect, the gas flow in the
gasflow volume is at about 3 meters per second. The gas may flow in
either the x or y direction.
[0057] The oxygen content of the second controlled atmospheric
environment is generally approximately equal to the oxygen content
of the first controlled atmospheric environment, although it
doesn't have to be. The oxygen content of both controlled
atmospheric environments is preferably relatively low. For example,
it may be 1% or less, or more preferably 0.5% or less, or still
more preferably 0.1% or less. The non-oxygen gases may be any
suitable gas for the process. For instance, nitrogen obtained by
separating ambient air may be a convenient option for some
applications. Some applications may use other gases such as helium,
neon, or argon. An advantage of the invention is that it is much
easier to maintain a low-oxygen environment in the relatively small
volume of the first and second controlled atmospheric environments.
In prior art systems and methods, the larger environment around the
entire apparatus and object must be tightly controlled to have a
relatively low oxygen content, for instance 1% or less. This can be
time-consuming, expensive, and technically difficult. Thus it is
preferable that only relatively smaller volumes require such
relatively tight atmospheric control. Therefore, in the present
invention, the first and second controlled atmospheric environments
may be, for example, 100 times smaller in terms of volume than the
build environment. The first gas zone, and likewise the gasflow
device, may have a largest xy cross sectional area that is smaller
than the smallest xy cross sectional area of the object. There is
no particular upper limit on the size of the object relative to the
first gas zone and/or the gasflow device. Advantageously, the
irradiation emission beam (illustrated, for example, as 402 and
502) fires through the first and second gas zones, which are
relatively low oxygen zones. And when the first gas zone is a
laminar gasflow zone with substantially laminar gas flow, the
irradiation emission beam is a laser beam with a more clear line of
sight to the object, due to the aforementioned efficient removal of
smoke, condensates, and other contaminants or impurities.
[0058] One advantage of the present invention is that, in some
embodiments, the build plate may be vertically stationary (i.e. in
the z direction). This permits the build plate to support as much
material as necessary, unlike the prior art methods and systems,
which require some mechanism to raise and lower the build plate,
thus limiting the amount of material that can be used. Accordingly,
the apparatus of the present invention is particularly suited for
manufacturing an object within a large (e.g., greater than 1
m.sup.3) build envelope. For instance, the build envelope may have
a smallest xy cross sectional area greater than 500 mm.sup.2, or
preferably greater than 750 mm.sup.2, or more preferably greater
than 1 m.sup.2. The size of the build envelope is not particularly
limited. For instance, it could have a smallest xy cross sectional
area as large as 100 m.sup.2. Likewise, the formed object may have
a largest xy cross sectional area that is no less than about 500
mm.sup.2, or preferably no less than about 750 mm.sup.2, or still
more preferably no less than about 1 m.sup.2. There is no
particular upper limit on the size of the object. For example, the
object's smallest cross sectional area may be as large as 100
m.sup.2. Because the build envelope retains unfused powder about
the object, it can be made in a way that minimizes unfused powder
(which can potentially be wasted powder) within a particular build,
which is particularly advantageous for large builds. When building
large objects within a dynamically grown build envelope, it may be
advantageous to build the envelope using a different build unit, or
even a different build method altogether, than is used for the
object. For example, it may be advantageous to have one build unit
that directs an e-beam, and another build unit that directs a laser
beam. With respect to the build envelope, precision and quality of
the envelope may be relatively unimportant, such that rapid build
techniques are advantageously used. In general, the build envelope
may be built by any suitable means, for instance by Mig or Tig
welding, or by laser powder deposition. If the wall is built by
additive manufacturing, then a different irradiation emission
directing device can be used to build than wall than is used to
build the object. This is advantageous because building the wall
may be done more quickly with a particular irradiation emission
directing device and method, whereas a slower and more accurate
directing device and method may be desired to build the object. For
example, the wall may be built from a rapidly built using a
different material from the object, which may require a different
build method. Ways to tune accuracy vs. speed of a build are well
known in the art, and are not recited here.
[0059] For example, as shown in FIG. 8, the systems and methods of
the present invention may use two or more build units to build one
or more object(s). The number of build units, objects, and their
respective sizes are only limited by the physical spatial
configuration of the apparatus. FIG. 8 shows a top down view of a
large-scale additive manufacturing machine 800 according to an
embodiment of the invention. There are two build units 802A and
802B mounted to a positioning system 801. There are z crossbeams
803A and 803B for moving the build units in the z direction. There
are x crossbeams 804A and 804B for moving the build units in the x
direction. The build units 802A and 802B are attached to the x
crossbeams 804A and 804B by mechanisms 805A and 805B that move the
units in the y direction. The object(s) being formed are not shown
in this view. A build envelope (also not shown in this view) can be
built using one or both of the build units, including by laser
powder deposition. The build envelope could also be built by, e.g.,
welding. In general, any number of objects and build envelopes can
be built simultaneously using the methods and systems of the
present invention.
[0060] Advantageously, in some embodiments of the present invention
the wall may be built up around the object dynamically, so that its
shape follows the shape of the object. A dynamically built chamber
wall advantageously results in the chamber wall being built closer
to the object, which reduces the size of support structures
required, and thus reduces the time required to build the support
structures. Further, smaller support structures are more stable and
have greater structural integrity, resulting in a more robust
process with less failure. In one embodiment, two build envelopes
may be built, one concentric within the other, to build objects in
the shape of, for example, circles, ovals, and polygons. If the
wall is built by welding, then support structures such as
buttresses may be advantageously built on the wall as needed, to
support overhangs and other outwardly-built features of the object.
Therefore, according to an embodiment of the present invention, a
dynamically built chamber wall enables object features that would
be either impossible or impractical using conventional
technology.
[0061] FIGS. 9A-9C illustrate an object built vertically upward
from powder, within a dynamically grown build envelope, on a
vertically stationary build plate according to one embodiment of
the present invention. In this illustration the object 900 is built
on a vertically stationary build plate 902 using a build unit 901.
Since the build unit 901 may be capable of selectively dispensing
powder within the build envelope 903, the unfused deposited powder
904 is generally entirely within the build envelope 903, or at
least a substantial portion of the unfused deposited powder 904
stays within the build envelope 903. As shown in FIG. 9C, the build
unit 901 may be moved away from the object 900 to more easily
access the object 900. Mobility of the of the build unit 901 may be
enabled by, for instance, a positioning system (not shown in this
view).
[0062] FIGS. 10A-10D illustrate a system and process of building an
object 1000 and build envelope 1001 layer by layer on a vertically
stationary build plate 1002, using a build unit 1003. The object
1000 has a topmost fused layer 1004 and the build envelope 1001 has
a topmost fused layer 1005. There is unfused deposited powder 1006.
In this particular illustration of one embodiment of the present
invention, a first layer of the build envelope 1001 is built, as
shown by element 1007 in FIG. 10B. Then the build unit may provide
a fresh layer of powder 1008 (FIG. 10C). Then the fresh layer of
powder may be irradiated to form a new topmost fused layer of the
object 1009 (FIG. 10D). Mobility of the of the build unit 1003 may
be enabled by, for instance, a positioning system (not shown in
this view).
[0063] FIG. 11 shows an object 1100 being built by a build units
1102 and a build envelope 1105 being built by a build unit 1101 on
a vertically stationary build plate 1103. There is unfused
deposited powder 1104. Mobility of the of the build units 1101 and
1102 may be enabled by, for instance, a positioning system (not
shown in this view).
[0064] FIG. 12 shows two objects 1200 and 1201 being built by a
single build unit 1202 on a vertically stationary build plate 1203.
There is unfused deposited powder 1204 and 1205. Mobility of the of
the build unit 1202 may be enabled by, for instance, a positioning
system (not shown in this view).
* * * * *