Note: Descriptions are shown in the official language in which they were submitted.
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BLUE LASER METAL ADDITIVE MANUFACTURING SYSTEM
[0001] This application: (i) claims under 35 U.S.C. 119(e)(1) the
benefit of
the filing date of, and claims the benefit of priority to, US provisional
application serial
number 62/722,198 filed August 24, 2018; and (ii) claims under 35 U.S.C.
119(e)(1)
the benefit of the filing date of, and claims the benefit of priority to, US
provisional
application serial number 62/726,233 filed September 1, 2018, the entire
disclosure of
each of which are incorporated herein by reference.
BACKGROUND OF THE INVENTION
Field of the Invention
[0002] The present inventions relate to laser processing of
materials and in
particular laser building of materials including laser additive manufacturing
processes
using laser beams having wavelengths from about 350 nm to about 700 nm.
[0003] Infrared red (IR) based (e.g., having wavelengths greater than 700
nm,
and in particular wavelengths greater than 1,000 nm) additive manufacturing
systems
suffer from, among other things, two short comings, which limit both the build
volume
and the build speed. In these IR systems the build volume is limited by the
finite size of
the scanning systems and the spot that can be created for a given focal length
collimator and f-theta lens. For example, in such prior IR systems, when using
a 14 mm
focal length collimator and a 500 mm F-theta focal length lens the spot size
is on the
order of 350 gm for a diffraction limited IR laser beam. This gives an
addressable foot
print on the raw build material, e.g., a powder bed, of approximately 85 mm x
85 mm,
which in turn creates or establishes the finite limitation on the build volume
for that given
resolution (e.g., spot size). The second limitation on the build speed for IR
laser
systems is the absorption of the laser beam by the materials. While
originally, most raw
build materials had a modest to low reflectivity for wavelengths in the
infrared spectrum,
as additivity manufacturing started to use metals, such as gold, silver,
platinum, copper
and aluminum and alloys thereof, which materials have high and very high IR
reflectivity, problems were encountered with using these high reflective IR
types of build
materials in IR additive manufacturing. As a consequence, the coupling of the
infrared
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laser energy into the raw build materials, e.g., powder bed or particles, is
limited with a
significant portion of the energy being reflected away, backward or deeper
into the raw
build material. These limitations are in a way further tied or linked
together,
compounding the problems and deficiencies of IR additive systems. Thus, the
finite
penetration depth of the Infrared laser light determines the optimum layer
thickness and
as a consequence, limits the resolution of the process. Thus, IR laser
systems,
because of their reflectivity to the typical raw build material have limited
layer
thicknesses and thus limited resolution.
[0004] As used herein, unless expressly stated otherwise, "UV",
"ultra violet",
"UV spectrum", and "UV portion of the spectrum" and similar terms, should be
given
their broadest meaning, and would include light in the wavelengths of from
about 10 nm
to about 400 nm, and from 10 nm to 400 nm.
[0005] As used herein, unless expressly stated otherwise, the
terms "visible",
"visible spectrum", and "visible portion of the spectrum" and similar terms,
should be
given their broadest meaning, and would include light in the wavelengths of
from about
380 nm to about 750 nm, and 400 nm to 700 nm.
[0006] As used herein, unless expressly stated otherwise, the
terms "blue
laser beams", "blue lasers" and "blue" should be given their broadest meaning,
and in
general refer to systems that provide laser beams, laser beams, laser sources,
e.g.,
lasers and diodes lasers, that provide, e.g., propagate, a laser beam, or
light having a
wavelength from 400 nm (nanometer) to 500 nm, and about 400 nm to about 500
nm.
Blue lasers include wavelengths of 450 nm, of about 450 nm, of 460 nm, of
about 460
nm. Blue lasers can have bandwidths of from about 10 pm (picometer) to about
10 nm,
about 5 nm, about 10 nm and about 20 nm, as well as greater and smaller
values.
[0007] As used herein, unless expressly stated otherwise, the terms "green
laser beams", "green lasers" and "green" should be given their broadest
meaning, and
in general refer to systems that provide laser beams, laser beams, laser
sources, e.g.,
lasers and diodes lasers, that provide, e.g., propagate, a laser beam, or
light having a
wavelength from 500 nm to 575 nm, about 500 nm to about 575 nm. Green lasers
include wavelengths of 515 nm, of about 515 nm, of 532 nm, about 532 nm, of
550 nm,
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and of about 550 nm. Green lasers can have bandwidths of from about 10 pm to
10
nm, about 5 nm, about 10 nm and about 20 nm, as well as greater and smaller
values.
[0008] Generally, the term "about" and the symbol "¨" as used
herein, unless
specified otherwise, is meant to encompass a variance or range of 10%, the
experimental or instrument error associated with obtaining the stated value,
and
preferably the larger of these.
[0009] As used herein, unless stated otherwise, room temperature
is 25 C.
And, standard ambient temperature and pressure is 25 C and 1 atmosphere.
Unless
expressly stated otherwise all tests, test results, physical properties, and
values that are
.. temperature dependent, pressure dependent, or both, are provided at
standard ambient
temperature and pressure, this would include viscosities.
[0010] As used herein unless specified otherwise, the recitation
of ranges of
values herein is merely intended to serve as a shorthand method of referring
individually
to each separate value falling within the range. Unless otherwise indicated
herein, each
individual value within a range is incorporated into the specification as if
it were
individually recited herein.
[0011] Typically, a method employed today in additive
manufacturing is the
use of an infrared laser and a galvanometer to scan the laser beam across the
surface
of a powder bed in a predetermined pattern. The IR laser beam is of sufficient
intensity
.. to create a keyhole welding process that melts and fuses the liquified
powder to the
lower layer or substrate. This approach has several limitations that
determines the
speed of the process. For example, a single laser beam is used to scan the
surface
and the build rate is limited by the maximum scanning speed of the
galvanometers (7
m/sec). Manufactures strongly embrace IR technology, and typically believe
that it is
the only viable wavelength, thus they are working, but with limited success,
to overcome
this limitation by integrating two or more IR laser / galvanometers into a
system, where
the two can work in conjunction to build a single part or they can work
independently to
build parts in parallel. These efforts are aimed at improving the throughput
of the
additive manufacturing systems, but have been focused solely on IR and have
been of
limited success, not meeting the long felt need for improved additive
manufacturing.
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[0012] An example of another limitation in IR processing is the
finite volume
that can be addressed by the IR laser / galvanometer system. In a stationary
head
system the build volume is defined by the focal length of the f-theta lens,
the scanning
angle of the galvanometer, the wavelength of the IR laser and the beam quality
of the
infrared laser. For example, with a 500 mm F-theta lens the IR laser creates a
spot size
on the order of 50 gm for a diffraction limited infrared laser. If the laser
beam is
operating at 100 Watts optical power, then the intensity of the beam is
greater than the
intensity required to initiate a keyhole welding mode. The keyhole welding
mode
creates a plume of vaporized material that must be removed out of the path of
the laser
beam by a cross jet otherwise the laser beam is scattered and absorbed by the
vaporized metal. In addition, because the keyhole mode of welding relies on
creating a
hole in the liquid metal surface that is maintained by the vapor pressure of
the vaporized
metal, material other than vaporized metal can be ejected from the keyhole.
This
material is referred to as spatter and results in molten materials being
deposited
elsewhere on the build plane that can lead to defects in the final part. While
the
manufactures of additive manufacturing systems have had some limited success
in
developing rapid prototyping machines, they have failed to meet the long felt
need, and
achieve the requirements needed to produce commercial or actual parts in
volume. To
accomplish this a breakthrough in the method of patterning the parts, which
prior to the
present inventions the art has not achieved.
[0013] In general, a problem and failing with IR processing and
systems is the
requirement or need to fuse the powder in a keyhole welding mode. This can be
typically because of the use of a single beam to process the powder. If the
laser beam
is operating at 100 Watts optical power, then the intensity of the beam is
greater than
the intensity required to initiate a keyhole welding mode. The keyhole welding
mode
creates a plume of vaporized material that must be removed out of the path of
the laser
beam by a cross jet otherwise the laser beam is scattered and absorbed by the
vaporized metal. In addition, because the keyhole mode of welding relies on
creating a
hole in the liquid metal surface that is maintained by the vapor pressure of
the vaporized
metal, material such as the vaporized metal can be ejected from the keyhole.
This
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material is referred to as spatter and results in molten materials being
deposited
elsewhere on the build plane that can lead to defects in the final part.
[0014] Recent work by Lawrence Livermore National Laboratories
using an
Optically Activated Light Valve (OALV) has been attempted to address these IR
limitations. The OALV is a high-power spatial light modulator that is used to
create a
light pattern using high power lasers. While the pattern on the OALV is
created with a
blue LED or laser source from a projector, the output power from the four
laser diode
arrays are transmitted through the spatial light modulator and used to heat
the image to
the melting point and a Q-switched IR laser is required to initiate a keyhole
weld. The
IR laser is used in the keyhole mode to initiate the weld, especially when
fusing copper
or aluminum materials, and is generally required for these materials. This
keyhole weld
process typically creates spatter, porosity in the part, as well as high
surface roughness.
Thus, the OALV systems as do typical IR systems does not eliminate the adverse
effects of keyhole initiation of the building process. While it would be
better to
completely avoid the keyhole welding step, the art has failed to overcome this
problem
and has not provided this solution. This failure has primarily occurred
because at the IR
wavelengths the absorption properties of many metals are so low that a high
peak
power laser is necessary to initiate the process. Since the OALV is only
transparent in
the IR region of the spectrum, it is not feasible to build, or use this type
of system using
a visible laser source as the high energy light source. The cost of the
components in
this system are very high especially the OALV which is a custom unit.
[0015] Prior metal based additive manufacturing machines are very
limited in
that they are either based on a binder being sprayed into a powder bed
followed by a
consolidation step at high temperatures, or a high-power single mode laser
beam
scanned over the powder bed by a galvanometer system at high speeds. Both of
these
systems have significant fallings that the art has been unable to overcome.
The first
system is capable of high volume manufacturing of parts with loose tolerances
due to
the shrinkage of the parts during the consolidation process. The second
process is
limited in build speed by the scan speeds of the galvanometer limiting the
maximum
power level laser that can be used and consequently, the build rate. Builders
of
scanning based additive manufacturing systems have worked to overcome this
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limitation by building machines with multiple scan heads and laser systems,
which has
not provided an adequate solution to these problems. This does indeed increase
the
throughput, but the scaling law is linear, in other words a system with two
laser
scanners can only build twice as many parts as a system with one scanner or
build a
single part twice as fast. Thus, there is a need for a high throughput, laser-
based metal
additive manufacturing system that does not suffer from the limitations of the
currently
available systems.
[0016] This Background of the Invention section is intended to
introduce
various aspects of the art, which may be associated with embodiments of the
present
inventions. Thus, the forgoing discussion in this section provides a framework
for better
understanding the present inventions, and is not to be viewed as an admission
of prior
art.
SUMMARY
[0017] The present inventions solve these and other problems with
IR additive
.. manufacturing systems and process, and address these and other long felt
needs, as
well as future needs as additive manufacturing process and systems achieve
greater
prevalence. The present inventions, among other things, solve these problems
and
needs by providing the articles of manufacture, devices and processes taught,
and
disclosed herein.
[0018] Thus, there is provided 3-D systems using a spatial light modulator,
an
array of spatial light modulators and both to form an energy pattern on a
powder bed to
either directly fuse a plastic or nylon material or to simply control the
temperature of the
zone to just below the melt point of the region where the primary laser is
about to be
scanned. It is theorized that the reason for considering this approach is to
improve the
energy efficiency of the system. At present either a radiant heater, a zone
radiant heat
or a build plate temperature control system is used to pre-heat the entire
bead to be
processed. By reducing the size of the region to be pre-heated, the overall
energy
consumption of the system can be reduced.
[0019] Further, an embodiment of the present inventions are based
on using a
.. Digital Mirror Device (DMD) spatial light modulator, an array of DMD
devices and both
assumes that the power density must be limited to 100 W/cm2 or less when
operating in
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a continuous mode which is sufficient to melt and flow plastics but
insufficient to melt
and fuse metals.
[0020] There is provided an additive manufacturing system for
metals that
uses a laser and a spatial light modulator, an array of spatial light
modulators and both
to form an energy pattern on a powder metal layer that is fused to the layer
below, a
gantry system to step and repeat the image across the powder bed, a motion
control
system, an elevator to displace the part down as each layer is fused, and a
powder
distribution system that can both spread the powder and compact it before
fusing, and
an air tight build chamber.
[0021] Moreover, there is provided these lasers, systems and methods having
one or more of the following features: a laser in the wavelength range of 300-
400 nm; a
laser in the wavelength range of 400-500 nm; a laser in the wavelength range
of 500-
600 nm; a laser in the wavelength range of 600-800 nm; an infrared laser in
the range of
800 nm ¨ 2000 nm; the laser is homogenized by a light pipe, micro-lens
homogenizer, a
diffractive element and combinations and variations of these; the laser is
time shared
between multiple print heads or multiple printer systems; the spatial light
modulator is a
Digital Micro-Mirror Device (DMD) array which is an array of micro-mirrors;
the spatial
light modulator is any of a class of spatial light modulator capable of
handling multi-W to
mutli-kW power levels; the DMD is air cooled; the DMD is water cooled; the DMD
is
water cooled by a water cooler such as a micro-channel cooler; the DMD is
cooled by a
Peltier cooler; includes zonal radiant heaters for maintaining the build
chamber
temperature; includes a heated build plate; includes a pyrometer or a FLIR
camera to
monitor or control the build plate temperature; includes a thermocouple or RTD
embedded in the build plate to monitor or control the temperature of the build
plate;
includes software for determining the optimum build strategy; includes a
separate
secondary laser for heating the powder bed only where the pattern will be
illuminated;
uses an inert atmosphere for the part build; uses an inert atmosphere for
keeping the
optics in the system clean; and wherein the laser-spatial modulator
combination creates
and image on the powder bed that has a multi-kW/cm2 power density which is
required
for fusing metals.
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[0022] Moreover, there is provided an additive manufacturing
system for
metals that uses a laser and a spatial light modulator, an array of spatial
light
modulators, and both to form an energy pattern on a powder metal layer that is
fused to
the layer below, by for example, using a conduction mode welding process with
the aid
of a second laser to pre-heat the powder bed, a gantry system to step and
repeat the
image across the powder bed, to continuously print the image by scrolling the
image
across the DMD synchronized with the movement of the head, the bed and both to
provide a time, and preferably a greater amount of time to melt the powder, a
motion
control system an elevator to displace the part down as each layer is fused,
and a
powder distribution system that can both spread the powder and compact it
before
fusing, and an air tight build chamber.
[0023] Further, there is provided these systems and methods having
the
feature of the build plate include any number of metal materials, including
aluminum,
anodized aluminum, titanium, steel, stainless steel, nickel, copper,
combinations of
.. these, as well as, any other material which may be the same material as the
powder or
different.
[0024] Still further, there is provided these lasers, systems and
methods
having one or more of the following features: wherein the laser is
approximately a 450
nm blue laser; wherein the laser is in the wavelength range of 300-400 nm;
wherein the
.. laser is in the wavelength range of 400-500 nm; wherein the laser is in the
wavelength
range of 500-600 nm; wherein the laser is in the wavelength range of 600-800
nm;
wherein the laser is an infrared laser in the range of 800 nm ¨ 2000 nm;
wherein the
laser is homogenized by either a light pipe or micro-lens homogenizer; wherein
the laser
can be time shared between multiple print heads or multiple printer systems;
wherein
there is a secondary laser; wherein the secondary laser is a 450 nm blue
laser; wherein
the second laser is in the wavelength range of 300-400 nm; wherein the
secondary
laser is in the wavelength range of 400-500 nm; wherein the secondary laser is
in the
wavelength range of 500-600 nm; wherein the secondary laser is in the
wavelength
range of 600-800 nm; wherein the secondary laser is an infrared laser in the
range of
800 nm ¨ 2000 nm; is homogenized by either a light pipe, micro-lens
homogenizer or a
diffractive optical element; wherein the secondary laser is time shared
between multiple
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print heads or multiple printer systems; wherein the system has a spatial
light
modulator; wherein the spatial light modulator is a Digital Micro-Mirror
Device (DMD);
wherein the spatial light modulator is any of a class of spatial light
modulator capable of
handling multi-Watts to mutli-kW power levels; wherein the system includes
zonal
radiant heaters for maintain the build chamber temperature; wherein the system
includes a heated build plate; wherein the system includes a pyrometer or a
FLIR
camera to monitor or control the build plate temperature; wherein the system
includes a
thermocouple or RTD embedded in the build plate to monitor or control the
temperature
of the build plate; wherein the system includes software for determining the
optimum
build strategy; wherein the system uses an inert atmosphere for the part
build; wherein
the system uses an inert atmosphere for keeping the optics in the system
clean;
wherein the system includes a laser-spatial modulator combination that creates
and
image on the powder bed that has a multi-Watt to multi-kWatt power density.
[0025] Moreover, there is provided these lasers, systems and
methods having
one or more of the following features: having a second laser, wherein in the
second
laser is used for preheat in the system and creates and region overlapping the
image of
the spatial-filter laser system on the powder bed that has a multi-Watt to
multi-kWatt
power density; and, wherein laser system has a powder bed that has a multi-
Watt to
multi-kWatt power density.
[0026] Yet further, there is provided an additive manufacturing system for
metals that uses a laser and a spatial light modulator to form a pattern on a
powder
metal layer that is fused to the layer below, a gantry system to step and
repeat the
image across the powder bed, a motion control system, an elevator to displace
the part
down as each layer is fused, and a powder distribution system that can both
spread the
.. powder and compact it before fusing, and an air tight build chamber.
[0027] Additionally, there is provided these systems, subsystems
and
methods having one or more of the following features: wherein the laser is is
in the
wavelength of a 450 nm blue laser; wherein the laser has a wavelength range of
300-
400 nm; wherein the laser has a wavelength range of 400-500 nm; wherein the
laser
has a wavelength range of 500-600 nm; wherein the laser has a wavelength range
of
600-800 nm; wherein the laser is an infrared laser in the range of 800 nm ¨
2,000 nm;
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wherein the laser is homogenized by either a light pipe or micro-lens
homogenizer;
wherein the laser is time shared between multiple print heads or multiple
printer
systems; wherein the spatial light modulator is a Digital Micro-Mirror Device
(DMD)
array which is an array of micro-mirrors; wherein the spatial light modulator
is any of a
class of spatial light modulator capable of handling mutli-W to multi-kW power
levels;
wherein the DMD is air cooled; wherein the DMD is water cooled by a water heat
exchanger such as a micro-channel cooler; wherein the laser is the DMD is
cooled by a
Peltier cooler; wherein the system includes zonal radiant heaters for maintain
the build
chamber temperature; wherein the system includes a heated build plate; wherein
the
system includes a pyrometer or a FLIR camera to monitor or control the build
plate
temperature; wherein the system includes a thermocouple or RTD embedded in the
build plate to monitor or control the temperature of the build plate; wherein
the system
includes software for determining the optimum build strategy; wherein the
system of
claim 1 that includes a separate secondary laser for heating the powder bed
only where
the pattern will be illuminated; wherein the system uses an inert atmosphere
for the part
build; wherein the system uses an inert atmosphere for keeping the optics in
the system
clean; and wherein the laser-spatial modulator combination of the system
creates and
image on the powder bed that has a multi-kW power density.
[0028] Yet further there is provided an additive manufacturing
system for
metals that uses a laser and a spatial light modulator to form a pattern on a
powder
metal layer that is fused to the layer below with the aid of a second laser to
pre-heat the
powder bed, a gantry system to step and repeat the image across the powder
bed, a
motion control system an elevator to displace the part down as each layer is
fused, and
a powder distribution system that can both spread the powder and compact it
before
fusing, and an air tight build chamber.
[0029] Still further there is provided an additive manufacturing
system for
metals that uses multiple lasers and multiple spatial light modulators to form
a single
larger pattern on a powder metal layer that is fused to the layer below, a
gantry system
to step and repeat the image across the powder bed, a motion control system,
an
elevator to displace the part down as each layer is fused, and a powder
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system that can both spread the powder and compact it before fusing, and an
air tight
build chamber.
[0030] Moreover there is provided an additive manufacturing system
for
metals that uses multiple lasers and multiple spatial light modulators to form
a
checkboard pattern of images and non-images on a powder metal layer that is
fused to
the layer below, a gantry system to step and repeat the image across the
powder bed, a
motion control system, an elevator to displace the part down as each layer is
fused, and
a powder distribution system that can both spread the powder and compact it
before
fusing, and an air tight build chamber.
[0031] Yet further there is provided a laser spatial-light modulator
combination
that creates an image and moves the image across the DMD to create a
stationary
image on the moving gantry system to extend the exposure time for printing the
pattern
in the material being fused. Still further there is provided an additive
manufacturing
system for forming metal objects from metal powders, the system having: a
laser source
to provide a build laser beam along a build laser beam path; a heating means
for
heating a metal powder; a Digital Micro-Mirror Device (DMD) on the laser beam
path,
whereby the build laser beam is directed into the DMD, wherein the DMD creates
a 2-D
image pattern that is reflected from the DMD along the laser beam path to an
optical
assembly; and, the optical assembly directing the laser beam to the metal
powder,
whereby the 2-D image pattern is delivered to the metal powder.
[0032] Additionally, there is provided these systems, subsystems
and
methods having one or more of the following features: wherein the heating
means is
selected from the group consisting of electric heaters, radiant heaters, IR
heaters and a
laser beam; wherein the heating means is a laser beam having a wave length in
the
blue wave length range; wherein the metal powder forms a bed of metal powder;
wherein the laser beam has a wave length select from the group consisting of
blue and
green; wherein the laser beam has a wave length selected from the group
consisting of
about 450 nm, about 460 nm, about 515 nm, about 532 and about 550 nm; wherein
the
laser source has a power of about 1 kW to about 20 kW; wherein and the 2-D
image
delivers a peak power density to the metal powder of from about 2 kW/cm2 to
about 5
kW/cm2; wherein the DMD has maximum average power density level; and wherein
the
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peak power density level of the 2-D image on the metal powder is at least 500x
greater
than the maximum average power density level of the DMD; wherein the DMD has
maximum average power density level; and wherein the peak power density level
of the
2-D image on the metal powder is at least 1,000x greater than the maximum
average
power density level of the DMD.; wherein the heating means is configured to
heat the
powder to within 200 C of a melting point of the metal powder; wherein the
heating
means is configured to heat the powder to within 100 C of a melting point of
the metal
powder; wherein the heating means is configured to heat the powder to about
400 C of
a melting point of the metal powder; wherein the heating means is configured
to heat
the powder to about 600 C of a melting point of the metal powder; wherein the
heating
means is configured to heat the powder to about 400 C of a melting point of
the metal
powder and maintain the powder at that temperature; wherein the heating means
is
configured to heat the powder to about 600 C of a melting point of the metal
powder
and maintain the powder at that temperature; wherein the heating means is
configured
to heat the powder to within 200 C of a melting point of the metal powder and
maintain
the powder at that temperature; having a second laser source to provide a
second build
laser beam along a second build laser beam path; a second Digital Micro-Mirror
Device
(DMD) on the second laser beam path, whereby the second build laser beam is
directed
into the second DMD, wherein the second DMD creates a second 2-D image pattern
that is reflected from the second DMD along the second laser beam path to a
second
optical assembly; wherein the 2-D image pattern is delivered to a first area
of the metal
powder, and the second 2-D image pattern is delivered to a second area of the
metal
powder; wherein the first area and the second area are different; and, wherein
the first
area and the second area are adjacent.
[0033] Additionally, there is provided these systems, subsystems and
methods having one or more of the following features: wherein the DMD array is
optimized for wavelengths in at least one of the following wavelengths: the
blue
wavelength range, 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and
about 460 nm, the green wavelength range, 515 nm, about 515 nm, 532 nm, about
532
nm, and the red wavelength range of 600 nm to 700 nm.
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[0034] Additionally, there is provided these systems, subsystems
and
methods having one or more of the following features: wherein the build laser
beam
has a wavelength selected from at least one of the following wavelengths: the
blue
wavelength range, 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and
about 460 nm, the green wavelength range, 515 nm, about 515 nm, 532 nm, about
532
nm, and the red wavelength range of 600 nm to 700 nm.
[0035] Yet further there is provided an additive manufacturing
system for
forming metal objects from metal powders, the system having: a laser source to
provide
a build laser beam along a build laser beam path; a second laser source for
providing a
heating laser beam; a Digital Micro-Mirror Device (DMD) on the laser beam
path,
whereby the build laser beam is directed into the DMD, wherein the DMD creates
a
image that is reflected from the DMD along the laser beam path to an optical
assembly;
and, the optical assembly directing the laser beam to the metal powder,
whereby the
image is delivered to the metal powder.
[0036] Still further there is provided a laser spatial-light modulator
combination
that projects a 2-D pattern onto a powder bed with an optimized grey scale in
time or in
the pattern, such that the heat manipulates the molten puddle into the desired
build
shape yielding sharper transitions and denser parts.
BRIEF DESCRIPTION OF THE DRAWINGS
[0037] FIG. 1 is perspective view of an embodiment of an additive
manufacturing system in accordance with the present inventions.
[0038] FIG. 2 is a cut away perspective view an embodiment of a
laser DMD
print head in accordance with the present inventions.
[0039] FIG. 3 is chart comparing pulse width to repetition rate for
embodiments of a given power in accordance with the present inventions.
[0040] FIGS. 4A and 4B are photographs of printed patterns using
an
embodiment of a laser spatial light modulator in accordance with the present
inventions.
[0041] FIG. 5 is chart comparing blue light absorption in powder
bed for
embodiments of systems in accordance with the present inventions, in
comparison to IR
laser systems.
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[0042] FIG. 6 is a schematic view of an embodiment of an overlap
pre-heat
beam and build laser beam in accordance with the present inventions.
[0043] FIG. 7 is a flow diagram of an embodiment of the timing for
a system
and method in accordance with the present inventions.
[0044] FIG. 8 is a flow diagram of an embodiment of the timing for a system
and method in accordance with the present inventions.
[0045] FIG. 9 is a schematic diagram of an embodiment of a multi-
DMD laser
printer system in accordance with the present inventions.
[0046] FIG. 10 is a schematic diagram of an embodiment of a multi-
DMD
laser printer system in accordance with the present inventions.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0047] In general, the present inventions relate to laser
processing of
materials, laser processing by matching preselected laser beam wavelengths to
the
material to be processed to have high or increased levels of absorptivity by
the
materials, systems configurations that provide for greater speed, efficiency
and size of
objects that are built, and in particular laser additive manufacture of raw
materials into
large structures, parts, components and articles with laser beams having high
absorptivity by starting raw materials.
[0048] An embodiment of the present systems and methods can use any
laser wavelengths, but the preferred embodiment is to use a pair of blue
lasers to print
and fuse the layers of the part in a parallel fashion using a spatial light
modulator as the
means of defining the pattern on the powder bed that is to be fused. The laser
source
and the laser beam in embodiments can have wavelengths in the blue wavelength
range and preferably can be 450 nm, about 450 nm, 460 nm, about 460 nm and
have
bandwidths of about 10 pm, about 5 nm, about 10 nm and about 20 nm, and from
about
2 nm to about 10 nm, as well as greater and smaller values. The laser source
and the
laser beam in embodiments can have wavelengths in the green wavelength range
and,
for example, can be 515 nm, about 515 nm, 532 nm, about 532, nm, 550 nm, about
550
nm and have bandwidths of about 10 pm, about 5 nm, about 10 nm and about 20
nm,
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and from about 2 nm to about 10 nm, as well as greater and smaller values.
Combinations and variations of these various wavelengths can be use in a
system.
[0049] The print engine for an embodiment of the present systems
and
methods is based on a Digital Micro-Mirror Device (DMD) array, embodiments of
which
can be obtained from Texas Instruments (TI), which creates the 2-D energy
pattern to
be printed. All of the DMD products made by TI are candidates for this
process, the
DMD used to print the pattern in Figures 4a & b is a DLP9500. By 2-D energy
pattern it
is meant the image that the laser beam, or laser beam pattern forms on the bed
of
powder to be fused. As discussed in this specification while this image is
observed as a
2-D energy pattern, i.e., an image on the bed of powder, it will have depth,
i.e., 3-D
properties as the energy penetrates into the bed and fuses the material to
lower layers
of the build object. These print engines can be used with any of the laser
additive
manufacturing systems and methods provided in this specification, as well as
others. A
blue laser reflected off the DMD array which when reimaged can provide multi-
Watt to
multi-kWatt power densities in a 2-D energy pattern on the powder bed. A
second blue
laser can be added to preheat the powder bed in the exact spot where the 2-D
energy
pattern is imaged to reduce the energy required from the laser - spatial light
modulator
pair to fuse the patterned powder to the underlying layers. This print engine
is mounted
on a precision gantry system that allows the 2-D image to be stitched together
to form a
larger 2-D image which is a single layer of the part. The system preferably
includes a
powder spreader as part of the gantry system or separate from the gantry
system and
an elevator as part of the build volume. The build volume is preferably very
low oxygen
and more preferably oxygen free and can be filled with either an inert gas
such as
Argon, or a mixture of gases to promote the fusing process such as Argon-0O2.
The
powder bed and chamber can be directly heated by electric heaters, radiant
heaters,
and combinations and variations of these and other types of heaters, to reduce
the heat
loss from the part during the manufacturing process. In an embodiment, the
conduction
mode welding process is the preferred method for fusing each layer together
which
eliminates the spatter normally encountered in the keyhole process which is
the typical
process for all additive manufacturing scanned laser systems, prior to the
present
embodiments taught and disclosed in this specification.
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[0050] In general, a Digital Micromirror Device (DMD), is a
device that uses
very small mirrors that can be made of aluminum to reflect light to make an
image. The
DMD may also be referred to as DLP chip. Embodiments of these devices can be a
couple of centimeters (cm), from about 1 cm to about 3 cm, from about 1 cm to
about 2
cm, a centimeter or less, less than 0.5 cm, less than 0.2 cm, or smaller, for
their cross
sectional dimension, (e.g., side of square, diameter of a circle, or long side
of a
rectangle, these devices may also be other shapes). These DMDs can contain
from
about 100,000 to 4 million, at least about 100,000, at least about 500,000, at
least about
1 million, about 2 million, or more, mirrors, with each mirror, measuring
about 4 pm or
less, about 7.56 pm or less, about 10.8 pm or less, about 10 pm or less, from
about 4
pm to about 20 pm and combinations and variations of these and larger and
smaller
sizes. The mirrors can be laid out in a predetermined pattern, such as matrix,
for
example, like a photo mosaic, with each mirror representing one pixel.
[0051] In an embodiment the DMD includes: a CMOS DDR SRAM chip,
which
is a memory cell that will electrostatically cause the mirror to tilt to the
on or off position,
depending on its logic value (0 or 1); a heat sink; an optical window, which
allows the
laser to pass through while protecting the mirrors from dust and debris.
[0052] In embodiments the DMD has on its surface several hundred
thousand
microscopic mirrors, or more, arranged in typically a rectangular array which
correspond
to the pixels in the image to be formed and displayed. The mirrors can be
individually
rotated, e.g., 10-12 , or more or less, to an on or off state. In the on
state, the laser
from the laser source, e.g., the build laser and build laser beam, is
reflected into the
lens making the pixel direct the build laser energy into the image on the
powder bed. In
the off state, the laser beam, e.g., the build laser, is directed elsewhere,
e.g., to a beam
dump, making the pixel not contribute to the image or the fusing of the
powder. It being
understood that in embodiments the pre-heat laser beam many also be directed
to and
reflected from a DMD device to form a pre-heat image on the powder in the bed.
[0053] In an embodiment, which could be theorized as being
analogous to
greyscales of picture, the mirror is toggled on and off very quickly, and the
ratio of on
time to off time determines the amount of fusion or bonding of the powder in
the powder
bed. This provides the capability to control laser power, and power density
(e.g., kW/
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cm2), of the laser beam on the powder bed, without changing the power of the
output
beam from the laser source. In some embodiments more than 500 different powers
and
power densities, more than 700 different powers and power densities, and more
than
100,000 different powers and power densities can be obtained. An alternative
method
to achieve a grey scale affect is to pixelate the image, dropping out
individual pixels that
are small in size compared to the thermal diffusion length in the material
being
processed. This effectively reduces the average power delivered to the image.
This
grey scale, whether in time or in space can be used to manipulate the melt
pool and
force it into a preferred shape.
[0054] Embodiments of DMDs for use in the present systems, print heads and
print engines, can be obtained from TI, these DMDs would include: DLP2010,
DLP3000,
DLP3010, DLP4500, DLP4710, DLP5500, DLP6500, DLP7000, DLP9000, DLP9000x,
DLP9500, with digital controllers; DLPA2000, DLPA3000, DLPA3005, DLPC3430,
DLPC3433, DLPC3435, DLPC3438, DLPC3439, DLPC3470, DLPC3478.
[0055] Turning to FIG. 1 there is shown an embodiment an additive
manufacturing system 100. The system 100 has a base 108 that has a gantry
system
101 mounted on the base 108. The gantry system 101 provides for movement of
the
DMD print head 103. This movement can be in the x-axis 102, or in the y-axis
102a.
The system 100 has a powder bed elevator 104 (for moving the part down as it
is built
allowing the next layer to be deposited on the part), a powder bed spreader
105 and a
powder roller 106. An image 107 from the DMD print head 103 is shown in the
figure on
the surface of the powder. The system has a laminar flow air knife 109 and a
pyrometer
or FLIR camera 110. The base 108 and the gantry system 101 have wiring harness
111, that can contain for example, gantry power, control lines and fiber
optics for laser
beam transmission. The laser source, or a part of it, in embodiments may be
located on
and move with the gantry. In embodiments the laser source is located away from
the
base, away from the laser head, or both, and is connected to, e.g., placed in
optical
communication with, the laser head 103 by optical fibers. The laser source may
also be
connected by a flying optic head design where the laser beam traverses free
space to
the print head.
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[0056] Turning to FIG. 2 there is shown a cut away perspective
view of an
embodiment of a laser DMD print head 200. This embodiment can be used with any
of
the systems of the present inventions, including the system of FIG. 1, as well
as others.
The laser DMD print head 200 has a housing 230, which contains the optical
components, and has first laser input 201 and a second laser input 212, and an
output
or exit window 209. The laser beams travel into the housing 230 are directed
and
shaped by the optics and then exit the housing 230 through exit window 209 to
form
patterns (on the powder bed, which is not shown in this figure). In an
embodiment
these laser inputs 201, 212 are connectors and fibers for transmitting the
laser beam
from the laser source, such as QBH fiber optic cables that are in optical
communication,
e.g., connected to, the laser source to transmit the laser beams to the print
head. The
optics within the house 230 define two laser beam paths, one for each input.
Along the
first laser beam path, in the direction of the laser beam propagation, are
input 201, a
collimating lens 205, a turning mirror 206, DMD 202 (which is cooled by cooler
203), an
off state beam dump 204 (which may also have cooling), and DMD imaging lens
208,
from which the laser beam travels through window 209 to form image 210. Along
the
second laser beam path, in the direction of the laser beam propagation, are
input 212, a
collimating lens 210, turning mirror 207, (imaging lens 208, may or may not be
in the
second beam path and a second or separate imaging lens may be employed), and
then
through the window 209 to a location on the powder bed.
[0057] In an embodiment, of the additive manufacturing systems,
the first
laser beam path is the build laser beam and the build laser beam path, as it
is the laser
beam that fuses the powder to build an object. The build laser beam can have a
wavelength in the blue wavelength range and preferably 440 nm, about 440 nm,
450
nm, and about 450 nm, 460 nm and about 460 nm, in the green wavelength range
and,
for example, can be 515 nm, about 515 nm, 532 nm, about 532 nm. The build
laser
beam can have any of the powers, power densities, peak powers and repetition
rates
set forth in this specification. The second laser beam path and the second
laser beam
which travels along that path, is a pre-heat laser beam. It does not need to
be the same
wavelength, and can be anything from 440 nm to 1,100 microns, or it can be the
same
wavelength as the build laser, it has a lower, similar or higher power density
on the
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powder bed and is used to pre-heat the powder bed, as well as maintain the
temperature of the powder bed, to facilitate the build laser's ability to fuse
the powder to
build an object.
[0058]
In an embodiment of printer head 230, the second laser input 212 is
connected to a laser source for pre-heating the bed of powder. In this manner,
the
second laser beam path, and its associate optics are for a pre-heating system.
Thus, in
this embodiment the first beam path and components from connector 201 through
window 209 to image 210, as described above, provides a laser beam for fusing
the
powder bed material together, i.e., a build laser beam, or fusing laser beam;
and the
.. second beam path is for providing a pre-heating laser beam.
[0059] An embodiment of the present systems and methods can use any
laser wavelength, but the preferred embodiment is to use a pair of blue lasers
to print
and fuse the layers of the part in a parallel fashion using an array of
spatial light
modulators combined with an array of lasers as a means to define a 2-D energy
pattern
on the powder bed to be fused. The energy pattern may be contiguous or
separate,
when separate portions of the part or separate parts are processed in
parallel. By
combining multiple energy patterning systems together, a higher total power
can be
delivered to the surface of the powder bed and as a result a larger part can
be printed
with a single pulse resulting in a substantial improvement in the build rate
for the
.. machine. Multiple DMDs are used because of the limitation on the power
handling
capability of the DMD. An off the shelf DMD system is capable of handling from
25
W/cm2 up to 75 W/cm2of blue laser light on a continuous basis depending on the
backplane temperature and cooling method. The larger the part to be produced,
the
greater the amount of total power required to completely melt the 2-D pattern
across the
surface. Since the DMD in embodiments can be the limiting factor for the power
delivered, multiple DMDs in parallel can be used to provide the area scaling
necessary
to achieve the high build rates desired. Furthermore, this print engine can be
mounted
on a precision gantry system that allows the 2-D image to be stitched together
to form a
larger 2-D image which is a single layer of the part. Embodiments of the
system can
include a powder spreader as part of the gantry system or separate from the
gantry, and
an elevator as part of the build volume. The build volume should have reduced
oxygen,
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and preferably is oxygen free and can be filled, for example, with either an
inert gas
such as Argon, or a mixture of gases to promote the fusing process such as
Argon-0O2.
The energy patterned areas can be pre-heated by a secondary laser source or
directly
heated by electric heaters and radiant heaters to reduce the heat loss from
the part
during the manufacturing process. The secondary laser or secondary heat source
raises
the base temperature of the powder bed and reduces the energy requirements for
melting the powder by the laser / spatial modulator system, i.e., the fusing
or build laser
beam or sub-system of the additive manufacturing system. In embodiments, the
conduction mode welding process is the preferred method for fusing each layer
together
which eliminates the spatter normally encountered in the keyhole process which
is the
baseline process for all additive manufacturing scanned laser systems.
[0060] 2-D Energy Patterning System (for 3-D build)
[0061] A preferred embodiment for this system is a Digital Micro-
Mirror Device
(DMD) from TI. This array consists of micro-mirrors that tilt when commanded
to turn-
off or turn-on the transmitted light. Grey scale is accomplished by modulating
the
position of the mirrors or the power setting of the laser at a high speed
during the
process to set the amount of energy to be delivered to the surface or by
randomly
turning mirrors to the off state throughout the image to reduce the average
power
density in the image. A preferred DMD arrays is one that has been optimized
for use
with the wavelength of the laser beam, e.g., optimized for wavelengths in the
blue
wavelength range and preferably 400 nm, about 440 nm, 450 nm, and about 450
nm,
460 nm and about 460 nm optimized for wavelengths in the green wavelength
range
and, for example, can be 515 nm, about 515 nm, 532 nm, about 532 nm and in the
red
wavelength range of 600 nm to 700 nm. Typical DMDs for light in the visible
wavelengths have a reflectivity of 88% at 450 nm and a diffraction efficiency
in excess
of 64%. This high transmissivity enables these devices to handle an average
power
density of 25 W/cm2 or greater depending on the cooling method, and to handle
build
laser beams in the blue, green and red wavelengths, (visible light). Tests
conducted on
the DMD with a micro-channel cooler have shown that it is safe to operate the
device at
power densities of up to 75 W/cm2. DMDs can have operating power densities,
e.g.,
average power density rating, of from about 25 W/cm2to 160 W/cm2, about 50
W/cm2to
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100 W/CM2, and about 25 W/cm2to 75 W/cm2, as well as greater and smaller
values.
The average power density rating is the continuous heat load rating for this
device.
Because of the high reflectivity, short pulses at low repetition rates can
have a
substantially higher power density than the continuous power rating of the
device.
Turning to FIG. 3 there is shown a chart providing the calculation of the
maximum pulse
width for a given repetition rate to maintain this average power density. The
calculation
is performed for laser power levels ranging from 150 W (Watts) to 6 kW
(kiloWatts). At
6 kW, the instantaneous power density, or peak power, on the DMD device is 2.5
kW/cm2for a DLP9500 device, a factor of 1,000 greater than the average power
density
rating of the device. This level of power throughput can be achieved because
the laser
pulse width is short, and the duty cycle is low resulting in the average power
on the
device not exceeding maximum ratings. Optical coatings, in this case, enhanced
aluminum, are capable of sustaining very high peak power levels as long as the
energy
absorbed does not exceed the damage threshold of the coating or mirror. The
damage
level of an aluminum optical coating in the pulsed mode is typically 10-50
MW/cm2 for
short pulses, this application in the present systems is well below this
damage limit. In
addition, the thermal mass of the mirror serves to absorb the 12% of incident
energy
and determines the maximum exposure time for a given power density to maintain
the
temperature of the mirror to within the recommended operating range.
Consequently,
the present DMD systems and methods can deliver peak intensities to the powder
bed
that are capable of directly fusing metal powders, without damaging the DMDs.
[0062] Thus, in embodiments of the present system the DMD devices
in
additive manufacturing systems and methods are subject to, and reflect and
direct laser
beams to form an image on the powder bed, where the laser beams have a peak
power
density (kW/cm2) on the powder bed that is 2x, 10x, 100x, 1,500x, from 100x to
1,000x
and greater, than the average rated power density for the DMD.
[0063] Turning to FIGS 4A and 4B, there are shown photographs of
printed
patterns. In FIG. 4A there is shown a directly fused metal powder, in this
case it is a
copper powder layer that is 100 ilm thick, and the image of the "N" is
directly printed by
the laser/ spatial modulator system. The melting point of the copper powder is
1085
C. FIG. 4B shows a second letter "U" directly printed by the laser / spatial
modulator
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system. The powder was pre-placed by hand and heated to 100 C to drive off
impurities before processing. The printing process begins by downloading an
image of
the letter N to the DMD. The blue laser system is then pulsed on for 4
mseconds at a
duty cycle that maintains the 25 W/cm2 recommended operating point and
delivers 85
.. Watts peak power on the surface of the powder bed which corresponds to a
power
density of 3.7 kW/cm2. Since a low power laser was used for this test, the
image on the
DMD was scrolled in such a way that the image on the moving gantry system was
stationary until sufficient energy was deposited to heat the powder and fuse
it into an
image. The image was then changed to the next letter and the process repeated.
The
.. powder bed was at 20 C, so all the energy for heating and melting the
powder came
from the laser! spatial light modulator system. The letters are approximately
500 um
high and 500 um wide. With higher laser powers and a heated bed, it is
feasible to melt
the powder with a single pulse.
[0064]
In an embodiment, a 6 kW blue laser source (a build laser beam) is
.. operated with a pulse width of 6.5 mseconds and a repetition rate of 3 Hz,
this
corresponds to a build rate in excess of 75 cc/hr when using copper powder. A
homogenizer is used to evenly distribute the laser energy across the DMD. The
power
density on the DMD is 2.5 kW/cm2 which is 2 cm wide by 1.1 cm high. The DMD
has a
resolution of 1,920 mirrors by 1,080 mirrors on a 10.8 um pitch. The
reflectivity of the
.. DMD mirrors at this wavelength is approximately 88%, the transmissivity of
the device's
window is 97%, the diffraction efficiency of the DMD is ¨62% at this
wavelength and the
transmissivity of the imaging optic is assumed to be 99%. Using a 2:1 imaging
optic, a
10 mm x 5.5 mm image is relayed to the powder bed and the estimated losses
results in
¨6 kW/cm2 power density on the powder bed from the laser ¨ spatial light
modulator
combination which is a factor of 1.6x above the intensity used in the test in
FIGS 4A and
4B, and the total energy deposited is greater by a factor of 60x. The "system"
image
resolution is approximately 5.04 um, giving the system higher resolution than
any other
laser sintering approach. Since the published average power density of the DMD
chip
is limited to 25 W/cm2, a pulse width of 6.5 msec was chosen for the 6kW laser
source
.. which corresponds to approximately 21 Joules of energy being deposited in
the powder
bed. In the experiment shown in FIGS 4A and 4B, significantly lower energy
deposition
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(0.34 Joules) was required because the illuminated region was only 0.5 mm x
0.5 mm.
Assuming a bed temperature of 600 C, it is estimated that it takes 14 Joules
of energy
to melt a volume of copper powder that is 10 mm x 5.5 mm x 0.1 mm with a 25%
void
content. This analysis does not consider any heating of the substrate, which
can drive
the energy requirements higher. The highest energy requirement occurs when
printing
the first layer of the part, there the diffusion of thermal energy into the
substrate can
increase the energy requirements by a factor of 3 to melt and fuse the powder.
The
secondary heating laser can be used to supplement the imaging system to
deliver the
extra energy required at this step. As the build progresses, the thermal
diffusion is now
a factor of the mass in the preceding layer, the thinner the part, the lower
the power
requirement, the greater the dimension of the preceding layer, the greater the
power
requirement, with the highest power requirement occurring during bonding of
the first
layer to the build plate.
[0065] By resolution of the system or method, it is meant that
objects built by
the system can have their smallest part, or smallest dimension, equal to the
stated
resolution, e.g., the resolution defines the smallest dimension of an object
that can be
built. Thus, by resolution of the laser systems, resolution of the method, it
is meant that
the system and method have the ability to build a part, or have features in
that part, that
are at the resolution. Thus, by way of example a 75 gm resolution would
provide the
ability to build parts having their smallest dimension at 75 gm, having their
smallest
feature at 75 gm, or both. Embodiments of the blue laser 3-D additive
manufacturing
systems, e.g., 3-D blue laser printers, and embodiments of the blue laser 3-D
additive
manufacturing methods have resolutions from about 0.5 gm to about 200 gm, and
larger, about 0.5 gm to about 100 gm, about 0.5 gm to about 50 gm, less than
about
100 gri, less than about 75 gri, less than about 50 gri, less than about 25
gri, less
than about 10 gri, and less than about 5 gri. The systems can have both the
capability
for large resolution, e.g., greater than 200 gm, and very fine resolution of
about 0.5 gm
to about 10 gm, and 1 gm to about 5 gm. Further, embodiments of the present
systems
and methods, including the embodiments and examples in the specification, as
well as
those embodiments having, wavelengths of blue, 440 nm, about 440 nm, 460 nm,
green, 515 nm, about 515 nm, 532 nm, about 532 nm, 550 nm, about 550 nm, have
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resolutions from about 10 p.m to about 0.5 m, less than 10 m. less than 5
m, less
than 2 m, from about 3 p.m to about 0.9 m, about 1 m, and smaller values,
as well as
the other values in this paragraph.
[0066] FIG. 5 is a comparison of how rapidly the blue laser light
is absorbed in
a copper powder bed compared to an IR laser. The high absorption rate of the
blue
laser light is a factor for making this process obtain the desired
resolutions, build speeds
and both, since the IR laser would be scattered into the powder bed outside of
the
pattern to be fused and much higher power level lasers would be necessary and
the
resolution is limited in the IR by the high scattering factor. Therefore, the
assumption
that 100% of the light is absorbed can be used. If the powder layer is 75%
dense, then
the energy required to heat the powder layer to 1085 C from 600 C, which is
the
melting point of copper, can be calculated based on the heat capacity
equation. Since a
phase transition is involved, the heat of fusion is included in the energy
requirement
calculation. Based on the sum of the two components, the energy required to
melt a 10
mm x 5.5 mm x 100 p.m volume of copper is approximately 14 Joules. Based on
this
calculation, typical DMD arrays available today are suitable for use in a
metal based
additive manufacturing system, preferably if the base temperature of the
powder is
adjusted to compensate for the energy required to melt the metal or a
secondary laser
is used to pre-heat the image area.
[0067] An embodiment using a 500 Watt blue laser source to heat the copper
powder bed through the DMD, can provide a pulse wide of up to 78 msec when
pulsed
at a 1.5 Hz repetition rate. Under these conditions, the 500 Watt blue laser
source
would deliver 39 Joules to the copper powder bed which is sufficient energy to
go from
a 400 C background bed temperature to melting the copper.
[0068] In some embodiments, while the laser ¨ spatial light modulator
combination is capable of providing sufficient energy to melt the 50 pm thick
powder
layer, it may not be sufficient energy to fuse to the layers below. Since a
conduction
mode weld proceeds through the layers of material in a spherical fashion, the
weld is as
wide as it is deep. For example, a 50 pm deep weld bead would be at least 50
pm
wide. To make certain that the powder layer is fused to the layer beneath it,
then the
minimum feature size will have to be at least 1.5-2x the depth of the powder
layer. This
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means that a 75-100 pm wide bead is used to fuse the powder layer to the lower
layer.
Taking the energy required to fuse to the lower solid layers into
consideration increases
the energy required to melt and fuse the powder from 36 Joules to 86 Joules
when
going from 400 C to the melting point of copper. In embodiments, this is not
achievable with just the laser-spatial filter combination, so either the bed
temperature is
raised or a separate source of heat is added. By adding a second laser,
preferably
without a spatial light modulator, the additional heat is added to raise the
temperature of
the powder, without melting it. Thus, this second laser, can pre-heat the
powder and
maintain the temperature of the powder layer and the build object above
ambient
temperature, for example the powder can be pre-heated to and maintained at
temperature of greater than 100 C, greater than 200 C, greater than 300 C,
greater
than 400 C, from about 300 C to about 600 C, within 300 C of the melting
point of
the powder, within 200 C of the melting point of the powder, within 100 C of
the
melting point of the powder, up to and just below the melting temperature of
the powder,
and high and lower temperatures.
[0069] As used herein, unless expressly stated otherwise, spatial
light
modulator, laser/spatial light modulator, DMD systems, laser¨spatial, and
similar such
terms, refer to the same general type of system, or subsystem, using micro-
mirrors,
micro-reflective assemblies, or similar reflective components having micro
level or sub-
.. micro level resolutions, to create the laser pattern and images for the
build laser beam
on the powder bed as well as liquid crystal and other types of crystal based
spatial light
modulators.
[0070] The second laser (e.g., second beam path of FIG. 2, as
discussed
above) illuminates the same area as the laser-spatial light modulator does as
shown in
FIG. 6. In FIG. 6 there is a bed of metal powder 600. The pre-heat laser beam
forms a
pre-heat laser pattern 601 that heats an area 605 of the bed 600. There is
also shown
build laser patters 602 and 603 on the bed of metal powder 600. Thus, the
material in
area 605 is heated by the second laser beam, e.g., the pre-heat laser beam,
and the
heated material in laser patterns 602 and 603 is fused into an object. For the
case
discussed above, 86 Joules of heating is required to melt and fuse the powder.
If the
500 Watt laser-spatial filter combination provides 39 Joules to the pattern,
then the
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second laser provides the balance or 47 Joules. To accommodate the time to
move,
coat and perform other functions, the pulse width of the pre-heat laser can be
10% of
the duty cycle or 66 msec. This corresponds to a pre-heat laser power of 750
Watts.
Assuming the second laser heats the powder bed region to within 200 C of the
melt
point, then when the laser-spatial light modulator illuminates the part, it
raises the
temperature of the patterned area on the powder bed and the lower layers to
the
melting point of the copper. FIG. 7 illustrates the timing for the system.
This sequence
results in the melt and complete fusion of the 50 ilm powder layer to the
fully dense
layer below it.
[0071] In an embodiment, the laser-spatial light modulator pair is based on
a
6,000 Watt blue laser operating at a repetition rate of 1.5 Hz. The pre-heat
laser is a
750 Watt laser. The pre-heat laser operates for the same duration as mentioned
above
(66 msec) to increase the powder bed temperature to within 200 C of the melt
temperature of the material to be melted (e.g. the powder in the powder bed),
in this
case copper. A pyrometer or FLIR camera is used to monitor the temperature of
the
powder bed during this pre-heat process and controls the laser power to
maintain that
temperature until the laser-spatial light modulator image illuminates the
powder bed
region and fuses the powder to the lower layer. The 6,000 Watt laser is on for
6.5
msec, while the 750 Watt laser may be on for 66 msec or longer. In this
embodiment,
the chamber temperature is assumed to be at or near room temperature.
[0072] In an embodiment, the laser-spatial light modulator pair
is based on a
500 Watt blue laser operating at a maximum repetition rate of 1.5 Hz. The pre-
heat is a
1,000 Watt laser. The pre-heat laser operates for the same duration as the
case above,
about 78 msecs. However, the pre-heat laser with the higher power level now
operates
for only 25 msecs, giving additional time to reposition the pattern. In this
embodiment,
the chamber is assumed to be at or near room temperature.
[0073] The laser printing engine described is mounted on a
precision gantry
system, such as the embodiment of FIG. 1, in an air-tight enclosure. The air-
tight
enclosure if filled with an inert gas, which is continuously circulated to
clear out any
welding fumes as the process proceeds. The inert gas environment ensures there
is no
surface oxidation during the build which can lead to porosity in the part. The
gantry
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system allows the head to be positioned in the x-y direction, while an
elevator is used to
move the part down as each new layer is printed. In principle, this approach
to step and
repeat of the 2-D energy pattern can be applied to any large volume, e.g., 0.5
m3, 1 m3,
2 m3, 3 m3, 10 m3, from 1 m3, to 10 m3, and larger and smaller volumes, with
the
constraint being the accuracy of the gantry system employed.
[0074] The build begins with a Computer Assisted Design file,
typically a step
file. Software first divides the object into 50 pm slices, less or greater
depending on
resolution and shape. The surface revealed after the slicing is then divided
up into
sections that are the same image size as the spatial light modulator. The
build strategy
is then decided by the software as to which portion of the pattern to expose
first, what
the exposure levels should be and what support structure if any should be
used. The
software also determines the optimum on-time for the pre-heat laser as well as
the
laser-spatial modulator system. The pre-heat time may vary depending on the
density
of the base material, the melt temperature of the base material, the amount of
material
in the layer below the layer to be fused and the density of the material in
the layer below
the layer to be fused. Based on the size of the part, the part complexity and
the
orientation of the part, radiant heaters may be used to keep the bed, walls or
ceiling of
the build chamber at an optimum temperature to prevent heat loss at the wrong
rate to
the build environment. This processing sequence is outlined in FIG. 8.
[0075] The following examples are provided to illustrate various
embodiments
of the present laser systems and components of the present inventions. These
examples are for illustrative purposes, may be prophetic, and should not be
viewed as
limiting, and do not otherwise limit the scope of the present inventions.
[0076] EXAMPLE 1
[0077] An embodiment of an additive manufacturing system as generally
shown in FIG. 1. The system 100 consists of an x-y Gantry System 101 mounted
on a
vibration isolation platform. The x-axis of the gantry system 102 consists of
a pair of air
bearings and a linear motor capable of positioning to an absolution position
of 1 micron
or less. The motor for the x-axis of the gantry system can also move the
Powder
Spreader 105 in a bi-direction fashion to spread the powder. The powder can be
delivered either by a second elevator section filled with powder or a powder
hopper that
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drops the powder onto the powder bed. The powder hoppers are not shown in this
figure but would be mounted at the front and back of the gantry system. The
entire
system will be enclosed in an air-tight enclosure which is also not shown in
this figure.
The DMD laser print head 103 is mounted on the y-axis of the gantry system and
can
traverse the bed and be positioned to within a micron of any position along
the axis
repeatably. The powder bed 104 is on a high precision elevator that enables
the bed to
be lowered a minimum of 10 ilm after each process step. This allows the powder
spreader 105 to place a uniform layer of powder over the previously fused
image. A
roller 106 which rotates in the opposite direction of the motion is used to
smooth and
compress the powder layer. The powder bed has built in heaters to enable
elevated
temperatures to be used in the build cycle. A laminar flow air knife is placed
directly
below the DMD laser print head 109 to prevent debris or smoke from reaching
the
window that the DMD image and secondary pre-heat laser emerge from. The DMD
image 107 is positioned on the powder bed according to the slicing software
and the
.. pattern is varied as the image is stepped over the width of the image to
complete the
adjacent portion of the part. The image may also be stepped further away
depending
on the management of the heat buildup in the part and the desire to minimize
warpage
and stress in the part.
[0078] EXAMPLE 2
[0079] An embodiment of the DMD print head as generally shown in FIG. 2.
The main laser power to be modulated is delivered to the print head 200
through an
industry standard QBH fiber cable 201. The second laser that will be used for
pre-
heating is also delivered through an industry standard QBH fiber cable 212.
These
cables are designed to be robust and provide a seal to the external
environment during
.. operation. The cables both 400 pm or smaller diameter fibers inside of a
protective
sheath. A pair of 40 mm collimating lens 205, 210 are used to collimate the
output of
each of the optical fibers. Depending on the shape and the uniformity of the
beam from
the optical fiber, a homogenizer and beam shaping optic would be inserted just
after the
collimating optic. Both the primary laser source (build laser) and the
secondary laser
.. source (pre-heat laser) may use the homogenizer to provide a uniform enough
intensity
that the fused print is uniform. A turning mirror 206 is used to direct the
collimated
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beam from the main laser's optical fiber 201 onto the DMD at the requisite
angle of 24
degrees from the surface normal of the DMD. When the laser is in the on state,
the
DMD 202 mirrors are tilted toward the incoming beam and redirect the beam
normal to
the DMD surface. When the laser is in the off state, the DMD 202 mirrors are
tilted
away from the incoming beam and redirect the incoming beam 48 degrees away
from
the incoming beam from the vector normal to the DMD surface. This is where the
beam
dump 204 is located because it has to intercept any beam energy that will be
in an off
state in the image. The beam from the DMD 202 is now reimaged with a 100 mm FL
lens to a spot 200 mm below the laser printing head. This is a 1:1 imaging
arrangement, other ratios may be employed depending on the size and accuracy
of the
part required. The secondary laser's optical fiber output 212 is collimated by
the lens
205 and may go through a beam homogenizer to achieve the desired uniformity of
fusing. After the beam conditioning of the secondary beam, it is directed or
reimaged
onto the same spot as the DMD image using mirror 207. This system does not go
through the same imaging lens as the DMD beam. The two beams, both the DMD
beam and the secondary beam do however exit the print head through a common
window 209. However, a second window can be used to allow the pre-heat laser
to
exit depending on the geometry of the system. The net result is the overlapped
DMD
image 210 with the secondary laser beam on the powder bead as depicted in FIG.
6.
[0080] EXAMPLE 3
[0081] An embodiment of the present invention relates to using
multiple DMD
within the same imaging aperture or parallel imaging apertures. Turing to FIG.
9 there
is shown a schematic of a multi-DMD laser printing system 200. The system has
two
laser build subsystems 941, 942. Subsystem 941 has a laser source 901, a
collimator/homogenizer 903, a DMD 905, a mirror 905a, a 2:1 image size
reduction
optical assembly having lens 907 and lens 909, a mirror 911, and imaging lens
920,
which are located along laser beam path 913. In this manner the laser beam for
fusing
the powder, e.g., the build laser beam, travels along laser beam path 913
through these
various components and provides an image as image tile 950a. Is it seen that
the
image tiles 950a, 950b, 950c, 950d form a tiled image that can have a large
number of
tiles. Subsystem 942 has a laser source 902, a collimator/homogenizer 904, a
DMD
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906, a mirror 906a, a 2:1 image size reduction optical assembly having lens
908 and
lens 910, a mirror 912, and imaging lens 920, which are located along laser
beam path
914. In this manner the laser beam for fusing the powder, e.g., the build
laser beam,
travels along laser beam path 914 through these various components and
provides an
image as image tile 950b.
[0082] Two additional laser build subsystems of the same
configuration as
system 941, 942, would be used in this system, but are not shown in the
drawing.
These additional two systems would provide images for image tiles 950c, 950d.
In this
embodiment the tile images are preferably adjacent.
[0083] For additional laser build subsystems of the same configuration as
system 941, 942, would be used in this system, but not shown in the drawing.
These
four additional systems would provide images for image tiles adjacent to 950a,
950b,
950c and 950d into the paper to create a 2-d tiled image.
[0084] This system can have lens configurations that provide
either an
inverting or non-inverting image.
[0085] Each DMD has its own laser source and the image space of
each
DMD can be tiled used shearing mirrors to create a continuous image space over
a
much larger area than a single DMD system can achieve. There can be some dead
space between each DMD image space which can be minimized with proper
positioning
of the shearing mirrors. The image space can also be effectively spliced
together by
adjusting the tilt and position of each shearing mirror. FIG. 9 shows the
tiling of 2 DMD
image spaces together in one axis to make a larger composite image on the
powder
bed surface. This can be extended to N x M DMD image spaces by compressing
each
DMD image with a reducing optic, shearing each reduced image together, then
using a
single lens to reimage or magnify the image back to the desired size.
[0086] EXAMPLE 4
[0087] An embodiment of the present invention relates to using
multiple DMD
within different imaging apertures to create a parallel build capability.
Turning to FIG.
10 there is shown a multi-DMD system 1000, which has a first DMD subsystem
1040
and a second DMD subsystem 1041 for providing two parallel build laser beams
to
create separate images on the powder bed. Subsystem 1040 has a DMD 1005 that
is
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positioned along a laser beam path 1013. Subsystem 1040 provides image 1050a.
Subsystem 1041 has a DMD 1006 that is positioned along a laser beam path 1014.
Subsystem 1041 provides image 1050b.
[0088] Each DMD has its own laser source and the image space of
each
DMD is tiled on the surface of the powder bed creating a checkboard pattern of
images
and non-image areas. The build strategy can be to either use each single DMD
image
space to build an individual part. Or to use each individual DMD image space
to build a
larger part by building multiple sections in parallel.
[0089] A second, third or fourth set of systems extending into the
paper or
adjacent to the shown systems can be added to expand the addressable image
area on
the powder bed.
[0090] This system can have lens configurations that provide
either an
inverting or non-inverting image.
[0091] EXAMPLE 5
[0092] An embodiment of the present invention relates to using laser beams
having visible laser beams, and in particular having wavelengths from 350 nm
to 700
nm, in additive laser manufacturing process, and in an additive laser
manufacturing
system, to build articles (e.g., structures, devices, components, parts,
films, volumetric
shapes, etc.) from raw materials, such as starting powders, nanoparticles,
particles,
pellets, beds, powder beds, spray powders, liquids, suspensions, emulsions and
combinations and variations of these and other starting materials known, or
later
developed, in the laser additive manufacturing arts, including the 3-D
printing arts.
[0093] EXAMPLE 6
[0094] In an embodiment to build articles from raw materials in
laser additive
processes, wavelengths are used that have lower reflectivity, high
absorptivity, and
preferably both for the starting raw material. In particular, in an embodiment
laser beam
wavelengths are predetermined based upon the starting materials to preferably
have
absorption of about 10% and more, about 40% and more, about 50% and more, and
about 60% and more, and in the range of 10% to 85%, 10% to 50%, about and
about
40% to about 50%. In particular, in an embodiment laser beam wavelengths are
predetermined based upon the starting materials to preferably have
reflectivity's of
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about 97% and less, about 60% and less, about 30% and less, and in the range
of 70%
to 20%, in the range of 80% to 30%, and in the range of about 75% to about
25%. In
embodiments combinations of both these high absorptions and these low
reflectivities
can be present. In a preferred embodiment of the systems and processes, the
laser
beam or beams have wavelengths from about 400 nm to about 500 nm are used to
build articles from starting materials made up of gold, copper, brass, silver,
aluminum,
nickel, alloys of these metals, and other metals, non-metals, materials, and
alloys and
combinations and variations of these.
[0095] EXAMPLE 7
[0096] In an embodiment the use of blue lasers, e.g., about 380 nm to about
495 nm wavelength, to additive manufacture articles from gold, copper, brass,
nickel,
nickel plated copper, stainless steel, and other, materials, metals, non-
metals and
alloys, is preferred. Blue laser beams are highly absorbed by these materials
at room
temperature, e.g., absorptivities of greater than about 50%. One of several
advantages
of the present inventions is the ability of a preselected wavelength laser
beam, such as
the blue laser beam, that is better able to better couple the laser energy
into the
material during the laser operation, e.g., the additive manufacturing process.
By better
coupling the laser energy to the material being built into an article, the
chance of a
runaway process, which typically can occur with the infrared lasers is greatly
reduced
and preferably eliminated. Better coupling of the laser energy also allows for
a lower
power laser to be used, which provides capital cost savings or enables multi-
laser
systems to be cost effective. Better coupling also provides for greater
control, higher
tolerances and thus greater reproducibility of built articles. These features,
which are
not found with IR lasers and in IR laser additive manufacturing operations,
are
important, to among other products, products in the electronics, micro-
mechanical
systems, medical components, engine components and power storage fields.
[0097] EXAMPLE 8
[0098] In an embodiment a blue laser that operates in a CW mode
is used.
CW operation can be preferred over a short pulse laser, in many additive
manufacturing
applications, because of the ability to rapidly modulate the laser output and
control the
building process in a feedback loop, resulting in a highly repeatable process
with
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optimum mechanical and other physical and esthetic properties, such as reduced
surface roughness, improved porosity and improved electrical characteristics.
[0099] EXAMPLE 9
[00100] Preferably, in some embodiments active monitoring of the article being
build is used to check the quality of the article and the efficiency of the
additive
manufacturing process and systems. For example, when the laser is processing a
high
resolution region of the part being printed, a thermal camera can be used to
monitor the
average temperature of the surface and a feedback loop can be used to decrease
or
increase the laser power to improve the weld puddle and ultimately the surface
quality
.. of the part. Similarly, when the laser beam is defocused to sweep through a
large low
resolution region of the part, the feedback loop can command more laser power
to keep
the average temperature at the optimum processing point, greatly reducing the
time to
print a part.
[00101] EXAMPLE 10
[00102] Examples of scanners and optics that can be used with the present
systems include mirrors mounted on high speed motors, rotating polygon mirrors
or high
speed galvanometers. A mirror mounted on axis of a high speed motor can create
a
scanning beam as the mirror is rotated through 360 degrees. The higher the
speed of
the motor, the faster the scan. The only issue with this approach is that the
laser must
be turned off once the mirror is no longer reflecting the beam as the back
side of the
mirror passes by the laser beam entrance aperture. The high speed mirror can
be used
to scan either the x axis or the y axis, whichever axis is chosen, the mirror
which scans
the other axis must scan at a slow speed proportional to the time it takes to
complete
one full scan in the initial axis. It is preferred to use a high speed stepper
motor in this
axis to enable the mirror to be moved in discrete steps while remaining
stationary while
the first axis is completing its scan. Similarly, a multi-faceted mirror or
polygon mirror
can be used to perform the high speed scan function allowing higher scan
speeds
because the scan is reset to the starting position as the beam transitions
across each
facet of the mirror. These types of mirrors are currently being used in
supermarket
scanners to scan a product's bar code as it passes by. The primary axis can
also be
scanned with a high speed galvanometer type mirror which is a resonant type
motor
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and oscillates at a continuous frequency producing high speed movement of the
beam.
It is also possible to precisely position galvanometer mirrors to a
predetermined
position, allow systems based on the first and second axis being a
galvanometer driven
mirror to draw in a vector mode where any point on the process bed can be
rapidly
addressed by simultaneously moving both mirrors. It is also feasible to
combine mirrors
mounted on translation stages in a "flying optic" type design where the beam
is
delivered through free space to a mirror mounted on a gantry style system and
is moved
in a two dimensional, raster or vector mode at very high speeds.
[00103] EXAMPLE 11
[00104] Embodiments of the present system do not contain and do not require
a scanner to build an object.
[00105] EXAMPLE 12
[00106] The systems and methods of examples 1 ¨ 11 where the build laser
beam has a wavelength selected from one of the following wave lengths: the
blue
wavelength range, 400 nm, about 440 nm, 450 nm, and about 450 nm, 460 nm and
about 460 nm, the green wavelength range, 515 nm, about 515 nm, 532 nm, about
532
nm, and the red wavelength range of 600 nm to 700 nm. And, were the build
laser
beam has one or more of the beam properties, e.g., power, power density,
repetition
rate, etc. set forth in these specifications.
[00107] It is noted that there is no requirement to provide or address the
theory
underlying the novel and groundbreaking processes, materials, performance or
other
beneficial features and properties that are the subject of, or associated
with,
embodiments of the present inventions. Nevertheless, various theories are
provided in
this specification to further advance the art in this area. The theories put
forth in this
specification, and unless expressly stated otherwise, in no way limit,
restrict or narrow
the scope of protection to be afforded the claimed inventions. These theories
many not
be required or practiced to utilize the present inventions. It is further
understood that
the present inventions may lead to new, and heretofore unknown theories to
explain the
function-features of embodiments of the methods, articles, materials, devices
and
system of the present inventions; and such later developed theories shall not
limit the
scope of protection afforded the present inventions.
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[00108] It should be understood that the use of headings in this specification
is
for the purpose of clarity, and is not limiting in any way. Thus, the
processes and
disclosures described under a heading should be read in context with the
entirely of this
specification, including the various examples. The use of headings in this
specification
.. should not limit the scope of protection afford the present inventions.
[00109] The various embodiments of systems, equipment, techniques,
methods, activities and operations set forth in this specification may be used
for various
other activities and in other fields in addition to those set forth herein.
Among others,
embodiments of the present inventions can be used with the methods, devices
and
.. system of Patent Application Publication Nos. WO 2014/179345, 2016/0067780,
2016/0067827, 2016/0322777, 2017/0343729, 2017/0341180, and 2017/0341144 the
entire disclosure of each of which are incorporated herein by reference.
Additionally,
these embodiments, for example, may be used with: other equipment or
activities that
may be developed in the future; and with existing equipment or activities
which may be
modified, in-part, based on the teachings of this specification. Further, the
various
embodiments set forth in this specification may be used with each other in
different and
various combinations. Thus, for example, the configurations provided in the
various
embodiments of this specification may be used with each other. For example,
the
components of an embodiment having A, A' and B and the components of an
embodiment having A", C and D can be used with each other in various
combination,
e.g., A, C, D, and A. A" C and D, etc., in accordance with the teaching of
this
Specification. Thus, the scope of protection afforded the present inventions
should not
be limited to a particular embodiment, configuration or arrangement that is
set forth in a
particular embodiment, example, or in an embodiment in a particular Figure.
[00110] The invention may be embodied in other forms than those specifically
disclosed herein without departing from its spirit or essential
characteristics. The
described embodiments are to be considered in all respects only as
illustrative and not
restrictive.
