U.S. patent application number 17/558575 was filed with the patent office on 2022-08-25 for method and apparatus for fabrication of articles by molten and semi-molten deposition.
The applicant listed for this patent is +Mfg, LLC. Invention is credited to THOMAS R. KRUER.
Application Number | 20220266371 17/558575 |
Document ID | / |
Family ID | |
Filed Date | 2022-08-25 |
United States Patent
Application |
20220266371 |
Kind Code |
A1 |
KRUER; THOMAS R. |
August 25, 2022 |
METHOD AND APPARATUS FOR FABRICATION OF ARTICLES BY MOLTEN AND
SEMI-MOLTEN DEPOSITION
Abstract
A method and apparatus for depositing metals and metal-like
substances in two and three dimensional form without a substrate in
a safe, rapid and economical fashion using gas shielded arc welding
equipment and programmable robotic motion. The method and apparatus
includes the use and application of robotic controls, temperature
and position feedback, single and multiple material feeds, and semi
liquid deposition thereby creating near net shape parts
particularly well suited to rapid prototyping and lower volume
production.
Inventors: |
KRUER; THOMAS R.; (EDGEWOOD,
KY) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
+Mfg, LLC |
Erlanger |
KY |
US |
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|
Appl. No.: |
17/558575 |
Filed: |
December 21, 2021 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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14518121 |
Oct 20, 2014 |
11235409 |
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17558575 |
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61892526 |
Oct 18, 2013 |
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International
Class: |
B23K 9/04 20060101
B23K009/04; B23K 9/173 20060101 B23K009/173; B23K 9/167 20060101
B23K009/167; B23K 9/23 20060101 B23K009/23 |
Claims
1. An additive manufacturing apparatus for fabricating a three
dimensional object comprising: a multi-axis robotic system
configured to support and move a deposition head; the robotic
system contained within a sealed enclosed space; an oxygen sensor
within the enclosed space.
2. The additive manufacturing apparatus as set forth in claim 1 for
fabricating a three dimensional object further comprising means for
introducing a gas and monitoring the oxygen concentration within
the enclosed space.
3. The additive manufacturing apparatus as set forth in claim 2
further comprising a means for reducing or discontinuing gas flow
in response to said oxygen monitoring.
4. The additive manufacturing apparatus as set forth in claim 1
further comprising an air filtration system.
5. An additive manufacturing apparatus to fabricate objects by
depositing metal or metal like materials in three dimensions
comprising: a build table; a deposition head configured to deposit
the metal objects on the build table; a multi-axis robotic system
configured to support the deposition head; wherein said build table
is configured to be adjustably located in a tank, said tank having
a quenching fluid therein; wherein material is deposited at a set
distance from the level of the quenchant.
6. The additive manufacturing apparatus as set forth in claim 5
wherein said deposition head is capable of being fully submerged in
said quenchant.
7. The additive manufacturing apparatus of claim 6 further
comprising use of wire with internal inert gas filler.
8. An additive manufacturing apparatus to fabricate objects by
depositing metal or metal like materials in three dimensions
comprising: a build table; a plurality of deposition heads
configured to deposit the metal objects on the build table, wherein
each of the deposition heads includes a tool bracket; a multi-axis
robotic system configured to support the deposition head; wherein
said build table is configured to be adjustably located in a tank,
said tank having a quenching fluid therein; wherein the plurality
of nozzle assemblies are configured to deposit different wire sizes
of metal or metal-like material.
9. The method of claim 8 further comprising each of the plurality
of deposition heads configured to deposit a different material.
10. The method of claim 8 further comprising one welding power
supply and changing computer control programs for each deposition
head.
11. The method of claim 10 further comprising using switchable
power buss to provide power to each of said multiple deposition
heads.
12. An additive manufacturing method for fabricating a three
dimensional object formed from a metal or metal-like material,
wherein the geometry and temperature of the object is continually
monitored and deviations from the desired geometry or temperature
are corrected prior to continuing.
13. The additive manufacturing method of claim 12 further
comprising using the arc current to continually monitor the height
of the object.
14. The additive manufacturing method as set forth in claim 12
further comprising using a computer control program capable of
depositing one or more layers using one power setting alternated
with one or more layers deposited using a second power setting.
15. The additive manufacturing method of claim 12 further
comprising using a computer control program to correct defects by
moving the deposition head back over low sections prior to
proceeding with the next layer.
16. The additive manufacturing method as set forth in claim 15
further comprising using a computer control program to correct
surface defects by changing the robotic travel speed, and by
changing the deposition parameters of the next layer when reaching
the location of the detected defect.
17. The additive manufacturing method of claim 16 further
comprising the step of using a computer control to abort the build
process prior to completion of the object.
18. The additive manufacturing method of as set forth in claim 17
further comprising using a memory storage device and recording all
locations of any detected defects for later analysis.
19. The method of claim 18 further comprising creating a visual
display of the locations of any detected defects.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation application of U.S.
patent application Ser. No. 14/518,121, filed Oct. 20, 2014
entitled "Method and Apparatus for Fabrication of Articles by
Molten and Semi-molten Deposition" which claims the benefit of U.S.
Provisional Patent Application Ser. No. 61/892,526 entitled "Method
and Apparatus for Fabrication of Articles by Molten and Semi-molten
Deposition", filed Oct. 18, 2013, the disclosures of which are
herein incorporated by reference in their entirety.
FIELD OF THE INVENTION
[0002] The present invention relates to equipment and processes
used for the fabrication of parts by depositing layers of metallic
material, commonly referred to as additive manufacturing, and more
particularly to equipment and processes which fabricate metallic
items formerly made by processes such as casting, welding,
subtractive machining, and forging, and generally does so without
the need for specialized tooling and long lead times associated
with these manufacturing processes.
BACKGROUND OF THE INVENTION
[0003] Fabrication of three-dimensional metal articles by
deposition of successive layers of metallic powder or weld beads,
where the layers are heat bonded together to build the object, is
well known in the field.
[0004] Processes using plasma or laser fused deposited metals have
been used for many years to produce a layered structure on a
substrate, but are typically very energy intensive and extremely
slow. The required equipment is expensive to purchase and operate
as a high energy plasma generator is needed to vaporize the powder
stream or high energy laser beam is needed to generate the
melt-pool on the growth surface.
[0005] Similarly, processes using energetic wire deposition enable
the rapid prototyping and manufacture of fully dense, near-net
shape components on a substrate. However, the deposition must be
done slowly to allow each layer to cool prior to the next layer
being added. In addition, the resulting items produced by these
deposition methods often require the removal of the substrate as a
secondary operation, which can increase the cost, destroys the
substrate when being removed, can damage the object from which the
substrate is being removed, or require careful engineering to
incorporate the substrate into the structure of the item being
manufactured, thereby limiting the configurations that can be
produced.
[0006] The bonded layers from these current processes are sometimes
milled to a final shape either after each layer is formed, or after
all layers have been made. Those knowledgeable in the art accept
that parts fabricated using this welding method, are either
small--due to the large amount of heat inputted through the welding
process- or extremely expensive due to the long time needed to
fabricate them.
[0007] Sintered metal processes use powdered materials and a high
power laser beam to selectively melt the powdered material, layer
upon layer. Although relatively accurate, these processes are also
slow and require a high temperature post processing operation to
obtain a usable part. Even after post processing, the resulting
part has the physical properties of a sintered metal part rather
than being homogeneous. Furthermore, post processing can result in
significant distortion and the required equipment is expensive.
Laser melting of powered materials can be used and thus eliminate
the need for oven post heating, but are even slower due to the
increased heat.
[0008] These processes used to fabricate three dimensional metallic
items by adding layers of material have many disadvantages.
Similarly, processes such as casting and forging require large
investments in tooling and equipment and thus fundamentally suited
only for large volume production processes such as welding are
generally labor intensive, require highly skilled personnel and
require a great deal of pre-assembly preparation and post assembly
finishing. In addition, these processes typically require long
periods of time to complete the production of a single part due to
all the drawings and preparation required for the individual
components. What is needed, therefore, is a method and apparatus to
reduce the amount of capital equipment investment, process expense,
and time needed to fabricate a 3 dimensional part, including the
amount of time needed to form the part and the amount of time to
finish the part for final use.
SUMMARY OF THE INVENTION
[0009] A method of and apparatus for depositing metals and
metal-like substances in three dimensional form in a rapid and
economical fashion is herein disclosed, such that the new process
satisfies an unmet need of single and smaller volume production in
creating near-net shape parts, and providing an avenue to limited
production heretofore unavailable, while not precluding its use in
large volume production as well. As described herein, the new
process of the present invention can form a metal part or a
metal-like part comprising a composite including a metallic
material, a combination of different metallic materials, a ceramic
material, and components of various other materials.
[0010] The present invention uses modified gas shielded arc welding
equipment referred to as GMAW (Gaseous Metallic Arc Welding) and
also known as MIG (Metallic Inert Gas). It can also use TIG
(Tungsten Inert Gas) processes and apparatus in the same
embodiment. The MIG or TIG welding torch is mounted onto a multiple
axis robotic mechanism to automatically deposit one or more metals
in layers according to the part design while simultaneously heating
or cooling the resulting built-up structure to achieve a faster
deposition of material and to maintain and improve dimensional
accuracy.
[0011] The metal-like part exhibits some metallic properties while
not being entirely made of a metal. In one embodiment, the
metal-like material is provided as a feedstock by enclosing the
non-metallic components within a tube of metal. While some
currently known MIG welding wire uses a tube of metal surrounding a
flux core, a metal-like feedstock as used herein, in one
embodiment, includes a tube of metal having a core other than a
flux core.
[0012] In addition, a method is disclosed whereby a metallic three
dimensional item is produced without the need of being permanently
attached to a preform or substrate during the manufacturing
process. The resulting part does not require removal of a difficult
to remove substrate, to provide a near-net shape part requiring no
further removal of structure.
[0013] The present invention provides, in different embodiments, an
object, part or item which does not include a permanently attached
base or substrate. As discussed herein, the build table upon which
the object is formed is removably adhered to the object, such that
the object remains fixed to the build table during forming of the
part, but is removable from the build table without significantly
altering the form of either the part or the build table.
Consequently, the build table is reusable to form additional
objects of the same or different sizes or different designs.
[0014] In one or more embodiments of the present invention, there
is provided a method and apparatus to rapidly produce one or more
parts to be used in place of castings, weldments, and forgings,
while eliminating the need for tooling or molds to produce the
part.
[0015] In one or more embodiments of the present invention, there
is provided a method and apparatus to provide a near net shape part
with optimum dimensional accuracy. As used herein, a near net part
is a part produced by a manufacturing process which is close to a
finished part. The near net shape part requires a minimal amount of
after-part finishing processing typically a limited and controlled
material removal process and polishing, if necessary.
[0016] In one or more embodiments of the present invention, there
is provided a method and apparatus configured to control the built
in stresses in the part, so that the desired physical material
properties of the part are obtained.
[0017] In one or more embodiments of the present invention, there
is provided a method and apparatus configured to control the grain
structure of the material in the part, so that the desired physical
material properties of the part are obtained. In one or more
embodiments, a submerged deposition process takes place below the
top surface of the quenchant which provides properly controlled
parameters, wherein the quenchant fluid and decomposition
byproducts are excluded from the hot zone primarily by the action
of mechanical shielding, shield gas, and deposition byproduct
outflow. An inverted process allows gravity to assist in shielding
the hot zone.
[0018] In one or more embodiments, a means of determining the
temperature of the quenchant at a predetermined distance from the
part as a means of temperature direction and control is provided.
Such means of monitoring temperature includes optical monitoring or
sensor based monitoring.
[0019] In one or more embodiments of the present invention, there
is provided a method and apparatus configured to control and
prevent an outflow of molten material from a hot zone wherein
material is being deposited in a deposition, or hot zone, where the
material is still molten or semi-molten.
[0020] In one or more embodiments of the present invention, there
is provided a method and apparatus configured to control and
prevent a plastic flow or sag of deposited material in and adjacent
to the hot zone.
[0021] In one embodiment, the part is deposited layer by layer on a
build table of copper, copper clad, or other suitable metallic
material to provide the electrically conductive surface. In a
second embodiment, the deposition is made using at least two wires
of differing polarities to allow for the initial layer to be
deposited on either a platen of metallic surface or a non-metallic
surface such as a ceramic table. The use of the two wire approach
also minimizes the heat input to the structure being fabricated and
the energy needed to produce it. This reduced energy input allows
the part to be fabricated more quickly. In this two wire
embodiment, the material is deposited in a range of temperatures
that include the material's temperature in plasma, molten and
semi-molten states.
[0022] Generally, the semi-molten state is used during a first pass
in order to produce a continuous initial deposition surface or
trace partially adhering to the surface of the platen, such
adhesion being sufficient to prevent lifting of said trace during
subsequent passes, but insufficient to preclude easy removal of the
completed item or part, said adhesion being achieved by adjustment
of deposition parameters and selection of suitable platen materials
for the type materials being deposited. Suitable platen materials
include heat resistant conductive and non-conductive materials and
are capable of being temperature controlled by the quenchant
fluid.
[0023] In different embodiments, the deposition process benefits
from a light dusting of a metallic powder on the surface of the
platen to ensure electrical conduction.
[0024] In one or more embodiments of the present invention, there
is provided a method and apparatus configured to provide a safe
environment for an operator and to control the unrestricted
discharge of process byproducts. Byproducts are removed and
processed by conventional means if desired, as is well known in the
field of welding and other manufacturing processes.
[0025] In one or more embodiments, a gas sensor is provided to
monitor the presence of undesired atmospheric or by product gasses,
as well as a means for controlling the influx of additional shield
gasses to exclude the atmospheric or by product gasses from the
deposition zone.
[0026] In different embodiments, computer controls are integrated
into the other process controls, as is known in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
[0027] FIG. 1 is a block diagram of the major components and
subassemblies of a fabrication system.
[0028] FIG. 2. illustrates a deposition nozzle module of the
present invention.
[0029] FIG. 3. illustrates a prototype part made by an embodiment
of the present invention.
[0030] FIG. 4. illustrates a two wire deposition device of the
present invention.
[0031] FIG. 5. illustrates an alternative two wire deposition
device of the present invention.
[0032] FIG. 6 illustrates another embodiment of a portion of a
fabrication system.
[0033] FIG. 7 illustrates an underneath perspective view of a
platen assembly.
[0034] FIG. 8 illustrates a top perspective view of a platen
assembly including deposition of material.
[0035] FIG. 9 illustrates a side view of a nozzle head fixture and
a nozzle assembly.
[0036] FIG. 10 illustrates a back view of a nozzle head fixture and
a docked nozzle assembly.
[0037] FIG. 11 illustrates a front perspective view of a nozzle
head fixture and a docked nozzle assembly.
[0038] FIG. 12 illustrates a perspective view of a part being
formed with a part fixture.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0039] The present invention is directed to the fabrication of an
object using three-dimensional computer models and computer
numerical control (CNC) robotics to control the position of the
application of a metal or metal-like deposit. The present invention
is directed to form a metal-based or metallic two or three
dimensional object, as contrasted with known three dimensional
plastic printing technologies in use today for providing objects
made of plastic. The fabrication of these objects formed of metal
does not require the use expensive tooling or molds. Additionally,
the present invention is particularly well suited to rapid
prototyping and lower volume production of metallic parts.
[0040] The preferred embodiment of the apparatus includes an inert
gas arc nozzle fed with wire and gas, a non-stick build surface
mounted to a moving table, a multi-axis robotic actuators, a master
controller, sensors, a tank full of quenchant, an enclosure, and an
air filtering system.
[0041] At least one distance sensor, or alternatively, electronic
arc length sensing, as currently employed by welding manufacturers
such as Lincoln, Fronius, Miller, ESAB etc, continuously monitors
the height of the previously deposited metallic layer and compares
the actual height of the pervious layer to the specified height. If
any section of the layer is lower than specified, the system can go
back and fill it prior to starting the new layer, or the speed of
deposition can be modified to deposit additional material at the
low section.
[0042] A temperature monitoring means and simultaneous partial
submersion of the part in a bath of quenchant fluid while building
layers is used to heat or cool the part as each new layer is
deposited in the preferred embodiment. This feature allows control
of built in stresses as well as manipulation of the final grain
structure and material properties. The supplemental control of part
temperature, near but not coincident with the hot zone of the
deposition, provides fine control of item characteristics including
the ability to prevent outflow of deposited material from the
vicinity of the hot zone and to preclude plastic flow or sag
adjacent to the hot zone. In addition, submersion in a bath of
quenchant fluid is the preferred method of heat control over a
spray or a quenchant cascade, as liquid does not remain on the
surface to which material is being deposited during the next pass
nor is liquid introduced into the hot zone. Consequently, the risk
of steam, hydrogen and oxygen production which can cause
embrittlement or porosity is thereby reduced or eliminated.
[0043] The present invention provides a safe environment for the
operator and controls the unrestricted discharge of process
byproducts by providing an enclosure to trap toxic fumes generated
during the deposition process. The enclosure also retains the inert
gas used to shield the welding arc from undesired atmospheric
gases, so that less inert gas is needed. In addition, the inert gas
within the enclosure, in different embodiments, is purged and
reused for the next part.
[0044] As depicted in FIG. 1, a fabrication system 1 includes a
Build Table 5 acting as a support for the part being fabricated.
The Build Table 5 is supported by Build Table Supports 6 and is
raised or lowered by way of Build Table Height Actuators 7 into a
bath of quenchant Fluid 10, which is contained in a tank 11. As
illustrated, the actuators 7 are located outside the quenchant
fluid 10 and the tank 11 such that the actuator and the support are
not immersed in the fluid. In this embodiment, the actuators 7 are
located within an enclosure 40. The temperature of the quenchant
Fluid 10 is maintained by a Temperature Control Unit 12. A
quenchant Level 15 is maintained at a monitored, fixed position so
that the Build Table 5 and a portion of the fabricated part are
cooled or heated, as discussed herein. As used herein, the term
"build" is used to refer to a part being produced or "built". In
the preferred embodiment, the quenchant fluid 10 includes a
quenchant configured to cool the object being formed on the build
table 5.
[0045] A multi-axis Robotic Actuator System 20 is positioned above
the Build Table 5. The Robotic Actuator System 20 includes at least
one Z Axis Actuator 21 which moves a Z Axis Rod 25 vertically, as
illustrated, relative to the Build Table 5. A Deposition Nozzle
Module 30 is attached to the end of the Z Axis Rod 25 and is
connected to a Deposition Power Supply 35 and a supply of Inert Gas
36 by way of a Welding Tether 37. The described welding and
deposition equipment is familiar to those knowledgeable in MIG or
TIG welding processes, but modified to deliver much lower power and
very different waveforms than typically used for welding
applications. The inert gas 36 is also known as a shield gas.
[0046] The Build Table 5, bath of quenchant Fluid 10, Robotic
Actuator System 20, and Deposition Nozzle Module 30 are all
contained within an Enclosure 40. The Enclosure 40 creates a
controlled, Enclosed Space 45 for the process and in the preferred
embodiment is isolated from outside temperature variations and air
currents. The inert gas is contained within the Enclosed Space 45
and maintained at a desired Inert Gas Level 46, thus minimizing the
chance of contamination of the material being deposited to form the
part. While the inert gas level 46 is shown as a clearly defined
gas level, this level is for illustrative purposes only. During
operation of the system 1, the gases present in the enclosure 40
intermix, with the level of shield gas being determined by the
concentration of the mixture rather than a physical level as
shown.
[0047] The byproducts generated by the process are also contained
in the Enclosed Space 45 and in the preferred embodiment are vented
by way of a Vent Fan 47 to appropriate filters, scrubbers or
environmental controls in order to ensure operator safety. An
oxygen sensor 48 is operatively connected to the controller 50 to
monitor and control the level of oxygen gas within the chamber. If
the chamber is determined to have too much oxygen gas, or not
enough inert gas, the controller 50 delays the start of the
deposition process or turns off the system, so that repairs or
adjustments can be made.
[0048] In another embodiment, the sensor 48 is used to provide for
a reduction of shield gas during material deposition. The higher
the concentration of shield gas in the chamber, the lower the
requirement for shield gas input at the nozzle. Initially the
chamber contains normal air, with that air being excluded from the
deposition zone by the shield gas being input present at the
nozzle. In other optional operating settings, normal air is
completely removed from the chamber and the chamber is filled with
a shield gas before beginning the formation of the part.
[0049] In the preferred embodiment, the enclosure 40 is a sealed
container in which an inert gas, such as carbon dioxide, or argon,
or a selected mix of inert gases is used in the part forming
process. The enclosure 40 is coupled to a gas circulation system
(not shown) as would be understood by those skilled in the art. The
inert gas, such as carbon dioxide and argon are removed and trapped
from the air and reused in the enclosure 40.
[0050] A central Computer Controller 50 is connected to all
subassemblies of the apparatus by means of a Temperature Control
Cable 53, a Robotic Control Cable 54, and a Deposition Power Supply
Control Cable 55. The Computer Controller 50 has master control
over each of the subsystems along with control over the entire
process, as described below.
[0051] As depicted in FIG. 2, the Deposition Nozzle Module 30
incorporates a Holding Device 61 for securing a Deposition Nozzle
Assembly 63 as well as the Welding Tether 37. A Part Temperature
Sensor 66, an Electronic Height Gauge 67, and a Gas Monitoring
Probe 68 are also mounted to the Deposition Nozzle Module 30 so
that all supported components remain in the same relational
position as they move together. These sensors are connected to the
Computer Controller 50 by way of a Nozzle Module cable 69. It is
important to note that the Part Temperature Sensor 66 is positioned
and oriented so that it can accurately measure the temperature of
the part at some preset distance between the top of the part, where
the new materials layer is being deposited, and the build table or
quenchant Level 15.
[0052] The Electronic height gauge 67 determines if any areas of
the part are lower than desired. Optionally, in one or more
embodiments, additional height sensors are mounted to ensure that
the top of the part is in the correct position as determined by the
height of the build table 5 with respect to the nozzle module
30.
[0053] It is known in the art that the Robotic Actuator System 20,
in different embodiments, include multiple axes and thus allow
manipulation of more than one Deposition Nozzle Module 30. Multiple
Deposition Nozzle Modules 30 allow for faster deposition rates or
deposition of two materials at the same time. In the preferred
embodiment where the nozzle assembly 63 incorporates a MIG welding
head, the welding head is inputting heat during formation of the
part with up to 7,000 watts of power.
[0054] The typical Direction of Travel 70 for the Deposition Nozzle
Module 30 is depicted. An angular orientation 71 of the nozzle
relative to the part is employed for the purposes of maximizing
deposition rate and minimizing heat buildup while narrowing the
spread of the deposited material. This angular orientation 71 is
not an essential element of the invention, but is shown for clarity
and as an illustration of established practice. In this case, an
additional rotational element would be added to the nozzle as is
already common in the art to enable omnidirectional movement. In
the preferred embodiment, feed wire is used to provide material for
the build-up of the item being produced, and the wire discharge
means can be a MIG nozzle, TIG feed wire dispenser, or any similar
means available to the art. Feed wire is preferred over powdered
metal for cost, environmental, and safety reasons.
[0055] The sample part 80 depicted in FIG. 3 was made without use
of the quenchant Fluid 10. The uneven Top Surface 81 of this sample
part, which includes sag 82, illustrates how improper cooling
results in a part which lacks dimensional stability during
fabrication and which includes unwanted defects. The teachings of
the present disclosure, in contrast however, provide a dimensional
stability of the part which, in some cases, reduces the amount of
after-processing needed finish a part or the number of
dimensionally inaccurate parts.
[0056] Prior to operating the apparatus, a 3D solid computer model
of the desired part is sliced into virtual layers and saved into an
electronic file (not shown). This electronic file is then entered
into the Computer Controller 50 of the apparatus. At the start of
operation of the apparatus, a set of commands from the Computer
Controller 50 causes the Build Table 5 to be initially positioned
in or above the quenchant Level 15 and the Robotic Actuator System
20 and the Z Axis Actuator 21 to position the Deposition Nozzle
Module 30 at a starting point and a predetermined optimum distance
above the Build Table 5. The Enclosure 40 is optionally filled at
this time with the Inert Gas 36, by turning on the flow or
re-introducing gas which was saved from previous runs.
[0057] After checking and confirming that the environment within
the Enclosure 40 is being maintained at proper operating conditions
by way of the oxygen sensor 48, the Computer Controller 50 turns on
the Deposition Power Supply 35 and the flow of the Inert Gas 36.
Feed wire is delivered to the nozzle and an arc is struck. The
first layer of the part is deposited onto the Build Table 5
according to the profile in the sectioned 3D model file. Subsequent
layers, as determined by the 3D solid computer model and the
virtual layers thereof, are deposited to form a complete part.
[0058] The speed, power settings, and direction of the material
deposition are determined by preloaded parameters within the
Computer Controller 50. Since the temperature sensor 66 is mounted
as part of the nozzle module 30, the temperature sensor 66 is
adjacent to the location of the deposition of material, i.e. the
deposition or hot zone, and records the instantaneous temperature
at a set distance from the deposition or hot zone. This data is
received by the controller 50 and used in a computer modeling of an
overall part temperature. For example, upon completion of a layer,
the average temperature of an aluminum part is read using readings
from the temperature sensor 66 and the Build Table 5 is lowered or
raised to cool or heat the part to a desired temperature prior to
moving on to deposition of the next layer. The build can be delayed
or slowed down if the part is not within an acceptable temperature
range, and thus ensure one or more of: 1) proper bonding between
layers, 2) prevention or reduction of part sagging from addition
heat input, 3) obtaining the desired material grain structure, and
4) achieving desired physical properties. Also, under the right
conditions, the build is continuous and includes one, homogeneous
material including the transition from layer to layer. Travel speed
control is, therefore, an additional parameter which, can be used
to control part temperatures. As is known in the art, distortion
control in forgings, castings and thin sheet metal parts as well as
minimal residual stresses in forgings and castings can be achieved
by hot water quenching using hot water or water/polyalkalene glycol
mixtures.
[0059] Movement of the build table 5 is combined with movement in
the Z axis of the Z Axis Rod 25 and is controlled by the controller
50 to vary the distance between the quenchant and the hot zone of
the part while keeping the deposition parameters constant.
Therefore, the distance between the hot zone and the quenchant
level 15 and the portion of the part submerged, is continuously
varied based on instantaneous temperature readings, or is varied
based on a model of overall part temperature and varied in discrete
steps as desired.
[0060] The temperature of the part as measured by the small single
point temperature sensor 66 is received by the controller 50 and is
used to determine an average temperature over time, as the nozzle
assembly 63 moves along the path to deposit the material. In this
embodiment, a line can also be used for the temperature sensor, to
achieve some mechanical averaging of the signal sent to the
controller. In either case, the controller 50 is configured to use
the received temperature values to average the temperature over
time as would be understood by those skilled in the art.
[0061] During the deposition of each subsequent layer, the Z Axis
Actuator 21 positions the Deposition Nozzle Module 30 at a
predetermined height from the top of the part, as predetermined by
previous experimental testing of the apparatus. The Electronic
height gauge 67 determines if any areas of the part are lower than
desired. In another mode of operation, the arc provided by the
nozzle assembly 63 is used to obtain a localized visual reference
point corresponding to the height of the part being formed.
[0062] The build is correctable by going back over the low
sections, changing speed and deposition parameters, or aborting the
process if the part height or position is found to be out of an
acceptable tolerance.
[0063] Note that it is envisioned that the X-Y starting point for
each layer, is moved slightly relative to a previous starting point
of the previous layer, so that there is minimal effect from the
transient deposition during arc start up. Furthermore, material
deposition proceeds along a continuous path without interruption to
minimize the number of starting points.
[0064] In an alternate operating mode, the use of an analysis of
deposition voltages, currents, and other deposition supply
characteristics which are affected by the deposition process, are
used to monitor height. Common in the welding industry is the use
of voltage monitoring to determine arc length and "stick out" which
is the length of wire protruding from a MIG nozzle during a welding
operation. With a known distance for arc length, a known Deposition
Nozzle Z axis position, and a known "stick-out", dynamic
determination of material height in the deposition zone is a simple
subtraction operation. This result is then be used to control the
deposition rate, robotic motion speed, and maintain optimal build
height either in conjunction with height sensor 66 and other
sensors or as a standalone control.
[0065] In the preferred embodiment of the present invention, the
wire used in forming the part is a standard MIG welding wire but
having a reduced amount of silicon. A typical silicon concentration
for a currently available E70 MIG wire is in the range of 0.5-0.9%
SI. In a preferred embodiment for use herein, the feedstock wire
includes a silicon level of approximately 0.2% or below SI.
[0066] Given that the Inert Gas 36 is typically heavier than air,
the inert gas 36 tends to sink to the bottom of the Enclosure 40.
The Inert Gas Level 46 is continuously monitored so that the
deposition process is always performed in an inert gas environment.
Furthermore, monitoring of other, undesirable gases, such as
hydrogen near the deposition site, is performed to help ensure
optimum conditions for the metal deposition process. In this way,
porosity, material embrittlement, and other deposition flaws are
reduced or avoided resulting in a part that has the desired
mechanical properties.
[0067] Once the last layer is deposited and the part is therefore
completed, the inert gas is purged from the enclosed space with the
Vent Fan 47 and through a filter to clean the air of undesirable
fumes. The Deposition Nozzle Module 30 is moved out of the way by
the Robotic Actuator System 20 and the build table 5 is raised out
of the quenchant 10 to allow the part to be unloaded from the
apparatus. At least one door in the enclosure 40 provides access to
remove the completed part.
[0068] FIG. 4 illustrates the optional use of two MIG Welding
Nozzles 91 to rapidly deposit metal without the need for a
conductive Build Table 5. Either an AC waveform or DC- polarity is
provided by one Large Feed Wire 92 and DC+ polarity is provided by
another Small Feed Wire 93. In one or more embodiments, other
combinations of waveforms optimized to achieve the preferred
semi-molten state of the Large Feed Wire 92 are provided. The size
of the wires and the relative speed of the wire feeds are set in
conjunction with the waveforms, voltages, currents and polarities
so that the Small Feed Wire 93 softens the Large Feed Wire 92 but
does not completely melt it to the "droplet" stage. Thus, the Large
Feed Wire 92 is then able to be laid down in a semi-molten state to
make the first pass, with no need for conduction through the Build
Table 5. After the first layer is deposited, the waveforms are
switched so that one or both of the wires produces fully molten
droplets on the subsequent passes in order to help minimize the
heat input to the part and to optimize bonding and other deposition
qualities.
[0069] Varying the heat input and the quenching affects the
material properties in the deposited material, as well as providing
control over warpage tendencies. As depicted, the deposition
nozzles are angled towards each other so that the Large Feed Wire
92 and Small Feed Wire 93 intersect at a convenient distance above
the build table 5. Practitioners in the art will readily recognize
that the relationship between an included angle between the
deposition nozzles and the height above the build table 5 allows
for variations in order to achieve optimum results and either or
both angles are varied as needed.
[0070] FIG. 5 illustrates an alternate embodiment which substitutes
a non-consumable TIG Electrode 100 for the Small Feed Wire 93 in
the above embodiment, such as is commonly used in Tungsten Inert
Gas (TIG) welding. In this embodiment, the TIG Electrode 100 is
used to soften the Large Feed Wire 92 to allow deposition of the
material, allowing switching of current between the TIG Electrode
100, the MIG Large Feed Wire 92, and the Build Table 5 if a
metallic build table surface is used. This allows controlling the
initial deposition as well as subsequent passes by using suitable
configurations of currents for each purpose.
[0071] It should be understood that a combination of a Large Feed
Wire 92, a smaller wire and a TIG electrode, or more than one wire
of equal or different diameters might be used to practice the
invention, or that a single wire with a TIG Electrode 100 might be
used to deposit material onto the Build Table 5 as initially
described herein in lieu of feeding current through the feed wire
and using a typical MIG process.
[0072] In the preferred embodiment, regardless of the type of
nozzle or nozzles installed, the size of the feedstock wire and the
relative speed of the wire feeds are determined in conjunction with
the waveforms, voltages, polarity, and currents to be used by the
deposition nozzles. It should be noted that the first pass requires
different settings than subsequent passes and on subsequent passes
after the first pass, the configuration and parameters are such as
to create some localized heating of the formerly deposited layer in
the deposition zone, either by current flow or by proximity such
that acceptable bonding is achieved.
[0073] FIG. 6 illustrates the preferred embodiment of the
fabrication system 1 including a build table 102 disposed within a
tank 104. The tank 104 is filled with a quenchant and the build
table 102 is lowered into the tank 104 by supports 106, as
previously described. In this embodiment, the build table 102
includes a frame 108 which defines a planar support plane. The
frame 108 includes a plurality of cutouts 110, each of which is
configured to accommodate a removable platen 112 having a build
surface 114. The build surface 114 includes non-stick deposition
surface including a high-temperature-resistant flat plate 116 which
provides a smooth flat plane for the molten and semi molten
material being deposited. The flat plate 116 includes a sufficient
thickness configured to provide the necessary strength to support
the part being fabricated. The shape and size thereof is sufficient
to avoid warping when subjected to the heat of deposition. In the
preferred embodiment the flat plate 116 includes a copper or a
copper alloy.
[0074] As can be seen in FIG. 6, each of the cutouts 110 is formed
in the frame 108 with crosspieces 118 of appropriate shape to
receive one of the platens 112, wherein one or more edges 120 abut
an edge 120 of an adjacently located platen 112. In the preferred
embodiment, the adjacent edges 120 form a seam that is sufficiently
narrow to substantially prevent the heated material from entering
the gap between the adjoining platens 112. While a table 102 having
twelve cutouts 110 is illustrated, the present disclosure is not
limited to a table 102 having twelve cutouts, and more or less
cutouts of varying sizes are possible.
[0075] As seen in FIG. 6 and FIG. 7, platens 112 include a flat
plate 116. Fixedly attached to the underside surface of the flat
plate 116 is a plurality of heat dissipating fins 122. Each of the
fins includes a length sufficient be in contact with the quenchant
10 and in sufficient quantity to draw the heat from the flat plate
116 and to dissipate the heat into the quenchant 10. The length of
the fins 122, extending from the underside surface of the flat
plate 116, is such that when the build table 102 is in the
uppermost position, the ends of the fins 124 are immersed in the
quenchant 10. In this manner, the quenchant 10 is below the surface
114 of each of the flat plates 116 and does not interfere with the
deposition. The number and length of the fins 124 can vary and
still achieve the desired heat transfer.
[0076] As further illustrated in FIG. 7, the plate includes an
engaging portion 126, which in the disclosed embodiment, is formed
as part of the fin structure. Different engaging structures are
possible. The engaging portion defines a channel 128, between the
flat plate 116 and the engaging portion 126, and is configured to
receive a portion of the frame 108, which in the embodiment of FIG.
6 is a portion of one of the crosspieces 118. In this way, each of
the platens 112 is forced into maintaining good electrical contact
with the table 102 during the formation of a part to provide the
electrical connection to strike and maintain a consistent arc.
[0077] Referring again to FIG. 6, the tank 104 includes a back wall
130 having a horizontally located rectangular aperture 132, also
known as a weir, which provides for the overflow of quenchant
through the aperture 132 and into an overflow reservoir 134. The
overflow reservoir 134 includes a capacity sufficient to collect
overflow of quenchant as the table 102 and the part being formed
are lowered into the tank 104. The aperture 132, therefore,
provides precise fluid level control of the quenchant remaining in
the tank 104. The quenchant in the overflow reservoir 134 is cycled
back into the tank for circulation and then pumped back into the
tank 104 when the build is complete.
[0078] A heat exchanger 135 includes a radiator 136, located at the
back wall 130, and a fluid exchange device 138, fluidically coupled
to the radiator 136. The fluid exchange device 138 includes a pump
which circulates a temperature controlled fluid, such as a
refrigerant, through the radiator 136 thus cooling the quenchant
located in the tank 104. In the preferred embodiment a sensing
device is immersed in the quenchant to determine the temperature of
the quenchant. Eliminating the heat exchanger 135 and circulating
the quenchant through the fluid exchange device is equivalent.
[0079] The fluid exchange device 138 is configured to adjust the
temperature of the temperature controlled fluid moving through the
radiator 136. The temperature of the quenchant 10 located in the
tank 104 is thereby raised or lowered to provide a preferred
temperature for controlling the temperature of the part being
formed. In this way, the build process is optimized for providing
usable parts having the desired properties.
[0080] FIG. 8 illustrates a portion of the platen 108 including the
flat plate 116 defining the surface 114. As described above, the
surface 114 includes a non-stick deposition surface which provides
a smooth flat plane for the molten and semi molten material being
deposited. Using the deposition nozzle module 30 of FIG. 1
including the deposition nozzle assembly 63, a part is formed
through the deposition of molten or semi-molten metal or metal-like
material at the surface 114. To begin the formation of the part, a
plurality of spots 140 of the material are deposited at spaced
locations on the surface 114. To deposit the spots 140, the power
supply 35 is adjusted to deliver a current to the nozzle assembly
63 which is sufficient to adhere the spots 140 to the surface 114,
in a relatively secure fashion, such that a metal bond is formed
between the surface material and the deposited spot material. If
the plate 116 is formed of copper, for instance, the power is
adjusted sufficiently to break through the oxidation at the surface
to provide good, consistent, electrical contact.
[0081] Each of the spots 140 includes a mound of material, which
provides a stable structure electrically connected to the plate 116
upon which the remainder of the part is formed. Once the spots 140
are deposited, a bead of molten or semi-molten metal or metal like
material 142 is deposited between each of the spots 140 to connect
one spot 140 to the next spot 140 or alternatively over or next to
the spots 140. In forming the beads 142, the power of the power
supply is adjusted to provide a current typically lower than the
current used to form the spots 140. In this fashion, the beads 142
do not form a metal bond with the surface 114, but do form a bond
with the spots 140. Once a first layer 144 of the part, including
spots 140 and beads 142 are formed, additional layers 146 formed of
continuous beads of material are deposited on previously formed
layers, as described above. As a result, the deposition nozzle
assembly 63 does not act as a welder, but instead is used to merely
melt the metal wire fed through the nozzle. The power does not bond
the metallic beads 142 to the no stick plate 116. The application
of the beads 142 are either continuous or segmented as illustrated
and is varied depending on the spacing of the spots 140 and other
parameters including sensed temperatures, material types, and speed
of deposition.
[0082] The part is easily removed from the build surface 114 by
tapping the part or the build surface or by the application of a
minor impact force to the part or build surface.
[0083] The power setting of the power supply 35 during the
deposition of the beads 142 and subsequent layers 146 is not at a
level typically used in a metal to metal welding process, but is
reduced from that level and is generally a fraction of that used in
a typical welding process. In one embodiment, the power level being
used is approximately twenty five percent or less than the power
typically required in a welding operation for the same metal. The
power supply setting can also be adjusted to vary the current or
voltage used to form the layers in response to the temperature
being sensed by the temperature sensor 66. For instance, as
additional layers are formed, the temperature being sensed changes
due to part geometry and the power supply setting is adjusted
accordingly. In the preferred embodiment, the polarity of the
electrode of the nozzle assembly 63 is alternated from positive to
negative depending on the layer and material of deposition. To
facilitate the change in polarity, a silicon controlled rectifier
(SCR) is used within the wire feed circuit of the nozzle assembly
and build table to change polarity as necessary.
[0084] The controller 50 is configured to control the application
of the material being deposited by the nozzle module 30 during
formation of a part. The controller includes one or more computer
processors configured to operate according to software based
routines which are written to implement the embodiments of the
invention. Whether implemented as part of an operating system or a
specific application, component, program, object, module or
sequence of instructions the software routines are hereafter
referred to herein as "computer program code", or simply "program
code". The computer program code typically comprises one or more
instructions that are resident at various times in various memory
and storage devices in the controller, and that, when read and
executed by one or more processors in the controller, causes the
robotic actuators, welding power supply, and chilling device to
perform the steps necessary to execute formation of the object or
parts.
[0085] In addition, it should be appreciated that the method or
methods described herein are implementable in various program code
and should not be limited to specific types of program code or
specific organizations of such program code. Additionally, in view
of the typically endless number of manners in which computer
programs may be organized into routines, procedures, methods,
modules, objects, and the like, as well as the various manners in
which program functionality may be allocated among various software
layers that are resident within a controller or computer if used,
(e.g., operating systems, libraries, APIs, applications, applets,
etc.), it should be appreciated that the invention is not limited
to a specific organization.
[0086] The controller 50 and resident program code is configured to
form a 3 dimensional metallic part of any shape through the control
of a number of parameters and conditions including material
temperatures, hold times, deposition speed, tool identification,
and power settings of the power supply to optimize deposition rates
for a given layer of the part. In addition, as described herein
different materials and different wire sizes can be used, either in
a single nozzle assembly or in multiple nozzle assemblies which are
changed by hand or automatically in the system 1. Weld parameters
and temperature sensor emissivity is also controllable for
different materials.
[0087] FIG. 9 illustrates a side view of a preferred embodiment of
a nozzle head fixture 150 and a nozzle assembly 152. The nozzle
head fixture 150 is configured to engage a plurality of different
nozzle assemblies 152, each of which is directed to forming a bead
of material of a different type. For instance, a plurality of
nozzle assemblies 152 are parked at a docking station (not shown)
for intermittent use during the formation of a part. One of the
nozzle assemblies 152 is selected by the controller 50, based on
the type of material to be deposited, and that nozzle assembly 152
is picked by the nozzle head fixture 150 from the appropriate
location of the docking station where the pick is made. The nozzle
head fixture 150 is coupled to the Z axis actuator 21 Z-rod 50 of
FIG. 1 which in turn is coupled to wrist actuator 156. The wrist
actuator 156 is configured to rotate the head fixture 150 about the
z-axis defined by the z-rod 50. A temperature probe 160, such as
that previously described, is coupled to the nozzle head fixture
150 and is configured to sense the temperature of the product being
formed. In another embodiment, each of the nozzle assemblies
includes a temperature probe. A tool bracket 164 which is coupled
to a torch portion 166 of the nozzle assembly 152. A nozzle head
167 extends below the tool bracket 164. A flexible conduit 168
coupled to the torch portion 166 supplies the predetermined type of
wire and gas. The master bracket 158 includes an aperture 170
configured to receive a portion of the tool bracket 164. As seen in
FIG. 9, the tool bracket 164 includes a channel 172 configured to
hang the tool from the docking station or other storage rack when
not in use. In the preferred embodiment, the storage rack is
located within the enclosure 40.
[0088] FIG. 10 illustrates a back view of the nozzle head fixture
150 and the nozzle assembly 152. The nozzle head fixture 150 is
configured to support a position sensor 176.
[0089] FIG. 11 illustrates a front perspective view of the nozzle
head fixture 150 and the docked nozzle assembly 152. As can be
seen, the beam of the temperature sensor extends below the bottom
edge of the tool bracket 164.
[0090] FIG. 12 illustrates a perspective view of a part 180 being
formed with a part build fixture 182. The part build fixture 182 is
located adjacently to a side 184 of the part 180 and includes a
non-stick surface 186 upon which a shelf 188 is formed by the
deposition process. The part fixture 182 provides support for the
shelf 188 such that the shelf 188 extends from the wall 184 in a
cantilever and accurate fashion. Removal of the part fixture 182,
after completion of the part 180 leaves a space or void below the
shelf 188. Additionally, a specially made form 190 of non stick
material is added to during formation, as needed, to provide a
desired geometry to the finished part 180. Alternatively, cavities,
elevated surfaces and smooth surfaces are similarly formed. The use
of such fixtures and forms provides for a more accurate control of
the geometric shapes, dimensional sizes and finishes of the objects
being formed. In the preferred embodiments, however, the formation
of overhangs, arches and similar structures are formed without the
use of supplemental supports. The formation of these types of
structures are provided with the addition of one additional axes of
movement which enables the nozzle to be angled upwards through an
selectable and controlled angle of 90 degrees or more to enable the
deposition of material in a horizontal direction, a direction
angled from horizontal, or upwards from horizontal.
[0091] While exemplary embodiments incorporating the principles of
the present invention have been disclosed herein, the present
invention is not limited to the disclosed embodiments. Instead,
this application is intended to cover any variations, uses, or
adaptations of the invention using its general principles. Further,
this application is intended to cover such departures from the
present disclosure as come within known or customary practice in
the art to which this invention pertains and which fall within the
limits of the appended claims.
* * * * *