US20220266371A1 - Method and apparatus for fabrication of articles by molten and semi-molten deposition - Google Patents

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.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS
• 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
• 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
• 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.
• 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.
• 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.
• 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.
• 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.
• 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
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• 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.
• In different embodiments, computer controls are integrated into the other process controls, as is known in the art.
BRIEF DESCRIPTION OF THE DRAWINGS
• FIG. 1 is a block diagram of the major components and subassemblies of a fabrication system.
• FIG. 2. illustrates a deposition nozzle module of the present invention.
• FIG. 3. illustrates a prototype part made by an embodiment of the present invention.
• FIG. 4. illustrates a two wire deposition device of the present invention.
• FIG. 5. illustrates an alternative two wire deposition device of the present invention.
• FIG. 6 illustrates another embodiment of a portion of a fabrication system.
• FIG. 7 illustrates an underneath perspective view of a platen assembly.
• FIG. 8 illustrates a top perspective view of a platen assembly including deposition of material.
• FIG. 9 illustrates a side view of a nozzle head fixture and a nozzle assembly.
• FIG. 10 illustrates a back view of a nozzle head fixture and a docked nozzle assembly.
• FIG. 11 illustrates a front perspective view of a nozzle head fixture and a docked nozzle assembly.
• FIG. 12 illustrates a perspective view of a part being formed with a part fixture.
DESCRIPTION OF THE PREFERRED EMBODIMENT
• 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.
• 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.
• 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.
• 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.
• 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.
• As depicted inFIG. 1, afabrication system1 includes a Build Table5 acting as a support for the part being fabricated. The Build Table5 is supported by Build Table Supports6 and is raised or lowered by way of Build Table Height Actuators7 into a bath ofquenchant Fluid10, which is contained in atank11. As illustrated, the actuators7 are located outside thequenchant fluid10 and thetank11 such that the actuator and the support are not immersed in the fluid. In this embodiment, the actuators7 are located within anenclosure40. The temperature of thequenchant Fluid10 is maintained by aTemperature Control Unit12. Aquenchant Level15 is maintained at a monitored, fixed position so that the Build Table5 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, thequenchant fluid10 includes a quenchant configured to cool the object being formed on the build table5.
• A multi-axisRobotic Actuator System20 is positioned above the Build Table5. TheRobotic Actuator System20 includes at least oneZ Axis Actuator21 which moves aZ Axis Rod25 vertically, as illustrated, relative to the Build Table5. ADeposition Nozzle Module30 is attached to the end of theZ Axis Rod25 and is connected to aDeposition Power Supply35 and a supply ofInert Gas36 by way of aWelding Tether37. 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. Theinert gas36 is also known as a shield gas.
• The Build Table5, bath ofquenchant Fluid10,Robotic Actuator System20, andDeposition Nozzle Module30 are all contained within anEnclosure40. TheEnclosure40 creates a controlled, EnclosedSpace45 for the process and in the preferred embodiment is isolated from outside temperature variations and air currents. The inert gas is contained within the EnclosedSpace45 and maintained at a desiredInert Gas Level46, thus minimizing the chance of contamination of the material being deposited to form the part. While theinert gas level46 is shown as a clearly defined gas level, this level is for illustrative purposes only. During operation of thesystem1, the gases present in theenclosure40 intermix, with the level of shield gas being determined by the concentration of the mixture rather than a physical level as shown.
• The byproducts generated by the process are also contained in the EnclosedSpace45 and in the preferred embodiment are vented by way of aVent Fan47 to appropriate filters, scrubbers or environmental controls in order to ensure operator safety. Anoxygen sensor48 is operatively connected to thecontroller50 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, thecontroller50 delays the start of the deposition process or turns off the system, so that repairs or adjustments can be made.
• In another embodiment, thesensor48 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.
• In the preferred embodiment, theenclosure40 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. Theenclosure40 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 theenclosure40.
• Acentral Computer Controller50 is connected to all subassemblies of the apparatus by means of aTemperature Control Cable53, aRobotic Control Cable54, and a Deposition PowerSupply Control Cable55. TheComputer Controller50 has master control over each of the subsystems along with control over the entire process, as described below.
• As depicted inFIG. 2, theDeposition Nozzle Module30 incorporates aHolding Device61 for securing aDeposition Nozzle Assembly63 as well as theWelding Tether37. A Part Temperature Sensor66, an Electronic Height Gauge67, and aGas Monitoring Probe68 are also mounted to theDeposition Nozzle Module30 so that all supported components remain in the same relational position as they move together. These sensors are connected to theComputer Controller50 by way of aNozzle Module cable69. It is important to note that the Part Temperature Sensor66 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 orquenchant Level15.
• The Electronic height gauge67 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 table5 with respect to thenozzle module30.
• It is known in the art that theRobotic Actuator System20, in different embodiments, include multiple axes and thus allow manipulation of more than oneDeposition Nozzle Module30. MultipleDeposition Nozzle Modules30 allow for faster deposition rates or deposition of two materials at the same time. In the preferred embodiment where thenozzle assembly63 incorporates a MIG welding head, the welding head is inputting heat during formation of the part with up to 7,000 watts of power.
• The typical Direction ofTravel70 for theDeposition Nozzle Module30 is depicted. An angular orientation71 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 orientation71 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.
• Thesample part80 depicted inFIG. 3 was made without use of thequenchant Fluid10. Theuneven Top Surface81 of this sample part, which includessag82, 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.
• 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 theComputer Controller50 of the apparatus. At the start of operation of the apparatus, a set of commands from theComputer Controller50 causes the Build Table5 to be initially positioned in or above thequenchant Level15 and theRobotic Actuator System20 and theZ Axis Actuator21 to position theDeposition Nozzle Module30 at a starting point and a predetermined optimum distance above the Build Table5. TheEnclosure40 is optionally filled at this time with theInert Gas36, by turning on the flow or re-introducing gas which was saved from previous runs.
• After checking and confirming that the environment within theEnclosure40 is being maintained at proper operating conditions by way of theoxygen sensor48, theComputer Controller50 turns on theDeposition Power Supply35 and the flow of theInert Gas36. Feed wire is delivered to the nozzle and an arc is struck. The first layer of the part is deposited onto the Build Table5 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.
• The speed, power settings, and direction of the material deposition are determined by preloaded parameters within theComputer Controller50. Since the temperature sensor66 is mounted as part of thenozzle module30, the temperature sensor66 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 thecontroller50 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 sensor66 and the Build Table5 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.
• Movement of the build table5 is combined with movement in the Z axis of theZ Axis Rod25 and is controlled by thecontroller50 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 thequenchant level15 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.
• The temperature of the part as measured by the small single point temperature sensor66 is received by thecontroller50 and is used to determine an average temperature over time, as thenozzle assembly63 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, thecontroller50 is configured to use the received temperature values to average the temperature over time as would be understood by those skilled in the art.
• During the deposition of each subsequent layer, theZ Axis Actuator21 positions theDeposition Nozzle Module30 at a predetermined height from the top of the part, as predetermined by previous experimental testing of the apparatus. The Electronic height gauge67 determines if any areas of the part are lower than desired. In another mode of operation, the arc provided by thenozzle assembly63 is used to obtain a localized visual reference point corresponding to the height of the part being formed.
• 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.
• 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.
• 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 sensor66 and other sensors or as a standalone control.
• 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.
• Given that theInert Gas36 is typically heavier than air, theinert gas36 tends to sink to the bottom of theEnclosure40. TheInert Gas Level46 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.
• Once the last layer is deposited and the part is therefore completed, the inert gas is purged from the enclosed space with theVent Fan47 and through a filter to clean the air of undesirable fumes. TheDeposition Nozzle Module30 is moved out of the way by theRobotic Actuator System20 and the build table5 is raised out of thequenchant10 to allow the part to be unloaded from the apparatus. At least one door in theenclosure40 provides access to remove the completed part.
• FIG. 4 illustrates the optional use of two MIG Welding Nozzles91 to rapidly deposit metal without the need for a conductive Build Table5. Either an AC waveform or DC− polarity is provided by oneLarge Feed Wire92 and DC+ polarity is provided by another Small Feed Wire93. In one or more embodiments, other combinations of waveforms optimized to achieve the preferred semi-molten state of theLarge Feed Wire92 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 Wire93 softens theLarge Feed Wire92 but does not completely melt it to the “droplet” stage. Thus, theLarge Feed Wire92 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 Table5. 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.
• 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 theLarge Feed Wire92 and Small Feed Wire93 intersect at a convenient distance above the build table5. Practitioners in the art will readily recognize that the relationship between an included angle between the deposition nozzles and the height above the build table5 allows for variations in order to achieve optimum results and either or both angles are varied as needed.
• FIG. 5 illustrates an alternate embodiment which substitutes anon-consumable TIG Electrode100 for the Small Feed Wire93 in the above embodiment, such as is commonly used in Tungsten Inert Gas (TIG) welding. In this embodiment, theTIG Electrode100 is used to soften theLarge Feed Wire92 to allow deposition of the material, allowing switching of current between theTIG Electrode100, the MIGLarge Feed Wire92, and the Build Table5 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.
• It should be understood that a combination of aLarge Feed Wire92, 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 aTIG Electrode100 might be used to deposit material onto the Build Table5 as initially described herein in lieu of feeding current through the feed wire and using a typical MIG process.
• 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.
• FIG. 6 illustrates the preferred embodiment of thefabrication system1 including a build table102 disposed within atank104. Thetank104 is filled with a quenchant and the build table102 is lowered into thetank104 bysupports106, as previously described. In this embodiment, the build table102 includes aframe108 which defines a planar support plane. Theframe108 includes a plurality ofcutouts110, each of which is configured to accommodate aremovable platen112 having abuild surface114. Thebuild surface114 includes non-stick deposition surface including a high-temperature-resistantflat plate116 which provides a smooth flat plane for the molten and semi molten material being deposited. Theflat plate116 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 theflat plate116 includes a copper or a copper alloy.
• As can be seen inFIG. 6, each of thecutouts110 is formed in theframe108 withcrosspieces118 of appropriate shape to receive one of theplatens112, wherein one ormore edges120 abut anedge120 of an adjacently locatedplaten112. In the preferred embodiment, theadjacent edges120 form a seam that is sufficiently narrow to substantially prevent the heated material from entering the gap between the adjoiningplatens112. While a table102 having twelvecutouts110 is illustrated, the present disclosure is not limited to a table102 having twelve cutouts, and more or less cutouts of varying sizes are possible.
• As seen inFIG. 6 andFIG. 7,platens112 include aflat plate116. Fixedly attached to the underside surface of theflat plate116 is a plurality ofheat dissipating fins122. Each of the fins includes a length sufficient be in contact with thequenchant10 and in sufficient quantity to draw the heat from theflat plate116 and to dissipate the heat into thequenchant10. The length of thefins122, extending from the underside surface of theflat plate116, is such that when the build table102 is in the uppermost position, the ends of thefins124 are immersed in thequenchant10. In this manner, thequenchant10 is below thesurface114 of each of theflat plates116 and does not interfere with the deposition. The number and length of thefins124 can vary and still achieve the desired heat transfer.
• As further illustrated inFIG. 7, the plate includes an engagingportion126, which in the disclosed embodiment, is formed as part of the fin structure. Different engaging structures are possible. The engaging portion defines achannel128, between theflat plate116 and the engagingportion126, and is configured to receive a portion of theframe108, which in the embodiment ofFIG. 6 is a portion of one of thecrosspieces118. In this way, each of theplatens112 is forced into maintaining good electrical contact with the table102 during the formation of a part to provide the electrical connection to strike and maintain a consistent arc.
• Referring again toFIG. 6, thetank104 includes aback wall130 having a horizontally locatedrectangular aperture132, also known as a weir, which provides for the overflow of quenchant through theaperture132 and into anoverflow reservoir134. Theoverflow reservoir134 includes a capacity sufficient to collect overflow of quenchant as the table102 and the part being formed are lowered into thetank104. Theaperture132, therefore, provides precise fluid level control of the quenchant remaining in thetank104. The quenchant in theoverflow reservoir134 is cycled back into the tank for circulation and then pumped back into thetank104 when the build is complete.
• Aheat exchanger135 includes aradiator136, located at theback wall130, and afluid exchange device138, fluidically coupled to theradiator136. Thefluid exchange device138 includes a pump which circulates a temperature controlled fluid, such as a refrigerant, through theradiator136 thus cooling the quenchant located in thetank104. In the preferred embodiment a sensing device is immersed in the quenchant to determine the temperature of the quenchant. Eliminating theheat exchanger135 and circulating the quenchant through the fluid exchange device is equivalent.
• Thefluid exchange device138 is configured to adjust the temperature of the temperature controlled fluid moving through theradiator136. The temperature of thequenchant10 located in thetank104 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.
• FIG. 8 illustrates a portion of theplaten108 including theflat plate116 defining thesurface114. As described above, thesurface114 includes a non-stick deposition surface which provides a smooth flat plane for the molten and semi molten material being deposited. Using thedeposition nozzle module30 ofFIG. 1 including thedeposition nozzle assembly63, a part is formed through the deposition of molten or semi-molten metal or metal-like material at thesurface114. To begin the formation of the part, a plurality ofspots140 of the material are deposited at spaced locations on thesurface114. To deposit thespots140, thepower supply35 is adjusted to deliver a current to thenozzle assembly63 which is sufficient to adhere thespots140 to thesurface114, in a relatively secure fashion, such that a metal bond is formed between the surface material and the deposited spot material. If theplate116 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.
• Each of thespots140 includes a mound of material, which provides a stable structure electrically connected to theplate116 upon which the remainder of the part is formed. Once thespots140 are deposited, a bead of molten or semi-molten metal or metal likematerial142 is deposited between each of thespots140 to connect onespot140 to thenext spot140 or alternatively over or next to thespots140. In forming thebeads142, the power of the power supply is adjusted to provide a current typically lower than the current used to form thespots140. In this fashion, thebeads142 do not form a metal bond with thesurface114, but do form a bond with thespots140. Once a first layer144 of the part, includingspots140 andbeads142 are formed,additional layers146 formed of continuous beads of material are deposited on previously formed layers, as described above. As a result, thedeposition nozzle assembly63 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 themetallic beads142 to the nostick plate116. The application of thebeads142 are either continuous or segmented as illustrated and is varied depending on the spacing of thespots140 and other parameters including sensed temperatures, material types, and speed of deposition.
• The part is easily removed from thebuild surface114 by tapping the part or the build surface or by the application of a minor impact force to the part or build surface.
• The power setting of thepower supply35 during the deposition of thebeads142 andsubsequent layers146 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 sensor66. 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 thenozzle assembly63 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.
• Thecontroller50 is configured to control the application of the material being deposited by thenozzle module30 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.
• 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.
• Thecontroller50 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 thesystem1. Weld parameters and temperature sensor emissivity is also controllable for different materials.
• FIG. 9 illustrates a side view of a preferred embodiment of anozzle head fixture150 and anozzle assembly152. Thenozzle head fixture150 is configured to engage a plurality ofdifferent nozzle assemblies152, each of which is directed to forming a bead of material of a different type. For instance, a plurality ofnozzle assemblies152 are parked at a docking station (not shown) for intermittent use during the formation of a part. One of thenozzle assemblies152 is selected by thecontroller50, based on the type of material to be deposited, and thatnozzle assembly152 is picked by thenozzle head fixture150 from the appropriate location of the docking station where the pick is made. Thenozzle head fixture150 is coupled to the Z axis actuator21 Z-rod50 ofFIG. 1 which in turn is coupled towrist actuator156. Thewrist actuator156 is configured to rotate thehead fixture150 about the z-axis defined by the z-rod50. Atemperature probe160, such as that previously described, is coupled to thenozzle head fixture150 and is configured to sense the temperature of the product being formed. In another embodiment, each of the nozzle assemblies includes a temperature probe. Atool bracket164 which is coupled to atorch portion166 of thenozzle assembly152. Anozzle head167 extends below thetool bracket164. Aflexible conduit168 coupled to thetorch portion166 supplies the predetermined type of wire and gas. Themaster bracket158 includes anaperture170 configured to receive a portion of thetool bracket164. As seen inFIG. 9, thetool bracket164 includes achannel172 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 theenclosure40.
• FIG. 10 illustrates a back view of thenozzle head fixture150 and thenozzle assembly152. Thenozzle head fixture150 is configured to support aposition sensor176.
• FIG. 11 illustrates a front perspective view of thenozzle head fixture150 and the dockednozzle assembly152. As can be seen, the beam of the temperature sensor extends below the bottom edge of thetool bracket164.
• FIG. 12 illustrates a perspective view of apart180 being formed with a part build fixture182. The part build fixture182 is located adjacently to aside184 of thepart180 and includes anon-stick surface186 upon which ashelf188 is formed by the deposition process. The part fixture182 provides support for theshelf188 such that theshelf188 extends from thewall184 in a cantilever and accurate fashion. Removal of the part fixture182, after completion of thepart180 leaves a space or void below theshelf188. Additionally, a specially madeform190 of non stick material is added to during formation, as needed, to provide a desired geometry to thefinished part180. 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.
• 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.

Claims (19)

I claim:

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 inclaim 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 inclaim 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 inclaim 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 inclaim 5 wherein said deposition head is capable of being fully submerged in said quenchant.

7. The additive manufacturing apparatus ofclaim 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 ofclaim 8 further comprising each of the plurality of deposition heads configured to deposit a different material.

10. The method ofclaim 8 further comprising one welding power supply and changing computer control programs for each deposition head.

11. The method ofclaim 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 ofclaim 12 further comprising using the arc current to continually monitor the height of the object.

14. The additive manufacturing method as set forth inclaim 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 ofclaim 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 inclaim 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 ofclaim 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 inclaim 17 further comprising using a memory storage device and recording all locations of any detected defects for later analysis.

19. The method ofclaim 18 further comprising creating a visual display of the locations of any detected defects.

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