MANUFACTURING

FIELD OF THE INVENTION

[0001] This invention relates to additive manufacturing (AM) and, more particularly, to neutralization of condensate in an AM system.

BACKGROUND OF THE INVENTION

[0002] AM enables fabrication of three-dimensional objects from a digital model or another electronic data source through additive processes in which successive layers of material are laid down. A laser beam or electron beam is used to fuse a previously-leveled powder surface layer into a thin sheet of solid material. A further layer of powder is applied on top of the previously-fused thin sheet and the process is repeated until a three-dimensional object is built layer-by-layer. This process is known as, for example, powder bed fusion (PBF), laser selective melting, or direct laser metal sintering. The process may be applied to metals, plastics, or other materials that can be fused together.

[0003] The AM process may be contained in a chamber filled with an inert gas to prevent unwanted chemical reactions or the oxidation of molten metal. This inert gas may be, for example, argon. During the layer fusion process of, for example, a metal, the surface of the melt pool overheats and vaporizes. Vaporized material cools and condenses within the inert atmosphere into nanometer-sized dust, referred to herein as "condensate." These condensate particles may be approximately 10 nm to 100 μιη in diameter or longest dimension. This condensate is initially suspended in the inert gas within the chamber. Condensate in the chamber may settle on a surface or remain suspended in the inert gas as a smoke. This poses a safety hazard because the condensate may be highly reactive in the presence of oxygen, which can result in a severe risk of explosion or fire.

[0004] FIG. 1 is a schematic of an AM system 100 of the prior art. The AM system 100 includes a build chamber 101, which is where the layer fusion process occurs. To reduce the risk to personnel, convection currents of the inert gas can direct the condensate out of the build chamber 101. The inert gas and suspended condensate (represented by the solid arrow) can be pumped through a filter 102 to capture the solid material. Inert gas with less condensate or even no condensate (represented by the dashed arrow) is then pumped to the build chamber 101 using the circulating fan

103. Large quantities of condensate can be captured in the filter 102, but the filter 102 may not capture all of the condensate and not all the condensate may be directed out of the build chamber 101. Thus, while some condensate is directed toward the filter 102, a significant portion of the condensate may accumulate in and around the chamber 101.

[0005] Settled condensate may build up on the walls of the chamber 101, the transparent window through which the laser beam is directed, or the object being manufactured. The laser beam may be obscured and the AM process may be interrupted or degraded if condensate settles on the transparent window. This can result in the production of poor-quality parts. For example, an object may take 10 to

200 hours to build in an AM system. However, the transparent window may be obscured after only approximately five hours of use due to deposits that have formed. It may be necessary to pause and clean the system if the transparent window is obscured. [0006] Any condensate build-up on the object being manufactured can impact the quality or properties of this object. For example, condensate may reduce fidelity or impact the shape, dimensions, or physical properties of the object being

manufactured. The condensate build-up may even ruin the object being

manufactured. Thus, there may be a maximum build time that can be performed before the chamber 101 and transparent window need to be cleaned due to the presence of the condensate. This may render AM unsuitable for fabricating large or geometrically-complex objects.

[0007] Condensate build-up on the walls of the chamber 101 can be a fire risk, which presents a safety issue for operators during manual cleaning. Some materials in the condensate may be highly-reactive in air, which may lead to spontaneous ignition if enough condensate has accumulated and the chamber 101 is opened for cleaning or maintenance. For example, titanium or aluminum condensate can be formed during laser processing. Titanium or aluminum dust is a fire hazard and, when exposed to air, may pose an explosion hazard. Fires or explosions can occur while cleaning the chamber 101, especially in vacuum cleaners or other cleaning equipment used during the cleaning process. Serious accidents have occurred while cleaning condensate or handling filters 102 contaminated with condensate.

[0008] Contaminated filters 102 must be manually removed during replacement and disposed of in a specialized facility for hazardous waste. Changing or handling the filter 102 increases the risk of spontaneous combustion and serious accidents. Several injuries have been reported during filter cleaning or replacement.

To reduce fire risk with the filter 102, the dimensions of the filter 102 are kept small.

However, this limits the maximum build time during the AM process before the filter 102 must be replaced. Furthermore, not all the condensate is collected in the filter

102 and the explosion or fire risk in the chamber 101 remains.

[0009] Therefore, what is needed is a system and method of condensate neutralization during AM and, more particularly, neutralization of condensate during AM process that converts the condensate to a safe form. BRIEF SUMMARY OF THE INVENTION

[0010] Metal condensate can be neutralized by converting it to a safe compound or a safe form of the metal. Titanium is one example of a metal condensate that can be converted. In an example, reactive titanium nano-scale condensate is transformed into an inert macro-scale titanium deposit. This can be a closed process. DESCRIPTION OF THE DRAWINGS

[0011] For a fuller understanding of the nature and objects of the invention, reference should be made to the following detailed description taken in conjunction with the accompanying drawings, in which: FIG. 1 is a schematic block diagram of an AM system of the prior art;

FIG. 2 represents a chemical reaction process that can be used in an AM system in accordance with an embodiment of the present invention;

FIG. 3 is a schematic block diagram of an AM system using a halide gas in accordance with an embodiment of the present invention;

FIG. 4 is a flow diagram representing a process of using the AM system of FIG. 3;

FIG. 5 is a schematic block diagram of an AM system using a halide gas in accordance with another embodiment of the present invention;

FIG. 6 is a flow diagram representing a process of using the AM system of FIG. 5;

FIG. 7 is a schematic block diagram of an AM system using a halide gas in accordance with another embodiment of the present invention; and

FIG. 8 is a flow diagram representing a process of using the AM system of FIG. 7.

DETAILED DESCRIPTION OF THE INVENTION

[0012] Although claimed subject matter will be described in terms of certain embodiments, other embodiments, including embodiments that do not provide all of the benefits and features set forth herein, are also within the scope of this invention.

Various structural, logical, process step, and electronic changes may be made without departing from the scope of the invention. Accordingly, the scope of the invention is defined only by reference to the appended claims.

[0013] FIG. 2 represents a chemical reaction process that can be used in an AM system embodying the present invention. A solid halide is vaporized in step 120.

The gaseous halide that is formed is contacted with the metal condensate. While titanium is specifically disclosed as the metal condensate, aluminum, vanadium, or other metals also may be used. This causes a reaction in step 121. A gaseous metal halide compound is formed in step 122. A filament is used to separate the metal from the halide and reverse the reaction in step 123. The gaseous halide is then cooled and solidifies in step 124.

[0014] For example, the solid halide may be a solid material containing iodine. The I(s) can be vaporized by raising its temperature above, for example, approximately 150°C. The pressure in the AM system also may be reduced. Solid titanium condensate reacts with the I ₂ (g) to form Til ₄ (g) using the following reaction:

Ti(s) + 2I ₂ (g)→TiI ₄ (g)

[0015] The filament may be controlled to approximately 1400°C to separate the Til ₄ (g) using the following reaction:

TiI ₄ (g)→Ti(s) + 2I ₂ (g)

[0016] When cooled, the I ₂ (g) will solidify into the I(s). For example, the

I ₂ (g) may be cooled below 150°C to form I(s). During solidification, the pressure in the AM system may be increased. [0017] The particular halide or gaseous halide species can be selected based on, for example, the metal in the condensate, the AM process parameters, the component being manufactured, or the desired condensate removal level. Instead of I ₂ , other halides like F ₂ , Br ₂ , or Cl ₂ may be used. A mixture of different halides or one or more halides with other gaseous species also may be used. The temperature to melt the solid halide material, condense the gaseous halide material, dissociate the gaseous metal halide compound, heat components in the AM system, or cool components in the AM system may vary based on the vaporization temperature and condensation temperature of the halide, halides, or gas mixture that is used.

[0018] FIG. 3 is a schematic of an embodiment of an AM system 200 using a halide gas. In FIG. 3, the solid arrows represent inert gas and suspended condensate and the dashed arrows represent inert gas with less condensate or even no condensate. By less condensate, the flows represented by the dashed arrows have less condensate than the flows represented by the solid arrows.

[0019] The build chamber 201, where the AM process occurs, is upstream of the filter 202 and circulating fan 204. The build chamber 201 may use, for example, a laser beam or electron beam. Between the build chamber 201 and the filter 202 are valves VI and V4. Between the build chamber 201 and the circulating fan 204 are valves VI and V2.

[0020] Downstream of the circulating fan 204 is the halide vessel 205 and dissociation chamber 206. The dissociation chamber 206 and filter 202 are connected to the build chamber 201 through valve V3 and fan 203.

[0021] The halide vessel 205 is connected to the build chamber 201 and has a halide gas source that is configured to generate a gaseous halide. The halide vessel

205 includes a heating system to raise the temperature of and vaporize a solid halide material. This generates a gaseous halide, such as I ₂ . [0022] The dissociation chamber 206 has a replaceable filament, which may be fabricated of tungsten or other materials. The filament in the dissociation chamber

206 may be placed in a flowpath of the gaseous halide or gaseous metal halide compound.

[0023] The embodiment of FIG. 3 may be used to clean the filter 202. FIG. 4 is a diagram representing a process of using the embodiment of FIG. 3. In step 300, valves VI and V3 are closed and valves V2 and V4 are opened. The filter 202 and halide vessel 205 are heated to vaporize the solid halide material and form a gaseous halide in step 301. The filament in the dissociation chamber 206 is heated in step 302. The gaseous halide is circulated between valve VI and V3. The gaseous halide reacts with the metal condensate to form a gaseous metal halide compound in step 303. The gaseous metal halide compound is circulated to the dissociation chamber 206 and the metal dissociates onto the filament in step 304. There, the metal may collect, coalesce, or otherwise be deposited on the filament. Once the cleaning is finished, the halide vessel 205 is cooled in step 305 to cause the gaseous halide to condense.

Valves VI, V3, and V4 are then opened and valve V2 is closed in step 306.

[0024] To clean the build chamber 201 , either all valves V 1 , V2, V3 , and V4 in FIG. 3 are opened or only valve V4 is closed and valves VI, V2, and V3 are opened. This enables the gaseous halide to circulate to the build chamber 201.

[0025] When the filter 202 is sufficiently cleaned and condensate has been deposited on the filament in the dissociation chamber 206, the halide gas is transported back to the halide vessel 205 to be solidified. The solid halide material can remain in solid form until needed for another cleaning cycle. Other parts of the AM system 200 may be kept at an elevated temperature to prevent or reduce solidification other than in the halide vessel 205.

[0026] The filament in the dissociation chamber 206, which may be a tungsten filament, is periodically replaced. The used filament may be discarded. In the example of titanium condensate, the titanium metal adheres to the filament and is inert in the presence of oxygen. Thus, the filament is safe to handle and dispose of normally.

[0027] FIG. 5 is a schematic of another embodiment of an AM system 400 using a halide gas. In FIG. 5, the solid arrows represent inert gas and suspended condensate and the dashed arrows represent inert gas with less condensate or even no condensate. By less condensate, the flows represented by the dashed arrows have less condensate than the flows represented by the solid arrows.

[0028] The build chamber 401, where the AM process occurs, may use, for example, a laser beam or electron beam. The build chamber 401 is upstream of the filter 402 and circulating fan 404. Between the build chamber 401 and the filter 402 is valve VI . Between the build chamber 401 and the circulating fan 404 is valve V2.

[0029] Downstream of the circulating fan 404 is the halide vessel 405 and dissociation chamber 406. The dissociation chamber 406 and filter 402 are connected to the build chamber 401 through valve V3 and fan 403. The halide vessel 405 may be similar to the halide vessel 205 of FIG. 3. The dissociation chamber 406 may be similar to the dissociation chamber 206 of FIG. 3.

[0030] Downstream of the dissociation chamber 406 between this dissociation chamber 406 and the valve V3 is a heater 407. The gaseous halide may need to remain hot (such as > 350°C) in order for the titanium iodide reaction to occur. The heater 407 helps maintain the gaseous halide at this temperature.

[0031] The heater 407 also may be attached to or disposed in the build chamber 401. Gaseous halide leaving the halide vessel 405 is hot. If the pipes in the AM system 400 are lagged the gaseous halide will remain hot. The build chamber 401 may include the heater 407 to maintain the gaseous halide at the desired temperature.

[0032] The embodiment of FIG. 5 may be used to clean the build chamber

401. FIG. 6 is a diagram representing a process of using the embodiment of FIG. 5. In step 500, valve VI is closed and valves V2 and V3 are opened. The build chamber 401 and halide vessel 405 are heated to vaporize the solid halide material and form a gaseous halide in step 501. The filament in the dissociation chamber 406 is heated in step 502. The gaseous halide is circulated and reacts with the metal condensate to form a gaseous metal halide compound in step 503. The gaseous metal halide compound is circulated to the dissociation chamber 406 and the metal dissociates onto the filament in step 504. There, the metal may collect, coalesce, or otherwise be deposited on the filament. Once the cleaning is finished, the halide vessel 405 is cooled in step 505 to cause the gaseous halide to condense. Valve VI is then opened and valve V2 or valves V2 and V3 are closed in step 506.

[0033] FIG. 7 is a schematic of another embodiment of an AM system 600 using a halide gas. In FIG. 7, the solid arrows represent inert gas and suspended condensate and the dashed arrows represent inert gas with less condensate or even no condensate. By less condensate, the flows represented by the dashed arrows have less condensate than the flows represented by the solid arrows. [0034] The build chamber 601, where the AM process occurs, may use, for example, a laser beam or electron beam. The build chamber 601 is upstream of the filter 602 and circulating fan 604. Downstream of the filter 602 are valves VI, V2, and V3. VI is between the filter 602 and the fan 603. V2 is between the filter 602 and circulating fan 604. V3 is between the heater 607 and the fan 603.

[0035] Downstream of the circulating fan 604 is the halide vessel 605 and dissociation chamber 606. The halide vessel 605 may be similar to the halide vessel 205 of FIG. 3. The dissociation chamber 606 may be similar to the dissociation chamber 206 of FIG. 3. The heater 607 may be similar to the heater 407 in FIG. 5. [0036] The embodiment of FIG. 7 may be used to clean the build chamber 601 and filter 602. FIG. 8 is a diagram representing a process of using the embodiment of FIG. 7. In step 700, valve VI is closed and valves V2 and V3 are opened. The build chamber 601 and halide vessel 605 are heated to vaporize the solid halide material and form a gaseous halide in step 701. The filament in the dissociation chamber 606 is heated in step 702. The gaseous halide is circulated and reacts with the metal condensate to form a gaseous metal halide compound in step 703. The gaseous metal halide compound is circulated to the dissociation chamber 606 and the metal dissociates onto the filament in step 704. There, the metal may collect, coalesce, or otherwise be deposited on the filament. Once the cleaning is finished, the halide vessel 605 is cooled in step 705 to cause the gaseous halide to condense. Valve VI is then opened and valves V2 and V3 are closed in step 706.

[0037] The halide vessel can be located upstream or downstream of the build chamber. In an alternate embodiment, the halide vessel is located upstream of the build chamber and the dissociation chamber is located downstream of the build chamber. Of course, other designs are possible.

[0038] The circuit illustrated in FIG. 3, FIG. 5, or FIG. 7 may be kept at an elevated temperature when the halide gas solidifies in the dissociation chamber 206, 406, or 606. This prevents the solid halide from depositing elsewhere in the AM system 200, 400, or 600. Heaters may be located in the various chambers or gas lines to prevent such solidification. However, the temperature of the gaseous halide may be controlled within a particular range to prevent the gaseous halide from excessively corroding the wall materials.

[0039] The gaseous halide may circulate in the build chamber 201 , 401 , or 601 during the build process or in between steps of the build process. The effect on the component being manufactured or the powder in the build chamber 201, 401, or 601 may be negligible, may be controlled, or may be compensated for.

[0040] In yet another embodiment, electrostatic or other methods known to those skilled in the art may be used to cause the metal halide compound or condensate to converge on a heated wire, such as the filament in the dissociation chamber 206,

406, or 606.

[0041] Condensate that did not react with the gaseous halide may still melt in the dissociation chamber 206, 406, or 606 and form a deposit after the molten metal cools. [0042] The cleaning process disclosed herein may be separate from the build process in the build chamber 201, 401, or 601. The cleaning process also may be used during the build process in the build chamber 201, 401, or 601 if the impact to the component being manufactured is negligible, controlled, or compensated for.

[0043] The cleaning process disclosed herein may be a closed cycle or an open cycle. An open cycle may be possible depending on the nature of the halide and reaction products.

[0044] Components manufactured using an AM process may have a surface with partially- fused or loose powder particles on it. These particles become detached during assembly and use, and may cause subsequent problems during component operation. Such particles may be small and may be of large relative surface area. For example, these particles may be approximately 15 μιη to 45 μιη in dimension. When exposed to the gaseous halide, the particles may be consumed in a reaction and removed from the component. The surface of the component may be rendered free of the loose or partially-attached particles without subsequent bead blasting, HF treatments, or other particle removal steps. Thus, this cleaning process also can be used during or as an additional step to the AM process to clean the component being manufactured. [0045] In an alternate embodiment, a separate cleaning chamber is located in the AM system. This cleaning chamber may be connected to the dissociation chamber and halide vessel. Additional valves and gas lines are used to flow the halide gas to this cleaning chamber. A finished or incomplete part may be moved from the build chamber to the cleaning chamber to remove particles. Instead of a cleaning chamber connected to the AM system, a separate standalone cleaning booth with a dissociation chamber and halide vessel also may be used.

[0046] The safety of an AM process is improved using embodiments disclosed herein due to elimination or reduction of dangerous condensate. Personnel may not need to handle filters contaminated with condensate or clean contaminated build chambers. Manufacturing costs are lowered due to the elimination of hazardous waste materials. The build chamber and transparent window will remain cleaner for a longer period, which will enable longer build times, improve system uptime, and reduce the necessary preventative maintenance. The laser optics will remain cleaner for a longer period, which will provide improved laser beam quality and improved product quality, fidelity, and consistency. Parts produced using the AM process may be cleaner or have fewer undesired particles attached to surfaces. These benefits can be provided without impacting the quality of the components being manufactured using the AM process.

[0047] The following are sample claims that are presented for illustrative purposes and are not intended to be limiting.