WO2017029276A1

WO2017029276A1 - Methods of additive manufacturing using chemical removal of support structure

Info

Publication number: WO2017029276A1
Application number: PCT/EP2016/069398
Authority: WO
Inventors: Scott LATHROPE; Matthew SCOVELL; David SKOLNIK
Original assignee: Meggitt Aerospace Ltd
Current assignee: Meggitt Aerospace Ltd
Priority date: 2015-08-14
Filing date: 2016-08-16
Publication date: 2017-02-23
Anticipated expiration: 2018-02-14

Abstract

A process of creating a metal part using additive manufacture is provided. In preferred embodiment, the process comprises: using additive manufacture to manufacture a metal part with a first element and a second element; using additive manufacture to manufacture one or more metal support structures that couple the first element to the second element; and using a chemical process to remove the one or more metal support structures.

Description

METHODS OF ADDITIVE MANUFACTURING USING CHEMICAL REMOVAL OF

SUPPORT STRUCTURE

FIELD

The present patent document relates to methods for additive manufacturing. More particularly, the present patent document relates to methods of additive manufacturing using chemical removal of support structure.

BACKGROUND

In Selective Laser Sintering (SLS) with plastics, there are no limitations to structures. In SLS with plastics, the final product does not warp substantially and the solidified material does not sink in the powder bed. Consequently, supports are typically not required. However, when using metal as the material in the additive process instead of other materials like plastic or resin, support structures may be needed. Some typical design rules for internal structures in additive manufacturing require that any diameter in excess of 0.25" be supported and that any surface which is less than 45^° to the horizontal be supported. To this end, in metal additive manufacturing, support structure is often used. In many cases where the support structure is required, the support structure may be extremely difficult or impossible to remove. Once a surface is inside a structure and mechanically inaccessible, these design rules become a limiting factor on design. It would be helpful to have a process that would allow these internal structures to still be used in designs, thus opening up a wider range of design possibilities and taking full advantage of the capabilities of the additive manufacturing processes. SUMMARY

One object of the embodiments described herein is to alleviate or mitigate the difficulties in removing support structures in additive manufacturing of metal parts. The processes described herein accomplish this through the use of chemical and electrochemical processes. Accordingly, processes of creating a metal part using additive manufacture are provided. In a preferred embodiment, the process includes: using additive manufacture to manufacture a metal part with a first element and a second element; using additive manufacture to manufacture one or more metal support structures that couple the first element to the second element; and using a chemical process to remove the one or more metal support structures.

While the processes used herein can be used with any material, preferably the processes are for use with metal and the first element, second element and support structure of the part are all made of metal.

The embodiments described herein may be used with various different chemical process. In some embodiments, the chemical process is an electro-chemical process such as electro-polishing. If an electro-chemical process is used, nitric acid may be preferably used. If nitric acid is used and the support structures are around 0.025 inches, the part may be electro-chemically polished for around 75 minutes.

In some embodiments, the part and support structure are both made from a material that may be electro-polished. In some embodiments, stainless steel is used. In some of those embodiments, the stainless steel may be selected from the group consisting of 15-5 stainless steel and 17-4 stainless steel. In yet other embodiments, the part and support structure may be made from Inconel. In some of those embodiments, the Inconel is Inconel 718 or Inconel 625.

The purpose of the support structure is to support the second element 12. In some embodiments, the support structure rigidly attaches the first element to the second element.

Any number of support structures may be used throughout the part and any number of support structures may be used for a single element of a part. In most embodiments, a plurality of support structures are used for supporting one element and a plurality of support structures are used throughout the part. In some embodiments, 10 or more support structures may be used to support a single element of a part.

The support structures may be any shape. Ideally, the shape of the support structures may be selected to maximize the effect of the chemical process on the support structures. In some embodiments, the support structures are a cylinder with a diameter of approximately 0.025 inches.

In order to help prevent bumps being left behind after the support structures are removed, in some embodiments, the support structure has a hollow volume at each base.

In yet other embodiments, a chemical process that attacks all the surfaces of a part uniformly may be used. In such embodiments, hydrochloric acid may be used to remove the support structures. In some embodiments, the dimensions of the part are increased to form a tolerance adjustment layer. The tolerance adjustment layer is removed by the chemical process. This is preferably used when the chemical process uses hydrochloric acid or other chemicals that attack all portions of the part evenly but is not limited to any particular chemical or process. In particular, a tolerance adjustment layer may be useful in holding a tighter tolerance on certain elements of the part or the entire part.

In some embodiments, the first element and the second element of the part are made of a first metal, and the one or more metal support structures are made from a second metal, which is different from the first metal. The second metal is designed to be more easily removed by the chemical or electro-chemical process and particularly, electro- polishing. In yet other embodiments, the support structures may be made from a non- metal, such as plastic for example, while the part is made from metal.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates an embodiment of a part made of a first element and a second element wherein the second element is supported by at least one support structure.

Figure 2 illustrates the part of Fig. 1 with a tolerance adjustment layer surrounding the first and second elements.

Figures 3A-3C illustrates time lapse images showing a plurality of support structures being removed from a part.

Figure 4A illustrates a cross-section of one embodiment of a support structure with hollow cylindrical volume at its base.

Figure 4B illustrates a cross-section of another embodiment of a support structure with hollow cylindrical volume at its base.

DETAILED DESCRIPTION OF THE EMBODIMENTS Additive manufacturing, also known as three-dimensional printing, can make extremely complex parts. Depending on the material used in the additive manufacturing process, support structures may be required. The embodiments described herein use chemical and electro-chemical processes to dissolve and remove those support structures. Chemical and electro-chemical process have the ability to dissolve and remove small structures on immersed parts when the chemistry is aligned to the part material.

The embodiments described herein alleviate or mitigate the difficulties in removing the support structures in additive manufacturing parts through the use of chemical and electro-chemical processes. Consequently, the embodiments described herein open up the design process to many more possibilities. In many embodiments, the processes may be used with parts that have support structures in complex and inaccessible structures within an additive structure. The use of chemical and electrochemical processes to remove support structures in parts made using the additive manufacturing process opens up the possibility of building more complicated parts. As examples, both internal structures which are otherwise not possible as well as relative motion structures may be created.

Figure 1 illustrates an embodiment of a part 5 made of a first element 10 and a second element 12 wherein the second element 12 is supported by at least one support structure 14. The part may be any part a client is desirous of manufacturing. As is known in the additive manufacturing process, the part 5 may be made of many different materials including, metals, plastics and resins, to name a few.

As may be seen in Fig. 1 , the part 5 may be comprised of a number of elements 10 and 12. Although only two elements are shown in the part of Fig. 1 , any number of elements may be present. An "element" of the part 5 is any portion of the part 5 that is intended to be a permanent portion of the part. As may also be seen, a first element 12 may be supported by at least one support structure 14 to a second element 10. In the embodiment shown in Fig. 1 , two support structures 14 are used but in other embodiments any number of support structures may be used. In most embodiments, a plurality of support structures 14 will be used to support a single element. However, any number of support structures 14 may be used to support a single element including only one support structure 14. In some embodiments, a minimum of 10 support structures may be used to support a single element. In other embodiments, 20, 30 or even more support structures may be used.

A support structure 14 is any portion of the part that is not intended to be permanent and attaches a first element 12 of the part 5 to a second element 10 of the part 5. The purpose of the support structure 14 is as the name implies, to support a first element 12 during the additive manufacturing process. These support structures 14 are often small but may be any size.

As may be seen in Fig. 1 , the support structure 14 is formed like a truss between the first element 12 and the second element 10. Preferably, the support structures 14 have a circular cross-section. The circular cross-section allows the support structure 14 to be more easily and uniformly dissolved during the latter part of the process, as explained below. However, in other embodiments the support structures 14 may have other shapes for their cross-section including, oval, square, rectangle, hexagon octagon, triangle and others. In some embodiments, the cross-section may vary along the length of the support structure 14. As just one example, the support structure 14 may be thinner at each end and thicker in the middle. In yet other embodiments, the support structure 14 may be thicker at the ends and thinner in the middle.

In preferred embodiments, the supports have a cross-section that is approximately 0.025 inches across. To this end, the support structures have a thickness of approximately 0.025 inches. In other embodiments, the support structures may be thinner or thicker and may range from approximately 0.01 inches to 0.1 inches. In embodiments where the cross-section is a circle, the thicknesses listed above are equal to the diameter of the support structure 14.

In preferred embodiments, the support structures 14 are significantly smaller than the elements 10 and 12 of the part. In particular, the support structures 14 are significantly thinner than other elements of the part. This allows the dissolving process to work more effectively on the support structure while not ruining the part. In preferred embodiments, the thickness of the thinnest portion of the part 5 is five times the thickness of the support structure 14. In other embodiments, the thinnest portion of the part 5 is ten times, twenty times, or even thirty times the thickness of the support structure 14.

The processes described herein are designed for use with Additive Manufacturing (AM). Additive manufacturing includes all types of manufacturing where parts are grown or printed including selective laser sintering (SLS), direct metal laser sintering (DMLS), Electron Beam Melting (EBM), and selective laser melting (SLM), to name a few. As is known, AM is an umbrella term to collectively describe all such processes. In a preferred embodiment, a model of a part 5 is designed for additive manufacturing. The part 5 has a first element 12 and second element 10 that are connected by at least one support structure 14. In the next step, the part 5 is manufactured using an additive manufacturing process. Finally, the part 5 is put through a chemical or electrochemical processes to remove the support structures 14.

In preferred embodiments, the support structure 14 rigidly attaches the first element 12 to the second element 10. In such embodiments, the support structure physically attaches directly to the first element 12 and the second element 10. This allows the support structure 14 to mechanically support the first element 12 during the manufacturing phase of the process. However, in some embodiments, the support structure 14 may more loosely couple the first element 12 to the second element 10 as long as mechanical support is provided. Although this application is not limited to any particular metal, chemical or combination thereof, the following may be used by way of example. For metals like 15-5 stainless steel, standard electro-polishing using nitric acid works well. A similar process may be used on 17-4 stainless steel as the non-chrome and nickel elements are identical. Other material like Inconel 718 may also be used, however, Inconel 718 may not work in the standard nitric acid electro-polishing bath. Inconel 718 can be electro-polished, but the process is different from that for stainless steels. Accordingly, it is important to align the chemistry to the material.

Certain materials respond to certain acids in an electro-polish bath. Electro-polish will tend to attack the supports more than the surrounding material because the process erodes material particularly where charge accumulates. As the supports are small and pointed, charge will accumulate. When the support initially severs from erosion, the two points attract even more charge, and the remaining support is rapidly removed. Although the main structure may lose some material, as compared to the support structures 14, the loss is minimal. In embodiments where the support structures 14 are approximately 0.025", the process may require approximately 75 minutes of electro- polishing time to remove. If the support structures 14 are thicker than 0.025 inches, a longer electro-chemical process may be used. Similarly, if the support structures 14 are thinner than 0.025 inches, a shorter electro-chemical process may be used. The correlation between the chemical process time and the thickness is not necessarily linear such that if the support structures thickness is doubled, the processing time more than doubles.

In another embodiment, a highly concentrated hydrochloric acid may be used. Hydrochloric acid attacks all surfaces evenly and relatively aggressively as compared to electro-polishing. For embodiments using a hydrochloric acid, the processing time may be reduced, but the part would have to be oversized to allow degradation of the part as well. For embodiments using hydrochloric acid, the processing times are more critical and a post-process neutralization is required. One benefit of hydrochloric acid is that it attacks many materials and may therefore be used with just about any part material. In yet another embodiment, hydrochloric acid may be pumped through internal channels to remove material. To this end, the part may have specific structures such as channels designed to facilitate the application of the chemicals to specific support structure within the part.

Fig. 2 illustrates the part of Fig. 1 with a tolerance adjustment layer 13 surrounding the first and second elements 10 and 12. The tolerance adjustment layer 13 increases the thickness of the parts such that when the chemical or electro-chemical process is performed, the dimensions of the parts finish within their desired dimensions and tolerances. In most embodiments, the tolerance adjustment layer 13 is not a separate layer but rather an increase in the dimensions of the part. The increase in dimensions creates the extra material that will then be removed by the chemical or electro-chemical process used to remove the support structure 14. The tolerance adjustment layer 13 may be added to all dimensions of the part or only to certain dimensions. As explained above, the tolerance adjustment layer may be especially beneficial when the chemical or electro-chemical process attacks all surfaces uniformly, like with hydrochloric acid. However, where very tight tolerances are needed, the tolerance adjustment layer 13 may be used with any process and on any portion of the part.

In a preferred embodiment, the chemicals used are aligned to the part material. As explained above, this means that the chemicals and chemical processes are chosen based on the material that needs to be removed. Stainless steel may use a different process from Inconel and other materials may use yet other chemicals and chemical processes. Although by no means exhaustive, Table 1 below illustrates some materials and chemical combinations that may be used together in an electro-polishing process. These are just possible choices and others may be possible including combinations of the chemicals listed in Table 1 or solutions using the chemicals listed as ingredients. The 2013/2014 Universal Metal Finishing Guidebook, which is hereby incorporated by reference in its entirety, lists a number of metals and chemicals for electro-polishing those metals. A digital copy of the 2013/2014 Universal Metal Finishing Guidebook, may be found at: http://metalfinishing.epubxp.eom/t/12238-metal- finishing-guide-book

Stainless Steel 15-5 Nitric Acid, Sulfuric Acid, Phosphoric Acid, Citric Acid, Glycolic

Acid

Stainless Steel 17-4 Nitric Acid, Sulfuric Acid, Phosphoric Acid, Citric Acid, Glycolic

Acid

Stainless Steel 316L Nitric Acid, Sulfuric Acid, Phosphoric Acid, Citric Acid, Glycolic

Acid

Aluminum and Alloys Fluoboric Acid, Sulfuric Acid, Chromic Acid

Copper and Alloys Chromic acid, Acetic Acid, Sulfuric Acid, Boric Acid

Nickel and Alloys Nitric Acid, Sulfuric Acid, Chromic Acid, Ammonium sulfate, including Inconel 625 Potassium Chloride

and 718 Titanium Alloys Hydrofluoric acid, perchloric acid

Table 1.

In some embodiments, the support structures 14 may be made from a different material than the material used for the actual part 5. The material for the support structure 14 may be designed to be more susceptible to removal by the chemical process than the material used to make the part. Accordingly, the support structures 14 can be more easily removed by the chemical or electro-chemical process. For example, the part 5 may be made from Inconel 718 while the support structures 14 are made from a metal much more easily removed by a chemical bath or electro-polishing such as Stainless Steel 17-4. The materials chose for the part 5 and the support structures 14 are specific to the chemicals chosen for removal of the support structures.

In embodiments where a separate material is selected, the system may use two different hoppers, wire extruders, or laser blown powder heads to select material from. This allows the additive process to use one material for the part 5 and a second material for the support structure 14. In dual hopper systems, the system lays down different powder materials from each hopper based on the build location. In a dual extruder system, two multi-axis extruders melt two different material wires and deposit the liquid to solidify in discrete locations. In systems with dual laser-blown powder heads, two multi-axis lasers are used and a different powdered material may be blown through each one. One laser head would create the part structure and the other laser head would be used to create the support structures.

In some embodiments, although the material used for the support structures 14 may include the same material as the part 5, the properties of the material used for the support structure 14 may be altered in order to make it more easily removed using a chemical or electro-chemical process. For example, a filler may be mixed with the material used for the support structures 14. The filler that is mixed with the material used for the support structures 14 is designed to make the support structures 14 more susceptible to removal during the chemical or electro-chemical process. For example, small plastic particles or other small impurities may be mixed into the metal. These small impurities create imperfections in the support structures 14. Not only are the imperfections very quickly removed using the chemical process but once removed, the voids created by the removal of the impurities leave imperfections. These imperfections in the support structures 14 cause processes like electro-polishing to more aggressively attack the support structures 14 and thus, remove them more easily. In yet other embodiments, the support structures 14 may be made from a non-metal while the rest of the part 5 is made from metal. This allows the support structures 14 to be removed by choosing a chemical that attacks the non-metal support structures 14 while leaving the metal part 5 unharmed.

In yet other embodiments, although the support structure 14 and the part 5 are made from the same material, the integrity of the support structures 14 is purposely affected during the additive manufacturing process. For example, during the sintering process, the support structures 14 may not receive the same level of laser hardening such that their final state is different from the portions that comprise the part 5. Although sintering is used as an example here, the same process may be used for any type of additive manufacturing of metal. The key is that during the additive manufacturing process, the portions of material that will end up comprising support structures 14 are not hardened/cured to the same extent as the portions that will comprise the part 5. To this end, the support structures 14 are weaker and more easily removed by a chemical or electro-chemical process.

In some embodiments, the melt pool is controlled such that the support structure material is more easily removed via the chemical process than the material used for the structure of the part. To this end, the part material is melted while the material for the support structure is not. When building the actual portions of the part, the temperature is increased to melt the higher melting point material or to create an allow between two different materials. This technique also allows the manufacture of alloyed metal additive layered manufactured parts.

Figures 3A-3C illustrate time lapse images showing a plurality of support structures being removed from a part 5. As may be seen in figure 3A, the part 5 consists of a spiraling outer portion and each rung of the spiral is supported by a plurality of support structures 14. The first image on the left, Fig. 3A, shows the part 5 directly from the additive manufacturing process. As may be seen, the part 5 has many support structures 14. The middle image, Fig. 3B, shows the part after chemical/electro- chemical processing for 45 minutes. As may be seen, much of the support structures 14 are completely removed but very thin remnants remain. Only small nubs may remain where the support structures used to connect to the parts elements. Finally, the far right image, Fig. 3C, shows the same part 5 once the chemical/electro-chemical processing has completed and a satisfactory amount of the support structures 14 have been removed. In the final image of the embodiment shown in Fig. 3C, the part was processed for 75 minutes.

In preferred embodiments, the entire support structure is gone once the process is complete. However, in some embodiments, small remnants may remain. In order to make sure the entire support structure is removed, the support structure may be specially designed. For example, in some embodiments, hollow volumes may be left in the material at the base of each pin. Fig. 4A and 4B illustrate a cross-section of the interface between the base of a support structure 14 and an element of a part 10 or 12. As may be seen in Fig. 4A and 4B, hollow volumes 15 may be formed in the base of the support structure 14 to ensure the support structures may be completely removed and "nubs" are not left behind. As may be seen in Figs. 4A and 4B, the hollow volumes 15 are preferably shaped like a cylinder or a cone. However, in other embodiments, other shapes for the hollow volumes may be used. In yet other embodiments, other designs may be used to help facilitate the chemical removal of the support structures. Although the embodiments have been described with reference to preferred configurations and specific examples, it will readily be appreciated by those skilled in the art that many modifications and adaptations of the processes and methods described herein are possible without departure from the spirit and scope of the teachings herein. Thus, it is to be clearly understood that this description is made only by way of example and not as a limitation on the scope of the embodiments.

Claims

CLAIMS What is claimed is:

1. A process of creating a metal part using additive manufacture comprising:

using additive manufacture to manufacture a metal part with a first element and a second element;

using additive manufacture to manufacture one or more metal support structures that couple the first element to the second element; and using a chemical process to remove the one or more metal support structures.

The process of claim 1 , wherein the part and one or more metal support structures are made from stainless steel and electro-polishing is used to remove the one or more metal support structures.

The process of claim 2, wherein the stainless steel is selected from the group consisting of 15-5 stainless steel and 17-4 stainless steel and nitric acid is used to electro-polish the stainless steel.

The process of claim 1 , wherein the part and the one or more metal support structures are made from Inconel and electro-polishing is used to remove the one or more metal support structures.

The process of claim 4, wherein the Inconel is selected from the group consisting of Inconel 625 and Inconel 718 and nitric acid is used to electro- polish the Inconel.

The process of claim 1 , wherein the one or more metal support structures rigidly attach the first element to the second element.

The process of claim 1 , wherein the one or more metal support structures is a plurality of support structures.

The process of claim 7, wherein the plurality of support structures is 10 or more.

The process of claim 1 , wherein the one or more metal support structures is a cylinder with a diameter of approximately 0.025 inches.

The process of claim 1 , wherein the one or more metal support structures has a hollow volume at each base.

The process of claim 3, wherein the part is electro-polished with nitric acid for approximately 75 minutes.

The process of claim 1 , wherein a chemical process using hydrochloric acid is used to remove the one or more metal support structures.

The process of claim 12, wherein a plurality of dimensions of the part are increased to form a tolerance adjustment layer.

The process of claim 13, wherein the tolerance adjustment layer is removed by the chemical process using hydrochloric acid.

The process of claim 1 , wherein the first element and the second element are made of a first metal, and the one or more metal support structures are made from a second metal, which is different from the first metal.

A process of creating a metal part using additive manufacture comprising:

using additive manufacture to manufacture one or more metal support structures that mechanically attach the first element to the second element; and

removing the one or more metal support structures by electro-polishing the metal part with nitric acid for approximately 75 minutes.

17. The process of claim 16, wherein the metal part and each of the one or more metal support structures are made from stainless steel selected from the group consisting of 15-5 stainless steel and 17-4 stainless steel.

18. The process of claim 16, wherein the metal part and each of the one or more metal support structures are both made from Inconel selected from the group consisting of Inconel 625 and Inconel 718.

19. The process of claim 16, wherein the one or more metal support structures is a plurality of support structures.

20. The process of claim 16, wherein the one or more metal support structures has a width of approximately 0.025 inches.

21. The process of claim 19, wherein the one or more metal support structures is a cylinder with a diameter of approximately 0.025 inches.

22. The process of claim 16, wherein the one or more metal support structures has a hollow volume at each base.

23. The process of claim 16, wherein the first element and the second element are made of a first metal, and the one or more metal support structures are made from a second metal, which is different from the first metal.