1 6 A D V A N C E D M A T E R I A L S & P R O C E S S E S | O C T O B E R 2 0 2 2 wall approximately four times higher than its MIM counterpart. On average, the vertical “layered” wall will have a surface roughness of 125 Ra while the “flat” wall will have a surface roughness of 70 Ra. As with MIM, surface treatments can improve the finish of binder jet 3D-printed components. ALLOY DEVELOPMENT Binder jet 3D printing development has accelerated during the past few years. With strong interest in the technology, various research and com- mercial groups are evaluating a wide range of alloys. These alloys are typically produced by gas atomization, which is also used to produce MIM powders. The alloys must be processed in the same sintering equipment as MIM alloys. Thus, if the alloy can be processed by binder jet 3D printing, it can be metal injection molded. 3D printing can be used as a test environment for alloy development that will help grow the MIM industry and lower the price of raw materials. BRIDGING THE DEVELOPMENT GAP Binder jetting is a natural extension of metal injection molding as both processes use many of the same materials and equipment. Binder jet 3D metal printing is the ultimate bridge between prototype and production MIM parts. Metal 3D printing affords speed and design flexibility at a fraction of the cost of MIM, and can save thousands of dollars in tooling costs when bringing any complex, high-volume part to full production. 3D printing used in conjunction with MIM not only saves time and money, but also reduces the risk of faulty parts by serving as a flexible tool for making adjustments when and where required during development. ~AM&P For more information: Nick Eidem, director of business development, Advanced Powder Products Inc., 301 Enter- prise Dr., Philipsburg, PA 16866, 814. 342.5898 ext. 128, neidem@4-app.com. obtain a Cp greater than 1.33, a tolerance of +/- 0.75% to 1% must be used. To improve tolerances, 3D-printed parts are often coined or machined to ensure assembly functionality. SURFACE FINISH The distinct difference between a MIM component and a binder jet 3D-printed component is surface finish. The surface finish of a MIM part is determined by the particle size of the powder and the sintering process and therefore is highly controllable. Without secondary processing, a MIM part can achieve an average surface finish or 32-40 Ra. The surface finish can be improved through a secondary process such as chemically aided vi- bratory surface treatment (such as REM) or electropolishing. Due to the nature of the stereolithographic layered printing process described above, 3D metal printed components have a higher surface roughness than MIM compo- nents. Further, 3D- printed components exhibit a surface finish disparity between the vertical side showing the layers and the top and bottom of the part. In the as-printed state, a 3D-printed component has a surface roughness of the vertical The shrinkage of a MIM component is controlled by custom tooling that is oversized to match the feedstock formulation. It is expected that a MIM part will shrink isotopically toward the center of gravity, although this is not always the case. The dimensional capability of binder jet 3D printing differs slightly when compared to MIM components. Just like a MIM component, a 3D-printed component is scaled approximately 20% larger to account for binder removal and sintering shrinkage. However, with binder jet 3D printing, a 3D-printed component may shrink differently on the x-y plane than on the z plane. To TABLE 2 — ALLOY PROPERTY COMPARISON Process Density, g/cc Hardness, HRC YS 0.2%, ksi UTS, ksi Elongation, % MPIF Standard 35 7.5 38-42 158 172 6 MIM 7.60 41 163.0 179.6 14 Printalloy 7.60 38.5 160.7 180.6 10.3
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