February 2023 Volume 5

FORGING RESEARCH

Fabrication of Forging Preforms via Additive Manufacturing Methods By James Elder1, David Schwam 1 , Kevin Seidel 2 , and Tushar Borkar 1 , * 1 Mechanical Engineering Department, Cleveland State University, Cleveland, Ohio, 44115 2 Canton Drop Forge, Canton, Ohio, 44706

Forging is a traditional manufacturing method that uses a series of dies to gradually change a piece of heated metal to a final desired shape and size. Manufacturing custom set dies specific to part shape and size is very expensive and takes a long time. The Binder Jet printer is an example of a relatively new form of additive manufacturing process with a variety of materials including metals, ceramics, and glass. In this investigation, the binder jet process has been used to print blocks of Stainless Steel 316 which were then sintered and forged. This is to provide a proof of concept for printing a part further along the die forging path as to require fewer dies and cut down forging cost significantly. The Binder Jet process is a type of additive manufacturing process that uses ink-jet technology to print a binder onto powder layer by layer. This type of printer has many advantages over other additive manufacturing processes, such as cost effectiveness, material recyclability, material versatility, controllable porosity, etc.1 Using low heat printing means less material waste, as the support powder does not deform and can be reused at much higher rate than that of sintering printers that use either laser or electron beam as a thermal source for inducing fusion between metallic powder particles 1,2 . The part will still be sintered at a later stage in the process and thus will not compromise the integrity of the rest of the powder or future prints. Also, during printing, the Binder Jet uses significantly less power than other metal printers thus increasing the cost effectiveness1. Another major advantage of this printer is its versatility with many materials. Any powder, including ceramics and metals, can be bound together using this method and post processing of the green parts can be tailored depending on the material used 3,4,5 . As with most additive manufacturing methods, this printer is great for complex shapes and especially prototyping of new parts 1,7 . For this project, themaximumbuild volume for the ExOne Innovent Printer was used to make the block of size, 160 x 65 x 65 mm (Figure 1 (a)). The printed blocks were sent to Canton Drop Forge to be preheated and compressed using open dies and a hydraulic press. Open dies were selected at this stage in order to gain a proof of concept as there was a possibility that even with the preheating, the blocks would fall apart easily. The blocks were preheated to 2160 F

for a few hours. This is a fairly standard process for solid blocks of stainless steel of this size. During the heating and forging process, large cracks formed but the center of the blocks densified proving the blocks would not disintegrate. The first block was compressed in the same orientation that the part was printed as to ‘compress the layers’ (Figure 1(b)). The second block was first compressed in this same direction as well as against the layers; 90° from the first compression (Figure 1(c)). A vacuum sintered sample was also used to compare with these forged samples.

Figure 1 (a)

(b) Z-Axis compression (c) Z+X-Axes Compression Figure 2(a) shows SEM images of vacuum sintered samples exhibiting highest density and little to no oxidation compared to that of forged samples. This is largely due to the open atmosphere heating. The Z+X-Axes (Figure 2 (c)) sample shows slightly higher density than the Z-Axis forged sample (Figure 2 (b)) but still relatively high porosity with oxidation in the pores. Another interesting fact is the forged parts, aside from the major pores, had

FIA MAGAZINE | FEBRUARY 2023 74