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for the manufacturing method and/or secondary machining. “Additive manufacturing can


The prosthetic arm produced by the binder jetting process reduced part count and weight.


be game-changing for future engine programs and designs.”


Alternative Approaches


Tough powder bed fusion is the most utilized process, a variety of 3-D-printing methods using metal are on the market. One alternative is directed energy deposition, which deposits wire or powder into thin layers that are then melted using an energy source. Unlike powder bed fusion, though, directed energy deposi- tion often requires additional process- ing to improve surface finish. Binder-based jetting systems is


another 3-D-printing process, which is similar to techniques already familiar to metalcasters in the production of cores and molds. Te process features a print head selectively spraying a binder solution over a metal powder bed. Te layer is dried with a heating lamp and then a new layer of powder is spread on top. Tis process repeats until the object is fully formed. Te object is carefully removed from the non-bonded metal powder and placed in an oven to fully cure the binder. Te fragile part then is placed in a kiln where it’s infused with bronze powder to create a highly solid metal matrix component. “Really what we print is a matrix,


instead of an alloy,” said Bernie Potts, sales manager, ExOne, Troy, Michi- gan. “For example, it could be 60% stainless steel with 40% bronze infil- trated into it. Using this process, we’re able to produce components with 97 or 98% density.” The capabilities of a binder jet-


ting system can be seen in a case study featuring a medical prosthetics manufacturer looking to improve


48 | MODERN CASTING May 2015


production of a component used in a prosthetic hand. It was looking for alternatives for what had been parts produced via investment cast- ing. The components printed in a stainless steel/bronze matrix reduced weight and integrated multiple pieces into a single assembly. Direct metal printing more than halved lead times, from as long as eight weeks to two or three, while the cost per part dropped from $250-$1,500 to $25-$150. Laser powder forming is an addi-


tive manufacturing technology that uses a metal powder injected into a molten pool created by a high power laser beam. Te process can go from metal and


metal oxide powder to metal parts, in many cases without any secondary operations. Metal powder is applied only where material is being added to the part at that moment and has primary applications in repair and overhaul, rapid prototyping, rapid manufacturing, and limited-run manufacturing for aerospace, defense, and medical markets. Te technology covers several


alloys, including titanium, stainless steel, aluminum, and other specialty materials. Mechanical testing reveals outstanding as-fabricated mechanical properties Tis process holds oppor- tunities for die and tooling repair.


Competing Considerations


Te design freedoms associated with building something layer by layer is the biggest advantage of additive manufacturing. Cavities, internal pas- sages and other complex features can be designed directly into the compo- nent, without as much consideration


resolve a lot of constraints in tradi- tional manufacturing,” said Andrew Snow, senior VP, EOS of North America Inc. “You can reduce part numbers through design, you can reduce weight by getting rid of unnecessary material, you can produce fully customized parts for on-demand-type applications.” Additionally, 3-D-printed metal


components do not require gating or risers and can be produced without upfront investments in tooling. If a small number of parts are needed quickly, they can be printed and shipped in a matter of days, thanks to a reduction in up-front work necessary to manufacture the part. “In direct metal printing, you don’t


have to worry about designing gating and risering. You are just printing the part,” Potts said. “If you’re going to pour metal into a mold, you have to go through quite a bit of engineering to make sure you’ll get a sound casting. But with metal printing, you don’t really have that early work.” While engineers are afforded


design freedoms not seen in other manufacturing processes, includ- ing metalcasting, production speeds have hampered the technology’s ability to produce large amounts of components in a relatively short time. The sheer time needed to build a metal part layer-by-layer is the biggest driver of cost. “Te two major cost drivers solely


in printing parts—not post machining, heat treating, etc.—are materials and machine costs. Materials are a factor, but a relatively small one. What the cost really comes from is the time to run the machine.” A component’s design can improve


efficiency; by decreasing a build’s height, the 3-D printer can complete the layering process more quickly. But the technology is not at a point where it can produce production parts in the hundreds or thousands. It has been a commercially viable short-run production method for a half-decade, but larger volumes will require faster


Photos courtesy of ExOne


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