From RP to AM: A Review of Prototyping Methods
Need help sifting through all the additive manufacturing methods available? Unsure of what additive manufacturing is? This review can help.
William Shambley, Viridis3D LLC, Tyngsboro, Massachusetts A
dditive manufac- turing (AM) is the process of joining materials to make objects from 3-D
model data, as outlined by the ASTM International standards committee that oversees the process. Many in the U.S. manufactur- ing economy still think of these technologies as “rapid prototyping” systems, characterized by high cost, low performance methods of creating components generally used for fit-check or communication. But as these technologies have evolved, the applications for objects made by them have expanded. According to industry
ist. Some of the oldest methods fused layers of sheet stock into blocks, carving away the undesired materials on the outside of the part. Current equipment uses a variety of lasers as an energy source to initiate a chemical reaction or selectively melt powdered metals into a dense article. Forming a pool of resin, extruded tape or disparate powder granules into a solid object of any material requires energy. These so- lidification mechanisms are outlined in Fig. 1. Generally, part strength
analyst Terry Wohlers, 41% of the AM parts produced domestically are used either as tooling, patterns or as a functional prototype (15%). In the past several years, the U.S. install base of AM ma- chines has risen steadily, with 1,500 units sold in 2009. The 2010 Wohlers Report indicates that AM service bureaus (typically small contract manufactur- ers or prototyping houses with an assortment of AM and traditional technolo- gies) generated revenues estimated at $537 million in 2009. To help you under-
stand this fast-growing and changing industry, following is an overview of the available AM tech-
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Fig. 1. Shown is a basic overview of the solidification mechanisms used in additive manufacturing. (Note: This figure omits some post- processing steps that can change or improve the original part proper- ties, such as post firing or infiltration with molten metal or resin.)
nologies and how they relate to the metalcasting process.
The Technologies A wide array of AM mechanisms ex-
increases with processing temperature, energy input and degree of consolidation during the process. Part strength typically decreases with the porosity of the final article, though secondary processes, such as infiltra-
tion, can overcome this limitation to some degree. Direct melting of metal powders or filaments into dense parts produces the strongest parts, though at proportional equipment, material and operational costs.
Many in U.S. manufacturing still think of additive manufacturing as “rapid prototyping” systems, characterized by high cost, low performance methods of creating components for fit-check or communication. But as these technologies have evolved, the applications for objects made by them have expanded.
Utility in Metalcasting For utility in metalcast-
ing markets, the production of a metal part must be the end goal of all AM meth- ods. The manner by which the step from solidification mechanism to application in technology is taken can be broken down into two catego- ries—direct part fabrication and indirect part fabrication.
MODERN CASTING / July 2010
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