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
model data, as outlined by the ASTM International standards committee that oversees the process. Many in the U.S. manufacturing economy still think of these technologies as “rapid prototyping” systems, characterized by high-cost, low-performance methods of creating components used for fi t-check or communica- tion. But as the technology has evolved, the applications for objects made by it has expanded. According to industry analyst Terry Wohlers, 41% of the
A
dditive manufac- turing (AM) is the process of joining materials to make objects from 3-D
Many in U.S. manufacturing think of additive manufacturing as “rapid
prototyping,” characterized by high cost, low performance methods of
creating components for fi t-check or communication. But the applications for the technologies have expanded.
any material requires energy. These solidifi cation mechanisms are outlined in Fig. 1. Generally, part strength in-
creases with processing temper- ature, energy input and degree of consolidation during the pro- cess. Part strength typically de- creases with the porosity of the fi nal article, though secondary processes, such as infi ltration, can overcome this limitation to some degree. Direct melting of metal powders or fi laments into
dense parts produces the strongest parts, though at proportional equipment, material and operational costs.
AM parts produced domestically are used either as tooling, patterns or as a functional prototype (15%). In the past sev- eral years, the U.S. base of installed AM machines has risen steadily, with 1,500 units sold in 2009. The 2010 Wohlers Report indicates that AM service bureaus (typically small contract manufacturers or prototyping houses with an assort- ment of AM and traditional technologies) generated revenues estimated at $537 million in 2009. To help you understand this fast-growing and changing
industry, following is an overview of the available AM tech- nologies and how they relate to the metalcasting process.
The Technologies A wide array of AM mecha-
nisms exist. 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 met- als into a dense article. Forming a pool of resin, ex-
truded tape or disparate powder granules into a solid object of
Utility in Metalcasting For utility in metalcasting markets, the production of a
metal part must be the end goal of all AM methods. The manner by which the step from solidifi cation mechanism to application in technology is taken can be broken down into two separate categories—direct part fabrication and indirect part fabrication.
Direct Part Fabrication Direct part fabrication involves the creation of a metal
Additive manufacturing involves the fusing of materials layer by layer to form a solid object. Here, a component is created in the stereolithography process, which uses a laser to convert a liquid resin into a polymeric object.
34 METAL CASTING DESIGN AND PURCHASING
part from powder or fi lament feed by melting or sintering material via a point energy source, typically a laser. Some of these technologies can be used to repair or “re-grow” a metal part (e.g. replacing a broken tip from a fan blade). Direct metal parts do not necessarily have the full prop- erties of cast metal, but they can be created quickly, with- out tools or setup. They also can be used in many cases as tooling for molding tech- nologies. Depending on the required properties for the ap- plication, these parts often can have functional uses, some of which are in medical implants,
JULY/AUGUST 2010
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