Univ. of Pittsburg School of engineering,www.engrng.pitt/edu
If the recent Rapid 2009 event held in Schaumburg, Ill., is any indication, rapid prototyping has grown up. The term has come to refer to several relatively new manufacturing techniques that build 3D plastic or metal parts, layer-by-layer, directly from CAD data. But rapid prototyping is being supplanted by the moniker “direct digital manufacturing (DDM). ”The Society of Manufacturing Engineers, the event sponsor, is now pushing this as the formal, standard term. In addition, there was a lot of buzz about the recent approval of an official ASTM Committee to create industry standards for DDM.
Several research labs and companies are now using DDM to make lattice structures. Lattices withstand large mechanical stresses while being lighter than solid components. A problem until now has been that traditional CAD cannot handle the huge, complex file sizes these designs entail. German-based Netfabb has developed software with a CAD-like interface called Selective Space Structures for designing lattices. The software lets users combine cell types and automate their distribution with a script module to build what is called a “tree,” an arbitrarily complex lattice. “The size of an STL file for a 3.5-m-tall tree would exceed 1,000 Gbytes. In our software, the file would be just 1.7 Gbytes,” says Netfabb Business Development Manager Ulf Lindhe.
A Swedish company, Arcam, makes machines that use an electron beam to melt metal powder layer by layer to make physical parts including lattices. The technology lets doctors build medical implants with engineered porosities that facilitate bone ingrowth. Using CT-scan data as the basis of designs, users build implants shaped to match a specific patient’s bones out of biocompatible metals such as Ti6Al4V ELI, Ti Grade 2, and cobalt chrome.
Contributions to DDM from Howard A. Kuhn, Adjunct Professor at the Univ. of Pittsburgh School of Engineering involve making implantable scaffolds for medical use. His research team used a magnesium alloy developed by the National Science Foundation that can provide a regenerative rather than a replacement implant. The alloy lattice implant slowly dissolves in the body as new tissue forms. The trace amounts of the magnesium do not harm the body.
EOS, based in Germany, also makes DDM machines, but in this case, the machines laser-sinter powdered metal or plastic to make parts. Laser sintering is useful in dental manufacturing. Previously, porcelain-fused-to-metal crowns were made using traditional lost-wax casting. The advent of dental CAM/CAM software did nothing to improve this process because CNC is inefficient and costly in the machining of the crowns. Laser sintering, however, lets dental labs make metal copings directly from CAD data, which speeds designs and cuts costs.