A Primer on Rapid Manufacturing

Newer Techniques Build Everything from Tools to Hip Implants

May 12, 2009

So-called "rapid" techniques let users build models of products early in the design cycle to cut development costs. Some methods even build finished parts.

The term "rapid" arouse because — unlike conventional manufacturing, in which, say, an injection molding machine makes plastic parts, or a lathe cuts parts from metal bar stock — rapid machines "build" parts directly (i.e., rapidly) from 3D CAD data. Different technologies fall under this moniker, but their underlying principle is similar.

Slicing CAD models

First, special software "slices" a 3D CAD model of a product into thin layers. A build machine imports this data and fabricates the part from proprietary plastics, resins, or metals, layer-by-layer, as dictated by the corresponding CAD slice.

Because rapid technologies build parts directly from CAD data, they are increasingly lumped under the term "direct digital manufacturing (DDM)." One DDM technique is fused deposition modeling (FDM), which produces parts by heating and extruding thermoplastics.

Another technology, sterolithography (SL), uses a laser to cure photo-sensitive resin. Selective laser sintering (SLS) also uses a laser which melts and sinters powdered metal instead of a resin. And a method similar to inkjet printing creates colorful 3D parts by depositing liquid binder onto thin layers of powder.

Electron beam melting

DDM techniques produce parts ranging from prototypes for testing form, fit and function, to tools such as jigs, fixtures, and molds. End-use parts include hearing-aid shells, razor-blade handles, and even aerospace housings. A relatively new method called electron beam melting (EBM) lets designers build components such as hip implants with intricate, latticed structures that facilitate bone ingrowth. Here, e-machines blast electrons at powdered metal such as titanium, melting the material and welding the layers together at the same time.

Denis R. Cormier, associate professor of Industrial and Systems Engineering at North Carolina State Univ. in Raleigh, N.C. and his colleague Ola L. A. Harrysson have explored using EBM to build latticed hip implants. Arcam AB, the Swedish company that builds the e-machines, reports in its Rapid News online publication, "... major factors for orthopedic implants is the implant’s ability to fix itself to the hosting bone, by enabling the bone to grow into it and make the implant almost an integral part of the body." The News describes how an Italian company used EBM to develop an acetabular cup in accordance with European CE standards for medical implants.

As DDM processes get more sophisticated, it's only a matter of time until they are used in surprising applications such as space exploration. For example Cormier and Harrysson have explored ideas such as placing e-machines on Mars in the future to build stuff the astronauts need directly from Martian soil.

The copyright of the article A Primer on Rapid Manufacturing in Manufacture Engineering is owned by Leslie Gordon. Permission to republish A Primer on Rapid Manufacturing in print or online must be granted by the author in writing.