Rapid Manufacturing Using Infiltration Selective Laser Sintering

Selective Laser Sintering (SLS) is tooless, computer-controlled layerwise additive manufacturing using a laser and a powder bed. The scanning laser locally melts the surface of a powder bed selectively, followed by deposition of a fresh layer of powder and repetition of the process. SLS has been developed for plastic powder. Creation of non-metallics and metal parts is more challenging. One approach is to mix the master powder with a transient binder. SLS melts the binder which wets the master powder, creating a green part. Subsequent post-processing is required to either remove the binder or convert it to a usable form. The last step is infiltration with a molten substance. Fundamentals of infiltration theory will be reviewed. A study of dimensional changes associated with various stages of processing reveals that overall linear dimensions vary less than one percent compared to the computer solid model. Several examples demonstrating the utility of an infiltration approach to freeform fabrication will be presented. These include silicon carbide with a phenolic binder, infiltrated with silicon; graphite with a phenolic binder infiltrated with epoxy; and tool steel with a proprietary low-ash binder infiltrated with cast iron.