Study of the selective laser sintering of metal-polymer powders

Selective Laser Sintering (SLS) is a novel prototyping technique for the manufacture of three dimensional solid objects directly from a computer model without part specific tooling or human intervention. This process uses a laser and thermally fusible polymers for part manufacture. The objective of this work was to advance the capability of SLS for the manufacture of metal parts using a thermoplastic binder and develop post-processing techniques to produce functional composite parts from "green" metal-polymer SLS parts.; Polymethylmethacrylate (PMMA) and copolymers of methylmethacrylate (MMA) and butylmethacrylate (BMA) were used as the thermoplastic binders for metal powder in SLS. Copper and iron were the two metal powers studied in this work. Raw powder for SLS was prepared either by mixing metal powder with polymer binder in the desired proportion or by coating the metal powder with a polymer emulsion using a spray dryer. SLS green parts made from coated powders were found to yield higher strengths than those made from mixed powders at the same polymer content. The effects of Energy Density (i.e., the energy per unit area) during laser processing, of vector length (i.e., the length of a scan vector during laser scanning of a part), of bed temperature, of polymer Melt Index, and of initial binder content on part strength and density were studied. The green part strengths and densities were found to increase with Energy Density up to a value of 6.0 cal/cm{dollar}sp2{dollar} and to decrease thereafter due to polymer degradation. Parts made with lower vector lengths yielded higher strengths and densities than those with higher vector lengths. Parts processed with a low Melt Index polymer binder (around 6.0 g/10min) showed higher strengths than parts processed with higher Melt Index binders. High strength values were obtained for green parts made from powders that had a greater initial binder content. Bed temperature did not have a significant effect on part strength and densities.; Molds, suitable for the injection molding of plastics, were prepared by post processing SLS green mold shapes. The SLS mold shape was subjected to a firing cycle during which the polymer was gradually removed and the metal was oxidized to ensure good bonding between the particles of the porous oxidized metal preform with minimal change in geometry. The porous oxidized metal preform was subsequently infiltrated with a liquid epoxy resin and cured and postured to prepare an injection mold with high strength and density. Parts with strengths of 10,000 psi were fabricated with this material system. Plastic parts were successfully injection molded with the same material system. This mold making system is unique and shows great potential for rapidly and easily preparing molds for prototype plastic part manufacture. The main advantage of this process is its ability to form shapes rapidly with negligible dimensional changes ({dollar}<{dollar}1%) through the use of inexpensive post-processing equipment.