SELECTIVE LASER SINTERING OF POLYMER-COATED SILICON-CARBIDE POWDERS

Selective Laser Sintering (SLS) produces three-dimensional objects dir ectly from a computer-aided design (CAD) solid model, without part-spe cific tooling, by repeatedly depositing thin layers of fusible powder and selectively sintering each layer to the next with a rastered, modu lated, CO2 laser beam. This technology, originally intended to produce parts and patterns from powdered waxes and thermoplastics, can be ext ended through use of thermoplastic-coated inorganic powder to producin g ''green'' shapes which contain metal or ceramic powder bound togethe r with the thermoplastic. These shapes can be subsequently processed i nto metal, ceramic, or composite metal/ceramic parts by various method s. Generally, the strength of the green shape critically depends on th e layer to layer fusion that is achieved. A model of the SLS process i s presented that correctly estimates the sintering depths in poly(meth yl methacrylate) (PMMA) and coated silicon carbide (SiC) powders that result from operating parameters including laser power, beam scanning speed, beam diameter, scan spacing, and temperature. Green part densit ies and strengths are found to correlate with a combination of paramet ers, termed the energy density, that arise naturally from consideratio n of the energy input to the powder bed.