SELECTIVE LASER SINTERING OF POLYMER-COATED SILICON-CARBIDE POWDERS

Selective Laser Sintering (SLS) produces three-dimensional objects directly from a computer-aided design (CAD) solid model, without part-specific tooling, by repeatedly depositing thin layers of fusible powder and selectively sintering each layer to the next with a rastered, modulated, CO2 laser beam. This technology, originally intended to produce parts and patterns from powdered waxes and thermoplastics, can be extended through use of thermoplastic-coated inorganic powder to producing ''green'' shapes which contain metal or ceramic powder bound together with the thermoplastic. These shapes can be subsequently processed into metal, ceramic, or composite metal/ceramic parts by various methods. Generally, the strength of the green shape critically depends on the layer to layer fusion that is achieved. A model of the SLS process is presented that correctly estimates the sintering depths in poly(methyl 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 densities and strengths are found to correlate with a combination of parameters, termed the energy density, that arise naturally from consideration of the energy input to the powder bed.