Selective laser sintering of HIPS and investment casting technology

A selective laser sintering (SLS) pattern made of polystyrene (PS) is not suitable for investment casting of complex parts due to its poor mechanical properties. Therefore, high impact polystyrene (HIPS) should be used to make complex parts. The sintering characteristics of HIPS are as good as those of PS, and the mechanical properties are much higher than those of PS. In order to further improve the performance, post-processing is employed infiltrating with wax in this study. Through post-processing, the void fraction is decreased from 52.8% to 8.1%, correspondingly the tensile strength and impact strength are increased 64% and 97%, respectively. Because of high-melting temperatures and high-melting viscosities, it is very difficult to dewax completely for the SLS pattern. In order to avoid carbonization residues, the proper dewaxing technology is developed in this study: (1) the wax is removed first at low temperature, (2) the temperature is then increased to 200–250 °C to allow most of the HIPS to flow out and finally (3) baking is performed at a temperature higher than 500 °C. Furthermore, examples are performed to illustrate the settings of slag extraction risers, riser vents and associated running channels for producing complex parts.