On Some Physical Aspects of Process Control in Direct Selective Laser Sintering of Metals|Part I

Selective laser sintering (SLS) of metals is a complex process exhibiting multiple modes of heat, mass and momentum transfer, and chemical reactions. The strong interplay between these physical mechanisms directly impacts the SLS process, determining whether a given material can be processed and if so, how the microstructure and properties of the processed material are in uenced. In order to understand the complex nature of these mechanisms, their interplay and impact on process control in SLS, it is appropriate to rst understand them at a fundamental level. The next step should involve developing simple models that can quantitatively reveal the in uence of these mechanisms as functions of processing conditions. Following this step, increasingly detailed models that take into account the coupling between di erent mechanisms should be developed. In this review paper, a rst step is taken towards identifying and understanding some of the important physical mechanisms in direct SLS. This study not only provides an insight into phenomena observed during direct SLS of a variety of metallic materials, but also helps in selecting materials that are most amenable to processing by direct SLS. Physical mechanisms discussed include oxidation, wetting, epitaxial solidi cation, elemental vaporization, melt ow instabilities and powder bed caking. Understanding these physical mechanisms is essential for the design of direct SLS machines and their process control.