ABSTRACT
SLS is well recognized as one of the most diffused techniques for layer-by-layer construction, thanks to the wide variety of available materials. In particular, the processes using metal powders are largely applied for Rapid Tooling [Gatto A. & Iuliano L., 2000, Gatto A. & Iuliano L. 2001, Gatto A. & Iuliano L., 1998, Iuliano L. et al. 2003, Khaing M.W. et al. 2001, Abe F. et al. 2001]. Different versions of the process can be distinguished [Kathuria Y.P., 1999, Morgan R.H. et al. 2002]:
• Solid state SLS, or Indirect Metal Sintering, using metal powders mixed with a polymeric binder. After laser forming the part is furnace treated and infiltrated, to obtain a higher density. In the early versions of the SLS process, two subsequent furnace cycles of 24 hours each were needed. During the first step the green parts are placed in a furnace where the polymer binder is removed and the steel particles are partially sintered. The resulting “brown” part is approximately 60 percent dense. Then the brown part is returned to the furnace and infiltrated with a low melting point alloy to produce a fully dense final part. In a more recent development, green parts can undergo a single 24 hours cycle, during
which both particles sintering and infiltration occur.
