Raster scan selective laser melting of the surface layer of a tool steel powder bed

摘要

Square areas, 15 mm × 15 mm in size, have been melted in the surface of powder beds made from H13 tool steel, using a raster-scanning CO{sub}2 laser focused to a beam diameter of 0.6mm. Laser powers from approximately 50 to 150 W and scan speeds from 0.5 to 300mm/s have been used, at two scan spacings, 0.15mm and 0.45mm. The appearances of the layers in the different conditions, dense or porous, have been observed by low-magnification scanning electron microscopy. The masses of the layers have been measured and simulations have been carried out to predict the masses. The variation of mass with scan speed, at a constant laser power, has been found to be much less than might be expected from a constant absorptivity of laser energy into the bed. The simulations suggest that absorptivities range from 0.25 to approximately 1.0 and that, during any one scan, heating of the bed by previous scans must be considered in order even partially to explain the observations. The work is relevant to attempts to build metal parts without supports, by selective laser melting.