Investigation On The Beam Path Designing For Selective Laser Micro Sintering And Sintering Behavior

Selective laser micro sintering (SLMS) can fabricate micro metal parts with any required three-dimensional shape directly from CAD model. SLMS technology can meet the needs of micro-manufacturing process well because of its advantages of simple process, low cost and fast speed. The feasibility of SLMS has been approved,now the researches are focused on the material broaden, mechanism research, process optimization and so on. This thesis designed the beam path for SLMS, and investigated the influence of process parameters on the width of the sintering line and sintering behavior. Some valuable results have been obtained:(1) The methods of micro beam spot size have been analyzed and the beam path for SLMS has been developed. The beam path for SLMS includes using a short wavelength diode pumped acoustic-optic Q-switched Nd:YAG (Neodymium-doped Yttrium Aluminum Garnet) laser, selecting laser beam mode with a inside aperture, a short focus lens, and an expander in front of the lens to expand the laser beam diameter.(2) The influence of the powder performance and laser parameters, such as average laser power, the Q-switched pulse width and frequency, the scanning speed, the laser focus diameter, et al., on the width of the sintering line has been experimentally investigated. For the Cu-based double component mixed metal powders, the higher the laser average power, the lower the scanning speed or the bigger the laser focus diameter is, the wider the sintering line is. As the sintering mechanism of double component mixed metal powders is liquid phase sintering mechanism, the width of sintering line of Cu-based metal powder is much wider than that of Ni powder since the sintering regime of Ni powder is melting-solidifying.(3) The influence of the parameters, such as the Q-switched pulse width and frequency, the scanning space and the powder thickness, on the sintering quality has also been experimentally investigated. The results show that, 1) Optimal laser peak power exists for obtaining good sintering quality. If the laser peak power is too high, the splashing phenomenon of the powders and melting pool is extremely serious, which will bring bad sintering quality, even cause the sintering being hard to go on. If the laser peak power is too low, the density of the sintering part decreases. 2) Appropriate scanning space can sinter high-density parts. If the scanning space is too large, the combination of the sintering lines will be not closed enough, which will cause big holes appeared in the parts and non-smooth surface. If the scanning space is too small, the sintering region will redundant melt, then the sintering-neck vanish a lot because of vaporization, which will cause the sintering body not compact. 3) As the powder thickness is too thick, the sintering layer can not connect with the sintered layer, which will cause warping separation or even abscission. As the powder thickness is too thin, it will be hard to pave the powder.(4) Finally, through the optimization of process parameter, micro Cu-based metal part with complex three-dimensional shape and 150μm resolution, and Ni sintering line with 50μm width and good quality have been successfully sintered.