Nanjing University Of Aeronautics And Astronautics The Graduate School

Rapid prototyping (RP) is a new technique which was developed in thelater 1980s. It is an integration of CAD, laser technology, CNC andmaterials science. As an important branch of RP, selective laser sintering(SLS) is attractive to many researchers owing to such advantages as a widerange of materials that can be used, and its special material increasingmanufacturing (MIM) method. In the present paper, the effects of material properties and laserprocessing parameters on laser sintering of metal powder were studied. Amulti-component metal powder mixed by pure Ni, pre-alloyed CuSn andCuP powder has been developed for the exclusive use of SLS. Through aseries of SLS experiments, the laser processing parameters which mayaffect the quality of the sintered parts were made certain. The processingmap at various laser powers and scan speeds was drawn, in which themelting-solidification behavior of the powder can be divided intosolid-phase sintering, liquid phase sintering with partial melting of thepowder, and liquid phase sintering with continuous melting of the powder.The experimental results demonstrate that the sintered parts with soundquality can be obtained in the conditions that the partial melting of thepowder occurred. With the suitable sintering mechanism permitted, the effects of laserprocessing parameters on distortion of the sintered parts were investigated.In a certain range of laser processing parameters, increasing laser power orlowering scan speed resulted in higher deformation rate of the sintered parts.With optimized laser processing parameters used, SLS experiments weresuccessfully carried out and the sintered parts with slight deformation wereobtained. Metallography and the scanning electron microscope (SEM)analyses show that Ni powder with higher melting point acts as thestructural metal and remains unmelted or slight melted during lasersintering, while the CuSn powder with lower melting point acts as thebinder and melts to form the liquid phase, wetting the Ni particles andleading to a densification. The element phosphors acts as flux and reactswith oxygen to form CuPO3 in SLS process, which prevents the Ni particlesform oxidation. Microstructure of the sintered samples aftermelting-solidification process was combined of the characteristic featuresof flat crystal, cellular crystal, and fir-tree crystal. And the bondingmechanism of this process is liquid phase sintering.