Research On Sintering Parameters And Prototyping Quality Of SLS Polymer Powders

Selective laser sintering (SLS) is a rapid prototyping technology in which at three-dimensional object is created layer by layer from heat-fusible powdered materials with heat generated from a laser. The polymer powders are the ordinary SLS materials. Their parts are used for functional parts or instead of traditional wax pattern investment casting. These are the important development trend of SLS.At the present time, the fabrication processes of SLS polymer powders are in privacy condition. There are no complete or public fabrication processes of SLS polymer powders. In this paper, according to the fabrication methods of polymer powders and the data analysis, the feasible fabrication processes and methods of cryogen and solvent are reached.The reasonable combination of process parameters is important to get the better quality. The process parameters are relation to the materials'properties .In this paper, four SLS polymer powders were selected as the experiment materials, and the four materials'properties, for example distribution of particle size, stacking density, melt index, bonding temperature, were measured. The influences of materials'properties to sintering process parameters were analyzed, for example: the preheating was separated two parts. For amorphous materials the firing preheating temperature is between at vitrification point and bonding temperature. The steady temperature is below at vitrification point 3～5℃. The slicing thickness is determined by distribution of particle size and flowing power of the material. The results can be the theoretical reference of optimizing process parameters.According to the condition of unstable quality, which is formed by unreasonable process parameters in SLS, the method of orthogonal experiment was used to optimize the process parameters of the experiment materials. Through the experiment the influence regularities of process parameters to prototyping density were obtained: the density increase with the increasing of laser power and preheating temperature, and reduce with the increasing of slicing thickness and scanning speed. The combination of process parameters for the experiment materials was defined precisely. The method and the rule of determining the process parameters for SLS polymer powders were presented. The experimental specimens were sintered with the optimized process parameters. The dimension errors and mechanical properties are measured in detail. According to the plane dimension error and the height dimension error are analyzed, got the average dimensional discrepancy and the relative dimensional discrepancy of every materials at their optimized the process parameters. The compensations of dimension errors were achieved.Through observing the experiment phenomena sintering properties of each test material were contrasted. From the sintering condition, the prototyping property of PSB is steady. The sintered parts of STP1 and PSC curled easily, their prototyping need higher preheating temperature. The sintered part of PA is warping seriously, and the borders are fuzzy, the surfaces are rough. So the properties of PA need further improvement.