Large Shell Features Design And Rapid Prototyping And Manufacturing Applications

Selective laser sintering (SLS) technology is related to many subjects such as CAD/CAM, laser processing technology, materials science and so on. In this dissertation, a CAD feature model of Liebao automotive body is established as well as the application of the Rapid Prototyping (RP) technology in the manufacture of some decorate parts. In order to realize the design and manufacture of large-scale thin shell parts using SLS technology, three fundamental problems including the establishment of the CAD model based on the feature technology, energy delivery on SLS process and the mainly factors that affect the molding precision and efficiency to large-scale thin shell parts are studied as follows:1. A product's feature model covers the relative information for its design and manufacture, so it is the first step to establish the CAD triaxiality intelligence feature model in RP technology, which is completed firstly in the dissertation. The measure of the institution of the parts intelligence model using feature technology is presented. Using such model, an engineering drawing conversion under different industry standard is realized.2.After the establishment of the feature model, through CAM technology, prototype materials are solidified and molded heating by laser, which is the principle of RP technology. The energy deliver process on RP, especially SLS is studied. The energy deliver on SLS is divided into two parts: one is the preheating before the powder molding; the other is the laser multi-scanning heating during molding. After analyze, it is drawn a conclusion that radiation is the best heat exchange way for powder in SLS technology.3.Large-scale thin shell parts are character as in large volume and thin wall, which induce some technology difficulties in the RP manufacture process because of its layered overlap manufacture process. The laser scanner parameters influencing on laser scanning energy and its distribution are discussed qualitatively and quantitatively. It is revealed that the relation of laser power density with scanning space and sintering thickness is nonlinear. A feasible range of the scanning space and sintering thickness to realize the scanning energy uniformity is presented. Furthermore, in order toimprove the molding precision and efficiency, it is important to selecting the appropriate scanning method. It reveals that direction adjustable zone-partition scanning is the best way to meet the request of the manufacture of the large-scale thin shell parts.The influences of the major factors in the process are analyzed in, the last part of the dissertation. A series of experiments, with HBl powder as prototype material, have also been made. To optimize the sintering procedure, improvement measures have been put forward on the basis of the theoretical analysis and experimental data. At last, a typical large-scale thin shell part of Liebao header board is sintered successfully.