| Selective Laser Sinter (SLS) can produce high complicated parts, but with high porosity and low strength. Isostatic pressing, which is divided into Cold Isostatic Pressing (CIP) and Hot Isostatic Pressing (HIP), transfers uniform pressure on parts in the incompressible liquid or gaseous medium, and the part have excellent performance with the organizational structure of uniform, high size precision, and low deformation rate. But there are some defects about Isostatic pressing, such as difficulties in design of container, difficulties in forming precision to control, not forming high complicated parts, and so on. Therefore, it will be a combination formed SLS/CIP complex process to achieve high performance and complicated parts, which can utilize fully their own specific advantages.In traditional application of HIP, it often use the method that is repeated tests, but structure and performance of parts are difficult to guarantee, and the method is complicated, which has a long cycle, and requires a large amount of labor resources and high costs. If doing a precise numerical simulation for HIP, it will lower the deformation of part, and enhance the quality. Since the early 1990s, some western countries developed in manufacturing, such as Sweden, French, United States, et al, have done a large number of studies in the area. But there are no reports about simulation of SLS/Isostatic Pressing. So using Numerical simulation and experimental study the two methods, Two compound forming technologies which are SLS/CIP and SLS/HIP are studied in the paper, and the content and conclusions are as follows :The processes of densification about CIP and HIP are described and analysed. And based on the assumption of "compressible continuum", two material models of the SLS parts are established. while Cam-Clay model used in CIP, a combined model which is combined Cam-Clay model with porous metal plasiticity model is used in HIP. Meanwhile, the finite element software --ABAQUS 6.4 is introduced in the paper.SLS/HIP process is discussed. And SLS part such as cuboid which is formed using 316L stainless steel material, is simulated under HIP, and it is achieved that the stress distribution, deformation and displacement distribution, as well as the relationship between deformation with time of key point. Finally, HIP experiment is carried out. But as low and ununiform packing density of BN powder, loading of SLS parts is ununiform, which cause that their deformation is much ununiform, and errors of precision is large. Because of a large difference between simulated condition with experimental condition, results of simulation can't be verified.SLS/CIP process is discussed. And firstly, numerical simulation of SLS parts such as cuboid which are formed using 304L stainless steel power, is carried out to achieve the relationship between relative-density with pressure in ABAQUS platform, which will provide basis for selection of pressure. Secondly, as the basis, the simulation of cuboids degreased in different temperatures (850℃and 1100℃) and gear are carried out to predict the structure of SLS parts after CIP. Finally, CIP experiment is carried out, and compared with results of simulation, it is found that cuboids have greater error rate in the Z direction, and gear in tooth root. In addition, through simulation and experiment of CIP, it is also found that difference of the parts degreased in different temperatures (850℃and 1100℃) is not large in shrinkage ratio after CIP. At the end, model of CAD design is building, and SLS prototype such cuboids are designed in the basis of simulation and experimental study to provide an effective basis for the near-net shape parts of the SLS/CIP.With Study on Simulation and Experimentation of SLS/Isostatic Pressing complex processes, and CAD design of simple part, it is provided the basis for the structure design for the subsequent complex parts, and effective guidance for near-net shape parts of SLS/ Isostatic Pressing.
|
PDF Full Text Request