Powder Injection The Forming Catalytic Skimmed Study

Powder injection molding (PIM) is an advanced near net shape process with well recognized capability for efficiently producing complex parts. PIM consists of four processes:mixing, molding, debinding and sintering. The debinding process is the most complex and difficult step. There are some usual approaches for debinding, eliminating the binder with thermal solvent and capillary extraction techniques. The catalytic debinding is a new trend of the development direction of debinding techniques of PIM due to it has inherent advantages- no flaws of debound body, and quick debinding rate.A new type of powder injection molding Catalytic debinding binder was explored in the paper. The 17-4PH stainless steel powder as a raw material, catalytic debinding feedstock was prepared by self-propagating high-temperature synthesis. The rheological property of feedstock was discussed in the paper. The effects of debinding time, debinding temperature and composition of feedstock on the debinding efficiency were studied. The mechanism of catalytic debinding is discussed in detail by SEM of catalytic debound. At last, the catalytic debinding binder was evaluated by the property of sintered sample. The main results were sumerized as follows, (1) The catalytic debinding type binder is an ideal binder systems for PIM, which is composed of Polyoxymethylene 85%～92%, high density Polyethylene 5%～8% and a little others components, such as compatilizer and surfactant. The binder and powder were well compatible, the result of injection and debinding using catalytic debinding type binder was very well. (2) The catalytic debinding feedstock had good uniformity and moldability, which was pseudoplastic fluid for their viscosity decreased with temperature and shear speed increased. So the feedstock was appropriate to the practical injection molding. (3) The catalytic debinding binder could be quickly removed by catalytic decomposition, and debound part had good shape retention and no obvious defects. The debinding rate can be controlled easily by the debinding temperature and the concentrantion of catalytic HNO3 gas. The appropriate debinding process:HNO3 feed rate at 0.010～0.050cc/min; debinding at 120-125℃. (4)The catalytic reaction proceeded exclusively at the gas/binder interface and steadily progressed from the surface of the injected body to inside. Therefore, this debinding method could avoid cracking or blistering. This process was called as "shrinking core". (5)The sample after sintered has density of 7.63g/cm3, relative density of 97% and hardness of 26.6HRC.