Tungsten Copper Powder Injection Molding Research

Based on conventional molding process and combines plastic molding industry technology, PIM (Powder Injection Molding) has excellent applicability in some tungsten copper products with small size and complex shape or structure. So we study from mixing, injection, degreasing, sintering and several key process of tungsten copper powder injection molding, and analyze and summarize the advantages of the process and the defects.

The first is the selection of the binder and the preparation of mixture. Binders can reduce caking of the powder, which has good flowability, and plays the role of maintaining the shape of the body until degreasing sintering. Thus the choice of the binder is injection molded in a key ring, it should meet the deformation and cracking does not occur before the product sintering defect, and easy to be removed. Now more use thermoplastic or some polymers as binders, such as paraffin, stearic acid, HDPE, EVA and so on. In the process of mixing, paraffin and stearic acid are liquid phase, which does not destroy the nature of the binder. In addition, wherein the order of addition of powder and a binder is the final state of the blank has a certain influence. The next is granulating, and select particles about 2-3mm for injection molding.

Many parameters of injection molding should be perfectly controlled, such as the temperature, the pressure, the speed and so on. Theoretically, in the process of injection molding, the temperature and pressure are the largest influencing factors of molding properties. In order to press tungsten copper powder mixture into the mold cavity, the temperature inside the injection machine must be high enough so that moderate viscosity mixing, the two-phase does not separate. For injection pressure (to overcome the flow mixing cavity flow resistance, provide filling speed and compaction of the melt) and speed in the experiment demonstrated that there is an optimal match range, pressure and speed should not be too large or too small. From the figure above, we can also find the optimum temperature range for injection, injection pressure and speed. Since the injection process to fill the cavity is more complex, many parameters must be well controlled, once appear unreasonable control can cause a variety of defects. We introduce some common defects and the corresponding solutions: 1. Under-injection, it refers to the injection process feed can not fill the mold cavity, the corresponding solution is three-pronged approach from the injection temperature, feeding quantity and viscosity of the feed itself causes analyzed; 2. The pores, it is the most common type of defect, the corresponding method is to pay attention to whether the injection and mixing of air entrainment and make adjustments, check the injection speed, the injection pressure, etc; 3. Unstable quality, it should be considered that whether the powder is uniform and the segregation with the binder.