Tungsten Alloy Injection Molding Technology Development Problems

However, since the PIM using a large number of organic binder , an organic binder in a volume percentage content of 40% -60 % . In these organic binder before sintering must be removed clean. Otherwise they will have many flaws , the sintered product performance has a great influence . Especially for injection molding process especially in the case , this is mainly because :

First, because the fine particle size , irregular shape , was reunited shape, powder large surface area , the required wetting powder binder content more powder volume content ( ie powder loading ) lower , only 45 % to 55 % or so. Adhesive surface of the powder and the powder formed in the inner hole of the adsorption layer is very thick , adhesive removal of more complex and difficult. Incorrect difficult to skim through the cracks caused by the subsequent densification remedy , which performance is very sensitive to pore and crack high-density alloy very unfavorable ; powder loading is low, degreasing process prone to warping , easy deformation ; in the liquid phase sintering shrinkage is too large , the deformation is more serious , making control of dimensional accuracy and stability of physical and mechanical properties is very difficult.

Second, the high density of the alloys are very sensitive to impurities and microstructure , porosity and porosity are important. - Areas produced during removal of large pores and other defects is difficult to compensate by sintering , large pores and high residual porosity ( porosity of> 1.0% ) of the performance is very harmful . On the other hand , the high -density alloy elements are very sensitive to carbon . Degreasing binder removal process is not complete, even if only a small amount of residual carbon will lead to copper and tungsten, nickel, iron , to form brittle intermetallic compounds , thereby reducing the tensile strength , ductility and toughness .
These factors severely restrict the PIM technology in high -density alloy application and development. At home and abroad by powder injection molding technique can only be prepared relatively complex shape , the thickness ( or diameter ) smaller (10mm) parts. For the cross-section changes, large diameter , thickness and width of the ring is very small changes in the large size of a large shotgun and larger diameter tungsten ring tungsten alloy penetrators bomb core ( greater than 20mm), powder injection molding using current technology to prepare very difficulties at home and abroad were no patents and literature reports .

Is to obtain high-quality injection preform having a high dimensional accuracy and high performance components a very critical factor. Unstable injection process , injection preform serious impact generated defect control of dimensional accuracy and performance. The injection process stability depends directly on the binder , and thus in research and development of high-density alloy near net shape technology , adhesive , injection , skim a few important research aspects .




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