1, the hard alloy powder injection molding advantage
Production technology of powder metallurgy parts of raw material powder demanding injection molding, products in 0.1-10 μ M size range of powder production is easy to achieve high precision. The hard alloy used for production of raw material basically belong to the size range, meet the requirements of MIM technology on the raw material powder, the powder of hard alloy can be directly applied to the injection molding process, the raw material cost is not increased, this is a big advantage of cemented carbide injection molding
Cemented carbide with high hardness, high strength, wear resistance, corrosion resistance, high temperature resistance and a series of advantages such as small expansion coefficient, is indispensable in metal processing, mining, oil drilling, such as national defense tool material, in addition, in recent years the hard alloy in the watch shell wear-resistant decorative parts have been widely applied. The traditional method of cemented carbide production (pressing - sintering method) products only the production of simple shapes, thus limiting the scope of application of cemented carbide. Cold, hot isostatic pressing products production of complex shape, but the cost is very high, is not suitable for mass production. Cemented carbide injection molding to produce and widen the application fields of cemented carbide, the technology to lower the cost of production of products with complex geometry of near net shape, while the ordinary molding and other method to produce.
Research progress of 2, hard alloy MIM Technology
In 1977 Curry acquired using paraffin as cemented carbide injection binder forming technology patents, and later transferred to Leco company, a Leco process. But due to the single component paraffin as binder can lead to skim a long time, easy to produce defects, which makes the patent influence range is not big. But after entering 80 age, along with the MIM technology in the binder, breakthrough degreasing technology, the forming technology of cemented carbide injection matures provides powerful technical support, coupled with the hard alloy injection molding technology of the advantage be richly endowed by nature itself, from the early 80's in the world emerged a group engaged in the production and research of cemented carbide injection molding manufacturers and research institutions.
A American Leco carbide Leco company under the branch, the company are the first to use the method of injection molding production of cemented carbide products company. The company by the two method of WC based hard alloy, one is the traditional pressing - sintering method, products accounted for sales of 60%; another is the use of cemented carbide injection of new forming method (Cemented Carbide Injection Molding), products accounted for 40% of sales. The company's CCIM product weight in the range of 0.3-2kg, the maximum diameter is 10.59 ". The company says it is the world's largest cemented carbide injection molding production plant products. The German company Degussa MIM from the 80's began on 1986, officially out of products. They are using a mixture of polyethylene, polypropylene, polystyrene, thermoplastic and wax, resin and other special additives as forming agent, compared with about 0.8 μ m WC-Co alloy powder, then granulating, injection molding, binder removal and final sintering. The company is mainly engaged in the production of the feed frame and a cutting tool or cutter head. Now they have to the small batch and multi varieties, according to the requirements of the users of multi material production. Products the largest volume of 1000cm3, the longest for 100mm, the most important is about 100g, product deviation is 0.3%, the thickness of 1-5mm, the final density can reach 95% of the theoretical density. In addition Forn physical production with tungsten carbide carbide rotary cutting, is a binder group two yuan of above, the first component chemical solvent extraction removed, the remaining thermoplastic binder removal during sintering. Many other manufacturers such as Singapore Phimax company, IBM company, Shandong Jinzhu powder injection domestic manufacturing company limited, Shanghai Fu Chi Technology Co. Ltd, Qingdao Tongxiang Special Powder Metallurgy Co., Ltd., Beijing iron and Steel Research Institute, Central South University, powder metallurgy, into research and production of CCIM technology, output in the steady rise
The British Loughborough industry university polymer technology and Materials Engineering Institute of British science and Engineering Research Council, UK hard alloy Association and the British Nonferrous Metals Technology Center funded, since the beginning of 1985 injection of cemented carbide forming technology. Focus on powder properties, adhesive technology, blending, rheological properties, flow and deformation, extrusion molding integrity forming agent, sintering and speed, the research involves many fields. The following is the results they got , also represents the main achievements obtained in the research of CCIM technology in the past.
(1) because of rheological hard alloy powder is poor, should not use hard alloy powder volume ratio of mixture is higher than 65% for injection molding;
(2) the polar waxes, mainly lignite ester waxes, because of its rheology suitable for powder injection molding, can produce high volume percentage of mixture powders and meets the requirement of the. This kind of wax and favourable volatilization kinetics, he is in control of degreasing, tendency and less polar paraffin in shear stress from the mixture and low volume percentage of segregated. Full use of lignite wax crystalline ester also has a tendency to crack in the forming blank, but that by mixing the appropriate proportion of different types of wax can be adjusted;
(3) of the high shear melt mixing technique can effectively produce mixture uniform;
(4) through the analysis of the rheological behavior and the viscous flow activation energy, the formability of the various formulations are effective.