In recent years, the growth trend of the PIM industry has been very strong. BCCResearch's market survey and forecast analysis of the MIM industry shows that the world's MIM product market was US$382 million in 2004 and is expected to grow to US$571 million in 2009, with an average annual growth rate of 8.4%.
1.2 Continuous expansion of the application field of powder injection molding The PIM process is suitable for mass production of small metal, ceramic or carbide parts with complex shapes. With the development and gradual maturity of PIM technology, its application field is constantly expanding and is no longer limited to watch parts, electronic mechanical parts, medical equipment and light weapons parts. The industrial promotion and application of PIM must be combined with its own process characteristics to make it have obvious technical suitability compared with processes such as die-casting sintering, precision casting and machining. 1) Mass production of complex products Compared with traditional die-casting sintering, MIM process is suitable for manufacturing complex metal parts. Sandvik Osprey's public opinion survey on the future market of MIM shows that among the automotive industry, aerospace, medical equipment, electronic communications, consumer goods and other industrial fields, 81% of people believe that the automotive industry will be the fastest growing field in the MIM product market, while 19% believe that it will be the medical equipment field. Therefore, MIM automotive parts made of stainless steel, Fe-Ni low alloy steel, Ni-based alloy and master alloy, and MIM medical equipment made of stainless steel, CoCrMo (F75) and titanium alloy will be the main growth points of the future MIM market. In the field of electronics and electrical appliances, MIM has been used to manufacture products with increasingly complex shapes. The heat dissipation capacity of the LCD radiator manufactured by the ARCSeibersdorf Research Center in Austria using copper powder injection molding technology is 4 times that of the original G-AlSi material die-casting product. Fotec in Austria also uses copper powder injection molding technology to manufacture chip heat sinks with extremely complex shapes.
2) Forming of complex products of difficult-to-process and refractory materials. PIM has broad prospects in the forming of complex products of materials such as WC-Co cemented carbide, tungsten and tungsten alloys, rhenium, and alumina ceramics. The French National Atomic Energy Center (CEA) uses PIM technology to manufacture new micro-alumina heat exchangers. The Froschungszentrum Karlsruhe Research Center in Germany and the ARC Seibersdorf Research Center in Austria have both used pure tungsten injection molding to manufacture divertors in nuclear reactors. At the same time, the former has also developed injection molding feedstocks for W1La, W-Ni-Fe and WCu alloys, which are expected to be used in heat shields, microelectronics and automotive industries. Powdermet in the United States has developed the injection molding process of refractory metals rhenium, WC-Co, and WC-Cr3C2-Co and has been used to manufacture parts such as ball cages, valve bodies, and rings.
3) Forming of customized material products. The PIM process has the advantages of powder metallurgy. Process personnel can design the composition of materials according to product needs. This feature broadens the application field of PIM and has obvious advantages over processes such as precision casting and machining. The research institute led by Professor German R M of the University of Mississippi is studying the injection molding process of aluminum-based composite materials and nano W-Cu pseudo-alloy powders. On the other hand, co-injection technology has also begun to be applied to the MIM field. The Fraunhofer IFAM Institute in Germany uses this method to manufacture 17PH/316L and 316L/Fe micro parts with different physical properties in different parts. Different materials in co-injection are connected together to form a whole during the sintering process, while the MIM in-mold assembly (Assembly moulding) technology uses the incompatibility of materials during the sintering process to form and assemble parts during the injection stage. This technology originated from the assembly injection molding technology. Arburg has used this method for MIM to produce hinges by in-mold injection assembly and co-sintering of 17-4PH spheroidized powder and 17-4PH master alloy powder.
The process requirements of μ-PIM, a related technology of powder micro-injection molding, are higher than those of ordinary PIM, which is reflected in its various production links. The powder size used in μ-PIM is generally one order of magnitude smaller than the smallest internal size of the formed part. For metal materials, it is generally less than 5μm. For ceramic materials, it is generally less than 0.5μm. The use of fine powder is beneficial to the precision, surface quality and shape retention of the product during the degreasing process, but the cost of the powder is also increased. The binder used in μ-PIM should be low enough to facilitate the filling of micro-cavities during the injection process. At the same time, the binder should ensure that the blank after injection molding has sufficient strength so that its tiny features will not be damaged or deformed during demolding and subsequent operations. Since the size of the powder is very fine, the gap between the powder and the binder is reduced, and the difficulty of mixing increases accordingly. The feed should have a reasonable powder charge. If there is too much powder, the binder will not be able to infiltrate all the powder particle surfaces, making it difficult to fill the mold; if there is too much binder, the viscosity of the feed will decrease, and the powder and the binder will separate during the injection process, resulting in uneven density of the formed blank. Therefore, μ-PIM must use a uniform feed with a reasonable charge.
The micro-injection molding machine used by μ-PIM has the characteristics of high injection rate, accurate injection volume measurement, and fast servo device response. At present, the micro-injection molding machines used by the industry and research institutions related to μ-PIM are mainly Battenfeld Microsystem 50ArburgAllrounder series and Ferromatik Milacron series models. The injection molds used by μ-PIM can be processed by LIGA, UV-LIGA, laser ablation, micro-EDM, rapid prototyping and other methods. Different processing methods have different processing ranges, precisions and economies. The wear resistance of the mold is an important issue for μ-PIM. The Karlsruhe Research Center in Germany has studied the wear resistance of mold cores made of low-alloy steel, high-alloy steel, cemented carbide, nickel and other materials. The wear of the core is related to the powder material and the binder. The test shows that corrosion is the main mechanism of wear. Improving the micro-homogeneity of the mold material is beneficial to its wear resistance, but the direct relationship between the hardness of the mold material and the wear resistance has not yet been found. In the μ-PIM injection process, the process parameters such as mold temperature, feed temperature, demoulding speed, injection pressure, speed, time, etc. must be reasonably controlled. It is very necessary to use numerical simulation to optimize the injection molding mold and process parameters. In the demoulding process of μ-PIM parts, the parts may fall off partially in the mold cavity, which directly affects the accuracy of the parts. In order to ensure the reproducibility of parts during mass production, Battenfeld has designed a visual monitoring system to observe the integrity of parts after demolding and whether there are parts falling off in the mold cavity.
For μ-PIM, the reduction in the size of parts will reduce the time required for degreasing, but fine powder particles will increase the time required for degreasing. When paraffin-based binders are used for μ-PIM, the shape retention and strength of the blanks during the degreasing process need to be improved. Studies have shown that μ-PIM binders composed of polymers PAN, EVA and HDPE have better effects in the degreasing process. The powder used in μ-PIM is finer than that of ordinary PIM, which reduces the temperature required for sintering. The effects of grain growth, oxidation and spheroidization need to be controlled during the sintering process.
The research and application of PIM technology is developing rapidly and giving full play to its own characteristics and advantages. μ-PIM and light metal injection molding have broad development prospects and are research hotspots in the field of PIM. The use of computer numerical simulation to optimize PIM process design is an inevitable trend in the future. Since PIM involves powder metallurgy, chemical industry, machinery manufacturing and other fields, regional and international cooperation is very necessary.
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