The Importance of Powder Size Detection for MIM

1. Stainless steel powder

Metallic stainless steel powder made from stainless steel alloys. The shape of the particles is regular spherical shape, and the average particle size is <33 μm. It has excellent corrosion resistance and durability. Its spherical particles can be positioned parallel to the surface of the coating film and distributed throughout the coating film, forming a barrier layer with excellent hiding power to block moisture.

Stainless steel powder uses low carbon steel as raw material, that is, stainless steel containing 18% to 20% chromium, 10% to 12% nickel, and about 3% molybdenum. After atomization, it is ball milled and sieved in the presence of lubricant (stearic acid). It can be graded to make pigments or wet ball milled directly.

Mainly used in maintenance coatings, heat-resistant and durable coatings, stainless steel flake pigments produce attractive natural metallic colors in decorative paints. It is also widely used in surface finishing of aluminum castings, copper and zinc castings, sandblasting and polishing of various metal surfaces, deburring and burring of casting workpieces, sandblasting and polishing of blade surfaces and cast product surfaces, etc. It can make your products smooth, smooth, shiny and achieve whitening effect.

2. Industry development status

It was invented by Parmatech Company in California, USA, in 1973. In the early 1980s, many European countries and Japan invested great efforts in researching this technology, and it was rapidly promoted. Especially in the mid-1980s, this technology has developed by leaps and bounds since its industrialization, increasing at an alarming rate every year. So far, more than 100 companies in more than 10 countries and regions including the United States, Western Europe, and Japan are engaged in product development, research and sales of this process technology. Japan is very active in competition and has outstanding performance. Many large companies are involved in the promotion of the MIM industry. These companies include Pacific Metal, Mitsubishi Steel, Kawasaki Steel, Kobe Steel, Sumitomo Mining, Seiko-Epson, and Daido. Special steel, etc. At present, there are more than 40 companies specializing in the MIM industry in Japan. The total sales value of its MIM industrial products has already surpassed Europe and is catching up with the United States. So far, more than a hundred companies around the world are engaged in product research and development, development and sales of this technology. MIM technology has therefore become the most active cutting-edge technology field in new manufacturing industries and is known as a pioneering technology in the world's metallurgical industry. Represents the development direction of powder metallurgy technology.

3. Metal powder injection molding technology (MIM)

Metal Powder Injection Molding (MIM) is a new powder metallurgy near-net-shape forming technology that introduces modern plastic injection molding technology into the field of powder metallurgy. The basic process is: first knead the solid powder and organic binder uniformly, and after granulation, use an injection molding machine to inject into the mold cavity to solidify in a heated and plasticized state (~150°C), and then use chemical or thermal The decomposition method removes the binder from the parison, and finally the final product is obtained through sintering and densification. Compared with traditional processes, it has the characteristics of high precision, uniform structure, excellent performance and low production cost. Its products are widely used in electronic information engineering, biomedical equipment, office equipment, automobiles, machinery, hardware, sports equipment, watch industry, Weapons, aerospace and other industrial fields. Therefore, it is generally believed internationally that the development of this technology will lead to a revolution in parts forming and processing technology, and is known as "the most popular part forming technology today" and "the forming technology of the 21st century".

Selection of Powder for MIM From a technical point of view, the selection of powder raw materials must consider its flow characteristics, debonding characteristics and sintering characteristics after mixing with the binder. As a MIM manufacturer, you must comprehensively consider the price of powder raw materials, the limitations of industrial powdering technology, the shape and performance of MIM products, and their sales prices. The following three major factors should be considered when using powder raw materials for MIM.

    Powder average particle size: Average particle size is an important factor in MIM process performance and part performance. The finer the powder, the higher the filling density and uniformity, which is beneficial to increasing the density of the sintered body. Powder for MIM usually refers to powder with an average particle size of 20 μm or less (mostly 1 to 10 μm). The smaller the particle size of the powder, the higher its price. At present, there is still a gap between the average particle size and price of the powder raw materials provided by powder suppliers and the production requirements of MIM products.

Tap density: When the particle size of the powder is the same and homogeneous, the tap density that reflects the shape of the powder is also an important factor affecting the filling characteristics of the powder. As far as water atomized powder is concerned, under the same average particle size, a small amount of binder with high tap density can also maintain the fluidity of the injection material, so that the amount of powder entering the mold cavity can be uniformly Increase to reduce the amount of binder. As a result, the shrinkage rate of the sintered body is reduced, thereby reducing the dimensional error of the parts.

Oxygen content of the powder: The degree of oxidation on the powder surface not only affects the sintering performance, but is also an important factor affecting the properties of magnetic materials, high-alloy steel containing strong oxidizing elements such as titanium and aluminum. In order to ensure the sintering performance and material properties of MIM parts, the lower the oxygen content of the powder used, the better.

    The above factors of powder play an important role in the density and dimensional accuracy of MIM products, affecting their commercial value. Therefore, the price of the powder should be combined to comprehensively optimize the selection.

4. The importance of powder particle size testing for MIM

MIM is a new metal forming process that combines traditional powder metallurgy and modern plastic injection molding technology. The metal injection molding process has strict standards for the selection of metal powder because the shape of the powder particles can affect the quality of the product. Only good metal feed can form good products, and good powder will make good metal feed. This means that the quality of metal powder affects the performance of MIM products. So what is considered a good metal powder? After years of production practice and theoretical research by industry experts, the industry has found that the finer the particle size, the uniform particles, and the nearly spherical powder particles, the more suitable they are for making feed materials. Feed materials made from such powders The material has good fluidity during the subsequent product forming process, which is conducive to the smooth completion of the entire MIM process, and it is easy to debond. The debonded blank shrinks evenly and to a small extent during the sintering process. Therefore, it is very important whether the particle size of MIM meets the process requirements, and particle size detection has also become an important link.

In addition, the average particle size is also an important indicator for price differentiation of MIM. If MIM wants to develop in competition with ordinary powder metallurgy and mechanical processing forming technologies, it is necessary to significantly reduce the price of powder raw materials. Compared with the 100-mesh powder used in ordinary powder metallurgy (the average particle size is at the 60um level), the price of stainless steel powder for MIM is more than three times, thus restricting the application of MIM. The reason for the high price is that the yield of MIM powder is lower than that of 100 mesh powder.

This MIM particle size detection experiment used the Winner2000ZDE laser particle size analyzer. The test report is as follows: