How to select powder and binder for MIM injection molding?

In order to meet the needs of the market, MIM technology has continuously developed into a process for producing small, precise and complex parts. The conventional powder metallurgy technology for such parts is different. This kind of parts suitable for the production of MIM process have several commonalities, that is, the price of raw materials is relatively expensive, the utilization rate of materials is relatively low, the machining is relatively complex, and the usage is relatively large. MIM is a technical term. The raw materials used in this technology are not limited to metals, but all materials including ceramics, synthetic materials, intermetallic compounds can be used to produce complex parts. This technology has long been developed by plastic injection molding - ceramic injection molding - metal injection molding. Due to its unique advantages, it has been applied in electronic communication, automobile industry, chemical industry, aerospace, computer, medical, firearms and other fields.

For the parts produced by the conventional powder metallurgy pressing process, the size of the sintered parts is close to the compact, so it is not difficult to ensure the tolerance value. However, MIM metal injection molding process is different. Because injection molded parts contain a lot of adhesives, the sintered parts will shrink a lot. Therefore, the parts produced by MIM process are suitable for large quantities of parts to better control the size. The advantage is that the density of MIM injection molded parts is more uniform than that of conventional powder metallurgy parts. This can solve the possibility of warping due to uneven density in mold parts.

The viscosity of the MIM process injection material must ensure that it can flow into the mold evenly, and the viscosity of the mixture will not change within the range of forming temperature. When cooling, the mixture must be fully solidified with the metal materials to form hard parts. In order to achieve the smooth completion of the process before injection, the requirements for metal powders and adhesives are very high. This is also the preliminary work of MIM injection molding compared with conventional powder metallurgy pressing.

1. Selection of metal powder

The powder particles of MIM injection molding are usually 4-8 microns, not more than 20 microns, and spherical or similar spherical particles are selected. The price of raw materials is about 8-10 times higher than that of conventional materials, and the smaller the particles are, the easier it is to sinter. The materials used in MIM include low alloy steel, stainless steel, high-speed steel, copper base alloy, ceramics, tungsten alloy in high ratio, die steel, etc. Different materials are selected according to the performance of parts. The metal powders that cannot be used in MIM are aluminum and magnesium, because they are not suitable for sintering. In terms of material utilization rate, MIM injection molding process has a relatively high utilization rate, so the more expensive raw materials, the greater the advantage of using this technology.

2. Requirements for binder

The final state of MIM injection molding * * * needs to remove the adhesive. Several conditions must be met

(1) It can be mixed with a large amount of fine powder to completely wrap the particle surface

(2) Binder materials can be plasticized and can be injection molded at high temperatures

(3) Uniformity and consistency

(4) The raw materials of gates and parts are easy to be recycled

(5) Price economy