The new process of metal injection molding must know: MIM

The new process of metal injection molding must know: MIM

1. MIM part is a metal processing and molding process

MIM (Metal injection molding) is the abbreviation of metal injection molding. It is a molding method of injecting the plasticized mixture of metal powder and its binder into the model. It is the shape required by mixing the selected powder and binder, then granulating the mixture, and then injection molding.

2. MIM Part Process Flow Steps

The MIM part process combines the flexibility of injection molding design with the high strength and integrity of precision metal to achieve a low-cost solution for extremely complex geometric components. The MIM part process is divided into four unique processing steps (mixing, molding, degreasing and sintering) to realize the production of parts and components, and determine whether surface treatment is required according to the product characteristics

blend

 

Fine metal powder is mixed with thermoplastic and paraffin binder in precise proportion. The mixing process is carried out in a special mixing equipment and heated to a certain temperature to melt the adhesive. In most cases, mechanical mixing is used until the metal powder particles are uniformly coated with adhesive and cooled to form granules (called raw materials), which can be injected into the mold cavity.

 

forming

 

The equipment and technology of injection molding are similar to injection molding. Granular raw materials are fed into the machine for heating and injected into the mold cavity under high pressure. The green part is formed and demoulded after cooling. The above whole process can be carried out only when the binder is melted (fully fused with the metal powder) at about 200 ° C. The mold can be designed as multi cavity to improve productivity. The shrinkage of metal parts during sintering shall be considered in the design of mold cavity size. The shrinkage change of each material is accurate and known.

 

Degrease

 

Degreasing is the process of removing the binder from the molded parts. This process is usually completed in several steps. Most of the binder is removed before sintering, and the residual part can support the parts to enter the sintering furnace.

Degreasing can be accomplished by a variety of methods, most commonly solvent extraction. The degreased parts are semi permeable, and the residual binder is easy to volatilize during sintering.

 

sinter

 

The degreased parts are put into a high temperature and high pressure controlled furnace. The component is slowly heated under the protection of gas to remove residual adhesive. After the adhesive is completely removed, the part will be heated to a very high temperature, and the gap between particles will disappear due to the fusion of particles. The component is directionally shrunk to its design size and transformed into a dense solid. For most materials, the typical sintering density is theoretically greater than 97%. The high sintering density makes the product performance similar to that of forging materials.

 

surface treatment

 

According to specific requirements, some parts may require surface treatment after sintering. Heat treatment can improve the physical properties of metals. Electroplating and coating can be applied to high-density materials. Provide welding or cooling treatment

 

technology.

 

Process video presentation:

3. MIM part products usually have the following characteristics

 

complexity

Like injection molding, MIM parts have no restrictions on shape design. Because MIM parts are a molding process, additional product features will not increase costs, which makes MIM an ideal way to combine independent parts into multi-functional products. MIM part design rules are very close to injection molding, so they are applicable to almost all products.

 

Precision

The reference design for net forming accuracy of MIM parts is usually ± 0.5% of the size. The net forming of some characteristics can reach ± 0.3%. As with other technologies, the higher the accuracy requirements, the higher the cost. Therefore, it is encouraged to moderately relax the tolerance requirements when the quality allows. The tolerance that can not be reached by one forming of MIM parts can be realized by surface treatment.

 

Weights and dimensions

MIM parts are particularly suitable for parts weighing less than 100g, and less than 50g is the most economical. However, parts weighing up to 250 grams can also be handled. The main cost of MIM parts process is raw materials, so MIM parts can reduce the weight of parts as much as possible through new technologies. Like plastic products, the weight of parts can be reduced through the core and bracket without affecting the integrity of the product. MIM parts are outstanding in terms of tiny and micro components, and it is feasible to weigh less than 0.1 g. Weight is not a limiting factor, and products longer than 250mm can also be processed.

 

Thinness

A wall thickness of less than 6mm is most suitable for MIM. Thicker outer wall is also acceptable, but the cost will increase due to long processing time and additional materials. In addition, the extremely thin wall less than 0.5 mm can also be realized for MIM, but it has high requirements for design

 

yield

MIM parts are highly flexible processes, and the annual demand of thousands to millions of production can be realized very economically. Like castings and injection molded parts, MIM parts require customers to invest in mold and tool costs, so for small batch products, cost estimation is usually affected.

 

raw material

MIM parts can handle many materials, including ferroalloys, super alloys, titanium alloys, copper alloys, refractory metals, hard alloys, ceramics and metal matrix composites. Although nonferrous alloys aluminum and copper are technically feasible, they are usually treated by other more economical methods, such as die casting or machining.

 

4. MIM part design guidance

MIM parts are widely used in various industries such as automobile, medical, electronics, industry, and consumption. The products include auto parts, aerospace equipment, mobile phones, dental instruments, electronic radiators and sealed packaging, electronic connector hardware, industrial tools, optical fiber connectors, spray systems, disk drives, medical equipment, hand-held electric tools, surgical instruments, and sports equipment.

 

Keyword: MIM injection medical device accessories metal powder injection molding powder metallurgy MIM application MIM process Shenzhen MIM