Metal forming new process must know: MIM

1.MIM is a metal forming process
MIM (Metal injection Molding) is the abbreviation of metal injection molding. It is a forming method in which the plasticized mixture of metal powder and its binder is injected into the model. It is to mix the selected powder with the binder first, then granulate the mixture and then inject the desired shape.

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

Mixing

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

Molding

The equipment and techniques of injection molding are similar to those of injection molding. The granular raw material is fed into the machine to be heated and injected into the mold cavity under high pressure. This link to form (green part) after cooling demoulding, only under the condition of about 200 ° c to melt the binder (and metal powder fully fused), the whole process can be carried out, the mold can be designed as a multi-cavity to improve productivity. The cavity size design should consider the shrinkage of the metal parts during sintering. The shrinkage change of each material is precisely known.

degreasing

Degreasing is the process of removing the binder from the molded part. This process is usually done in several steps. Most of the binder is removed before sintering, and the remaining part can support the part into the sintering furnace.
Degreasing can be accomplished by a variety of methods, the most common being solvent extraction. The part after degreasing is semi-permeable, and the remaining binder is easily volatilized during sintering.

sintering

The degreased parts are placed in a high temperature, high pressure controlled furnace. The part is slowly heated under a gas shield to remove residual adhesive. After the binder is completely removed, the part is heated to a very high temperature, and the voids between the particles disappear due to the fusion of the particles. The part is directionally contracted to its design size and transformed into a dense solid. For most materials, the typical sintered density is theoretically greater than 97%. The high sintered density makes the product performance similar to that of wrought materials.

Surface treatment

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

Process video show:

3. MIM products usually have the following characteristics

Complexity

MIM, like injection molding, has no restrictions on shape design. Because MIM is a molding process, additional product features do not add cost, which makes MIM an ideal way to combine individual parts into multi-functional products. MIM design rules are very close to injection molding and thus apply to almost all products.

Precision

The reference design for MIM net forming accuracy is typically ± 0.5% of the dimension. Some characteristics of net forming can reach ± 0.3%. As with other technologies, the higher the accuracy requirement, the higher the cost, so moderate relaxation of tolerance requirements is encouraged where quality permits. Tolerances that cannot be achieved by MIM one-time molding can be achieved with the help of surface treatment.

Weight and Dimensions

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

Thin

A wall thickness of less than 6mm is most suitable for MIM. A thicker outer wall is also possible, but the cost will increase due to the long processing time and the addition of additional materials. In addition, very thin walls of less than 0.5mm can also be realized for MIM, but there are high requirements for design.

Yield

MIM is a flexible process, the annual demand of thousands to millions of production can be very economical to achieve. Like castings and injection molded parts, MIM requires customers to invest in molds and tooling costs, so for small batches of products, it usually affects cost estimates.

Raw material

MIM can process many materials, including ferrous alloys, superalloys, titanium alloys, copper alloys, refractory metals, cemented carbides, ceramics, and metal matrix composites. Although non-ferrous alloys of aluminum and copper are technically feasible, they are usually processed by other more economical means, such as die casting or machining.

4, MIM Design Guidance
MIM is widely used in various automotive, medical, electronics, industrial, consumer and other industries. The products include auto parts, aerospace equipment, mobile phones, dental instruments, electronic radiators and sealed packaging, electronic connector hardware, industrial tools, fiber optic connectors, spray systems, disk drives, medical equipment, hand-held power tools, surgical instruments and sports equipment.