Detailed explanation of the process from metal injection molding (MIM) to post-processing

1. Introduction to Metal Injection Molding (MIM)

Metal injection molding (MIM) is an advanced metal manufacturing technology, which combines the advantages of plastic injection molding and powder metallurgy. Many products with high performance requirements use MIM, involving electronics, people's livelihood, auto parts, medical devices, military, aerospace and other industries. Such as mobile phones, electronic radiators, sealed packaging, junction boxes, industrial tools, optical fiber connectors, fluid spraying systems, sports equipment, hard disks, automotive oil supply and ignition systems, dental instruments and dental reinforcement tools, pharmaceutical equipment, pumps, surgical instruments, aerospace and national defense systems, etc.

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. Metal Injection Molding (MIM) Process

The MIM 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 parts.

The MIM process is divided into four unique processing steps (mixing, molding, degreasing and sintering) to realize the production of parts, and determine whether surface treatment is required according to the product characteristics.

The manufacturing process of MIM generally includes mixing granulation, injection molding, degreasing, sintering and secondary treatment.

3. Main technical features of MIM process:

Suitable for the forming of various powder materials, the products are widely used;

High utilization rate of raw materials, high degree of production automation, suitable for continuous mass production.

It can directly form small parts with complex geometry (0.03g~200g);

High dimensional accuracy of parts (± 0.1% ～ ± 0.5%), good surface finish (roughness 1 ～ 5 μ m）；

The product has high relative density (95~100%), uniform structure and excellent performance;

4. Common Surface Treatment Processes of MIM Parts

Polishing treatment

Use mechanical, chemical or electrochemical effects to reduce the surface roughness of the workpiece to obtain bright and flat surface processing.

Electroplating treatment

The process of using electrolysis to attach a layer of metal film to the surface of metal or other materials. Electroplating can prevent metal oxidation (such as rust), improve wear resistance, conductivity, reflective property, corrosion resistance (copper sulfate, etc.), and improve aesthetics.

PVD treatment

The process of transferring atoms or molecules from the source to the surface of the substrate through physical processes. Its function is to make some particles with special properties (high strength, wear resistance, heat dissipation, corrosion resistance, etc.) sprayed on the matrix with lower performance, so that the matrix has better performance.

Blackening treatment

It is a common chemical treatment method to produce a layer of oxide film on the metal surface to isolate air and achieve the purpose of rust prevention. When the appearance requirements are not high, blackening treatment can be adopted. The main components of blackening liquor are sodium hydroxide and sodium nitrite.

Phosphating treatment

It is a process of chemical and electrochemical reaction to form phosphate film. The main purposes of phosphating are:

1) Provide protection for the base metal to prevent the metal from corrosion to a certain extent;

2) It is used for priming before painting to improve the adhesion and corrosion resistance of the paint film.

Spraying treatment

It refers to the coating method that is applied to the surface of the object to be coated by means of a spray gun or a disc atomizer, with the help of pressure or centrifugal force, to disperse into uniform and fine droplets.

In summary:

1) Polishing and phosphating are mainly pre-treatment to prepare for other post-treatment;

2) Electroplating and PVD are two kinds of treatment technologies that are widely used;

3) Blackening and spraying will greatly change the surface of products, which is more suitable for large workpieces.

5. Applicable materials and application fields:

MIM is widely used, including daily necessities, such as automobiles, aerospace industry, military industry, mobile phones, watches, medical appliances, household appliances, cameras and power tools with MIM parts. MIM technology can be applied to any material that can be made into powder,

6. The current applied MIM material systems mainly include:

Stainless steel, iron base alloy, magnetic materials, tungsten alloy, hard alloy, fine ceramics, etc.