Metal Injection Molding

Application of metal injection molding MIM in the field of military precision parts

The metal injection molding business of Qinhuangdao Zhongwei Precision Machinery Co., Ltd. is mainly divided into pistol series metal accessories and titanium alloy metal injection molding parts. The products are widely used in aviation, aerospace, construction machinery and other fields. Some products are exported to Europe and the United States. country and region.

MIM Overview

MIM (Metal Injection Molding) is the abbreviation of Metal Injection Molding. It is a molding method in which a plasticized mixture of metal powder and its binder is injected into a mold. It is firstly mixing the selected powder with a binder, then granulating the mixture and then injection molding the desired shape.

The MIM process combines the design flexibility of injection molding with the strength and integrity of precision metals to achieve low-cost solutions for extremely complex geometry parts. The MIM process is divided into four unique processing steps (mixing, molding, debinding and sintering) to achieve the production of parts, with or without surface treatment depending on the product characteristics.

Metal Injection Molding (MIM) Production Process

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

1. Main technical features of MIM process:

(1) It is suitable for the forming of various powder materials, and the product is widely used;

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

(3) It can directly form small parts with complex geometric shapes (0.03g ~ 200g);

(4) The dimensional accuracy of the parts is high (±0.1%～±0.5%), and the surface finish is good (roughness 1～5μm);

(5) The product has high relative density (95-100%), uniform organization and excellent performance;

2. Several commonly used surface treatment processes for MIM parts

●Polished

Using mechanical, chemical or electrochemical action, the surface roughness of the workpiece is reduced to obtain a bright and flat surface.

●Electroplating treatment

The process of attaching a metal film to the surface of a metal or other material by electrolysis. Electroplating can prevent metal oxidation (such as rust), improve wear resistance, electrical conductivity, reflectivity, corrosion resistance (copper sulfate, etc.) and enhance aesthetics.

●PVD processing

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

●Blackening

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

●Phosphating

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

1) Provide protection to the base metal and prevent the metal from being corroded to a certain extent;

2) It is used as a primer before painting to improve the adhesion and anti-corrosion ability of the paint film.

●Spray treatment

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

●In summary:

1) Polishing and phosphating are mainly pretreatments to prepare for other post-treatments;

2) Electroplating and PVD are two types of processing technologies that are widely used;

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

3. Applicable materials and application fields:

The application of MIM is extremely wide, including daily necessities, such as automobiles, aerospace industry, military industry, mobile phones, watches, medical treatment, household appliances, cameras and power tools equipped with MIM parts. MIM technology can be applied to any material that can be made into powder. The currently used MIM material systems are:

Stainless steel, iron-based alloys, magnetic materials, tungsten alloys, hard alloys, fine ceramics and other series.

MIM technology makes up for the technical deficiencies of traditional processing methods or the shortcomings of inability to manufacture. It is not only competitive with traditional processing methods. MIM technology can exert its strengths in the field of parts that cannot be produced by traditional processing methods.

From the analysis of the process essence of MIM, it is currently the most suitable process for mass production of high melting point materials, high strength and complex shape parts. Its advantages can be summarized as follows:

(1) MIM can form various metal material parts with complex three-dimensional shapes (as long as this material can be made into fine powder). The density and performance of each part of the part are consistent, that is, isotropic. Provides a greater degree of freedom for part design.

(2) MIM can maximize the production of parts close to the final shape, with high dimensional accuracy.

(3) Even in solid phase sintering, the relative density of MIM products can reach more than 95%, and its performance is comparable to that of forging materials. Especially the dynamic performance is excellent.

(4) The price of powder metallurgy (PM) automatic molding machine is several times higher than that of injection molding machine. MIM can easily use a multi-cavity mold with high molding efficiency, long service life of the mold, and convenient and quick replacement and adjustment of the mold.

(5) The injection material can be used repeatedly, and the material utilization rate is over 98%.

(6) The product turns quickly. High production flexibility and short time from design to production for new products.

(7) MIM is especially suitable for mass production and has good product performance consistency. If the parts produced are selected properly and the quantity is large, higher economic benefits can be achieved.

(8) MIM has a wide range of materials and wide application fields. The materials that can be used for injection molding are very wide, such as carbon steel, alloy steel, tool steel, refractory alloy, cemented carbide, high specific gravity alloy, etc.

MIM Device

According to the processing process of MIM, the equipment involved in MIM includes a mixing and granulating integrated machine, a special injection molding machine for MIM, a degreasing furnace, a sintering furnace, and various testing and secondary processing equipment.

MIM Process Application

(1) Auto parts: parts for airbags, parts for car locks, parts for seat belts, car door lift systems, pinions, small parts for air conditioning systems for cars, racks in brake systems, etc. small parts in the sensor;

(2) Military parts: gun parts, ammunition parts, fuze parts;

(3) Computer and IT industries: such as mobile phone card trays, mobile phone structural parts, printer parts, magnetic cores, striker pins, drive parts, optical communication ceramic plugs;

(4) Tools: such as drill bits, cutter heads, nozzles, spiral milling cutters, pneumatic tools, parts for fishing gear, etc.;

(5) Household appliances: such as watch cases, watch chains, electric toothbrushes, scissors, golf heads, jewelry links, cutting tool heads and other parts;

(6) Parts for medical machinery: such as orthodontic frame, scissors, tweezers;

(7) Electrical parts: micro motors, sensor devices;

(8) Mechanical parts: such as textile machines, crimping machines, office machinery parts, etc.