Metal Powder Injection Molding Technology (MIM) is a new powder metallurgy near-net-form molding technology formed by introducing modern plastic injection molding technology into the field of powder metallurgy.

• Technical introduction

Metal powder injection molding technology combines multi-disciplinary technologies such as plastic molding technology, polymer chemistry, powder metallurgy technology, and metal materials science. It uses molds to injection mold blanks and quickly manufactures high-density, high-precision, three-dimensional complex shapes through sintering. Structural parts. First, the solid powder and organic binder are uniformly kneaded, and after granulation, they are injected into the mold cavity with an injection molding machine in a heated and plasticized state (~150°C) for solidification, and then the parison is formed by chemical or thermal decomposition. The binder in the product is removed, and finally the final product is obtained by sintering and densification.

This process technology not only has the advantages of conventional powder metallurgy processes such as fewer steps, no or less cutting, and high economic benefits, but also overcomes the shortcomings of traditional powder metallurgy products such as uneven materials, low mechanical properties, and difficulty in forming thin walls and complex structures. It is especially suitable for mass production of small, complex and special-required metal parts. It has the characteristics of high precision, uniform structure, excellent performance and low production cost.

• Process flow

Process flow: binder → mixing → injection molding → degreasing → sintering → post-processing.

Mineral powder

The particle size of metal powder used in the MIM process is generally 0.5~20μm; theoretically, the finer the particles, the larger the specific surface area, making it easier to shape and sinter. The traditional powder metallurgy process uses coarser powders larger than 40μm.

Organic adhesive

The function of the organic adhesive is to bond the metal powder particles so that the mixture has rheology and lubricity when heated in the barrel of the injection machine, that is to say, it is a carrier that drives the powder to flow. Therefore, the binder is chosen to be the carrier for the entire powder. Therefore, the choice of sticky pull is the key to the entire powder injection molding. Requirements for organic adhesives:

1. The use of less adhesive can produce better rheology of the mixture;

2. No reaction, no chemical reaction with metal powder during the adhesive removal process;

3. Easy to remove, no carbon remains in the product.

Mixing

The metal powder and organic binder are uniformly mixed together to make various raw materials into a mixture for injection molding. The uniformity of the mixture directly affects its fluidity, thus affecting the injection molding process parameters, as well as the density and other properties of the final material. This step of the injection molding process is consistent in principle with the plastic injection molding process, and its equipment conditions are also basically the same. During the injection molding process, the mixed material is heated in the barrel of the injection machine into a plastic material with rheological properties, and is injected into the mold under appropriate injection pressure to form a blank. The injection molded blank should be microscopically uniform so that the product shrinks evenly during the sintering process.

Extraction

The organic binder contained in the molded blank must be removed before sintering. This process is called extraction. The extraction process must ensure that the adhesive is gradually discharged from different parts of the blank along the tiny channels between the particles without reducing the strength of the blank. The rate of binder removal generally follows the diffusion equation. Sintering can shrink and densify the porous degreased blank into products with certain structure and properties. Although the performance of products is related to many process factors before sintering, in many cases, the sintering process has a great or even decisive impact on the metallographic structure and properties of the final product.

Post-processing

For parts with more precise size requirements, necessary post-processing is required. This process is the same as the heat treatment process of conventional metal products.

• Process advantages

MIM uses the characteristics of powder metallurgy technology to sinter mechanical parts with high density, good mechanical properties and surface quality; at the same time, it uses the characteristics of plastic injection molding to produce parts with complex shapes in large quantities and efficiently.

1. Structural parts with highly complex structures can be formed.

Traditional metal processing generally involves processing metal plates into products through turning, milling, planing, grinding, drilling, boring, etc. Due to technical cost and time cost issues, it is difficult for such products to have complex structures. MIM uses an injection machine to inject the product blank to ensure that the material fully fills the mold cavity, thus ensuring the realization of the highly complex structure of the part.

2. The product has uniform micro structure, high density and good performance.

Under normal circumstances, the density of pressed products can only reach a maximum of 85% of the theoretical density; the density of products obtained by MIM technology can reach more than 96%.

3. High efficiency, easy to achieve mass and large-scale production.

The metal mold used in MIM technology has a lifespan equivalent to that of engineering plastic injection molding molds. Due to the use of metal molds, MIM is suitable for mass production of parts.

4. Wide range of applicable materials and broad application fields.

MIM can use almost most metal materials, and considering economy, the main application materials include iron-based, nickel-based, low alloy, copper-based, high-speed steel, stainless steel, gram valve alloy, cemented carbide, and titanium-based metals.

5.Significantly save raw materials

Generally, the utilization rate of metal in metal processing and forming is relatively low. MIM can greatly improve the utilization rate of raw materials, which is theoretically 100% utilization.

6. The MIM process uses micron-level fine powder.

It can not only accelerate sintering shrinkage, help improve the mechanical properties of materials, extend the fatigue life of materials, but also improve resistance to stress corrosion and magnetic properties.

• Application areas

Its products are widely used in industrial fields such as electronic information engineering, biomedical equipment, office equipment, automobiles, machinery, hardware, sports equipment, watch industry, weapons and aerospace.

1. Computers and their auxiliary facilities: such as printer parts, magnetic cores, striker pins, and driving parts;

2. Tools: such as drill bits, cutter bits, nozzles, gun drills, spiral milling cutters, punches, sockets, wrenches, electrical tools, hand tools, etc.;

3. Household appliances: such as watch cases, watch chains, electric toothbrushes, scissors, fans, golf heads, jewelry links, ballpoint pen clamps, cutting tool heads and other parts;

4. Parts for medical machinery: such as orthodontic frames, scissors, and tweezers;

5. Military parts: missile tails, gun parts, warheads, powder covers, and fuze parts;

6. Electrical parts: electronic packaging, micro motors, electronic parts, sensor devices;

7. Mechanical parts: such as cotton loosening machines, textile machines, curling machines, office machinery, etc.;

8. Automobile and marine parts: such as clutch inner ring, fork sleeve, distributor sleeve, valve guide, synchronization hub, airbag parts, etc.