Metal Powder Injection Molding High Specific Gravity Tungsten Alloy

At present, MIM has become the most promising near-net-size forming technology in the international powder metallurgy field. It is known as one of the “hottest metal parts forming technologies in the world”. The metal powder injection molding technology (MIM) is a plastic molding process. 

The products of technology, polymer chemistry, powder metallurgy, metal materials and other disciplines infiltrate and cross each other. It is a new change in manufacturing technology industry that the mold can be injected into the blank with high density, high precision and three-dimensional complex shape by sintering, and it can quickly and accurately materialize the design ideas into products with certain structural and functional properties and produce parts directly in batch.

The technology of making heavy tungsten alloy with metal powder injection molding (MIM) technology includes:

1. Ingredients: A tungsten alloy feeding material having a granular moisture content of ≤ 0.2% is provided. The tungsten alloy feeding material is a mixture of a high-density tungsten alloy powder and an organic binder. The tungsten alloy includes at least W, Ni, Cu, Fe and Co, in which W accounts for the mass percentage of the tungsten alloy ≥ 85%, so that the density of the tungsten alloy reaches 16.5-19.0 g/cm3.

2.Forming: The tungsten alloy feeding is injected into the mold at an injection temperature of 100-195 ℃, an injection pressure of 600-1800 bar, and an injection speed of 30-140 mm/s. The preferred injection cycle is 25 s. The mold temperature of the mold is preferably selected at 35 ℃, and the pressure holding pressure therein is sequentially selected to be 750 bar, 750 bar, and 100 bar, and the corresponding holding pressure time is 0.2 s, 0.8 s, and 0.1 s in this order. According to the actual size of different products, the injection cycle, packing pressure and holding time need to be adjusted to form tungsten alloy blank without defects.

3.Solvent degreasing: the tungsten alloy green body is placed in a water bath at a temperature of 25-45 degrees Celsius for solvent degreasing 8-24h, and the preferred degreasing agent is n-heptane.

4.Atmospheric thermal degreasing: The tungsten alloy green body after solvent degreasing is placed in an ammonia decomposition gas, and the 20-45min/ boat's boat speed is heated to 10-28h in the push rod furnace with the highest degreasing temperature of 600-1000.

5.Atmosphere sintering: The green alloy of tungsten alloy after thermal degreasing is placed in ammonia decomposition gas, and the sintering temperature is 1400-1500° C., and the boat speed is 20-45 min/boat push rod furnace for sintering for 10-28 hours. After cooling, a tungsten alloy with a high specific gravity is obtained.

The high density tungsten alloy sintered by the new technology has high density, high hardness, no magnetic, low sintering temperature and low coefficient of thermal expansion. It can meet the requirements of high temperature, high humidity, salt fog and so on, and has the physical, chemical and mechanical properties close to the forgings.

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