The applications of MIM process has involved various fields

The applications of MIM process has involved various fields of national economy and has a broad market prospect.

Such as:

Computer and auxiliary facilities: such as printer parts, magnetic cores, pins and driving parts;

Tools: like gun drills, drill chucks, electric tools, hand tools, wrenches and other parts, milling head, nozzles, etc.

Household appliances: such as watch case, watch chain, electric toothbrush, scissors, fans, golf ball head, simulation jewelry, cutter head and other parts;

Medical equipment parts: such as dental orthodontic frame, scissors, tweezers;

Military ordnance parts: missile tail wing, gun parts, warhead, liner, fuze parts;

Electrical parts: micro motor parts, electronic parts, sensor parts, mobile phones, BP machine parts;

Machinery parts: small and complex parts of all kinds of machinery, such as pine cotton machine, textile machine, sewing machine, office machinery, etc.

Automobile and ship parts: such as clutch inner ring, rocker arm insert, fork shift sleeve, distributor sleeve, automobile airbag parts, automobile locks;

All kinds of special-shaped carbide nozzles for drilling in oil fields.

Compares between MIM and investment casting

Most plastic products after injection molding is the finished products which can be assembled and shipped. However, for MIM, injection molding is only the first step, followed by degreasing, sintering, shaping and other complex processes. These complex processes prevent many people who want to enter MIM industry. But those plastic companies that have already entered or are ready to should fully understand the differences between injection moulding and MIM.

First, the understanding of feeding:

In MIM process, the only function of plastics is that they act as a carrier to bring metal powder into the cavity through injection, and form the parts we want by cooling.

Usually we use plastic as the binder in the feed, and its volume is about 40% of the whole part. What specific ingredients are there in the binder?

A, Wetting agent, make the surface of metal powder humid, which can reduce the tension of the interface between binder and powder.

B, A macromolecule component. When degreasing, it is removed first, and form a network of voids, so that other binders are more easily decomposed.

C, Skeleton polymer. After degreasing, it is used to maintain the shape of the parts until the temperature rises to the sintering temperature.

D. Another material that mix the main binder and the skeleton polymer. According to different metal powders, various kinds of feeds can be produced, such as low alloy steel (iron-nickel), high alloy steel (stainless steel series), carbide (tungsten carbide-cobalt), non-ferrous metal (titanium, copper), precious metal (gold), magnetic metal (neodymium-iron-boron), etc. The size, distribution and shape of these powders affect the feed flow.

Second, the transformation of molds design:

There are several differences between MIM and standard plastic molds. MIM thermal conductivity of the feed is several times higher than that of plastic, so the fluidity is worse. The shrinkage rate of MIM moulds is usually 15%~22%, which is much larger than that of plastic moulds, so it is more difficult to control embryogenic density and sintering size. Many companies make mistakes on this issue. In addition, metal powder is more destructive to the die than plastic. Above all, we need to make some changes in the design of MIM moulds:

A, Tool steel. High wear resistant heat treated steel should be selected.

B, Hot runner. The liquid hot runner is more stable than the electrothermal runner, and more uniform embryogenesis can be obtained, so the sintering deformation will be smaller.

C. Runner and rubber port. Because of the high shrinkage rate and the high thermal conductivity of the feed, the layout of the runner and the rubber port must be balanced, otherwise the shaping work after sintering will be more troublesome. Sometimes, it is even necessary to modify the dimension by CNC machining, which will increase the manufacturing costs.

D. The length of the feed head in the mould nozzle should be as short as possible, and the flow path of the feed should be shortened to reduce the heat loss.

E, Surface treatment of the die cavity. Blackprint is a common problem in MIM products. The treatment of die surface will improve it. In general, VDI18 discharge treatment is used in die processing.

Third, injection moulding:

Because metal powder is more destructive to molds than plastic, injection moulding machines should be equipped with special MIM nozzles, screw rods, rocket heads, check rings and seat rings.

A, Screw. Because metal powder accounts for 60% of the total feed volume, screw compression ratio should be less than that of plastic, about 1.5, avoiding heat accelerating the decomposition of binder.

B, Check ring. Different kinds of feeding materials, such as stainless steel, titanium, tungsten, have different backlash clearances. The powder sizes of different manufacturers are different, and the requirements for the size of the backlash ring are also different. The clearance is generally one to three times the maximum powder diameter.

C. Injection speed. It’s enough to inject at a certain speed. Don’t use the plastic injection method, which is slow, fast and slow, because the fluidity of the feed does not allow us to do so.

D, Melt glue. High melting speed will lead to the degradation of binder polymers. First, it will affect the density uniformity of blanks. Second, it will reduce the utilization of recycled materials. The service life of the rocket head and check ring will be reduced. Normal speed: 50 rpm, back pressure: not more than 30 bar.

Fourth, when the product is ejected from the mould, the direction of plastic products and MIM parts is completely different.

Harber Metal Ltd. is a powder metallurgy manufacturing company created since 2014, with good production facilities and advanced technology, and is now into the production of iron-based powder metallurgy and stainless steel powder metallurgy. The company covers an area of 5,000 square meters, with 1,600 square meters of workshop, and dozens of sets of automatic presses from 100 tons to 5 tons for powder metallurgy. There are dozens of sets of automatic presses for powder metallurgy ranging from 100 tons to 5 tons, as well as complete product testing equipment and matching powder metallurgy mold processing equipment. Now the company has an annual output of 500 tons, about 5 million pieces of powder metallurgy products. products per year.