Difficulties in processing powder metallurgy parts

Although the development of P / M industry one of the goals is relieving machine and process of P to a main attraction is only a small amount of processing is needed, but many parts still need processing accuracy and better surface finish. Unfortunately the processing of these parts is extremely difficult. Most of the trouble encountered is caused by the porous.

Porous lead to micro fatigue of blade. Cut out the cutting edge of the cut, it is passed between particles and holes. The impact caused by the repeated small cracks on the cutting edge of the. The fatigue crack growth until the cutting edge chipping. This is usually very small micro chipping, abrasive wear is usually normal.

Also reduce the thermal conductivity of P/M porous parts. The result is on the cutting edge of a high temperature and can cause crater wear and deformation. Path connected to the internal porous structure provides cutting fluid discharged from the cutting area. This will cause thermal cracks or deformation, especially important in drilling.

The surface area of the porous structure caused by inner increase also allows oxidation and / or carbonation occurred during heat treatment. As previously mentioned, the oxide and carbide hard wear.

This is extremely important porous structure is also given failure parts hardness readings. When one intends to measure the macro hardness of P/M parts, which includes hole hardness factor. The porous structure leads to the collapse of the structure, the relatively soft parts of the wrong impression. A lot of hard particles to the individual. As described above, the difference is dramatic.

In the powder metallurgy parts of inclusions is negative. In the process, the particles are pulled from the surface when it is rubbed out of the cutting tool and can form a scratch or scratch on the surface of the part. These inclusions are usually large, leaving visible holes on the surface of the part.

The carbon content of the mixed lead to inconsistent workability. For example, the carbon content of FC0208 alloy is between 0.6% and 0.9%. A batch of 0.9% of the material with carbon content is relatively hard, resulting in poor tool life, while the other batch of carbon content of 0.6% of the material has excellent tool life.Two kinds of alloys are within the allowable range.

The final machining problem is related to the type of cutting which occurs on the P/M part. As the parts are close to the final shape, the cutting depth is very shallow. This requires free cutting edge. The built-up edge of the cutting edge often leads to micro collapse.

PM parts performance summary

Although one of the original intention of the P/M industry is to eliminate all of the processing, but this goal has not been reached. Most of the parts are "close to the final shape", it must be some kind of finishing. However, the removal of a small amount of material from the P/M component is typically very wear-resistant compared to castings and forgings.

Porous structure is one of the characteristics of P/M parts, which are widely used, but the tool life was damaged by porous structure. Porous structure can be oil storage and noise, but also produce intermittent cutting on the micro. When from the hole to solid particles moving to and fro nose continuously by the impact, which can lead to very small fatigue deformation and fracture along the cutting edge of the tiny chip. What is worse, usually hard particles.

Even if the macro hardness detected between Rockwell 20~35 degrees, but part of the particle's 60 degrees high of talok. These hard particles lead to severe and rapid wear of the blade. Many P/M parts are heat treated, and they are much harder and stronger after heat treatment. Finally, due to sintering and heat treatment technology and the use of gas, the surface will be hard and wear resistant oxide and / or carbide.

The bulk properties of P/M parts, including machinability, are not only related to the chemical composition of the alloy but also to the level of the porous structure. Many structural parts with hole rate up to 15~20%. The hole rate of the part used as a filter device may be as high as 50%. At the other end of the series, or HIP (forging die casting parts with hole thermionic) rate of 1% or less. This is especially important in the automotive and aircraft applications, because they can get a higher level of strength.

The tensile strength, toughness and ductility of P/M alloy will increase with the increase of the density, and it may also improve the workability. This is because the porous harmful effect on the nose. The increase of the hole rate and the sound insulation performance of the parts. Standard parts generally damped oscillations in the P/M parts to reduce. This is very important for machine tools, air conditioning duct and pneumatic tools. The high porosity of self lubricating gear is also necessary.

Prospects for MIM Powder Injection Molding Process

Compared with conventional technology, MIM powder injection molding process has high accuracy, homogeneous, high performance, and low production cost, which are widely used in electronic information engineering, bio-medical equipment, office equipment, vehicles, machinery, hardware, sports equipment, watches and clocks, weapons and aerospace industries.

Therefore, it is generally believe in worldwide that the development of this technology will lead to a revolution in parts forming and machining technology. It is known as "the hottest parts forming technology" and "21st Century forming technology."

At present, Chinese consumption of iron powder and copper powder have surpassed Japan, ranking first in Asia. In the future, major application  of powder metallurgy parts is still automotive field. In the technical point of view, high-density powder metallurgy parts, new powder metallurgy materials, high efficient and precise equipment etc are the future development trends of powder metallurgy industry.

Future development of MIM Powder Injection (http://www.zcmim.com/) mainly in materials and design. To take advantage of the technology to help customers improve product design and reduce costs, thereby expanding powder injection molding applications.