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.