Causes Of Burrs In Powder Metallurgy Parts

1, The gap of the mold

Powder metallurgy technology is a metal powder molding technology. The negative sliding between the die and the die, the die punch and the mandrel must have a matching gap. When the metal powder or the finished sintered blank is pressed in the mold, Flow or plastic deformation occurs during forming. The filling effect of the molded part at the gap of the mold is the root cause of the burr.

2, The accuracy of the mold

The powder pressing method adopts the powder filling method. The surface of the mold is in direct contact with the powder, and the fine powder particles easily enter the gap of the mold to form multi-body friction. In the production practice, after the work-hardening of the powder particles between the molds, the mold gap is further reduced, and the surface of the mold leaves a slight scratch. As the wear is intensified, the surface roughness of the mold is reduced, the friction between the powder and the mold is increased, and burrs are easily formed during demolding, and it is impossible to form. In addition, the accuracy or manufacturing accuracy of the mold will also have an impact on the quality of the product. The shape of the burr depends on the surface quality of the mold. The surface of the general part is rough and has no metallic luster.

3, The damage of the mold

Powder metallurgy parts are often chamfered. In order to reduce the subsequent machining and save cost, the chamfer is added to the mold when designing the mold, so that the mold is prone to thin edges and even sharp corners, which are easily damaged in these places. Due to the complicated shape of the mold and the high manufacturing cost, it is often served without prejudice to the final quality of the product, and flash burrs will appear. The shape of the burr is relatively regular and exists in the mold defect.

4, Mold installation and use

The mold installation is generally from bottom to top, from the inside to the outside, depending on the fit of the mold itself. Due to the existence of the mold matching gap, when the mold is installed and debugged, the uniform distribution of the matching gap cannot be ensured, and the side with a large gap is prone to burrs, and the side with a small gap is liable to generate dry friction and cause local adhesive wear; Secondly, due to the defects of the installation itself, the die is unevenly stressed during operation, and under the action of huge pressure, slight lateral movement is likely to occur, resulting in an increase of the gap in one direction. Especially in the case of forming shaped parts, the instability of the mold pressure center deviation and the pressure center of the machine tool is not stable, which not only produces large burrs, but also accelerates the wear and tear of the mold, which also has a certain influence on the accuracy of the equipment. These problems can result in local shape irregular burrs.

5, The accuracy of the equipment

In addition to the design and manufacturing precision of the mold itself, the operation accuracy of the mold is related to the accuracy of the forming equipment itself. The mold is installed on the mold frame as required, and the guiding of the upper and lower molds during the running process, as well as the guiding of the mold frame itself, determines the running state of the mold. In the forming of multi-step parts, it often takes 3 to 5 mold punches, and the accuracy of the equipment is particularly important. Insufficient precision of the equipment leads to deterioration of the working conditions of the mold and promotes the generation of burrs. In addition, if the height of the powder exceeds the range of the equipment, the excessive pressing pressure leads to insufficient tonnage of the equipment, resulting in unstable operation of the equipment and burrs. These burrs are randomly distributed on the surface of the part.