1, mold gap
Powder metallurgy technology is a kind of metal powder die forming technology. The relative sliding between the die and the die, the die and the core rod must have a coordination gap. When the metal powder or the fine sintered blank piece is subjected to pressure in the mold, When forming, Will produce flow or plastic deformation. The filling effect of the molding parts at the gap of the mold is the root cause of the burr.
2, the precision of the mold
Powder suppression mostly uses volumetric powder method. The surface of the mold is in direct contact with the powder. Small powder particles can easily enter the mold gap to form multiple body friction. In production practice, after the powder particles between the molds are hardened, the mold clearance is further reduced, and the surface of the molds will leave minor scratches. With the increase of wear, the surface roughness of the mold is reduced, and the friction between the powder and the mold is increased. When the mold is demolded, burrs can easily appear, and even can not be formed. In addition, the precision or manufacturing precision of the mold will also have a certain 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, mold damage
Powder metallurgical parts often have inverted corners. In order to reduce subsequent mechanical processing and save costs, the inverted corners are added to the mold when designing the mold. This makes the mold prone to thin edges and even sharp corners, which are easily damaged in these places. Due to the complex shape of the mold and the high manufacturing cost, it is often still in service without affecting the final quality of the product. There will be flying burrs, and the shape of the burrs will be compared to the rules, which exist in the mold defects.
4, mold installation and use
Mold installation is generally from the bottom up, from the inside to the outside of the installation, depending on the mold itself to coordinate positioning. Due to the existence of the mold with the gap, when installing and debugging the mold, it is impossible to ensure the uniform distribution of the gap. The side with the large gap is prone to burrs, and the side with the small gap is prone to dry friction and leads to local adhesion wear.; Second, due to the defects of the installation itself, the mode impulse is not uniform at the running time, and under the action of great pressure, it is easy to produce small lateral movements, resulting in an increase in the gap in one direction. Especially in the formation of allotype parts, due to the fact that the mold pressure center runs away from the pressure center of the machine tool and does not coincide, it not only produces large burrs, but also accelerates the wear and damage of the mold, and has a certain impact on the accuracy of the equipment. These problems produce irregularly shaped burrs.
5, the precision of the equipment
The operation precision of the mold depends on the design, manufacturing accuracy and installation and debugging of the mold itself, but also related to the precision of the forming equipment itself. The mold is installed on the die frame according to the requirements, and the direction of the upper and lower die punching during the running process, as well as the direction of the die frame itself, determine the operating status of the die. In the forming of multi-step parts, it often takes 3 to 5 molds, and the accuracy of the equipment is particularly important. The lack of precision of the equipment leads to the deterioration of the working conditions of the die, which promotes the production of burrs. In addition, if the powder height exceeds the range of the equipment, the pressure pressure is too large and the equipment tonnage is insufficient, resulting in unstable operation of the equipment and burrs. This kind of Burr is randomly distributed on the surface of the part.
The above is the reason for the occurrence of burrs in powder metallurgical parts. With the improvement of industrialization and automation, the requirements for the manufacturing accuracy of mechanical parts are getting higher and higher, the requirements for the use conditions are becoming more and more harsh, and the burrs are gradually attracting high attention. The removal of burrs becomes a key process in the processing of parts.