Fatigue fracture of pressing die of tablet press

Fatigue fracture of pressing die of tablet press

The punching die of the tablet press is a part of repeated motion, so the probability of fatigue fracture exists. Once the die breaks in the work, the consequence is very serious. Therefore, the fatigue fracture of the die should be strictly prevented. We know that the fatigue fracture of steel has a development process of crack formation, expansion and fracture, and the fatigue fracture formation stage generally accounts for 70%~80% of the fatigue life. Therefore, preventing the premature formation of fatigue crack is the key to improve fatigue fracture.

Fatigue fracture is the part under the action of cyclic load, starting from some weak links, the weak links of the punching die is in the punch arc transition which is easy to produce stress concentration, to prevent the formation of fatigue crack, the first is the selection of the punching die, that is, the punch and the punch body of the arc can not be too small; Secondly, the roughness of the arc transition should not be too low, at least below the surface roughness Ra1.6. The most effective method is to use the technology of shot peening on the surface to improve the ability of resisting fatigue of steel.

The existence of crack on die surface is the root of fatigue fracture. Such surface microcracks often occur during heat treatment. Of course, the selection of materials with high hardenability, the probability of surface microcrack will be greatly reduced. In order to prevent the existence of surface microcracks, the finished die should be nondestructive tested. Commonly used methods are magnetic particle inspection and penetration inspection. Permeable inspection is simple, easy to perform, low cost, and effective.