The main failure types of cold working molds are overload failure and wear failure, accounting for 80%-90% of the total failure. Cold heading die is mainly caused by cracking or abnormal wear (partial shedding), cold extrusion die is mainly brittle or wear failure, and cold die is mainly caused by wear failure. The high working stress, the large undulating stress and the cold squeezing die have a significantly higher rate of brittle cracking failure than the low working stress cold dies.
The proportion of fatigue fractures collected is less. This is more than the high-carbon and high-alloy steel used in the cold-working mold materials. The hardness is as high as 60HRC, and the fatigue fracture morphology is difficult to distinguish and statistically. In fact, there are many reasons for the failure of cold-working molds. In addition to the factors of the mold materials, it is also related to the accuracy and condition of the working equipment, the material and surface quality of the products, the structure of the mold and the precision of the processing, and the quality of the operators. Some random factors give failure analysis. Increase the difficulty.
Relationship between working stress, hardness and life of cold work die steel
The measurement statistics show that for the steel material, the average working stress of the cold extrusion die material is about 2500MPa, the hardness is 62-64HRC, the cold heading die is about 1500MPa, the hardness is 58-62HRC, the cold die is about 500MPa, the hardness is used. 60-62HRC, in which the cold extrusion die has the greatest stress.
In fact, it must withstand a random load of 10%-20%, and the local stress of the mold should exceed the above stress. The effect of working hardness on the service life of cold work die steel is the result of comprehensive action. It is the working hardness, failure type and service life chart of cold extrusion W6Mo5Cr4V2 steel punch (extruded 20Cr steel). For early failure cold work dies, the effects of material and other factors should be carefully analyzed.