Analysis Of The Early Die Cracking In Hydraulic Machine Fine-Blanking

Fine-blanking, as a near net forming process, has been widely used in industrial field especially in the automotive industry since it has excellent quality. With the acceleration of industrial modernization, automatic blanking machine has been more and more widely used. Nevertheless, the hydraulic machine is still welcomed in small and medium enterprises on account of its economic advantages. The hydraulic die-set attached cylinder is an approach to realize fine-blanking on general hydraulic machine since triaxial compressive stress is guaranteed. At present, the hydraulic machine with die-set is widely used in the production of varieties of small fine-blanking parts below 4 mm. Based on the enterprises investigation, the early fracture in the back of the die has been researched on the hydraulic machine.The initiation of the crack depends on the combined effect of the strength and stress at certain point of the material.A large number of carbide in net structure which showed the metallurgical defects and the brittle fracture of the die had been observed by microscope and SEM. And the excessive Cr has been tested compared with standard ASSAB88. Besides, the hardness testing showed that the hardness of the failure die was non-uniform and far less than the standard.The comparative structural static finite element analysis result shows that a large deflection directly caused the fracture since the local stress had exceeded the tensile strength in the stress concentration site of the die. The bearing strength in the back had an important impact on the deformation of the die. In die structure design, cone positioning and general frame should be avoided, and the bearing strength of the back of the die should be increased for the blanking of thick parts.The research came to a conclusion that the early fracture was the result of the combined effects of metallurgical defects, material and structure defects, the shortage of the rigidity of the die and the die-set. The insufficient support strength of the frame and poor assembling accuracy was the main reason. The general die-set structure didn't apply to the production of the parts which are 3 mm or above, two pieces per stroke.