Failure Analysis And Structural Optimization Of The Typical Fine Blanking Punch

Fine blanking is a precise plastic forming technology, which can be used to process parts with high dimensional precision and smooth sheared surface. Based on these satisfactory advantages, fine blanking has been widely used in many industrial fields. The forming process and die structure are becoming more and more complicated.However, the long development cycle and low lifetime is the bottle neck for the fine blanking future development. Thus it is significant to analyze of the failure types and the main factors affecting the die life, and make future improvement for the die structures. The fine blanking dies of the pawl and the chute used for the seat recliner were firstly introduced in this thesis, and failure analysis has been carried out in view of mechanical calculation, metallographic test, hardness test and SEM. The results showed that the material Cr12MoV with poor banded distributed carbides and low hardness was the main cause for the longitudinal rupture of the pawl punch. For the chute punch, the powder metallurgy high speed steel S790 was selected and had a good comprehensive performance. While the intercrystalline fracture, secondary crack and microporous pattern have been examined in the SEM test. It could be concluded that the rupture of the chute punch was brittle fatigue fracture.Secondly, the different structures and fixed modes for the punch were comparatively analyzed. The stress and deformation distribution of the chute punch was analyzed by ANSYS Workbench. There was stress concentration at the screw thread hole caused by the screw preload and blanking force. The structure improvement was proposed. Finally, the ratchet die structure was researched by finite element method. The result showed that the stress of the semi-piercing punch was over the material ultimate strength. The thin-walled punch was optimized and the maximum stress was decreased by 40%.