Microstructure Affecting Cutting Quality in Fine Blanking Process

Problem statement: Fine blanking process is a high precision process and worldwide in developed countries. Since specimen does not occur fracture on the cutting edge and it is not necessary to decorate again in the finishing process for the fine blanking which can be reduced some operation steps. For example, if chain wheel of motorcycle is produced by conventional blanking, it needs nine steps. But, if it is produced by fine blanking, it requires only three steps. With these reasons, fine blanking is boom for the metal forming industry in Thailand. But, due to some mechanical properties for some kinds of metal such as low elongation or imperfect microstructure, it is not cut by using fine blanking directly. Approach: Objective of this research was to investigate microstructure of specimen for fine blanking process in order to avoid fracture surface on blank. The optimum condition will result in higher elongation while having small decrease in tensile strength. The circular specimen with diameter of 16 mm and thickness of 2 mm was chosen. Material was steel which contains 0.45% carbon. Results: Microstructures contained pearlite and ferrite grains. The grains sizes were expanded with temperature of heat treatments at 700, 800 and 900°C, respectively, for 1 h. The specimen exposes to heat treatment in each temperature results in the increase of overall shear surface and the decrease of fracture surface when compared with no heat treatment. This is due to no appearance of strain hardening. For the microstructures exposed to heat treatment at 700°C for 10-20 h were almost spherroidite. It revealed that facture surface became shear surface after heat treatment over 10 h. Conclusion/Recommendations: The changes of microstructure for 0.45% carbon steel significantly affected to the overall shear and fracture surface and yield strength due to increasing of spherroidite, thus fracture was decreased with time.