Automatic centring with moving die for cold small clearance punching of die-quenched steel sheets

• Cold small clearance punching of die-quenched steel sheets.
• Comparison of punching without and with automatic centring in eccentric condition.
• Shift of the moving die by imbalanced force.
• Improvement of sheared edge quality and prevention of tool failure.

An approach for automatically correcting the eccentricity of the die to the punch with a moving die in small clearance punching of die-quenched steel sheets having low ductility was developed to improve the quality of the sheared edge and tool life. Although small clearance punching has the advantage of high quality of sheared edges for high strength steel sheets, it is not easy to set the die and punch for the small clearance concentrically. This brings about deterioration of the quality of the sheared edges and failure of the tools. In automatic centring, the position of the moving die is corrected by an imbalanced force during punching. It was found that small clearance punching with automatic centring is effective for not only the improvement of surface quality of the sheared edge but also the prevention of tool failure and delayed fracture in cold punching of die-quenched steel sheets having 1500 MPa in tensile strength.

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