Discussion on the influence of metal stamping die blanking gap on the quality of stamping parts

The gap between the cutting edge of the punch of the punching die and the cutting edge of the female die in the production of stamping parts is called the blanking gap. Through analyzing the process of punching sheet metal by stamping die, the force of sheet metal, the deformation mechanism and the state of forming section, the influence of different clearance conditions on the punching section and the influence of punching clearance on the quality of punched parts are discussed, so that the die punching process And the abnormalities that will appear are presented in more detail, so as to explore how to select a suitable blanking gap and deal with the blanking abnormalities in a targeted manner. 1. The effect of clearance on dimensional accuracy Due to the existence of elastic deformation, elastic recovery occurs after the end of punching, which causes a size deviation between the size and the edge size of the convex and concave die, and the size of the elastic deformation has a direct relationship with the punching gap. The gap changes, punching and blanking, the gap increases, the metal is pulled inwardly, and the elastic recovery increases the size of the workpiece (hole size). The stretch of the metal increases, and the elastic recovery reduces the size of the workpiece (the size of the lower workpiece); As the size of the metal becomes smaller, the degree of pressure increases, and the size of the hole decreases. 2. The influence of the gap on the punching force The rule of the impact of the punching gap on the punching force is that the smaller the gap, the larger the compressive stress component in the deformation zone. The smaller the tensile stress component, the greater the deformation resistance of the material and the greater the punching force. Conversely, the larger the gap, the greater the tensile stress component in the deformation zone, the lower the deformation resistance, and the smaller the punching force. When the gap reaches 5%-20% of the material thickness, the punching force will not decrease significantly. When the unilateral gap Z increases to 15%-20% of the material thickness, the discharge force is zero. 3. The effect of the gap on the quality of the section is normal: the upper and lower cracks overlap, the bright band is large, the collapse angle, burr, and the taper are small, and the surface is smooth; too large: the upper and lower cracks do not overlap, tearing and breaking, the section is thick, the bright band is small, and the surface is flat. Angle and thorn taper are large; Too small: the upper and lower cracks do not overlap, secondary shearing occurs, forming a second bright band, with large burrs; Uneven: low-quality section features appear on the side with small gap, and large gap section appears on the side with large gap Quality characteristics. 4. The effect of gap on the life of hardware molds. Because there is friction between the workpiece and the side walls of the convex and concave molds, the gap is small, the friction is large, and the mold life is short. During the punching process, there is friction between the punch and the punched hole, the die and the valve of the blanking part, and the smaller the clearance, the more serious the friction. Therefore, a too small gap is extremely detrimental to the life of the mold, and a larger gap can reduce the friction between the side of the punch and the die and the material, and can reduce the impact of uneven gaps, thereby increasing the life of the mold. 5. Determination of reasonable gap value. The selection of gap should make the punching achieve better section quality, higher dimensional accuracy, smaller punching force, and higher die life. The reasonable clearance refers to a range value, the largest reasonable clearance, and the smallest reasonable clearance. The clearance is determined by comprehensively considering the influence of the above-mentioned factors, and selecting an appropriate range of clearance as a reasonable clearance. The upper limit is the maximum reasonable clearance, and the lower limit is the minimum reasonable clearance. The reasonable clearance refers to a range value. When designing the mold in its body, it can be selected according to the specific requirements of the workpiece and production according to the following principles: (1) When the quality of the cross-section of the workpiece is not strictly required, in order to increase the life of the mold and reduce the punching force, you can choose a larger one. The gap value. (2) When the workpiece section quality and manufacturing tolerance requirements are high, a smaller gap value should be selected. (3) When calculating the blade day size of the blanking die, considering that the wear of the die during use will increase the blade day gap, the calculation should be based on the Zmin value. It can be understood that the blanking gap is a very important parameter in the blanking die through the force form of the sheet material and the forming process of each area of u200bu200bthe blanking section. The value and uniformity of the gap directly affect the quality, dimensional accuracy and mold life of the part. In order to ensure the life of the mold and improve the quality and accuracy of the product, a reasonable gap value must be used, and the uniformity of the gap must be adjusted and controlled. Recommended article: Analyze the basic structure and function of metal stamping dies Previous: How to choose stamping oil in stamping processing