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Influence of punching clearance of metal mold on stamping quality

2018/10/12 9:48:56 Viewers:
First, the concept of punching gap


The blanking gap refers to the gap between the punch edge and the die edge.


Z normal: the upper and lower micro-cracks coincide.


There are unilateral gaps and bilateral gaps.


 


Second, the impact of punching clearance on stamping


 


1. Influence of clearance on section quality


Normal: the upper and lower cracks coincide, the bright band is large, the sag angle, burr, taper is small, and the surface is flat;


Too large: the upper and lower cracks do not coincide, the tear is broken, the section is thick, the light band is small, the sag angle is large, and the thorn angle is large;


Too small: the upper and lower cracks do not coincide, secondary shear occurs, forming a second bright band, and the burr is large;


Unevenness: Small mass section features appear on the side with small gap, and large gap section quality characteristics appear on the side with large gap.


 


2. The effect of gap on dimensional accuracy


Due to the existence of elastic deformation, the elastic recovery occurs after the blanking, so that the size and the size of the edge of the convex and concave die are deviated, and the elastic deformation has a direct relationship with the blanking clearance.


 


3, the impact of clearance on the cutting force


The influence of the punching clearance on the punching force is that the smaller the gap is, the larger the compressive stress component in the deformation zone is, the smaller the tensile stress component is, the more the material deformation resistance increases, and the punching force is larger. On the contrary, the larger the gap, the larger 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 decreases not significantly.


When the one-side gap Z is increased to 15%-20% of the material thickness, the discharge force is zero.


 


4, the impact of the gap on the life of the mold


Due to the 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 blanking process, the punch and the punched hole, the die and the valve of the blanking member have friction, and the smaller the sound gap, the more severe the friction. Therefore, the too small gap is extremely unfavorable for the life of the mold, and the larger gap can reduce the friction between the side of the punch and the die and the material, and the well can reduce the influence of the unevenness of the gap, thereby improving the life of the mold.


 


5. Determination of reasonable gap value


The clearance is selected to achieve better cross-section quality, higher dimensional accuracy, smaller punching force, and higher die life.


Reasonable gap refers to a range of values, the maximum reasonable gap, and the minimum reasonable gap. The gap is determined by considering the influence of each of the above factors, and selecting an appropriate gap range as a reasonable gap. The upper limit is the maximum reasonable sound gap, and the lower limit is the minimum reasonable gap, that is, the reasonable gap refers to a range value. When designing the mold in its body, it can be selected according to the following principles according to the specific requirements of the workpiece and production:


(l) When the cross-section quality of the workpiece is not strictly required, in order to improve the life of the mold and reduce the punching force, a larger gap value can be selected.


(2) When the workpiece section quality and manufacturing tolerance requirements are high, a smaller gap value should be selected.


(3) When calculating the daily size of the blanking die, taking into account the wear of the mold during use will increase the edge clearance, which should be calculated according to the Zmin value.