Huagong machinery - metal mold blanking clearance, must not be a little bit wrong!

I. The concept of blanking gap
Blanking clearance means the gap between the die edge of the metal die and the die edge of the die.
Z normal: the upper and lower micro cracks coincide.
There is a gap between the single side and the bilateral gap.
Two, blanking clearance impact on stamping
1, the gap on the quality of the cross section
Normal: the upper and lower cracks coincide, the bright band is large, the collapse angle, burr, taper is small, and the surface is smooth;
Too big: the upper and lower cracks do not coincide, tear, break, cross section thick, bright, with small, collapsed angle, big taper;
Too small: the top and bottom cracks do not coincide, the two shear, forming second bright band, burr large;
Uneven: small gap on the side of the small quality of the characteristics of the gap, the large side of the large gap cross section quality characteristics.
2. The influence of clearance on dimensional accuracy
Because of the existence of elastic deformation, the elastic recovery occurs at the end of the blanking, so that the size of the die has a size deviation from the edge of the punch, and the size of the elastic deformation is directly related to the blanking gap.
When the gap increases, the metal increases inward and the elastic recovery increases the size of the workpiece (hole size), the tensile strength of the metal increases, and the elastic recovery reduces the size of the workpiece (the size of the lower workpiece).
When the clearance becomes smaller, the degree of metal compression increases, the pore size decreases, and the internal pressure increases, and the size of the workpiece increases.
3, the gap between the impact of cutting force
The influence laws of the blanking clearance blanking force is the smaller the gap, the deformation zone stress component was large, the tensile stress component is small, the material deformation resistance increases, the greater the blanking force. On the other hand, the greater the gap, the deformation zone tensile stress component is greater, the deformation resistance decreased, blanking force is small. When the clearance reaches 5%-20% of the material thickness, the blanking force is not obvious.
When the single clearance Z increases to 15%-20% of the material thickness, the discharge force is 0.
4. The influence of clearance on die life
Because of the friction between the workpiece and the side walls of the convex and concave die, the gap is small, the friction is large, and the die life is short. During the blanking process, the punch and the hole are punched, the die and the valve of the falling material have friction, and the smaller the clearance, the more serious the friction. Therefore, the small clearance is extremely unfavorable to the life of the die, and the larger clearance can reduce the friction between the side of the punch and the die and the material, and can reduce the uneven influence of the gap, thereby improving the service life of the die.
5, determine the reasonable gap value
The selection of clearance should make the blanking reach better cross section quality, higher dimension precision, smaller blanking force and higher die life.
Reasonable gap means a range of value, the largest reasonable gap, the smallest reasonable gap. The gap is determined by considering the effects of each of these factors, and a suitable gap is chosen as a reasonable clearance. Its upper limit is the maximum reasonable sound gap, and the lower limit is the minimum reasonable gap, that is, reasonable gap means a range value. In the design of the mold, according to the specific requirements of the workpiece and production
The following principles can be selected:
(1) when the cross section quality of the workpiece is not strictly required, in order to improve the die life and reduce the blanking force, a larger gap value can be chosen.
(2) when the quality of workpiece cross section and manufacturing tolerances are higher, smaller clearance should be chosen.
(3) when calculating the edge size of blanking die, taking into account the wear of the mold during use, it will increase the gap between the blade and the blade. It should be calculated according to the Zmin value.