In the blanking process of precision Stamping Parts, there is friction between the punch and the punched hole, and between the female die and the blanking part. The smaller the clearance, the greater the compressive stress exerted by the die, and the more serious the friction.  Therefore, too small a gap is extremely unfavorable to the service life of the mold.  However, a larger gap can reduce the friction between the side surface of the punch and the material, and slow down the adverse effect of uneven gap due to the limitation of manufacturing and assembly precision, thus improving the service life of the die.

As the gap increases, the tensile stress on the material increases, and the material is easy to fracture and separate, thus the blanking force decreases.  In general, the reduction of blanking force is not significant. When the unilateral clearance is about 5 ~ 20% of the material thickness, the reduction of blanking force is not more than 5 ~ 10%.  Gap has a significant effect on unloading force and pushing force.  After the gap increases, it is labor-saving to unload the parts from the male die and push out the parts from the female die. When the unilateral gap reaches about 15 ~ 25% of the material thickness, the unloading force is almost zero.  However, the gap continues to increase, because the burr increases, which in turn will cause the unloading force and jacking force to increase rapidly.  

From the above analysis, it can be seen that the clearance between male and female dies has a great influence on the quality of precision stamping parts, blanking process force and die life.  Therefore, a reasonable clearance must be selected when designing the die to ensure that the section quality and dimensional accuracy of precision Plastic Injection Parts meet the requirements of products, the required blanking force is small, and the die life is long.  However, the reasonable clearance determined from the requirements of quality, blanking force and die life are not the same value, but close to each other.  Considering the deviation in mold manufacturing and wear in use, only an appropriate range is usually selected as the reasonable clearance in production. As long as the clearance is within this range, good parts can be punched out. The minimum value of this range is called the minimum reasonable clearance cmin, and the maximum value is called the maximum reasonable clearance cmax.  Considering that the wear of the die increases the clearance during use, the minimum reasonable clearance value cmin should be adopted when designing and manufacturing new dies.  There are two methods to determine the reasonable gap: theoretical method and empirical method.