In sheet metal stamping processing, shearing is a common processing technology, mainly used to cut sheets into the required shape. The setting of the shearing clearance is one of the key factors affecting shearing quality, die life, and production efficiency. This article will introduce in detail the definition, influencing factors, and calculation methods of shearing clearance in sheet metal stamping.



1. Definition and Function of Shearing Clearance



The shearing clearance refers to the gap value between the male die (punch) and the female die during the shearing process, which is usually expressed as the total gap (i.e., the total gap between the male die and the female die). An appropriate shearing clearance can ensure good fracture quality, reduce die wear, lower shearing force, and improve production efficiency.



If the clearance is too small, it will cause the blanking force to increase, the shearing area of the material to become narrower, the fracture to appear double bright bands, and the burrs at the edge to be serious; while if the clearance is too large, it will cause the material to tear, forming a distinct conical fracture, and the surface quality to decline.



Two, Factors affecting blanking clearance



1. Material type and thickness: Different materials (such as low-carbon steel, stainless steel, aluminum alloy, etc.) have different plasticity and strength, and the required reasonable clearance is also different. Generally speaking, the thicker the material or the poorer the plasticity, the larger the required clearance.



2. Mold material and heat treatment: The hardness and wear resistance of the mold will also affect the selection of the clearance. A mold with high hardness can be appropriately reduced to improve the blanking quality.

　　3. Blank speed and lubrication conditions: Under high-speed blanking or good lubrication conditions, the clearance can be appropriately reduced.



4. Blank quality requirements: If higher quality requirements are placed on the fracture, a smaller reasonable clearance should be selected.



Three, Common calculation methods of blanking clearance



The calculation of blanking clearance usually adopts two methods: empirical formula method and table lookup method.



# (i) Empirical formula method



The blanking clearance \( Z \) can be estimated by the following empirical formula:



\[



Z = K × t



\]



Among which:



- \( Z \): Double-sided blanking clearance;



- \( t \): Material thickness;



- \( K \): Coefficient, selected according to the material type and thickness, the K values of common materials are as follows:



| Material type | Material thickness (mm) | K value range |



|-----------------|----------------|----------|

　　| Low-carbon steel | <1 | 6%～8% |



| | 1～3 | 8%～12% |

　　| | >3 | 12%～18%|

　　| Stainless steel | | 12%～20%|



| Aluminum alloy | | 4%～7% |



For example: if the blanking material is 2mm thick low-carbon steel, the reasonable clearance Z = 10% × 2mm = 0.2mm, that is, the double-sided clearance is 0.2mm.



# (ii) Table lookup method



In actual engineering, it is often referred to the blanking clearance tables provided in 'The Stamping Manual' or relevant industry standards, and the recommended reasonable clearance values are directly obtained according to the material type and thickness. This method is more suitable for engineering design and mold manufacturing.



Four, Conclusion



The accurate calculation and reasonable setting of the blanking clearance are of great significance for ensuring the quality of the blanking parts, improving the mold life, and reducing production costs. In practical applications, comprehensive considerations should be made based on factors such as material characteristics, mold conditions, and process requirements, and appropriate calculation methods should be selected, combined with trial molding adjustments, to achieve the best blanking effect.



In summary, although the blanking clearance is small, it is a key parameter that cannot be ignored in the stamping process. Only by scientifically and reasonably determining the blanking clearance can high-efficiency and high-quality sheet metal stamping be achieved.