Die clearance is one of the most critical parameters in the stamping process. Its magnitude and uniformity directly affect the sheared surface quality, dimensional accuracy, die life, and material utilization. A properly designed clearance ensures smooth fracture surfaces, controlled deformation, and stable mass production.
1. Fundamental Principles of Clearance Design
- Determine Clearance Based on Material Thickness: The typical single-side clearance is 5%–10% of the material thickness. Softer materials require smaller values, while high-strength or harder materials need larger clearances to reduce die wear and prevent edge cracking.
- Ensure Uniform and Consistent Clearance: Uneven clearance causes excessive burrs, out-of-round holes, and tapered edges. Therefore, precise alignment and reliable guiding between the punch and die are essential.
- Adjust Clearance According to Part Requirements: Parts requiring a wide burnished (shear) zone: use smaller clearance; Parts requiring high perpendicularity: prioritize uniform clearance; Structural components tolerant of rougher surfaces: use larger clearance to extend die life.
2. Impact of Clearance on Stamping Quality
- Burr Height: Excessive clearance leads to high burrs due to material elongation, while insufficient clearance causes severe edge compression and accelerated die wear, resulting in burrs over time.
- Fracture Surface Characteristics：Proper clearance produces a balanced burnished zone and fracture zone. Too small: wide burnished zone but noticeable galling; Too large: narrow burnished zone and rough fracture surface
- Dimensional Accuracy and Shape Error：Non-uniform clearance can cause oval holes, tapered profiles, and inaccurate dimensions, negatively affecting assembly performance.
- Die Life and Material Utilization：Small clearance increases shear force and accelerates edge wear. Optimal clearance extends die life and reduces scrap width, improving material efficiency.
3. Practical Recommendations for Optimization
- Evaluate clearance range using tryout data before mass production;
- Use high-precision guiding systems to maintain consistent clearance;
- Fine-tune clearance based on material batch variations;
- For high-strength steel, use coated punches and increase clearance appropriately;
- Measure edge wear regularly and regrind dies to restore proper clearance.
Although clearance is a small parameter, it plays a decisive role in stamping quality. Scientific design and precise control are essential to achieving ideal sheared surfaces while balancing die life and production cost.
