Clearance Decides the Edge Before the Press Runs
In stamping, the gap between punch and die sets how the material fractures. Too small and the edge shears with a secondary burr and rapid tool wear. Too large and the material tears, leaving a rough edge and a burr that varies along the contour. Neither problem can be fixed by slowing the press.
The Practical Rule
Clearance is usually quoted as a percentage of thickness per side, and the percentage depends on material:
| Material | Clearance per side | Note |
|---|---|---|
| Soft copper, brass | 4 to 6 percent | Lower end for thin strip |
| Low carbon steel | 6 to 8 percent | Standard range |
| Stainless steel | 8 to 10 percent | Work hardening raises wear |
| Phosphor bronze | 5 to 7 percent | Spring back affects the form station |
On a 0.3 mm terminal, 6 percent is 0.018 mm per side. That is smaller than most people estimate, which is why die making is a grinding and fitting discipline rather than a milling one.
Why One Clearance for the Whole Tool Fails
- Different features cut different proportions of the strip: a narrow lance behaves differently from a full contour cut.
- Bend stations need relief that a piercing station does not.
- Coining and swaging stations work by material flow, not by fracture, and need their own allowance.
Clearance is therefore set per station, and sometimes per segment within a station, during die design rather than applied as a single plant standard.
Burr Height as an Acceptance Criterion
Burr is measured on functional edges and normally held below five percent of material thickness, with the measurement point marked on the drawing. On a 0.3 mm terminal that is 0.015 mm, which is why the measurement is done with a profile projector rather than a fingernail. If the drawing does not state a burr limit, the die builder will pick one, and it may not match the assembly machine's tolerance.
Wear, Maintenance and the Second Year
A die that produces acceptable parts in month one and marginal parts in month twelve is a die with a maintenance plan that was never written. Record the sharpening interval, the number of strokes between grinds, and the burr height trend. The trend tells you when to pull the tool, before the customer's assembly line does.
Station design, burr limits and plating options for the progressive die stamped terminal are described with the strip layout approval step that happens before any steel is cut.
