Punch dies
Sheet-metal punch-press dies, total versus per-side clearance, slug control and product-specific maintenance limits.
Tags: tooling, sheet-metal, punching, dies
On this page
With a concentric 10.0 mm punch in 2.0 mm sheet, an assumed 20% total clearance gives a 10.40 mm die and a 0.20 mm radial gap. If 20% is per side, the die is 10.80 mm with a 0.40 mm radial gap. These are geometric conversions. Specify the convention and use material- and operation-specific guidance to select clearance.
Role in sheet-metal punching
The cutting die supports the sheet around a clearance opening. The holder locates and supports the die. Mate tooling glossary, Die and Die Holder
Check station size, working height, orientation, load and penetration separately from the opening. Fracture and springback can change the measured hole profile.
Total clearance and per-side clearance
Clearance is reported using different conventions. Dayton Progress's High Speed Stamping explicitly uses per-side clearance: the gap between cutting edges around the perimeter. Mate's guide tabulates total clearance, summing the gaps on opposite sides. Both conventions are valid; an unqualified percentage is ambiguous. Dayton clearance definition, p. 3; Mate guide, printed p. 3
For concentric round tools, let P be punch diameter, D die diameter, c the radial clearance per side and C the total diametral clearance:
C = D − P = 2c
D = P + C = P + 2c
Worked example, assumed clearance: for 2.0 mm sheet, a 10.0 mm punch and 20% total clearance, C = 0.20 × 2.0 = 0.40 mm. The die diameter is 10.40 mm and each radial gap is 0.20 mm, or 10% of thickness. If 20% were instead specified per side, the die would be 10.80 mm. The 0.40 mm difference arises solely from the convention, not a change of material. These are geometric examples, not recommended settings.
For a shaped tool, the relevant clearance follows the cutting contour. Simply enlarging a drawing by one scale factor does not generally produce a uniform offset around its perimeter or corners.
Material- and thickness-specific guidance
These Mate piercing recommendations assume the chart's typical shear strengths, not certified alloy properties. Source: Technical Solutions Guide, LIT00682 Rev E 2021. Mate piercing/blanking table, printed p. 3
| Chart material | Typical shear strength | Sheet thickness T | Total piercing clearance |
|---|---|---|---|
| Aluminum | 25,000 psi | T < 2.50 mm | 15% of T |
| Mild steel | 50,000 psi | T < 3.00 mm | 20% of T |
| Mild steel | 50,000 psi | 3.00–6.00 mm | 25% of T |
| Stainless steel | 75,000 psi | T < 1.50 mm | 20% of T |
The same chart separately specifies blanking, where the removed piece is the product; for mild steel below 3.00 mm it gives 15% total clearance rather than the piercing value of 20%. These are process-specific starting values, not one universal percentage.
Select clearance for the actual thickness, material condition, retained part, edge quality and tooling.
Slug retention and suction
Slug pulling occurs when the separated material returns upward with the withdrawing punch rather than clearing the die. Dayton describes a vacuum pocket between the punch face and bowed slug, with lubricant capable of sealing that pocket. Its stamping examples use a vented ejector pin to release the vacuum and push the slug away; effectiveness still depends on speed, lubricant and slug behavior. The report carries copyright 2003 and addresses high-speed stamping, not every turret tool configuration. Dayton slug-pulling discussion, p. 7
Rolleri identifies vacuum, oil adhesion, magnetism and burr interaction as possible contributors. Its slug-catcher die geometry has explicit exceptions: blanking tools, minimum dimensions below 2 mm and clearance below 0.1 mm. Its Cyclone design instead creates suction beneath the die and is restricted to compatible Amada vacuum systems. Rolleri slug-control designs
Interpretation: suction above a slug can encourage pulling, while engineered suction below it can assist evacuation. Slug retention features and a clear discharge path have different jobs. Neither an anti-pull feature nor a nominal clearance establishes that a particular machine can evacuate every slug without packing.
Support, mounting and sharpening boundaries
A die's cutting edge depends on the surrounding body and holder for support. Seating, orientation and height remain distinct from the clearance dimension; a nominally correct opening cannot compensate for a tilted or unsupported die. A sharpened die is shorter, so restored working height and remaining grind allowance are part of its product-specific assembly geometry.
A concrete example is PASS's ps:MT5 punching multitool: its manual, marked 05/2024-WW, allows 0.5 mm maximum punch regrinding and 1.0 mm maximum die regrinding. It specifies compensating die shims of 0.1, 0.3 or 0.5 mm after regrinding. These are limits for that system, not general sharpening allowances for all dies. PASS multitool manual, p. 11
Worked height example: removing 0.20 mm from a die face lowers its nominal cutting plane by 0.20 mm if nothing else changes. Equal height compensation restores that plane arithmetically; it does not restore consumed grind life, repair edge damage or prove that a particular shim stack is permitted.
Coverage limits
This reference covers cutting dies for sheet-metal punch presses, with a separate stamping example explaining slug suction. It does not supply a complete die drawing, allowable press load, universal punch penetration or guaranteed finished-hole tolerance. Machine interface, material properties, die steel/condition, alignment, lubrication and discharge equipment remain assembly-specific.
Mate's guide explicitly identifies revision E and 2021; PASS's manual identifies 05/2024-WW; Dayton's report carries copyright 2003 without a separately established issue date. No issue date was established for the cited Mate glossary or Rolleri page. Upload-path and crawl dates are not editions. The reviewed date describes this article's research review.