A shank reduction either fits in one blow or it does not. Enter your wire diameter, the finished shank diameter and the material, and this tool returns the extrusion ratio, the true strain, whether a single-blow die is viable, and a station split you can take to the toolroom.
Enter the wire diameter and the finished shank diameter to see the ratio.
- Area reduction
- —
- Diameter reduction
- —
- True strain ε
- —
- Minimum blows
- —
How the ratio is calculated
The extrusion ratio compares the cross-section of the wire with the cross-section of the finished shank. It is an area ratio, not a diameter ratio:
R = A₀ / A₁ = (D₀ / D₁)²
That single detail is where most quoting errors start. A 10 mm wire reduced to 8 mm looks like a 20% reduction, but the die sees 36% of the area removed. Every pressure, every lubricant decision and every station count follows from the area figure, not the diameter figure.
The calculator also returns true strain, ε = 2·ln(D₀/D₁). Strain is the number to compare between different reductions and between different materials, because it does not depend on the starting size.
Safe single-blow limits by material
These are the working limits we use when quoting. They assume clean, properly annealed wire, a die with a generous approach angle, and a press in reasonable condition.
| Material | Max R, single blow |
|---|---|
| Low carbon steel 1008-1018 | 1.50 |
| Medium carbon steel 1035-1045 | 1.40 |
| Boron steel 10B21 / 10B38 | 1.40 |
| Alloy steel 40Cr / SCM435 | 1.35 |
| Stainless steel 304 / 316 | 1.30 |
| Copper T2 / brass | 1.60 |
When the ratio exceeds the limit
An over-loaded shank die does not wear out gracefully. It cracks its casing, or it tears the part internally in a way dimensional inspection will never catch. There are only four honest ways out:
- Split the reduction across stations. The cheapest fix on a multi-station former. The calculator gives you the intermediate diameters for an even split.
- Start from smaller wire. Only viable if the head can still be formed from the reduced diameter.
- Anneal the wire. Spheroidise annealing buys roughly 0.1 of ratio and costs a process step.
- Change the die architecture. Where the shank also has a feature that will not release from a solid die, a split die solves release and reduction together.
The full engineering reasoning behind these limits, including work-hardening behaviour and the effect of die angle, is in our extrusion ratio guide. If the part also has an undercut or a cross feature that a solid die cannot release, read the split die page before you commit to a station sequence.
What this calculator does not tell you
It does not know your press. A worn ram with visible play will crack a die at a ratio the numbers say is safe. It does not know the cut-off quality — off-square wire enters the die off-axis and that, not the ratio, causes most of the chipped nibs we see. And it does not model friction: the right coating and lubricant pair can effectively buy 0.05 to 0.1 of ratio.
Treat the output as a design starting point, not a warranty. If the number sits close to the limit, send us the drawing and the machine model — we will check the casing interference and the approach angle before anyone cuts carbide.
?d0=9.6&d1=7.2&m=1045. Hit Copy link and paste it into an email or a forum thread.Next step
Our cold heading dies page covers how a die set is built around these numbers — nib, shrink ring, punch and closing ring as one matched assembly. For material selection at a given ratio, see the die material guide. To have a specific part checked, send the drawing, the wire grade, the machine model and the annual volume through the quotation form.