On a stamped part, the material line is usually the largest single cost - larger than the press time and often larger than the tooling amortised over the programme. That makes the strip layout the most valuable drawing in the shop, and it is frequently the one nobody re-opens after the first tryout.
How do you reduce scrap on a progressive die?
Scrap on a progressive die divides into three parts, and only one of them is easy to change. Edge scrap is the material outside the part outline - the carrier, the bridge between parts and the coil edge trim. Internal scrap is the holes and cut-outs inside the part, and it is fixed by the part design rather than the tool. Process scrap is what the die loses to short feeds, slug pulling, misfeeds and start-up. Edge scrap is reduced by nesting, by re-checking the pitch and bridge width, and by narrowing the coil rather than buying a wider one and trimming it back. Typical strip utilisation runs from roughly 75% on a simple, near-rectangular part down to below 50% on an irregular outline with a wide carrier. The audit that pays is measuring utilisation on the actual strip layout against the coil width you buy, not against the part outline on the drawing.
The three kinds of scrap, and which ones you can act on
- Edge scrap - carrier, bridges, coil edge trim. This is the recoverable one: it is decided by the strip layout and by the coil width you order.
- Internal scrap - holes, slots and cut-outs inside the part. This is a part design decision. If the design can be changed, moving a hole or widening a bridge changes the cost far more than any press setting.
- Process scrap - short feeds, slug pulling, misfeeds, start-up and stop scrap. This is where a die that runs well and a die that runs badly diverge, and it does not show up in the layout at all.
The strip layout decisions that move the number
- Nesting. Rotating or staggering a part in the strip is the single largest lever on edge scrap, and it is free at the design stage and expensive after the die is cut.
- Bridge and edge width. These are set by strength and by strip handling, not by habit. If the bridge is wider than the material and the feed need, you are buying scrap.
- Coil width. Ordering a standard width and trimming it to size means paying for the trim twice - once as material and once as scrap handling.
- Carrier design. A narrower carrier or a different carrier position can recover material, but only if the strip still feeds reliably at production speed.
- Number of stations. More stations can allow a tighter nest, so the scrap saved may pay for the extra tool length - or it may not. It is a calculation, not a default.
Put the scrap allowance in the quote, not in the argument
A quote that assumes a coil scrap figure and does not state it is a quote that will be renegotiated the first month the nest runs differently. The material line and the processing line should be separable: processing is fairly stable across a year, while the material position has a validity window. Stating the assumed strip utilisation and the scrap basis turns a monthly argument into a line item that can be checked against the actual coil consumption.
Process scrap: the part that shows up as downtime
Slug pulling, misfeeds and short feeds rarely appear on a scrap report as material loss, but they stop the press. A pulled slug usually means the clearance, the slug geometry or the die lubrication is wrong for the material actually running, and a short feed usually means the feed length or the strip straightness has drifted. Both are worth tracking per shift, because a die that stops twice a shift loses more money than a layout two percentage points off.
Key point
Reduce edge scrap by re-checking the nest, the bridges and the coil width. Reduce internal scrap by changing the part design, not the press. Reduce process scrap by tracking slug pulling and misfeeds per shift. Only the first of those is free after the die exists.
Frequently asked questions
What is a normal material utilisation on a progressive die?
It depends almost entirely on the part outline. A simple near-rectangular blank can reach roughly 75% of the coil, while an irregular outline carried on a wide carrier can fall below 50%. The number that matters is measured against the coil width you actually buy, not against the part outline on the drawing.
Can scrap be reduced on an existing progressive die?
Yes, but only within limits. Narrowing the coil, changing the feed length, adjusting bridge and edge widths in a rebuild, and tightening slug control are all available. Changing the nest angle or the part outline usually means a new die, so those are design-stage decisions.
Why does a quote need a stated scrap allowance?
Because strip utilisation is an assumption, and an unstated assumption becomes a renegotiation the first month it does not hold. Separating the material line from the processing line, and stating the utilisation the quote assumes, makes the difference checkable against real coil consumption.
What causes slug pulling on a progressive die?
Usually a combination of clearance, slug geometry and lubrication for the material actually running rather than the one the die was designed around. It rarely registers as material loss, but it stops the press, so it belongs in a per-shift tracker alongside misfeeds and short feeds.