The two costs behave differently
Machining charges you for material removed and for time on a lathe. Cold heading charges you for a die and then very little per piece. That means the two cost curves cross: below a certain volume the die dominates, above it the per-piece saving dominates. In practice, for a part of moderate complexity, the crossover sits somewhere around 20,000 pieces — but the exact number depends on how many stations the die needs.
What heading cannot do
Heading forms metal by displacement, so it cannot create a bore that runs across the part, an undercut, or a thread relief without a secondary operation. Deep axial holes and very tight concentricity usually push a part to turning. It also cannot produce a part whose diameter change is too abrupt: the reduction ratio between stations has limits, and exceeding them cracks the head.
What turning cannot do at volume
Turning removes material, so it wastes it — often 40–60% of the bar. It also takes time proportional to the part, which is why a turned part at 200,000 pieces costs several times a headed one. On simple shapes the gap is large enough that the die pays for itself in the first production run.
The grey zone: heading plus secondary operations
Many parts are neither. A headed body with a turned bore, or a headed blank that is then rolled and deburred, often beats either pure route. This is where suppliers differ most: a shop that only heads will quote heading, a shop that only turns will quote turning, and both answers are wrong for a part in the middle.
Typical economics
| Route | Best volume | Main cost driver | Typical tolerance |
|---|---|---|---|
| Cold heading | 20,000+ pcs | Die cost, amortised | ±0.05 mm as formed |
| Turning | Under ~10,000 pcs | Machine time per piece | ±0.02 mm routine |
| Heading + secondary | Any, if geometry demands | Die + operation count | ±0.02 mm on machined features |
Send the annual volume with the drawing. A quote without volume is a guess — and it is usually the wrong route.