⚡ Key takeaways
1. Unit cost: at volume, cold heading is 60–90 % cheaper than CNC. For standard M3–M12 parts above one million pieces a year, cold heading typically costs one fifth to one tenth of turning.
2. Minimum batch is the dividing line. Cold-heading tooling runs from ¥5,000 to ¥30,000, which needs roughly 5,000–20,000 pieces to amortise. CNC can deliver a first article the same day and will take an order of 50.
3. Fatigue strength is actually higher with cold heading. Continuous grain flow raises head fatigue life 20–40 % over turning — the reason almost every class 10.9 and above automotive or aerospace bolt is cold headed.
4. CNC wins on unusual geometry, small batches and complex features. Asymmetric heads, steps, double ends, integral flanges: one setup on a lathe, whereas cold heading needs more stations and more dies or cannot do it at all.
5. There are physical size limits. Cold heading below M1.0 and turning below M0.6 both degrade quickly. M0.6–M2 micro screws are in practice "cold headed plus secondary milling or turning".
6. Material utilisation is the hidden line item. Turning uses 30–50 % of the bar; cold heading uses over 95 %. On 304 stainless at ¥30/kg that gap pays for itself quickly.
7. It is not either-or. The mainstream route is cold heading for the body, CNC for secondary features (grooves, flats, cross holes, face grinding), and thread rolling rather than thread cutting.
1. Why an engineer needs to know both processes
2. The physics of each
3. Six dimensions compared
4. Where the cost actually sits
5. When CNC is mandatory
6. When cold heading wins
7. The hybrid route: what factories really do
8. Common misconceptions
9. FAQ: ten real engineering questions
10. Standards and references
1. Why an engineer needs to know both processes
The easiest way for a supplier to mislead a buyer is the process route. The same M6×20 socket head cap screw comes back at ¥0.12 from one factory and ¥0.35 from another — a threefold gap that usually has nothing to do with material or quality. One is cold headed, the other is turned.
A 2024 survey of 47 fastener buyers by Primetzhofer & Associates found that 62 % of engineers do not specify a process on the first enquiry, so the quote reflects whatever suits the supplier. Above 100,000 pieces a year that gap is worth tens of thousands of dollars annually.
More importantly, the process determines fatigue life, dimensional consistency and minimum order quantity. An M3×8 bolt for a humanoid robot joint, turned rather than cold headed, may reach only 60 % of the head fatigue life — and at 10⁷ cycles that is the difference between a two-year joint and a ten-year joint.
This article compares cold heading and CNC turning across principle, cost, strength, batch size, size range and material, and ends with a decision table you can hold against a drawing.
2. The physics of each
2.1 Cold heading
Wire is cut from a coil at room temperature and fed through several die stations on a high-speed header. Impact pressure forces the metal into shape without heating, so the grain flow follows the part contour continuously.
A typical three-station header:
- Station 1 — cut off: the coil is sheared to length.
- Station 2 — pre-form: one end is upset to pre-shape the head.
- Station 3 — finish form: the final head geometry (socket, hex, pan, cheese).
The thread is afterwards rolled at room temperature, not cut.
Typical equipment: Chang Hong (Taiwan), Kyowa, Sakamura (Japan), HBF (Korea). A domestic three-station header costs ¥300,000–800,000, an imported multi-station machine ¥2–5 million, and output runs 80–300 pieces per minute.
2.2 CNC turning
Bar stock is gripped in a chuck and material is removed by a rotating tool, step by step, until the profile is finished.
Typical sequence:
- Bar fed into the spindle and cut to length.
- Shank turned to diameter.
- Face and chamfer.
- Second setup: head profile turned, hex socket milled.
- Thread turned, or rolled in a second operation.
Swiss-type lathes (Tornos, Star, Citizen L20) handle micro parts; Mazak and Tsugami cover the larger sizes. A Swiss lathe costs ¥400,000–800,000 and cycles at 30 seconds to 3 minutes per part.
2.3 The thread is rolled, not turned
3. Six dimensions compared
3.1 Material utilisation
Cold heading deforms metal rather than removing it, so utilisation is typically above 95 %, with loss limited to the cut-off stub. Turning removes material, so utilisation is 30–50 %: a 10 mm bar turned down to M6 leaves most of its mass as swarf.
Run the numbers. 304 stainless wire is about ¥28/kg in 2026 and an M6×20 screw weighs 2.2 g.
- Cold heading: 2.3 g of input, ¥0.064 of material.
- Turning: 4.5 g of input at 50 % utilisation, ¥0.126 of material.
Material alone doubles. At a million pieces a year that is ¥620,000 of difference — before depreciation, labour and energy.
3.2 Unit cost at volume
Real 2026 quotations for an M6×20 socket head cap screw in South China (including 17 % VAT, excluding plating):
| Annual volume | Cold headed + rolled | Turned + rolled | Gap |
|---|---|---|---|
| 1,000 | not quoted / ¥0.8–1.5 | ¥0.8–1.5 | Equal |
| 10,000 | ¥0.18–0.25 | ¥0.55–0.80 | 3× |
| 100,000 | ¥0.10–0.15 | ¥0.45–0.65 | 4–5× |
| 1,000,000 | ¥0.06–0.09 | ¥0.35–0.55 | 5–7× |
These are 304 stainless figures. Carbon steel cold headed parts are cheaper still: ¥0.03–0.05 at a million pieces.
3.3 Cycle time and lead time
Once set, a header runs by the second: 120–200 strokes a minute, 7,000–12,000 pieces an hour. A million-piece order is one machine for one day.
A Swiss lathe runs by the minute: 30 seconds to 2 minutes per part, 30–120 pieces an hour. A million pieces needs ten machines for a month.
The trade-off is front-end time: cold-heading dies take 7–15 days to make and 2–3 days to set. CNC delivers a first article the same day and production the next.
3.4 Fatigue strength
This is the most under-rated advantage of cold heading. Grain flows continuously around the contour, so the flow line is never cut. Turning severs it and leaves stress raisers at the thread root and under-head fillet.
Yang et al. (2019) compared axial fatigue life for class 10.9 M10 bolts made both ways:
- Cold headed: 1.8×10⁷ cycles at 120 MPa stress amplitude.
- Turned: 1.1×10⁷ cycles.
Roughly 40 % — and on con-rod bolts, tower flange bolts or robot joint bolts running at 10⁷ cycles, that is the difference in safe life. It is why ISO 898-1 recommends cold heading for class 8.8 and above, and why aerospace standards such as HB require it outright.
3.5 Minimum order quantity
Tooling is the hard threshold for a cold-headed part. For an M6 socket head cap screw:
- Pre-form die, finish die and trim die: ¥5,000–15,000 in total.
- Special heads (cheese, button, flanged): ¥10,000–30,000.
- Thread rolling dies: ¥1,000–3,000.
Holding tooling to about 10 % of unit cost implies annual volumes of 5,000–10,000 pieces or more. Below that, tooling amortisation makes cold heading dearer than turning.
Turning has no tooling, only programming (typically ¥200–500 per part), and will take 50 pieces.
3.6 Size range
| Size | Cold heading | CNC turning | What is actually done |
|---|---|---|---|
| M0.6 – M1.0 | Very difficult (wire breaks) | Swiss possible but very slow | Cold headed head + secondary turn/mill |
| M1.0 – M2.0 | Viable on micro headers | Standard Swiss work | Cold heading, standard for micro screw plants |
| M2.0 – M12 | The sweet spot | Viable but expensive | 90 % cold headed |
| M12 – M24 | Viable on large headers | Viable | Mostly cold heading, CNC for large parts |
| M24 – M48 | Very difficult (capital cost) | Standard | 90 % CNC or hot forging |
| > M48 | Not done | CNC or hot forging | Hot forge + CNC |
4. Where the cost actually sits
Breaking an M6×20 screw into five cost blocks shows where the money goes:
| Cost item | Cold headed + rolled | Turned + rolled | Note |
|---|---|---|---|
| Material | ¥0.064 | ¥0.126 | 95 % vs 50 % utilisation |
| Depreciation | ¥0.010 | ¥0.080 | Fast cycle, low cost per piece |
| Labour | ¥0.005 (one operator, many machines) | ¥0.050 (one operator, one machine) | CNC needs attendance for quality |
| Tooling amortisation | ¥0.020 (100k pieces) | ¥0.005 (programming) | Volume makes cold heading cheaper |
| Energy and consumables | ¥0.005 | ¥0.020 | Coolant, tool wear |
| Total | ≈ ¥0.10 | ≈ ¥0.28 | At 100,000 pieces |
5. When CNC is mandatory
5.1 Unusual heads
Cold heading suits axisymmetric or simply rotationally symmetric heads (socket, hex, cheese, button, flange). The following push die complexity up exponentially:
- A flat milled on one side of the head for anti-rotation
- Eccentric or non-circular holes in the head
- Angled heads such as 45°
- A head more than three times the shank diameter
CNC produces these in one setup; cold heading needs compound dies from ¥50,000 upward.
5.2 Non-cylindrical shanks
Square, hex or stepped shanks, double-end studs with a hex centre, ball-nose screws, flanged specials — all lathe work.
5.3 Very small batches (under 5,000)
Tooling of ¥5,000–30,000 spread over 5,000 pieces is ¥1–6 each, worse than turning. Prototypes and pilot runs go straight to CNC.
5.4 Difficult materials
Cold heading needs good cold-formability: SWRCH grades, ML08–ML35, 304HC. These are difficult or impossible:
- High-carbon steel above C45 (cracks)
- Titanium alloys (high flow stress, die life collapses)
- Precipitation-hardening stainless such as 17-4PH and A286
- Beryllium copper
5.5 Large sizes above M24
Headers above M24 need 200 tonnes of force, few plants have them, and dies are expensive. Above M24 the route is CNC or hot forging.
6. When cold heading wins
6.1 Standard parts at volume (over 10,000)
Standard socket, hex, pan and countersunk screws from M3 to M12 above 10,000 a year: cold heading, no debate.
6.2 Fatigue-critical parts
Con-rod bolts, main bearing bolts, tower flange bolts, robot joint bolts — anything above 10⁶ cycles. A turned part of the same size may reach only 60 % of the life.
6.3 Micro precision screws (M1.0–M2.0)
Many assume micro screws are turned. The mainstream micro screw plants use micro headers: 200–400 pan, countersunk or cheese head screws a minute, where CNC struggles to make two.
6.4 Multi-station compound parts
A modern header can cut, upset, reduce, trim, pierce and form in one pass. Stepped, flanged, pierced bolts come off in one cycle where CNC needs three to five operations.
7. The hybrid route: what factories really do
Very few parts are purely cold headed or purely turned. The mainstream route is cold head the body, machine the details:
- Cold heading: head and shank pre-form.
- Thread rolling: form the thread.
- CNC second operation: flats, grooves, cross holes, face turning, chamfers.
- Heat treatment: quench and temper for class 8.8 and above.
- Surface finish: zinc, Geomet, zinc-nickel.
Take the tooling screws in our catalogue: 90 % are cold headed, then CNC mills the flat at the bottom of the socket and turns the shank to tolerance, then the thread is rolled. Pure cold heading cannot make the flat; pure turning is too expensive.
8. Common misconceptions
No. Dimensional consistency (Cpk) is often better than turning because the die fixes every dimension. Turning drifts with tool wear and thermal growth. The only thing cold heading cannot do is a face flatter than ±0.01 mm — that needs machining or grinding.
Partly true. If that 1,000 is a first order and 50,000 more will follow within a year, cut the die now. ¥8,000 spread over 50,000 is ¥0.16 per piece; staying on CNC at ¥0.50 costs ¥17,000 more.
Wrong. 304HC and 316L are standard heading grades and hundreds of plants in Foshan and Dongguan head stainless every day. The difficult grades are precipitation-hardening alloys such as 17-4PH and A286.
No. Rolled threads are 30–40 % stronger in fatigue because the grain flow stays continuous. GB/T 3098.1 implicitly requires rolled threads for class 8.8 and above.
Half true. Changing a program is easy, but at volume every change costs more lathe hours than modifying a die. Iterate in CNC before design freeze, then transfer to cold heading. That is the standard path.
9. FAQ: ten real engineering questions
Q1. M6×20, 50,000 a year — cold heading or CNC?
Cold heading. Tooling of about ¥8,000 spread over 50,000 is ¥0.16 per piece, half the ¥0.40 of turning.
Q2. I designed an M5 with a flat and only need 2,000 for the first order. What now?
Run 2,000 on CNC to validate, and tell the supplier 50,000 will accumulate within a year so the die is cut in parallel. The next batch goes straight to cold heading.
Q3. Why is there a parting line on a cold headed screw?
It is the flash line where the two die halves meet. Normal. Above 0.05 mm it means die wear or a setup problem.
Q4. Can cold heading make screws below M1.0?
M0.6–M1.0 is the process boundary. The usual route is a cold headed head plus a turned shank. Below M0.6 almost everything is Swiss turned.
Q5. Why are titanium bolts so expensive?
Titanium resists cold forming, die life is one fifth of steel and parts crack. 99 % are turned, with 40 % material utilisation — hence the price.
Q6. Can class 10.9 bolts be turned?
Yes, but fatigue life is 30 % lower. Automotive OEM standards require cold heading above 10.9; only aftermarket replacements are turned.
Q7. How can I tell the process by looking at a part?
Look at the flow lines. A cold headed part shows continuous flow through the head-to-shank transition after etching; a turned part shows tool marks under the head fillet and usually a centre mark on the head face.
Q8. How long do cold-heading dies last?
Carbon steel 200,000–500,000 pieces; stainless 50,000–150,000; alloy steel 30,000–80,000. Wear shows up as burrs and an irregular under-head fillet.
Q9. Can cold heading make a non-standard thread profile?
The thread is rolled, and rolling dies can be made to any profile. Below 10,000 pieces the die cost (¥3,000–8,000) usually argues for thread cutting instead.
Q10. Is there a carbon footprint difference?
Yes. Cold heading uses roughly one fifth of the energy of turning (no coolant, little material removal) and about 40–60 % less embodied carbon. Under EU CBAM and EPD declarations that affects export cost.
10. Standards and references
Chinese standards
- GB/T 3098.1 Mechanical properties of bolts, screws and studs
- GB/T 699 Quality carbon structural steels
- GB/T 1231 High-strength large hexagon bolts, nuts and washers for steel structures
International standards
- ISO 898-1 Mechanical properties of fasteners
- SAE J429 Mechanical and quality requirements for fasteners
- ASTM F606 Standard test methods for determining the mechanical properties of externally and internally threaded fasteners
Key literature
- Yang X., Zhu L., He L. Fatigue performance comparison of cold-forged and CNC-turned high-strength bolts. Chinese Journal of Aeronautics, 2019.
- Pretty C. Cold heading vs. CNC: a cost-benefit analysis for high-volume fastener production. Primetzhofer & Associates, 2024.
- ASM Handbook Vol. 14A: Metalworking: Bulk Forming. ASM International, 2005.
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