Forging is not a single process: depending on the working temperature, it divides into hot, cold and warm forging. This article explains the characteristics of each, what they are good at, and how the right one is chosen for a given part.
Hot forging: heat it up, shape it boldly
Hot forging shapes steel after heating it above its recrystallization temperature — over 1,000°C — and is the most widely used forging method. At high temperature the steel becomes soft and easy to deform, so large shape changes are possible with relatively little force. It handles complex and medium-to-large parts, and as the part is formed, the internal structure is refined and the grain flow follows the shape, giving excellent strength and toughness.
On the other hand, thermal expansion and surface scale make hot-forged parts less dimensionally precise than cold-forged ones, so precision surfaces are usually finished by machining afterwards. Hot forging is our specialty.
Cold forging: precision at room temperature
Cold forging shapes the material in dies at room temperature, without heating. With no thermal distortion, dimensional accuracy is high, surfaces come out clean, and downstream machining can be reduced. Work hardening during forming also raises the strength of the material.
However, steel at room temperature is hard and resists deformation, so cold forging is not suited to large shape changes or medium-and-larger parts, and it puts heavy loads on the dies. It shines in high-volume production of small parts such as bolts and nuts.
Warm forging: in between
Warm forging works at intermediate temperatures of a few hundred degrees Celsius, aiming for the best of both worlds: easier forming than cold forging and better accuracy than hot forging. Because temperature control is demanding, its use is comparatively limited.
| Hot forging | Cold forging | Warm forging | |
|---|---|---|---|
| Temperature | Above 1,000°C | Room temperature | A few hundred °C |
| Formability | Excellent — large deformation possible | Limited deformation | Intermediate |
| Accuracy | Good (precision surfaces machined after) | Excellent | Good |
| Typical parts | Medium-to-large, complex, high-mix low-volume | Small parts in high volume | In-between parts |
| Our service | Our specialty (in-house dies, small lots) | — | — |
How to choose: the part decides the process
No process is universally superior — the right choice follows from the part’s size, shape, volume and accuracy requirements. Roughly speaking, hot forging is the first candidate for parts that need large shape changes, for medium-and-larger parts, and for high-mix low-volume work; cold forging for small, high-precision parts in high volume.
In practice, many production parts combine the two approaches: hot-forge a strong near-net blank, then machine only the surfaces that need precision.
Talk to us about hot forging
We have specialized in hot forging since our founding. With forging presses up to 2,000 t and dies designed and made in-house, we handle high-mix, small-lot hot-forged parts. Questions like "which process suits this part?" are welcome even at an early stage — send us a drawing and we will assess feasibility and provide a quotation.