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Forging with rigid tools

Cold forging is a cold mass forming process in which the material is made to flow in an enclosed state. A press exerts a high force instantaneously on a component. This force causes a pressure load be created in the material. When this load exceeds the material's pressure yield point (RP0.2), the material begins to flow.
When no further force is exerted on the component, following elastic recovery, a plastic deformation of the component remains. Cold forging creates a surface with extremely good roughness values and high dimensional and form accuracy. Manufacturing components by cold mass forming is particularly worth while when working with high piece numbers in the region of several tens of thousands to millions of components a year.

I. Prior to forming
II. II. After forming (UT)

a) Punch
b) Die
c) Pressed part

d) Ejector
e) Counterpunch
f) Mandrel

Cold forging is subdivided into different process principles in accordance with DIN8583-6: Full, hollow and can extrusion. Each of these methods can in turn be subdivided into different processing directions: forward, transverse and reverse extrusion. According to DIN8583-6, transverse can extrusion does not exist. If a tapering process takes place in a closed tool – in other words the punch is only immersed into the die before it touches the component – this is referred to as forward extrusion.

Frequently, a single forming process is not sufficient. In this case several so-called stages are required to achieve the final component geometry. In addition, reworking is required if the specified tolerances cannot be achieved in any other way, or the required geometry cannot be manufactured by forming alone.

Reverse can extrusion

Can extrusion processes are subdivided into forward can and reverse can extrusion.

In the case of forward can extrusion, the material and the punch move in the same direction, while with reverse can extrusion the material flow is directed against the direction of movement of the punch. When using this method, the limits for cross-section reduction are at least 15% to a maximum of 98% depending on the material.


By combining these different forming methods, it is possible to produce articles to an extremely high level of precision within close tolerances.

  • Starting from a solid body, a hollow body with a predominantly thin wall (can, sleeve with floor, beaker) is manufactured.
  • The opening which gives the workpiece its shape is formed by the die and punch.
  • The material flows in the opposite direction to the punch movement.

Two-sided can extrusion

Hole punching and trimming

During hole punching, a blank is initially centered, and the can extrusion process is performed partially from both sides. The remaining material in the interior of the part is punched out in another forming station. If particularly stringent requirements are imposed on the surface quality and tolerances of the hollow area, this can be achieved by subsequent calibration of the borehole in a downstream forming stage. In the event of complex asymmetrical head or collar shapes, a bolt is produced with material overflow. This surplus material is then trimmed at an additional forming station.

Full forward

We refer to full forward cold forging when the material flow and punch movement take place in same direction. The blank is completely incorporated into the tool and made to flow by means of a radius or incline. Depending on the material, the limiting value for cross-section reduction is 55 to 85 %.

Full forward-reverse

What is known as reduction is a special form of cold forging. Using this method, the material's own inherent rigidity is used. Across a flat reduction angle, the cross-section can be reduced by around 30 %. As the blank does not need to be fully guided when using this method, it is possible for an additional forming process such as compression to be carried out.

Hollow forward-reverse

In the same way as with full forward cold forging, when using this method the material flows in the direction of operation of the machine.

However, in contrast to full forward cold forging, a hollow body is formed at the same time, and the workpiece is geometrically changed not only on the outside but also on the inside.

Transverse cold forging principle

Transverse cold forging involves the material flow running at right angles to the movement of the punch.


By combining these different forming methods, it is possible to produce articles to an extremely high level of precision within close tolerances.

  • The essential requirement here is that the forming tool opening remains unchanged during the pressing process.
  • Transverse cold forging is used for the manufacture of parts such as secondary design elements with a hollow profile - hollow transverse cold forging and can-shaped secondary design elements - transverse can extrusion