Impact Extrusion Dies

The most widely used cold forming process is impact extrusion. This method is generally used to form cylindrical tubes, rectangular or square containers, and similar parts from soft materials.

impact extrusion die, backward and forward extrusion

With these dies, parts can be produced by extruding either backward or forward. The figure above shows two forming processes: backward extrusion and forward extrusion.

In the impact extrusion process, the punch and the die axis must be aligned in the same position. Otherwise, the formed parts will not be symmetrical.

The forming process is successful if the cross-sectional area reduction of parts produced with impact extrusion dies can reach up to 85% in a single operation. Under normal conditions, the percentage cross-sectional area reduction is taken as 60 for the first extrusion operation, and 40 for the second or finishing extrusion operation.

Material type	Compressive stress kg/mm²
Aluminum	64-112
Brass	84-180
Copper	40-112
Steel Ç1010	80-264
Steel Ç1020	96-320

The compressive stresses of the materials used for parts to be produced with impact extrusion dies are given in the chart above. The press machine that will perform the forming process should be selected based on the dimensions of the part to be extruded and the type of material.

A relationship can be established between the extruded part’s wall thickness and the percentage (%) reduction in area. The diagram showing the relationship between increasing punch force and the resulting extruded part wall thickness is shown in the figure below. According to this diagram, as punch pressure increases, the extruded part’s wall thickness decreases.

punch pressure vs. extruded part wall thickness diagram

In impact extrusion, the material trapped between the die and the punch is extruded out through the die opening. The extruded tube’s outer diameter matches the die bore diameter, and its inner diameter matches the punch tip diameter.

So that the formed part can come off the punch easily, the punch tip diameter is made slightly larger than the body diameter. In addition, a movable stripper plate is fitted onto the punch.

open and closed position of the backward extrusion forming process

The figure above shows the open and closed positions of the backward extrusion forming process.

Impact Extrusion Principle

Impact extrusion dies are used to transform sheet or slug material into a conical or cylindrical shape in a single stroke.

High Surface Quality

The impact extrusion method can achieve a smoother internal surface finish compared to some other forming methods.

Advantage for Small-Batch Production

Thanks to their low tooling cost, impact extrusion dies are an economical option for small- and medium-scale production runs.

Related Questions

If the axes are misaligned, the material flows unevenly inside the die. This uneven flow causes the produced part’s wall thickness to come out thin on one side and thick on the other — in other words, not symmetrical.

Trying to form the material at a very high ratio in a single pass can cause cracking or die damage due to excessive stress. Splitting the process into stages provides a more controlled and safer shape change at each step.