There is a clear trend toward cold extruded parts with more and more complicated geometry. The reasons are the cost and quality advantages compared to other methods of metal forming.

BASIC TYPES OF COLD EXTRUSION:

Depending on material flow, one speaks of forward or backward extrusion. Combinations of the two basic types of cold extrusion technique are also possible in a single work cycle. In addition, there is also lateral extrusion: the flow of material is perpendicular to the stamping motion. As a rule, the workpiece is phosphatized and lubricated prior to each pressing cycle to improve friction characteristics.

STRENGTH CHARACTERISTICS OF COLD EXTRUSION:

Due to work hardening during the forming process, cold extrusion leads to a substantial change in the strength characteristics of the material: hardness, breaking strength, and tensile yield strength increase, while elongation and contraction at the break site increase. Thus it is possible to achieve strength characteristics in low-carbon steels comparable to those of steel alloys. Under very high stress it has been shown that the fatigue strength – and thus the durability – of cold-extruded workpieces is substantially higher than for machined, sintered, or welded parts.

FIBER ORIENTATION IN COLD EXTRUSION:

During the cold forming of cold extruded workpieces, the material develops a fiber orientation corresponding to the respective direction of forming. This has a great influence on the strength characteristics of the finished parts, especially on fatigue strength. When designing and producing cold extruded parts, it is always necessary that the fiber orientation be adapted to correspond to the direction of stress of the workpiece.

PRECISION IN COLD EXTRUSION PARTS:

In cold extrusion many influences affect the precision of dimensions, position, and form. The most important factors are the perfection of the tools as well as the respective distribution of material. Especially with complicated forms, it is not always easy to select the dimensions of the starting material so that the displaced material fills the desired final form completely.