◼︎ COLD FORMING –
| THE TECHNOLOGY OF COLD IMPACT EXTRUSION
Impact extrusion is a manufacturing process used in metal forming in which steel blanks, discs or tube sections are made into a variety of differently shaped objects. The process of metal forming involves extruding the raw material through an open die or extrusion container by applying pressure through an extrusion punch. A change in the cross-section is thus achieved and the workpiece is plastically deformed. If the cross-section is altered greatly or in the case of complex workpieces several forming stages such as compressing, setting, press forming, flange compression or tapering may be required. Often so-called recrystalisation annealing may be necessary in between the individual forming steps in order to make the material formable again.
| THE BASIC TYPES OF COLD IMPACT EXTRUSION
Depending on the material flow, one can differentiate between forward and reverse impact extrusion. Combinations of the two basic types are also possible in a single work step. During lateral extrusion the material flows diagonally to the movement of the punch. Before forming, the workpieces are generally subjected to phosphating and lubricated in order to improve frictional behaviour.
| SUITABLE STEEL TYPES
Steel types that have a low yield point and high expansion rate with a preferably flat flow curve in a soft-annealed condition are best suited for cold impact extrusion.
| THE SPECIFIC MECHANICAL PROPERTIES OF COLD IMPACT PARTS
Due to the strain hardening during forming, a considerable change in the strength properties takes place during extrusion. Hardness, breaking resistance and yield strength are improved greatly, while expansion and contraction at fracture are reduced. In that way steels with low carbon content can reach strength properties that are similar to those of alloyed steels. The endurance strength as well as durability of cold extrusion parts is much higher than that of machined, sintered or even welded components.
| FIBRE FLOW
During cold forming of extrusion parts the fibre flow corresponds to the respective deformation direction. This has a great influence on the strength properties of the prefabricated parts, in particular dynamic strength. When constructing and assembling extruded components one must generally make sure that the fibre flow is in line with the form and stress direction of the workpiece.
| ONLY GREAT PRECISION ENABLES HIGH ACCURACY
A large amount of influencing factors have an effect on the dimensional, positional and contouring accuracy during cold impact extrusion. The most important factors are the precise tools as well as the respective material compositions. Especially when it comes to complicated forms, the dimensions of the initial raw workpiece must be chosen in such a way as to ensure that the displaced material will exactly fill the desired final shape. And that is a task that can only be achieved with a great deal of experience and exact precision to the thousandth.