Pierced forgings: tool development for a combined single step process

Many forged parts e.g. connection rods or box spanners feature cavities, holes or apertures, which have to be produced in an additional process step (in many cases warm piercing). The residual material, that remains at the cross sectional area of the piercing punch, so called web, has to be pierced in an additional manufacturing step. By integrating this separately performed operation into the final forging step the process chain can be shortened. However, up to date there is no information available on how the process parameters influence quality relevant factors like dimensional accuracy, surface quality, and fibre orientation in the pierced area when forming and piercing operations are combined. Therefore, a combined forging-/piercing process was designed and performed in two projects. In the first project, not discussed in this paper, forging temperature, tool and work piece material as well as the thickness of the web have been investigated. The results of these investigations showed that the variation of the inserted mass and the forging temperature have a distinct effect on the dimensional and form accuracy of the work pieces. The second project investigated different geometries of the piercing punch and the influence of a different forming sequence on tool stress and material flow. The geometry of punch shows no effect on the geometrical tolerances of the piercing while an inappropriate forming sequence leads to failure of the tool.