Processing of cylindrical hollow parts: piercing vs. extrusion

As work principle, piercing (P) and backward extrusion (BE) are similar deforming processes. However, working-load, strain and material flow are quiet different depending on real conditions. Since punch diameter d and workpiece diameter D are the defining parameters for both P and BE, there is a critical d/D ratio separating them as distinctive operations. To have a complete description of P and BE in terms of working load and yield pressure as function of d/D ratio, experimental tests and numerical predictions were conducted. Tridimensional finite element analysis (FEA) for different process designs (i.e. different d/D ratios) revealed distinctive evolutions of the material flow establishing the effective limits of P and BE respectively. Experimental and numerical results can be used in practice to provide estimates of working-load, critical yield pressure and tool dimensions for optimal P and BE in processing of cylindrical hollow parts.