Increasing the fatigue life of cold forged components through the use of a counter punch

Residual stresses (RS) are known to critically influence the mechanical performance of cold-formed components, particularly in fatigue loading scenarios. This study focuses on enhancing fatigue life, with particular emphasis on the low-cycle fatigue (LCF) regime in which cyclic stresses exceed the material’s yield strength. The approach involves targeted control of RS in a modified forward extrusion process, achieved by applying variable counterforces during forming. The investigation was carried out in two stages. In the first stage, workpieces were produced under different counterforce levels, which allowed the RS state to be tailored by promoting a more homogeneous material flow and a locally increased hydrostatic pressure during the forming process through optimized counter punch support. Experimental measurements and numerical simulations showed that increasing the counterforce up to 80 kN led to a consistent reduction of tensile RS near the surface. In the second stage, rotating bending fatigue tests were conducted to assess the fatigue performance.