Finite Element Analysis of Manufacturing Micro Lubrication Pockets in High Strength Steels by Hot Micro-Coining



The tribological properties of lubricated machine elements can be improved by micro lubrication pockets. Depending on the application's tribological system, the pocket dimension needs to be adjusted to achieve an optimum in friction and wear reduction. With respect to production efficiency, a forming operation would be suited to manufacture these pockets. In this work, finite element models were developed to study the steps of the hot micro-coining process: heating, cutting, and coining of micro lubrication pockets. Experiments have been conducted to validate the models and to investigate the emissivity and heat transfer coefficient between tool and specimen by inverse modeling. It was found that the results of the simulations agree well with the experiments as long as the elastic tool deformation is taken into account, which influences the process time. Thus, suitable process parameters and limits have been determined for the coining of hemispherical lubrication pockets in stainless steel AISI 304. An initial forming temperature above 540 °C is recommended to avoid plastic deformation of the die. Complete form filling was achieved at a normalized pressure of three due to the high specimen temperature of 785 °C.