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

Abstract

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.

Effects of Multi‐Scale Patterning on the Run‐In Behavior of Steel–Alumina Pairings under Lubricated Conditions

“…In Szurdak et al, the influence of the coining temperature on the maximum tool stress was studied by FEM simulations. [28] Temperatures higher than 540 C were determined, in which the tool stresses will not induce plastic deformation of the tool. Therefore, the heating parameters that result in the lowest load on the die were used in this study.…”

Friction Reduction Induced by Elliptical Surface Patterns under Lubricated Conditions

“…A closed die hot micro‐coining setup as described in refs . was utilized to manufacture elliptical surface patterns on steel substrates.…”

“…The tool (punch, cutting ring, and die) was made from hardened tool steel X37CrMoV5‐1 (AISI H11) and the coining die was structured by laser ablation. Due to the high yield strength of the material to be coined, pre‐heating is necessary in order to lower the flow stress, as well as the load on the die . A conductive heating system was used in order to adjust a specific temperature in a short period of time.…”

“…A conductive heating system was used in order to adjust a specific temperature in a short period of time. The current density and heating time were set to 35 A mm −2 and 5 s (reaching a peak temperature of 1200 °C) for all experiments …”

Wear behavior of micro-coined steel surfaces under mixed lubrication

“…The structuring of the samples was performed using a closed die hot micro-coining setup and a servo-hydraulic testing machine, as described by Szurdak and Hirt (2015), Szurdak et al (2014). To improve the form filling (area ratio of coined pocket depth to structure height of the tool) and to reduce the load on the die, the sample was heated before coining by using a conductive heating device.…”