A New Concept of the Sliding Compression Test to Independently Investigate the Contact Normal Stress and the Surface Enlargement

Cold forging is a highly efficient process to produce components. However, the occurring tribological loads are tremendous. Therefore, complex tribological systems are necessary. They can be influenced by numerous factors. Most important are the tribological loads, which can usually be investigated independently. On the other hand, the contact normal stress and the surface enlargement are coupled in tribometer tests. In order to investigate them independently, a new concept for the Sliding Compression Test is presented and verified. This procedure reveals that both values have an influence on the friction coefficient. However, the influence of the surface enlargement is with about two-thirds higher.

Cold Forging with Lubricated Tools

Cold forging processes require high-capability tribological systems in order to ensure sound forming results. Due to a rising ecological awareness, alternatives to the established and reliable conversion coatings are necessary. Single bath systems like polymers and salt wax coatings with integrated lubrication appear to be the most promising approach to prevent galling. For an optimization and investigation of the tribological system a definition of the tribological loads is necessary. However, only insufficient values are available in literature. Especially, long sliding distances, which occur in multistage operations, can cause a breakdown of the lubricant. Therefore, approaches are necessary to enable long sliding distances. This paper presents the results obtained with a cold forging tribometer, the Sliding Compression Test, which reveal the high impact of remaining lubricant on the friction coefficient. Also, tests with prelubricated tools show the ability to reduce the friction and the results of investigations with rough tool surfaces are presented.