The performance of grinding tools in grinding processes and the resulting surface and subsurface properties depend on various factors. The condition of the grinding tool after dressing is one of these factors. However, the influence of the dressing process on the condition of the grinding tool depends on the selected process parameters and is difficult to predict. Therefore, this paper presents an approach to describe the influence of the dressing process on tool wear of toric grinding pins and the resulting subsurface modification. For this purpose, toric grinding pins with a vitrified bond were dressed with two different strategies and the wear and operational behavior were investigated when grinding AISI M3:2 tool steel with two different grinding strategies. In general, the investigations have shown that the dressing process influences the performance and wear behavior differently depending on the grinding strategy used. The degree of clogging is influenced by the geometric contact sizes. In the case of small engagement cross sections with simultaneously large contact lengths the thermal tool load is distributed over a small annular area of the tool and favors clogging. Crushing and additional transverse loading of the grains result in an almost clog-free tool surface. This also leads to a lower G-ratio. Crushing leads to an intensified decrease of the torus radii. The influence of the dressing strategy can also be observed in the induced residual stresses. Toric grinding pins dressed by crushing induce lower compressive residual stresses into the workpiece, which can be attributed to the self-sharpening effect. This effect reduces the mechanical and thermomechanical load of the workpiece during machining.
The influence of different mechanical and chemical pre-treatments for heat-treated AISI M3:2 tool steel (~ DIN S 6-5-3) on the coating adhesion of a CrAlN coating is investigated. Surface topography and residual stresses before and after the PVD coating process are examined. Nitriding and grinding with toric grinding pins results in compressive residual stresses in the subsurface, whereas polishing leads to tensile stresses. After the deposition process a decrease of the residual stresses in the substrate material is observed, whereas the stresses in the nitrided surface are not affected. The resulting residual stresses and roughness profiles are correlated with the adhesion of the PVD coating showing a clear dependency on the substrate pre-treatments. Additionally, interactions between the residual stresses in the subsurface and the resulting stress gradient in the PVD coating could be determined by depth profiles. Based on these findings an optimized grinding process can therefore make the additional process step of nitriding obsolete and can provide an improved coating adhesion for an enhanced wear resistance.
The microstructure and the residual stress state have a significant influence on the service life of the component. The deep rolling process already enables a significant increase in the strength and service life of highly stressed components. By using the hybrid manufacturing process of turn rolling, the edge zone properties can be influenced to such an extent that the service life is further increased compared to conventional deep rolling. In addition to a change in the residual stress state, the use of the turning process temperature also leads to a significant grain refinement in the edge zone area, which has a positive effect on the component service life. This modification of the edge zone can be significantly influenced by the machining speed.
Frictional losses occur in tapered roller bearings, particularly at low rolling speeds, which pose a risk of wear. The increased friction losses are a result of insufficient lubricant film thicknesses in the rolling and rib contact. Micro-lubrication dimples can be used to induce additional lubricant into the contact zone and minimize friction. The aim of this paper is therefore to implement a suitable machining strategy for the production of defined microstructures for tribologically optimized applications and to identify relationships between geometry formation and process parameters. For this purpose, the microstructure milling process was first modelled with a material removal simulation, including tool displacement. Additionally the kinematic limits of the machine tool were determined. The tool displacement was determined experimentally for this purpose. Subsequently, the findings from the simulation were used to induce microstructures in a defined manner on tapered roller bearings made of hardened 100 Cr6 steel. The investigations showed that the defined generation of lubrication dimples is possible with the developed machining strategy. Due to the inclination of the inboard bearing, there is a deviating depth of engagement when the tool penetrates, which also increases the tool displacement. As a result of the microstructure milling process, burr formation occurs, which shows a dependence on cutting speed and structure alignment. Increased burr formation and tool wear at structure orientations of 45° and 70° were found.
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