Material removal mechanisms for rough grinding with large CBN-grains

• Applicant: Professor Dr.-Ing. Berend Denkena
• Subject Area: Metal-Cutting and Abrasive Manufacturing Engineering
• Term: since 2022
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 504720447

For rough machining of components, machining processes with geometrically defined cutting edges are primarily used before fine machining by means of grinding. This is due to the fact that the chip removal rate during grinding is usually significantly lower than during machining with geometrically defined cutting edges. However, novel manufacturing processes now make it possible to synthesize large CBN grains with a high edge quality and mechanical stability. The use of these grains for high-performance grinding opens up new dimensions with regard to chip thicknesses and material removal rates in machining with geometrically undefined cutting edges. The predominant removal mechanisms under these conditions in high-performance grinding of hardened steel are unknown today. The aim of the project is therefore to know the material removal mechanisms during rough grinding with CBN grains with a grain size of more than 300 µm. First of all, knowledge about the distribution of heat flows during grinding with large CBN grains is gained. With the now identified process parameters, the single grain chip thicknesses, which are in the range of high-speed and high-performance grinding, are specifically selected in order to gain knowledge about the transition of material removal mechanisms as a function of the grain geometry during single grain grinding. The evaluation of the continuously increased chip cross section and the lateral throwups allows for the quantification of the existing material separation mechanisms as well as wear phenomena at the tool. If the single grain chip thicknesses are known at which a change of the predominant material removal mechanism takes place, knowledge of the chip formation during grinding with large CBN grains is acquired. For this purpose, interruptions of cut during grinding are carried out. In addition to validating the material removal mechanisms identified during single grain grinding for the grinding process, the chip formation variables can also be determined in this way. This in turn allows the classification of grinding with the new coarse-grained CBN grinding wheels with respect to the machining with geometrically defined cutting edges. Subsequently, the residual stress depth curves associated with the grinding tests are analytically recorded. A correlation with the previously determined process forces and temperatures permits the breakdown of the proportion of thermal and mechanical workpiece loads and consequently the knowledge of the relationship between subsurface damage and material separation mechanisms. Finally, a material removal simulation is created and the real grinding wheel topography, which is measured by using a laser triangulation sensor, is taken into account. The project is concluded with the availability of a scale spanning modelling for the mapping of the transition from the chip formation microscale to the macro scale of the grinding wheel.

• DFG Programme: Research Grants