Chip formation mechanisms and tribological process behaviour in grinding at low speeds

Main objectives of the present work are characterisation of the chip formation mechanisms and tribological process behaviour in grinding at low speeds. The technological area of interest was marked off by cutting speeds of some few meters per second and depths of cut in the magnitude of a micron typical machining parameters in a number of abrasive gear finishing processes, e.g. gear honing. The chip formation mechanisms have been investigated by single grain scratching tests. It has been shown, that low cutting speeds in combination with small chip thickness enhance micro-ploughing and make the chip formation less efficient. Higher values for cutting speed and larger chip thickness result in increasing micro-cutting. For the most efficient chip formation, the values for cutting speed and chip thickness have to be chosen as high as possible. Investigations of the tribological process behaviour have been carried out in grinding experiments. They were aimed at quantifying the influence of friction and tool specification on the effective material removal. Experimental findings allow to differentiate the friction influence dependent on the chosen cutting speed and (equivalent) chip thickness by application of the Stribeck diagram. The most efficient material removal was achieved at a boundary lubrication condition, when the cutting speed and chip thickness were set at their highest values. This result confirms the single grain tests findings. Applying an abrasive wear map, process behaviour of different tool specifications at constant grinding conditions was found out to correlate with the effective single grain chip thickness. The higher it is, the higher are the process friction, effective material removal and tool wear. At low chip thickness values, due to dominating micro-ploughing, high compressive residual stresses in the workpiece subsurface are induced. A principle transferability of the experimental results to the technology of gear honing has been shown