Development and Validation of a Resource-Efficient Tribometer for Cutting Fluid Evaluation

Guide pads provide radial support of the tool head and thereby enable high dimensional accuracy and low surface roughness of the borehole. Due to their direct contact with the borehole wall, guide pads are exposed to complex tribo-mechanical loads, which can lead to pronounced adhesive wear when machining difficult-to-cut materials such as austenitic steels. To systematically evaluate the influence of different cutting fluids on guide pad wear, a tribometer was upgraded with a closed-loop coolant supply system. This modification enables resource-efficient wear testing under process-relevant normal stresses and sliding velocities. Five cutting fluids were investigated with respect to their time-dependent wear behaviour using optical 3D measurements based on focus variation and a profile-based evaluation method that allows reproducible quantification of wear scar evolution. The results reveal significant differences between the tested fluids: While one cutting fluid exhibited almost no material removal due to the formation of a protective tribofilm that effectively suppressed adhesion, other fluids resulted in material losses, irregular wear craters. The experimentally determined ranking of the cutting fluids aligns with observations from industrial deep hole drilling operations, validating the functionality and suitability of the tribometer. Results have implications for cutting fluid developers, as only 15 liters of liquid are required for evaluation.