Investigation on Hole Quality and Tool Wear of CFRP Drilling With Cryogenic-Minimal Quantity Lubrication

Carbon fiber reinforced polymer (CFRP) is extensively utilized in various fields, including aerospace and automotive industries, where drilling serves as a common method for mechanical assembly. However, the inherent anisotropy and inhomogeneity of CFRP, combined with its sensitivity to temperature, often result in significant damage during drilling; finally, it leads to component scrap. This study aims to explore the hole quality and tool wear of CFRP utilizing cryogenic-minimal quantity lubrication (CMQL), investigating its influence on cooling and friction reduction by comparing it with dry drilling (Dry), liquid nitrogen cooling (Cryo), and minimal quantity lubrication (MQL). The results show that CMQL significantly relieves hole damage in terms of entrance damage, exit burrs, exit delamination, and hole wall damage. Although CMQL does not perform excellently in the hole's roundness error, it can effectively maintain the accuracy of hole diameters under different parameters. Notably, there is a high-viscosity chip sludge formed by the combination of lubricating oil and chips in the cutting zone. It intensifies squeezing and scraping interactions at the tool-workpiece interface, resulting in severe frictional wear. The chip sludge under CMQL and MQL has a more pronounced impact on the rounding of cutting edges than the Cryo condition. Observations of wear on the secondary flank face corroborate the protective role of lubricating oil, which significantly mitigates tool burn. In summary, the application of CMQL not only enhances the surface integrity of CFRP drilling but also holds significant promise for extending the lifespan of cutting tools.