Wear behavior of all-ceramic micro end mills in micro milling of PMMA

Micro milling is a state-of-the-art micro manufacturing method employed, for instance, in the context of prototyping applications. Due to the high specific cutting forces and small tool diameters inherent to micro milling, tool wear represents a significant challenge for the fabrication of large, high-quality structures. In conventional cutting applications, ceramic tool substrates have been demonstrated to exhibit greater wear resistance than cemented carbides. In the case of micro milling of polymethylmethacrylate (PMMA), all-ceramic micro end mills made from zirconia (Y-TZP) have been observed to exhibit less tool wear than common cemented carbide micro end mills. In previous experiments, these tools exhibited a feed per tooth-dependent wear behavior, regardless of the spindle speed employed. The objective of this study was to investigate the wear behavior of the all-ceramic micro end mills at higher feeds per tooth (up to 7.5 mu m) and spindle speeds (up to 110,000 rpm) in PMMA. The objective was to fully characterize the interactions between the all-ceramic micro end mills and the milling parameters for this thermoplastic workpiece material. The wear at the cutting edge was quantified by analyzing the topography with an atomic force microscope, and the results were correlated with the cutting forces and process outcomes. The results were found to be highly sensitive to the spindle speed used, with higher speeds leading to higher temperatures in the cutting zone and thus softening of the PMMA material. In general, micro milling parameters of 110,000 rpm and a feed per tooth of 5 mu m resulted in significantly reduced tool wear with no adverse effect on surface quality when micro milling PMMA with all-ceramic micro end mills.