4. Grooving and planing experiments4.1 Comparison of elliptical vibration cutting with ordinary cuttingAt first, investigations are undertaken to compare elliptical vibration cuttingperformance with ordinary cutting. The binderless workpiece of BL4 is grooved by theordinary cutting and the elliptical vibration cutting. Figure 4 shows the scanning electronmicroscope (SEM) images of the grooved surface on BL4 at a depth of cut of 0.2 μm. Inthese experiments, the nominal cutting speed is set to 150 mm/min. Amplitudes ofelliptical vibration in the nominal cutting and depth of cut directions Ac and Ad are set to4 μmp-p and 2 μmp-p to realize an elliptical vibration locus. As noted from Fig. 4, thegroove formed by the ordinary cutting is filled with numerous brittle defects. In contrast,a smooth surface can be obtained by the elliptical vibration cutting. As no brittle crackand asperity can be observed on the surface in the elliptical vibration cutting, ductile mode machining was attained successfully. From this fact, it can be expected that theinside of tungsten carbide grains existing at the topmost layer of the remained surfacewas cut without fracture generation on the surface or pull-out of the grains, which areobserved in the ordinary cutting Next, Fig. 5 shows the cutting edges after grooving of the binder-containingworkpiece of Co1. Considerable adhesion of the workpiece material can be observed onthe rake face of the tool used in ordinary cutting, which may result in adhesion wearand/or considerable thermo-chemical reaction. The same phenomena was observed inthe ordinary cutting of other binder-containing materials. On the other hand, noadhesion was observed in the elliptical vibration cutting. This fact indicates that theelliptical vibration cutting may be effective to suppress tool wear progress and to attainbetter surface quality in machining of binder-containing tungsten carbide as well as steelmaterials. Mechanism of the ductile mode machining shown in Fig. 4 is considered as follows.In elliptical vibration cutting, the tool cuts the surface that is finished in the previous vibration cycle. Thus, the actual uncut chip, i.e., instantaneous uncut chip thicknessshown in Fig. 1, becomes extremely thin. Note that this uncut chip thickness becomesgenerally smaller as compared with the nominal depth of cut. The instantaneous uncutchip thickness in each vibration cycle becomes significantly small especially when thetool cuts the finished surface around the bottom of the elliptical vibration. Because ofthis process, the actual depth of cut becomes smaller than the critical value for ductilemachining due to the size effect in fracture toughness, resulting in significantimprovement of nominal critical depth of cut for ductile machining of tungsten carbide.The process is similar to that in milling, and Arif et al. (2012) clarified similarimprovement in milling process through experiments with the