# Experimental Study on Milling CFRP with Staggered PCD Cutter
## 4 Comparison of Cutting Performance between Two Different PCD Cutters  
Figure 9 shows the comparison of machining surface quality between the staggered PCD cutter and the straight-teeth PCD cutter in milling CFRP. It can be learned from Figure 9 that in the state of no tool wear, compared with the staggered PCD cutter, the straight-teeth PCD cutter produced better machining surface roughness, and the surface topography was more regular and smoother. With an increase of the cutting-edge radius, the surface roughness Sa of the staggered PCD cutter varied slightly, while the Sa of the straight-teeth PCD cutter increased significantly. When the cutting-edge radius reached 38 \(\upmu\)m, the surface roughness of the straight-teeth PCD cutter exceeded that of the staggered PCD cutter, and with the accumulation of cutting edge wear, the gap of surface roughness between the two PCD cutters widened increasingly. When the cutting-edge radius reached 61 \(\upmu\)m, a certain number of burrs appeared on the machining surface of the straight-teeth PCD cutter. However, in the same wear condition, only a few burrs occurred on that of the staggered PCD cutter; the reason for this is that the cutting edge of the staggered PCD cutter has an alternate sinistral-dextral inclination angle structure. Thus, in the machining process, both the upper and lower surfaces of the workpiece can bear alternately sinistral-downward and dextral-upward cutting forces, which puts a more even and stable stress on the fiber layer. In addition, in the inclination-angle cutting condition, the fiber layer on the upper and lower surfaces of the workpiece is more likely to be cut off, so that the burrs on both of the surfaces can be effectively suppressed.  
Figure 10 shows the comparison of the wear morphologies between the two PCD cutters after milling CFRP 60 m long. It can be learned from Figure 10 that the cutting-edge wear degree of the staggered PCD cutter was obviously smaller than that of the straight-teeth PCD cutter. By comparison of cutting forces without the tool wear, the main cutting force of the staggered PCD cutter increased by 26.4%, while that of the straight-teeth PCD cutter increased by 41.6%. Moreover, for the staggered PCD  
Figure 8: Burr formation on the machined workpiece surface: A-upper surface B-lower surface.  
Figure 9: Comparison of the surface quality between the two PCD cutters.  
cutter, burrs were mainly concentrated on the upper machining surface, while for the straight-teeth PCD cutter, a large number of burrs existed on both the upper and lower machining surfaces. This is because, in the cutting process with the staggered PCD cutter, the effect of the inclination angle and axial rake angle increased the contact edge length of the cutter and workpiece, and thus the load on the unit cutting edge decreased so that the cutting got brisker. Meanwhile, compared with the linear contact of the straight-teeth PCD cutter, the staggered PCD cutter formed point contact, which resulted in the periodical variation of the edge length during cutting in and out. The cutting edge of the staggered PCD cutter was involved in cutting alternately, so that the instantaneous resistance decreased obviously and the cutting was more stable, and thus the rate of tool wear slowed down.