# Reconditioning of Diamond Coated Tools and Its Impact on Cutting Performance for CFRP Laminates
## 3 Results and Discussion
### Drill Flank Wear Evaluation  
In the cutting tests, tool wear was evaluated as the maximum flank wear land width (VB\({}_{\text{max}}\)) as a function of the drilled hole number, as shown in Figure 12. Based on trial cutting test results, the VB\({}_{\text{max}}\) was always determined on the secondary cutting edge at 6 mm from the drill tip, which was placed close to the rounded corner connecting the secondary and the tertiary edges. Since there was a gradient in the tool wear from the corner of the drill cutting edge to the center, the area of the second cutting edge indicated above kept higher values of the flank wear measured in preliminary cutting tests compared to other areas of the drill edges. The results, shown in Figure 12, indicated that the evolution of the VB\({}_{\text{max}}\) values for the TLC0, the TLC1, and the TLC2 can be divided into two regions. The first region was the primary wear taking place, when \(\
eg 40\) holes were drilled. The second region was the region of steady-state wear observed between \(\
eg 40\) and \(200\) drilled holes. This was a normal operating region for the cutting tool. Some minor differences between the flank wear values were observed for the new and reconditioned diamond-coated drills. The abrasion of rough grains of the B-MCD film occurred with a fast increasing trend of the flank wear value, until 40 holes were drilled. Then, the smoothed diamond film led to the gradually increased wear, until 200 holes were drilled. However, the flank wear progress of the TLC2 showed a dramatically increasing trend after drilling 180 holes, which is typical for an accelerated wear region with the vanishing of the diamond film and the progressive substrate wear.  
Figure 11: Change of the CER (11 mm measured point).  
Figure 12: Variations of the maximum flank wear as a function of the drilled holes number.  
Figure 13 shows the wear morphologies of the tested drills after drilling 200 holes. For the TLC0, only the abrasion wear of the diamond film along the cutting edge was observed clearly, as shown in Figure 13b,c. The TLC1 images (Figure 13e,f) showed the worn diamond film with localized film flaked areas, while the film detachments and the worn areas of the substrate were observed for the TLC2, as shown in Figure 13i.  
During drilling, the cutting force instability produced by the altered orientation in the CFRP layers resulted in an intermittent cutting, which may have led to fatigue failure in the coating layer. In addition, a contact area was enhanced between the cutting edge and the machined surface due to the wear progress, which resulted in continuous or intermittent impacts and fluctuations of the cutting forces, which may induce additional shear stress and cracks beneath the film surface. Such a cutting force combined effects, and the propagation of cracks along the film-substrate interface with the film detachment can occur. Therefore, the film detachment that occurred on the TLC2 could be attributed to the deteriorated adhesion between the diamond film and the WC-Co substrate by the 2 nd-time reconditioning procedures, as discussed in the previous sections.  
On the other hand, the drill tip areas of the TLC1 and the TLC2, as shown in Figure 13e,h, had abrasion only, which can be explained as influencing the load of the thrust force mainly.  
Despite that diamond film detachment occurred on the TLC2, it can be considered that all reconditioned drills showed flank wear values comparable with the new drill.