**3.3 Surface roughness analysis**

The most critical factor in improving surface roughness analysis is the quality of the cutting tools. **Table 9** compares the Ra results of machined 7075 Aluminium Alloy for coated and uncoated cutting tools. The data indicates Test 8 of HSS coated tools; high level of cutting speed and a medium level of feed rate produced a good surface finish, Ra 0.251 μm. In comparison, the combination of feed rate at high level and cutting speed at low level in Test 3 give a high surface roughness of Ra 1.22 μm. This finding demonstrates the combination of high-value feed rate and spindle obtaining a


### **Table 9.**

*Data of design experiment and surface roughness.*

*Characterisation and Application of Nickel Cubic Boron Nitride Coating via Electroless Nickel… DOI: http://dx.doi.org/10.5772/intechopen.105364*

better surface finish [52, 53]. According to Mohammed [54], the interaction between cutting speed and feed rate will significantly impact the surface finish.

#### **3.4 Tool wear and tool life analysis**

Tool wear for every 0.2 mm of machining was examined using Zeiss Stemi 20,000-C Profile Optical. In accordance to ISO 8688-21:1989, the end mill cutting tool with the lowest tool wear is the best and most durable. **Figure 13** shows the tool wear on the cutting tool before and after the machining process.

Comparing the flank wear trends in **Figures 14** and **15**, the coated cutting end mill tool performed better in terms of both cutting time and tool life. Test 3 and Test 5 produced the most extended tool life, 195 min. **Figure 15** depicts an uncoated end mill's cutting time-based flank wear trend. The substrates performed better than the coated end mills in terms of scattering. Test 3 yielded the most extended tool life for the uncoated tools at 143 min. High-value of feed rate, spindle speed and depth of cut and cutting time will cause significant tool wear. The previous studies found that the cutting speed and feed rate interaction is significantly affecting the tool wear [52, 55, 56].

**Figure 13.** *Flank wear on HSS cutting tool on machining (test 9): (a) before; and (b) after.*

**Figure 14.** *Flank wear versus cutting time of uncoated HSS.*

#### **Figure 15.**

*Flank wear versus cutting time of coated HSS.*


#### **Table 10.**

*An investigation via L9 OA of Ni-CBN HSS coated end mills.*
