**2.4 Surface roughness, tool wear and tool life**

Surface roughness was measured every 0.2 mm, and each pocket had a pitch of 0.2 mm. **Figure 5** shows the Mitutoyo surface roughness tester SJ-301, a tool used to test surface roughness. The tool wear was measured using the Zeiss Stemi 20,000-C Microscope Profile optical video measuring system, as shown in **Figure 6**. Tool life is measured by the number of cuts taken by the end mill to reach average flank wear criterion 0.3 mm. All the tools failed primarily on the plank face. For all machining conditions, the machining was stopped when the flank wear land reached about 0.3 mm to ensure that the tool life data is more reliable. The flank wear was measure using Zeiss Stemi 20,000-C Microscope Profile optical video measuring system. The effect of interaction between high cutting speed and feed rate is most significant in shorten tool life. This is claimed by J.P. Urbanski et al. found that tool life decrease drastically as cutting speed is increased because at high cutting speed high temperature will be generated, which accelerates tool wear and consequently shortens tool life [47].

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

**Figure 4.** *Field emission scanning electron microscope (FESEM)—JSM-7800F.*

#### **Figure 5.**

*Mitutoyo surface roughness tester SJ-301.*

### **2.5 Taguchi method**

MINITAB 14 software was used to study the influence and range of parameters' effect on the surface roughness of 7075 Aluminium Alloy. The experiments, based on Taguchi L9, selected spindle speed, depth of cut, and feed rate as the process

#### **Figure 6.**

*Zeiss Stemi 20,000-C microscope profile optical video measuring system.*


#### **Table 5.**

*Level of machining cutting parameters.*


#### **Table 6.**

*The OA arrangement of the machining process.*

variables and were conducted at three different levels. The machining parameters are listed in **Table 5**.

**Table 6** illustrates the Orthogonal Array (OA) L9 for each substrate was determined using the Taguchi method of experimental design (DOE) with three parameters at three levels. The Ni-CBN HSS coated end mill, and uncoated cutting tools were analysed via 18 tests in this study. The preferences of the end mill manufacturer determined the feed rate and depth of cut and had moved the experiment to the "high cutting speed" category [48, 49].

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

#### **Figure 7.**

*Cutting tool image for HSS end mill cutting tool (a) uncoated; and (b) coated.*

#### **Figure 8.**

*Machining profile on aluminium alloy 7075 material.*

#### **2.6 Process of machining**

The DMU 50 CNC machine was utilised in the machining process. After coating the HSS end mills with CBN composite material, the Mitotuyo digital micrometre was used to measure the thickness of the cutting tool. The average thickness was determined through the three measures taken from each tooltip.

The workpiece is an aerospace material Aluminium Alloy 7075 to determine machining performance. The cutting tools were then examined for their machining capabilities. The profile was machined with 18 pockets and two cutting tools. Both coated and uncoated HSS end mills (**Figure 7**) were used to machine nine pockets each. **Figure 8** shows the machining profile of the machine pockets with 40 mm x 35 mm dimension on the workpiece.
