## 4 Case Study
### The Method Employed in this Study Is Illustrated in Figure 7
#### 4.1.2 Phases 2 and 3: Do and Check
This stable foundation allows for the development of reliable improvement plans. [52]. Figure 11: Epoxy curing station. Figure 12: Individual control chart for armature temperature at the start of laminating and degreasing (in \({}^{\circ}\)C). \begin{table}
\begin{tabular}{l c c c c c} \hline \hline  & \multicolumn{4}{c}{**Short-Side Armature**} \\ \hline
**Process Data:** & \multicolumn{4}{c}{**Overall Capability**} & \multicolumn{4}{c}{**Potential (Within) Capability**} \\ \hline LSL (lower specification limit) & 100 & Pp & 2.63 & Cp & 28.41 \\ \hline UPL (upper specification limit) & 500 & PPL & 1.92 & CPL & 20.70 \\ \hline Sample mean & 245.714 & PPU & 3.34 & CPU & 36.12 \\ \hline Sample N & 35 & Ppk & 1.92 & Cpk & 20.70 \\ \hline Overall StDev (standard deviation) & 25.3546 & & & & \\ \hline StDev (within) & 2.34668 & & & & \\ \hline Performance: & & & & \\ \hline  & Observed & Expected Overall & Expected Within \\ \hline PPM \textless{} LSL & 0 & 0 & 0 \\ \hline PPM \textgreater{} USL & 0 & 0 & 0 \\ \hline PPM total & 0 & 0 & 0 \\ \hline Long-Side Armature & & & & \\ \hline Process data: & & Overall Capability & Potential (Within) Capability \\ \hline LSL (lower specification limit) & 100 & Pp & 3.76 & Cp & 25.57 \\ \hline UPL (upper specification limit) & 500 & PPL & 2.68 & CPL & 18.26 \\ \hline Sample mean & 242.857 & PPU & 4.83 & CPU & 32.87 \\ \hline Sample N & 35 & Ppk & 2.68 & Cpk & 18.26 \\ \hline Overall StDev (standard deviation) & 17.7518 & & & & \\ \hline StDev (within) & 2.60743 & & & \\ \hline Performance: & & & & \\ \hline  & Observed & Expected Overall & Expected Within \\ \hline PPM \textless{} LSL & 0 & 0 & 0 \\ \hline PPM \textless{} USL & 0 & 0 & 0 \\ \hline PPM total & 0 & 0 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Process capability measures for epoxy coating thickness. Figure 17: Process capability histograms for epoxy detachment force: (**a**) short-side armature; (**b**) long-side armature. Adjusting the Voltage at the Epoxy Coating Curing Station to Optimize Curing Conditions  
To investigate the cause of low detachment force, two targeted experiments were conducted. In the first experiment, the voltage at the curing station was increased from 3 kV to 3.1 kV to explore whether enhanced curing could harden the epoxy and prevent cable penetration, a potential contributor to hipot failures. This test involved sampling 30 pieces, with separate detachment force measurements for both the short and long sides of the armature, referring to the rotation axis as defined in Figure 18. In the second experiment, the thickness of the epoxy coating was increased from 0.250 mm to 0.350 mm, aiming to provide a stronger physical barrier against cable abrasion. Again, detachment force was measured on both sides of a sample of 30 pieces. Table 6 shows the results of a mean difference test for breaking force before and after the voltage change experiment in the curing station. The aim was to evaluate the following hypotheses:  
**H0. **: \(\mu_{before\ voltage\ change}\) = _Hafter voltage change_
**H1. **: \(\mu_{before\ voltage\ change}\) \(\
eq\) _Hafter voltage change_