## 4 Results and Discussion
### Preliminary Data Analyses
In the second week, the number of occurrences of D1 and D2 remained consistent, with D2 exhibiting a slight lead. Defect D3 remains at a moderate level of occurrence, while D4 increases slightly, and D5 and D6 remain at a low level of occurrence. In the third week, there is a notable increase in the prevalence of defect D2, which becomes the most common defect type during this period. Moderate levels of D1, D3, and D4 are observed, while the levels of D5 and D6 remain relatively low. In the fourth week, D2 reaches a peak level comparable to that observed in the fourth week of April. The counts for D1 and D3 are moderate, while those for D4, D5, and D6 remain low. This analysis demonstrates that defects D2 and D3 are the most prevalent throughout the period under review, with D2 peaking frequently in May and D3 peaking in late April. Defects D4, D5, and D6 demonstrate consistently lower counts, indicating a lesser impact compared to D1, D2, and D3. Both April and May's fourth weeks exhibit elevated counts for specific defects, suggesting potential end-of-month process variations or batch-specific issues that may necessitate further investigation. The preliminary analysis of the impact of individual process parameters on defect occurrence is presented in Figure 4. The preliminary analysis indicated that the curing temperature (X1) (Figure 4a) exhibited a correlation with the type of defect, with defects D1 and D2 occurring with greater frequency at higher temperatures. This suggests that a reduction in temperature may prove to be an effective strategy for the mitigation of these defects, especially that some outliers (black dots) for D2 defect can be observed. Defect D5 manifests at lower temperatures, thereby underscoring the necessity to adjust the temperature to curtail its prevalence. Figure 3: Distribution of defect types (D1 to D6) across specific weeks. Moreover, the cooling speed (X3) (Figure 4b) has a considerable influence on defect D6, which manifests at elevated values of this parameter. It can be posited that a reduction in cooling speed may prove to be an effective method of limiting the occurrence of this defect. Furthermore, the control of this parameter may also prove beneficial in reducing the incidence of other defects, especially that some outliers (black dots) for the several types of defects can be observed. Furthermore, the feed rate (X4) (Figure 4c) is found to be correlated with defect D5, which manifests at lower feed rates. It can be posited that an increase in the feed rate may serve to reduce this particular type of defect. Furthermore, it is conceivable that a meticulous calibration of the feed rate for each specific defect type could have a beneficial impact on the overall quality of the product. Furthermore, the cutting speed (X6) (Figure 4d) has an impact on the occurrence of various defects. Defects D1 and D2 are more prevalent at higher cutting speeds, while defects D3 and D4 are more common at lower speeds. The implementation of an effective control strategy for cutting speed has the potential to reduce the prevalence of nonconform  
Figure 4: Impact of individual process parameters on defect occurrence. (**a**) X1 vs. Defect, (**b**) X3 vs. Defect, (**c**) X4 vs. Defect, (**d**) X6 vs. Defect, (**e**) X8 vs. Defect, (**f**) X9 vs. Defect. ing products. Regarding the grinding wheel speed (X8) (Figure 4e), it was observed that defect D1 occurs at higher values, while D5 occurs at lower values. Optimisation of this parameter may prove to be an effective method of reducing the occurrence of these defects. The grinding time (X9) (Figure 4f) also plays an important role in this process; the occurrence of defect D4 is more common with longer grinding times. This may suggest that overheating or excessive wear from extended processing times contributes to its occurrence. It can thus be surmised that optimising the grinding time may prove to be an effective method of reducing the number of defects associated with this particular parameter.