## 3 Results and Discussion
### Force Profile Correlation  
On 24 to 25 February for 4P, as shown in Figure 4a, the force signal correlation deviated shortly after machine start-up from 0.99996 to 0.99893 initially at 09:28. The fall worsened to bottom out at a sustained lower level, providing a time to quality adjustment--tolerance, tilt and roundness--of 2 h 41 min. The worsening deviation reflected the change in the moulds' tolerance, which increased the surface area of the workpiece impacted by the die. A wire change at 16:22 was preceded by a smaller downward correlation movement. After restarting the machine, unplanned maintenance occurred at 02:59 due to collision of the fourth clamp, fifth clamp, and fifth mould. Although the machine failed, the wear on the 1P, 4P, 5P, and 9P dies was minimal. The first indication of the impending collision occurred at 21:58--5 h 1 min prior to the collision--and was likely caused by some clamp rotation due to the loosening of the screw at the base of the machine. The changing force impact on the workpiece manifested in a small but consistent decline that began 1 h 41 min before collision. The 9P correlation in Figure 4b showed a fluctuating decrease that started at 09:30 and spanned 2 h 39 min before the quality adjustment. The decrease was linked to the steady increase in the dimension tolerance of the moulds that led to greater deformation of the material hit by the 9P die. Following the quality adjustments, correlation values declined as the spool of raw material reared its finish. After the spool change, fluctuations \begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Date**} & \multirow{2}{*}{**Maintenance Time**} & **Maintenance** & **Severity** \\ \cline{3-4}  & & **Record** & **1** \\ \hline \multirow{3}{*}{24 February} & Before 08:00 & 4P and 9P dies changed before machine starts & None \\ \cline{2-4}  & 12:09–14:53 & Quality adjustment; tilt and roundness adjustment & Minimal \\ \cline{2-4}  & 16:22–17:49 & Raw material wire change & None \\ \hline \multirow{3}{*}{25 February} & \multirow{3}{*}{02:59–end} & Collision damage and change of fourth clamp, fifth clamp, and fifth mould; minimal wear on and change of 1P, 4P, 5P, 9P dies; quality adjustment & Severe (unplanned) \\ \hline \multirow{3}{*}{9 March} & 10:09–10:22 & Wire change; quality adjustments & None \\ \cline{2-4}  & \multirow{3}{*}{19:51–end} & Crash repair requiring change of 4P (breakage), 5P (fusion with nut); change 1 through to 5 sleeves; raw & Very severe (unplanned) \\ \cline{1-1} \cline{3-4}  & & material wire change; quality adjustment & (unplanned) \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Maintenance log. from the start-up force profile were clearly visible. The earliest fault indicator occurred at 21:58--5 h 1 min prior to unplanned maintenance. This was followed by a declining trend, which continued for 2 h 41 min prior to malfunction. The accelerated wear of the 5P and 9P dies reduced surface contact with and lessened the force transmitted to the workpiece. Additionally, damage to the fifth clamp and fifth mould changed the force impact. The twisting of the clamp created an uneven surface contact area. The damage to the fifth mould--responsible for the creation of the large indentation located in the centre of the unfinished nut--changed the transmission of the force throughout the workpiece, thereby reducing nut quality. The 9P results were more magnified and, therefore, more useful than those of 4P, since it captured both 5P and 9P deterioration and damage within a time period that could allow maintenance to be conducted as needed and forestall machine failure. In the case of the 4P data for 9 March shown in Figure 5a, the first maintenance was to put in a new material spool and to adjust the tolerance responsible for quality assurance by securing the screw at the base of the six-die nut manufacturing machine. These maintenance works were preceded by an early alert of 1 h 41 min. An unplanned maintenance occurred at 19:51.