Process Control, Monitoring, and Statistical Analysis of Multi-Position Slitting and Rewinding in the Paper Industry

The study investigates position-dependent variability in the slitting and rewinding process of filtration paper rolls under industrial conditions. Although individual cutting positions operate under identical machine settings, systematic differences between them lead to quality deviations and reduced process performance. Spatial variability was analyzed using descriptive statistics, control charts, and process performance indices (Pp, Ppk), complemented by non-parametric statistical testing. The results revealed a significant spatial effect, with one slitting position responsible for most nonconforming products, highlighting the limitations of global capability indices, which may mask local systematic deviations in a multi-stream process. Potential root causes were identified using the 5 Whys method within the Quick Response Quality Control (QRQC) methodology. Following the implementation of corrective actions, including parameter adjustments, position-dependent control, and revised operating procedures, the observed proportion of nonconforming products reduced from 14.7% to 6.0%. Furthermore, after excluding the first rolls from the start-up phase, process performance improved to Pp = 1.36 and Ppk = 1.21. The study suggests that integrating global and position-level analysis in multi-stream manufacturing systems enables more targeted identification and mitigation of quality deviations.