Quality control of cardboard using MEWMA and MEWMV control chart (case study in PT. y Kediri Indonesia)

Cardboard is one type of paper that has a grammatic value above 200 g/m2. Controlling the quality of competing products is important to improve product competitiveness. The purpose of this study was to analyze carboard quality and provide improvements at PT. Y Kediri East Java. The research methods used were MEWMA (Multivariate Exponentially Weighted Moving Average) and MEWMV (Multivariate Exponentially Weighted Moving Variance). The data used were nine variables of quality of cardboard, that were grammage, thickness, pull resistance, PS surface smoothness, BS surface smoothness, print surface smoothness, oil print, PS color, and BS color, with a time span between 2016 and 2018. Data were taken for ICB 230, ICB 210, WHI 230 and ICB 250 type of cardboard. From the MEWMV control chart, the types of ICB 230, ICB 210, WHI 230, and ICB 250 successively have out-of-control points of 19, 10, 6, and 5, while in the MEWMA control, types of ICB 230, ICB 230, ICB 210, WHI 230, and ICB 250 respectively have out of control points of 13, 9, 9, and 6. The main causes of product defects were repeated machine configurations and uneven spraying of pulp, and dew dripping over the production machine. In addition, other causes were adhesives and coating materials which were too thick/runny, and materials which were not suitable for production enter the process. Some suggestions for improvement that can be done are placing filters at the entrance of the coating material, and adjusting the temperature of the production machine's environment.