Analysis of Statistical Quality Control by Control Chart to Reduce the Variability of The Product

This study aims to analyze how the condition of process quality in the manufacture of "shoulder" as one of the spare parts of railroads in Indonesia. The methodology used is quantitative research with naturalistic alignment, process dictation tool is statistical quality control with p control chart and to analyze correlation between disability effect using Pearson correlation regression with 99% confidence level. The data analyzed were 66,655 pcs produced from July to December 2016. Based on the results of the study, six types of disabilities were found in each stage of the process ie early frozen disability, sand inclusion, slag inclusion, dimensions, air cavity deficiency and Mold Defects. From the control chart on each type of disability indicates that the process is out of control, with data always outside the upper control limit and lower control limits. The data also indicate a very significant relationship and influence between the defects occurring in the initial process of defects in the subsequent process. Thus the management must make efforts to work hard to investigate the cause of uncontrolled process, which is suspected due to engine factors, raw materials and also weak control. Subsequent research is proposed to examine it in more detail so that management can take precautions.