Authors: Yonathan Tesfaye Sissay, Dereje Balcha
Abstract: This research work applied some of the basic SPC tools in a selected case factory to improve production quality and establish a way of monitoring quality in a better way than the conventional way of inspection.
Most of the data for analysis was collected through primary method with secondary data being used for defect categorization and Pareto analysis. The primary data was collection of variable data for measurement of shirt critical parts (3-measurement positions) as stated by the manufacturer and on a total of 330 samples; with 22 subgroups of 5 observations each.
An X and R Control charts were developed for the collected data, and it was found out that the process was out of control for body length and round collar measurements.
Later, a cause-and-effect analysis was conducted to reach the possible causes for the process to be out of control. A scatter diagram was also developed and was found out that the variation in measurements of the selected parts keep increasing through time. Accordingly, poor machine maintenance, use of old pattern papers, and carelessness of operators were identified as the causes.
After implementation of identified gaps, data was recollected on the same parameters. 20 samples of 5 observations each were made on front body length to see if the process was still out of control or has moved within the control limits and it was able to remove 9% of the observed assignable causes (quality problems) from the process.
Keywords: Statistical Process Control Tools, Assignable causes, Normal causes, Pareto, Control chart, fishbone