An SPC (Statistical Process Control) program was implemented in the foundry department in January 1990, after which one change was made to the foundry operations, apparently resulting in a 4% reduction in the scrap rate from the 1989 average rate of 28%. The standard deviation was 2%. The table provided summarizes the weekly scrap rate data for the first half of 1990. The tasks are to: a) Construct a CUSUM (Cumulative Sum) chart to analyze the data for the purpose of verifying the engineer’s claim regarding the scrap reduction, with h (decision interval) = 5 and k (reference value) = 0.25. b) Determine when the process was last in control. c) Calculate the magnitude of the mean shift.
