Over the last year, a company that manufactures golf clubs has received numerous complaints about the performance of its graphite shafts and has lost several market share percentage points. In response, the company decided to monitor its shaft production process to identify new opportunities to improve its product. The process involves pultrusion. A fabric is pulled through a thermosetting polymer bath and then through a long heated steel die. As it moves through the die. the shaft is cured. Finally, it is cut to the desired length. Defects that can occur during the process are internal voids, broken strands, gaps between successive layers, and micro cracks caused by improper curing. The company's newly formed quality department sampled 10 consecutive shafts every 30 minutes and nondestructive testing was used to seek out flaws in the shafts. The data from each eight-hour work shift were combined to form a shift sample of 160 shafts. Data on the proportion of defective shafts for 36 shift samples arc presented in the table on page 698, followed by data on the types of flaws identified. [Note: Each defective shaft may have more than one flaw.
a. Use the appropriate control chart to determine whether the process proportion remains stable over time
b. Does your control chart indicate that both common and special causes of variation are present? Explain.
c. To help diagnose the causes of variation in R rocess output, construct a Pareto diagram for the types of shaft defects observed. Which are the "vital few"? The "trivial many"?