An inspector at an aerospace composites facility has logged the number of resin-rich defects occurring at 20 different points in the bend radius of a flanged component in 12 random samples. A summary of her inspection data is given in Table 4.

(a) State, with justification, the type of control chart you would use to monitor the inspection process. (b) Construct a fully annotated three-sigma control chart, using the information in Table 4. (c) Show on your control chart the mean, the UCL and the LCL. (d) Comment on the results.

Table 4. Summary of Composite defects Random Number of Number of pre-defined Sample ID resin-rich points inspected defects 1 6 20 3 20 5 20 4 O 20 1 20 8 20 2 20 2 LD CO 20 5 20 10 3 20 11 1 20 12 0 20