6.33 Control charts have been constructed for a process used to stamp sheet metal parts. The specific quality characteristic of interest is the surface fin- ish of the part. While the R chart shows stability in the process variation, the X chart reveals a number of statistical signals. In order to identify the underlying root cause of the statistical signals, it is decided to construct scatter plots for the X values as a function of several process variables, i.e., operator, die temperature (F), and the cumulative number of hits on the die. The accompanying table displays the levels of the process variables and the X values for each sample. Prepare the scatter plots and comment on what the scatter plots seem to suggest regarding which process variable merits further investigation. Die Operator Temp. Die Hits Sample Sample 1 12 13 14 2 3 4 5 6 7 8 9 10 11 Ken Ken Ken Ken Pete Pete Pete Pete Ken Ken Pete 212 2342 28 193 2716 36 195 3089 32 186 3487 17 211 3867 21 220 4267 36 187 4644 33 188 5042 31 201 5416 38 197 5797 27 189 6160 24 15 16 17 18 19 20 21 Die Die Operator Temp. Hits Pete 211 6533 27 Ken 194 6926 32 Ken 200 7311 47 Pete 208 7681 36 Pete 191 8049 33 Pete 194 8413 38 Pete 204 8784 57 Ken 215 9163 30 Ken 198 9558 27 Ken 204 9953 37 Ken 196 10338 47 (Continued) 22 32 Chapter 6 Shewhart Control Charts for Variable Data Sample X 14600 39 Die Die Hits Sample Operator Temp. 23 Pete 192 10727 40 24 Pete 192 11123 48 25 Ken 193 11523 30 26 Pete 201 11901 43 27 Ken 207 12294 45 28 Ken 197 12692 50 29 Ken 181 13067 48 30 Pete 215 13451 47 31 195 13847 39 32 33 34 35 36 37 38 39 40 Die Die Operator Temp. Hits Pete 187 14231 40 Pete 201 Pete 188 14978 58 Pete 202 15363 43 Pete 20915726 37 Ken 189 16107 45 Pete 195 16491 Pete 203 16887 61 Ken 201 17271 42 Pete 63