Parts manufactured by an injection modeling process are subjected to a compressive strength test. Twenty samples of five parts each are collected, and the compressive strengths (in psi) are shown in Table 5E.6.

a. Establish x̅ and R control charts for compressive strength using these data. Is the process in statistical control?

b. After establishing the control charts in part (a), 15 new subgroups were collected; the compressive strengths are shown in Table 5E.7. Plot the x̅ and R values against the control limits from part (a) and draw conclusions.

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