Copper wires are coated with a thin plastic coat­ing.

Chapter 10, Problem 12E

(choose chapter or problem)

Copper wires are coated with a thin plastic coating. Samples of four wires are taken every hour, and the thickness of the coating (in mils) is measured. The data from the last 30 samples are presented in Table E12 on page 788. The means are  \(\overline{\overline{X}}=150.075\), \(\overline{R}=6.97\), and \(\overline{s}=3.082\).

a. Compute the \(3\sigma\) limits for the R chart. Is the variance out of control at any point? If so, delete

the samples that are out of control and recompute \(\overline{\overline{X}}\) and \(\overline{R}\).

b. Compute the \(3\sigma\) limits for the \(\overline{X}\) chart. On the basis of the \(3\sigma\) limits, is the process mean in control? If not, at what point is it first detected to be out of control?

c. On the basis of the Western Electric rules, is the process mean in control? If not, when is it first detected to be out of control?

Equation Transcription:

Text Transcription:

overline{overline{X}}=150.075

overline{R}=6.97

overline{s}=3.082

3{sigma}

overline{overline{X}}

overline{R}

3{sigma}

overline{X}

3{sigma}