Question

Tire Pressures. Six samples, each consisting of 10 automobile tires, were selected, and the pressure (in kilopascals, kPa) in each tire was measured. The tires were filled by a machine on an automobile assembly line. The means and ranges for the samples are shown here. Construct and analyze an ?X chart and an R chart for the data.

Sample | 1 | 2 | 3 | 4 | 5 | 6 |

Mean | 223.2 | 242 | 238 | 223 | 229 | 242 |

R | 26.2 | 14.5 | 25.5 | 15.2 | 20.7 | 21.4 |

Answer #1

From the given data , we get

For n = 10, A_{2} = 0.308, D_{3} = 0.223,
D_{4} = 1.777

Chart

R Chart

Analysis : The process average is out of control because sample 1, 2 4 and 6 lie outside the control limits, and the process variability is in control because all the sample points fall within control limits.

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