The inner diameter in millimeters of a bearing seat in a pressure plate is a cri

Question

The inner diameter in millimeters of a bearing seat in a pressure plate is a critical quality characteristic in achieving the correct press fit of a roller bearing. The following table presents the inner diameter measurement from a sample of 25 randomly selected individual pressure plates. (a) Assess process control and stability. What is the standard deviation estimate of the in control, stable process? (b) Prepare a normal probability plot of the inner diameters. At ?= 0.05, do the data fit a normal distribution? (c) If the hole specification is 125.500 0.035 mllimeter, estimate the process capability. 1. 125.506 125.498 125.507 125.503 125.490 125.504 125.504 125.495 125.519 125.512 125.514 125.516 125.512 125.500 125.503 125.519 125.501 125.502 125.495 125.524 125.503 125.500 125.504 125.508 125.509

Explanation / Answer

a) To assess the process control and stability, the Xbar-S chart is used.

Interpretation: For the given sample data, after using the Xbar-S chart, the mean estimate is 125.505 which lies with in the upper control limit = 125.510 and lower control limit = 125.500. The standard deviation estimate is 0.008231 which is also lies with in the upper control limit = 0.011813 and lower control limit = 0.004649. Hence we can conclude that the given process in control is stable process.

b) for normal probability plot,

Interpretation: For the given data, when we fit a normal proability plot, the corresponding p-value comes out as 0481 which is much higher than 005. Hence we can conclude that the given data fits a normal distribution.

c) For process capability analysis,

interpretation: From the output report, the the ppk and cpk determine the overall and potential capability of the given process respectively. The accepted minimum value for both these term is 1.33. but for the given data, it is found that, ppk is 1.18 and cpk is 1.17 which are much smaller than the accepted value i.e. 1.33. Hence we can conclude that the process is not capable.

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