The production manager of a soap manufacturing company wants to monitor the weig
ID: 428791 • Letter: T
Question
The production manager of a soap manufacturing company wants to monitor the weights of the bars produced on the line. Twenty bars are taken during a stable period of the process. The weights of the bars are shown in the following table. Bar Weight 74 82 97 86 71 68 83 90 Bar Weight 2 3 4 12 13 75 6 8 10 15 16 17 18 19 20 82 93 70 87 76 84 94 64 a. Compute control limits for individual observations and moving-range charts. Determine whether the process is in statistical control. (5 points) b. Estimate the process mean and standard deviation for the in-control process. What process capability is this operating, if LSL = 60 and USL-110? (5 points)Explanation / Answer
a. The table
The average Xbar = 82
Avg of Moving range MRbar = 12.947
UCL = xbar + 3 xMRbar /1.128 [ Here 1.128 corresponds to value of d2 for n=2]
= 82+3x12.947 /1.128 = 82+34.43 =116.43
LCL = xbar - 3 xMRbar /1.128
= 82-34.43= 47.57
The process is in control as all values fall within the range.
(b) Mean = 82
S.D. = MR /d2 = 12.947 /1.128 = 11.477
Cp = USL - LSL / 6sigma = 110-50 /6 x11.477 = 0.8713
Bar No. Weight Moving range 1 74 2 82 8 3 97 15 4 86 11 5 71 15 6 68 3 7 83 15 8 90 7 9 88 2 10 64 24 11 99 35 12 75 24 13 77 2 14 82 5 15 93 11 16 70 23 17 87 17 18 76 11 19 84 8 20 94 10Related Questions
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