Plastic keychains are being produced in a company named Hot Shot Plastics. The plastic material is first molded and then trimmed to the required shape. The curetimes (which is the time for the plastic to cool) during the molding process affect the edge quality of the keychains produced. The aim is to achieve statistical control of the curetimes using X¯ and R-charts. Curetime data of 25 samples, each of size four, have been taken when the process is assumed to be in control. These are shown as follows. (Note: The spreadsheet â13 Statistical Process Controlâ has these data.)
Questions
1. Prepare X¯ and R-charts using these data with the method described in the chapter.
2. Analyze the charts and comment on whether the process appears to be in control and stable.
3. Twelve additional samples of curetime data from the molding process were collected from an actual production run. The data from these new samples are shown as follows.
Update your control charts and compare the results with the previous data. The X ¯ and R-charts are drawn with the new data using the same control limits established before. Comment on what the new charts show.
Sample No. Observations Мean Range 1 27.34667 27.50085 29.94412 28.21249 28.25103 2.59745 27.79695 26.15006 31.21295 31.33272 29.12317 5.18266 3 33.53255 29.32971 29.70460 31.05300 30.90497 4.20284 4 37.98409 32.26942 31.91741 29.44279 32.90343 8.54130 33.82722 30.32543 28.38117 33.70124 31.55877 5.44605 29.68356 29.56677 27.23077 34.00417 30.12132 6.77340 7 32.62640 26.32030 32.07892 36.17 198 31.79940 9.85168 8 30.29575 30.52868 24.43315 26.85241 28.02750 6.09553 28.43856 30.48251 32.43083 30.76162 30.52838 3.99227 10 28.27790 33.94916 30.47 406 28.87447 30.39390 5.67 126 11 26.91885 27.66133 31.46936 29.66928 28.92971 4.55051 12 28.46547 28.29937 28.99441 31.14511 29.22609 2.84574 13 32.42677 26.10410 29.47718 37.20079 31.30221 11.09669 14 28.84273 30.51801 32.23614 30.47 104 30.51698 3.39341 15 30.75136 32.99922 28.08452 26.19981 29.50873 6.79941 16 31.25754 24.29473 35.46477 28.41126 29.85708 11.17004 17 31.24921 28.57954 35.00865 31.23591 31.51833 6.42911 18 31.41554 35.80049 33.60909 27.82131 32.16161 7.97918 19 32.20230 32.02005 32.71018 29.37620 31.57718 3.33398 20 26.91603 29.77775 33.92696 33.78366 31.10110 7.01093 21 35.05322 32.93284 31.51641 27.73615 31.80966 7.31707 22 32.12483 29.32853 30.99709 31.39641 30.96172 2.79630 23 30.09172 32.43938 27.84725 30.70726 30.27140 4.59213 24 30.04835 27.23709 22.01801 28.69624 26.99992 8.03034 25 29.30273 30.83735 30.82735 31.90733 30.71869 2.60460 Means 30.40289 5.932155 2. Sample No. Observations Мean Range 1 31.65830 29.78330 31.87910 33.91250 31.80830 4.12920 2 34.46430 25.18480 37.76689 39.21143 34.15686 14.02663 3 41.34268 39.54590 29.55710 32.57350 35.75480 11.78558 4 29.47310 25.37840 25.04380 24.00350 25.97470 5.46960 25.467 10 34.85160 30.19150 31.62220 30.53310 9.38450 46.25184 34.71356 41.41277 44.63319 41.75284 11.53828 7 35.447 50 38.83289 33.08860 31.63490 34.75097 7.19799 34.55143 33.86330 35.18869 42.31515 36.47 964 8.45185 43.43549 37.36371 38.85718 39.25132 39.72693 6.07178 10 37.05298 42.47056 35.90282 38.21905 38.41135 6.567 74 11 38.57292 39.06772 32.22090 33.20200 35.76589 6.84682 12 27.03050 33.63970 26.63060 42.79176 32.52314 16.16116
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