Plastic key chains are being produced in a company named Hot Shot Plastics. The plastic material is first molded and then trimmed to the required shape. The current curetimes (which is the time for plastic to cool) during the molding process affect the edge quality of the key-chains produced. The aim is to achieve statistical control of the curetimes using Xbar and R-charts
Curetime data of 25 samples, each of size 4 have been taken when the process is assumed to be in control. These are shown below.
Sample no | Observations |
1 | 27.34667 | 27.50085 | 29.94412 | 28.21249 |
2 | 27.79695 | 26.15006 | 31.21295 | 31.33272 |
3 | 33.53255 | 29.32971 | 29.70460 | 31.05300 |
4 | 37.98409 | ...view middle of the document...
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 below. Update your control charts and compare the results with the previous data. The charts are drawn with the new data using the same control limits established before. Comment on what the new chart shows.
Sample no | Observations |
1 | 31.65830 | 29.78330 | 31.87910 | 33.91250 |
2 | 34.46430 | 25.18480 | 37.76689 | 39.21143 |
3 | 41.34268 | 39.54590 | 29.55710 | 32.57350 |
4 | 29.47310 | 25.37840 | 25.04380 | 24.00350 |
5 | 25.46710 | 34.85160 | 30.19150 | 31.62220 |
6 | 46.25184 | 34.71356 | 41.41277 | 44.63319 |
7 | 35.44750 | 38.83289 | 33.08860 | 31.63490 |
8 | 34.55143 | 33.86330 | 35.18869 | 42.31515 |
9 | 43.43549 | 37.36371 | 38.85718 | 39.25132 |
10 | 37.05298 | 42.47056 | 35.90282 | 38.21905 |
11 | 38.57292 | 39.06772 | 32.22090 | 33.20200 |
12 | 27.03050 | 33.63970 | 26.63060 | 42.79176 |
Company introduction: Hot Shot Plastics
Hot Shot Plastics, Inc. filed as an Articles of Incorporation in the State of California and is no longer active. This corporate entity was filed approximately fourteen years ago on Monday, June 05, 2000, according to public records filed with California Secretary of State.
Manufactures processed plastics Plastic cutting machinery, Plastic grinding machinery, Rubber or plastic mills, Rubber or plastic extrusion dies, Plastic injection molds, Thermoforming molds, Ejector pins, In mold decoration IMD cylinder, Blow molding machines, Coating machines, Extruders.
Plastics 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 X̅- and R-charts.
1. Prepare X̅- and R-charts using these data with the method described in the chapter.
Factor for Determining from R̅ the Three-Sigma Control Limits for X̅- and R-Charts
| | Factors for R-Chart |
Number of observations in each samplen | Factor for X̅-ChartA2 | Lower Control LimitD3 | Upper Control LimitD4 |
4 | 0.73...