Assignment Task
A component used as a part of a power transmission unit is manufactured using a lathe.
Twenty samples, each of five components, are taken at half-hourly intervals. Within the flow of the day a number of (non-)technical incidents appear. These include taking a lunch break and adjusting or resetting the machine.
For the most critical dimension, the process mean (????¯) is found to be 3.500 cm, with a normal distribution of the results about the mean, and a mean sample range (????¯) of 0.0007 cm.
With the above scenario in mind, complete the following tasks considering the data.
- Use this information to set up suitable control charts.
- If the specified tolerance is 3.498 cm to 3.502 cm, what is your reaction? Would you consider any action necessary?
- The following table shows the operator’s results over the day. The measurements were taken using a comparator set to 3.500 cm and are shown in units of 0.001 cm. What is your interpretation of these results? Do you have any comments on the process and/or the operator?
| Time | Component 1 | Component 2 | Component 3 | Component 4 | Component 5 |
| 7.30 | 0.2 | 0.5 | 0.4 | 0.3 | 0.2 |
| 7.35 | 0.2 | 0.1 | 0.3 | 0.2 | 0.2 |
| 8.00 | 0.2 | -0.2 | -0.3 | -0.1 | 0.1 |
| 8.30 | -0.2 | 0.3 | 0.4 | -0.2 | -0.2 |
| 9.00 | -0.3 | 0.1 | -0.4 | -0.6 | -0.1 |
| 9.05 | -0.1 | -0.5 | -0.5 | -0.2 | -0.5 |
| Machine stopped -tool clamp readjusted | |||||
| 10.30 | -0.2 | -0.2 | 0.4 | -0.6 | -0.2 |
| 11.00 | 0.6 | 0.2 | -0.2 | 0.0 | 0.1 |
| 11.30 | 0.4 | 0.1 | -0.2 | 0.5 | 0.3 |
| 12.00 | 0.3 | -0.1 | -0.3 | 0.2 | 0.0 |
| Lunch | |||||
| 12.45 | -0.5 | -0.1 | 0.6 | 0.2 | 0.3 |
| 13.15 | 0.3 | 0.4 | -0.1 | -0.2 | 0.0 |
| Reset tool by 0.15 cm | |||||
| 13.20 | -0.6 | 0.2 | -0.2 | 0.1 | -0.2 |
| 13.50 | 0.4 | -0.1 | -0.5 | -0.1 | -0.2 |
| 14.20 | 0.0 | -0.3 | 0.2 | 0.2 | 0.4 |
| Batch finished – machine reset | |||||
| 16.15 | 1.3 | 1.7 | 201 | 1.4 | 1.6 |