A quality engineer for a plastic parts company monitors an injection molding process. A machine has a die that creates five parts at one time. The engineer collects 20 subgroups of five parts each. The engineer monitors both the within-subgroup variation between parts that are created at the same time and the between-subgroup variation between the batches.
The engineer creates an I-MR-R/S chart to monitor the injection molding process.
One subgroup failed Test 1 on the Moving Range chart, and one point failed Test 1 on the R chart. The between-subgroup variation and the within-subgroup variation are not in control. No subgroups failed the test for special causes on the I chart. The I chart shows no evidence of lack of control in the process location.
TEST 1. One point more than 3.00 standard deviations from center line. |
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Test Failed at points: 14 |
TEST 1. One point more than 3.00 standard deviations from center line. |
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Test Failed at points: 8 |
Between | 0.165737 |
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Within | 0.243244 |
Between/Within | 0.294341 |