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.