Johnson Company produces plastic bottles to customer order T

Johnson Company produces plastic bottles to customer order. The quality inspector randomly selects four bottles from the bottle machine and measures the outside diameter of the bottle neck, a critical quality\' dimension that determines whether the bottle cap will fit properly. The dimensions (inch) from the last six samples are provided below. What are the control limits for the R chart? What are the control limits for the x-bar Chart? Is the process in control?

Solution

Answer:

The solution is given here below:

2. For each subgroup, the subgroup average was calculated. For example for subgroup 1, the subgroup average is given by:

Subgroup avg. (X bar) = (0.602+0.596+0.582+0.631+0.597+0.584)/6 = 0.599

and so on.

1. The subgroup range for the first subgroup is given by :

R = Maximum - Minimum = 0.631 - 0.582 = 0.049

This was done for all subgroups in the above table.

3. Yes, the process is in contol.

Subgroup No.	Sample 1	Sample 2	Sample 3	Sample 4	Sample 5	Sample 6	Subgroup Average	Subgroup Range
1	0.602	0.596	0.582	0.631	0.597	0.584	0.599	0.049
2	0.613	0.602	0.551	0.604	0.623	0.579	0.595	0.072
3	0.574	0.607	0.584	0.596	0.609	0.621	0.599	0.047
4	0.601	0.606	0.598	0.576	0.603	0.578	0.594	0.030