Control Charts (2 problems)

A company makes ball bearings for high quality engine components that demand very close tolerances. The company randomly selects 10 ball bearings every hour. Past experience shows the mean diameter to be .37mm with an average range of .04mm (Average R = .04).

a. Set up the X-bar control chart.

b. Set up an R-bar chart.

A new customer is interested in buying your companies ball bearings. They have three potential uses, each with its own tolerances. They are:

1. Mean = .37mm, tolerance = ± .03mm

2. Mean = .40mm, tolerance = ± .035mm

3. Mean = .38mm, tolerance = ± .02mm

Prepare a memo to the marketing department on how to respond to this potential new customer.

A member of the marketing team suggested that if necessary the process control limits be reduced to + or - 2 standard deviations, so that the control limits are within the tolerance limits set by the prospective buyer. Address this issue in your memo.

Another marketing person has suggested that we increase the sampling to 40 ball bearings every hour, and thus catch process errors faster. How would you address this suggestion?

The Highway Patrol has a target of 28 traffic tickets per week with standard deviation 5 tickets per week for a stretch of mountain highway. The number of tickets issued for 15 consecutive weeks is given below. t = number of week, x = number of tickets

a) Make a control chart for the above data.

b) Determine whether the process is in statistical control. If it is not, specify which out-of-control signals are present.