This case study looks at the behavior of a circuit board process through the use of control charts. At least two control charts will need to be constructed, and from them you will be asked to provide an assessment of what you see.
Fujiyama Electronics, Inc. has had difficulties with circuit boards purchased from an outside supplier. Unacceptable variability occurs between two drilled holes that are supposed to be 5 cm apart on the circuit boards. Thirty samples of four boards each were taken from shipments from the supplier as shown in the data from the worksheet below. Data in the worksheet below can also be accessed in Doc Sharing in a file named Fujiyama Electronics Sample Data.
The student will complete and/or answer the following questions:
Calculate X-Bar-Bar, R-Bar, and associated control limits using the data in the table above. Create X-Bar•R (Average & Range) Control Charts from the data in the table above. Discuss notable out-of-control conditions displayed in the completed X-Bar•R (Average & Range) Control Charts. Only consider points outside the control limits. Do not consider runs, set of points within certain zones, and so forth. If the conditions you note could be defined as assignable conditions, and they are removed from the process, then what will happen to the X-Bar•R Control Chart?
Remove the data related to the out-of-control points you observed from the original data, and recalculate new X-Bar-Bar, R-Bar, and associated control limits. Create new X-Bar•R (Average & Range) Control Charts from your updated data. Discuss how the two sets of Control Charts are different. What has changed?