Many different companies produce electrical items that require fuses. These fuses act as a safety precaution, to terminate the flow of electrical current to a product if an excessive current starts to flow through it. The fuse prevents the possibility that the excessive current will cause components to burn out inside the product. This excessive power flow can result from various malfunctions inside the product itself, or from problems with the power source.
Crouse Fuse Company (CFC) produces very large amounts of inexpensive fuses for a number of different customers. Manufactures of strings of outdoor lights use one of its primary product lines. These particular fuses consist of high-resistance thin metallic wires that are mounted inside a small glass tube, and the resulting heat from any excessive current flow will melt the fuse wire. Once the fuse wire melts, the current flow stops immediately. The dimeter of the fuse wire and the makeup of its metallic content determine the current level at which the fuse will “blow out.”
The most critical factor in fuse quality is the metallic content and the diameter of the wire inside the fuse. The wire making operation can be calibrated periodically to reset its operation to precise specification for the particular fuses being processed. The wire making process tends to “drift” over relatively short time periods, as replaceable components start to wear out. This “drift” is a natural part of the operation, and there is no feasible way to change it.
As calibration is critical to maintain the good quality of the fuses, shift supervisors have been instructed to calibrate the wire making operation before shift starts and during the shift break (4 hours after work starts). This calibration process takes 20 minutes and it drastically slows down the whole system, reason why supervisors have been requested to do it while production is not happening (before the start of the shift and during break).
CFC wants to use statistical process control (SPC) to control their fuse production process, and the results can be used as the basis for stablishing control charts and applied analysis of process data.