Before statistical process control (SPC), quality control was hit or miss. A customer could get a great product one day but a lousy one the next. With the advent of SPC, product uniformity in terms of quality has become the norm, and customers can rely on a consistent product.
Uniformity is a key benefit of SPC. For example, a customer buys a shirt that is a size medium, and it fits him perfectly. He likes the shirt so much that he buys another one exactly like it the next day. The new shirt fits tightly because it was made too small, even though the label states "medium." Another example is soft drinks. All must taste the same, even though thousands of bottles are manufactured per day. SPC assures uniformity of the final product, whether one unit or a thousand units are made per day.
SPC is very helpful in cost control. By keeping an eye on the quality of the products, defects are caught before the products are shipped out the door. An example of ineffective SPC is car recalls. It costs a manufacturer hundreds of thousands of dollars to rework cars to fix a problem. If SPC was used correctly, the problem would have been caught before the final product left the manufacturing plant. According to Montana State University, scrap and rework defects can be reduced by instituting SPC.
A manufacturer running an assembly line has fixed costs. These costs can be significant, running into thousands of dollars per hour. The only way to recoup the cost is the profit on the units per hour made on the line. The more units, the more efficient the assembly line. If the line is shut down because of a problem, no money is incoming, but the fixed costs are still outgoing. Without SPC, problems only surface at the very end of the line, such as parts having defects. A line has to be shut down completely to pinpoint the location of the problem causing the defect. Pinpointing and repairing the problem take up valuable time. With SPC, problems are caught during the manufacturing process, and only a small part of the line has to be shut down. The work flow of the particular problem area can be diverted to a backup mini assembly line. The entire line never shuts down completely, and constant production is maintained. The same units per hour of output is possible while the problem area of the line is under repair. Once repaired, the mini line is taken out of the system, and normal operation resumes.
The goal of any business is to become a trusted supplier to a customer. For example, a car manufacturer must rely on its parts supplier for good parts. If a supplier sometimes ships low-quality parts, the manufacturer may take its business elsewhere. By using SPC, the supplier is assured customer loyalty because the manufacturer can depend on a good product.
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