Monitoring & Analysis

Results

50,000 strips were produced over a four week period. The chart shows a weekly breakdown. The expected initial high level of faults fell after the first week. The tolerance of the Hole Pitch (distance between the two holes) caused a problem.

At the end of the four weeks, the Hole Pitch is still giving a higher level of faults than the other Quality Indicators. The batch is accepted as meeting the Quality Standards. It is even acceptable at the higher AQL (acceptable quality level) of 1.5%. The quality could be improved still further if the tight tolerance of the Hole Pitch was relaxed.

With a sample size of 315 and AQL of 2.5% — Accept = 14 or less — Reject = 15+
If the AQL is dropped to 1.5% then Accept = 7 or less — Reject = 8+

There is no reason why cutting the bar to length should be producing failures. The tolerance is sufficiently large. Perhaps the method of measuring is wrong. Similarly, the distance of the first hole from the edge should be producing zero defects.

Defects per day

This chart shows how defects are distributed daily for the four weeks. It highlights a known problems with workers being distracted by social activities at the weekend. English car manufacturers were notorious for their "Friday" cars.

Frequency Distribution

At the begining of the production of any new product, it takes time for quality to be achieved. Production and inspection techniques have to be altered in the light of problems. So instead of inspecting the whole batch, smaller samples are taken and their results shown as a "Frequency Distribution" in the form of a chart or graph. It is easy to see how actions taken after each small batch have improved quality.