When we come across a problem, sometimes we know ore about the problem itself than we do about the cause of the problem. In manufacturing, there may be many variables and contributing factors. The more complex the production process, the more difficult it may be to sort out the problem's cause.
Our mission needs to be to find and cure the causes using the symptoms as sign posts. Luckily, we have Seven Quality Tools in our "quality toolbox" to help us identify causes.
The cause and effect diagram was developed by Kaoru Ishikawa to sort out possible causes associated with production problems. This method is commonly referred to as a fishbone diagram because of how the sorting process is illustrated.
The diagram is best constructed by a group that is knowledgeable about the process at hand. The group starts with the fishbone framework composed of the five M's: Materials, Machines, Measurements, Man, and Methods. The group brainstorms what variables in each category may contribute to the current problem.
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This exercise stirs the thought processes of the group's members and extracts core process knowledge to identify likely contributing factors. Along the way, each person in the group asks and answers questions about possible relationships of the five M categories.
Other tools may also be used in order to test causes and provide solutions. Check sheets may be used to determine frequency of various cause occurrences. But how do we use a list or check sheet to capture information?
For example, what if we examining a pile of defective parts? We found that there were several key defects. This check sheet allows us to capture that information and quantify the frequency of these defects.
We can total the frequency of each defect and generate a picture of the greatest defect problem. In this example, we use the data collected on the check sheet by plotting the totals in descending order of occurrence. This is the Pareto chart shown in Figure 3.
Pareto charts, histograms, and control chart use may also point to significant causes. Flowcharts can help map the process to establish where factors are introduced.
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What is a histogram? How does that tool work? It works by showing the relative bell curve of data distribution. Figure 5 is an example. The part size is to...