In Part 2 of this series, I introduced four problem-solving methods and tools every manufacturing manager should use: 1) Run Chart, 2) Pareto Chart, 3) Cause and Effect Diagram, and 4) Causal Chain. I explained the purposes and provided examples of the Run Chart and Pareto Chart.
In today’s post, I will continue this discussion on problem-solving tools by looking at the Cause and Effect Diagram and the Causal Chain.
Identify, organize, and display causes with the Cause and Effect Diagram
Our third tool, the Cause and Effect Diagram, is one of the most widely used problem-solving tools ever developed. It is referred to by some as the Fishbone Diagram, because its structure resembles the skeleton of a fish, and by others as the Ishikawa Diagram, after its creator, the esteemed Japanese consultant Dr. Kaoru Ishikawa.
A Cause and Effect Diagram is a tool which helps to identify, organize, and display possible causes of a specific problem. It graphically illustrates the relationship between a given outcome (the effect) and all the factors that might influence the outcome (the causes). The structure of the diagram enables a team to think in a highly systematic way as they look for potential causes of a problem they are trying to solve.
Developing this diagram can be very useful when attempting to identify potential causes of a problem if the work is done with an open mind and without bias or preconceptions.
Take a stepwise approach to identifying a problem’s cause with the Causal Chain
The final tool we will discuss in this post is the Causal Chain. When a problem occurs, we know that a chain of events took place to alter the performance of the process. We aren’t certain as to what happened, so we need some kind of technique to help us develop a theory. The Causal Chain enables us to do this by demonstrating a theoretical stepwise evolution of a problem’s cause. Each step in the Causal Chain represents an object in either a normal or abnormal state. The object is placed on the line to the far right of the chain with its state listed directly beneath it.
The primary purpose of this problem-solving tool is to develop a stepwise chain of events that can explain a performance shortfall. Once this is complete, hypotheses or theories can be formulated as to why a problem exists. In my opinion, the Causal Chain is one of the most simple and effective, yet under-utilized tools available for problem solving in manufacturing.
At the far right in the Causal Chain example above, we see that a punch press has stopped working. The object (the press) is represented on top of the line with its state directly below it (stops). We then ask “why?” in a stepwise fashion until we arrive at the root cause. From right to left we see that the press stopped because
- the motor stopped,
- because the current stopped,
- because the pressure switch opened,
- because the air pressure was too low,
- because the air compressor failed,
- because oil level was too low,
- (finally) because a gasket failed.
We have now developed a potential theory as to why the press stopped. Along the way, we have identified culprits that we can test to prove our theory. Each step is a possible cause of the next step and the possible effect of the preceding step. In this example, the failed gasket was the possible root cause of the punch press failing.
For any given problem, conducting one or more Causal Chain analyses is highly advisable in the process of working toward identifying the culprit(s) and arriving at the solution(s).
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