In many companies the problem solving process is defined as a technical problem solving process regarding quality issues a product or (production-) process might have. As result of this technical problem solving process we have the 8D-Report (in automotive industries) or the CAPA process and report in pharmaceutical industries and others. An overview of problem solving approaches you can find in a previous post.
Typical for technical problem solving is that a special matter expert is dealing with this and that he or she knows the root cause very soon or at least the direction where to search for the root cause. In many cases the problem solver is the developer of the product (or process) or a well-trained quality engineer. Therefore the problem solver is able to come up with a preliminary or final corrective action very soon.
But, what happens when you have a complex production process or complex transactional processes where many functions and departments are involved? In this case the special matter expert also comes up with a solution very quick, but he will be wrong in 90% of the issues. In addition to that there are often several different root causes that generate the observed problem. What we need here is an interdisciplinary approach with several experts from different departments. A common and well-known approach for collecting possible root causes is to do a brainstorming together with the interdisciplinary team by using a visual tool, the Fishbone Diagram or Ishikawa Diagram.
The Ishikawa Diagram, developed by Japanese scientist Kaoru Ishikawa in the beginning of the 1940s, looks like the bones of a fish and is therefore often called Fishbone Diagram (please see image above). The head of the fish represents the problem (the defect of the product, the deviation inside a process, … ). The bones of the fish help to sort the possible root causes by categories.
As generic high-level categories the 6 M’s are often proposed
- Man Power
- Mother Nature
Use these categories only if you have no idea how to focus your problem solving on a smaller aspect of your product or your process (e.g. reflow soldering in manufacturing). In fact you do not need any of these categories, but as Ishikawa Diagram is a visual tool, it helps to direct your attention through various perspectives of the problem. Another important thing for working with Ishikawa Diagram is to work with it interactively on a huge sheet of paper. Do not use a beamer and a piece of Ishikawa software. Although there are many Ishikawa software tools around, they add no value to your collection of possible root causes. Just take a picture of your hand drawn Ishikawa Diagram for archiving purposes. As for any brain storming techniques you should follow the standard brain storming rules also for drawing the Ishikawa Diagram (e.g. never judge the inputs during brain storming session).
Example: The Broken Crystal Issue
Imagine a small electronic control unit manufactured in a series of process steps. As last step the customer performs a thermal cycle stress test and observes a failure rate of 20%. The crystal that provides the CPU clock for the control unit does not work anymore. An X-raying of the crystal shows that it is broken. What could be the root cause?
First get clear about the process. Draw the process map.
In the next step, collect all the data available for each process step (production data, serial numbers of products, process parameters, … ). Now you can start with analyzing and searching for the root cause. Just start a brainstorming session with your interdisciplinary team by using the Ishikawa Diagram. Typically your team will collect between 30 and 50 possible root causes. For sorting out the unlikely root causes you my use a couple of tools like Cause & Effect Matrix, Is / Is Not table, Process FMEA and so on.
In the end, when you have eliminated the unlikely root causes, only 3 – 5 root causes should be left over. In this example it is only one root cause: Damage of PCB/Crystal during In Circuit Test (ICT). There was too much pressure from test needles induced into the PCB and therefore into the crystal.
Now you may start with another tool to dig deeper into the root cause: use the 5 Why’s Method.
- Why was the crystal broken?
The equipment for ICT was not adjusted properly.
- Why was the ICT not adjusted?
There was no maintenance plan for ICT with adjustment parameters.
- Why was there no maintenance plan?
There was no maintenance plan because a transfer of the production equipment to another production site happened short before series release.
- Why …
Besides having found the root cause, collecting all possible root causes and learning more about the product and the process is the most important thing of the problem solving process. The Ishikawa Diagram is a powerful, easy to learn and easy to apply tool to support problem solving and a learning organization.