Root cause analysis (RCA) is a method of problem solving that seeks to identify the root causes of faults and a method for addressing them. A root cause is a cause that once removed, prevents the unsatisfactory component from being reproduced. Root cause analysis addresses questions such as “Why is the product nonconforming in the first place and how do we avoid having more of it in the future?”
Manufactured parts and assemblies can fail due to a defect in a single component or the integration of multiple components in an assembly or finished product. During root cause analysis all aspects must be considered including raw materials, processing conditions, environmental conditions, etc.
There are many root cause analysis techniques but some of the more common techniques in manufacturing operations may involve the five whys or fishbone diagrams or some combination of the two.
The “five whys” is a technique that explores the cause and effect relationship for a specific quality issue. This technique involves asking why until the chain of events leading to the defect is understood. Because not all problems have a single root cause, this process may even reveal additional root causes that need examination.
Fishbone diagrams, also known as Ishikawa diagrams, are diagrams that show the causes of a specific quality defect. These causes are grouped into major categories such as personnel, machines, materials, methods, measurements and environment as seen below, and can reveal key relationships between these factors and quality issues.
No matter which root cause analysis method is chosen, the goal is to find the problem and implement a permanent corrective action. Root cause analysis and continual improvement are very important in a successful manufacturing quality management system.