Quality Assurance - Lecture - Root Cause, Lecture notes of Material Engineering

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Root Cause Analysis

Learning Objectives

To learn some of the tools and techniques used to determine the root cause of the problem being analyzed.

Root Cause Analysis definition

• (^) Root cause is the factor that caused a defect or nonconformance
• (^) Root cause analysis (RCA) is a sequential and investigative process used to determine the root cause of the problem

General rules to perform root cause analys

• (^) Team effort
• (^) The team must fully understand the problem prior to start the analysis
• (^) Look beyond the obvious and immediate solutions
• (^) Do not confuse “symptoms” and “causes”
  • (^) Symptom is a manifestation of a cause
  • (^) Cause is the factor which when removed, the problem is cured
• (^) Use factual data

Constraints (continuation)

• (^) Lack of documentation, data or information on how the problem occurred
• (^) Lack of recompilation of the events that occurred before the problem.
• (^) Failure to document data as evidence of the problem
• (^) Lack of team approach
• (^) Lack of training in performing root cause analysis

Root Causes Sources

• (^) Some possible sources causing a problem are:
  • (^) Inadequate knowledge of how the process works
  • (^) Inadequate knowledge of how the process should work
  • (^) Errors and mistakes in executing established procedures
  • (^) Inadequate procedures
  • (^) Inadequate steps and wasteful measures
  • (^) Variation in inputs to the process

Immediate Corrective Actions (continuation

• (^) Benefits
  • (^) It is quick
  • (^) Does not take too much effort to develop
  • (^) Inexpensive
  • (^) Keeps management happy
  • (^) It saves the process from being shut down

Immediate Corrective Actions (continuation

• (^) Disadvantages:
  • (^) Not process oriented
  • (^) Because of time constraints, it lacks thorough analysis
  • (^) Usually, it is one person opinion
  • (^) Misinterpreted cost effectiveness
  • (^) Often, lacks data and documentation

• (^) The most common methods used in root cause analysis are: - (^) 5-why’s, or Why-why analysis. - (^) Cause and effect diagram (covered in Module 3) - (^) Fault tree
• (^) RCA process is extremely efficient when performed as a team effort.

Root cause analysis techniques

Why-why analysis

• (^) Technique for determining the root cause or contributing causes of a problem.
• (^) It shows the relationship of causes by repeatedly asking the question “why?”
• (^) It usually, takes 5 levels of “why?” to determine the root cause

• (^) Assemble multifunctional team
• (^) Use a large area board or a flip-chart
• (^) Write the problem statement at the bottom
• (^) The “level 1 why” is determined by answering the question why? To the problem statement.
• (^) Write all the answers from the team on a line above the problem statement

Process for constructing a Why-why chart

• (^) The “level 2 why” is determined by answering the question why? to each of the answers on level 1.
• (^) Continue building the “level 3”, “level 4”, and “level 5” question-answer relationships.
• (^) Connect all answers as applicable
• (^) It is the team decision to stop at level 5, or to continue, or even stop before level 5

Process for constructing a Why-why chart

(continuation)

Request supplier Corrective action plan Defective fastener installation Improper inspection method Poor quality hardware Engineering; Drawing Customer Specification not followed Feeler gauges not used Did not insert feeler gauge all around perimeter of head/collar Procedure not followed or followed incorrectly Usage of appropriate tools Drill Blocks / eggcups Hand drilling Relief chamfer dimension is not measured Lack/insufficient Relief chamfer Some areas have Limited access De-burring/chamfer not performed Lack of Experience/ Not familiar with requirements Different acceptance Criteria for different Type of fasteners Collars break - off too easy not allowing to seat properly Supplier deficiency Requirement to use Relief washers not clear at shop level Review training module. QE to create summary Matrix acceptance criteria for type of fasteners Clarify specification in the use of relief washers vs chamfer relief to shop personnel Establish team to determine Best chamfer - relief Inspection practice No measuring gauge Available for relief Chamfer inspection Identify areas of Limited access Why? Level 1 Why? Level 4 Why? Level 3 Why? Level 2 Why? Level 5 Corrective Action Problem:

Why-why example

Inadequate supplier surveillance Not in the “preferred supplier” list Shop personnel do not understand requirements

Fault Tree analysis

• (^) It is a deductive procedure using the major functions that have inputs to a process
• (^) It is very useful when using multifunctional team members
• (^) The Tree-fault analysis identifies contributing causes within a functional hierarchy common to the process.