2. Variation in process
• Variation is deviation from the
precise pattern
• No two products are same
• Differences are called variation
3. Common causes
• Stable and repeatable
• Present in the process
• 85% of them are common
causes
• Process under statistical control
• EX-Normal wear and tear,
measurement error
4. Special/Assignable cause • Under influence of special
factors
• Not present in the process
• Output cannot be predicted
• Needs local action for
correction
• 15% of causes are special
causes
• Process is out of statical
control
• Ex-Poor Batch of Material,
Inexperienced Operator,
Maintenance Check
overlooked
6. Case study
Background of the study
• An Indian engineering industry faced problems for the following
reasons
• Dimensional variations, rejections and rework were very high.
• Repeatability of the readings were not found for many of the
critical dimensions.
• Complaints from the assembly shop were increasing day by day.
About the process
• CNC machine used to Grind aluminum alloy clamping pressure O to
100 kg /sq. cm.
Indian Statical institute 8th Mile Mysore Road, Bangalore
7. • Causes of variation
1. Poor Batch of Material
2. Inexperienced Operator
3. Tool damage
4. Maintenance Check
overlooked
• Solution
1. Introduce x̅ and R chart to
the process
2. Reaction plan was given to
the operators
If we could measure the product with 100% precision there will be errors from one to another
There will be some differences from one another and that difference is called variations
Poor maintenance of machines
Normal wear and tear
Insufficient training•
Not one way of working•
Poor working conditions
Measurement error
. Ambient temperature / humidity
Not stable and not repeatable cannot be predicted
Not always present in the process
Out put of the product can be good and damaged at any time in the process
People near to the process need to observer closely to identify the problem
Almost 15
Cannot be predicted
Examples
Poor Batch of Material
Inexperienced Operator
Out of Date Drawings
Tool Damage
Maintenance Check overlooked(Doesnt replace items that doesn’t look essential )
Misread Drawing /
Planning Instruction
Machine Breakdown
The first goal of root cause analysis is to discover the root cause of a problem or event.
The second goal is to fully understand how to fix, compensate, or learn from any underlying issues within the root cause.
The third goal is to apply what we learn from this analysis to systematically prevent future issues or to repeat successes.
Fish bone (Also known as cause and effect diagram )
statistical analysis to test the degree of differences between two or more groups of an experiment.
Analysis of Variance (ANOVA) is a statistical analysis to test the degree of differences between two or more groups of an experiment.
Computer Numerical Control Can turn upto 18k RPM
Maintenance Check overlooked(Doesn't replace items that doesn’t look essential )
Categories material man machine method measurement system method
mean and range of a normally distributed variables simultaneously, when samples are collected at regular intervals from a business or industrial process.
