Assignable causes with examples and a case study

Types of causes

1. Assignable causes with examples and a case study Tejas V

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

5. Correction of variation Root cause analysis Fish bone diagram ANNOVA table

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. In dian Statical institute 8th Mile Mysore Road, Bangalore

7. Causes of variation Poor Batch of Material Inexperienced Operator Tool damage  Maintenance Check overlooked Solution  Introduce x̅ and R chart to the process  Reaction plan was given to the operators 

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