Monday, August 17, 2015

Chance & assignable causes of variation

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Variation in quality of manufactured product in the respective process in industry is inherent & evitable. These variations are broadly classified as-
i) Chance/ Non assignable causes
ii) Assignable causes
i) Chance Causes:
In any manufacturing process, it is not possible to produce goods of exactly the same quality. Variation is inevitable. Certain small variation is natural to the process, being due to chance causes and cannot be prevented. This variation is therefore called allowable.
ii) Assignable Causes:
This type of variation attributed to any production process is due to non-random or so called assignable causes and is termed as preventable variation.
Assignable causes may creep in at any stage of the process, right from the arrival of the raw materials to the final delivery of goods.
Some of the important factors of assignable causes of variation are-
i) Substandard or defective raw materials
ii) New techniques or operation
iii) Negligence of the operators
iv) Wrong or improper handling of machines
v) Faulty equipment
vi) Unskilled or inexperienced technical staff and so on.
These causes can be identified and eliminated and are to discovered in a production process before the production becomes defective.
SQC is a productivity enhancing & regulating technique (PERT) with three factors-
i) Management
ii) Methods
iii) Mathematics
Here, control is two-fold- controlling the process (process control) & controlling the finished products (products control). 

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