Process can be defined as a set of interrelated activity that converts a set of inputs to a desired output.
Inputs are from various sources Man. Machine, Material and Method.
Output is the desired result of any process.
The quality of the product is based on two parameters, input quality and variability in the process.
We will discuss the impact of variability in connection to defects.
Given below process with less variability.
The chances of producing a defective sample (Out of specification) is less as variability in the process compared to specification is less.
Given below process with more variability.
The chances of producing a defective sample (Out of specification) is very high as variability in the process compared to specification is high.
In simple terms ” More variability in the process have more chances of producing defects and less variability in the process have less chances of producing defects”.
Let us discuss the types of variation.
Any process will have variation. The variation is of basically two sources Common cause variation and Special cause variation.
Common cause variation: The variation that is inherent of the process is identified as common cause variation. Common cause variation can be reduced but cannot be eliminated.
Example: Voltage measured in the welding process will have variation. This variation cannot be eliminated but however can be reduced.
Special cause variation: The variation that occurs due to specific reasons is called as special cause variation.Since the reason for the variation is known the variation can be eliminated.
Example: Diameter oversize in a machining process due to a broken fixture clamping bolt is a special cause variation. since broken clamping bolt is the reason the same can be eliminated by replacing it.
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