The best way to manage variations is to understand them first. This means understanding what causes them, why they happen, and how to predict and control them. Once you understand the process well enough, you can take steps to prevent them from happening.
There are two broad types of process variation:
1. Common Cause Variation
2. Special Cause Variation
Let's understand each of these.
1.Common Cause Variation:
It is the inherent variation in the system. It is caused by the nature of the material being processed, the equipment used, the environment, etc. The common cause variation cannot be controlled easily. But we can reduce its impact on our production by using good quality raw materials and equipment, maintaining them properly, and controlling the environmental conditions.
2. Special Cause Variation:
This type of variation occurs because of something that is not part of the normal operation of the process. These special causes include human error, operator mistakes, machine failures, calibration issues, etc. They are also called assignable causes.
Managing process Variation
The first step in managing variation is to understand its cause: Is it a common cause or a special cause variation?
If it is a common cause variation, you can do nothing about it. You just have to accept it as an unavoidable part of your business. On the other hand, if it is a special cause variation, you can try to eliminate it.
But How Would I Know if it is Common or a Special Cause?
To determine this, you should study the history of the variation. If the variation was present before, it is likely that it is a common cause variation. If the variation started recently, it might be due to some change in the process or the people involved.
I am sure the above statement does not help. In reality, you use Control Charts to keep the history of the process. Control Charts can help you identify special causes. Special causes could lead to taking some action to eliminate them.
Eliminating Special Causes:
Here are some examples of special causes in the manufacturing industry:
- Change in machine setting
- Tool wear
- Operator mistake
- Machine failure
- Calibration issue
- Improper maintenance
Once you identify the special cause, you can take corrective actions to eliminate it. For example, if the tool wear is causing variation, you can replace the worn parts with new ones.
In addition to eliminating the causes, you can also plan for future changes. For example, if you find out that the tool wear is increasing over time, you can make plans to purchase more tools or get the old ones replaced with new ones.
In summary, the main objective of managing process variation is to eliminate the special causes and plan for future changes.