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Our first objective when implementing SPC is to get the process under control. In order to properly do this, we work collaboratively with our clients to identify and eliminate the special causes of variation.

 

Once that is done, we can test if the process is in-control if it is consistently producing parts within tolerance limits. After a process is in control (stable) and producing consistently within its natural balance, it can be then compared to the engineering tolerance limits which is the second step.

 

Our second step here is to test the capability of the process if it is capable of producing parts (or delivering the service) consistently within the drawing tolerance limits for manufacturing industries (or within specified limits for service industries). Capability cannot be studied until the process is in control

 

One important thing to mention here regarding variation: when it comes to defining variation, it is important to understand the difference between the two kinds of variation:

Random (Common) Variation:

This is the variation that has several common causes. Common causes of variation are things like vibration, heat, and humidity that either individually or collectively cause variation

Non-random (Special) Variation:

This is the variation that is not built into the process. Causes of variation like this are called special causes. Special causes of variation are those that can be directly identified and corrected, things like training, machine or tool maintenance, the use of special software programs by customer service teams, etc.