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About this lesson
Lean Six Sigma projects strive to characterize project performance through the creation of a process formula. This formula allows the team to predict and optimize process performance.
When to use
The Y = F(x) formula is developed during the first three phases of a DMAIC project and optimized during the final two.
To improve a process it is very helpful to understand how it works and what it does. The Y=F(x) formula is the Lean Six Sigma shorthand for this approach.
“Y” is the process output. It could be quantity, quality, feature performance or any other attribute that is important to the customers and stakeholders. They identify what the “Y” should be and will often set targets for the “Y” performance. The “Y” is normally established as part of the Define phase activities.
The “x” in the equation represents the process inputs and controls. These are typically identified as the process map or value stream map is created and are both discovered and measured during the Measure phase of the project.
The “F” in the equation represents the functional combination of all the “x” inputs so as to achieve the “Y” output. This is determined both from the process map/value stream map and from analyzing data collected during the Measure phase and analyzed in the Analyze phase. The first three phases of the DMAIC build the formula and then analyze it to determine if the current process is able to achieve the desired “Y” output.
Based upon the analysis of the formula, the process is either redesigned with a different “F” and possibly different “x” factors, or the process is tuned and tweaked to get the desired performance from the existing process. This is occurring during the Improve phase.
Finally, when the new or improved process is put in place during the Control phase, a control plan is established that will allow the process operators to achieve and maintain the desired “Y” performance level. The operators can accurately predict the process performance given any set of “x” factors as inputs and controls.
Hints & tips
- You are seldom able to develop an absolutely perfect formula. However, if it is close it will still work well for process control.
- Once the formula is discovered, target values and tolerances can be set for all process parameters and inputs through simulation testing rather then expensive testing with actual products or systems.
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