The purpose, benefit and outcomes of deploying Six Sigma are reduced waste and defects, reduced variation, improved processes and increased customer satisfaction. This article will focus on the three strategies associated with reducing variation in your process.
Overview: What is Six Sigma strategy?
The Six Sigma approach for dealing with process variation consists of three strategies: shift, shrink and stabilize. Let’s look at each.
Shift – In many cases, you will have specifications (specs) for some characteristic of your process. You often want your process to be centered within your specifications, assuming you have an upper spec limit and lower spec limit. If it is not, your initial strategy might be to adjust the process and shift the mean up or down so it is centered within your specs. This can be accomplished with such simple things as resetting a dial.
Shrink – Sometimes, your process may be centered within your specs but your variation is wide and therefore, you will have some portion of your process outside of the upper and/or lower spec limits. In this case, you will have to embark upon the strategy of reducing or shrinking your variation. This strategy is usually more complicated than just adjusting or shifting your process.
Stabilize – Once you have your process centered where you want and your variation is at an acceptable level, you will want to keep it there. This will require ongoing documentation, standardization and monitoring of your processes. You will want the process to remain stable and be only exhibiting common cause variation. The control chart will be your tool of choice for ongoing monitoring of your process.
An industry example of Six Sigma strategy
A manufacturer of corrugated containers started receiving complaints from their customers that one of their major products was coming in short. As a result, boxes were being rejected because they were outside of the lower spec limits.
Upon investigation, they found that one of the machine settings had been improperly set. By resetting the dial at the correct dimension, the overall process shifted so the average was now centered within the specs. Fortunately, the variation of the overall process was small so the shift did not cause any product to now be out of spec on the high side.
Frequently Asked Questions (FAQ) about Six Sigma strategy
1. Who developed Six Sigma?
The Six Sigma methodology was developed in 1986 by Bill Smith, an engineer at Motorola. Subsequently, the methodology and concepts were adopted by such companies as Honeywell, Allied Signal, and GE.
2. If a process is exhibiting only common cause variation, can I consider it to be stable?
Yes. A process with only common cause variation means it is stable and will continue at that level unless there is a change in the process. By monitoring your process with the appropriate control chart, you will be able to see if the process is stable.
3. If my process is not centered within my upper and lower specification limits, what should I do?
It will depend on the variation of your process. If your process variation is small enough, a simple shifting of the process mean may be enough to bring everything into the spec limits. This could be as easy as resetting a dial.
It may not be necessary to always be centered within your specs. If your variation is small enough, it might be advantageous to move left or right of center as long as you stay within the specs.