Written by: Jim Gilbert, CMTC Senior Consultant
This is the first in a series of postings about Six Sigma (6 Ϭ). I have found that there is some misunderstanding generally regarding 6 Ϭ and so I will share my understandings and my reasons for them.
6 Ϭ is usually understood to refer to three distinct elements:
- 6 Ϭ is a Philosophy (Continuous Improvement)
- 6 Ϭ is a Toolkit of Statistical Tools that are applicable to variation in manufacturing and, it turns out, any process.
- 6 Ϭ is a Measure of Quality
Generally speaking there are two approaches to process improvement:
- Radical Change: A paradigm change where the process is completely redesigned. Often new technologies are introduced that significantly change the labor percentage per unit produced and the equipment percentage per unit produced.
- Small incremental changes where the process is gradually improved.
Improvement, by definition, means that one or more of the following are improved:
- Cycle Time
- Workability of the Cell (Workplace)
6 Ϭ supports the gradual incremental approach. We will discuss later how the six sigma tools help us better understand the variation in processes and how they are used to develop strategies to reduce this variation.
Many readers will be familiar with the term Lean Manufacturing or the Toyota Production System. Lean is “another” approach to improve processes. I put the word another in quotations because I do not view Lean and 6 Ϭ as different. My reason is the following:
In Lean there are seven traditional categories of waste:
- Excess Inventory
- Over Processing
- Excess Motion
Let’s focus on the waste of Defects. Defects can be either Scrap or Rework. If you think about it all a defect is is an item that contains excess variation. On manufactured parts there are specifications with upper and lower limits that define a good part. If a part is manufactured that does not fall within the specification range it is deemed to be a bad part. It is either oversized or undersized. Again, the part has too much variation to measure within the specification range.
6 Ϭ is a statistical toolkit that enables us to understand this variation and help us identify its root cause(s).
Also, the only way to effectively solve a problem is to permanently eliminate its root cause(s).
Therefore, I understand 6 Ϭ to be part of Lean Manufacturing since it is directly involved in reducing the Lean Manufacturing waste of defects. Some will disagree and some take the position that 6 Ϭ is the overarching discipline and Lean is subordinate to it. In the big picture I am not sure that it really matters.
If you know how to apply Lean Manufacturing, 6 Ϭ and Theory of Constraints appropriately and well, you should get the desired outcome.
Our next post will be dedicated to some of the underlying principles for the statistical tools and why we can reasonably use them to predict results or outcomes. We will also identify specific tools and how they can be used. One of the more well known statistical tools is Statistical Process Control, also known as (SPC).
Measure of Quality
The term 6 Ϭ is also a measurement. A random sample that has a measurement of its overall variation of 6 Ϭ is considered to be performing at a level of “Perfect Production.” This is because Sigma (Ϭ) is a measure of variation and 6 Ϭ is equivalent to 3.4 defects out of one million opportunities.
The next blog post will summarize some 6 Ϭ projects and their benefits to aid the reader in deciding whether 6 Ϭ is worth learning more about.