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The Six Sigma methodology seeks to reduce and ultimately eliminate variation within a process. It applies a five-phase project management approach and uses the standard deviation (sigma) as the controlling attribute for the process.

Quick reference

Six Sigma Principles

The Six Sigma methodology seeks to reduce and ultimately eliminate variation within a process.  It applies a five-phase project management approach and uses the standard deviation (sigma) as the controlling attribute for the process.

When to use

The Lean Six Sigma methodology is both a principle-based methodology and a tools-based methodology.  The principles should guide the project team through the process and with the selection of tools.

Instructions

The Six Sigma methodology has several key principles that are embodied within it.  These principles were tested and proven at Motorola on the manufacturing product lines. 

Six Sigma is a problem-solving methodology that is based on data. It achieves breakthrough performance by reducing variation and often shifting the mean value of a process. The problem-solving uses the relationship Y= f (x) to focus on the vital few factors that impact the process output.

The measures of Defects per Million Opportunities (DPMO) and process sigma are used to measure the level of variation and out-of-specification conditions of the result from the business process.  Variation is the enemy of process control and the Six Sigma analysis first measures this variation and then strives to reduce or eliminate the sources of variation. 

Another key principle is that of an orderly and structured process that is based on the analysis of data.  The five-phase approach of Define, Measure, Analyse, Improve and Control guides the team through this approach. 

The first two phases, Define and Measure, are used to articulate the real problem. The first phase determines the problem from a business and customer perspective.  The second phase then collects data about the product or process in order to determine what is actually happening and the magnitude of the problem. The third phase is the statistical analysis of the problem. Data is used to statistically validate the real problem that is causing the variation and out-of-specification conditions. The final two phases are associated with the problem solution. The Improve phase designs the solution and validates that it is effective. The Control phase implements that solution and changes all associated processes, procedures, and systems that must change to ensure the improvement becomes the new standard operation.

Six Sigma strives to create processes where the normal variation is much less than the allowed variation based on the process specification limits. Understanding the sources and magnitude of variation are essential elements of the Six Sigma methodology.

Hints & tips

  • The DMAIC process guides the team through the analysis and ensures they don’t jump to the wrong conclusion.
  • Variation is the enemy of process control.  Stay focused on sources of variation and don’t get lost in the statistical analysis.
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  • 00:04 Hi, I'm Ray Sheen.
  • 00:05 Well, we've looked at the foundational elements of Six Sigma and
  • 00:09 Lean Manufacturing, it's now time to blend them together to get Lean Six Sigma.
  • 00:14 Six Sigma projects are structured to solve problems.
  • 00:19 At the strategic level,
  • 00:20 Six Sigma solves the problem of achieving breakthrough performance improvement.
  • 00:24 It finds and eliminates the root cause that creates problems and
  • 00:28 issues for internal and external customers.
  • 00:32 One way it does this is to change the mindset about quality.
  • 00:36 The conventional quality mindset is that anything within specs out is good.
  • 00:41 Outside the specs, it's bad.
  • 00:43 A product or process could be operating just barely within spec, and that's not
  • 00:48 considered to be a problem, even though a minor hiccup will turn things out of spec.
  • 00:53 From a problem-solving perspective, we don't want to
  • 00:56 rely on just barely being in spec in order to get desired performance.
  • 01:00 We want a stable, predictable process that we can tune for exactly what is needed.
  • 01:06 We want the formula so
  • 01:07 we can precisely choose the input variables to get the desired output.
  • 01:12 One of the values of Six Sigma is that it separates out the most significant root
  • 01:18 causes, the vital few inputs to axis, that will deliver the desired output or why.
  • 01:25 When Six Sigma delivers breakthrough performance,
  • 01:28 it often changes the average output value known as the process mean to make it
  • 01:33 much higher, lower, or closer to the target value.
  • 01:36 It also reduces the uncertainty or variability.
  • 01:40 This improves the predictability of the output and
  • 01:44 can again change the game since the customer using the y output now
  • 01:49 has rock solid confidence in the exact performance they will see.
  • 01:54 Let me highlight some of the key principles.
  • 01:57 In order to better understand the Six Sigma principles,
  • 02:00 let's start with a quick review of the background of Six Sigma.
  • 02:04 It was developed at Motorola for
  • 02:06 the purpose of improving the quality of manufacturing products.
  • 02:10 So it wasn't esoteric and philosophical, it was very practical and
  • 02:15 implemented in manufacturing shops.
  • 02:18 The methodology relies on the elimination of variation in the process,
  • 02:22 inputs and outputs.
  • 02:23 When variation occurs, the process must add steps to measure whether
  • 02:28 the variation is beyond the allowable performance limits.
  • 02:31 This adds inspection costs, and when that variation is too large, the business must
  • 02:37 scrap or rework the product which adds additional costs and delays in production.
  • 02:43 Variation is the enemy of smooth, low-cost manufacturing processes.
  • 02:49 Six Sigma uses several measurements to monitor variation.
  • 02:54 One that has become very well known is defects per million opportunities,
  • 02:59 sending the message that any defect is a problem.
  • 03:02 This measure and the process standard deviation can be translated into
  • 03:07 a process sigma, which is a way of measuring the level of
  • 03:10 uncertainty in any process input or output.
  • 03:13 The Six Sigma methodology has a structured process for how the analysis is conducted.
  • 03:19 The five phases define, measure, analyze, improve, and control,
  • 03:24 guide the team through the problem-solving and problem-solution process.
  • 03:29 In fact, these five steps are so
  • 03:31 important to the methodology that I want to spend a little time on them.
  • 03:35 The DMAIC process, which again stands for define, measure, analyze,
  • 03:40 improve and control, provides a logical process for Six Sigma teams to follow.
  • 03:46 The first two phases create the problem definition.
  • 03:49 The define phase identifies the problem from the business standpoint and
  • 03:54 sets the boundaries for the project.
  • 03:56 The measure phase digs into the process and
  • 03:59 the data to find the real problem and specify the magnitude of that problem.
  • 04:04 Six Sigma has a reputation for going overboard on statistical analysis.
  • 04:09 If that happens, it's during the analyze phase.
  • 04:12 A key principle of this phase is that the analysis of the problem must be based on
  • 04:17 statistically demonstrated facts.
  • 04:19 It isn't enough that you think you know the reason for the problem, you must be
  • 04:23 able to demonstrate with statistical data that you have the root cause or causes.
  • 04:28 There is a structured approach for how you work through this phase.
  • 04:31 The final two phases, improve and control, are now focused on the problem solution.
  • 04:37 The first of these phases, improve, is the design and validation of the solution,
  • 04:42 and the final phase, control, is the implementation of that solution.
  • 04:47 Things don't get better just because someone did a study or issued a memo.
  • 04:52 The process and procedures must be changed, people trained, and
  • 04:56 an ongoing control plan put in place to make sure the improvements sticks.
  • 05:00 Let me finish this session with a discussion about sigma.
  • 05:05 Sigma takes its name from the Greek letter that is used to represent the standard
  • 05:10 deviation, a statistical measure of the spread within a set of data.
  • 05:15 The term process sigma refers to the ability of the process to consistently
  • 05:20 provide results that are within the allowable limits of the process.
  • 05:25 As I already mentioned, every process parameter has some inherent variability.
  • 05:30 When that variability is due to a random cause, the bell-shaped curve is
  • 05:35 a good representation of the level of variability.
  • 05:39 That means that it is mostly in the center of the curve, but
  • 05:42 occasionally things are higher or lower than normal.
  • 05:46 In this picture you see two lines,
  • 05:47 consider them to be the allowable process performance specification limits.
  • 05:52 The first bell-shaped curve represents a two sigma process, and
  • 05:56 you can see that the curve stretches beyond those specification lines.
  • 06:00 That means that there will be some instances of the process output
  • 06:05 being outside of specification.
  • 06:08 As you progress up the series of bell-shaped curves,
  • 06:11 we finally get to Six Sigma.
  • 06:12 In this case, the curve easily fits in between the customer specification limits.
  • 06:18 When a process is operating at the Six Sigma level,
  • 06:22 the process should virtually never create an output that is out of specification.
  • 06:28 The Process Sigma, then, is a way for process managers and business managers
  • 06:32 to manage the quality of business processes and predict performance.
  • 06:37 Again, the key is to eliminate variability and to get the width of that bell-shaped
  • 06:42 curve of data to be much smaller than the allowable specification limits.
  • 06:46 So now we've set the stage for taking the best of both Lean and Six Sigma and
  • 06:51 combining them to make a truly outstanding process improvement methodology.

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