March 26

Process Improvement Explained: What is Lean Six Sigma?


A lot of people new to the subject often ask what lean six sigma is. Here’s a guide to answer just that! For those that want it, the quick answer is as follows…

What is lean six sigma? Lean six sigma is the amalgamation of 2 process improvement tools, namely lean manufacturing and six sigma. The objective is to use the power of both under one seamless delivery. Together, the lean six sigma practitioner can ensure that processes are highly efficient and agile (using lean), and of highly repeatable and consistent quality (using six sigma).

If you want to know what lean six sigma is in greater depth, here’s the rest of the article. You’ll know the ins and outs of both in next to no time…

Table of Contents

The Official Definition of Lean Six Sigma

Lean in Detail

Key Lean Tools

Six Sigma Explained

Key Six Sigma Tools

The Tree and the Garden

Lean Six Sigma – Selecting What to Use

Related Questions

Definition from ASQ

The American Society of Quality state that lean six sigma is…

… a fact-based, data-driven philosophy of improvement that values defect prevention over defect detection. It drives customer satisfaction and bottom-line results by reducing variation, waste, and cycle time, while promoting the use of work standardization and flow, thereby creating a competitive advantage. It applies anywhere variation and waste exist, and every employee should be involved.

Let’s break this definition down a little, starting with lean.

Lean in a Little More Detail

Lean really is about one main thing. And that is, reducing lead time.

It focuses on making process improvement by eliminating waste. This in turn, improves efficiency. By improving efficiency, you get things done faster.

If you get things done faster, you can ultimately reduce the time it takes for a customer to receive their products or service. Products, information and the service you provide will be a lot smoother and will be delivered quicker.

And because you make things more efficiently, it will cost less to process for you.

It’s truly a win-win.

The 5 Principles

At the heart of lean are 5 core principles. These 5 factors or steps, are used when analysing a business and how it provides its services or products.

They are:

  1. Understand Value in the eyes of the customer
  2. Map the Value Stream so you can see waste
  3. Make it Flow by removing wasteful activities
  4. Create Pull to link processes and prevent over production
  5. Continuously Improve and challenge the current way of doing things

Here’s What the 5 Principles of Lean Mean

Lean ensures that we put the customer first. By understanding what they want, how they want it, and what customer service they expect, we can then re-design our processes to effectively deliver this, consistently and efficiently.

We do this by mapping our processes first, and identifying the wasteful activities or the things that are slowing us down and draining time, effort and other resource.

When we spot this waste, we make our processes flow better by removing as much of it as possible.

Next, we link processes together so they work to the same pace and to stop them pushing too much work through to the next stage, too soon. This prevents overproduction and ensures our processes are optimised and working together.

Lastly, by constantly challenging how we work today, and striving to improve our efficiency and effectiveness, we continuously improve. This is the fifth principle of lean.

It enables us to:

  • Innovate and define tomorrow’s delights – things the customer will be wowed by when we offer them this new service / product / experience.
  • Ways to speed up lead time to customer delivery – Every time you offer faster and more agile services, you’re normally offering even more value to your customers.
  • Improved reliability – which allows us to offer even better guarantees and after service
  • Improved profitability – consistently getting more out with what you already have means stronger profit margins and financial performance

It’s why Kia were the first to offer a 7 year warranty.

And Oxo backs everything they sell with a full refund…

Nordstrom offer free shipping and returns

And all the global manufacturers in the world adopt lean just to compete with each other.

Examples of Lean in Action

It’s also why a construction project management company I worked with, successfully reduced their lead time from 68 days to 30 days, to ensure that they could get their projects completed fast and accurately for their clients.

How a Door Manufacturer turned their lead time from a few months to 2 weeks.

How a fulfilment business went from offering 2 day deliveries to next day.

And how a furniture manufacturer went from 3 weeks to 5 day delivery and 10 times more customisation options for online orders.

Lean: Speed and Consistency

Think of lean as providing speed. Speed of output. And doing it consistently.

Using it doesn’t involve cracking the whip and getting people to work harder and under even more duress.

It’s the opposite.

Strip the waste out of processes and you’ll shorten the time it takes.

NVA Before an improvement
A process is full of Value Added Steps (what the customer is willing to pay for) and Non Value Added (wasteful) steps

And by doing this, you’ll be able to create a higher value added ratio.

How Does Lean Production Give a Competitive Advantage? Lead time reduced after improvements
By stripping waste from processes, you shorten the time it takes to complete the activities. Your value added ratio improves and lead time reduces.

Key Lean Tools

There are several common lean tools, which you’d expect deployed in any lean facility:

Value stream Mapping – Value Stream Mapping (VSM) is a visual tool that maps the product, material and information flows from the customers’ order to the receipt of finished goods. It allows you to see the waste and how you can improve your processes for better performance.

5S5S is the basis for Lean and the foundation for a disciplined approach to the workplace. It involves (1) Sort, (2) Set, (3) Shine, (4) Standardize and (5) Sustain. The net result: A visual workplace where everything is to hand and fit and proper for use.

TPM – TPM involves restoring your equipment’s condition to as good or better than new status. It also allows you to develop and implement procedures and check-lists that ensure the equipment stays at that level of performance… so no time is lost to downtime.

Error Proofing – Error Proofing is a systematic approach to preventing potential defects from being passed on. Using error proofing allows us to identify opportunities for errors and eliminate or control them at source.

Standard Work – Standard Work involves defining the optimum combination of operators, machines and materials to ensure that a task is completed the same way every time, with minimum waste and at the rate of customer demand. This ensures that work is completed in the current most efficient way.

Pull – Pull is a system of signals to previous process steps telling them to process what’s been consumed. By linking processes to pull principles, you’re controlling your entire value stream in terms of what to produce and when. That means little planning, and over production – just a signal to make when the next step tells you to.

Set up Reduction – Set up Reduction is a systematic approach used to reduce the non-productive time during set up. By deploying quick set ups, you can turn your machines around faster. This means you’ll need less stock and smaller batches. Both are ways to make your processes agile and faster.

Continuous Flow – Continuous Flow is defined as movement of material or information from one value-added process to another without stopping. This means no transport time or storage in buffers. Everything is processed in a spirit of “make one – move one”. In a continuous flow environment, rate of production of the entire product stream exactly matches the customer demand (Takt). This means that these processes are fast and efficient.

There are of course, others but the above are the main tools. All are geared to reduce the waste in processes, which in turn allows for them to be faster and more effective.

Six Sigma Explained

Six Sigma improves the quality within processes. It aims to reduce errors to a minuscule amount. Statistically, this amount is 3.4 defects per million opportunities.

So, if we’re making 1 million widgets, and we had a six sigma process, we’d expect roughly 3 errors.

If we made 1 million cars, the same would apply.

Or processing 1 million claims… you guessed it, we’d expect around 3 errors.

That’s the ultimate goal of Six Sigma – to improve processes so they are accurate and precise enough to provide 3.4 defects per million.

Six Sigma and Statistics

There are 2 key components of Six Sigma:

  1. The improvement roadmap, which you work through in your process improvement project
  2. The statistics used to identify and eliminate the factors that are preventing near perfect output

The Six Sigma Roadmap

Six Sigma has a robust improvement roadmap that practitioners follow. It’s called DMAIC and stands for:

  • Define – Define the problem and understand the situation, using data.
  • Measure – Measure the problem to identify the accuracy and precision of the process
  • Analyse – Analyse the process to see what factors are statistically causing the defects
  • Improve – Eliminate these factors and re-design the processes to support the improved way of working
  • Control – Create process standards and measures to ensure the new process is followed and sustained
The output is the sum of all its inputs….

It’s All About “Y=fX”

Six Sigma is all about the formula Y=fX (or Y = the function of X).

Here’s what I mean:

  • A process has an output. Let’s call this ‘Y’
  • There are variables that go into the process. Each variable is an ‘X’
  • Therefore, the quality of the output of this process is dependant on the variables that go into it – Y=fX

Here’s a diagram to help:

Six Sigma: Inputs-and-Outputs
A process output (y) is only as good as the variables (x’s) that go into it

The quality of the inputs to a process have an impact. Is the material to the right specification? Is the information correct?

So too, the controls. Is the standard work sufficient? How good is the equipment? What about the samples and jigs?

The resources also affect the quality of the process. Are people trained to a competent level? Are they working the right way? Is there enough resource?

All these variables (or X’s) have an affect on the output of the process in their own right.

It’s Six Sigma’s job to find the big hitters and prove that they affect the quality of the process… and then eliminate them.

The Funnel

Whilst lean has a lot more practicality – focusing on observation whilst making quick improvements… Six Sigma is enveloped in statistics. It does this to statistically and categorically prove which variables affect the outcome you’re trying to improve.

Think of DMAIC as a way of helping you get down this funnel to identify the vital few X’s.

When we engage in a Six Sigma project, we use the DMAIC process to ensure that we constantly learn more about our process.

As we go through the DMAIC steps, we inherently uncover more.

At the start of our project, we will have many X’s. These are all the ideas we have that may be causing the problems that we’re trying to overcome.

As we progress through DMAIC, we continue to weed out those factors that do not have an impact, until we are left with the variables that are causing the problem…or the vital few.

These variables (or X’s) can be verified using statistics and analysis.

The relationship between the X’s and the DMAIC process can be seen in this funnel above.

Key Six Sigma Tools

Some of the main Six Sigma Tools can be shown across the DMAIC roadmap.


Process Mapping – Allows us to see the lower level steps in the process, so we can start to identify all the potential X variables. We may well have over 70 X’s identified after this exercise.

Cause and Effect Matrix – This then allows us to score each X, so we can disregard those that the team feel are not significantly affecting the output of the process. After this exercise, we could have around 20 or so X’s left.

Failure Mode Affects Analysis – This allows us to drill down even more, cutting some more X’s away, further.

Statistical Process Control – Allows us to see how stable our process is, and what we need to do to improve it.

Components of Variation Study – Allows us to really drill down to a few variables (X’s), and run experiments (Design of Experiments), to see how these factors statistically relate to each other. All the time, we’re looking to eject some variables, so we’re left with the vital few that are proven to impact our process.

Capability Study – Allows us to determine how capable our process is and should be when those factors that are causing the problems, are removed. (Remember our 3.4 defects per million goal? Well, we can analyse the process to see how it should perform once the vital few have been eliminated)

Control Plans – Allow us to make changes to the process, based on our findings… and keep it that way, so the process is stable, standardised and controlled.

Once a project has been completed, you’ll see a complete transformation.

There is a bit of heavy lifting when it comes to Six Sigma, but it’s worth it in the end.

The Tree and the Garden

The truth is that when your job is to improve processes, you may as well have both lean and six sigma in your toolbox, so to speak. Combined, they form the common phrase “lean six sigma.”

You’ll get consistently high quality and efficient processes, all in one project.

Imagine a tree at the end of a garden.

This tree is creating a poor yield of fruit. The fruit produced is often too small and of poor quality in so much as it’s just not edible.

Create easy access and flow to the tree…

Also in the garden are weeds that’s covering the path, overgrown grass and shrubs, a broken fence… and a generally poorly kept garden.

In our analogy, you’d use lean to improve the ‘flow’ or easy access to the tree, fixing the broken fence, improving the housekeeping, and reducing the hard labour that would go into maintaining the garden.

Perfect fruit, (nearly) every time!

You’d then use Six Sigma to improve the yield of the tree, so that you can get consistently high quality and repeatable fruit.

You now have a clean and controlled garden, which produces wonderful fruit with only (statistically) 3.4 inedible fruit per million picked…

Lean Six Sigma Combined

With lean, you get speed. It’s brought to you through waste elimination, and standardisation. Using pull and flow further improves agility and efficiency.

With Six Sigma, you’ll focus on identifying the vital few X’s that cause the defects. Once eliminated, you get process stability and accuracy, so you can produce top quality output practically every time.

When you combine the two tools, you get process stability and accuracy AND speed and throughput.

Lean Six Sigma: Selecting What to Use

The tools you use can often be intertwined at times.

If you were using either lean or six sigma as a standalone project, you would see similarities. For instance, a VSM may well be used at the start of either a lean project or a Six Sigma one.

You can use process maps in both projects.

Failure Mode Effects Analysis is also used across projects…

And so too is standard work, work instructions and even cause and effect diagrams.

The point is to use the tool you need to get the job done and improve what needs to be fixed.

Sometimes you may only need to dip into statistical process control, whilst using the core lean tools to fix a process.

Other times, you may need to look at the whole process using DMAIC in a detailed way.

The point is this:

If You Know What to Fix… Then Fix It!

If you really don’t know how to fix the problem and it seems a pretty technical issue… then it may well be a Six Sigma project, whereby you’ll need some of the more detailed tools to help expose those vital few X’s.

As a practitioner, Lean Six Sigma gives you the ability to know what tool to use to improve a process, without adding unneeded complexity.

What Typical Sequence Would You Follow Using Lean Six Sigma?

Here’s a rule of thumb to follow with most processes. These steps combine lean six sigma as a methodology:

  1. Always focus on the customer and how you can add more value
  2. Map the value stream and see how the work gets completed.
  3. Eliminate waste to make the vale streams flow
  4. Use data to reduce variation and root causes to problems
  5. Use the people in the processes to drive improvements. Change can’t be done for them.
  6. Use DMAIC as a powerful memory jogger to help improve processes and overcome problems.

Is there a Lean Six Sigma qualification? The answer is yes! Lean Six Sigma follows the standard Six Sigma grading structure. The grading increases as you learn more and prove your skills through successful projects.

The grades are as follows:

  • White Belt – simple understanding of lean six sigma
  • Yellow Belt – simple understanding of lean six sigma and helps collect data
  • Green Belt – Can lead projects and deliver the lean six sigma tools
  • Black Belt – Can lead multiple projects and coaches the Green Belts
  • Master Black-belt – Helps deploy Lean Six Sigma as a strategic initiative and ensures that the culture of the business adopts Lean Six Sigma


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