1. Origins
Lean traces its roots to post-war Japan, where Kiichiro Toyoda, Taiichi Ohno, and others at Toyota took a hard look at Ford’s production model. Ford’s system was highly efficient, but also rigid. Toyota’s response was the Toyota Production System: a fundamentally different approach that shifted focus from individual machines to the flow of the product through the entire process, end-to-end. Waste, in all its forms, was to be identified and eliminated at every step. The term “Lean” itself came later, popularised in 1996 by James Womack and Daniel Jones in their book Lean Thinking.
Six Sigma was developed at Motorola in the 1980s by Mikel Harry and Bill Smith, initially to reduce defects in manufacturing processes. It evolved from statistical quality control into a full problem-solving methodology, and gained widespread recognition after General Electric’s implementation under Jack Welch in the 1990s, which reportedly delivered $12 billion in savings over five years.
Lean Six Sigma as a combined approach emerged from the recognition that Lean and Six Sigma address different but complementary problems. Many organisations use one or the other; an increasing number use both, deliberately, because the combination tends to deliver better results than either alone.
2. Core principles of Lean Six Sigma
Lean: eliminating waste and improving flow
Lean is about designing work in a way that makes sense for the customer, for the people doing the job, and for the operation as a whole. It focuses on what actually adds value, and removes what doesn’t.
That includes steps that could be eliminated, delays that have been accepted as normal, and complexity that has accumulated over time without ever being questioned. Lean brings these to the surface and gives teams a structure to address them.
The foundation is learning to see waste. Lean identifies eight categories:
Once teams can recognise these, they start noticing them everywhere. The next step is making waste visible across the whole process, which is where Value Stream Mapping comes in: a tool that maps each step end-to-end, identifies where time is lost and inventory builds, and shows where flow breaks down.
The five core principles of Lean give it direction:
- Identify value from the customer’s perspective
- Map the value stream and challenge every step that doesn’t add value
- Create flow so the product moves through without unnecessary stops or delays
- Establish pull so work is triggered by actual demand, not forecasts
- Seek perfection continuously, because there is always more waste to find
In practice, Lean tends to start with visible, accessible improvements: repositioning tools to reduce motion, simplifying a form, removing a redundant approval step, cleaning up a workspace so problems are easier to spot. While these aren’t dramatic changes, they create momentum. Over time, the focus shifts from pushing things through to making sure the process flows properly in the first place.
Six Sigma: reducing variation and solving problems properly
Six Sigma is harder to explain than Lean because it requires a little theory before it starts making sense. But once it does, it becomes a powerful tool for the kind of problems that Lean and common sense alone cannot fix.
What the name means
The term comes from statistics. In a normal distribution, results cluster around the average, with fewer falling further out. Sigma (σ) represents standard deviation: a measure of how spread out the results are. A Six Sigma process is one where the variation is so tightly controlled that fewer than 3.4 defects occur per million opportunities.
For context: a three sigma process produces roughly 2,700 defects per million opportunities (0.27%, assuming a centred process average). Most modern car plants run between 4 and 5 sigma. Commercial aviation safety is estimated near 6. You don’t need to hit those levels in most areas of your operation – but the numbers illustrate how much the gap between three and six sigma actually means in practice. Understanding how variation connects to quality, efficiency, and daily firefighting is what makes the thinking useful, even at a basic level.
The belt system
In formal Six Sigma programmes, practitioners are trained and certified using a belt system modelled on martial arts. Yellow Belts cover the basics, Green Belts support projects, Black Belts lead them, and Master Black Belts train and coach others.
It is worth noting that there is no single global authority governing certification, so standards vary between providers. Smaller organisations typically don’t need the full structure, but some level of trained expertise is needed to apply the more analytical tools reliably.
DMAIC: the practical backbone
Whether applying Lean, Six Sigma, or both, the most widely used problem-solving framework is DMAIC: Define, Measure, Analyse, Improve, Control.
Define: Clarify the problem. What is actually going wrong, where, and what would “better” look like?
Measure: Collect the right data. How is the process really performing, and where is variation hiding?
Analyse: Identify root causes. This is where Six Sigma tools come in — Fishbone diagrams, Pareto charts, 5 Whys — to move past symptoms and find what is actually driving the problem.
Improve: Test solutions. Run trials, adjust, and focus on fixing the root cause rather than the symptom.
Control: Lock in the improvement. Update the process, train the team, and put checks in place so the fix holds.
What makes DMAIC valuable, more than the structure itself, is what it prevents: teams rushing to a solution before they understand the problem. Many recurring issues persist because the fix addressed the symptom rather than the cause. DMAIC slows that impulse down and replaces it with discipline.
Lean and Six Sigma together
Lean and Six Sigma address different problems, which is exactly why they complement each other.
Lean improves speed, flow, and efficiency. It removes clutter, exposes problems, and makes processes easier to run day to day. Six Sigma improves consistency and control. It tackles the variation that causes defects, rework, and unpredictable performance, especially when the problem keeps returning despite repeated attempts to fix it.
In many operations, Lean comes first. Teams build habits, reduce waste, and start solving visible problems. Over time, some issues prove harder to shift: performance that varies across shifts, defect rates that won’t come down, or problems that seem fixed until they aren’t. That is when Six Sigma adds the most value – going deeper, with data and structure, to get to the underlying cause.
The practical implication is that having both methodologies available gives teams more options. Some problems are best addressed with Lean tools. Others need Six Sigma’s analytical approach. Many need both. The point is to fit the tool to the problem, not the other way around.
Benefits
When applied well, Lean Six Sigma delivers improvements that are both operational and organisational:
- Quality improves because defects are traced to their root causes and eliminated, rather than managed as an accepted cost
- Efficiency increases as waste is removed from processes and flow becomes more reliable
- Costs fall as a natural consequence of less rework, less waste, and fewer disruptions
- Employee involvement grows: both methodologies rely on the people closest to the work to identify problems and test improvements, which tends to build capability and engagement over time
For SMEs in particular, the absence of large dedicated project teams is not the barrier it might seem. Both Lean and Six Sigma can be applied in targeted ways, starting small and building from there, without a full programme rollout.
Challenges
The most significant challenge is cultural. Both methodologies require teams to move from intuition-based to data-based decision-making, and that is a genuine shift for many organisations. It takes time, and it requires visible commitment from leadership – not just in words, but in how decisions are actually made.
The investment in training is real, though often more modest than expected. No special equipment is required, and most analytical tools are freely or cheaply available. The main cost is time: training people, and then giving them the space to apply what they’ve learned.
Resistance to change is also worth taking seriously, particularly from people who are confident in their own judgement and experience. This is not unusual, and it is not insurmountable. Clear communication about why the change matters, and early wins that demonstrate it works, tend to move things faster than persuasion alone.
Looking ahead
Lean Six Sigma continues to evolve alongside the technologies available to support it. Advanced analytics and digital monitoring tools are making it easier to collect reliable process data and detect variation earlier. Sustainability is also an increasingly natural fit: reducing waste and tightening process control both contribute directly to lower energy use and less material loss.
What has not changed is the underlying logic. As long as processes have waste to eliminate and variation to reduce, the methodologies remain relevant. Implementing Lean Six Sigma is a capability investment that retains its value for as long as it is maintained.
For more information on Lean Six Sigma, or to explore training and implementation support for your operation, get in touch with Delft Consulting.
