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Wiki Blu.e: Six Sigma, Lean and the Theory of Constraints

Six Sigma, Lean and the Theory of Constraints are three methods for improving industrial performance that all rely on a systemic approach. José Gramdi, founder of the Interaxys consulting firm, outlines the advantages of these three methods and delivers some advice for manufacturers keen to take the plunge.



1. Six Sigma


The Six Sigma method sets out to reduce variability in manufacturing processes. It can be used to identify the variability factors that might affect production quality and performance, such as energy efficiency. Manufacturers may or may not be aware of these factors, and may or may not have them under control. In practice, variability often depends on one of the “5 Ms”: Mother Nature (the Environment), Manpower, Materials, Machines and Methods.

   |   What the expert says

“With the Six Sigma approach, I’ll be able to find tips, rules and procedures that will help control my process output. For a factory, this method can be used to analyse variability in the Energy Performance Indicators (EPIs) for each Significant Energy Use (SEU), identify the operating settings that yield the best stable performance and measure the potential gain. The teams can then standardise the operating practices that help improve energy performance.”



2. Lean


The Lean method looks at the time it takes a process to change the inputs into outputs. This lead time is treated as a source of improvement and hence a potential performance gain. The Lean method accordingly analyses all of the steps in the process, from order to delivery, to identify all of the non-value-added tasks. The aim is to whittle down response times and, in so doing, shorten lead times.

   |   What the expert says

“For example, in a cannery, after the sterilisation step, the operational teams used to keep filling the cold room with pallets until there was no room left, to bring them down to 20°C. The Lean method helped avoid excessive use of the cooling unit by reorganising pallet cooling arrangements. A limit was set on the number of pallets that could be placed in the cold room at any one time, so they cooled more quickly. By agreeing to hold the pallets further upstream and send them down in batches, the team optimised the line’s production capacity and reduced the need for refrigeration.”



3. Theory of Constraints


The Theory of Constraints aims to increase the quantity of items that the process is capable of delivering per unit of time. According to this theory, the process throughput depends on just one of its resources, dubbed the “bottleneck”. To improve performance, the aim is not therefore to work on all of the resources, but instead to identify the bottleneck and concentrate on increasing its throughput. This alone will make the whole process more effective.

   |   What the expert says

“In practice, the bottleneck is the point at which queues form. To identify it, sometimes all it takes is to walk around the shop floor and trust your instinct. Are there products queueing up at a particular spot? That’s probably where you’ll find the bottleneck. You can also use more scientific methods to locate this critical point. This will entail analysing the manufacturing times of all of the products and so identifying the machine with the highest load factor.”



4. Before you start

> Some industrial managers seem to think they have to pick just one of the three methods: Six Sigma, Lean or the Theory of Constraints. This is a mistake, because the three approaches are not in contradiction: in some cases, they can even be used in combination.

> Managers should be wary of going with the crowd and opting for any particular method without prior analysis. That would be akin to prescribing the same medicine for every illness. It is important to be able to use the right method at the right place and the right time. This necessarily involves a thorough diagnosis of your industrial facility.


Go further

To read the article “Industrial performance: new paths to excellence” (march 2017)



About José Gramdi (CEO Interaxys)

After graduating as a robotics engineer, José Gramdi worked as an industrial IT consultant for 15 years before joining the Université de technologie de Troyes in 2002 as a research teacher. In 2014, he founded the consulting firm Interaxys with three partners.