The contribution of Lean and Six Sigma® methods to Industry 4.0 approaches

Lean management and Six Sigma® are improvement methodologies that you have probably already heard of. They have, in fact, become essential in businesses in general and in industry in particular. Between the search for optimization and the need for efficiency, companies have every interest in developing new approaches aimed at performance at all levels of production. While recalling the main principles of Lean and Six Sigma®, Frédéric Rouzeau, expert in the field of industry, demonstrates their great complementarity and their close link with industry 4.0.

The Lean method: origins and principles

In the 1950s, Taiichi Ohno, industrial director of Toyota, implemented the Toyota Production System (TPS), a new method of managing industrial activities. Its main objective is then to eliminate any activity that does not add value in the eyes of customers.

At the beginning of the 1980s, a team of researchers from MIT led by James P. Womack looked into the success of Toyota. They quickly became convinced that Toyota's TPS is applicable in all companies in all sectors and in all countries. They decided to name this new approach “lean” (“lean”, “fat-free”, in French), a term which perfectly illustrates this obsessive tracking of different forms of waste within processes.

In 1991, James Womack and two other MIT researchers published The Machine That Changed the World (Harper Collins, 1991), which presents their findings from the Toyota TPS study. This work contributes to the deployment of lean manufacturing throughout the world and remains, even today, a reference work in industrial management. Lean management has since become widely used in all sectors of activity (industry, services, office, health, etc.).

Lean management: a global vision of the industry

This type of management relies on the strong involvement of all staff. This will work in teams to identify and propose improvements aimed at eliminating waste. These can take three different forms depending on their nature:

1. Muri: saturation of a resource, an excessive task, too difficult or even impossible;
2. Mura: irregularities, variability;
3. Muda: tasks with no added value. These can be divided into eight different types:
   1. overproduction (producing too much or too soon): the worst of all because it alone generates all the others;
   2. unnecessary stocks;
   3. unnecessary transport and handling (of products);
   4. overprocessing (superfluous operations, overquality);
   5. unnecessary movements and travel (of employees);
   6. errors, defects and rejects;
   7. waiting time and delays;
   8. underutilization of skills.

The Six Sigma® method: origins and principles

The Six Sigma ® method is a little more recent. It originated in the late 1980s when Bill Smith, an engineer at Motorola, developed it to improve the manufacturing processes and quality of their products. It was then a matter of better satisfying customers. The method became famous in the 90s, thanks to General Electric and its charismatic president Jack Welch. Indeed, it was he who decided to improve it and apply it throughout the GE group with resounding success.

The Six Sigma® method aims to reduce process variability to eliminate or reduce the risk of the product (or service) being rejected by its recipient under the pretext that it is outside of expectations or specifications. This method is mainly based on statistical tools which will make it possible to identify and put under control the key parameters of the product or process. It is deployed in project mode: managed by a Green or Black Belt certified project manager. It is structured into five distinct phases: Define, Measure, Analyze, Improve, Control, this is “DMAIC”.

Each stage of the DMAIC project has specific objectives and uses different tools:

1. Define : frame the project, identify operational and financial gains, understand customer expectations and CTQ (critical to quality) also called Yi, map the process, etc.;
2. Measure : list the potentially influential factors of the process (called Xi) and simultaneously measure the Yi and Xi after ensuring the reliability of the measurement processes;
3. Analyze : carry out data analysis to identify the Xi factors most influential on Yi (responses);
4. Improve : find improvement actions relating to the most influential Xi;
5. Control : implement process management tools such as MSP (statistical process control).

Lean-Six Sigma®

Building on their main point in common (customer orientation), the two methodologies were combined in the early 2000s to give birth to Lean-Six Sigma® (LSS). There is indeed a great deal of complementarity between these two approaches:

But how does the implementation of this combination of methods apply in practice in the field of Industry 4.0? What are the specificities of this field that make them particularly relevant?

Industry 4.0

L'industry 4.0Digitalisation, also frequently referred to as the "connected factory", marks the fourth industrial revolution, following on from mechanisation (1.0), mass production (2.0) and automation (3.0). Thanks to digitalisation, industry is becoming a global interconnected system. Organized into technological blocks, the numerous innovations have a direct or indirect impact on all of the industry's functions. Some examples of the most frequently encountered bricks:

• efficient processes (advanced machining, additive manufacturing, etc.);
• automation, transitics;
• measurement and analysis of product data (real-time connected sensors, etc.);
• workstations and communicating machines (connected operator, augmented reality, MES (Manufacturing Execution System), intelligent and collaborative machines, etc.);
• the digital model (product/process simulation, digital model, digital twin, virtual reality, etc.);
• predictive maintenance, connected maintenance of machines;
• the steering and management of the company (collaborative work, workflow/EDM (Electronic Document Management), etc.).

What are the links between Lean, Six Sigma® and industry 4.0?

It is unthinkable to deploy a technological brick without first having a strong culture lean within the company. Indeed, even automated, waste remains waste. This applies in particular to handling and storage.

Conversely, certain building blocks will strongly contribute to strengthening the Lean method. Some examples :

• augmented reality: it can avoid or detect errors;
• real-time performance monitoring;
• communicating machines and connected operators: they simplify monitoring and traceability;
• robotics, transit systems: they reduce arduousness;
• operator training using virtual or augmented reality;
• accessibility and reliability of working documents thanks to the EDM.

Regarding Six Sigma®, the link with MES, intelligent and collaborative machines, predictive maintenance, efficient processes, etc. is obvious because identifying and monitoring key parameters appears essential. It is therefore very likely that during the DMAIC improvement phase, 4.0 type solutions will be considered.

By appropriating “modern” technological tools and processes, Industry 4.0 is a ready-made terrain for the application of Lean Six Sigma® and its quest to eradicate the superfluous. In addition, by analyzing each production step according to the DMAIC methodology, Industry 4.0 fully enters into optimization.

We therefore have on the one hand, an approach aimed at the systematic improvement of processes (Lean) and, on the other, a method whose objective is to reduce all forms of variation (Six Sigma®). A combination of these two concepts, Lean Six Sigma® allows for the continuous improvement of processes while placing the customer at the center of concerns and is a clear path to excellence. However, Lean Six Sigma® is part of a quality approach which can only function and continue with the support of management and strong awareness among employees. In other words, industry 4.0 cannot ignore a more collaborative organization and the training of key players in the project.