Many models of Lean Manufacturing coexist as we have seen in our article « 2, 5, 7 or 14 Lean principes ? » and each one has its own merits.
On the other hand, we see two problems:
- The principles of Lean are getting confused. Indeed, these models present principles that are sometimes common, or with complementary points or visions, or at a different level of detail or with a different vocabulary.
- They do not always explicitly or visibly associate "technical" principles (including processes and methods) with "human" principles.
Beyond the models or principles of Lean Manufacturing, many tools or methods are described. It is not always easy to understand what principles they meet and where or when they apply.
In the end, the inexperienced reader risks being lost and Lean Manufacturing becomes a complicated, confusing science confined to Lean experts.
Our aim here is to give a clear view of Lean Manufacturing by reconciling the different existing models and positioning the different methods and principles in this reconciled model.
The three major models of Lean Manufacturing
We use the three major models: the "TPS house" (Toyota Production System), the "Lean thinking" and the "Toyota Way 2001", illustrated as follows:
Our unified Lean Manufacturing model
We have developed a model that reconciles these three models as follows:
- The "Continuous Improvement" principle of the "Toyota Way 2001" model replaces the "Seek perfection" principle of "Lean thinking"; because they are very similar
- The "Respect" principle of the "Toyota Way 2001" is added to the other four principles of "Lean thinking".
- The TPS house is integrated into the level 2 detailed version.
- The "Just-in-time" principle is naturally integrated into the "Establish Pull" principle
- The "Jidoka", "Heijunka" and "Standardized work" principles are all integrated into "Create flow".
This gives the following unified Lean manufacturing model illustration:
Finally, we integrate the different tools or methods to get a complete overview of Lean Manufacturing. They are positioned at the second or third level of detail depending on whether they are directly dependent on another element.
Description of the unified Lean Manufacturing model
Value refers to all the characteristics or functions of the product that meet the customer's needs and for which the customer is willing to pay.
This is the starting point of the Lean Manufacturing approach. It actually begins at the product marketing stage. It is crucial to properly identify value, by product and customer in order to define in the next step (Map Value Stream) the best flows and critical production steps. However, identifying it is not enough, it must be characterised in order to be able to measure it, control it and prioritise the actions to be implemented. For example, a very critical element of value will have more expensive tooling or more frequent control.
Two useful approaches or tools can be mentioned for this purpose:
- Critical To Quality characteristics (CTQ). A characteristic is CTQ when it is essential for the customer, measurable and a specification can be written to validate that the product meets the characteristic
- The Quality function Deployment (QFD). It is an approach to identify and translate customer needs into technical specifications and plans to design, manufacture and assemble the components or sub-assemblies of a product so that it meets these needs at the best cost to the company.
Map Value Stream
Value streams are the different sequences of activities required to design, produce and deliver a product to the customer, including information processing and raw material supply.
They must be designed to reduce or even eliminate activities that do not add value for the customer, which are considered losses.
The real difficulty often comes from the fact that there are several products to manufacture for several customers (who do not necessarily have the same needs in terms of volume, quality, cost or lead time). Compromises will have to be made between single-product, product type, single-customer or multi-customer production lines. So with different value flow choices.
The term "Map Value Stream" should in fact be taken in the broader sense of "design, mapp, measure, optimise" value streams. It therefore begins with the design of products, production equipment and even the design of the entire plant.
Four key elements (principle, method or tools) Lean Manufacturing are associated with this step: the seven wastes, the design for manufacturing and assembly (DFMA), the value stream mapping (VSM), and the factory layout:
- The seven wastes. It is a principle that any activity that does not add value for the customer is considered a waste; they must be reduced or even eliminated. However, wastes are nevertheless necessary and cannot be eliminated. For example, quality control: the customer does not pay for quality control, but wants a reliable product and therefore control (or quality assurance) is necessary. However, it can be greatly reduced by implementing preventive measures or by optimising the control process.
- Design for Manufacturing and Assembly (DFMA). It is associated with this principle because it allows several losses to be minimized from the design stage. This is particularly the case for unnecessary movements and defects. The DFMA approach is a major lever for value creation; 70 to 80% of production costs are linked to decisions taken at the time of product design.
- The plant layout. It is the physical location of production equipment and tools. It is not a method per se, but it must meet two objectives:
- Be as aligned as possible with finished products or customers. This corresponds to making autonomous production cells dedicated to each product category, in which all manufacturing operations are carried ou
- Minimise the movement of products, parts, tools and people
- The Value Stream Map (VSM) is obviously the essential method of this step to properly visualise, understand and improve the value flows.
The principle is to achieve continuous production by batch of a single part at a time, with no intermediate stocks and no waste.
More pragmatically, production must be as fluid as possible, eliminating unnecessary waste as much as possible. Necessary waste that cannot be eliminated must be realised more effectively and efficiently.
This principle, which is an ideal to be achieved, is central to the Lean Manufacturing approach. Because it is strongly based on the achievement of the two previous principles. And above all, it is the realisation of the "flow" that makes it possible to achieve, to benefit from the main advantages of Lean.
It is also where production teams have the greatest operational impact, once product and equipment designs have been completed (see DFMA and TPM). This explains the large number of approaches or tools associated with this principle, briefly described below.
- Jidoka. It is a mechanism for automatically stopping a machine or equipment in the event of fault detection. It promotes the "flow" indirectly, by forcing (to avoid stoppages) to resolve the causes of defects as soon as they appear.
- Heijunka. It is the smoothing of production to compensate for irregular orders.
- Standardised work. Standardisation brings several benefits. It improves the reproducibility of production and limits variations. It facilitates the learning of methods (standardised and optimised training, facilitated exchange between employees, etc.). It increases the versatility of employees and the replacement of absent employees by others. Finally, it facilitates improvement because everyone can think about a single method, known to everyone. All this contributes greatly to the implementation of a continuous flow.
- The 5S method. The 5S method is associated with the flow principle for two reasons. It facilitates the search for tools or the movement of people. But above all, it prevents stoppages or malfunctions when the 5S is fully used. That is, for its "prevention" function beyond its "cleaning" function.
- The SMED method. The SMED (Single minute exchange of Dye) method contributes to the "flow" by reducing tool and product change times or cleaning times. In addition to direct productivity (less downtime), it makes production more flexible and reduces batch size; in the extreme (no changeover time, rarely possible) it allows the consecutive production of two totally different products.
- The TPM approach. The TPM (Total Productive Maintenance) approach actually covers several principles applied to maintenance. For example, it includes the design of machines or products to facilitate maintenance. However, we associate it with the "Flow" principle because continuous flow is its main objective. Indeed, it is guided by two ideas:
- Productive: to carry out as much as possible the maintenance without stopping production
- Total: include all factors influencing the proper functioning of the machines and involve everyone
The principle here is to set up a pull production system; each upstream production step is carried out at the request of the downstream step, starting from the customer.
This principle, although expressed after the flow principle in the "Lean Thinking" model, contributes to the achievement of the continuous flow. It reinforces or even strengthens it since it is necessary to produce only what is necessary at the downstream step; neither before nor of course nor after.
We're in Just-In-Time. It provides the final touch of reducing work-in-progress to a maximum.
Taken to the extreme, just-in-time is applied to every component and part in the factory but also at suppliers.
The most important method for the pull flow is the Kanban, a visual card system used as a production order from the downstream station to the upstream station, when the downstream station needs parts.
According to Toyota and the publication of "Toyota Way 2001" it is clear that the two most important principles, before any other "technical" principle or method, are continuous improvement and respect for people.
It is easy to understand why continuous improvement is so important. It took Toyota about 20 years to design, deploy and refine the Toyota Production System, with a challenging journey. This has been a continuous improvement...which is still ongoing.
Continuous improvement has three components, as articulated by Toyota:
- Challenges: "We form a long-term vision meeting challenges with courage and creativity to realize our dreams".
- Kaizen: "We improve our business operations continuously, always driving for innovation and evolution. »
- Genchi genbutsu: "We practice Genchi Genbutsu... go to the source to find the facts to make correct decisions, build consensus and achieve goals at our best speed".
Respect for people, or the people at the heart of Lean Manufacturing
Respect for people, or the people at the heart of Lean manufacturing
According to Toyota, respect for people has two aspects:
- Respect: "We respect others, make every efforts to understand each other, take responsibility to do our best to build mutual trust"
- Teamwork: "We stimulate personal and professional growth, share the opportunities of development and maximize individual and team performance".
These two definitions may seem strange to some. It is important to understand that the notion of respect according to Toyota is quite different from the one commonly used, especially in Western countries.
Respect for an individual is very important because he or she is considered responsible and competent enough to be able to solve problems, provide solutions and contribute to the performance of the team for which he or she works. If an individual is performing well, and brings value to the team, then he or she will be respected by the team.
However, the more traditional or "human" side is not overlooked; many writings or quotations indicate it: "respect for the human being", "treating each worker as an individual".
We conclude this unified model of Lean manufacturing by stressing that this dual definition of respect means that :
People are not only taken into account, but are at the heart of Lean Manufacturing.
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