Intended learning outcomes: Identify the basic concepts of the Toyota Production System. Produce an overview on lean production and a lean enterprise. Differentiate between the conventional view of inventory and the Japanese view.
The origin of the just-in-time concept is in the Toyota Production System. Here see [Toyo98].
The Toyota Production System (TPS) is a framework of concepts and methods for increasing productivity and quality.
The minimization of the so-called 3M, “muri”, “mura”, and “muda” is a basis of TPS.
Overstraining or excessive stress (Japanese “muri”) refers to an unreasonable overburdening of human beings (physically or mentally) or machines.
With human beings, “muri” can entail exhaustion, injuries, unplanned absence, diseases, and even burnout. With machines, “muri” can entail interruptions and decreased availability.
Variation (Japanese “mura”) describes unevenness in the production system.
“Mura” can result, for example, from discontinuous demand, but also from changing product mix, differing times required for individual operations, or badly organized workplaces. “Mura” can spread out to the whole supply chain, which can entail, among other things, the bullwhip effect (here see Section 2.3.5). Leveling of the production along the entire supply chain (Japanese “heijunka”) as an important tool for reducing “mura” requires a reduction of the lead time. For this, the following sections will deal with reduction of inventories, mixed-model and mixed production, as well as lot size reduction.
Waste, or useless effort (Japanese “muda”) is seen as all activities in development and manufacturing within the entire supply chain, extending to and including the consumer, that are non-value-adding from the customer’s point of view.[note 602].
Ohno’s seven wastes are overproduction, waiting, transportation, unnecessary inventory, unnecessary motion, making defects, inappropriate processing (e.g., physical work not suited to human beings or overprocessing that will not be paid by the customer). See [Ohno88].
The 3Ms interact mutually. Reducing “muda” without simultaneously reducing “mura” can result in “muri.” For example, reducing inventories and simultaneously satisfying heavily discontinuous customer demand will overburden the production system all too often. This will, among other things, decrease quality, and thus entail “muda.” Thus “mura” is a prerequisite of a durable reduction of “muda.” As “muri” entails, in general, “mura” and “muda,” avoiding “muri” has priority. An example is the famous cord, by which employees of Toyota’s assembly line can stop the line, not only because of defects (“muda”) but also if they cannot follow the takt time, for instance because of being overburdened. The short-term stop of the line will then not be considered as “mura” or “muda.” However, the reason for the overburdening as well as a feasible solution must be found quickly.
TPS encompass a set of methods, techniques, and tools to increase quality and speed without increasing “muri” or decreasing productivity. Jidoka and Just-in-time are the two pillars of the TPS. Both pillars encompass methods, techniques, and tools for reducing all 3Ms.
The Jidoka concept comprises approaches and techniques for immediately halting production when abnormal conditions occur. Jidoka means “automation (Jap. 自動化) with manlike sensors,” which is rendered by the artificial term “autonomation” (Jap. 自働化).[note 603].
Jidoka therefore is aimed at the elimination of production of defective products by building quality into the production process. This way of thinking stems from 1902, when Sakichi Toyoda, who later founded the Toyota Motor Corporation, patented a device to stop a weaving loom as soon as a thread broke. This prevented the weaving of defective fabrics and allowed operators to fix the problem itself, strand breakage, as soon as possible. Section 18.2.5 shows some of the techniques of the Jidoka concept.
The just-in-time (JIT) concept encompasses a certain set of approaches, methods, and techniques for planned elimination of all waste. The primary elements are to have only the required inventory when needed; to improve quality to zero defects; to reduce lead times by reducing setup times, queue times, and lot sizes; and to incrementally revise the operations themselves. Cf. [APIC16].
The just-in-time concept thus increases the potential for short delivery lead times for all types of production and for many service lines of business.[note 603]
The terms stockless production or zero inventories as synonyms for just-in-time are misleading and thus not used in this work. After all, the Kanban technique does require inventory in buffers at all production structure levels. The misunderstanding resulting from this misrepresentation is probably also responsible for the fact that JIT was frequently understood and applied incorrectly and that, finally, the new catchword “lean” took the place of the term JIT.
Lean production emphasizes the minimization of the amount of all required resources (including time) for the various activities of the company (cf. [APIC16]). It involves identifying waste (see definition above) and eliminating them.
A lean enterprise applies the principles of lean production to all areas within the organization.
Since the time it was introduced, the philosophy of lean production [WoJo07] has often been taken to extremes. It served as a convenient justification for firing and not replacing staff members. Some people postulated polemically that the contradictory objectives of the company, as outlined in Section 1.3.1, could be resolved. They did not consider at all explicitly the target area of flexibility, for its objectives are usually long term in nature. The customer does not readily recognize that the building of such competencies is value-adding. This view led to company anorexia and resulting paralysis. It proved to be wrong at the very latest when companies became no longer capable of achieving innovations.
The JIT concept originally introduced by the Japanese corresponds most extensively with the current concept of “lean,” which once again gives the target area of flexibility the consideration that it deserves. See here also Section 1.3.3. In any case, the aim is still to reduce useless effort, or waste. As to reducing inventory, Figure 6.1.1.1 shows the change in view of inventory that took place between 1970 and 1990.
Fig. 6.1.1.1 Alternative views of inventory.
High inventory acts as a high water level (light background) in a lake that has shallows and shoals (dark background). If the water level falls, the obstacles will be felt and must either be removed or avoided through a change in course. Reducing inventory exposes problems that must be corrected by means of appropriate concepts. Japan gained this insight early on (see also [Suza12]).
Course section 6.1: Subsections and their intended learning outcomes
6.1 Characterizing Lean / Just-in-Time and Repetitive Manufacturing
Intended learning outcomes: Explain Just-in-Time and Jidoka: Increasing productivity through reduction of overburdening, unevenness, and useless effort, or waste. Describe characteristic features for simple and effective planning & control techniques of repetitive manufacturing.
6.1.1 Just-in-Time and Jidoka — Increasing Productivity through Reduction of Muri (Overburdening), Mura (Unevenness), and Muda (Useless Effort or Waste)
Intended learning outcomes: Identify the basic concepts of the Toyota Production System. Produce an overview on lean production and a lean enterprise. Differentiate between the conventional view of inventory and the Japanese view.
6.1.2 Characteristic Features for Simple and Effective Planning & Control Techniques of Repetitive Manufacturing
Intended learning outcomes: Produce an overview on how the lean / just-in-time concept tends towards more simple techniques in place of more complicated techniques of materials and capacity management.
