Integral Logistics Management — Operations Management and Supply Chain Management Within and Across Companies

6.1.1 The Toyota Production System (TPS): 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 the so-called 3M: muri, mura, and muda.

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.

Continuation in next subsection (6.1.1b).

Course section 6.1: Subsections and their intended learning outcomes