The 7 wastes or MUDA of the Toyota Production System
MUDA, MURI, MURA, the 3 losses of the TPS system
Eliminating waste is essential to the proper functioning of LEAN. MUDA means waste in Japanese and are 7 in number. 7 MUDA are the best known and most exploitable in order to reduce waste. There are also other types of waste, MURI and MURA defined by Taïchi OHNO, creator of TPS, Toyota Production Systems. Eliminating waste helps to optimise the company's flows and processes and thus make a profit.
MUDA : Waste
Represents all waste, waste created by the company, involuntarily and likely to be eliminated. MUDA do not add value. They are therefore the easiest waste to identify, track and eliminate.
MURI : Excess
Muri is one of the 3 losses and means excess. It is linked to activities that are difficult for operators to carry out, particularly due to the company's equipment and materials. These losses are created through unreasonable activities and their consequences such as work accidents, ergonomic problems or musculoskeletal disorders (MSDs).
MURA : Irregularity
The MURAs include irregularities, variations in the production chain, in the work of operators. It represents the fact of making cuts, pauses, machine stops because one is waiting for a part, a material, an operator... The ideal is to create a work rhythm, to help this, the Heijunka exists, it is a method to level production.
Eliminating waste is part of LEAN's philosophy
1- WASTE RESULTING FROM OVERPRODUCTION
In Japan in 1945, any material or resource badly affected could lead to storage, i.e. to a deferred and reduced income. The pattern occurred on a smaller scale in 1973 during the oil shock and the following decades. Not forgetting the quota systems imposed in some European countries, which limited market capacity for Japanese manufacturers.
Maximizing sales was selling EXACTLY what different customers wanted. The generalization of this idea to the production system will lead to the KANBAN system. Although post-war shortages have subsided, offering a range of important models and producing only what is ordered remains essential to avoid overproduction.
A whole system for collecting information from its customers enables the brand to adjust its production "as accurately as possible". Maintaining this principle is also a means of maintaining margins for progress in shrinking markets, since it is easy to improve productivity by increasing the quantities produced, but it is difficult to do so in a context of declining production volumes.
Eliminating overproduction means paying great attention to planning but also agreeing not to seek the full use of resources. It can also involve losing stored objects, no longer finding them in an emergency context, in a hurry. This wastes time, energy and even money if the product is not reusable. Thus the 5S allow to give order, to organize, to arrange the storage area, production, teams.
This MUDA must be avoided as much as possible, because it is the most dangerous of LEAN Manufacturing's 7 wastes, for lack of necessarily generating all the other wastes afterwards.
2- WASTAGE FROM WAITING TIMES
An unoccupied resource is not necessarily a waste, because full employment must be distinguished from the activation of a resource.
Pending parts can be assimilated to stocks. The lack of punctual occupation of the labour force, resulting from a lack of balancing or hazards affecting the production flow, is minimised by the proximity of the substations, the operators being authorised to provide mutual assistance.
Unbearable expectations are downtime due to equipment failures or series changes. The first are fought using total productive maintenance (TPM) to self maintenance. The seconds are gradually eliminated using rapid tool change methods, SMED. But they're not the only ones. When overproduction is wasted, if the product stored in the storage area is not found, time is lost. To avoid searching it is possible to set up visual management in order to locate visually and quickly what one seeks in order to eliminate the waiting time.
3- WASTE CAUSED BY TRANSPORT
Transporting a part from one machine to another gives it no added value. Having the various machines in flow-shop, i.e. in specialised workshops, is a good way of reducing internal logistics.
In the flow-shop, all the necessary resources are available to carry out the various operations so that the production flow flows without turbulence.
The job-shop or specialized workshop groups together resources of the same type; turning workshop, drilling unit, milling workshop, etc.
Carrying out the different operations on the same part requires constant transport and waiting between the workshops. It is generally accepted by all manufacturers that the availability of resources in specialized workshops leads to a real logistical nightmare. The pieces cross circuits in''spaghetti dishes'' and remain a good part of the time to wait in the inter-stocks.
Placing the different resources very close to each other, reduces transportation needs and physically prohibits large inter-stocks.
Transport being identified as waste, after verifying that transport cannot be eliminated or further reduced, improvements can be sought.
What is the point of investing in complex technology that improves waste?
This kind of nuance applies to automated links between machines; if manpower can be eliminated by automation, it is preferable to do so, because this equipment will end up no longer costing anything, whereas humans require a perpetual investment.
Example of parts transport in the electronics industry
With the exception of highly automated processes, the trend observed in the Japanese electronics industry is quite significant. Manual operations inherited the era of the manufacture of heavy and cumbersome office machines and televisions, sophisticated transfer lines. The generalization of these lines was made even for small and light parts.
The extreme segmentation of the tasks resulting from the mass production reduces the cycle time per shift to such a level that the gripping and resting of the parts on the line become non-negligible compared to the operation itself.
With the end of mass production, to the benefit of the greatest variety of products, the search for flexibility imposes a redesign of the production system. Gradually the transfer lines are abandoned, cheap workbenches are placed in "cells", side by side, and transfers are made from hand to hand, between operators. The gains in space and efficiency are often spectacular, and the maintenance costs of sophisticated lines are eliminated.
4- WASTE DUE TO UNNECESSARY STOCKS
The definition of stocks must be understood in a broad sense; pending parts are a stock, parts on the way are a stock, perhaps in movement, but still a stock.
The distinction between transfer batch and production batch leads to the principle of just-in-time flow. It is certainly the best indicator and means of destroying hidden stocks.
The limited space available prevents storage. The layout of the various flow-shop resources considerably reduces transport requirements and allows little or no storage. Ideally, we try to put the resources in direct contact with each other and we try to work with transfer lots of size 1.
Automatic storers have the same characteristics as transitic means; they improve the storage operation but do not suppress it.
The objective is to eliminate waste due to unnecessary stocks, which implies the existence of "useful" stocks. These do exist and are even vital, to seek zero stock is nonsense.
5- UNNECESSARY MOVEMENTS
The notion of unnecessary movements is well known to all. The most obvious unnecessary movements are usually easily eliminated. More difficult to track are the bad habits that performers spontaneously develop. These can very well escape observation, either because these actions stop when an observer arrives, or because the latter lets himself be deceived by the ease of the performers. It is sometimes surprising to note the efficiency with which the operators manage to carry out complicated and unnatural gestures.
In the useless movements, it is necessary to include the useless comings and goings, the ergonomics of the stations, the arrangement of the workshops, the supply... So many avenues to explore.
6- WASTE DUE TO DEFECTIVE PARTS
The abundant literature on quality management and the dissemination of the quality spirit in companies have raised awareness of the costs of non-quality.
This cost exceeds that of the part in defect, of its reprocessing or replacement, because with just-in-time flows, the incidence of non-quality spreads downstream, delays, missing parts, loss of opportunity, etc. The important thing is to remove the cause of non-quality, not to treat the symptoms.
7- WASTE IN MANUFACTURING PROCESSES
It is hard to believe that in manufacturing processes there can be unnecessary machining, unnecessary operations.
However, the routine, the tradition of the trade, technological evolutions leave operations that the product itself does not require or more. A critical analysis of each operation can uncover this kind of waste.