Mar 13 2012
How to eliminate “Muri,” or overburdening
“Muri, Muda, Mura” is often mentioned in the Japanese manufacturing literature as a trio of evils to avoid. Of the three, Muda gets the most attention. Usually translated as waste, it designates everything we do in a factory that is unnecessary. For a change, let us focus on Muri.
Muri, in everyday Japanese, means impossible, with the nuance of unreasonable or unsustainable. A person working exceptionally hard is said to be doing Muri. Other words are used to say that something would violate the laws of physics, or that it is socially improper or inopportune. When there is Muri in your process, it means that you are asking people to work too hard, which results in defects, burnout, repetitive stress injuries, or even accidents. Conversely, removing Muri means making your process humanly sustainable, so that is can be executed as well at the end of a shift as at the beginning, by a 50-year-old or a 20-year-old, a man or a woman, 5 or 7 feet tall.
It cannot be repeated often enough that Lean is not about making people work harder but instead, in the tradition of Frank and Lillian Gilbreth, in making the work easier to do. When you observe a truly Lean plant, you do not see operators hurrying. Instead, you see them working steadily, at a sustainable pace, at jobs that are carefully choreographed for effectiveness and efficiency. A key example of Muri elimination is the raku-raku seat shown above. It is a device introduced at Toyota in the 1990s and now adopted by many car makers to remove the need for operators to crawl into car bodies in order perform assembly tasks inside.
There are many tools to remove Muri. You can easily notice that an operator is overburdened by direct observation in the shop. A more systematic approach is to use Toyota’s TVAL to rate jobs based on the weight operators have to carry and how long they have to carry it. TVAL establishes an equivalence between combinations, so that, for example, carrying 4 lbs for 200 seconds is equivalent in terms of fatigue impact to carrying 10 lbs for 4 seconds. You then focus on the jobs with highest TVAL ratings and improve these jobs to reduce it.
Once you know which job to focus on, you record it on video and review it with the operator to identify ways to make it easier or to offload parts of it to others with lighter burdens. If the job involves interactions between operators and machines, you analyze with with a work combination chart to improve task sequencing and identify tasks within the job that need better tooling or a better work station layout.
March 13, 2012 @ 11:46 pm
A few additional experiences with Muri:
1. Cycle times too long or too short. Too long (greater than a few minutes continuously) and operators become stressed out trying to remember all the steps and usually end up making “forgetting” mistakes resulting in missing parts or steps. Too short (less than 20 seconds) and the redundancy leads to extreme boredom, repetitive stress injuries and poor morale. Though all industries differ, a “sweet spot” that you see many process designers try to hit are cycle times between 30 seconds to 90 seconds. In automotive assembly, engines are done around the 30 second mark while vehicles are done around the 60 second mark.
2. Product and part designs which make assembly difficult. Examples: parts too small, difficult to see joining surfaces, sharp edges, slippery parts, parts too flexible and parts require too much adjusting. Assemblers become very frustrated handling these parts and end up misassembling or damaging them. Morale suffers because they see that management does not practice Gemba – does not understand the actual situation on the factory floor. Finding these issues during trials while doing New Product Introductions to the factory floor allows for improvements to be made before full production begins. Implementing DFMA (Design for Manufacturing and Assembly) practices during product and part design process can avoid these issues.
My experience has been that Muri “hides” easily from managers and engineers. Muda and Mura can be more obvious to see. Muri can only be understood by experiencing it first hand. It can not be understood by only watching it or talking to workers about it. Engineers and managers must step up to the line and do the processes themselves. Not for just a cycle or two – but for 20 cycles or more. During this longer time we can start to experience the frustration and fatigue.
When I joined Honda as a new engineer my first job was on the assembly line making the product for a few weeks. I was not even shown my desk until after I had experienced the actual situation, with actual parts and actual processes. This simple act completely changed my view of our roles as managers and engineers. I would never be the same.
Experiencing Muri yourself is the first step to eliminating Muri. Then as Michel explains, working with those who do the job day in and day out we can find solutions together.
March 14, 2012 @ 9:31 am
This is one of the least understood when it comes to knowledge workers too. Companies seem to think it’s wonderful when their engineers and other professionals are working 80 hours a week. But the brain can only do so much in a day. Working 40 hours a week and having an adequate number of people sharing the work may be a more optimal solution. Making it impossible for people to have a family life, time to read and learn, and time to exercise is not showing respect for people.
March 17, 2012 @ 8:10 am
Terrific explanation of a much overlooked and misunderstood term “muri”. That term and it’s relevance to lean methodology is crucial. But because of the difficulty in translatation from Japanese( it is a double negative) it has never received enough attention. Muda is easily understood when translated as ‘eliminate waste’, but ‘avoiding overburden’ doesn’t have that same slogan value to those of us in the west.
The sentiment behind ‘muri’ is in direct conflict with the American conventional wisdom of ‘always have enough’., ‘always schedule enough’, ‘always plan enough’ and etc, That trait suits the ‘American condition’ of ‘the curse of overabundance in the land of plenty’. Enough is why we have so many warehouses and why the Japanese have so many fewer. It also helps to explain why the concept of ‘continuous improvement’ was new to an American manufacturing world struggling to just ‘meet the plan’ and with no idle time available to make any improvements.
Muri is also a contradictory notion in a world where ‘experts’ set work standards that workers should meet, and standard work, where ‘that is the way we currently do it, with room for improvement’ is a new and novel way for most of us.
Michael: Next take on ‘mura’ and explain elimination of inconstantcy!
March 18, 2012 @ 5:16 pm
The discussion of Mura is next on my agenda.
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