Technology

Scale-space filtering

Nov 21 2012

Mitigating “Mura,” or unevenness

The Japanese word Mura (ムラor斑） is the third member of the Muri, Muda, Mura axis of manufacturing evils. It means unevenness. In terms of volume of activity, if Muri refers to overburdening resources, Mura then really is the conjunction of overburdening some resources while others wait, or of alternating over time between overburdening and underutilizing the same resources.

Unevenness, however, is not only about volumes, but about quality as well. Unevenness in products is even synonymous with bad quality. From production managers facing “unpredictable” environments to academics promoting genetic algorithms or other cures, everyone bemoans how variable, or uneven, manufacturing is. The litany of causes is endless. Following are a few points that I think may clarify the issues:

  1. Mura in space, Mura in time, and Mura in space and time
  2. Degrees of severity: Deterministic, random, and uncertain environments
  3. What is special about Manufacturing?
  4. Internal versus external causes of unevenness
  5. Most useful skills in dealing with Mura

Mura in space, Mura in time, and Mura in space and time

Mura in space is imbalance in the work loads or utilization among resources at the same time; Mura in time, variability in the work load of a resource over time. The two can be present in the same factory. You may notice a kitting team working feverishly while the next one is waiting but, two hours later, you find the roles reversed.
Mura is often symbolized by two trucks arriving in sequence with different loads. I tend to think of working with Mura as moving around a city built on hills. A city built on a plain is even and easy to cross, and is often planned with a grid of numbered streets, like Manhattan in New York, or Kyoto. A city built on hills is uneven and offers many obstacles. San Francisco is built on hills, but its planners have chosen to ignore the terrain and slap on it a grid of straight streets. It makes for great views and dramatic car chases, but its steep slopes challenge your engine, your suspension, and your parking skills. Most hilly cities, like Nagasaki, Japan, for example, instead have streets that follow contour lines and therefore meander. The path by car from point A to point B may be longer than a straight line, but it is a smooth ride.

Navigating the peaks and valleys of product demand is like driving in a hilly city. If you just go straight, you keep alternating between pressing the accelerator and the brake, but by hugging contour lines, you can reach to your destination while going at a steady pace. This is what fighting Mura is about.

Degrees of severity: Deterministic, random, and uncertain environments

Some businesses are deterministic. They are “boring” and predictable. They have no variability. A manager once explained to me the electricity meter business in the market his plant was serving, as follows: “There are 20 million households with electricity meters in the country. Each meter lasts 20 years. Every year, I have to make 1 million.” The same products are made for many years, in stable quantities, and with mature processes that have no problem meeting tolerances. Of course, it only lasts until the advent of a disruptive technology, like smart meters.

This kind of environment is not common but it does exist. If your are in one, you should focus your improvement efforts on the opportunities it offers, and avoid tools that are overkill for it. For example, large, diversified companies that make a corporate decision to deploy the same planning and scheduling system in all their plants burden their simplest and most stable business units with unnecessary complexity.

Other business have variations that can be best be described as fluctuations around a smooth trend. If you make consumer goods, the demand every day is the result of decisions from a large number independent agents and will vary in both aggregate volume and mix, but within ranges that can be predicted. In terms of quality characteristics, if you fire ceramics, they shrink, by factors that still vary, even though we have been using this process for thousands of years. This level of variability is very common. The best term to describe it is randomness, and there is a rich body of knowledge on ways to work with it, including the Kanban system to regulate fluctuating flows and techniques to adjust processes in order to obtain consistent results from materials that are not. In ceramics, for example, you make your parts from a slurry that is a moving average of batches of powders received from the supplier, in order to even out their characteristics.

Contrast this with a toy manufacturer who cannot tell ahead of time which one or two products will be hits at Christmas, when most of the year’s sales occur. In process technology, there are similar differences in variability between mature, stable industries and high technology suffering from events like “yield crashes” during which a manufacturing organization “loses the recipe” for a product. Various terms are used to describe such situations, which, following Matheron, I call uncertainty. In such circumstances, the best you can expect from the techniques used to deal with randomness is to let you know that they no longer work. For example, dealerships can shield your plants from fluctuations in consumer purchases, where direct selling would let you find out sooner when demand drops for good or when consumer tastes change.

Calling our environment deterministic, random, or uncertain is always a judgment call. The deterministic electricity meter business turns uncertain with the advent of smart meters. If you view your environment as random, you expect fluctuations with a predictable range, and the signal of a shift into uncertainty manifests itself in changes beyond this range. You can use a variety of tests to detect that such as shift has occurred. Furthermore, with the possible exception of quantum physics, randomness is always in the eye of the beholder, and not intrinsic to a phenomenon.

What is special about Manufacturing?

Manufacturing is not the only kind of business to have high overhead; others include aviation or hospitals. In all such cases, companies must invest upfront in resources that pay off over time, and this is easiest to achieve with activities that place a balanced load on all resources and don’t vary over time — that is, without Mura.

Internal versus external causes of unevenness

Some unevenness comes from outside the organization, in many forms:

  • Fickle customers.
  • Seasonal variations in demand as in the toy industry.
  • Seasonal variations in supply, such as crop seasons in the food industry.
  • Changes in the macro-economy, such as a financial crisis.
  • Natural disasters, like earthquakes, tsunamis, and floods.
  • Raw materials with uneven characteristics, like ores or electronic waste for recycling.
  • Epidemics, as when 10% of your work force has the flu.
  • Unreliable suppliers.
  • …

You do not have the power to eliminate this kind of unevenness, but you can use countermeasures to mitigate its effects. On the other hand, you can and should eliminate unevenness that is self-inflicted. If you have not paid attention to balancing the work load of the various stations on your production lines, you are likely to have both overburdened and underutilized operators. Because of the different roles machines play, the workload can rarely be balanced across machines in a line, but the workloads of operators can be.

If you order materials from suppliers, for example by relying on an ERP system to issue orders by an algorithm for timing and quantities that you don’t undertand, you may well cause alternations of feast and famine in your suppliers’ order books for materials that you, in fact, consume at a steady pace. This creates unevenness not only in your suppliers’ operations, but also in your internal logistics. In The Lean Turnaround, Art Byrne explains that, at Wiremold, he eliminated volume discounts and incentives for Sales to book the largest possible orders. Instead, he preferred a steady flow of small orders, that smoothed the aggregate demand.

Not all resources need to be treated the same way. You want resources that can be described as producers to be generating useful output all the time. Other resources, which we may call responders, must be available when needed, and this is a radically different objective. Unevenness is an enemy for producers, but, unless responders’ work loads provide enough slack, they are unable to respond. Firefighters fighting fires 100% of the time would be unavailable when a new fire breaks out, and the same logic applies to maintenance technicians and operators who work as floaters on a production line. And it applies to machines as well as people. In a machine shop, for example, machines that carry out the primary processes, like hobbing a gear or milling pockets in a slab, are producers, while devices used for secondary processes, like deburring or cleaning, are responders. This is often, but not always, related to the cost of the machines, with expensive machines as producers and cheap ones as responders. However, some of the most expensive equipment, like machining centers, may be bought for its flexibility more than for its capacity, in which case its primary role is to respond to orders for short runs or prototypes.

Most useful skills in dealing with Mura

Permanently uneven workloads among operators can be addressed by balancing, using Yamazumi charts for manual operations and work-combination charts for operations involving people and machines. If the unevenness pattern shifts or oscillates over time, then the workload itself needs to be smoothed, with is done by the various techniques known as heijunka.

Many organizations are not aware of Mura as a problem, and, when aware, are oblivious to patterns in the unevenness that can be used to mitigate or eliminate it. Management, for example, may be struggling to cope with occasional large orders and fail to notice that they arrive like clockwork every other Wednesday from the same customer. A modicum of data mining skills is needed to recognize such patterns in the records of plant activity.

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Nov 14 2012

Applying Lean to retail

In the Lean Logistics group on LinkedIn, Shouvik Chattopadhyay asked the following question:

Is it possible to implement LEAN in the retail industry?

Retail is a broad sector. The issues and opportunities will not be the same depending on whether you are selling shoes, books, or food.

Assume you are running a supermarket chain. Then there are opportunities in the customer interaction within your stores, in the shelf replenishment operations, in the receiving and preparation of the goods, and in all aspects of supply chain management.

On the floor, for example, you might work on the following:

  1. Reduce customer waiting times at check-stands.
  2. Lay out the shelves on the floor to make the most frequently bought items easily available.
  3. Collocate items that are frequently bought together.
  4. If you have deli counters, you can work on the kitchen where the items are prepared to increase productivity, reduce spoilage and assure the availability of all items on the floor.

Behind the scenes, there may be opportunities in the flow of goods from trucks to the shelves customers pick from. Trucks deliver in pallets or cases that need to be received, put away, and broken into the totes or display cases for customers. Observation of these operations usually uncovers improvement opportunities.

You may have a distribution center receiving some or all your items from suppliers, in which you may be able to do the following:

  1. Improve the breakdown between items that are delivered straight to stores or go through the distribution center.
  2. Organize delivery milk runs from the distribution center to stores.
  3. Organize collection milk runs to suppliers.
  4. Improve flow and visibility in warehousing or cross-docking operations within the distribution center.

Then you may pursue further opportunities in the information systems used to run the chain. It sells thousands of items to tens of thousands of individual consumers every day. There may be opportunities to improve the way this flow of transaction data translates into orders to suppliers, with their attendant consequences. These transaction data also need to be mined for differences in customer behavior in different locations, trends, or correlations between items.

Identifying opportunities is the easy part; changing the organization to take advantage of these opportunities, the hard part. The top management of the chain has to want it for strategic reasons, and to have the determination and perseverance to make it happen. Unlike manufacturing, retail is an area where the most successful innovations in recent decades have come from companies in the US, like WalMart or Amazon, or in Europe, like Auchan or Ikea. To the management of a supermarket chain, these may be more compelling sources of ideas than Toyota.

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Oct 31 2012

Takt time: can it be universally applied to all types of production?

This is the question Casey Ng asked in the TPS Only discussion group on LinkedIn. He elaborated as follow:

What are the essential conditions to implement takt time successfully? What are the cases when it fails and if you refer to the fundamental principle of takt and yet couldn’t find the solution? Then what are the exception areas and what alternate solution can be used?

To date, it has generated 43 comments, many with the high level of depth and the implementation examples that are characteristic to this group. It is a new LinkedIn group, with only 118 members — compared with 151,503 for Lean Six Sigma — but passionate and providing meaty technical content. I recommend it in general, and this discussion in particular. Here, I will be including only my own contributions on takt time, and its relevance to the following:

Monuments

With monuments — the very large machines used for heat treatment, electroplating, painting, cutting of sheet metal, etc. — you usually have to load multiple parts simultaneously in order to meet demand, but these parts often do not have to be identical. I don’t recall anyone mentioning this in the earlier comments, but the parts that you load together can be a matching set rather than a batch. If your takt times are long enough, as, for example, in aircraft production, you can actually process one plane-set at a time, to takt time.

Gigantic products with long takt times

Gigantic products, like oil tankers, with takt times of six months or more, are built out of vertical hull slices made at much shorter takt times in a shop, and then welded together in the dry dock. Pioneered in the US with Liberty Ships during World War II, this is now standard shipyard practice, and enhances of the repetitiveness of the process, applying the concepts of takt time and one-piece flow.

Refueling outages in nuclear power plants

I am puzzled by Todd McCann‘s use of the takt time concept in the context of nuclear plant refueling outages, a problem I had the opportunity to work on 20 years ago in France, not in the US. I don’t know who the top performers are in this area today. At the time, it was a tie between the French and the Japanese, at about three weeks from shutdown to restart for one reactor, which is substantially longer than the 193 hours you were quoting for 2006, assuming that the work continues 24 hours/day, 7 days/week.

The French performance was accomplished by standardization. They had 55 reactors with only two designs, producing respectively 900MW and 1300MW, run by a single company. The procedures were the same everywhere, with any improvement quickly shared. The Japanese performance was based on using techniques from TPM. They had nine different reactor designs, run by different utility companies.

Even though they had the best performance in the world, I saw many opportunities for improvement, based on borrowing techniques from SMED, improved planning and scheduling for materials, tooling, and the 1000+ contractors involved, and operational details. Such a detail, for example, was security. Their procedures were effective at controlling access, but inefficient, with utility employees at all levels spending too much time getting contractors into and out of the facility.

The concept of takt, on the other hand, did not strike me as particularly relevant, given that a refueling outage is a yearly burst of intense activity for any given reactor, as opposed to a repetitive process.

Rate work versus response work

More generally about takt time, most businesses have both what my colleague Crispin Vincenti-Brown called Rate Work and Response Work. In manufacturing, if you do a Runner-Repeater-Stranger analysis of your products, Your Runners and Repeaters are rate work; your Strangers, response work.

Runners are products with enough volume to warrant a dedicated line. Repeaters are products that you group into families that, in aggregate, have enough volume for a line. Strangers are all the other products, including R&D prototypes, sample quantities of new products, spare parts for obsolete products, and any other special request. Even in aggregate, they account neither for a high volume nor for high revenue, but you still must produce them promptly. They require a small job-shop set up with your most flexible equipment, staffed with your most versatile operators, and its own operating policies.

While takt time is fundamental to line design for Runners and Repeaters, it isn’t much use for Strangers.

Non-repetitive operations

I have a hard time seeing the relevance of takt time in the absence of repetitiveness. In an assembly process, the takt time gives you an upper bound for the process time at each operation. As you broaden the mix of products you assemble on the same line, it becomes more difficult to balance the work among stations. Past a certain point, you are better off using approaches like bucket brigades, a.k.a. bump-back system, or even a yatai, which are not based on takt time.

Takt time and its calculation

Outside of mathematics, concepts are not reducible to formulas. Time/Demand is the way you calculate takt time, but it tells you neither the rules by which you are supposed to use that number nor how it maps to shop floor activity.

In mass production plants, managers use the inverse of this ratio: Demand/Time, which gives you the same information. Mathematically, working at a takt time of 1 minute and making 60 units/hour (uph) is equivalent. Yet, you and I know that, depending on whether the manager thinks the plant is producing at a takt time of 1 minute or making 60 uph, the shop floor will be radically different.

If you think in terms of uph, it doesn’t matter if nothing comes out for the first 59 minutes of each hour as long as all 60 come out in the end. If you think in terms of takt, 1 unit will come out like clockwork every minute.

What this says is that there is more to takt time than the formula. This is discussed extensively in Lean Assembly, with the following definition of takt time:

“Assuming we complete the product one unit at a time at a constant rate during the net available work time, the takt time is the amount of time that must elapse between two consecutive unit completions in order to meet the demand.”

As I recall, this is,more formally, the way Ohno described the concept in Toyota Production System.

Takt-driven production as the ideal state

The takt time allows you to define an ideal state, that John Shook and Pascal Dennis call True North, but that I prefer to call takt-driven production. In this state, you perform all operations one-piece at a time with process times that exactly match the takt time, and with instant transfer to the next operation at every beat. Of course, it is never perfectly realized, even on an assembly line. Real lines can only be approximations of it. The point is that it gives us a direction.

All deviations from takt-driven production translate to Ohno’s waste categories, overproduction, waiting, excess inventory, etc. Since any local project that move production in this direction eliminates waste, it can be undertaken with the confidence that it contributes to global improvement and is not sub-optimization.

Chronos, kairos, and takt time

Joachim Knuf : “… The ancient Greeks differentiated between two types of time: chronos (chronological, sequence of intervals, typically of equal extension) and kairos, best thought of as ‘the opportune moment.’ In this case, intervals begin and end under sets of conditions. This concept applies, for example, to healthcare, when next process steps are initiated by a preset configuration of values (patient’s blood pressure, glycemic index, bowel movement), not by elapsed time…”

I had never heard of Kairos, but, if the ancient Greeks made the distinction between Kronos and Kairos, why shouldn’t we? There is a rich toolbox associated with the pursuit of takt-driven production. Where the concept of takt does not apply, we can’t use these tools. As you said, extending usage of the word to Kairos-driven activities just adds confusion. These activities need different tools, and Casey pointed out some of them in his comments on Strangers. Let us keep different words to hang them on.

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Press Detroit Rivera

Oct 15 2012

Lean in a press shop

Andrew Turner, Managing Director at Ramsay Engineering, in Pietermaritzburg, South Africa posted the following question on The Lean Edge on 9/22/2012:

“Our company is split in 2 sections, the one a JIT assembly plant, the other a mass production Press Shop. Implementation of Lean in the JIT plant has been relatively simple (not that Lean is ever really simple), however, we are struggling with the implementation in our Press Shop. I know the importance of items like SMED and Heijunka in driving this journey, yet we are battling to get the ball rolling forward. Where do you think we should start the process in the Press Shop?”

To date, he has received responses from the following authors:

  1. Art Byrne: First link the logical value streams through product families, then get change over times under 10 mins
  2. Mike Rother: Depends on Your Goals
  3. Peter Handlinger: Establish a daily pattern production schedule to sequence your presses
  4. Tracey Richardson: Start with Production Control and Empower People through Standards

Of these, Art Byrne’s is the most specific and actionable. None of them, however, address the issue of skills development. At the outset, neither the press operators nor their managers can be expected to have a working knowledge of Lean or how to implement it. Therefore, feasibility by the organization you have is key in your initial choice of projects.

This is why, in shops where people work with machines, the first pilot projects are so often about SMED. This includes not only press shops but machine shops, injection molding shops and diecasting shops, with different technical specifics. On press operations, see Chapter 7 of Sekine & Arai’s Kaizen for Quick Changeover. Keeping in mind the skills development goal, you don’t start with your largest machine that currently takes 8 hours to set up, but with a small one that takes 30 minutes and that you can take down to 4 minutes in 2 months. This kind of success fires up your teams to take on tougher challenges.

After a successful pilot, when you want to apply SMED as appropriate in the entire shop, you need to analyze your activity to establish where it is most useful and easily achievable, and you need to realize the engineering implications. You usually cannot achieve SMED on presses with organization and standard work only; you also need to modify the machines, standardize the dies, and improve the flow of dies to and from the machines, including die maintenance, storage and retrieval. You have to know what and how long it takes to do it. This is not the sort of goals you reach with a few Kaizen events.

Peter Handlinger is the only responder to mention the issues of high- versus low-volume items, but only in the context of setting up daily schedules. I prefer to refer to this as demand analysis, and do it upfront, far upstream from production scheduling, with the objective of breaking down the output of your press shop into the following:

  • Runners, to each of which you dedicate on or more press or press lines.
  • Repeaters,  that you group in families by feature similarity to make in flexible press lines.
  • Strangers, that are items with low and sporadic demand that you make in small job-shop inside your press shop.

You use this breakdown to drive changes in the layout of your shop. In particular, it tells you which presses or press lines you can integrate with an assembly line, as Art Byrne recommends. Then you apply different approaches to production control for the different types of lines.

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Jul 5 2012

Using iPads, QR scans, Sharepoint and Infopath to implement TWI

Franck Vermet‘s group at Schlumberger in Rosharon, TX, assembles and tests measurement instruments that operate deep inside oil wells. They are built for internal use by Schlumberger Oilfield Services, to collect data for customers. They are high-value products, with tight tolerances and the ability to operate in an environment that is not friendly to electronics.
With Mark Warren‘s help, Vermet’s group has been looking to TWI as a way to rely less on knowledge in the heads of experienced operators and more on documented processes for the following purposes:

  1. To ensure that the same work is done the same way by different individuals.
  2. To train new operators faster.
  3. To improve the processes systematically and in a controlled manner.
  4. To support the implementation engineering changes to the products and new product introduction.

In World War II, however, TWI was implemented with cardboard pocket cards and handwritten Job Breakdown sheets, but the Schlumberger team was determined to use more modern technology. After investigating the available options, they realized the following:

  • Sharepoint has a built-in revision management system that makes a Sharepoint site suitable as a repository of process specifications. This helps with traceability and ISO compliance.
  • Infopath is a form design tool they could use to generate TWI templates and store the filled out Job Breakdown sheets in the Sharepoint site.
  • iPads are an effective presentation device on the shop floor, not just for the equivalent of pocket cards,  but for drawings and photographs as well.
  • QR scans linking to job instructions are posted on equipment by means of printed magnets. They can be scanned using an iPad to retrieve the instructions from the Sharepoint site.

Implementation is still in its early days, but all indications from users are that it works. It should be noted also that the approach is sound from the point of view of data management. Unlike the proliferation of Excel spreadsheets that is so often seen in factories, with more or less accurate and up-to-date copies of master data floating around, this approach provides the necessary controls, with the current data retrieved from the server as needed.

As could be expected, the Schlumberger team is facing headwinds from two directions:

  • Among the TWI revivalists, there are those for whom, if it’s not handwritten on cardboard, it isn’t TWI, and they frown on the use of a gadget like the iPad. Never mind that many retail shops already use them as point-of-sale systems.
  • Within the company, TWI-authenticity is nor a concern, but the uncontrolled spread of computer and networking technology is, at least for the IT department. It supports the use of a standard configuration of tools, which does not include what Vermet’s group is using.

The Schlumberger team is  now training suppliers in these tools with the goal of getting them to inspect outgoing parts in such a way that incoming inspection at Schlumberger can be eliminated.

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