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Ask Art: How One-Piece-Flow Supports Quality

by Art Byrne
January 13, 2016

Ask Art: How One-Piece-Flow Supports Quality

by Art Byrne
January 13, 2016 | Comments (15)

Most companies have a hard time getting their arms around one-piece-flow. Not just logistically; the concept is the exact opposite of their traditional approach.

The basic idea behind one-piece-flow is fairly self-explanatory. Take a traditional manufacturing example to illustrate. Let’s say that it takes 10 machines to make Product B. All the machines are in their traditional functional departments. A company that ‘batches’ production in this manner will also have a traditional finance mindset—putting pressure on making the absorption hours so that the results for the month will look good.

Now, say that one of the machines is broken and can’t make any parts. So the decision is made to go ahead and run the other nine machines at full blast to get as many absorption hours as possible. Never mind that because one machine is broken we can’t complete a single thing today that we can sell to a customer. In addition, because the machines all run at different speeds we will be piling up parts in uneven amounts. Maybe we make 2,000 covers but only 300 bases, for example. The inventory buildup is, of course, a huge form of waste by itself.

Even worse is the fact that I tied up my equipment making inventory that I can only sell at a later date when I could have used that equipment to make something that I can sell today. The whole approach is nothing but a big pile of waste. And yet, at the end of the day the finance guy will still say, “you had a good day because you were still able to produce 95 percent of the absorption hours.”

One-piece-flow operates on a completely different approach. What you want to do is go get one of each of the machines that it takes to make Product A and lay them out next to each other in a cellular layout. Get the machines as close to each other as possible and leave no room for inventory other than the standard amount of work in process that is required (normally one piece per machine). We normally think of a cell as U-shaped, but a couple of parallel lines work just as well as long as they are near each other (close enough to stand in the middle and reach either side). Once you have a flow cell, if one of the machines is broken, you can no longer run the other nine. The whole cell shuts down and you put an intense focus on fixing the one machine that is broken. This is the exact opposite of the traditional approach.

Some folks will find that shutting down the whole line is pretty severe. But it’s worth it since making the shift to one-piece-flow will uncover a wide range of problems. The fact that you have excess machine capacity becomes clear right away, for example. This problem has always existed but was hidden by your batch state and six-week lead times. Now, when you run the line at takt time to meet customer demand, this will jump out at you. The finance guy may have an especially hard time with this. Don’t let it bother you. Having excess capacity is in fact normal and actually a good thing.

The second thing that will become very clear right away is that, in their batch state with long lead times, these machines were not well maintained. They break down all the time and stop the entire line. Being in one-piece-flow will force you to fix the problem immediately. Moreover, to be able to do this, you will have to develop a total productive maintenance (TPM) approach to prevent any breakdowns from occurring in the future. You have to commit to the mentality that unplanned downtime is simply no longer acceptable. This won’t happen overnight of course but you need to take the steps to put in a daily/monthly/yearly maintenance program that will eliminate future downtime.

One-piece-flow will also immediately highlight any problems you have with your vendors. These issues could concern delivery or quality; they will also shut down the line until you fix them. On the plus side, one-piece-flow allows you to easily observe what is going on—bottlenecks for example—and put fixes in place that lead to future gains.

Above all, one-piece-flow is the key to quality improvements. In my experience it is pretty common to get a 10x or better gain in quality once you are in a one-piece-flow. This will occur naturally and is something that you get for free.

Here’s why. In a batch configuration with a six-week lead time, when something goes wrong it may be six weeks before you find you have a problem, when you go to assemble the final product. At this point it is very hard to determine what went wrong. Let's imagine that you get lucky and can narrow down the problem to something that happened in department number 5. So now you go to department 5 and you find that the part could have been made on any of 10 different machines. It could have been made on one of two different shifts by a total of 20 different operators. In addition, you could have been using raw material that came from one of three different vendors but by the time you discover the problem you can no longer determine whose material we were using. Pretty tough problem to solve at all let alone get a permanent solution. Oh, and of course you have six weeks of bad inventory that you have to deal with in some fashion.

Once you have the product in a one-piece-flow you can see the work much easier and more immediately. Now when you discover the problem you know whose raw material you are using. You know which machine caused the problem and who the operator is. You only have ten pieces of work in process to deal with. So not only do you have all the information you need to solve the problem, but you now can get a permanent solution.

One of the key ideas in lean in any setting, manufacturing or non-manufacturing, and which one-piece-flow supports, is that you build quality into the product at every station in the line as opposed to trying to inspect quality at the end. It’s a simple and powerful shift in how people think about their work. Never pass a defect down the line.

The views expressed in this post do not necessarily represent the views or policies of The Lean Enterprise Institute.
Keywords:  flow,  manufacturing
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15 Comments | Post a Comment
Shermaine - January 13, 2016

Good article.

How about transactional world? We should apply one-pieces-flow on it as well??

e.g. Payroll running by monthly basis. All data maintenance is not urgent to update into system immediately. It can be waited and gathered together for next step. 

Mass checking and mass upload data into system will more fastter and save time compared with doing one-by-one.

 

 

 



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Ken Hunt January 13, 2016

Shermaine,

Absolutely yes! WIP is WIP and inventory is inventory regardless of the environment. I have consulted/facilitated many Kaizen events in the office environment, and once you see 1 piece flow starting to take hold, the light bulbs come on, and the results can far exceed expectations.

Ken

 



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Shermaine - January 14, 2016

Ken Hunt,

Good that you could share me some of transactional kaizen example. So that, I can visual it. Appreciate it.



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art byrne January 13, 2016

Shermaine, thanks for your comments. See Ken's reply. He is correct. In fact one piece flow in the transaction world usually gets better results than in the manufacturing world. Your approach to running payroll once per month in a big batch is just that, batching. I have never seen a case where batching is better than one piece flow, although certain operations are inherently batch in nature. What are the payroll clerks doing the rest of the month? Does the batching lead to a lot of errors? If something goes wrong is the payroll late? I know it makes no sense to you now but if you value stream map your entire process you will start to be able to see and remove the waste. Most companies in the transactional world are more prone to just automate the waste with a new even bigger, more complex and more expensive systems. Good luck.



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Shermaine - January 14, 2016

Art Byrne, thanks for your replied. One piece flow, it is mean that the good process is data should be verified and maintained into system one by one??

Bascially, the payroll clerk is verify the data generated from system vs report sent from another team in month end. The rest of month, payroll clerk is doing other job which not related with payroll. And you are right that if something goes wrong it may cause the payroll late. However, there is another team in charge to maintain the data into system by batch as well.

In transactional world, a lot of stuff is related with systems. usually, we will go to upgrade system or change the system configuration to eliminate those manual checking step. Then it is a right direction?? Thanks

 



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art byrne January 14, 2016
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Shermaine, without knowing your system it is hard to give you specific answers. All I am saying is that it is very common for transactional companies to see automating everything as the one fits all solution. This often results in automating a lot of waste and just building it into your cost and quality structure. If you looked at the whole value stream step by step and removed the waste before the next automation I think you will find a lot of opportunities to improve. Once you have done this then the automation you need will be very clear and it is ok to take the automation step. 



Christin January 13, 2016

While it's a good thing that these problems are being raised, stopping the line and identifying other problems can take a long time and have a very negative impact on customer service if not addressed effectively enough. 

Is there a way to prepare systems like root cause analysis/problem solving and Total Preventative Maintenance to reduce the potential impact of shutdowns after a transistion to one-piece flow?



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art byrne January 13, 2016

Christin, thanks for your input. See Mark Graban's response and follow his advice. Toyota built its approach on the line stop principle of never passing a defect down the line. Because you can't seperate quality and productivity every time you eliminate a problem the lead time goes down and the productivity goes up. One piece flow is intended to allow you to see the problems clearly and to force you to fix them right NOW. If you want to create a strong TPM routine for every process step before you move it to a one piece flow that could help you. Unfortunately it is more likely to just create a lot of excusses and delays in moving to a one piece flow. I think you are better off to just create the one piece flow on then make sure you are ready to respond to all the problems that will pop up. Once you create the flow then fix the problems. Never go back to a batch.



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Mark Graban January 13, 2016
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Those are the classic two pillars of TPS... improving flow (just in time, reducing batches) and built-in quality. Two mutually supportive concepts.

http://www.toyota-global.com/company/vision_philosophy/toyota_production_system/

 



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Tim January 13, 2016
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It's important to note that, while quality improves by implementing one piece flow due to mitigating risk (batch-at-a-time quality issues vs one-at-a-time quality issues), you must make the conscious, deliberate decision to act more quickly on quality issues as they occur. In this way, your management team leverages the reduced time from defect creation to defect detection to improve your root cause analysis and corrective actions.  This supports making the continuous, incremental quality improvements associated with true kaizen.



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art byrne January 13, 2016
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Tim, you are right of course to say that putting things in a one piece flow shortens the time from error identification to solution. I'm not so sure you have to say that in order to do this you have to "make a deliberate decision to act more quickly". After all, one piece flow should in effect force you to act imeadiately. If one machine shuts down the line stops. If a defect is passed to the next operation the line should also shut down until the reason is found and eliminated. a one piece flow line should be designed to never allow a defect to pass to the next step in the process. The only "deliberate decision" needed is "Hey, the line stopped, fix it, NOW."



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Tim January 20, 2016
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You do have to make the deliberate decision to act more quickly, because if you do not properly support your one-piece flow line with people who are capable of solving the specific version of the problem of "hey, the line stopped, fix it, NOW." (as you put it), then shop floor management naturally buffers with inventory.

Remember, one piece flow highlights the problems with your process.  It doesn't fix them by itself.  Implemetning one piece flow without thinking about how to support it can be disasterous.



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Art byrne January 20, 2016
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Tim, thanks for the clarification. Your right if you don't support you one piece flow lines you will have a problem. I think I may have taken your "deliberate decision" comment the wrong way. My apologies. Art.



Alan Rocker January 14, 2016
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One of the messages of "The Goal" (1984) was that cost accounting can create perverse incentives. Is it still doing so? Pervese incentives guarantee perverse results.

There seems to be a lot of "cargo-cult" thinking about accounting rules; "MegaCorp uses <insert fashionable buzzword here>, therefore we should". (Just because they're big, not because it makes any sense.)



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art byrne January 14, 2016
1 Person AGREES with this reply

Alan, thanks for your input. I think of standard cost accounting as the "anti-lean." The reason is that it incentivises all the things that lean is trying to get rid of. For example, absorption accounting incentivizes building inventory as it will help this months results look better while lean is trying to reduce inventory to free up cash and expose the waste. It also gives product cost information out to four didgets that almost no one in the company, except the accountants, beleives is correct. it will tell you your labor cost is less than 10% when it is really 34%. I think you get the point. If you are serious about lean one of the things you need to do early on is get rid of your standard cost accounting system.



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