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Flexible Assembly Lines

Flexible assembly lines are well known at Toyota – except that there are two types of “flexible assembly lines.” The well-known one is making multiple different models on the same line. But Toyota has developed a new type of flexible assembly line, where the entire layout of the assembly line can be changed quickly and easily. Confusingly, this is also called a flexible assembly line, although Toyota itself does not even have a name for it (different from the West, Toyota focuses more on doing something, while the West often puts the most effort into a catchy name). Their pilot line is in the Takaoka plant. Let me show you.


Introduction

Toyota pioneered the concept of having multiple models on the same assembly line, with such lines being common at Toyota already in the 1990s. Many tricks, like a triangular clamping base that simply rotates depending on the model, were used. A common platform nowadays also helps. This is commonly called a flexible assembly line.



Toyota is starting to roll out a new type of assembly line, where the flexibility is not (only) in the car models that can be made, but in the ability to change the line itself. The line can be made longer or shorter, and its routing can be changed. Toyota developed the concept in the last few years. I first wrote about this new type of flexibility four years ago, in early 2018, in my post Continued Evolution of the Toyota Assembly Line, which was already an evolutionary step from adding small buffers in the line. But it is time for an update. Toyota is using this new type of flexible assembly line in the Takaoka plant at line #2.


Why Do You Want to Change Your Assembly Line?


Flexibility allows us to handle fluctuations (mura). If possible, you should reduce fluctuations. However, if the fluctuations come from the customer, it is not always possible to reduce them, and then you have to handle it. The old type of flexible lines allowed multiple models on the same line, allowing the shifting of available capacity among different products, in the hope that a higher demand of one product is compensated by a lower demand of another product. The new type of flexible line allows the ramp-up and ramp-down of the capacity of the ENTIRE line by making the line (or critical segments of it) longer or shorter. Hence, one reason for such a new flexible assembly line is to adjust capacity to the changes in demand easier. This can also be done by increasing and reducing the work time (with the hard maximum limit of “around-the-clock” production). But it may be better to keep working times more stable, avoid an unpleasant and expensive third shift, and instead change the line.


A second reason is design changes or new models. Let’s make an example. Assume your assembly line is optimized for your current product line-up. On this line, the dashboard installation has just as much space as it needs. But now there is a model or design change, and the dashboard installation requires more time (e.g., you add a heads-up display). You can’t add more people, since there is no space. If you run the line slower, all other people on the line will have to wait for the slower dashboard assembly, and your capacity goes down too. If you want to create space, you have to rip out all the machines, move them by two meters, and put them back in, which will be expensive…unless you have a new type of flexible line where you merely unplug and pop up the machines, move them two meters, put them down, and plug ’em back in. Hence, this flexibility allows you to adjust the line layout to changes in a stations workload.


Finally, what if your wheel-installation robot has a serious breakdown, and it will take a week to get spare parts and fix it? Do you stop the line? At a new flexible assembly line, you can simply remove the robot from the line and add a few people who can take over until the robot is operational again. Hence, you may be able to quickly replace broken machines/robots with human workers and vice versa. Toyota believes that the flexibility of human operators is often worth the cost compared to a machine.


Other Ways and Examples

If you are running a "Single-Piece-Flow" line where you have Team Members moving product from Station to Station until you have a finished good, you can flex through-put to match Customer Demand by adjusting just how many Team Members are active within the Cell.


I personally have used "Indexed Lazy Susan's" where each pick face contains the components needed for a particular style. Yes, you may have redudancy of components on each indexed "Pick-Face" but with a simple swipe of the hand you have accomplished a change-over without losing momentum.


New Flexible Assembly Line at Toyota


Toyota is changing that – first at a pilot plant north of Sendai, and in a full-scale implementation at one of their main plants, with line #2 at Takaoka. The cars at the Takaoka #2 all move on AGVs, going from workstation to workstation. Machines are still bolted to the ground, but they no longer need large holes in the floor to place them. Instead, they are often on wheels for easy movement. One thicker cable is used instead of many small ones. Moving machines and the material flow around is easy. There is no overhead structure that would need expensive reconstruction. The lights and ventilation pipes (and a roof, of course) are usually the only things over the line. Below is a model of such an improved Toyota assembly line.


Now, go out, make your line more flexible in any way you can, and organize your industry!

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