In my previous post on the automotive assembly line I showed how the earliest chain-driven assembly lines evolved to modern moving platforms. However, in automotive assembly, you also need to work underneath the car. While I have seen truck assembly lines where the entire undercarriage is flipped on its back, in automotive, this is usually done while the car is hanging. Let’s have a look how this is done, and then I’ll wrap up this post with the last bit of the assembly line where the car stands on its own wheels.
Overhead Line
When building a car, you sometimes have to work underneath the car. In the past, they did this like older maintenance facilities: they merely dug a hole and put workers in there, as you can see here for the VW beetle in Wolfsburg in 1973. But this requires you to dig a deep hole in your factory floor, which may not work with whatever is underneath. You also need to put a poor worker into the hole AND provide him with material down there. This is a lot of headache for safety and logistics. It also makes it more difficult to relocate the station, as you have to fill in one hole and dig another one.
It is much better to hang the car from an overhead railing system, as shown here for the 1968 BMW plant in Munich, and many other pictures. In such a hanging system, you can adjust the height to suit the needs of the operator and hence improve ergonomics, safety, and efficiency.
If you put it low enough, you can even work on the sides or the engine or the passenger space inside of the car. However, the hanger system may be in the way, depending on what you want to to assemble. For example, I imagine that it would be tough to insert seats or the dashboard when the hanger is in the way.
C-Hangers
However, overhead work is tiring. Holding your hands over your head for eight hours per day is quite stressful and demanding, and pretty much impossible without rest. Hence, about 20+ years ago, the hanging line got a new modification: the ability to roll the car sideways. At Daimler these are called C-hangers, since the big rotating clamp looks like a gigantic letter “C.”
Depending on the car maker, some of these hangers can rotate 45%, 80%, or even a full 90% sideways. Now the worker no longer has to work overhead, but at a much more comfortable angle. The worker no longer has to work “on the ceiling,” but “on the wall.” This is much easier to do and hence also more efficient.
At the VW Gläserne Manufaktur in Dresden, these hangers can even rotate in two directions (roll and yaw). Similar to the Mitsubishi rotation of the car, this makes it easier to access the front or side of the car, depending on which one is rotated closer.
Automated Guided Vehicles (AGV)
The latest innovation in automotive assembly lines is the use of automated guided vehicles (AGV) to move the car bodies. This usage of a self-driving vehicle for automotive car bodies seemed to start around 2015, albeit AGV for transporting other material date back decades.
While initially more expensive, these AGV are becoming cheaper. They give the assembly line an unprecedented flexibility. Each car body can move at its own speed. The distance between cars can vary (which, for example, Fendt uses very well to handle some of its variability through their Variable Takt). A car body can even move completely outside of the assembly line if there is a need to go to a repair station. I have seen the use of AGV in quite a few assembly lines by now, from Porsche to farming vehicles. In automotive, however, it is usually only a part of the line that uses AGV, and rarely the entire line. While there is an obvious need for hanging systems to do overhead work, in automotive I have seen AGV usually combined with moving platforms for other segments of the line.
At the End on Its Own Wheels
For completeness’ sake, there is also the possibility to put the car on its own four wheels on a conveyor belt. Such a conveyor belt is much easier to loop around compared to the moving platform. The loop of the belt simply goes back underneath of the assembly line. This is common in automotive assembly lines for the end of the line, after the wheels have been installed. It is also often used for quality control after the assembly has been completed.
It is simply cheaper than a moving platform. On the downside, standing on a metal platform for the entire workday can be tiring. But for the last few years, pretty much all automotive assembly lines have this system before the car is driven off the line (hopefully) under its own power.
This concludes the different ways cars are moved on the assembly line. Of course, the way to move them is only one aspect of an assembly line. I have, for example, written in the past about the Evolution of Toyota Assembly Line Layout at Motomachi, as well as the evolution of flexible reconfigurable assembly lines at Toyota. In any case, I hope this very visual tour through history and the way to move an automotive assembly line was interesting to you, even if your products may not be cars. Now, go out, get your material moving, and organize your industry!