(EN) How to Turn Your Car for Assembly—Part 1

In this small blog post series I will do a deep dive on one aspect of automotive assembly—namely, how to position the car for assembly. While not all of you assemble cars for a living, understanding the approach on walking distances may be helpful to optimize other production systems. Read on …

Introduction

Cars are comparatively large products. Hence, they need more space on the assembly line in comparison to smaller products like a printer or a chair. On the other hand, multiple people can work on the product at the same time, which would be more difficult when assembling a printer.

The image below shows common locations in car assembly, specifically the left front, the right front, the left rear seat, the right rear seat, the front (usually the engine compartment), and the rear (usually the trunk). Do note that normally the car doors are added pretty late in the assembly process, as they would otherwise be in the way and could be damaged. If the car is elevated, then there are also two positions underneath, one for the front axle and one for the rear axle, although in this case there are usually no people working on the top part of the car (albeit there are some examples where people work both around and under the car at the same time, as in the historic image of the VW Beetle assembly from 1973).

These positions are common, albeit of course variations exist, and some companies have two people working on the right and left front respectively instead of one person working on the entire front. See for example the picture below.

In general, you can add multiple people around larger products, as long as they do not hinder each other while assembling or while getting the next part to assemble. If one worker accidentally whacks a larger part against another worker, you may have a work-related injury to deal with, possibly also a damaged part, and almost certainly a delay in the production.

Industry Status

Most assembly lines in industry have the cars bumper to bumper. But some also have them door to door. For example, in the Mitsubishi plant in Okazaki, they have a Tatami conveyor (see my blog post The Grand Tour of Japanese Automotive – Mitsubishi for more). In Toyota Georgetown, they call this “chassis bias,” and they assemble the drivetrain (the “marriage”) as well as most of the underbody sideways. But most of the automotive industry still has a bumper-to-bumper-style assembly line.

Walking on a Moving Platform

So, the question is, when to turn the car which way? The answer is mostly (but not exclusively) related to the walking distance for the operators. Walking is waste, and the shorter the walk, the more value add is possible within the takt time.

There is a slight difference between a moving platform assembly line where the worker “joins the ride” and is moved along by the platform or inside the car, and an assembly line where only the car is moved and the worker has to walk along the moving car. If only the car moves, the worker has to walk along with the car for one station (his station), and then has to walk back one station. In other words, the total length traveled is two station lengths (assuming the worker uses the entire cycle and does not complete his tasks earlier).

On a moving platform assembly line, however, the worker is moved along with the car. On the way back, he still has to move two station lengths, walking against the moving platform. Hence, the total distance traveled is still two station lengths… unless he walks back after getting off the moving platform! In this case he is carried along with the platform in the direction of the flow, and must walk back only the length of one station outside of the moving platform. So generally, moving platforms can cut the sideways walking in half if the operator walks back after getting off the moving platform.

The same applies if the car is moved not bumper to bumper but door to door, as shown below, except that the station is only half as wide (the width of one car plus the space to the next car). So, at a first glance, a door-to-door movement would cut the walking distance from the length of a car plus the distance (average around 4.9 meters car length plus distance) to the width of a car plus distance (average 2 meters plus distance, so a total saving of 2.9 meters every cycle).

Moving In and Out Between the Vehicles Bumper to Bumper

However, this applies only if the worker works on the side of the car facing the edge of the assembly line. If the worker has to work between the cars, the worker has to move in and out between the cars. And he has to do this not only once per cycle, but every time he has to get a part from the side of the assembly line! (Hint: Moving tool carts can and do significantly reduce these walking times.) If the car is assembled bumper to bumper as shown below, the in-and-out walking for working on the front or rear of the car is around half a car width (about one meter), as shown below for the second worker.

In my next post, I will turn all of this sideways—in other words, door to door instead of bumper to bumper. This will increase the walking distance between the cars by around two meters every time someone has to walk between the cars, and there is often more work between the cars than to the side. I will also talk about tool access and space for material. Now, go out, see if turning your parts on the assembly line will reduce walking and improve efficiency, and organize your industry!