A car plant runs several workshops in a row: a press shop that starts the process, a body shop, a paint shop and assembly halls. A car is made of thousands and thousands of parts, and cars are built in very big factories, where people and machines make many cars every day.
Every new car starts as a drawing. Designers go from sketches to clay models to hand-built prototypes before the factory builds a new car, and the big clay models are cut and shaped by hand. A new car model takes about three years or more from the first sketch until it is on the factory line.
The press shop begins with big rolls of steel or aluminum, which are cut into flat pieces before they are pressed into shape. In stamping, a press forms a flat blank into a body part in several stations, and an overhead crane moves the right die into place. The parts are doors, side panels and other body pieces, stacked for the body shop. A press line can run up to 18 strokes a minute, and one press shop can make more than 10,000 car parts in a day.
Some makers now cast big sections instead of stamping and joining many pieces. Tesla says the front and rear sections of the early Model 3 each had more than 70 parts. On the very similar Model Y each is now one cast part. A cast part is made by injecting molten aluminum into a die, cooling and ejecting it, and trimming it. It is hard to do well because a single flaw can ruin the whole piece. Casting a big car section also needs a special aluminum alloy. Tesla developed one that lets it skip a heat-treating step after casting.
In the body shop, robots are many. A modern body shop line runs 400 to 600 six-axis robots, and BMW's Spartanburg plant says more than 2,000 robots work in its body shop. In 2021 about one million robots worked in car factories around the world, roughly one third of all industrial robots.
Robots in car factories are not new. A robot called Unimate was put to work in a General Motors factory in 1961. The first Unimate robot unloaded hot finished castings from a die-casting press, a dirty and dangerous job that people did not want.
Not every body is steel. A 2015 Ford F-150 pickup truck had a body and cargo box made of aluminum, which helped make it lighter than the steel one before it. The frame stayed high-strength steel while the body panels and cargo box moved to aluminum, so the truck mixes two metals.
The paint shop builds up layers: corrosion coats, a primer, a base color coat and a clear coat. At BMW's South Carolina plant a body gets five coats and the whole painting process takes about 12 hours. Primer is the layer that makes the surface smooth and even, so the color goes on well. The base coat gives the car its color, and the clear coat on top protects the color from sunlight and from air that can dull it.
The last stop is assembly. Cars move along a line from station to station while workers and machines add parts to them. The word marriage is used in car factories for the moment the car body is joined with its engine, axles and other mechanical parts.
A modern car plant cannot work without computer chips. Cars are loaded with chips that are not the same as the chips in phones and computers, so carmakers must compete with consumer electronics for chip supply. In 2021 a shortage of chips made carmakers stop work and cancel shifts.
A battery for an electric car is a stack of many cells, and each cell has two sides that are kept apart, with a liquid between them. A battery cell is made by coating slurries onto foil, cutting the foil to size, layering it with a separator, adding liquid electrolyte, and aging the finished cell. Completed cells are put together into modules, and several modules make up a battery pack.
At the end of its life a car goes back into the supply of steel. Old cars are recycled, and their steel is melted and made into new steel, which can become cans, appliances, buildings or new cars. Recycled steel is as good as new steel, and all new steel contains some recycled steel because scrap is a necessary ingredient. Cars are the most recycled thing people buy, since nearly all the cars that leave the road are recycled.
Words to know
- stamping: pressing metal
- primer: first paint layer
- alloy: mixed metal
- marriage: body-engine joining
