How is a car made? It starts as flat metal. 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. 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. Body parts are made from big rolls of steel or aluminum, which are cut into flat pieces before they are pressed into shape.
The press shop begins with stamping. Stamping places flat sheet metal, as a cut blank or from a coil, into a press where a tool and die surface forms it into a new shape. It includes punching, blanking, embossing, bending, flanging and coining, and it can be a single stage, where each press stroke gives the form, or a series of stages. In a car plant 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. As of November 2026, 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.
Hydroforming is a fundamentally different method of shaping metal, because in stamping a press and a die surface form the sheet, while hydroforming uses high-pressure hydraulic fluid to press room-temperature metal into a die. It shapes ductile metals such as aluminium, brass, low-alloy steel and stainless steel into lightweight, stiff, strong pieces. The car industry is one of its largest uses, because it allows complex shapes in unibody structures.
Die casting is a third way to make a metal part, and it works with molten metal. It forces molten metal under high pressure into a mold cavity. The cavity is formed by two hardened tool-steel dies, which work much like an injection mold, and most die castings are made from non-ferrous metals such as zinc, copper, aluminium, magnesium, lead, pewter and tin-based alloys. Tesla uses giant machines to cast big parts of a car body from molten aluminum in one piece, and as of November 2026 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.
Big castings have trade-offs. Voids can form inside big castings, the scrap rate is higher, and changes to the tooling are very costly. 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. A big car section also needs a special alloy, and Tesla developed one that lets it skip a heat-treating step after casting.
The body shop is where the separate parts are joined into a complete body. The stage it produces is called body in white. Body in white is the stage in which a car body's frame has been joined together, before painting and before the motor, chassis sub-assemblies or trim go in. The joining uses spot, MIG/MAG or friction stir welding, riveting, clinching, bonding and laser brazing, so one body combines several joining methods. Robots work in this shop in large numbers. A modern body-in-white line runs 400 to 600 six-axis robots, while BMW's Spartanburg plant says more than 2,000 robots work in its body shop.
Two ways to join a car body are welding methods. Spot welding joins sheet metal with heat from electrical resistance, and two copper-alloy electrodes clamp the sheets together and concentrate a large current into a small spot, which melts the metal to form the weld. The sheets are typically 0.5 to 3 millimeters thick, which covers most car body panels. Another is laser beam welding, which uses a concentrated heat source that allows narrow, deep welds at high welding rates, and it is frequently used in high-volume work that needs precision and automation, as in the automotive and aeronautics industries.
Next the body goes to the paint shop, where a car's paint is put on in layers, not all at once. A paint shop applies corrosion coats, a primer, a base color coat and a clear coat. Primer is the layer that makes the surface smooth and even, so the color goes on well, and 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. Modern automobile paint has a total thickness of around 100 micrometers, or 0.1 millimeter. At BMW's South Carolina plant, a body gets five coats and the whole painting process takes about 12 hours, as of November 2026.
Early Model T bodies were painted with several coats of varnish. Each coat had to dry for a long time before the next one could go on. The cars were stacked for drying for 24 hours after each step. Faster-drying paints came only in 1922.
Last comes final assembly, where the painted body is finished. Cars move along a line from station to station while workers and machines add parts to them. Before Ford's moving line, workers built each car by hand while it stayed in one place, and Ford's moving assembly line first ran at his Highland Park plant in Michigan in October 1913. Ford first tried the line on a small part, since a magneto took 20 minutes to build before the line and only five minutes after it. The Model T line then kept getting faster, so that at first it cut the build time from 12.5 hours to under 6, and within a year to 93 minutes.
A car's story does not end when it leaves the road for the last time. Old cars are recycled. 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, and nearly all the cars that leave the road are recycled. So the steel that was pressed and welded into one car can eventually become part of the next one, which closes the circle from raw metal to finished car and back to raw metal again.
Words to know
- hydroforming: fluid-pressure shaping
- stamping: pressing metal
- voids: empty pockets
- unibody: one-piece body
- electrodes: current carriers
