Historians argue about what Ford really added. His assembly line was revolutionary though not original, since it had been used at slaughterhouses. His most original contribution was breaking complex tasks into simpler ones with specialised tools, which made parts interchangeable and let the line change its components for the product being assembled. Charles Sorensen, who worked at Ford, wrote that Henry Ford is generally regarded as the father of mass production, but was not: he was the sponsor of it. Sorensen described a gradual, logical development of industrial engineering rather than individual inventors, and Ford's moving line was an evolution by trial and error by a team, not the work of one inventor. Ford's line combined standard parts with more efficient assembly. Together they raised output per worker and let Ford cut the cost and price of the Model T. Fordism rested on three principles: standardized products made by machines and molds, assembly lines using special-purpose tools so common-skilled workers could contribute, and higher 'living' wages so workers could afford the products they make.
The idea of a moving line came from older industries. The meatpacking industry of Chicago is believed to be one of the first industrial assembly lines in the United States, starting in 1867. Workers stood at fixed stations, and a pulley system brought the meat to each worker, who completed one task. At Ford, the assembly line was introduced by William 'Pa' Klann after he visited Swift and Company's slaughterhouse in Chicago and watched a 'disassembly line', where carcasses were butchered as they moved along a conveyor. Ransom Olds had earlier put each chassis on a stand with casters in what he called progressive assembly. The car was moved from station to station by hand, rope or chain, so it was a line but not a continuous, powered one. Ford borrowed from older industries when he made his line, and writers point to meatpacking and brewing, where work already moved past workers who each did one job. After the 1913 trial with a rope and winch, Ford added a powered conveyor, and the line kept being rebuilt and improved.
Breaking complex tasks into simpler ones cut down on the manpower the factory needed and deskilled the labour itself, which cut the cost of production. The work on a moving line was monotonous. Ford's workers quit and missed work in large numbers, which was part of why he raised pay. Ford substantially increased his workers' wages to combat absenteeism and employee turnover that approached 400 percent a year. Historians do not agree on one reason for the $5 day. Accounts say it was to keep workers who might quit, to hire better and steadier workers, or both. A byproduct was giving workers the means to become customers. In 1914 Ford began paying workers $5 a day, more than twice what most carmakers paid. Ford's high pay was later described as part of a 'virtuous cycle': when workers get more productive, wages can rise, and workers then have more money to buy products.
The story of the black Model T is also disputed. Many people think the Model T was always black, but it came in colors in its early years and again in 1926-27. One account says the line was so successful that only japan black would dry fast enough, until fast-drying Duco lacquer was developed in 1926. But the story that it was black because black paint dried fastest is not supported by Ford engineering documents or employee accounts, according to Products Finishing, and Ford's own history page calls it hard to confirm. Other reasons given for Ford's all-black Model T include that black was cheap and durable, and that it saved time because production did not have to stop to change paint. In the black years the Model T's paints were really color varnishes, and more than 30 kinds of black paint were used at once. Early Model T bodies were painted with several coats of varnish, and each step had to dry for a long time before the next.
Toyota's low inventory is an outcome of its system, not its starting point. Many Western businesses attacked high inventory levels directly without understanding what made the reductions possible, and imitating without understanding may have led those projects to fail. Toyota's way of building cars rests on two ideas: just-in-time and jidoka. Sakichi Toyoda built a loom that stopped by itself when a thread broke, and this idea became jidoka. Toyota's system was built over years by trial and error. Taiichi Ohno is credited with building it, and Kiichiro Toyoda is credited with the just-in-time idea from the 1930s. The Toyota system addresses eight kinds of muda, or waste, and overproduction is the largest of them.
The idea behind kanban predates Toyota. The simplest visual stock-replenishment signal, an empty box, was first developed in UK factories producing Spitfires in the Second World War as the 'two bin system'. In the late 1940s Toyota began studying supermarkets to apply shelf-stocking techniques to the factory floor. Taiichi Ohno saw the supermarket as the model for what he wanted in the factory, and a customer takes the desired amount of goods off the shelf while the store restocks enough new product to fill the shelf space. In the 1960s Shigeo Shingo applied the term poka-yoke to industrial processes designed to prevent human errors. Taiichi Ohno developed kanban to improve manufacturing efficiency, and it takes its name from the cards that track production within a factory. Kanban aligns inventory levels with actual consumption. When material is consumed, a signal tells the supplier to produce and deliver a new shipment.
Steel rusts, so a car body is protected in layers before the color goes on. Before the color goes on, a car body gets a chemical pretreatment. A phosphate coat protects the body against corrosion and prepares the surface for the E-coat. In the electro-coat tank a high-voltage current makes the body a cathode and the paint an anode, so the paint sticks to the metal surface, and the process uses the paint very efficiently, at about 99.9 percent. Galvanizing adds protection with a zinc coating, whose main function is to act as a sacrificial anode. Zinc is more reactive than iron, so the zinc coating preferentially oxidizes to zinc carbonate and keeps the iron from corroding, even if there are gaps in the coating. Electrogalvanized sheet steel is often used in automotive manufacturing to improve the corrosion performance of exterior body panels.
Paint chemistry has changed as mass production changed what factories needed. Hand-painting early Model Ts was slow because each coat had to dry. The cars were stacked for drying for 24 hours after each step, and one source says faster-drying paints came only in 1922, while another dates fast-drying Duco lacquer to 1926. As mass production of cars made slow drying untenable, paint began to be dried in ovens. Today two-component paint is usually applied by robotic arms and cures in a few hours. Lead, chromium and other heavy metals and toxic oil bases were used until environmental laws prohibited them, moving the industry to water-based paints. Modern automobile paint is applied in several layers with a total thickness of around 100 micrometers, or 0.1 millimeter.
Spot welding has side effects. It joins sheet metal with heat from electrical resistance, but the process tends to harden the material and can warp it. This reduces the material's fatigue strength, and the metal may also be stretched and annealed. Spot-welding guns come in two layouts. The C-type is rigid and is used for thick material and high forces. The X-type, whose electrodes move like scissors, is less rigid but reaches a far larger workspace, so it is common on thin, flat parts such as floor pans and roof panels.
Laser welding has its own refinements. Laser beam welding uses a concentrated heat source that allows narrow, deep welds at high welding rates. In remote laser welding, a laser scanner moves the beam along the seam, so the robot arm no longer has to follow the seam itself. The traditional method moves the laser output along the seam, usually with a robot, and the scanner method gives higher speed and higher precision. Laser-hybrid welding combines a laser with an arc method such as gas metal arc welding. The arc supplies molten metal to fill the joint, which gives more positioning flexibility, while the laser raises the welding speed above what arc welding alone allows. Weld quality also tends to be higher because undercutting is less likely.
Casting trades fewer parts for more risk. Tesla says the front and rear sections of the early Model 3 each had more than 70 parts, and on the very similar Model Y each is now one cast part, as of November 2026. A cast part is hard to do well because a single flaw can ruin the whole piece. Voids can form inside big castings, the scrap rate is higher, and changes to the tooling are very costly. Large casting is spreading beyond Tesla. Other automakers have announced investments, and Honda's six 6,000-ton machines in Ohio will cast its largest parts ever, though voids inside castings could pose structural risks, as of November 2026. Casting a big car section needs a special aluminum alloy, and Tesla developed one that lets it skip a heat-treating step after casting. By late 2019, press machines capable of die casting single pieces over 100 kilograms (220 pounds) were being used to produce aluminium chassis components for cars.
A robot called Unimate was put to work in a General Motors factory in 1961, and it took over a hot, dangerous job that people did not want. The first Unimate robot did a job that was dirty and dangerous: it unloaded hot finished castings from a die-casting press. Unimate robots were later used for welding on car bodies, a hazardous job that Japanese makers also struggled to fill with people. The first factory robot began with the kind of job that was hard on the people who did it.
George Devol thought of the Unimate, and he filed a patent for 'a general-purpose manipulator for performing repetitive tasks' two years before the robot's 1961 debut. Even the price of the first car-factory robot is argued over. Sources disagree on Unimate's price: IEEE says GM paid $18,000 for the first one, and Guinness says it cost $25,000 when new. In 1969 Victor Scheinman at Stanford invented the Stanford arm, an all-electric, 6-axis articulated robot that could accurately follow arbitrary paths in space. This widened robots' use to more sophisticated applications such as assembly and welding.
An electric car carries a battery that 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 battery cells are put together into modules, and several modules make up a battery pack. Making batteries takes a great deal of energy. About 67 megajoules are needed per kilogram of lithium-ion battery. One 2019 study estimated 73 kg of CO2e per kWh, but the figure depends strongly on the energy source used and is difficult to estimate. Effective recycling can reduce the carbon footprint of production significantly.
Car making still has open questions. Historians do not agree on one reason for Ford's $5 day: accounts say it was to keep workers who might quit, to hire better and steadier workers, or both. The story that the Model T was black because black paint dried fastest is disputed, and Ford's own history page calls it hard to confirm. Sources disagree on Unimate's price: IEEE says GM paid $18,000 for the first one, and Guinness says it cost $25,000 when new. The carbon cost of making a battery is hard to estimate, because it depends strongly on the energy source used.
Words to know
- deskilled: made less skilled
- muda: waste
- annealed: heat-softened
- inventory: stock on hand
- kanban: tracking cards
