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assembly line

industrial engineering
Also known as: continuous production system, production line
Written and fact-checked byThe Editors of Encyclopaedia Britannica
The Editors of Encyclopaedia Britannica
Encyclopaedia Britannica's editors oversee subject areas in which they have extensive knowledge, whether from years of experience gained by working on that content or via study for an advanced degree. They write new content and verify and edit content received from contributors.
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Table of Contents
Toyota assembly line
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Robotic welding on the automobile assembly line at the Toyota Motor Corporation, Japan.
Courtesy, Toyota Motor Corporation

assembly line, industrial arrangement of machines, equipment, and workers for continuous flow of workpieces in mass-production operations.

(Read Henry Ford’s 1926 Britannica essay on mass production.)

The design for an assembly line is determined by analyzing the steps necessary to manufacture each product component as well as the final product. All movement of material is simplified, with no cross flow, backtracking, or repetitious procedure. Work assignments, numbers of machines, and production rates are programmed so that all operations along the line are compatible.

Vintage engraving from 1878 of the spinning room in Shadwell Rope Works. View of the factory floor. Industrial revolution
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An automotive assembly line starts with a bare chassis. Components are attached successively as the growing assemblage moves along a conveyor. Parts are matched into subassemblies on feeder lines that intersect the main line to deliver exterior and interior parts, engines, and other assemblies. As the units move by, each worker along the line performs a specific task, and every part and tool is delivered to its point of use in synchronization with the line. A number of different assemblies are on the line simultaneously, but an intricate system of scheduling and control ensures that the appropriate body type and colour, trim, engine, and optional equipment arrive together to make the desired combinations.

Automated assembly lines consist entirely of machines run by machines, with little or no human supervision. In such continuous-process industries as petroleum refining and chemical manufacture and in many modern automobile-engine plants, assembly lines are completely mechanized and consist almost entirely of automatic, self-regulating equipment.

Many products, however, are still assembled by hand because many component parts are not easily handled by machines. Expensive and somewhat inflexible, automatic assembly machines are economical only if they produce a high level of output. However, the development of versatile machinery and the increased use of industrial robots have improved the efficiency of fully automated assembly operations.