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Production method requiring workers to perform a repetitive task on a product as it moves along on a conveyor belt or track. An assembly line has the advantages of part standardization and rationalization of work. See also Assembly Plant.
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The assembly line is often described as a process that uses machines to move material from one place to another, but in practice, machines are not always needed. For instance, mass-market jewelers often use assembly lines in which materials are handed from one worker to another, without the benefit of machinery. At its most basic, an assembly line is a series of stations at which people or machines add to or assemble parts for a product. One of the values of the assembly line is its versatility: it can be simple, but it has the capacity to be very complex. An assembly line can begin as many different lines each devoted to a different component of a product, with the lines converging upon one another, becoming fewer until only one line is left for the final product. Automotive companies often have assembly lines that begin with raw materials and end five miles away with a completed automobile. A structure for a complex assembly line begins as one main line with stations along it that are fed by lines running perpendicular to it, with each of these side lines feeding components for the finished product. Although the assembly line has occasionally been considered outmoded, it has survived by repeatedly changing its form.
Foundations of the Assembly Line
The idea of the assembly line has many parents. In the scientific revolution of the eighteenth century, scientists, especially mathematicians tried to quantify what made an industry productive and tried to find ways to make industries more productive. The goal was to create an industry that functioned without human labor. The most important people of the time for the development of the assembly line were the Americans Oliver Evans and Eli Whitney and the Frenchman Gaspard Monge. Evans is known for his invention of the first motorized amphibious vehicle, but his most influential achievement was to design a flour mill. During the late eighteenth century, he used steam engines to power mills that used belt and screw conveyors, as well as moving hoppers, to move grain through the process of becoming flour and then to move the flour to where it could be packaged. While his equipment was not exactly an assembly line, all the basic components were there.
Best known for creating the cotton gin, Eli Whitney also contributed to the development of the assembly line with his invention of interchangeable parts. Whitney created machine tools that could create parts so closely resembling each other they could be substituted for one another without harm. In 1798, the United States government ordered 10,000 muskets, and in a preview of the assembly line, Whitney set his employees to work on manufacturing parts that were assembled bit by bit into muskets. A Whitney musket could be repaired in the field with spare parts.
Gaspard Monge made his contribution while in Italy during the Napoleonic era. He took the principals of descriptive geometry and applied them to machinery. By breaking a machine down into its component parts, Monge found that he could show how each part related to the others; this would evolve into technical drawing, which allowed people to make machines they had never seen, machines that would share interchangeable parts with any other machine made with the same diagrams.
Henry Ford
Making automobiles was a hobby for many Americans, and Henry Ford began as a hobbyist, but he brought to his hobby an unsurpassed ambition. In 1899, he started his own automobile manufacturing company; he wanted to produce cars in large enough quantities to make them available to everyone. In 1908, he divided up the tasks involved in manufacturing an automobile; he broke these tasks down to the function of each autoworker, conceiving of each worker as a part of a machine that made cars. At first, he tried having chassis pulled along factory floors with towropes. Men walked alongside the chassis to stations, at each station parts were added. Manufacturing time for a single automobile decreased from twelve hours to five and one-half hours. In 1913, he installed conveyor belts in his factories. With these, workers stood at their stations, each doing the same repetitive task over and over again. Manufacturing time for one car fell to around an hour and a half. At such a pace, Ford could make a small profit on each car but could make much more money from selling the cars in the millions. By The end of 1914, his employees were the highest paid industrial workers in the world; a worker performing the simplest of tasks could, and some did, become rich.
World War II
When the United States entered World War II, its heavy industries were charged with manufacturing the matériel for the armed services. The assembly line was crucial to this production. In March 1941, Ford began building a factory and, by the end of 1942, was taking in raw materials at one end, processing them, and producing B-24 bombers. By The end of the war, Ford's factory was producing B-17 bombers at the rate of one every sixty-three minutes.
General Motors made an impressive innovation with its production of chassis for combat tanks. Despite being a big and heavy machine, a tank needed to be tight in its joints and fluid in its reactions to the men operating it. With early tanks, the impact of an enemy shell might not breach the American tank's armor but would blow bolts loose in the interior, killing the people inside. The management at General Motors was not alone in realizing that the bolts had to be replaced by welds, but it was their engineers who came up with the assembly line innovation that helped make the welds succeed. Instead of using machines to do the welding, they employed human welders as craftsmen; they created an enormous machine that could pick up a tank chassis and tilt it quickly to any angle the welders wanted. The assembly line station became a craftsman's shop, with the line responding to the workers rather than the workers just being parts of the machine. Decades later, the Japanese manufacturer Toyota would use a similar machine to weld its automobile chassis, and a similar concept for the work stations. General Motors did them both first.
The assembly line affected the lives of American women. Women fit into many assembly line jobs previously only done by men. The assembly line was successful enough at relieving workers of the tasks requiring brute strength. Historians note the millions of American women who left their jobs when American servicemen returned to civilian life; not so often noted is that women workers were so good at their tasks that aircraft manufacturers and auto makers kept many of them employed to handle tasks such as wiring.
Wounded But Still Alive
The wear and tear on workers created by relentlessly repetitive physical motions on assembly lines became increasingly public after World War II. Further, factories that relied on an assembly line seemed to have become inefficient. When Japanese automakers began to make inroads into American markets in the 1970s, American industry seemed less than up to the challenge. Toyota had introduced a concept called kaizen, meaning "continuous improvement." The idea was to have assembly line workers participate in the development of a product and to suggest changes even during the production process. This idea harkened back to when Ford and Chevrolet encouraged worker suggestions, back in the late 1910s and early 1920s, saving the companies millions of dollars by pointing out inefficiencies. By the 1980s, it was known as the Toyota Production System.
Although General Motors began using robots on the assembly line in the 1960s, it was not until the 1980s that robots were extensively used on the industrial assembly line. Robots could be very efficient at doing certain repetitive jobs, and Japanese manufacturers soon led the world in using them on their assembly lines. Station workers' costs were cut, because fewer workers were needed. Yet, the overall use of robots was by 1990 becoming a failure. Many people were required to maintain the robots and program the computers that directed them. In the 1990s, Ford and Chrysler developed "value engineering," a process by which the basics of a design were kept simple, allowing them to be repeated for several different products; about 70 percent of the parts for a new car would be shared with a previous design. This allowed for quick responsiveness to the public's desires, since a plant did not have to completely retool for each different car model. This development was combined with ergonomic workstations. By Asking workers on the assembly line for ideas, manufacturers discovered that something as basic as moving a convey or belt from the floor to waist height could increase productivity and decrease injuries. With robots proving not to be complete substitutes for human beings, the comfort and care of workers became ever more important. By Creating work stations that were comfortable and by combining work stations into groups, communication among workers increased. Most manufacturers found this led to increased productivity and improvements in quality. The fundamental concept of the assembly line still remains the basis for the most efficient mass production of manufactured goods.
Bibliography
"The Arsenals of Progress." The Economist (US) 330, no. 7853 (5 March 1994): M5–7.
Chow, We-Min. Assembly Line Design: Methodology and Applications. New York: Marcel Dekker, 1990.
De Camp, L. Sprague, and Catherine C. De Camp. The Story of Science in America. New York: Charles Scribner's Sons, 1967.
Hapgood, Fred. "Keeping It Simple." Inc. 18, no. 4 (19 March 1996): 66–70.
Nof, Shimon, W. Wilhelm, and H. Warnecke. Industrial Assembly. New York: Chapman & Hall, 1996.
Scholl, Armin, and A. Siedenberg, eds. Balancing and Sequencing of Assembly Lines. New York: Springer-Verlag, 1999.
Womack, James R., Daniel Roos, and Daniel T. Jones. The Machine That Changed the World: The Story of Lean Production. New York: Rawson Associates, 1990.
—Kirk H. Beetz
| Columbia Encyclopedia: assembly line |
| Economics Dictionary: assembly line |
A line of factory workers and equipment along which a product being assembled passes consecutively from operation to operation until completed.
| Wikipedia: Assembly line |
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This article needs additional citations for verification. Please help improve this article by adding reliable references. Unsourced material may be challenged and removed. (January 2008) |
An assembly line is a manufacturing process in which parts (usually interchangeable parts) are added to a product in a sequential manner using optimally planned logistics to create a finished product much faster than with handcrafting-type methods. The assembly line developed by Ford Motor Company between 1908 and 1915 made assembly lines famous in the following decade through the social ramifications of mass production, such as the affordability of the Ford Model T and the introduction of high wages for Ford workers. However, the various preconditions for the development at Ford stretched far back into the 19th century, from the gradual realization of the dream of interchangeability, to the concept of reinventing workflow and job descriptions using analytical methods. Ford was the first company to build large factories around the concept. Mass production via assembly lines is widely considered to be the catalyst which initiated the modern consumer culture by making possible low unit-cost for manufactured goods. It is often said that Ford's production system was ingenious because it turned Ford's own workers into new customers. Put another way, Ford innovated its way to a lower price point and by doing so turned a huge potential market into a reality. Not only did this mean that Ford enjoyed much larger demand, but the resulting larger demand also allowed further economies of scale to be exploited, further depressing unit price, which tapped yet another portion of the demand curve. This bootstrapping quality of growth made Ford famous and set an example for other industries.
Consider the assembly of a car: assume that certain steps in the assembly line are to install the engine, install the hood, and install the wheels (in that order, with arbitrary interstitial steps). A train can have only one of the three steps done at once. In traditional production, only one car would be assembled at a time. If engine installation takes 20 minutes, hood installation takes five minutes, and wheel installation takes 10 minutes,f assembling a car is split between several stations, all working simultaneously. When one station is finished with a car, it passes it on to the next. By having three stations, a total of three different cars can be operated on at the same time, each one at a different stage of its assembly. After finishing its work on the first car, the engine installation crew can begin working on the second car. While the engine installation crew works on the second car, the first car can be moved to the hood station and fitted with a hood, then to the wheels station and be fitted with wheels. After the engine has been installed on the second car, the second car moves to the hood assembly. At the same time, the third car moves to the engine assembly. When the third car’s engine has been mounted, it then can be moved to the hood station; meanwhile, subsequent cars (if any) can be moved to the engine installation station. Because it takes 20 minutes to finish work on the engine while it takes only 15 minutes to complete the installation of both the hood and wheels.
The assembly line concept was not "invented" at one time by one person. It has been independently redeveloped throughout history based on logic. Its exponentially larger development at the end of the 19th century and beginning of the 20th occurred among various people over decades, as other aspects of technology allowed.
The development of toolpath control via jigs, fixtures, and machine tools (such as the screw-cutting lathe and milling machine) during the 19th century provided the prerequisites for the modern assembly line by making interchangeable parts a practical reality. Before the 20th century, most manufactured products were made individually by hand. A single craftsman or team of craftsmen would create each part of a product. They would use their skills and tools such as files and knives to create the individual parts. They would then assemble them into the final product, making cut-and-try changes in the parts until they fit and could work together (the English System).
The assembly line evolved from these artisanal shops as division of labor and specialization took place. Electrification saw further advances in elementary assembly line production in the early 20th century. As electricity was increasingly used in factories as a more reliable, smoother and more precise form of power than previously available, it provided the means for the evolution of production through the automation of the assembly line. With the creation of unit drive motors, factories could be reorganized and the modern assembly line took shape with the optimal ordering and location of different parts of the production process. Large efficiency gains from assembly line production could then be realized.
The transition from prototypical to the modern assembly line thus took place as creativity and logic took advantage of the opportunities that technological changes presented. The prototypical forms of assembly lines in various industries, are outlined below.
The Terracotta Army commissioned by the first Chinese Emperor Qin Shi Huangdi is a collection of about 8000 life-sized clay soldiers and horses buried with the emperor. The figures had their separate body parts manufactured by different workshops that were later assembled to completion. Notably, each workshop inscribed its name on the part they manufactured to add traceability for quality construction.
At the peak of its efficiency in the early 16th century, the Venetian Arsenal employed some 16,000 people who apparently were able to produce nearly one ship each day, and could fit out, arm, and provision a newly-built galley with standardized parts on an assembly-line basis not seen again until the Industrial Revolution.
Probably the first linear and continuous assembly line of post-Renaissance times were the Portsmouth Block Mills created in 1801 by Marc Isambard Brunel (father of Isambard Kingdom Brunel), with the help of Henry Maudslay and others, for the production of blocks for the Royal Navy. This assembly line was so successful it remained in use until the 1960s, with the workshop still visible at HM Dockyard in Portsmouth, and still containing some of the original machinery.
Eli Whitney is sometimes credited with developing the armory system of manufacturing in 1801, using the ideas of division of labor, engineering tolerance, and interchangeable parts to create assemblies from parts in a repeatable manner. But Whitney's contribution was mostly as a popularizer rather than "the inventor" of repeatability. He was probably inspired by several others (including Honoré Blanc), or at least by the contemporary zeitgeist that was building around such ideas. Thomas Jefferson had tried to bring a French mechanic (who was almost certainly Blanc) and his methods to America in 1785, but the project never went anywhere.[1] A few years later, Whitney and his American contemporaries succeeded in introducing the relevant concepts (interchangeable parts, toolpath control via machine tools and jigs, transfer of skill to the equipment, allowing use of semi-skilled or unskilled machine operators) to American firearm manufacture.
The meatpacking industry of Chicago is believed to be one of the first industrial assembly lines (or dis-assembly lines) to be utilized in the United States starting in 1867. Workers would stand at fixed stations and a pulley system would bring the meat to each worker and they would complete one task. Henry Ford and others have written about the influence of this slaughterhouse practice on the later developments at Ford Motor Company (see below at Ford Motor Company (1908-1915)).
The Industrial Revolution in Western Europe and North America, but perhaps most especially in Great Britain and New England, led to a proliferation of manufacturing and invention. Many industries, notably textiles, firearms, clocks and watches,[2] buttons, horse-drawn vehicles, railroad cars and locomotives, sewing machines, and bicycles, saw expeditious improvement in materials handling, machining, and assembly during the 19th century, although modern concepts such as industrial engineering and logistics had not yet been named.
Ransom Olds patented the assembly line concept, which he put to work in his Olds Motor Vehicle Company factory in 1901, becoming the first company in America to mass-produce automobiles.[3] This development is often overshadowed by the independent redevelopment of assembly-line work at Ford Motor Company a few years later (see below), which introduced the ramifications of the method to a wider audience.
The assembly line developed for the Ford Model T had immense influence on the world. Despite oversimplistic attempts to attribute it to one man or another, it was in fact a composite development based on logic that took 7 years and plenty of intelligent men. The principal leaders are discussed below.
The basic kernel of an assembly line concept was introduced to Ford Motor Company by William "Pa" Klann upon his return from visiting a Chicago slaughterhouse and viewing what was referred to the "disassembly line", where animals were butchered as they moved along a conveyor. The efficiency of one person removing the same piece over and over caught his attention. He reported the idea to Peter E. Martin, soon to be head of Ford production, who was doubtful at the time but encouraged him to proceed. Others at Ford have claimed to have put the idea forth to Henry Ford, but Pa Klann's slaughterhouse revelation is well documented in the archives at the Henry Ford Museum[citation needed] and elsewhere, making him an important contributor to the modern automated assembly line concept. The process was an evolution by trial and error of a team consisting primarily of Peter E. Martin, the factory superintendent; Charles E. Sorensen, Martin's assistant; C. Harold Wills, draftsman and toolmaker; Clarence W. Avery; and Charles Ebender. Some of the groundwork for such development had recently been laid by the intelligent layout of machine tool placement that Walter Flanders had been doing at Ford up to 1908.
In 1922 Ford (via his ghostwriter Crowther) said of his 1913 assembly line, "I believe that this was the first moving line ever installed. The idea came in a general way from the overhead trolley that the Chicago packers use in dressing beef."[4]
Charles E. Sorensen, in his 1956 memoir My Forty Years with Ford, presented a different version of development that was not so much about individual “inventors” as a gradual, logical development of industrial engineering:
"What was worked out at Ford was the practice of moving the work from one worker to another until it became a complete unit, then arranging the flow of these units at the right time and the right place to a moving final assembly line from which came a finished product. Regardless of earlier uses of some of these principles, the direct line of succession of mass production and its intensification into automation stems directly from what we worked out at Ford Motor Company between 1908 and 1913. Henry Ford is generally regarded as the father of mass production. He was not. He was the sponsor of it."[5]
As a result of these developments in method, Ford's cars came off the line in three minute intervals. This was much faster than previous methods, increasing production by eight to one (requiring 12.5 man-hours before, 1 hour 33 minutes after), while using less manpower.[2] It was so successful, paint became a bottleneck. Only japan black would dry fast enough, forcing the company to drop the variety of colors available before 1914, until fast-drying Duco lacquer was developed in 1926.[2] In 1914, an assembly line worker could buy a Model T with four months' pay.[2]
Ford's complex safety procedures—especially assigning each worker to a specific location instead of allowing them to roam about—dramatically reduced the rate of injury. The combination of high wages and high efficiency is called "Fordism," and was copied by most major industries. The efficiency gains from the assembly line also coincided with the take-off of the United States. The assembly line forced workers to work at a certain pace with very repetitive motions which led to more output per worker while other countries were using less productive methods.
Ford at one point considered suing other car companies because they used the assembly line in their production, but decided against, realizing it was essential to creation and expansion of the industry as a whole.
In the automotive industry, its success was dominating, and quickly spread worldwide. Ford France and Ford Britain in 1911, Ford Denmark 1923, Ford Germany 1925; in 1921, Citroen was the first native European manufacturer to adopt it. Soon, companies had to have assembly lines, or risk going broke by not being able to compete; by 1930, 250 companies which did not had disappeared.[2]
Sociological work has explored the social alienation and boredom that many workers feel because of the repetition of doing the same specialized task all day long.[6] Because workers have to stand in the same place for hours and repeat the same motion hundreds of times per day, repetitive stress injuries are a possible pathology of occupational safety. Industrial noise also proved dangerous. When it was not too high, workers were often prohibited from talking. Charles Piaget, a skilled worker at the LIP factory, recalled that beside being prohibited from speaking, the semi-skilled workers had only 25 centimeters in which to move.[7] Industrial ergonomics later tried to minimize physical trauma.
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