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Assembly line

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 best known form of the assembly line, the moving assembly line, was realized into practice by Ford Motor Company between 1908 and 1915, and made famous in the following decade by 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. 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 costs for manufactured goods.

Concept

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 car on the assembly line can have only one of the three steps done at once. After the car has its engine installed, it moves on to having its hood installed, leaving the engine installation facilities available for the next car. The first car then moves on to wheel installation, the second car to hood installation, and a third car begins to have its engine installed. If engine installation takes 20 minutes, hood installation takes 5 minutes, and wheel installation takes 10 minutes, then finishing all three cars when only one car can be operated at once would take 105 minutes.

On the other hand, using the assembly line, the total time to complete all three cars is 75 minutes. This is possible because there are 3 different installation stations, an engine station, a hood station and a wheels station. By having 3 stations, a total of 3 different cars can be operated at the same time, albeit all working on different steps. After finishing on the first car, the engine installation crew can move onto the second car. While the engine installation crew works on the second car, the first car can be moved to the hood station and then the wheels station to be fitted with the hood and the wheels respectively. After the engine has been installed on the second car, the second car moves to the hood and then the wheels assembly (5 minutes after the wheels assembly is done with the first car), at the same time the third car moves onto the engine assembly. When the third car’s engine has been mounted, it then can be moved to the hood and then wheels installation facilities, meanwhile subsequent cars (if any) can be move 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 the wheels, the bottleneck is at the engine installation. Hence, additional cars will come off the assembly line at 20 minute increments.

Assembly lines don't increase the speed of producing a single unit, but only increases rate when there are a stream of units to be produced. In the example above, a car will still require 35 minutes to be made, however when there is a stream of cars it will only take 20 minutes to have a new car coming off the assembly line.

History

Overview: a culmination of many efforts

The assembly line concept was not "invented" at one time by one person, and no one person is the "father" of it. 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 by making interchangeable parts a practical reality. Before the 20th century, the way that most manufactured products were made was that a single craftsman or team of craftsmen would create each part of a product individually by hand, using their skills and such tools as files and knives, and assemble them together into an assembly, making cut-and-try changes in the parts so that they would fit and work together (the so-called English System). The transition to other methods began as creativity and logic took advantage of the opportunities that the aforementioned machining developments presented. Thus, before the modern assembly line took shape, there were prototypical forms in various industries, as outlined below.

The Terracotta Army (circa 215 BC)

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 control.

Venetian Arsenal (1500s)

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.

Block production at Portsmouth: Brunel, Maudslay, et al (1800-1820s)

Probably the first linear and continuous assembly line of post-Renaissance times was 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 (1780s-1820s)

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. 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.

Firearms, clocks, et al (1860s-1890s)

The Industrial Revolution in Western Europe and North America, but perhaps most especially in the United Kingdom and New England, led to a proliferation of manufacturing and invention. Many industries, notably textiles, firearms, clocks and watches, buttons, 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 E. Olds (1890s-1900s)

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. 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 work of Olds shows clearly the flaws in the oversimplistic storyline of Ford's having "invented" the assembly line.

Ford Motor Company (1908-1913)

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 5 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 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.

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:

“Years later in My Life and Work, a book which was written for him, Mr. Ford said that the conveyor-assembly idea occurred to him after watching the reverse process in packing houses where hogs and steers were triced up by hind legs on an overhead conveyor and disassembled. This is a rationalization long after the event. Mr. Ford had nothing to do with originating, planning, and carrying out the assembly line. He encouraged the work, his vision to try unorthodox methods was an example to us; and in that there is glory enough for all.”

“Henry Ford had no ideas on mass production. He wanted to build a lot of autos. He was determined but, like everyone else at that time, he didn’t know how. In later years he was glorified as the originator of the mass production idea. Far from it; he just grew into it, like the rest of us. The essential tools and the final assembly line with its many integrated feeders resulted from an organization which was continually experimenting and improvising to get better production.”

“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.” [Sorensen explains that Henry Ford did not invent all the aspects of mass production, but he knew that production efficiency meant low unit price, and so he encouraged his engineers to develop the methods.]

“Today historians describe the part the Ford car played in the development of that era and in transforming American life. We see that now. But we didn’t see it then; we weren’t as smart as we have been credited with being. All that we were trying to do was to develop the Ford car. [¶] The achievement came first. Then came logical expression of its principles and philosophy.”

Much has been written about the original layout of the assembly line at Ford. In an article published by Fortune Magazine in June 1944, Henry Ford said that he and Peter E. Martin did it.

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. 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 Durco lacquer was developed in 1926. In 1914, an assembly line worker could buy a Model T with four months' pay.

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.

Sociological problems

Some sociological theories assume that workers must feel alienated and bored because of the repetition of the same specialized task all day long. 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. Industrial ergonomics later tried to minimize physical trauma.

See also

References

Bibliography

  • Various republications, including ISBN 9781406500189. Original is public domain in U.S.
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  • . Various republications, including ISBN 9780814332795.
  • We-Min Chow (1990). Assembly Line Design.

External links

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