The assembly line manufacturing (or production line) is a production process applied in the industrial production of bulk goods. It represents a specialization in flow production, in which the products are transported individually, often continuously, from one workstation to the next for further processing.
Flow Production
In the case of flow production (or series production), the manufacturing of a product is divided into successive work processes, which in turn can be divided into individual work steps.
The list of the equipment follows this production process, the machines and tools are arranged at the work station as the sequence of the work process requires. The best-known example of assembly line production is the assembly lines in the automotive industry, which are divided into assembly cycles. Assembly line production is a further development or specialization of assembly line production. In this case, the equipment or workplaces are also already arranged in the row, as it corresponds to the work sequence. In the case of flow production, however, funding is still given in batches. In both concepts, the work steps are predetermined. In the case of assembly line production, the prescribed “cycle time” must be observed in the case of fixed interlinking. The planning and implementation of the production takes place on the product (workpiece), i.e. according to the object principle.
Floating Production
A floating production is mostly for procedural reasons. The arrangement of the production sites is an inevitable consequence of the technological circumstances of the production process, for example in the case of crude oil processing in refineries or steel production or organizational considerations.
Line
In assembly line production as the most consistent form of assembly line production, material is transported between the individual production sites with the help of interlinked conveyor systems (e.g. conveyor belts) in batch. The individual work steps are usually reduced to a few simple steps. In the classic form, a work step is a permanent repetition of a precisely determined sequence of handles.
The execution operations and the transport between the production sites take place in a fixed time rhythm. This means that the processing time at the individual stations is interdependent.
Optimal assembly line adjustment is crucial for a smooth process:
The individual work steps and work stations must be defined in such a way that their execution requires exactly a defined period of time, the cycle time. By specifying a fixed production process, scheduling and capacity planning problems can be solved efficiently, the most productive manufacturing process is enforced to a certain extent.
If the production sites are linked automatically, this is referred to as a (rigid) transfer line, and the production process is fully automated.
Due to the often high system intensity, this type of production is used above all for variety and mass production. Due to the low flexibility – the product structure must not be subject to short-term changes – a secure market analysis is also required.
For this, the variable costs can be kept relatively low (low costs of storage and transport, production and wages, little waste).
Conveyor belt production is used, for example, in automobile production, the publishing and printing industry and the food industry.
Advantages
- Semi-finished products are reduced to a minimum, thereby, intermediate storage are avoided largely.
- The consistent arrangement of the workplaces also saves space, transport routes are shortened and transport costs are reduced
- Cost advantages through division of labor and specialization
- Low throughput times enable a reduction in the total production time
Disadvantages
- Low flexibility with fluctuations in employment, the adaptability of the company is reduced
- High susceptibility to failure of the entire production in the event of machine or work failures
- High system intensity
- Often little room for maneuver for workers
- Monotonous work creates alienation, dulling and motivation problems
- Lack of communication opportunities creates social problems for workers
History
Already in the late 15th century, ships were built in assembly lines in the Arsenale Novissimo in Venice. In 1790, Oliver Evans received a patent for a mill that used various continuous transportation techniques. In 1833 an assembly line was introduced in the manufacture of ship’s rusks in England. Around 1870, elevated conveyor belts were used in the slaughterhouses of Cincinnati to transport the slaughtered pigs from one worker to the next. This technique was used in the Union Stock Yards of Chicago perfected and applied on a large scale. The so-called “disassembly lines” were also a model for the “assembly lines” for the production of the Ford Model T.
The Bahlsen company used the assembly line in Germany as early as 1905.
As early as 1902, Ransom Eli Olds used movable wooden frames (wheeled carts) for the production of its “Oldsmobile “, on which the chassis was pushed from station to station. Henry Ford mechanized and refined this principle by building a permanent assembly line with the help of his engineer Charles E. Sorensen and foreman Lewis in 1913, thus installing the first “moving assembly line”. As a result, Ford increased production to eight times, at the same time the price of its T-model “Tin Lizzy” decrease enormously and wages increased.
Because of his success, he built a brand new factory on the River Rouge in Detroit based on this principle, which became a mecca for engineers and automobile manufacturers from all over the world. Many of them then adopted Henry Ford’s production principles, such as Fiat, Renault or Volvo. In Germany, assembly line production in the automotive industry was first introduced in the 1920s by the Adam Opel company and by the Hanomag company. The Daimler performed this type of manufacturing organization only in the 1930s by William Friedlea, who was operations director of Daimler-Benz AG at the Sindelfingen plant. The Volkswagen plant in Wolfsburg, where the KdF car was to be built, was also designed in the 1930s, based entirely on the Ford factory on the River Rouge.
Assembly line production is still up to date in the automotive industry, and the assembly line principle is constantly being expanded. One example of this is just-in-time production, in which flow production is extended to the supplier and sometimes even to the pre-supplier. Several companies in other branches of industry, such as the aircraft industry (for example Boeing) and mechanical engineering (for example Gildemeister, Trumpf), are increasingly converting their production to flow production. Flow production is one of the essential foundations for the introduction of the pull system and for various methods and processes in production planning and control such as the progress number method or Kanban.
The initial welcome of the assembly line, which was hailed as a revolutionary, soon turned into strong rejection. The mechanical work processes to which the workers were exposed led to dulling and devaluation of the workforce, since only a few, monotonous steps were necessary for the individual.
The actor Charlie Chaplin has impressively illustrated the work on the assembly line in his film “Modern Times”.
