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Optimisation of production line significantly reduces work in progress
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Problem Statement
The existing layout of a production line in a truck and bus company for manufacture of truck swivel axles was not optimal and led to a considerable level of work in progress. |
Improvement Approach
New layout of workstations, modified production cycles, personnel assignments and machine dispatch were suggested and their effects simulated with appropriate tools. |
Benefits
The suggested changes lead to a significant reduction of work in progress, production lot manufacturing time, manufacturing costs and labour costs. |
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Contact information
Centre for Advanced Manufacturing Technologies
Zdzislaw Poltorak, Zaklady Samochodowe Jelcz SA, ul. Inzynierska 3, Jelcz-Laskowice, Poland
Phone +48 71 381 5132 ,
Fax
e-mail
zpoltorak@jelcz.com.pl
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Fot. Jelcz |
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A production line of truck swivel axles in Jelcz SA was designed in early 70s to manufacture swivel axles of one type. Later a second type was introduced, requiring a modified manufacturing process. Production volume was determined at the level of 10 000 axles per year. It has became necessary to reorganise the manufacturing processes in order to reduce costs related to production, especially to high level of work in progress, and machine maintenance, using the existing machine tools and keeping high production capacity of the line.The condition of keeping high production capacity of the line with the existing machine tools limited the optimisation problem to machine re-arrangement (maybe removing some equipment) and changes of cycles of the existing manufacturing processes. |
The optimisation criteria were:
-maximum use of work force,
-maximum use of machines,
-minimum manufacture time of a single lot.
The main element of the existing production line, defining its production capacity, was the transport system in a form of a chain conveyor, playing also the role of a dynamic store. The conveyor was equipped with several hangers, each for 9 swivel axles of one type (this determined the size of a production lot). Of the machine tools working at the production line about 80% were used in production of both types of axles and about 10% in production of individual types.The high level of work in progress was influenced by the layout of the work stations and the transportation/storage system. |
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The optimisation of the production line structure was expected to suggest a work station arrangement that would reduce costs related to production of swivel axles and costs of maintenance of the machine stock, keeping high production capacity of the line.It was decided that a production cell would be designed, customised to the technological processes of both types of axles, using machines from the existing line, and that the surface, where the work stations would be arranged, would be optimised.When optimising the existing line, first the improperly selected transport system was eliminated. The machine layout was designed from the beginning. |
Results of the optimisation were examined using simulation software. The analysis was carried out for a production lot of 9 swivel axles of one type (this number of axles can be hanged on one hanger of the production line).A series of simulations was performed to determine the most advantageous way of arrangement of the types of axles introduced in lots for production. It was found out that the best way was to use an alternative sequence.Further simulations were performed using the optimal arrangement of the machines. |
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The first simulations showed that the production line is underloaded. The planned annual production may be achieved as fast as in 67 working days.The existing line is characterised by a very low degree of resource utilisation (both machines and personnel). This is because of improperly selected transport system, poor arrangement of machines (inconsistent with the production technology) and a bottleneck revealed during simulation (which may be eliminated with an additional special boring machine). Simulation showed the way to remove bottleneck, increase workload of all machines (on average by about 10%) and to reduce manufacturing cost of one swivel axle (by about 37%, thanks to a lower cost of machine stock utilisation). |
For the existing line, a highest workload of a worker operating a special boring machine and a low workload of over a half of the other workers (below 40%) were clearly identified.Results of the optimisation suggested to move some of the workers to other tasks and to increase the other workers' workload by joining operation of several machines. The average personnel workload may then rise from 40% to 80%. The direct labour cost may then be reduced by about 56%.In the optimised cell work in progress was reduced over 10 times, primarily due to elimination of the improperly selected transport system. |
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