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Schedule Optimization of Car Painting
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Problem Statement
A German automotive company must reduce the costs and cycle times of car painting, where the production plans are very dynamic and rapid changing. Expected improvements were about 10% of the actual parameters. |
Improvement Approach
A simulation model of the production process was coupled with the optimiser ISSOP. A set of 7 different optimisation strategies changes the schedule of the painting jobs for better results in costs and process times. |
Benefits
Main benefits are reduced costs and process times. Secondary benefits are lower material consumption of colour coatings and cleaning supplies by reduced colour changes. |
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Contact information
DUALIS GmbH IT Solution Dresden
Prof. W. Krug
Tiergartenstraße 32
D-01219 Dresden
Phone ++49 351 47791 200 ,
Fax
++49 351 47791 99
e-mail
wkrug@dualis-it.de
www.dualis-it.de
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The simulation model of car painting process |
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Today nearly each car in automotive pro-duc-tion is different in results of specific customer requirements. In the production step of painting there are more than 100 different colours possible. Combined with different car shapes like standard or station wagon, engine varieties and other there is are large mix of different production sequences.
In difference to the assembling process, where tools and process steps are very similar and uncritical in sequence, the large number of colours is critical:
Each change of colour needs a cleaning operation before a new colour can be used. The cleaning operation requests extra time and cleaning supplies.
he cleaning process is easier and faster if the colours are changing all time from a bright to a darker colour.
The puffer before the painting station is limited in space.
In result, there must be calculated an optimised sequence of painting operations , where the puffer resrtictions are met and the number of colour changes is small. |
(click on image to enlarge)
Similar problems, like the above stated, can be found :
In any production, where the change of tools or helping supplies is time and material consuming,
Processes with batch sequences of nearly identical objects,
A improved batch sequence can lead to major savings in costs and time.
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A weakness of conventional planning tools is the fact that they can only deal with times and capacities. They are not able to take into account any technical or qualitative constraints which often put several limitations on the sequence of orders at a special machine. Simulation tools can model all these constraints. Optimisation techni-ques can be used to generate beforehand a plan which satisfies the constraints in an optimal way. The simu-lation approach increases the reliability of planning, reduces the throughput time and the work in progress.
The process was modelled with the commercial simulation system ARENA. Because Arena offers very comfortable editing functions, smaller changes in model parameters can be done also by technology experts at the side of the customer. So the model can reflect the last situation of the real process. This approach help also in discussing the model with the customer and for getting a common understanding.
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The simulation model parameters for the order and colour sequence are controlled by the ISSOP-optimisation system. The optimiser changes the sequences and compares the result values. After a number of experiments, which take between 5 and 25 minutes, improved sequences can be found. The resulting sequence can be used also for controlling the real process.
Additional advantages of the simulation model are the possibility of testing the sequence against disturbances like technical problems or delivery delays.
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Although the existing production sequencing was also calculated by software programs, the results achieved by the simulation & optimisation approach were better:
8% less changes of colours in the painting station,
in result of less colour changes and more optimised batch sequence 12% higher output of the painting station,
reduction of needed coating material,
less downtime and less breaks due to malfunction
In results of the saved material and time the Pay-Back Time was relatively short – about 8 months only. Annual Savings were about 12% compared to the time before.
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Additional benefits of the realised system are the practise oriented user interface functions. Changes of the production scheduling or new options of the process parameters can be defined by the customers planning staff without any knowledge of the underlying simulation and optimisation techniques. The interface to other IT-systems of he customer allows a fast and efficient data exchange for an up-to-date optimization of the next days or weeks.
(click on image to enlarge)
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