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Simulation-aided improvement of disassembly and re-assembly processes

Problem Statement
In order to provide good service, the most important goal for the company was to attain high service ability in such a manner that all orders coming in on one workday would be shipped on the same day.

Improvement Approach
This goal should be attained by using flexible working time models and flexible personnel in order to of flexibly aligning the personnel capacity to the customer driven personnel demand.

Benefits
The simulation-aided improvement of the work organization optimized the service rate by 20% to 25% and reduced the idle time by 44%.

Contact information
ifab-Institute of Human and Industrial Engineering
University of Karlsruhe, Kaiserstrasse 12, D-76128 Karlsruhe, Germany
Phone +49 721 608 4250 , Fax +49 721 608 7935
e-mail gert.zuelch@ifab.uni-karlsruhe.de
http://www.ifab.uni-karlsruhe.de

Simulation procedure OSim for the improvement of disassembly and re-assembly processes

PROBLEM STATEMENT

Since electric devices differ little, the electronic and electric industries are forced to improve their service processes in order to acquire new customers. The project partner, a manufacturer of electric devices, offers an "after sales service" for his broad product pallet, which mainly comprises the handling of repairs. Hence, the project partner’s intention is to improve their repair processes.
Therefore, the test case project SAIDER, started in cooperation with SimServ, encompasses the improvement of disassembly and re-assembly processes.
A repair line from the project partner, in which hammer drills in various weight classes are repaired, was chosen as the main object of investigation. The organizational structure of this line is orientated towards the hammer drill weight classes, e.g. with groups of mechanics for 2 kg, 3-6 kg, etc.

One problem is the stochastic nature of disassembly times and the feasibility of disassembly operations.
Another problem is the broad variability of the temporal load to the system due to the heavy fluctuations in and the low predictability of order flow. This had, on the one hand, a negative effect upon the service rate, while simultaneously creating disproportionately high idle-times.
Therefore, the most important goal was to attain high service ability. In this case service ability means that all orders coming in on one workday are shipped on the same day (represented by the key figure TITO-Rate, which means Today-In-Today-Out-Rate). At the beginning of the SAIDER-project the TITO-Rate was approximately 71-72 %.
A further essential goal was the reduction of idle times in manufacturing, which were 5.2 % at the beginning.

IMPROVEMENT APPROACH

In order to attain these goals, the basic approach was the implementation of flexible working times. Furthermore, it was examined to what degree later starting times (e.g. 7:30 instead of 6:30) had a positive effect upon the goal of reducing the idle times.
Additionally, the question was posed as to when the transfer of workers from one group to another (if a worker has little or nothing to do he could switch to another group in order to help those workers) would produce a sustained improvement in the processing of orders.
The configuration of a flexible working time model has turned out to be a very complex task. Therefore, the use of the personnel-oriented simulation tool OSim (see figure), developed at the ifab-Insitute, is a very promising approach since, with its help, the effects of different working time models can be analysed with respect to their implications and advantages prospectively.

Its conception was strictly object-oriented, making an expansion of the simulation functionality with novel representation elements very easy. Further on, action rules can be modelled with OSim. In this case, these action rules stated, for example, that the workers could end their operation and go home once the work was completed. Strategies for these rules, which might later provided insights as to how decisions should actually be made in reality, were deposited in OSim.
The first step of the simulation examination comprised modelling the initial situation and the validation of the developed model.
Afterwards, various working time models were examined, in which primarily the employee working times were varied.
Finally, the possibility of mechanics switching work groups when necessary was considered.

BENEFITS

Very positive results have already been attained by applying flexible working times (first examination phase): The TITO-Rate was thus increased by 10-15 %, while the idle time rate was reduced by 38 %. Additionally, the average lead time was reduced from the original 4.9 days to 2.9 days.
Combining flexible working times with the switch-over to another work group (second examination phase) it was possible to show, that only by effectively using the two independent variables ‘working time model' and 'personnel placement' could we increase the TITO-Rate by about 20-25 %. The idle times were thereby lowered to 2.9 %, representing a reduction of 44%.

By reducing the secondary processing time with this project the user attained savings of approximately 25 000 € per year. Since we only used different working time models and a flexible personnel placement as independent variables, it is possible to attain these results with an investment of 0.0 €.


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