Today one of the most important industrial needs is to reduce the time-to-market, in order to satisfy quickly changing demands and to comply with evolving prescriptions. As regards assembly, these requirements can be fulfilled by means of:
modular assembly plants, characterised by reconfigurability (off-process flexibility);
adaptive control strategies, taking into account the modules state and alternative routing and bypass rules
(on-process flexibility).
To apply this approach, each elementary function must be studied to have independent execution, performed by modular units, which can be divided into the following categories:
The economical investment for a flexible plant is higher in comparison with a traditional, rigid solution; moreover, the performance of any possible layout, each time a new production programme is forecast, has to be preliminary tested; for all of these reasons, computer-aided simulation is fundamental to support any strategic decision.
Plant Simulator
The plant simulator has been developed with a window-based user interface to build up the layout and manage the simulation. The configuration of the plant is interactively set up by the user, selecting the transport equipment (track type, pallet size and number), the parts feeders and auxiliary equipments features, the production work-cycles. During simulation, the workstation breakdowns are generated on the basis of the MTBF and MTTR indices.
The output supplies the plant global and individual module statistics, highlighting bottlenecks and clogging situations and allowing to assess the goodness of plant layout and control logic.
Simulation results
In fig. below some simulations results are shown, regarding the studied layout. The number of circulating pallets is a critical parameter for the plant behaviour. The production rate in case of 70 pallets is greater than with 85 or 100 pallets, since the smaller number of pallets allows a more fluid traffic and the plant is more agile to overcome clogging situations. The average throughputs with 70, 85 and 100 pallets are respectively 137, 126 and 131 parts per hour. It is possible to notice that in all three cases the production is very irregular.
The simulation package allows the user to design modular assembly plants, easy to be reconfigured each time the case arises, in order to modify the products enabling off-process flexibility. Moreover, the features of on-process flexibility can be assessed changing the rules associated to the transport items. The appointed modular assembly philosophy and simulation technique have been successfully applied to an industrial case, leading to effective and substantial improvements of an existing assembly plant.
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Simulation results
