A Flexible Approach to Production Capacity Planning: Assembly Line Modularity

Résumé:

This research presents a comparison of a modular and a non-modular assembly lines operated at a French supplier of automotive components. Both lines are operated in the same facility and are located next to each other. With this comparison we aim to understand better the perimeters of the benefits provided by the modular assembly line.
It is important to point out that the modular assembly line we examined in this research is different from the modular assembly lines which are commonly defined in the academic literature as reconfigurable manufacturing systems (RMS). The modular assembly line in this research has a U shape design and each station has its own conveyor belt. This type of modular assembly line has multiple programmable logic controllers (PLCs) for each station. Due to its design, stations can be easily plugged in and out. So, the modular line that we observed at this supplier has dedicated stations that are not flexible, but it has a flexible layout.
On the other hand, the non-modular assembly line has an oval loop shape design and a single conveyor belt connecting all stations. This type of assembly line has one PLC for automation of the electromechanical processes and control of stations. Therefore, modularity as defined here does not affect the mechanization of the system. Both lines operate using basically the same tools. However, the communication architecture of the modular line is quite different from the non-modular line.
Our main findings regarding the advantages of the modular assembly line over the non-modular assembly line can be described as follows:

➢ The main advantage of the modular assembly line seems to be the reduced lead time for the development of a new line. The reduction of lead time is achieved because the building phase of the development of a new modular system is shorter than the building phase of a non-modular system, and because the building phase starts before the study phase of the development is completed. The more complex stations are developed first. In the non-modular line all stations must be present before any line testing can start.
➢ It is possible to increase the capacity of the modular assembly line system in a few steps by adding more stations thus avoiding the necessity to buy the full final capacity (investing upfront). In the case of this supplier the full final capacity may not be realized for 5-6 years which penalizes the payback, making reduced upfront investment desirable.
➢ Also, in the modular assembly line it is possible to change a station for an engineering change order without shutting down the line for an extended time.
➢ In addition, a certain proportion of the modular line stations can be reused for another project or sent to other factories to rebalance capacity.

As product introductions become more frequent in response to increasingly volatile and competitive markets, decisions on assembly methodology become both more frequent and more critical to future profitability. The modular assembly line system we examined could offer the ability to plan capacity and cost in a more flexible way. The results of this research can prove useful for those who wish to purchase or market an assembly system that could perform well when demand uncertainty is high.