A parts feeding model for big size products: the active and idle assembly islands strategy

In fixed-position assembly systems (or assembly islands) for big-size highly customised products, workers and parts move around the sub-assemblies, which stay fixed in one place. Generally, there are several parallel assembly islands and a single product is assembled in each of them. In some cases, assembly workers can also do the parts feeding activities, which are considered as non-value added activities, with a consequent decrease in the system performance. In this paper, we propose a new mathematical model to reduce parts feeding costs by considering active and idle assembly islands, so that the parts feeding and the assembly activities can be done simultaneously by the respective operators. A sensitivity analysis is carried out to study the effects of the variables and of the parameters on the model results. Moreover, the model is applied to two real applications by evaluating how many idle assembly islands are required to improve the efficiency of the whole system. The results show that the main parameters that influence the final number of idle assembly islands are the percentages of time that assembly operators spend for parts feeding activities and the time required for material preparation and assembly activities.