Monolithic vs. hierarchical balancing and scheduling of a flexible assembly line

A monolithic and a hierarchical approach are presented for balancing and scheduling of a flexible assembly line (FAL). The system is made up of a set of assembly stations in series, each with limited work space, and is capable of simultaneously producing a mix of product types. The objective is to determine an assignment of assembly tasks to stations and an assembly schedule for all products so as to complete the products in minimum time. In the monolithic approach balancing and scheduling decisions are made simultaneously. In the hierarchical approach, however, first the station workloads are balanced, and then detailed assembly schedule is determined for prefixed task assignments and assembly routes by solving a permutation flowshop problem. Mixed integer programming formulations are presented for the two approaches. Numerical examples are included to illustrate and compare the approaches and some computational results are reported.