A closed loop facility layout model with an unidirectional material handling system

Closed loop layouts (CLLs) are a type of facility layout that connect all facilities by a single rectangular material handling path forming a closed loop. They have recently gained popularity due to advantages such as ease of adaptability of new processes and flexibility for expansion, and they lead to facility layouts that cause only marginal increases in material handling costs (MHCs) compared to optimal facility layouts. Other loop-based layouts use unidirectional material handling systems (UMHSs) that simplify the material handling system and the adaptation of agile material handling concepts such as milkrun and kanban systems. This paper proposes a new mathematical model that combines the CLL problem (CLLP) with an UMHS and accounts for clearances between facilities. Consistent with existing CLLs literature, MHCs are optimised while assuming fixed facility dimensions. The integration of UMHSs improves the suitability and operational relevance of the CLL for industrial applications. For solving the proposed model, we introduce a problem-specific branch-and-bound and a genetic algorithm with a novel granularity approach, reducing computational time without compromising solution quality. Computational experiments show improved performance and better results relative to earlier research on CLLPs, while also demonstrating practical applicability of one of the proposed solution algorithms.