Studying the impact of sequence-dependent set-up times in integrated process planning and scheduling with E-ACO heuristic

• Published in: International journal of production research Vol. 54; no. 16; pp. 4815 - 4838
• Main Authors: Zhang, Sicheng, Wong, T.N.
• Format: Journal Article
• Language: English
• Published: London Taylor & Francis 17.08.2016; Taylor & Francis LLC
• Subjects: Algorithms; ant colony optimisation; Fixtures; integrated process planning and scheduling; Job shops; job-shop scheduling; Optimization; Polypropylenes; Process planning; Production scheduling; Scheduling; sequence-dependent set-up times; Switching; Transportation
• ISSN: 0020-7543; 1366-588X
• DOI: 10.1080/00207543.2015.1098786

In job-shop scheduling, the importance of set-up issues is well known and has been considered in many solution approaches. However, in integrated process planning and scheduling (IPPS) involving flexible process plans, the set-up times are often ignored, or absorbed into processing times in IPPS domain, with the purpose to reduce the complexity. This is based on the assumption that set-up times are sequence-independent, or short enough to be ignored compared to processing times. However, it is not uncommon to encounter sequence-dependent set-up times (SDSTs) in practical production. This paper conducts a detailed investigation on the impact of SDSTs on the practical performance of the schedule: a comparative study is made for different cases where set-up times are (1) separately considered, (2) absorbed into processing times, or (3) totally ignored. An enhanced version of ant colony optimisation (E-ACO) algorithm is used to solve the IPPS problem, with the objective to minimise the total makespan. The following four types of set-up issues are considered: part loading/unloading, fixture preparation, tool switching and material transportation. Situations with various set-up time lengths have been studied and compared. A special case of IPPS problem involving a large number of identical jobs has been specifically studied and discussed. The results have shown that, set-up times should be carefully dealt with under different circumstances.