An investigation of change over sensitive heuristics in an industrial job shop environment

Abstract: The research in this thesis has investigated scheduling and Changeover Sensitive Heuristics (CSHs). The overall aim was to investigate the relationship between scheduling and changeovers and to develop and examine new scheduling heuristics that are intelligent enough to optimise both due dates and changeover requirements. Two new heuristics that incorporated the sequencing of jobs both according to product families and sub-product families were introduced. The new heuristics are named CSH12 and CSH12-K. A body of case studies have been undertaken. These are based on extensive data collected from the key collaborating company. In order to create generic data sets for a job shop environment, the case studies were extended to incorporate a range of parameters, such as several levels of processing times and job grouping strategies. Through discrete event simulation studies, the performance of the new heuristics has been compared to simple heuristics, semi-heuristics and existing changeover sensitive heuristics. In total, ten heuristics and two semi-heuristics were investigated. Scheduling according to product family (CSH1) compared to subproduct family (CSH2) was also studied and it is concluded that sub-product family sequencing performance better. Overall the new heuristics CSH12 and CSH12-Kshow a worthy performance and can reduce the changeover time the most through effective sequencing in a job shop environment with longer and shorter processing times. The research has also concluded that exhaustive heuristics perform better than non-exhaustive heuristics. Furthermore, CSHs are particularly effective for shorter processing times. This suggests that the choice of heuristic is more important for amix of jobs with shorter processing times. Or the reverse, a mix of jobs with comparatively long processing times is less sensitive to the choice of heuristic.Additionally, the research revealed that product families with overall longer processing times result in higher percentage of tardy jobs. Thus, suggesting that dissimilar due date setting is beneficial for different product families. The research has determined the importance of considering appropriate scheduling and sequencing approaches, especially when changeovers have been addressed through design and organisational changes. The application of CSHs has demonstrated that an increase of jobs into the shop is possible. Hence, applying CSHs will achieve a strong competitive advantage.