Dynamic scheduling problem has been an attractive area for researches to
investigate since a long time. Many techniques have been used to tackle such problems, but all of these techniques require high efforts to formulate the dynamic scheduling problems inorder to obtain optimal solution. Using Heuristic or dispatching rules to solve the dynamic scheduling problem is efficient and popular manner to reach an acceptable level of scheduling. In this paper hybrid techniques
are used in the proposed developed model. First the switching of four dispatching rules (Earliest Due Date (EDD), Slack Time (SLACK), Slack / Remaining Operations (S/ROP) and Priority Index) with the aim of choosing minimum tardy jobs. Second, scheduling-rescheduling approach is used to tackle the dynamic environment of job-shop problem depending on three level algorithms. Third, proposing three level algorithms, these levels are resource level, process planning level to improve scheduling with the aim of minimizing tardy jobs and shorten
"order-to-delivery", and job level to design rescheduling policy depending on identified factors of each job order. The developed model is applied to real data from the Heavy Engineering Equipment State Company/Baghdad, and considerable advantages are observed. Applying the proposed model lead to zero number of tardy jobs (NT) and zero mean tardiness (MT). It is obvious from the obtained results that by adopting such model, a better solution for job orders' due dates can be achieved; hence "order-to-delivery" time can be shortened