Issues & Constraints in Job Shop Production Scheduling

1. Job have different routings, process time requirements, priorities and due dates
2. Make-to-order rule is necessary for a majority of jobs
3. Final goods inventory is not to be maintained
4. Customer want changes in the existing sales orders
5. Hot jobs are accepted for large margins
6. Job priorities change due to customer requirements
7. Machines are multi-functional
8. Workers are multi-skilled
9. Machines breakdown and workers are absent sometimes
10. Alternative resources are available for operations
11. Bottlenecks keep changing over time
12. Setup time on some machines is sequence-dependent
13. Long operations need to be continued over many shifts with different workers in different shifts
14. Some operations of a job can run in parallel (with or without time lag) if resources are available
15. The total quantity of a job may be distributed to two or more similar resources at a work center
16. Workflow of a job may resemble project workflow
17. An operation may simultaneously require multiple resources (like machines and workers)
18. Vendor (external) operations must be included in production schedule
19. Actual hours of an operation may differ from the estimated hours to some extent
20. Lead times are long and / or uncertain for some materials.

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