Scheduling can be defined as “prescribing of when and where each operation necessary to manufacture the product is to be performed.”
Principles of Scheduling
- The principle of optimum task size: Scheduling tends to achieve maximum efficiency when the task sizes are small, and all tasks of same order of magnitude.
- Principle of optimum production plan: The planning should be such that it imposes an equal load on all plants.
- Principle of optimum sequence: Scheduling tends to achieve the maximum efficiency when the work is planned so that work hours are normally used in the same sequence
Inputs to Scheduling
- Performance standards: The information regarding the performance standards (standard times for operations) helps to know the capacity in order to assign required machine hours to the facility.
- Units in which loading and scheduling is to be expressed.
- Effective capacity of the work centre.
- Demand pattern and extent of flexibility to be provided for rush orders.
- Overlapping of operations.
- Individual job schedules.
Scheduling strategies vary widely among firms and range from ‘no scheduling’ to very sophisticated approaches.
These strategies are grouped into four classes:
- Detailed scheduling: Detailed scheduling for specific jobs that are arrived from customers is impracticable in actual manufacturing situation. Changes in orders, equipment breakdown, and unforeseen events deviate the plans.
- Cumulative scheduling: Cumulative scheduling of total work load is useful especially for long range planning of capacity needs. This may load the current period excessively and under load future periods. It has some means to control the jobs.
- Cumulative detailed: Cumulative detailed combination is both feasible and practical approach. If master schedule has fixed and flexible portions.
- Priority decision rules: Priority decision rules are scheduling guides that are used independently and in conjunction with one of the above strategies, i.e., first come first serve. These are useful in reducing Work-In-Process (WIP) inventory.