Production scheduling consists of the activities performed in a company to determine in detail how work should be executed on the shop floor. How production scheduling is performed and the scheduling methods used, can vary a great deal between different production environments, from applying simple rules when choosing the next job to execute, to the use of advanced optimizing methods that try to maximize the performance of the given environment.
The scheduling approach suitable for an environment is highly dependent on how much complexity, uncertainty and randomness there is in the production system. This, together with the goals of the company, must be considered when choosing a scheduling approach for a particular environment.
Since scheduling involves prediction of the future, it of course gets more and more difficult when the level uncertainty and randomness in the system increases. A general rule is that as the uncertainty increases, the value of scheduling deceases. Trying to predict and optimize the behavior of a complex system with many uncertainties and high level of randomness is in most cases a waste of time and resources. On the other hand, for more stable systems, putting more effort into scheduling often can improve performance and the use of advanced optimizing methods might in these cases be appropriate.
How scheduling is performed also depends on the management of the company and the organization around the scheduling function. Some companies may not have an explicit
scheduling method; it is just something that is done implicitly by for instance the workers or shop floor management, while others have very strict approaches that are decided upon by the management.
How the schedule is used can also differ between companies and also between different users in the same company. Besides the obvious use on the shop floor other potential uses are to determine system capacity for a higher level production planning system, where the generated schedule is used to determine the feasibility of the production plan or by the sales department to determine if an order with a given lead time should be accepted.
Scheduling fixes a time and date to each operation and outlines the commencement and completion time-frame for each process. Both subsequent stages of PPC depend on this timeline which makes it a very valuable asset in the production process. Scheduling looks to optimize the use of time; from each piece of work involved to project planning to customer delivery. The goal is to eliminate idle machines and laborers while enhancing efficiency. In order to schedule more efficiently, there are a variety of methodologies planners can apply. Let’s discuss two common scheduling processes that planners use in order to enhance their manufacturing schedules:
Scheduling is the process of arranging, controlling and optimizing work and workloads in a production process. Companies use backward and forward scheduling to allocate plant and machinery resources, plan human resources, plan production processes and purchase materials.
- Forward scheduling is planning the tasks from the date resources become available to determine the shipping date or the due date.
- Backward scheduling is planning the tasks from the due date or required-by date to determine the start date and/or any changes in capacity required.
The benefits of production scheduling include:
- Process change-over reduction
- Inventory reduction, leveling
- Reduced scheduling effort
- Increased production efficiency
- Labor load leveling
- Accurate delivery date quotes
- Real time information
Production scheduling tools greatly outperform older manual scheduling methods. These provide the production scheduler with powerful graphical interfaces which can be used to visually optimize real-time workloads in various stages of production, and pattern recognition allows the software to automatically create scheduling opportunities which might not be apparent without this view into the data. For example, an airline might wish to minimize the number of airport gates required for its aircraft, in order to reduce costs, and scheduling software can allow the planners to see how this can be done, by analyzing time tables, aircraft usage, or the flow of passengers.
Scheduling objectives
At the most basic level, the reason for scheduling is to satisfy the overall goals of the company. To be useful in the scheduling activity these goals are broken down into more detailed objectives. Some of the more common objectives are:
- Meet due dates
- Minimize work-in-process inventory
- Minimize the average flow time through the system
- Provide for high machine/worker time utilization
- Provide for accurate job status information
- Reduce set-up times
- Minimize production and worker costs
An aspect that adds to the complexity of scheduling is that some of these objectives are in conflict with each other. Their origins are often in different departments of the company and these departments have different goals. For instance meeting due dates is aimed at providing high customer service and is primarily a goal for the sales department whereas to minimize production cost and worker cost is primarily a goal for the production department. These two objectives can be in conflict if for example overtime is needed to keep due-dates. One important part of scheduling consists of balancing different objectives and to make decisions on how conflicts should be resolved.
