What is Forward and Backward Scheduling?
Scheduling and its importance
Scheduling is a method that aims for the most efficient use of resources to complete a task within a stipulated time. In in a production process or manufacturing process, scheduling of task pertains to scheduling of human activities and planning the use of equipment and facilities. They are used to efficiently strategize and allocate equipment, production processes, human resources, purchase and receipt of materials. The concepts of lean manufacturing and just-in-time manufacturing concepts have increased the significance of scheduling. Organizations and enterprises use different approaches to scheduling — forward and backward scheduling being the two of the most vital methods. The goal of “on time, on plan and on budget” completion of a project calls for a mix of forward and backward scheduling approaches.
Forward Scheduling and Backward Scheduling
Forward scheduling incorporates selecting a planned order release date and scheduling of subsequent activities thereafter. The method is fairly simple—you take a job consisting of various tasks and allocate resources to these tasks as soon as the resources are available. Forward scheduling algorithms are particularly useful in cases of serial production, where the production order is fulfilled in the shortest possible time. The method is a tradeoff between when the job can be completed versus completing the job when required; customer tells you what they need and you tell them the earliest delivery time. Forward scheduling may result in tasks being completed earlier than the requested due dates. Or, sometimes, production orders may get fulfilled long before they are required to be shipped since the resources or materials are utilized as early as they get available.
So, using a forward scheduling method you can know: The earliest time in which you can complete a task.
At times, when enterprises need to respond to make-to-order processes or produce according to an estimated sales forecast, applying forward scheduling may not be useful. In backward scheduling system, you begin with a planned receipt date or due date—the date typically given by customer. Then you move ‘backward’ in time, and allocate resources accordingly, until you reach a point where the order should be released. You can determine earliest possible goods receipt time at the customers’ site. The method is useful for a manufacturer to know if a due date is possible or hit based on the allocation of resources. This algorithm is useful to identify potential bottlenecks, estimate resource requirements and to complete the task.
So, using a backward scheduling method you can know: The start date depending on the availability of resources.
Usually, in case of forward scheduling, the pick/pack time, transportation time and transit time are added to the start date to calculate the due date or shipping date. While, in backward scheduling, the transit time, loading time, and pick/pack time are subsequently subtracted from requested delivery time by customers.
The key variables that need to be known are start date and due date or shipping date for forward and backward scheduling respectively. Other variables that affect both the scheduling processes include the type of jobs, the nature and availability of resources, processing time, changeover time, process routings, parallel and dependent tasks, number of work shifts and planned maintenances.
Which method should dominate?
Both the methods have their pros and cons; no method is the clear winner.
Some of the advantages of forward scheduling are:
Some of the advantages of backward scheduling are:
Scheduling of tasks is multi-faceted—taking into account various production variables and estimation occurs across each stage the project lifecycle. In practice, just-in-time schedule in modern production processes is accomplished with a mix of forward and backward scheduling methods. Some orders need to be filled as soon as a slot is available while other orders are planned for just-in-time delivery. MRP systems by leading vendors allow for both forward and backward scheduling features. These methods should complement each other for any production and manufacturing system to be efficient.