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Forward and Backward Scheduling

Forward and Backward Scheduling

Scheduling is a method that aims for the most efficient use of resources to complete a task within a stipulated time. In a production process or manufacturing process, scheduling of task pertains to the scheduling of human activities and planning the use of equipment and facilities. They are used to efficiently strategise and allocate equipment, production processes, human resources, purchase and receipt of materials.

Organisations 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

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. The method is a trade-off between when the job can be completed versus completing the job when required; the 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. This is where the use of a scheduling product like Opcenter APS (formerly Preactor APS) can become extremely useful. We can set fields such as earliest start dates to add more in-depth detail to the schedule and add constraints to when we want to start production on a job, so we can achieve the most efficient production schedule for our shop floor.

Some of the advantages of forward scheduling are:

• There is a high labour and machine utilisation rate.
• The time slack in the process allows space for any unexpected work to be loaded – especially as you can redirect your resources to help meet new orders.
• Greater chance of ensuring all jobs can be planned.

Some of the disadvantages of forward scheduling are:

• Jobs could be completed well before their due date meaning you have to the store the finished product.
• Material is consumed in advance – can cause shortages on new jobs which may have a shorter due date / higher priority customer.

Backward scheduling

In a backward scheduling system, you begin with a planned due date (the date given by the customer). 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.
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, dependent tasks, number of work shifts and planned maintenances.

Some of the advantages of backward scheduling are:

• Less WIP
• Lower cost of storing materials/inventory as materials are only bought and utilised when needed.

Some of the disadvantages of backward scheduling are:

• Chances are if you need a planning and scheduling software such as Opcenter APS (formerly known as Preactor APS), your demand is outstripping your supply capability and may have some late jobs. This will lead to Opcenter APS being unable to schedule the jobs as it should have been already started before now.
• If anything went wrong within the schedule, it could cause knock-on effects to jobs and cause due dates to be missed.
• Lack of safety buffer.
• Struggle to fulfil orders if an unusual or unexpected influx of orders came in.

If you would like more information on how a scheduling solution could benefit your business, please visit our Opcenter AS page. Alternatively, contact us for a demonstration today by calling us on 01709 578300 or filling out the Contact form here.