Capacity Planning
Capacity planning is the process of identifying necessary resources to support a production plan or a production schedule. Depending upon the time frame involved and whether or not bills have been exploded, more specific terms used to describe the process include resource requirements planning, rough-cut capacity planning, or capacity requirements planning.
Historically, capacity planning is done by backward scheduling requirements (or orders) infinitely (or without explicit regard to capacity). Starting with the due date of the order, the length of the last operation is used to calculate the start and finish time of that operation. Continuing to work backward in time, the start and finish of the next to last operation is calculated, often using a delay time between operations to approximate the time the operation would wait in queue due to constraints.
The sum of operation set up, run, and teardown times on routing operations are used to determine the load of the operation on the resource or resources. These times can also be used to calculate the length of the operation and, therefore, the start and finish time of the operation when it is scheduled. Alternatively, the length of the operation can be specified in another variable. Typically, the load time is then spread out over the length of the operation to determine the timing over which resources are required.
When capacity planning, the availability of resources is determined using shop calendars and shifts, labor staffing levels and quantities of machines and tooling. The availability of resources is expressed as available hours, which can vary over time. Using reports and time series graphs, the capacity planning load is then compared to the availability of the resources. In the example below load is shown versus available hours:
If in a capacity planning time period, the available hours exceed load, you should reduce available hours, reducing cost. If load exceeds available hours, you should add resources, increasing cost. Any competent scheduling or planning software system should be able to provide this minimum level of capacity planning. More precise production planning and capacity planning is available through use of Advanced Planning and Scheduling software.