What Is Routing?

Routing Explained

Where the bill of materials answers what goes into a product, the routing answers how it gets made. Each operation carries a sequence number, a work center, a setup time that is incurred once per order, a run rate expressed either as hours per piece or pieces per hour, and non-productive elements such as queue, move, and wait time. The sum of these across all operations produces the manufacturing lead time the planning engine uses when it offsets a work order release date.

Routings drive three separate ERP subsystems. Planning uses them to compute lead time and to load work centers for capacity requirements planning. Costing uses setup and run hours multiplied by work center labor and overhead rates to build the labor and burden portions of standard cost. Execution uses them to generate the operation-level dispatch list the shop floor reports against. Because one record feeds all three, an inflated run time simultaneously distorts the schedule, the cost, and the efficiency variance.

Alternate and parallel routings handle real shop flexibility. An alternate routing describes a different way to make the same item, typically on a slower backup machine, and is selected either manually or by a scheduling engine when the primary work center is saturated. Overlapping or parallel operations let a downstream step start before the upstream step finishes a full lot, which is how a plant compresses lead time on long-run parts. Outside processing operations model subcontract steps such as heat treat or plating, and generate a purchase order tied to the work order.

The most common data problem is that run times are inherited from an estimating quote rather than measured from production. Quoting rates are usually optimistic and rarely include the learning curve on new parts. When actual hours consistently exceed routed hours, the plant shows a permanent unfavorable labor variance that has nothing to do with operator performance and everything to do with a stale standard.