# 13.1.2 Operation Time and Operation Load

### Intended learning outcomes: Present the simplest formula for operation time using a graphic representation. Explain the simplest formula for operation load.

Operation time is the time required to carry out a particular operation. It is defined in Section 1.2.3 as the sum of setup time for machines and tools and the run time for the actual order lot.[note 1301] The latter is the product of the number of units produced (the lot or batch) and the run time for a unit of the lot produced (the run time per unit). The simplest formula for operation time occurs when run times are scheduled serially following the setup time, as in Figure 1.2.3.1.

Figure 13.1.2.1 shows the formula for operation time as a graphic representation.

Fig. 13.1.2.1       The simplest formula for operation time (graphic representation).

The formula for calculating operation time becomes more complicated when we include special effects such as splitting or overlapping. See also Section 13.4.

Operation load is the work content of the operation, measured in the capacity unit of the work center used for the operation. In Section 1.2.4, we saw that operation load is the sum of the setup load— the work content that is independent of batch size — and the run load for the actual order lot.[note 1302] The latter is the product of the number of units produced (the lot or batch) and the run load per unit for a unit of the lot produced.

Figure 13.1.2.2 shows the formula for the operation load shown in the simplest case. Compare here the formula given in Figure 1.2.3.1.

Fig. 13.1.2.2       The simplest formula for operation load.

Often, the capacity unit for the work center used for the operation is a unit of time. In this case, setup time and run time are generally identical with setup load and run load. There are, however, instances in which the operation time bears no relationship to the operation load.

• For subcontracted operations, e.g., a cost unit may be chosen as the capacity unit.
• For operations with an extremely complicated execution or for purely fictitious “waiting operations,” which have no influence upon the load of a work center or upon manufacturing costs, the chosen operation time must be different from the operation load.

If the inter­operation times exert the dominant influence on total lead time, scheduling does not require exact knowledge of the operation time. For purposes of capacity management, however, planners need the exact value of the operation load to gain a meaningful load profile for a work center. If they are now able to derive the operation time from the operation load, they can calculate the precise operation time as well as the operation load.