In order to reduce the lead time of a routing with parallel sequences, you specify that reduction is only carried out on operations, if a reduction in their execution time leads to a reduction in the overall lead time of the order. The sequence of such operations in the routing with parallel sequences forms the "critical path". If applying reduction measures to an operation, would not lead to an overall lead time reduction, this operation is not reduced.
In this reduction type reduction measures are carried out until the overall lead time has been reduced sufficiently. You can consequently retain floats for uncritical operations and prevent unnecessary splits or overlaps.
You set up reduction via the critical path in Scheduling parameters for planned orders and production orders by selecting the reduction type.
In the operation overview for the routing you can select another reduction type via the menu path Extras ®Scheduling ® Schedule. This overwrites the settings you made in Customizing (as do the other settings for reduction).
If a routing does not contain parallel sequences, there is no critical path. All operations are then reduced, irrespective of whether you have selected reduction via the critical path or not.
Process Flow for Reduction
In reduction via the critical path the system first determines which operations lie on the critical path. These operations are then lead time scheduled using the selected reduction strategy and reduction level 1. The floats in your order are also reduced according to the settings. If the overall lead time has been sufficiently reduced after this first reduction run, no further reduction is carried out.
If it is not sufficient, the system determines the critical operations (operations on the critical path) again. This could include different operations than in the first critical path. The reduction level of the operations on the new critical path is increased by one, the uncritical operations are left as they are. Lead time scheduling is carried out for the routing again. If the routing can be carried out within the framework dates or the basic dates respectively, the reduction is sufficient.
If the reduction is not sufficient , the system repeats this process until it is sufficient or in all operations on the critical path the maximum reduction level has been reached:
In this process only the critical operations are reduced in each reduction step. Consequently each operation is reduced by the smallest reduction level necessary.
Recommendations for Working with Reduction via the Critical Path
Reduction via the critical path places greater demands on the system as reducing all operations step-by-step. The following procedure is a good compromise between performance and effective scheduling.
All the operations are reduced to the same reduction level. You carry out this reduction, to determine the maximum reduction level, at which the critical operations have to be reduced, so that the overall lead time of the routing is sufficiently reduced.
Enter as the maximum reduction level the level you determined above.
Through this procedure, only the critical operations are reduced with the maximum level that is necessary to reduce the overall lead time. Other critical operations are reduced with a smaller reduction level. The operations whose reduction does not contribute to a reduction of the overall lead time are not reduced.