Integral Logistics Management — Operations Management and Supply Chain Management Within and Across Companies

13.4.4 Extended Scheduling Algorithms (*)

Intended learning outcomes: Identify various possible extensions of the scheduling algorithms. Describe possible cases arising in process industries.

We can now extend the scheduling algorithms presented in Section 13.3.3 to include the definitions introduced in the subsections above. These include:

  • The introduction of a lead-time-stretching factor that multiplies inter­operation times
  • The introduction of splitting and overlapping and an expanded formula for lead time
  • The inclusion of multiple partial orders for each production order
  • The inclusion of divergent product structures, as — for example — the case of temporary assembly
  • Ongoing planning for released orders with work remaining to be done

We can derive a generalized algorithm from the algorithm presented in Section 13.3.3, for both a sequence of operations and for a directed network of operations. This would complicate the algorithm further, and we will not present it here in detail.

The extensions introduced thus far may not be sufficient for lead time scheduling in every potential scenario. A first case is the undirected network of operations with a repetition of operations. During a chemical process or in the production of electronic components, for example, production has to repeat certain operations. This may be because inspection has uncovered defects in quality. Here, the number of iterations and the individual operations to be repeated become evident only during the course of work and cannot be planned in advance. In this case, it is not possible to calculate lead time precisely. Instead, we have to use expected mean values for the number of iterations and accompanying deviation. However, we have to take into account that each calculation of lead time itself is based on estimations of the time elements, particularly wait time in front of the work center.

Another case arises in process industries. The processor-oriented concept implemented in these industries may require sequencing or, more precisely, the planning of optimum sequences of operations, as early as the phase of long- and medium-term planning. Because of the extremely high setup costs, planners should establish suitable lots even prior to order release to keep changeover costs at a minimum. To this category belongs, for example, cut optimizations for glass, sheet metals, or other materials. The scheduling of an individual order will depend on whether it may be combined with other orders and with what orders, to achieve optimal usage of the raw material, the reactors, or processing containers.

Course section 13.4: Subsections and their intended learning outcomes