Günther Zäpfel

New concepts for production planning and control

Abstract Production planning and control (PPC) is of great importance for the competitive position of manufacturing firms. For over thirty years a large number of computer assisted PPC systems have been on offer, most of them based on the well-known MRP logic. Since these systems often lead to unsatisfactory results, a number of new concepts for PPC systems have been developed. In this paper we first describe the traditional PPC concept and its critique, then we review the new PPC concepts which are available for practical application (workload control, MRP II, OPT, JIT-Kanban, progressive figures) together with OR models which are relevant to these new concepts.

Planning and optimization of hub-and-spoke transportation networks of cooperative third-party logistics providers

Abstract Increased competition in the transport market has led to new cooperative arrangements between third-party logistics providers in the form of hub-and-spoke systems. In addition to the design problem, the operative planning task of a hub-and-spoke network is a challenging task for the management of such transportation networks. In particular, the transport management has to decide whether a pure hub-and-spoke system should be realized, where all quantities within the transportation network flow over the hub from or to the depots, or whether a hybrid hub-and-spoke network is preferred in which direct transports also take place. Mathematical models for these operative planning tasks are developed and applied to a real case of an Austrian parcel service provider. While the actual problem is taken from a real parcel service provider the model can also be applied in the general cargo industry. Cost savings of the hybrid hub-and-spoke system are described.

Production Planning and Control (PPC) systems including load-oriented order release -- Problems and research perspectives

Abstract In the last fifteen years order release has been increasingly recognized as a very important decision problem in production planning and control. In German-speaking countries, especially load-oriented order release (we use the acronym BORA from the German) has been discussed with great interest, both in theory and practice. In this paper we show that the performance of BORA depends on the parameter setting and the optimal parameter setting of BORA depends on the capacity load. We develop two LP models for rough-cut capacity planning which can be used to adjust dynamically the parameters of BORA to the capacity load. Simulation results show improvements compared to a BORA application using ‘standard’ parameter values.

Hierarchical model for production planning in the case of uncertain demand

The paper deals with hierarchical production planning for a multiperiod model consisting of an aggregate planning level and a detailed planning level in the case of uncertain demand. At the beginning the detailed demand for the actual planning period is known, whereas for future planning periods only upper and lower bounds of detailed demand are known. On the other hand, the aggregate demand on the product group level is supposed to be deterministic at each planning period over the whole planning horizon. For the aggregate planning level, robust production plans (i.e., aggregate production plans which can be disaggregated to a feasible detailed plan for every possible detailed demand) are proposed and a consistent disaggregation is executed for the detailed planning level. Two sets (static and dynamic) of sufficient conditions for robustness of the aggregate plan as well as dynamic disaggregation conditions are derived. These sufficient conditions are a generalization of the results of Lasserre and Merce. The performance of the sufficient conditions are demonstrated by a computational study which shows the potential advantage of the approach.

Customer-order-driven production: An economical concept for responding to demand uncertainty?

Abstract To gain competitive advantage, firms have increased their number of variants in recent years. But as a consequence it has become more and more difficult to forecast demand at the level of individual products over the planning horizon. In this situation customer-order-driven production becomes more and more important : Production quantities are determined at the moment the customer orders are known and therefore demand uncertainty is removed. Short delivery times (relative to the competitor) and sufficient capacities as well as a flexible production must be guaranteed. The new production concepts, e.g. JIT, and more general Lean Production or Time Based Manufacturing reinforce the tendency to a more customer-order-driven production. A mathematical model is presented to derive conditions for an economical customer order driven production.

Production planning in the case of uncertain individual demand Extension for an MRP II concept

Abstract To gain competitive advantage, firms have increased their number of variants in recent years. But as a consequence it has become more and more difficult to forecast demand data at the level of individual products over the planning horizon. However, practical experience shows that forecasts of aggregate demand are quite accurate. Exact data for individual products can be determined for the current but not for the remaining periods. For the remaining periods only upper and lower bounds of the demand data for individual products can be predicted with certainty in many cases. This means that production planning should follow a hierarchical planning concept: First, production planning should be conducted at the aggregate level over the planning horizon to determine simultaneously the resource requirements (regular capacity and overtime) and the quantities of the product groups in order to satisfy aggregate demand. Second, for the immediate scheduling period the detailed planning level should determine how available production resources have to be allocated to the individual products subject to some constraints imposed by the aggregate plan. MRP II (Manufacturing Resource Planning) is a production planning system which is based on a hierarchical concept and has been developed for such complex production situations. The paper concludes that the MRP II concept is only partially suited to production planning in the case of uncertain demand. A hierarchical model, which can be incorporated into the MRP II concept, is therefore proposed for uncertain demand. An alternative method for uncertainty reduction is also briefly discussed.

Produktionsplanung und -steuerung für die Fertigungsindustrie — ein Systemvergleich

Die zunehmende Verscharfung der Wettbewerbsbedingungen fuhrt zu hohen Anforderungen an die Produktionsplanung und -steuerung. Aus diesem Grund wurden in den letzten Jahren mehrere neue Ansatze zur Produktionsplanung und -steuerung vorgeschlagen und getestet. In der vorliegenden Arbeit werden diese Ansatze systematisiert, beschrieben und theoretisch fundiert.

An exact approach for single machine subproblems in shifting bottleneck procedures for job shops with total weighted tardiness objective

In this paper, we propose an exact solution method for single machine scheduling problems typically arising from bottleneck-based decomposition of weighted tardiness job shops. The encountered subproblems are characterized by delayed precedence constraints, multiple local due dates per operation and an objective function that is given by a weighted sum of maximum tardiness values. The key concept for solving these subproblems to optimality is a dominance rule whose underlying concepts have been newly developed to cope with the given structural properties. Furthermore, a simple lower bound and a dedicated constraint programming technique are presented. The efficiency of the proposed method is demonstrated by means of single machine problems collected during a run of a shifting bottleneck procedure for job shops in different size and due date tightness configurations.

Enhancing local search algorithms for job shops with min-sum objectives by approximate move evaluation

Exact move evaluation in local search-based job shop scheduling is known to be time consuming, especially for medium and large size instances. Therefore, approximation functions providing quick estimates for the cost induced by a move are often used in order to accelerate the search process. This paper describes the generalization of an existing cost estimation function for insertion moves towards min-sum objectives, such as total weighted tardiness, total weighted completion time and total weighted number of late jobs. Besides the transfer of the concept itself, shortcomings of the original approach are identified and eliminated and an enhanced approximation scheme is presented. The final estimation function is able to provide a considerably increased accuracy for the considered min-sum objectives compared to the existing approach. The advantage of the new function emerges most clearly when it is embedded into a tabu search algorithm, as verified based on benchmark instances from literature involving up to 100 jobs and 20 machines.

Computational study of neighborhood operator performance on the Traveling Salesman Problem with Time Windows in neighborhood search based frameworks (RTS, VNS)

In this work we analyze the performance of different neighborhood operators in terms of solution quality in different neighborhood search based frameworks, namely Reactive Tabu Search and Variable Neighborhood Search, on the Traveling Salesman Problem with Time Windows. We compare the impact of the two different search concepts on the solution quality by embedding the same operators and hence be able to precisely state the impact of the basic concept. Additionally, we analyze the improvement of those search strategies compared to a simple local search procedure. The neighborhood operators under consideration are 1-shift, nodeexchange, lexicographic 2-opt, lexicographic 3-opt and or-opt.