Abstract
Many manufactures are shifting from classical production environments with large batch sizes towards mixed-model assembly lines due to increasing product variations and highly individual customer requests. However, an assembly line should still be run with constant speed and cycle time. Clearly, the consecutive production of different models will cause a highly unbalanced temporal distribution of workload. This can be avoided by moving some assembly steps to pre-levels thus smoothing out the utilization of the main line. In the resulting multi-level assembly line the sequencing decision on the main line has to take into account the balancing of workload for all pre-levels. Otherwise, the modules or parts delivered from the pre-levels would cause congestion of the main line. One planning strategy aims at mixing the models on the main line to avoid blocks of identical units. In this contribution we compare two different realizations for this approach. On one hand we present a mixed-integer programming model (MIP), strengthen it by adding valid inequalities and enrich it with a number of relevant practical extensions. Also the actual objective of explicitly balancing pre-level workloads is considered. On the other hand, we illustrate how this strategy could be realized in an advanced planning system linked to an enterprise resource planning system, namely SAP APO. Finally, we perform a computational study to investigate the possibilities and limitations of MIP models and the realization in SAP APO. The experiments rely on a real-world production planning problem of a company producing engines and gearboxes.
Highlights
Product variety increased drastically over the last decade in a wide range of industries through a higher degree of product customization and the renunciation of standardized products (Meyr 2004; Pil and Holweg 2004)
We present computational experiments based on a real-world case study and compare the possibilities and limitations of modelling (Sect. 5) as well as the computational performance for the mixed-integer program (MIP) models compared to the realizations in SAP APO
One planning strategy to indirectly achieve balanced utilization is offered in the planning environment APO of the industry standard Enterprise Resource Planning (ERP)-system SAP
Summary
Product variety increased drastically over the last decade in a wide range of industries through a higher degree of product customization and the renunciation of standardized products (Meyr 2004; Pil and Holweg 2004). It remains as a demanding challenge for production companies to switch their organization from large batch sizes to lot size one without incurring excessive extra cost It is the classical task of assembly line production planning to balance the workload assigned to each work station and allow a constant speed and cycle time of the assembly line. Adapting workforce or line speed after each small batch are both infeasible in practice To overcome this obstacle to a flexible utilization of the assembly line and to reach a task allocation where the work intensity of all products lies within a limited range, manufacturers with a heterogeneous product portfolio can apply the following strategy: Firstly, for each product some assembly steps are outsourced to pre-levels to permit a more or less uniform remaining workload on the main line, while the variances in workload are shifted to the pre-level assembly stations. The MIP model, while SAP APO allows only a partial representation of these extra requirements
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