Sequencing (production)

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As sequencing or sequence planning (in the scientific field and by the English term sequencing and scheduling familiar) is in the production planning the formation of a production sequence of production orders referred. In many industries (chemical industry, automotive industry) it is unfavorable to carry out production orders in the order in which they arrive. Instead, the production sequence is designed in such a way that, for example, the utilization of machines and personnel is even or the set-up costs of machines are minimal. A business produces in batch production , not individual production orders, but all are lots sequenced.

Often only a part of all existing production orders is sequenced due to the usually high computational complexity. This can e.g. B. be the production program of a single shift or a day. The assignment of orders to daily or shift programs is inconsistently referred to in the literature as level scheduling, smoothing or balancing. This then results in planning hierarchies such as B. Month - day - cycle.

In the American-speaking world, the terms scheduling and sequencing are often equated. It should be noted, however, that a sequence usually denotes an unchangeable fixed production sequence (see also pearl chain ), while the scheduling generally describes the production sections in chronological order, in which the position of an order or several orders can change afterwards . (See also Scheduling .)

Scientific approaches and methods for solving the sequencing problem

In order to meet the requirements for a technical solution to the problem of determining optimized production sequences, the experts use a wide variety of approaches. Basically, two principles are applied here.

Calculation of a mathematically exactly determined solution using:

Finding a solution using heuristics such as B .:

Combinations of the above methods can also be used.

Systems for solving sequencing problems

The sharp drop in investment costs for computer systems already enables the use of modern, high-performance software solutions that are based on the order data from order-carrying ERP / PPS systems together with the specific requirements from production. Most of these tools use so-called solvers for this purpose , which are based on the methods already described above and are available on the market as function libraries, for example. With additional functions added, integration into existing PPS / MES environments is simplified or even made possible in the first place.

Increasing complexity and an increasing number of variants of the products to be produced have led the automotive industry to assume a pioneering role when it comes to the use of sequencing systems. Other branches of industry, which in the meantime have oriented themselves towards the production principles of the automobile manufacturers [see also Toyota production system], are increasingly thinking about the use of such planning tools. In particular, because such calculations should no longer serve exclusively to determine the daily requirements actually to be produced, but also because it is possible to simulate a wide variety of scenarios and to compare the results achieved in the simulation runs for analysis purposes.

In addition to the plant and labor capacities already mentioned, other assembly-relevant aspects can be taken into account as restrictions, such as B .:

  • different cycle times for heterogeneous production lines
  • Distances to be observed
  • Blocks to be formed (e.g. grouping bodies of the same color when painting vehicles)
  • wedge-shaped restrictions (e.g. only a few complex vehicles at the beginning of a shift)
  • Equal distribution of time-consuming work content.

literature

  • N Boysen, M Fliedner, A Scholl, production planning for variant flow production: planning hierarchy and hierarchical planning , - Jenaer Schriften zur Wirtschaftswwissenschaft, 2006, (PDF, 542 kB)
  • Lean material flow , Springer Berlin Heidelberg, ISBN 978-3-540-34337-0
  • Christine Solnon, Van Dat Cung, Alain Nguyen and Christian Artigues, The car sequencing problem: overview of state-of-the-art methods and industrial case-study of the ROADEF'2005 challenge problem , (PDF, 256 kB)