A Goal Oriented, Sequential Process Design of a Multi-Stage Hot Rod Rolling System

Abstract

The steel manufacturing process is characterized by the requirement of expeditious development of high quality products at low cost through effective and judicious use of available resources. Identifying solutions that meet the conflicting commercially imperative goals of such process chains is hard using traditional search techniques. The complexity embedded in such a problem increases due to the presence of large number of design variables, constraints and bounds, conflicting goals and the complex sequential relationships of the different stages of manufacturing. A classic example of such a manufacturing problem is the design of a rolling system for manufacturing a steel rod. This is a sequential process in which information flows from first rolling stage/pass to last rolling pass and the decisions made at first pass influence the decisions that are made at the later passes. In this paper, we present a method based on well-established empirical models and response surface models developed through simulation experiments (finite element based) along with the compromise Decision Support Problem (cDSP) construct to support integrated information flow across different stages of a multi-stage hot rod rolling system. The method is goal-oriented because the design decisions are first made based on the end requirements identified for the process at the last rolling pass and these decisions are then passed to rolling passes that precede following the sequential order in an inverse manner to design the entire rolling process chain. We illustrate the efficacy of the method by carrying out the design of a multi-stage rolling system. We formulate the cDSP for the second and fourth pass of a four pass rolling chain. The stages are designed by sequentially passing the design information obtained after exercising the cDSP for the last pass for different scenarios and identifying the best combination of design variables that satisfies the conflicting goals. The cDSP for second pass helps in integrated information flow from fourth to first pass and in meeting specified goals imposed by the fourth and third pass designed. The end goals identified for this problem for fourth pass are minimization of ovality (quality) of rod, maximization of throughput (productivity) and minimization of rolling load (performance and cost). The method can be instantiated for other multi-stage manufacturing processes such as the steel making process chain having several unit operations. In future, we plan to use the method for supporting decision workflow in steel making process by formulating cDSPs for the multiple unit operations involved and linking them as a decision network using coupled cDSPs.