DEVELOPMENT OF TUBE DRAWING SCHEDULES IN A COLD DRAWING PLANT USING EXPERT SYSTEM TECHNIQUE

Seamless tubes have gained wider applications and are being used extensively in nuclear and conventional power plants, refineries, machine tools and hydraulic equipment and pipelines for conveying oil and gases and are manufactured by the use of rotary or non-rotary processes to produce hollows, followed by cold drawing operations. These hollows are then cold drawn to attain high dimensional accuracy and required surface finish by any of the cold drawing processes such as sinking, mandrel drawing, fixed plug drawing or floating plug drawing. In order to achieve the required dimensions of the finished tube, it is common practice to carry out one or more passes depending upon many factors such as drawing capacity of the bench in terms of maximum safe load, stress/strain characteristics of material being used, prior work hardening and availability of tools. Traditionally, the tube drawing schedules are prepared by making use of personal shop floor experience, judgement and expertise in the field without giving much attention to the aforementioned process parameters. A prototype expert system is being developed for process planning in a seamless steel tube plant. Expert systems are computer programmes using domain-specific knowledge to achieve a high level of performance in a field which would otherwise require a human expert. This paper discusses the part of the process planning system which deals with the generation of tube drawing schedules. In the first section the theoretical approach for determining process parameters for fixed plug drawing such as stress/strain and hence the drawing loads is described. In the second section of the paper, the generation of alternative tube drawing schedules, selection of optimum schedule by the use of heuristic rules, selection of other secondary operations and operation sequence are discussed. The system is implemented in Turbo-Prolog language and has been tested on the actual data of the plant with satisfactory results. An operation sequence sheet for an example part is included at the end.