Pergamon PII S1359-6462(96)00390-9 Scripta Materialia, Vol. 36, No. 3, pp. 347-353, 1997 Elsevier Science Ltd Copyright 0 1997 Acta Metallurgica Inc. F’rintedin the USA. All rights reserved 1359~6462197$17.00 + .OO OPTIMIZATION OF MICROSTRUCTURE DURING DEFORMATION PROCESSING USING CONTROL THEORY PRINCIPLES S. Venugopal’*, E.A. Medina’, J.C. Malas III’, S. Medeiros’, W.G. Frazier’, W.M. Mullins’ and R. Srinivasan2 ‘Materials Process Design, Materials Directorate, Wright Laboratory, WPAFB, Ohio 45433-7746, USA ‘Dept. of Mechanical and Materials Engineering, Wright State University, Dayton, Ohio 45435, USA (Received August 2, 1996) (Accepted September 20, 1996) Introduction The development of optimal design and control methods for manufacturing processes is needed for effectively reducing part cost, improving part delivery schedules and producing specified part quality on a repeatable basis. Existing design methods are generally ad hoc and lack adequate capabilities for finding effective process parameters such as deformation rates, die and workpiece temperatures, and tooling system configuration. This situation presents major challenges to process engineers who are faced with smaller lot sizes, higher yield requirements, and superior quality standards. Therefore it is important to develop new systematic methodologies for process design and control based upon scientific principles which sufficiently consider the behavior of workpiece material and the mechanics of the manufacturing process. A new strategy for systematically calculating near optimal control parameters for hot deformation processes for m~icrostructural control is presented in this communication. This approach is based on modem control theory[l] and involves developing state-space models Corn available material behavior and hot deformation process models. The control system design consists of two basic stages and analysis and optimization are critical in both stages. In the first stage, the kinetics of certain dynamic microstructural behavior and the intrinsic hot workability of the material are used, along with an appropriately chlosen optimality criterion, to calculate optimum strain, strain-rate, and temperature trajectories for processing. A suitable process simulation model is then used in the second stage to calculate process control parameters, such as ram velocity, die profiles and billet temperature, which approximately achieve the strain, strain-rate, and temperate trajectories calculated in the first stage at selected areas of the workpiece. The validity of this approach has been demonstrated with an example on hot extrusion of steel, *On leave from Indira Gandhi Centre for Atomic Research, Kalpakkam-603 102, Tamil Nadu, India. 347