Dissertation > Industrial Technology > Metallurgy and Metal Craft > Metal pressure processing > Forging, forging and blacksmith > Forging Machinery and equipment

Research on Multidisciplinary Integrated Modeling and Low Speed Stability for the Heavy Forging Press

Author LiYiBo
Tutor HuangMingHui
School Central South University
Course Mechanical Engineering
Keywords heavy forging press multi-body dynamics low-speedhydraulic system forging force non-linear friction compensation control multidisciplinary
Type PhD thesis
Year 2013
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Heavy forging press is the strategically foundational manufacturing equipment of our country; it provides the majority of the large load-bearing components and forgings for advanced equipments in all fields of the national economy and thus plays an irreplaceable role in major national projects and national defense construction. With the establishment of a series of huge forging presses of the forging force from200MN to800MN, we have already had the ability to produce large overall forgings. However, because of the weakness or lack of the research work at the level of system integrated, a systematic and scientific performance evaluation criterion for the design, manufacturing and running control of the heavy forging equipments is still unavailable. Due to the impossibility of overall functionality and reliability prediction for heavy presses, the improvement of running performance and operation efficiency have been largely limited and restricted and the quality of forgings have been greatly decreased. On the other hand, with the development of precise forgings, new forming method and process are required to complete the high performance manufacturing of large forgings. Because of the significant effects of reducing deformation resistance, isothermal forging technology has been the key to accurate forming of large components to improve metal flow state and internal organization performance of the materials. It is clear that the forging force must be maintained up to500seconds during the whole isothermal process, which means the heavy press must be running under extreme low speed for a long time. High inertia of the press will lead to working under unstable status, such as oscillating, crawling and jittering, thus greatly degrade the quality of the products. Therefore, it is urgent to improve the certainty and stability of the heavy press under low speed.For the above-mentioned purposes, taking isothermal forging press of large precision forgings as the object, based on model constructions of system dynamics, hydraulic control system, metal forging process and real-time data interactions among such models, a multidisciplinary integrated simulation model of the heavy forging press is established and thus a evaluation and prediction method for the overall performance of the heavy press is built up. Due to the equipment-forming interaction driven evolution research of the material properties, the model can achieve the purpose of active control of the equipment and thus is theoretically significant and valuable in engineering application for improving not only the dynamic performance of the press but also the quality of the forgings.Here are the main contents of this paper.1) Elimination of statically indeterminate redundant constraints and system dynamics modeling of the Heavy forging press.Statically indeterminate structures introduce too many redundant constraints to the system and make it too difficult to build a systematic dynamic model of the heavy press. Faced with different structures, methods of "rigid body flexible, force-generation kinematic pairs and constraints simplistic" are proposed to eliminate redundant constraints; for the pre-stressed structures, pre-load files of the levels are written and a simple method is proposed for the exact modeling of the forces. Based on such works, a general system dynamics modeling process is formed and typical models are built up to analyze the dynamic performance of the presses. Comparing the simulation results with the test ones, correctness of the modeling method and simulation models are validated in the end.2) Co-simulation and parameters optimization of the hydraulic control system of the low speed running heavy forging press.To satisfy the need of stable running under low speed, a new design of the low-speed hydraulic system with electrical variable displacement pump driving, high response servo valve controlling, hydraulic pressure compensation and magnetic proporgation support balancing system is proposed to achieve the purposes of rapid response and extreme small flow compensation control of the system. PID or novel PID controlling is the main strategy of this design, and parameters tuning and optimization of the controllers and extreme importment for improving the system’s response and control accuracy; to do so, a Genetic Algorithm is proposed and validated to automatically tuning the controllers in this paper; then, to complete the whole electro-hydraulic control system model, numeral and physical models of all the hydraulic components are built up and a full model is integrated; finally, the new design of the hydraulic system is applied to the heavy forging press and the accuracy and reliability of the system and numerical models are examined.3) Processes of equipment running and metal forging interaction based on multidisciplinary integrating modeling and stability study of the press.Complexity of mechanical characteristics and discrete of the simulation results during metal forging simulation made it too difficult to be coupled with multi-body dynamics model and hydraulic system directly. To overcome such a difficulty, a principal stress based and multidisciplinary integration oriented forging force analytically modeling method is proposed and optimized by the experiments results to establish the forging force in this paper. Joint the force with multi-body dynamic and hydraulic models, a full forging process base and equipment-forming interaction model of the low speed heavy forging press are established. Finally, dynamic properties of the press are studied systematically and nonlinear friction force is found to be the key factor that causes the system unstable.4) Stability control of the heavy forging press under extreme low speed based on the friction feedback and compensation.To reduce the influence of nonlinear friction to the stability of the press, a precision dynamic testing system is built up to obtain the friction force of the low speed running system; Based on the study of friction properties, a modified LuGre model is established, by using least squares method, minimum norm search method and genetic algorithm, parameters of the modified LuGre model are identified and validated through the experiments. In order to improve the stability of the system, normal PID, two-dof PID, fuzzy adaptive PID and robustic adaptive comprehensive control algorithm are used to establish different friction compensation methods. Comparing the control accuracy and velocity tracking errors with each other, a best compensation method is found and applied to the heavy press. Experiment results show that, the fuzzy adaptive PID control algorithm is the best one. By applying the fuzzy PID controller to the system, lowest speed of the press is about0.005mm/s and the speed fluctuation is less than20%.

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