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Dynamic Analysis And Optimization Of Heavy-duty Manipulator During Metal Forging Process

Posted on:2013-07-24Degree:DoctorType:Dissertation
Country:ChinaCandidate:D S LiuFull Text:PDF
GTID:1221330395499235Subject:Engineering Mechanics
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The large forging is the important basis of national heavy machinery industry, which is important for the national safety and economic lifeline, also, it demonstrates the comprehensive national power. Large forging productions are widely used and needed in basic industries, such as electrics, petrochemical, shipbuilding, aeronautics and astronautics, military, et al. Large forging hydraulic press is the manufacturing machine of large forging workpieces. Until now, there are seven hydraulic presses in China whose capacities are more than10000ton, with the largest number all over the world, moreover, and the large forging hydraulic presses could be designed and manufactured independently. Heavy forging manipulator is the important auxiliary tool for the hydraulic press, which greatly improves the workpiece precision, working efficiency, material utilization, and the power consuming for production could be reduced. Unfortunately, the large forging manipulator could not be designed independently in China, so the research in this area is very important for domestic heavy equipment manufacturing industry.The motion of hydraulic press during metal forging produces large interface load at the clamp of the forging manipulator, which may cause the damages in the mechanical components of the manipulator and the workpiece. Especially in some accident the forging die drops on the workpiece directly without any control, and the huge impact force could possibly damage the clamp because of over loading. This dissertation is focused on the transient response and force flow of the "press-workpiece-manipulator" system, which provides theoretical support for manipulator design. The following works are included:(1) Dynamic compliance behavior of forging manipulator which clamps a slender bar workpieceThe slender bar workpiece is usually produced in forging industry. During the finishing phase of forging process, the hydraulic press moves fast, the impact vibration effect is significant, and the press position where the press works has a significant influence on the dynamic behavior of the manipulator.. The manipulator system is modeled as a vibration system with single degree of freedom (SDOF) according to some reasonable assumptions. Comparisons between the analytical results and the commercial FEM software LS-DYNA simulations are made to validate the proposed model. In the case of linear compliance without damping, the useful design formula could be derived which explicitly show the dependence of the dynamic load amplitudes on the press positition and system parameters, including the press paremeters, workpiece parameters and manipulator parameters. The compliance behaviors of the translational manipulator and rotational manipulator are compared, and the results show that the two kinds of manipulators are the same in dynamics essentially. The dynamic behaviors of manipulator with two kinds of bilinear compliance force are studied, then the compliance force is optimized to minimize the maximum force exerted to the clamp during the compliance motion.(2) Dynamic analysis and multi-objective optimization of forging manipulator under large amplitude compliance motionAt the beginning phase of the forging process, the workpiece is podgy, the hydraulic press moves slowly, however, the deformation of the workpiece is large as well as the compliance motion of manipulator which causes the nonlinearities of resilient stiffness and mechanism geometry change. The multibody dynamic model is established, which is used to investigate the influence of the above two kinds of nonlinearities on the dynamic behavior of the manipulator. The actual pressure equation of resilient cylinder is derived, and is validated by the workshop experiment.The performance requirements of the manipulator are different for different working periods of one forging stroke. During the compression period, the vertical force imposed on the clamp should be minimized to guarantee the safety of the structure; during the rebound period, the clamp needs to rebound to the initial working position as soon as possible to improve the working efficiency. Both criterions need to be satisfied simultaneously in the manipulator design. The multi-objective optimization formulation of the forging manipulator under the large amplitude compliance motion is established, in which the parameters of horizontal and vertical compliance cylinders, including the initial heights of the accumulator and the orifice areas, are optimized by NSGA-II method to obtain Pareto-optimal solutions.(3) Dynamic behavior of forging manipulator under the impact of dropping dieIn practical production, the upper die could possibly lose control due to the malfunction of the hydraulic system. As a result, it drops freely and finally hit the workpiece. producing the huge high frequency impact force instantaneously and exerted to the clamp, with the magnitude tens of times over the self weight of the workpiece, and the clamp could possibly be fractured due to overloading. The3D finite element model of the manipulator system is established in LS-DYNA to simulate the impact due to the dropping die. in which the influence of the system parameters are studied, including the manipulator parameters, workpiece parameters and press parameters.. The impact force is the largest when the impact occurs near the clamp, and the dynamic response of the system is dominated by the fundamental frequency, in such case, the manipulator system could be regarded as a SDOF system, by which the dynamic behavior of the system could be explained theoretically.
Keywords/Search Tags:Forging manipulator, Plastic deformation, Impact vibration, Transientresponse, Passive compliance, Multi-objective optimization
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