| As a high-end equipment in the forging industry,large-tonnage multi-link mechanical presses have advantages such as good quick return characteristics,high accuracy,and strong load-bearing capacity.They play an increasingly important role in forming manufacturing,especially in the field of cold and warm forging near net forming,playing an irreplaceable role.With the continuous expansion of the application field of multi-link mechanical presses,higher requirements have been put forward for the working accuracy and performance of multi-link mechanical presses.How to improve the design level of the transmission mechanism of multilink mechanical presses,ensure the dynamic characteristics and machining accuracy of multilink mechanical presses,has become an important issue in the research of key technologies of multi-link mechanical presses.In this paper,the key technologies needed in the development process of the multi-link heavy-duty mechanical press are studied in depth from the aspects of transmission mechanism configuration design,dimension optimization based on kinematics and dynamics analysis,precision and stiffness synthesis design,and dynamic characteristics analysis considering clearance.The cold and warm forging press that meets the design requirements is designed and manufactured,and the verification of relevant theoretical analysis is completed.This paper mainly completed the following research work:(1)The structural synthesis of the transmission system of the multi-link mechanical press is carried out.Firstly,based on the analysis of the characteristics of the transmission mechanism of existing multi-link mechanical presses,the constraint conditions and design demands for the drive mechanism of multi-link presses were proposed.Secondly,a structural synthesis method for single degree of freedom multi-link mechanisms based on composite hinge transformation was proposed based on graph theory;Based on the improved joint structure matrix,a detection method for redundant sub chains and isomorphism is proposed;Through structural synthesis,all possible configurations of ten and ten below links multi-link mechanisms suitable for mechanical presses were obtained.Finally,according to the design requirements of this article,an eccentric driven six links mechanism has been selected as the transmission mechanism of the multi-link cold forging mechanical press.(2)The multi-link transmission mechanism was optimized by considering kinematics and dynamics.The kinematics of the multi link transmission mechanism is analyzed,and the dynamic model of the transmission mechanism is established according to the d’Alembert principle;On the basis of analyzing and determining the optimization objectives,design variables,and constraint functions of the transmission mechanism of a multi link mechanical press,an optimization strategy for the multi link transmission mechanism was formed,and a multi-objective scale optimization mathematical model for the transmission mechanism was established;The improved NSGA-III algorithm was used to optimize the scale parameters of the multi bar transmission mechanism,and a quantitative comparison was made with the crank press and the transmission mechanism before optimization;We have developed an optimization design analysis software for multi link transmission mechanisms,which is used for rapid optimization design of multi link mechanical presses.(3)A precision synthesis and stiffness design method for multi-link transmission mechanisms is proposed based on error modeling and static stiffness modeling.Based on the theory of loop increment,the error transmission model for multi-link transmission mechanisms was established,and the output errors were defined as the position error of the bottom dead center of the slider and the tilt error of the slider;Conduct sensitivity analysis of error sources,and based on this,complete the optimization design of bar tolerance allocation;Through Monte Carlo method simulation,it is verified that the reliability of the sliding block bottom dead center position and tilt angle error under the optimized tolerance design reaches 91.26% and 98.72%respectively,meeting the design requirements.At the same time,based on the heavy-duty working conditions of the press,the output end error caused by rod deformation under load conditions was studied,and a static stiffness model of the transmission mechanism was established.On this basis,a flexible sensitivity analysis was conducted.(4)The dynamic characteristics of the multi-link transmission mechanism considering the mixed clearance and elastic characteristics are analyzed.The elastodynamic analysis model is established,and the effect of the elastic deformation of the mechanism on the lower dead point of the slider is obtained;On this basis,a rigid-flexible coupling model of the multi-link transmission mechanism with mixed clearance was established,taking into account the influence of the clearance of the mixed motion pair;The influence of the elasticity and mixed clearance of the link kinematic pair on the mechanical characteristics of the transmission mechanism is studied,and the influence of different kinematic pairs and different clearance values on the kinematics and dynamic characteristics of the mechanism is analyzed,which provides a theoretical basis for the design of the mechanism kinematic pair fit and the guarantee of the dynamic repeatability of the slider at constant forging speed.(5)On the basis of the above research,the manufacture and assembly of 10000 k N cold and warm forging mechanical press has been completed.Combined with the actual requirements of the project,the structure design of the machine body and auxiliary devices of the multi-link mechanical press was carried out,and the processing and inspection of the key parts were completed.Then,the cold and warm forging mechanical press is assembled and debugged,and the static characteristic test is completed.Subsequently,a test scheme for the dynamic performance of the press was established,and the dynamic performance of the press(dynamic accuracy of the lower dead center,acceleration and deceleration characteristics,and vibration of the fuselage reference point,etc.)was tested.The test results showed that the press reached the design goal,and the correctness and effectiveness of the previous theoretical models were verified by comparison. |
