| The use of multi-station press to punch the U-shaped longitudinal beam has the advantages of high punching frequency,high production efficiency and low overall cost.It is the development trend of U-shaped longitudinal beam processing technology,and it is still in the initial stage in China.This paper takes the U-shaped longitudinal beam belly punching multi-station press as the object,and researches the key technologies around the influence of main transmission system design,eccentric loading,tie rod preload and other factors on the body stiffness and strength.The purpose is to design the press that can meet the technical requirements of U-shaped longitudinal beam belly punching,and lay the foundation for the realization of the localization of U-shaped longitudinal beam punching technology of multi-station press.The main research contents and conclusions of this paper are as follows:(1)Analysis of the punching process of U-shaped longitudinal beam and determination of the main technical parameters of the multi-station press.Through the analysis of the types and positions of the diameter of the typical U-shaped longitudinal beam,it is known that the diameter of the abdominal face isФ6-Ф60,each longitudinal beam has 6-9 kinds of abdominal face,and with a diameter ofФ13 andФ15 groups of holes,the nominal pressure that can meet the punching process requirements is determined P_g=1600k N;Along the longitudinal beam feeding direction,12 combined punching units are arranged from left to right in the X direction of the workbench,and the left and right positions are symmetrical.Based on the punching process and the distribution of combined punching units,the main technical parameters of the multi-station press are determined.(2)Analysis and design of the main transmission form of multi-station pressure machine.Based on the punching technology of the abdominal surface and the requirements of the anti-offsetting load ability of the main body of the main engine,the longitudinal transmission form of the double crankshaft is designed.Under the condition of meeting the requirements of connecting rod strength and first-order precision of sliding block movement,the relationship between bar distance L and allowable load F’is obtained,and the bar distance L=2068mm is determined.The relationship between the rail spacingΔl and the allowable load F’in the front and rear directions was investigated,and the rail spacingΔl=400mm was determined.The kinematic analysis of the main drive system is carried out by using the mathematical analysis method,and the relation and motion curve between the slider displacement S,velocity v,acceleration a and crank Angleαare obtained,which verifies that the structure design meets the punching process requirements.(3)The influence of preload on the stiffness of composite fuselage.Taking the combined fuselage of press as the research object,finite element analysis method was used to study the different conditions of the combined fuselage of press,such as preloading,center loading and eccentric loading.The contact pressure distribution law of the contact surface between the column and the upper beam,the relationship between the preload coefficient k and the offset load coefficient i,the deformation of the upper beam in the Z direction,and the relationship between the offset load coefficient i and the maximum deformation differenceΔh are obtained.It is obtained that the deformation of the upper beam is basically symmetric about the Y-axis when the center is loaded.In eccentric loading,the upper beam deformation is larger near the side with larger partial load;When the force of the press is the nominal force,that is,F=P_g=1600k N,the preload coefficient k=3.0 when the partial load coefficient 1≤i≤3 is determined.(4)The influence of the main transmission system on the motion accuracy of the slider.Taking the main drive system as the research object,the influence of partial load on the motion accuracy was analyzed by finite element method,and the allowable load curve of the main drive system was obtained.When the offset load distanceΔx<798mm,the allowable offset load F’should meet the strength requirement;When the offset load distanceΔx>798mm,the allowable offset load F’must meet the accuracy requirements.The allowable load at each station is obtained;The influence of crank Angle phase difference,crank radius error and connecting rod length error is analyzed by analytical method.With the increase of crank Angle phase difference,crank radius error or connecting rod length error,the slider tilt increases,thus reducing the allowable load of the press.Therefore,the accuracy requirements should be guaranteed in the actual design,installation and manufacturing are put forward.(5)Structure analysis of multi-station press assembly.Taking the overall structure of1600k N closed double-point press as the research object,finite element analysis method was adopted.When the preload factor k=3.0,the strength,stiffness and modal analysis of the overall structure of the press were carried out by applying the central load of 1600k N and the allowable load to each station,and the equivalent stress,deformation and the deformation of the bottom surface of the slider along the Z direction of the whole machine were obtained.The maximum deformation difference of the slide block isΔh=0.338mm,which is less than the allowable value[h]=0.375mm,which proves that the overall design meets the strength requirements of the press and the first-order motion accuracy requirements of the slide block.Through dynamic modal analysis of press assembly,it is found that the press will not produce resonance phenomenon,and the overall structure of the press is stable under the condition of various vibration levels,which verifies the rationality of the structure design. |
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