Optimization Of Laser Welding Process Forpiston Rad And Research On Fixture

In this thesis,through theoretical and practical analysis,optimization design and experimental verification,laser welding technology is used to enhance the bonding ability between metal materials and prolong the service life of the piston rod which is composed of Q345 D material plug and 20Mn2 material plug rod interference fit.In laser welding,it is necessary to consider the weld morphology,weld penetration,weld hardness,weld microstructure and other comprehensive factors,so it is particularly important to grasp the laser welding parameters in the process of laser welding.After welding,the penetration of piston rod should be about 4mm,and there should be no pores,cracks,pits and other phenomena.In this thesis,Q345 D and 20Mn2 thin plate and piston rod are used to explore the laser welding parameters.The main welding parameters are laser power,scanning speed and defocus.The laser power reflects the energy density of the radiation on the metal material,the scanning speed reflects the action time of the energy density on the metal material,and the defocusing amount reflects the depth of the energy density on the metal material.12 groups of different parameters were used for laser welding of two kinds of welded joints.With the increase of laser power,the change of width is larger,but the change of depth is smaller.The experimental results show that according to the different welding parameters,the penetration and surface forming of the weldment are also different.There are even incomplete penetration,poor forming,undercut and pits,and the mechanical properties decrease.Through the large-scale finite element ANSYS simulation software,the numerical simulation of laser welding of piston rod is carried out.The temperature field distribution and thermal cycle curve of each period of laser ring welding are simulated and analyzed.At the same time,the influence of von Mises thermal stress on welding morphology and penetration is analyzed.The higher the laser power is,the greater the temperature gradient is,and the steady temperature field distribution of molten pool is presented.Under the influence of laser pressure and thermal stress,the surface of the weld pool is depressed,which verifies the existence of thermal stress in the weld.After the test,the surface of the piston rod has no air holes and cracks,and the surface quality is good,which provides a useful reference for the piston rod test.Welding fixture is involved in every welding process.For large laser,the programming is complex and the movement track is large,and the long-time complex movement has an impact on the life of the laser itself.In order to accurately form the ring welding track in the welding piston rod,the clamping and positioning function must be ensured.The welding fixture realizes the clamping and positioning of the piston rod through the combined connection of multiple parts.The rotation of piston rod is realized by stepper motor and PLC to ensure the accuracy of welding position and the adjustment of welding angular speed,prevent the occurrence of missed welding and residual welding,and realize the accuracy and automation in the welding process.Finally,AHP and gray correlation method are used to optimize the parameters of the data,and the orthogonal experiment is designed.The welding parameters are optimized by the gray correlation degree and gray correlation coefficient through the detection and evaluation standards of weld penetration,weld hardness,weld morphology and microstructure.The optimized parameters are compared with the original parameters after the experiment,and the results that affect the welding quality are obtained The relationship of the horizontal parameters is scanning angular velocity,defocusing distance and laser power.It provides a useful reference for experimental analysis and engineering application.