Research On Optimiation Of Vibration Assisted Laser Welding Process

Vibration welding is defined as a new technology to give sample exciting force.Its purpose is to decrease temperature gradient of molten pool,to refine grains,to reduce welding defects and improve welding quality.However,welding joints can’t be ensured to keep good mechanical properties when applying to vibration.If vibration parameters don’t match conventional welding process,it will contribute to imperfect weld formation and even reduce mechanical properties.Therefore,the optimization of vibration assisted laser welding process is of great significance.Based on high frequency micro-vibration platform,the 316L stainless steel is laser welded with vibration.The influence on microstructure of laser welded joint with high frequency micro-vibration process has been investigated.The results indicate that good welding surface can be got under vibration.No spatters can be found.No collapse and excess weld metal exist.Weld width forms uniformly in the back weld.Grain refinement is related to resonant vibration frequency during solidification in the weld.The smallest grain size and the most conspicuous grain refinement are obtained at the resonant frequency of1467.5Hz.In addition,the particles are spread and dispersed between the austenite grains.The new phase and the large particles are reduced with vibration.With the increase of the vibration frequency,weld microhardness increases,especially with the higher resonance frequency.At the resonant frequency of 1467.5Hz,vibration acceleration of 160m/s~2,the average microhardness value of weld is 206HV,which is increased by 5.6%compared to that with no vibration condition.Orthogonal experimental design is introduced to optimize process parameters,such as vibration frequency,vibration acceleration and vibration direction.The orthogonal table of three factors and three levels is established.Mechanical vibration is applied to sample during welding in the experiment at the same time.In this paper,tensile properties and microhardness of welding joints at different parameters were using variance analysis and range analysis respectively.And the influences of vibration parameters on tensile strength were also explored.Then,the best welding parameter was determined.Next,the microstructure and tensile fracture before and after optimization were compared and analyzed.At last,vibration controlling parameters are researched by coupling analysis.The optimized results show that best welding parameter is as follows,vibration frequency is1360Hz,vibration acceleration is 60m/s~2,vibration direction is that exciter should be perpendicular to the platform.Corresponding mechanical performance reaches the maximum value,tensile strength is 602MPa and microhardness of welded center is214.5HV.Tensile fracture is equiaxed and dimple.Its shape is regular and uniform.The dimple is small and deep.The tensile properties of optimized welding joints perform better.There are no more obvious tiny holes in fracture surface and no more micro defects exist.The microstructure near fusion line is more uniform compared with non-optimized weld.Coupling analysis results show that when input voltage is constant,the vibration frequency has the exponential relationship with the vibration platform power output current.The vibration acceleration can be equivalently altered by vibration amplitude.The vibration acceleration increases with the power output current increasing when the applied vibration frequency is close to the inherent vibration frequency of the material.Response surface method is introduced and regression equations of vibration frequency,vibration direction,vibration acceleration,vibration acceleration and width of middle of molten pool are established on the basis of Box-Behnken design.The influence of vibration parameters on surface morphology of the weld is analyzed and the optimized processing parameters are determined accordance with forming of weld surface.The results indicate that the main effect of vibration frequency has the greatest influence on the width of middle of molten pool,and the main effect of vibration acceleration is the next.The best combination of process parameter is vibration frequency 1360Hz,vibration acceleration 60m/s~2,vibration direction that exciter vertical to platform.The results are in agreement with the result of optimization of mechanical properties.