Numerical Simulation Study On Filling Process Of Liquid Solder Under Ultrasonic

Ultrasonic brazing can be used in non-vacuum environment without brazing flux to achieve good welding of hard-to-wet material.That the introduction of ultrasonic can produce cavitation effect in liquid solder,remove the oxide film on the base material,achieve a good wetting combination between the base metal to be welded,at the same time,it can also improve the filling rate of the filler metal greatly,so as to improve welding efficiency,which makes ultrasonic brazing possible for wide applications.The filling of liquid brazing filler metal as an important part of ultrasonic assisted brazing process,the effect will have a decisive impact on the quality of welded joints,the current research on it is mainly by changing the welding process parameters,observing the shape of the solder after solidification.And there is not a good revelation to the phenomenon associated with the process.At present,the capillary filling is mainly based on water as the research object,and several points of view have not yet unified.Therefore,this paper decides to study the dynamic behavior of filling process of liquid solder by the numerical simulation method,and to explore the driving force of the caulking process combining with the knowledge of fluid mechanics.And then trying to explain the physical phenomena associated with the caulking process,and analyzing the influence of the test parameters on the caulking process.Through the simulation of the dynamic behavior of filling process of liquid solder,it is found that the liquid solder has an alternating change of forward filling and backward retraction in an extremely short transient period.The total behavior of a cycle for the forward filling,the performance of the macro continuous forward seam with the continued effect of ultrasound and the accumulation of multiple ultrasound cycles,The study of the sound pressure value and velocity vector value inside the solder found that the two showed periodic sine changes.Combined with the dynamic behavior of the caulking process and the knowledge of fluid mechanics,the driving force of filling process of liquid solder is deduced.From this driving force formula,it can be found that the filling of the liquid solder is mainly affected by the average ultrasonic pressure gradient of the local area.When the average ultrasonic pressure gradient is positive and reaches a certain value after taking the filling direction as positive,the caulking process can occur.The greater the average ultrasonic pressure gradient at the initial moment,the faster the filling rate will be.In this paper,the dynamic behavior of liquid medium caulking in horizontal and vertical conditions is studied,and the influence of several main influencing factors on the caulking process is studied.According to the studies,it is found that on the condition of that the ultrasonic frequency,amplitude and gap size is small to a certain value,the caulking process can not occur,this is due to the average ultrasonic pressure gradient difference does not reach the required value of the liquid solder filling.When the greater the ultrasonic frequency and the amplitude and the smaller the gap in the appropriate gap size,the greater the average ultrasonic pressure gradient at the initial moment will be and the higher velocity the liquid solder will possess.Finally,the correctness of the numerical simulation results of liquid solder filling process under ultrasonic is verified experimentally.