Research On Surface Formation Mechanism Of Ultrasonic Extrusion Process With Longitudinal-flexural Vibration

Ultrasonic extrusion process with Longitudinal-flexural vibration(UEP-LFV)is a new surface finishing strengthen technology,which is combined the two-dimensional ultrasonic vibration processing with extruding processing depth of integration,complementary advantages,in order to obtain a better surface quality.In this thesis,7075-T6 aerospace aluminum alloy as the research object,the surface forming mechanism under UEP-LFV is explored from the theoretical analysis,numerical simulation and technology test these three aspects.The main work is as follows:Firstly,the models of kinematics and extruding indentation mechanical under UEP-LFV were constructed according to the processing principle of UEP-LFV,the relationship between the internal stress in the surface of the specimens under UEP-LFV and the specimens physical mechanical properties and extrusion process parameters is qualitatively analyzed.The influence law of process parameters on the internal stress of specimen surface was researched by numerical analysis method,the results were that the surface maximum limit stress increases with the increment of the static pressure,radius,the amplitude and frequency,and decreases with the increase of the extrusion speed and depth.Secondly,the numerical simulation of ultrasonic extrusion process with longitudinal vibration and the process of UEP-LFV was made respectively base on kinematics model of UEP-LFV,and the distribution of internal stress at different times was analyzed.The distribution of residual stress along the depth direction with the change of extrusion process parameters was obtained.The result was that the surface of the specimen was residual compressive stress,the compressive stress increased first and then decreased with the increment of depth,and then became tensile stress,and was closed to zero at the base.With the static pressure increased,residual stress and compressive stress layer of depth were increased to varying degrees,instead,extrusion speed effect on residual stress and compressive stress layer of depth was opposite,with an increase in the amplitude of residual stress and depth showed a slight increasing trend,the influence of phase change on residual was very small and could be neglected.Finally,the experiments of UEP-LFV and conventional extrusion process(CEP)were carried out respectively through the orthogonal test scheme designed by considering the interaction and the test analysis of surface roughness,surface hardness and surface microstructure was given,the influence of every extrusion processing parameter on surface roughness and surface hardness was studied.The mathematic models of predicting surface roughness and surface hardness were constructed and the optimum extrusion parameters for the lowest surface roughness and the highest surface micro hardness were obtained.The result was that the values of specimen surface roughness under UEP-LFV were superior to that by CEP with the same extrusion processing parameters,and the values of specimen surface hardness were higher than that by CEP.The specimen surface microstructure under UEP-LFV was superior to that by CEP and CNC machining.The research results of this thesis were helpful to further improve the mechanism of UEP-LFV,and provided references for the engineering application of this technology.