Acoustic-Thermal-Fluid Multi-Field Coupling Numerical Simulation Of Ultrasonic Vibration Assisted Friction Surfacing

Friction surfacing is an advanced green machining technology which uses friction heat to make the consumable rod material in the state of thermo viscoplasticity to realize welding.This welding method has the advantages of low energy consumption,no pollution and high efficiency.Using Friction surfacing technology,it can obtain a substantially non-dilution,highly integrated deposit,and has excellent wear resistance and corrosion resistance,and has been widely used in local surface engineeringThe energy input form of traditional friction surfacing is single,which mainly relies on the friction heat and plastic deformation heat between consumable rod and substrate to soften the material for welding.When welding high strength titanium alloy,aluminum alloy,magnesium alloy and other metals,with the improvement of the strength of the materials to be welded,more axial pressure and torque should be applied in the welding process.Because of the existence of high speed and large forging force,the structure of the technological device is huge,so it is difficult to realize the light weight and agility of the moving structure,which greatly limits its application.In order to solve the above problems,a new technology of ultrasonic vibration assisted friction surfacing is proposed,in which ultrasonic vibration is applied to the substrate in front of consumable rod.Through the interaction of ultrasonic and plastic materials in the fusion zone,the flow stress and yield stress of materials are reduced by the softening effect of ultrasonic vibration,thereby reducing the welding load,improving the welding quality and increasing the welding speed.The main research contents of the thesis include:(1)In order to deeply understand the physical mechanism of friction surfacing,a three dimensional thermal-flow coupling numerical model of traditional friction surfacing was established by using FLUENT software.The effects of process parameters such as rotation speed and welding speed on the flow of thermal and plastic materials and the torque of consumable rod in the welding process were analyzed.It is found that with the increase of the rotational speed during the welding process,the peak temperature of the welding and the flow velocity of the plastic material increase,and the torque of the consumable rod decreases.As the welding speed increases,the peak temperature and material flow rate decrease,and the torque of the consumable rod increases.(2)Based on the ultrasonic softening effect,a phenomenological model of ultrasonic vibration assisted friction surfacing was established.Quantitatively analyzed the ultrasonic field vibration at different amplitudes.The impact of material flow behavior.The results show that the thermal effect of ultrasonic vibration has no obvious effect on the temperature field of the fusion zone during welding,but with the increase of ultrasonic vibration amplitude,the ultrasonic softening effect is gradually enhanced,and the plastic material flow degree and flow range are obviously increased.(3)Based on the theory of computational ultrasound,the ultrasonic field model of ultrasonic vibration assisted friction surfacing is established.The distribution of sound pressure and ultrasonic energy on the consumable rod and the substrate after ultrasonic vibration is applied,and the ultrasonic vibration process parameters are summarized.The influence of the pressure field and the ultrasonic energy field.The results show that the sound pressure field and ultrasonic energy field of the fusion zone increase with the increase of the ultrasonic vibration frequency and amplitude.In the spatial distribution,with the increase of the distance from the ultrasonic vibration tool head,the sound pressure and ultrasonic energy reduced.(4)Based on the calculated ultrasonic field model,a three-dimensional acoustic-thermalflow coupled numerical model of ultrasonic vibration assisted friction surfacing is established.The thermal flow density and material flow behavior during the welding process are quantitatively analyzed.And the torque of the consumable rod is affected by the torque.The results show that the ultrasonic energy transmitted to the fusion zone can interact with the plastic material and reduce the yield stress and flow stress of the material.Although the introduction of ultrasonic vibration reduces the plastic deformation heat generation rate of the contact region,the flow velocity of the plastic material is increased,thereby expanding the plastic deformation region.Due to the decrease in the yield stress of the material,the torque of the consumable rod is reduced,and the torque of the consumable rod during the welding process is affected.