Design Of Micro-hammering System For WAAM Based On Piezoelectric Actuation

The uneven temperature field and strain field caused by metal additive manufacturing will generate large residual stresses in the formed part,and the existence of stress will cause hot cracks and cold cracks,as well as larger grain sizes.To overcome these problems,this paper proposes a micro-hammer forging technology based on piezoelectric actuation.Piezoelectric ceramic is a functional ceramic material that can convert mechanical energy and electrical energy into each other.Piezoelectric ceramics are made by using materials under mechanical stress to cause relative displacement of the internal positive and negative charge centers and cause polarization,resulting in opposite-side bound charges on the surface of the material,that is,the piezoelectric effect.It has a small volume and displacement.It has the advantages of high resolution,fast response speed and large output force,so it is suitable for arc additive manufacturing process.In order to solve the problems of porosity,residual stress and deformation easily during the additive manufacturing process,this subject designed a piezo-driven hammer-forging device that works under the principle of hammering with a hammer during the additive process.Welds,using a high-frequency vibration hammer,directly impact the workpiece surface,reduce the stress at the weld,promote the release of tensile residual stress in the heat-affected zone,and generate a certain compressive stress in the impact area,and achieve a certain refinement Grain effect,while vibrating the molten pool to accelerate pore escape.Firstly,based on Auto CAD and Solidworks,3D modeling and 2D drawing export of the tooling structure of hammer forging equipment.Aiming at the various working characteristics of piezoelectric ceramics,hammer head design,pre-tightening design,and cooling design were carried out,and the cooling design was simulated and verified using ANSYS finite element software.The results show that the cooling structure meets the actual working requirements.Secondly,based on Altai USB2833 acquisition card,develop high frequency hammer forging system hammer forging force waveform control(sine wave,square wave)system under VS2017 environment,and hammer forging data acquisition system(save data into CSV file for data processing),And adaptive tracking algorithm with surface welding,use Chart Control control to achieve real-time waveform display on the MFC interface.Import the collected data into Matlab for data analysis and processing.Then based on the working environment of a single robot,a follow-up control system for the trajectory of the welding hammer forging was developed.Thedeveloped transmission structure can control the axis distance between the welding gun and the hammer head within 70 mm,which meets the requirements of forging work with the welding hammer.Secondly,for different additive paths,a trajectory following algorithm is designed,and the relationship between the angular speed of the gear rotation and time is obtained,so as to obtain the corresponding motor control waveform and achieve trajectory following.Finally,the KUKA robot was used for debugging and process verification(microstructure,mechanical properties)of the CMT aluminum alloy arc additive with welding hammer forging system.The results showed that the grain size was refined to a certain extent after the addition of hammering,and the coarse columnar crystals were transformed.It is a small equiaxed crystal.In the vibration molten pool experiment,the effect of the amplitude on the grain refinement is more obvious than the vibration frequency,and the larger the amplitude,the better the grain refinement effect.However,when the vibration frequency is 100 Hz,it appears obvious Dendrites break.This may be because the frequency is closest to the resonance frequency of the dendritic crystal.At this time,the relative motion and collision generated in the melt are more frequent,and the degree of dendritic fracture is improved.The effect of frequency change on grain refining is more obvious than that of hammering force,and the greater the hammering frequency,the better the grain refining effect.