Research On The Electropulsing Assisted Turning And Ultrasonic-electropulsing Coupling Surface Process For The 304 Stainless Steel

On a self-built integrated experimental platform,the electropulsing assisted turning process(EP-TP)and ultrasonic-electropulsing coupling surface process(UECSP),that is the coupling of ultrasonic surface rolling process(USRP)and electropulsing,for the 304 stainless steel were carried out.The effects of electropulsing on machinability and properties of the surface strengthened layer that obtained in USRP were investigated systematically,and some mechanisms of the effects observed were suggested.The study of EP-TP for the 304 stainless steel indicates that the main cutting force,axial roughness and microhardness on machined surface are reduced dramatically under appropriate electropulsing parameters compare with traditional turning process.The electropulsing applied in turning process can improve the plastic deformation ability in cutting area,then the depth of rheological layer is increased but with lower hardness.The applied electropulsing causes the arising of plastic stripping tear based on pure shear plastic deformation in the forming process of the chip.The felt wear mechanism is observed on the rake face of YG6 X turning cutter basic on the original mechanical wear,and it is strengthened by stronger electropulsing.But mild oxidation on surface,the bounce axial roughness and microhardness are induced by overlarge electropulsing.Under the experiment condition in the present work,the optimized parameters of electropulsing for EP-TP are the root-mean-square current density of 1.28A/mm2,the peak current density of 9.15A/mm2 and frequency of 600 Hz.Base on theories of electroplastic effect,the matter wave theory in quantum mechanics and the tribology mechanism named resonance-selective mechanism for the dissipation of energy are introduced into a new potential theoretical explanation for the mechanism of EP-TP.The study of UECSP for the 304 stainless steel indicates that the introduction of electropulsing with optimal parameters can effectively facilitate surface crack healing and improve surface hardness and wear resistance dramatically,the tensile strength and the residual compressive stress are further enhanced compared with the original USRP.The mechanism of plastic deformation for the 304 stainless steel shows a significant change from deformation twinning to dislocation slippage due to the increased stacking fault energy and accelerated dislocation mobility and multiplication when electropulsing is introduced.Therefore,more martensite phase,fewer deformation twins and ultra-refined grains are found in the strengthened layer.The formed surface morphology in UECSP is a mosaic structure which consists of a small number of austenite which has lower hardness and a mass of martensite which has higher hardness.However,the lower surface hardness,the release of residual compressive stress and deteriorative surface quality are induced by overlarge electropulsing.Under the experiment condition in the present work,the optimized parameters of electropulsing for UECSP are the root-mean-square current density of 1.03A/mm2,the peak current density of 7.66A/mm2 and frequency of 600 Hz.Base on theories of dislocation multiplication and movement,a scientific concept called critical current density of electropulsing assisted plastic deformation process is proposed firstly,and the intrinsic mechanism of UECSP is discussed reasonably.The results obtained in this work have a guiding significance for the most effective machining and surface strengthening treatment of the difficult-to-process metal materials which is represented by the 304 stainless steel.