Research On Electrically Assisted Deep Drawing Spinning Method Of Cup-shaped Blank Used For Flexspline

Harmonic drive is a transmission part widely used in robot.With the large-scale application of robot in industry,the demand for harmonic drives is increasing.Flexspline is the core part in the harmonic drive,which directly affects the transmission accuracy and fatigue life of the harmonic drive.At present,the advanced manufacturing process of flexspline is monopolized by Japanese and American companies.The mature manufacturing process of flexspline is urgently needed in China.Spinning is suitable for processing the thin-walled revolving parts like flexspline.However,flexspline is commonly made of 30CrMnSiA alloy steel,which has the poor plastic forming properties at room temperature and is difficult to process plastic forming.The conventional forging and cutting methods have the disadvantages of low material utilization,unstable forming quality and low mechanical properties because of the difficulty of clamping parts and the destruction of metal flow lines.Current has positive influence on the plasiticy of metal material and the electro plastic effect?EPE?can improve the forming potential of difficult-to-form metal.The EPE was used to improve the plasticity and forming ability of 30CrMnSiA alloy steel and the near net forming method of flexspline which combined spinning and rolling was proposed in this paper.This paper focused on the spinning/rolling composite forming process of flexspline and took the cup-shaped blank used for flexspline as the research object.The electrically assisted deep drawing spinning?EADDS?method was studied in this paper.The electrically assisted uniaxial tensile test at different temperatures were carried out to research the EPE of30CrMnSiA alloy steel and a modified Johnson-Cook model was used to construct the constitutive equation of 30CrMnSiA alloy steel considering the EPE.Current application methods of the blank were proposed based on the theory of heat transmission and electrical contact and the feature of deep drawing spinning.The best of them was selected with comparison by experiments and the insulating method of spinning machine is design to secure the safety of equipment and operators.Based on ABAQUS software,the user subroutine of the constitutive equation of 30CrMnSiA alloy steel considering EPE was coded and the fully coupled electro-thermal-mechanical finite element model of the EADDS process was developed.The forming mechanism of EADDS process was studied by numerical simulation.The experimental platform of EADDS was set up and the response surface optimization of the forming quality of the EADDS process was completed by experiment.The result shows that current can significantly decrease the strength of 30CrMnSiA alloy steel but cannot improve its plasticity at the temperature from 200?to 600?.On the other hand,current can both decrease the strength of 30CrMnSiA alloy steel and improve its plastic at the temperature from 600?to 1000?.The constitutive equation of 30CrMnSiA alloy steel considering EPE can precisely predict the flow behavior of material under current,whose mean relative error is lower than 5%.The local heating method using dynamic contact has the advantages of high heating efficiency and can effectively reduce the requirements on power supply equipment and conductive equipment,which is suitable for the EADDS process.The spark discharge phenomenon is easy to occur in both three current application method and causes ablation of the blank.Among these heating methods,the method that uses the backplate as positive pole and the backstepping roller as negative pole can minimize the influence of ablation.There is a significant temperature gradient in the preheating stage of the blank and the blank may be over-burnt when the spinning temperature exceeds 1000?.EADDS process can significantly reduce the spinning force and the springback at the opening end area of the cup-shaped blank.The deviation of inner diameter first increases and then decreases with the increasing of the roller feed rate,and increases with the increasing of the relative clearance between roller and mandrel.The reverse cone angle of cup-shaped blank?,which is the angle between the generatrix of blank and the axis of mandrel,first decreases and then increases with the decreasing of the relative clearance between roller and mandrel,and increases with the increasing of current value.The optimal parameters of EADDS process are as follow:I=1200A,t₀=52s,f=0.36mm/r,?=-38%.