Study On Static Pressure Support-ultrasonic Viration Single Point Incremental Forming Accuracy And Influence Mechanism

Single point incremental forming is a new technology for plastic forming of sheet metal.A specific tool is used to locally load the sheet,resulting in overall cumulative deformation under a die-free and unconstrained condition,and finally the target part shape is obtained.It integrates the design and manufacture,has the advantages of flexible,green,fast and low cost.However,due to factors such as the partial loading of the tool head and the die-free constraints of the sheet,the forming process is prone to instability and sheet is prone to springback,which ultimately makes the accuracy of the part difficult to meet the service requirements.In addition,due to the inhomogeneous deformation behavior of the material and the complex evolution of the structure and the interaction of the forming parameters on the forming accuracy,the robust control of the part accuracy becomes difficult.Therefore,static pressure support and ultrasonic vibration have been attempted to be introduced into the single point incremental forming technology in order to effectively improve the part accuracy,and a new method of static pressure support-ultrasonic vibration single point incremental forming has been obtained.A static pressure support-ultrasonic vibration assisted single point incremental forming method is proposed,and the space spherical coordinate stress balance equation of the forming area sheet micro-element is established.According to the spatial geometric relationship between the tool head and the sheet contact area,the stress state of the sheet in the forming area is obtained by integrating the angles of the respective stresses.The analytical expression of the forming force is realized,and an analytical model for the static pressure support-ultrasonic vibration single point incremental forming force is established.A finite element simulation model of single point incremental forming process considering static pressure support and ultrasonic vibration is established.In the model,the tool head is given an axial ultrasonic vibration impact load,and the back of the sheet is given a flexible static pressure support.Through the numerical simulation of the whole forming process,the effects of static pressure support and ultrasonic vibration on the equivalent stress,strain,wall thickness reduction rate and formability of the forming process are studied.The results show that the static pressure support-ultrasonic vibration assisted single point incremental forming can significantly improve the deformation uniformity of the sheet,delay or avoid the fracture of the part.A set of static pressure support-ultrasonic vibration single point incremental forming experimental system is developed.The combination of simulation and experiment is used to study the single and coupling influence of static pressure support and ultrasonic vibration on the axial,normal and overall accuracy of the part.The experimental results are analyzed by variance,coupled analysis and optimization analysis.The results show that the static pressure support and ultrasonic vibration can effectively improve the axial,normal and overall accuracy of the part,and the two have a certain coupling effect when improving the overall accuracy.The influences of static pressure support and ultrasonic vibration on the forming force of the sheet and the residual stress of the part are studied.Through theoretical analysis,numerical simulation and experimental verification,the variation of forming force and residual stress under static pressure support and ultrasonic vibration is obtained,and the mechanism of the auxiliary parameters on the deformation form is revealed.The results show that the static pressure support has an increasing effect on the forming force,and the ultrasonic vibration can reduce the forming force.The degree of correlation between each parameter and the forming force is different.Static pressure support and ultrasonic vibration have no coupling relationship when affecting the forming force.Both static pressure support and ultrasonic vibration have a restraining and reducing effect on residual stress,which can effectively reduce the springback deformation of the part and enhance the plastic deformation ability of the material.