Research On Forming Mechanism Of Rotated Clinching Process For Aluminum Alloy

Sheet metal joining technology is widely used in mechanical manufacturing.The traditional round point clinching is to use a pair of special structure of the punch and die to process the sheet metal on a dedicated pressure equipment,causing plastic deformation in local areas of the sheet metal,and achieving mechanical interlocking connection.This technology has high requirements on the die structure,and the vertical stamping movement of the punch makes the neck of the joint thinner seriously,it is easy to cause cracks.A novel rotated clinching method is proposed in this dissertation,which uses a twin pair of arcshaped rotated punches to rotate around the horizontal axes to press the metallic sheets,and a mechanical interlocking joint is achieved in the fixed die with flat bottom,which can reduce the neck thinning to avoid cracks.In this dissertation,the Al1060 aluminum alloy sheet is taken as the research object,the forming principle,device structure,mechanical behavior,interface characteristics and joining strength of rotated clinching are studied,which will provide certain theoretical basis and guiding significance for the actual application of rotated clinching method.The main work and innovative achievements of this dissertation are as follows:(1)Analysis of connection forming principle and design of device structure.The forming principle and the influencing factors of forming of rotated clinching method are analyzed,the overall structure of the forming device and the rotated punch and fixed die with flat bottom are designed;The numerical model of rotated clinching is established by finite element method,and the forming characteristics of joint are analyzed,the neck thickness,interlocking and bottom thickness in the joint performance index parameters are taken as the target,key process parameters such as arc radius and transition fillet,spacing and center height of rotated punch;The length,width and depth of the cavity of fixed die are designed,the influence laws of key process parameters on the joint performance index parameters are revealed.(2)Analysis of forming force and determination of maximum forming force.Based on the structural design of the forming device,the characteristics of the deformation zone and the variation of stress,strain,and displacement in different contact areas during the process of rotated clinching are analyzed by finite element simulation,the relevant information such as the strongest stress,the largest displacement and the most vulnerable point of the joint are obtained.The numerical calculation model of forming force is established.The characteristics of forming force in the forming process are analyzed,and the variation law of forming force is obtained;The maximum forming forces required for the connection of different process parameters are discussed,and the relationship between them and the maximum forming force is established;The maximum forming force required for the rotated clinching is determined and verified by experiments.(3)Studying on contact and failure of joining interface.The interlocking mechanism of the joining interface,and the deformation characteristics of the materials in each contact area of the joining interface during the forming process are analyzed.The variation characteristics of contact area in the forming process are analyzed,and the variation rules of residual contact area and residual contact pressure of different process parameters are revealed,the variation rules of interface contact state parameters such as moldability,contact gap,neck thickness and interlocking value are studied.The failure mechanism of joining interface is discussed,the failure models of joining interface are constructed,and the failure forms of joints with different process parameters are determined.(4)Analysis and prediction of joining strength.The shear strengths along the length and width directions and the peel strength along the thickness direction of the joint with different process parameters are studied;The force model of the joint is established,and the relationship between the joining strength and the cross-sectional shape parameters,sheet thickness,and sheet performance is established by the force balance of the section element;Based on the response surface method,the relationship between the device structure parameters,material properties,sheet thickness and shear strength is established,the strengths of joints with different process parameters are predicted,and the prediction results are verified by experiments.(5)Experimental verification of the rotated clinching method.Through experiments,a comparative analysis is conducted between the rotated clinching joint and round point clinching joint in terms of forming force,joint performance parameters,joining strength and failure mode.The experimental results show that the rotated clinching can realize the connection of aluminum alloy sheets,and compared with the round point clinching,it can obtain the joint with larger neck thickness and interlocking value and better mechanical properties.This will provide a new method for sheet metal connection technology.