Study On Mechanism Of No-riveting Connection Of Sheet

In the face of the increasingly serious environmental pollution problem,lightweight has entered the public view.More and more lightweight materials,such as aluminum alloy,magnesium alloy and titanium alloy have been widely used in the fields of aerospace and automobile industry due to their performance advantages.Therefore,how to effectively realize the connection between materials has become an urgent problem to be solved.As a new type of connection technology,no-riveting connection technology has the advantages of low cost,simple process and no-stress concentration,and has become a hot research topic at home and abroad.In this paper,6061 aluminum alloy was taken as the research object,the forming mechanism of no-riveting connection,the influence of die structure and sheet metal properties on the quality of no-riveting connection are studied,and the relevant conclusions are obtained,which provide the basis for the development of no-riveting connection technology.The finite element model was established by finite element software to simulate the stress,strain and metal flow of the sheet in the process of forming the no-riveting connection.The forming mechanism of no-riveting connection was obtained: the area that the fillet of the punch contacted with the upper plate during the deformation process has the large stress and strain value,and the deformation degree of the sheet is large.As the punch continues to squeeze,the stress and strain values of the sheet continue to increase,the lower sheet material flows toward the groove under the action of the punch,the groove have less restrictions on the flow of the sheet material,the flow speed in the groove is fast.After the sheet is filled with grooves,the stress and strain value of the contact point increases,the flow of the sheet material is blocked,and can only flow in a vertical upward direction.However,due to the limitation of the flow of the sheetmaterial by the blank holder,the sheet material can only move towards the weak areas,that is the fillet of the punch,flows in contact with the upper sheet material.Because the flow speeds of the upper and lower sheet materials are different,the sheet material is inlaid together under the action of the punch to form the self-locking.Based on the analysis and study of the forming mechanism of the no-riveting joint,two kinds of die structures,fixed die and movement die,were designed.The influence of the radius of the punch,the punch fillet size,the depth of the concave die and the clearance of the punch and the concave die on the quality of the no-riveting connection were analyzed by DEFORM software.By means of orthogonal test,the optimum parameters of the fixed die are that the radius of the punch is 2.7 mm,the punch fillet size is 0.3 mm,and the depth of the concave die is 1.4 mm.The optimum parameters of the movement die are that the radius of the punch is 2.7 mm,the punch fillet size is 0.3mm,the clearance of the punch and the concave die is 1.6 mm.The influence of different the coefficient of normal anisotropy on the quality of riveted joints was analyzed by finite element method.The sheet metal with different the coefficient of normal anisotropy r was obtained by three different rolling schedules.The results of tensile test show that the r value of unrolled sheet is 0.67619,the r value of four-pass rolling sheet is 0.78954,the r value of six-pass rolling sheet is 1.35790,the r value of eight-pass rolling sheet is 0.83954.The geometric dimensions,shear strength and tensile strength of the riveted no-riveting specimens with different combinations were measured and analyzed.The results show that the coefficient of normal anisotropy is an important factor affecting the quality of no-riveting joints.When the materials of upper and lower sheet are exactly the same,the quality of no-riveting joints that the sheet with greater the coefficient of normal anisotropy is better;when the materials of upper and lower sheets are different,that is,when the coefficient of normal anisotropy are different,the sheets with higher coefficient of normal anisotropy should be placed on the side of the concave die.The sheets with the small coefficient of normal anisotropy is placed on the punch side,which is favorable for forming a larger self-locking value and improving the quality of the joint.