The Establishment Of Mechanical Model And Experimental Study Of Weld Line Movement Of Box Shaped Parts Made By Tailor Welded Blank In Stretch Forming Process

Recently, with the reducing of total energy and the worsening of environmental pollution, the development of automobile industry moves towards lightweight based on the security satisfaction. Tailor welded blank (TWB) and its forming technology is just a new technique to adapt to this development direction. Now this technology has been used more and more wildly in the automobile industry for the advantages of low cost, light weight, high strength and high stiffness brought by using TWB to produce automobile parts.The weld line will move adaptively along with the differences in the thickness, material properties, size in the two blanks on both sides of the weld .One of the major problems affecting the part's quality in the forming process of TWB is weld-line movement, resulting in a decrease to the forming stability of TWB. Therefore, mechanical model for the weld-line movement in the forming process of TWB needs to be studied in order to predict and control the weld-line movement.Basic theory in the forming of TWB square-box part was studied and on that basis the influences of some factors such as blank holder force (BHF), thickness ratio and material properties of the two blanks on both sides of the weld, friction coefficient, the speed of punch, etc. on the weld-line movement were analyzed.The deformation zone in the forming process of TWB square-box part was divided into five areas and they were flange area, fillet area of die, transfer area, fillet area of punch and bottom area. The analytic expressions of the stress-strain relation on the five areas were deduced. And according to these analytic expressions and the calculation formula of the weld-line movement, mechanical model of the weld-line movement was established. This can provide a theoretical basis for the study on the law of weld-line movement.The forming processes of TWB square-box part under different influencing factors, such as BHF, thickness ratio, friction coefficient and speed of the punch etc. were simulated by Dynaform. Thus the influencing laws of each factor, on the maximum weld-line movement at the flange and bottom of the square-box part, were obtained.In order to verify the numerical simulation and mechanical model, experimental study was carried out. The results of experiment, simulation and mechanical model calculation were mainly in agreement, and they showed that BHF, thickness ratio, friction coefficient and speed of the punch had different effects on the weld-line movement. Besides, proper BHF, thickness ratio and lubrication condition should be selected to control the weld-line movement.