Redesign Of Cowl-Top Of Car On The Characteristics Of Laser Tailor Welded Blanks

In the last 30 years,the rapid increase in automobile production has effectively pushed up the development of relevant industries and the promotion of social progress.Howerver,the large holdings of the world`s automobile now has also taken human society a serious negative impact especially on the performance of the energy crisis ,environmental pollution and road safety issues.Faced with the grim energy and environmental situation,international automobile industry are committed to the study and application of lightweight,so as to relieve themselves to achieve lower fuel consumption.In these studies,the light weight of steel car body has become a hot research topic.In this field,the applications of high strength steel blank and laser TWB(tailor-welded-blank)has become a hot spot.At present,over 40% of the automobile body in main industry developed countries has been made by high strength steel blank and laser TWB .So it is not only able to achieve lightweight,but also significantly improved the car body`s rigidity and crashworthiness.Practice shows that,the use of high strength steel blank and laser TWB will bring some quality defect in the process of stamping the car body parts such as:rupture ,wrinkling and resilience.So in order to widen the scope of using high strength steel blank and laser TWB in dometic automobiles,In this thesis,we made the research of a new type of car body component part Cowl Top `s pressing process basing on its traits of high strength laser TWB.In this paper,we have firstly analyzed the existing strength and rigidity weakness in the process of pressing the Cowl Top which originally was made by the ordinary steel blank(not high strength steel blank).After investigation and vertification,we decided to finish the following research work to realize the redesign of this body part by using the way of combining the experimental study and finite element analysis(FEA).The first,The experimental research of TWB(made by high strength steel blank)`s formability.In this paper,we have finished the study of dometic hight strength laser TWB`s capability of being processed,which is based on domestic resources.Finally we reached the following conclusions:1,TWB`s tensile limit and yield limit both had increased significantly compared to the parent metal,but its formability had decreased somewhat.2,The existence of weld line and the heat-affected zone is the main reason for the decreasing of TWB`s formability under the process of pressing.3,The difference between the parent metal`s thickness ratio and grade of intensity will affect the TWB`s intensity.The intensity of TWB(tailor-welded by two different intensity levels of parent materials) is largely depending on the strength of low-intensity of parent material,rather than the average of the two base material.4,The larger of the parent materials`thickness difference ,the smaller ratio of TWb(tailor-welded by same parent materials or different parent materials) and parent tailor,and the larger deformation of thinner parent tailor side.It indicated that the weld line zone and the other side of parental material were poor in flowing,and the deformation was uncoordinated.So finally resulted in plastic instability.5,Through the tensile test and the cupping test,we found that the wrinkle and crack all occur in the thinner parent tailor side,which indicated that the deformation resistence of TWB decreased,so its formability in pressing process fell down.6,During the experiments of tensile test and cupping test we also found that because of the existence of thickness difference between the parent materials, in the course of pressing process (still used the traditionary dies with equivalent height and the clamping ring with equivalent thickness) will occur some quality defects such as:early rupture and wrinkling,that is dued to the poor contact (between the blank and the dies) and the deficient blank holder pressure in the thinner side of parent materials.This founding will make practical significance in the punch dies`devising and improvement.The second,The forming simulation of original parts and the new parts(made by TWB).1, The forming simulation of original partsBecause the original parts was made by the pure high strength steel blank,so it has good formability.In this simulation study ,we used Dynaform software to simulate the process of pressing.Despite its good formability,the strength and stiffness of the part decreased owing to its large relative length,restrictions of assembly space and the heavy loads.In order to enhance the use of this part,we need to use advanced foreign experience and make redesign in the TWB.2,The forming simulation and analysing of new parts(made by TWB) Considering the characteristics of this part in shape and the poor performance in using.we change the materials in pressing process and try to redesign.In this way,we do not have to redesign the structure which will not affect the product`s assembly relationship.Apparently this is the most effective and simple redesign.But the feasibility of this changed part`s forming process will be simulated in the way of FEA(finite element analyse).So in this paper we use the way of FEA to analyse this Cowl Top which is made by TWB(tailor-welded by materials in different thickness) basing on the original part`s forming simulation and analysis.Firstly we changed the material from pure high strength steel blank to TWB.Specifically we designed two weld line in the direction of the load,at the both ends of the blank we used the parent material that its thickness is 2.0mm in order to increase its strength.But in the middle part the material`thickness is 1.0mm due to its complicate interface and small load.So this TWB was tailor-welded by three parts of parent materials.Then we used Dynaform software to simulate the drawing process of this redesigned part.Considering the TWB`s features of forming performance and the new technic problems,we made some modification in the drawing reinforcement and made some changes in blank holder pressure.Finally we got a satisfactory simulated result,which indicated that this redesigned part can satisfy the structural requirements and ensure the quality of pressing and the performance of using.In this paper,we use the method of FEA combined with doing practical experiments to achieve the redesignment of a typical car body bearing component Cowl.Top which has complicate shape.The result of this research not only shows the feasibility and the advancement of the parts in the process of pressing through changing the materials into the TWB ,but it also provides constructive effect in making up the process of pressing technology and designing the forming dies.