Study On Welding Spot Layout For A Car B-pillar Based On The Welding Spot Fatigue Lifetime

Although other connecting methods like glue adhesive, rivet connection, and laserwelding have been applied in the car body assembly，resistance spot welding is also the mostcommon connecting methods for steels metal parts in the automotive works. Generallyspeaking, there are more than3000welding spots on an ordinary sedan car, in some cases,the number of spots is likely to be5000or even more. The advantage of the resistance spotwelding are quicker connecting process, no use of filler material, and the connectionprecision is kept quite well under the local heating, and so on.In consideration of the complication of loading condition in the vehicle’s normal use,welding spot, which is the weakness the vehicle welding components, often under the severecircumstances, which puts forward high requirement on the design of welding spot’s fatiguedurability. According to statistics, almost80%fatigue failure problems of autobodycomponents are to do with welding spot. The welding spot layout schemes which based onthe general welding standards and designers’ guess, are more or less irrational, because lackof sufficient theoretical analysis and calculation. Maybe there are too many spots in someareas, which leads to waste of the use of the structure and material, meanwhile, somewherewith too less spots, which leads to the welding spots and structure in the danger. In theautomobile works, the price of an automatic welding device on the automotive weldingproduction line is about tens of thousands dollars, but the price to add one device to the lineto make up for a problem is much higher than that of one single device. If we are able topredict the welding spot fatigue lifetime for the welding components in the early period ofdesigning, optimize its welding spot layout scheme, decrease the number of welding spotproperly, and distribute welding spot rationally, and then, the fatigue durability of autobodycomponents will be promoted much, at the same time, make the manufacturing cost low level.Starting from the irrational welding spot layout of B pillar on some subsistent cars andthe initial B pillar welding spot layout scheme of the certain car, B pillar of the certain carwas selected as the object of study. And this paper’s research work is listed as follows:1. Proposed the idea of welding spot layout optimization research on the B-pillar basedon the fatigue lifetime of welding spot, on the base of research progress on welding spotfatigue lifetime prediction model and the new methods on welding spot layout schemes forcar components or overall vehicle model home and aboard.2. Finite element mesh the B-pillar by a finite element analysis software which iswidely used in the field of automobile designing, after refining and revising for local meshestime and time, established the FE model for B-pillar, including model for the basic sheetmetal and the welding spots.3. Introduced the stress-based and strain-based welding spot fatigue lifetime predictionmodels, and carried detailed discussion upon Coffin-Manson model and other modelsderived from this model, which is a common strain-based model. According to thecharacteristics of the welding spot fatigue analysis in this paper, made it clear what kind offailure type is most likely to occur to welding spot under cyclic load, and then consideredcomprehensively the stress and strain condition at the peripheries of spots, finallydetermined the prediction model for welding spot in this paper.4. Based on the initial spot layout scheme, several representative layout schemes ofB-pillar were proposed. In pre-processor, the same boundary conditions were conducted inthe different layout schemes, in post-processor, the areas where stress concentration occurredwere analyzed, and then the maximum stress value at the peripheries of spots was obtained.Calculated the fatigue lifetime of the welding spot via the prediction model. After that,conducted curve fitting upon the obtained statistics, the layout schemes and the fatiguelifetime. Concluded the rule between them, then the optimized layout scheme could be gotfor the B-pillar. After comparing the optimized scheme with the initial scheme, which provesthat the welding spot layout scheme based on the sectionalized equal spot interval is feasible to car B-pillar.