Experimental and Theoretical Analysis on Formability of Aluminum Tailor-Welded Blanks

Formability of tailor welded blanks (TWBs) and control of blank deformation during stamping is always a challenge for manufacturing designers due to different properties or thicknesses of the blanks. The plastic deformation capacity of TWBs is reduced even when the material and thickness are the same. Same material same gauge TWBs (SMSG- TWBs) are now widely applied to mass production of automobile components for raising the utilization ratio of materials and expanding the dimension of steel coil. The aim of this work is to investigate the formability of SMSG-TWBs by both numerical and experimental approaches. Local constitutive properties of laser welded beads are determined by tensile tests with the aid of digital image correlation (DIC). Based on these mechanical properties, the formability of TWBs and monolithic blank are evaluated by performing Erichsen cupping tests numerically and experimentally. The influence of weld on strain distribution is discussed as well. Comparisons with the experimental results showed general agreement.

The purpose of this study is to improve the mechanical properties and formability of friction stir welded tailor-welded blanks (TWBs) of Al6061 alloy with a new forming method called hot forming quenching (HFQ) in which solid-solution heat-treated aluminum sheets are formed at elevated temperature. Forming and quenching during HFQ are simultaneously performed with the forming die for the solid-solution heat-treated sheet. In this study, specimens of aluminum TWBs were prepared by friction stir welding (FSW) with a butt joint. The effectiveness of FSW joining was evaluated by observation of the macrostructure for different sheet thicknesses. In order to evaluate the formability of TWBs by HFQ, a hemisphere dome stretching test of the limit dome height achieved without specimen failure was performed with various tool temperatures. A Vickers test was also performed to measure weldment hardness as a function of position. The formability and mechanical properties of products formed by HFQ are compared with those formed by conventional forming methods, demonstrating the suitability of HFQ for sheet metal forming of friction stir welded TWBs.

True stress–strain analysis on weldment of heterogeneous tailor-welded blanks—a novel approach for forming simulation

The manufacturing industries are keen on understanding the effect of weld line orientation on the formability characteristics of tailor-welded blanks (TWBs) with sheets for the design and manufacture of structures with lightweight. The AISI 316L sheets of 2 mm and 1.6 mm were welded together by cold metal transfer (CMT) process using a welding current of 95 Amperes and a welding speed of 350 mm/min to fabricate TWBs. Two different TWBs were made with the welding line parallel to the rolling direction RD (WL||RD) and the weld line perpendicular to the RD (WL⊥RD). The quality of the TWBs was evaluated by microstructural examination, mechanical integrity by tensile, hardness and Erichsen cupping test with laboratory-scale specimens. The engineering stress–strain plot and formability characteristics of the TWBs were considerably influenced by the weld line orientation with respect to the RD. It was noticed that the formability of TWBs decreased slightly compared to the base metal (BM) and fracture appeared in the thinner region (1.6 mm side), away from the weld line. Finite element (FE) prediction of Erichsen cup height was performed with ABAQUS software considering the weld metal properties. FE analysis using Johnson–Cook damage criterion predicted a cupping height that showed good coherence with experimental measurements for BM and TWBs with an error percentage less than 5. The stress distribution was non-uniform in the deformed TWBs with more stretching, and the magnitude of deformation was higher in the thinner region.

Tailor-welded blank is one of the promising technologies in the application of lightweight materials for auto body parts manufacturing. The material discontinuity across the weld line results in an inhomogeneous deformation and weld line displacement. In this study, a two-dimensional analytical model is proposed to predict the tension distribution along the cross section. An energy method is used to calculate the restraining force due to bending, sliding, and unbending phenomena on the die and punch radii. To control the weld line movement, a blank holder force control strategy is proposed to achieve force equilibrium at the bottom of the part across the weld line. Finite element simulations are performed to study the effect of die and punch radii, friction coefficient, thickness ratio, and blank holder forces on the weld line displacement in strip drawing process. Under a uniform blank holder force, the weld line moves toward the thicker/stronger side implying a higher blank holder force is required for the thinner/weaker side. The results show that the weld line displacement can be controlled by an appropriate blank holder force adjustment. In order to control the weld line movement in square cup deep drawing, blank holder force on the thinner side is increased and its influences on the deformation process are investigated. Comparisons of material draw-in, weld line movement, and forming force show a good agreement between the theoretical, numerical, and experimental results.

Mechanical behaviour of dissimilar friction stir welded tailor welded blanks in Al–Mg alloys for Marine applications

The forming behaviour of tailor welded blanks (TWBs) has beenwidely studied since its development. In the numerical simulation studies,the TWBs are modelled as blanks composed of two different materials, and often,the presence of the weld bead is neglected in its finite element discretisation.In the present work, the influence of the weld bead shape on the formabilityof friction stir welded TWBs, is analysed. Several finite element meshes wereconstructed in order to represent different weld bead geometries and numericalsimulations of the cylindrical cup drawing were performed. Strong influenceof the weld bead shape on the formability of the TWBs was observed when theweld was in overmatch relatively to the base material, and little influencewhen the weld was in undermatch condition. Comparison of the numerical resultswith experimental ones shows that the numerical analysis is able to previewthe formability of the TWBs.

ABSTRACTAn attempt was made for the first time to fabricate tailor-welded blanks (TWBs) through the feasibility of selective alloying in the solid state of vertical compensation friction stir welding (VCFSW) technique. The results revealed that the production of TWBs by VCFSW technique had higher homogeneity without any defects when compared to the production of TWBs by conventional FSW process at constant tool rotational speed 2000 rpm, traverse speed 20 mm min−1 and an inclination angle 2.5°. The maximum mechanical properties of the fabricated TWBs were obtained when the width of compensation strip 1.5 mm was used. The fracture surface of TWB at the width of compensation strip 1.5 mm showed ductile fracture mode.

Using tailor-welded blanks (TWB) in automotive industry is on the rise. This is done due to advantages such as reduction in weight leading to more effective operational cost and lower energy consumption of vehicles. The main objective of this investigation was to study the effect of location change of weld zone and differences in thickness combination of TWB sheets on their tensile characteristics and forming capabilities. Quality evaluations of weld zone metallographic and tensile as well as ball punch tests have been conducted. Tension characteristics of welded samples have been determined by conducting a uni-axial tensile test perpendicular on the weld line in those samples. Forming capability of TWB samples were also studied by using sphere head chisel test. By moving weld line toward thick sheets direction and increasing thin sheets share of the weld in TWB, an increase in relative elongation in tensile test and in chisel test increase in cups height was observed. This indicates that forming capability of TWB samples by moving weld line toward thick sheet increases and weld zone does not have much effect on forming capability of TWB. By using the derived recommended relation induced from this study, it is conceivable to obtain the amount of increase in relative length of TWB from its base sheets. Results of this relation are confirmed with obtained results from tensile test. Also by reduction in thickness difference of TWB sheets, their formability increases.

Formability of automotive friction stir welded TWB (tailor welded blank) sheets isnumerically investigated in biaxial stretching based on hemispherical dome stretch (HDS) test infour automotive sheets of Aluminum alloy 6111-T4, 5083-H18, 5083-O and DP590 steel, havingdifferent thicknesses. The effects of the weld zone modeling and the thickness ratio on formabilityare evaluated. In order to carry out the numerical simulations, mechanical properties areconsidered according to Chung et al. [11] experimental results. von-Mises and Hill’48 quadraticyield functions are used to compare the isotropic and anisotropic behaviors of the used sheets. Inorder to simplify the problem, the anisotropy of the weld zone is ignored. The FEM results arecompared with experimental results of [11]. Anisotropic assumption for base materials and varyingthickness for the weld zone give more accurate prediction. Numerical results are in goodagreement with the experimental results. Failure onset locations and patterns are accurate. Sincethe formability is dependent on the stress concentration, asymmetric distribution of strength andcomplexity of weld zone properties, the thickness ratio in TWB affect formability.

Tailor welded blank (TWB) has many advantages over a traditional blank for manufacturing automobile sheet metal components, such as significant flexibility in product design, higher structural stiffness, and crash behavior. However, lower formability and weld line movement are some of the problems associated with forming of TWBs. Hydroforming is a potential technique to enhance formability. In this work, the effect of thickness ratio on maximum dome height and weld line movement in hydraulic bulging of laser welded interstitial-free (IF) steel blanks of different thickness combinations has been predicted using finite element (FE) simulations. The results are also validated with hydraulic bulging experiments on TWBs. It has been found that with increase in thickness ratio, the maximum bulge height decreased and weld line displacement toward thicker side increased. These results have been used to relocate the weld line toward the thinner side in the initial blanks and achieve a more uniform bulge profile of the dome. The peak pressure to achieve maximum safe dome height and percentage thinning has also been found out. The results showed huge improvement in uniformity of bulge profile with little reduction in dome height.

Formability of similar and dissimilar friction stir welded AA 5182-H111 and AA 6016-T4 tailored blanks

An investigation on the laser welding process parameter effects on the failure mode of tailor welded blanks during the formability testing

Determination of mechanical properties of the weld zone in tailor-welded blanks

<div class="htmlview paragraph">The automotive industry is continuously investigating means for producing lighter-weight vehicles in order to improve fuel efficiency and reduce emissions. Lightweight materials, such as aluminum, are often used to replace steel in automotive body structures, such as hoods, decklids, fenders, and their corresponding reinforcements. To further reduce weight and improve stiffness, sheets of different gages and/or properties are welded together prior to stamping to form “tailored” blanks. The presence of the weld and the gage mismatch in these blanks, often result in premature failure, which can be expressed as a shift in the forming limit diagram. Several process variables affect this change in deformation behavior including the welding process used to join the blanks, the weld orientation, the weld geometry, and the mechanical properties of the weld and the base materials.</div> <div class="htmlview paragraph">Developing an understanding of the deformation behavior of tailor-welded blanks has been the focus of many studies. However, to improve computational efficiency, researchers have, in general, ignored the weld line geometry and properties when modeling tailor-welded blank forming, even though different welding techniques produce welds with different widths, profiles, and properties. Therefore, this paper discusses the results of investigating the effects of weld material properties and weld geometry on deformation behavior in the vicinity of the weld line, and describes the different approaches that were used to represent the weld geometry. The findings indicate that if material behavior near the weld line is required, then shell element models are insufficient and models including weld material properties and/or weld geometry should be used.</div>