Tailor Welded Blanks Research Articles

Optimizing weld morphology and mechanical properties of laser welded Al-Si coated 22MnB5 by surface application of colloidal graphite

In the automotive industry, the demand for reduced vehicle weight, improved safety and enhanced crashworthiness qualities continues to rise which introduces the need for parts with tailored properties. This demand can be met by employing tailor-welded blanks which are made of two or more types of press-hardened steels that are laser welded together and then hot-stamped to produce highly optimized parts for use in vehicle body-in-white applications. The most commonly used press-hardened steel for high strength applications is the Al-Si coated 22MnB5 grade steel that has a strength of around 1500 MPa in the hot-stamped condition. Although the Al-Si coating offers excellent barrier protection against oxidation and decarburization during hot-stamping, the Al-Si coating proves to be problematic during laser welding as it melts and mixes into the weld pool increasing the Al-content in the fusion zone, which promotes the formation of ferrite during the heat-treatment stage of hot-stamping, resulting in a dual-phase fusion zone microstructure that consists of ferrite grains embedded in a martensitic matrix. The presence of the softer ferrite phase has been shown to be the principal reason for premature failure of hot-stamped laser-welded joints. Currently, this issue is resolved by an additional, and relatively costly, manufacturing step that involves the laser ablation of the Al-Si coating prior to welding. The present work shows that this step can be eliminated from the manufacturing process by welding Al-Si coated 22MnB5 steel through a colloidal graphite coating which results in the in-situ ablation of the Al-Si coating during welding. This changes the alloying chemistry of the fusion zone which affects the resulting morphology by preventing ferrite formation which improves the mechanical properties of the weld. Failure in these welded samples was successfully shifted from the fusion zone, where it normally occurs, to the base material.

Experimental Research on the Behaviour of Metal Active Gas Tailor Welded Blanks during Single Point Incremental Forming Process

The present paper aims to study the behaviour of Metal Active Gas (MAG) tailor welded blanks during the single point incremental forming process (SPIF) from an experimental point of view. The single point incremental forming process was chosen for manufacturing truncated cone and truncated pyramid shaped parts. The same material (S355) and the same thickness (0.9 mm) were selected for the joining of blank sheets because the main goal of the paper was to study the influence of the MAG welding process throughout the SPIF process. A Kuka robot, equipped with a force transducer and an optical measurement system were used for manufacturing and evaluating the parts by SPIF. The selected output data were major and minor strain, thickness reduction, forces and springback at the SPIF process. Another line test was performed to evaluate the formability in SPIF. The main conclusion of the paper is that during the SPIF process, fractures occur in one side welded blanks even at moderate wall angles, while in the case of double side welded blanks there is a decrease of formability but parts can still be produced at moderate angles (55 degrees) without any problems.

Formability of tailor welded blanks of high strength steel: A review

A tailor welded blanks (TWBs) are formed when sheets of several grades, various thicknesses and different coatings are joined by welding process, which are used to improve safety features, fuel consumption, crashworthiness, and weight reduction. TWB sheets are extensively used in auto-body design. The use of TWB in the body structure can significantly reduce the weight of the vehicle, thereby reducing material waste in the workshop, which also results in the reduction of the energy utilization during manufacturing. With this review paper, we highlight and focus the recent advances in the field of Tailor Welded Blanks which are investigated and analysed by researchers mathematically and numerically and found good agreement with the results.

Investigation of forming limit curves and mechanical properties of 316 stainless steel/St37 steel tailor-welded blanks produced by tungsten inert gas and friction stir welding method

The conventional welding method for joining dissimilar steels is the manual tungsten inert gas (TIG) method. Nevertheless, recently the benefits of solid state welding have been attracted attention of industrial manufacturers. In this article, TIG and friction stir welding method are compared based on the formability and mechanical properties of the welded sheets. Experimental evaluation of mechanical properties and forming limit curves have been carried out using uniaxial tensile test and Nakazima test, respectively. Results of experimental tests illustrated that formability of friction stir welded sheets was about 38% higher than the TIG-welded sheets. The microstructure analysis of TIG welded blanks revealed that grain growth in the heat-affected zone on the St37 steel, reduced the formability of welded joints in this method. Finite element simulation was used to estimate the forming limit diagram of the joints without considering the effects of welding heat on the material properties. The difference between the results of the FSW and finite element simulations was about 6%. While in the TIG welded blanks formability reduces significantly and difference between the result of experiment and simulation is about 33%. These results show that friction stir welding could more effectively preserve the sheets' formability after welding.

Formability prediction of tailor-welded blanks in hydraulic bulging using flow curves from biaxial tensile tests

In this work, the formability of laser-welded tailored blanks of low carbon steel of two different thickness combinations in hydraulic bulging has been studied by numerical simulation. For material modeling, flow curves of the parent sheets were obtained in biaxial stress condition by conducting hydraulic bulge tests. These curves were used to extrapolate the uniaxial tensile curves up to large strains using the work equivalence principle. The limiting dome height in conventional forming and hydraulic bulging of tailor-welded blanks has been predicted in finite element simulations using the flow curves obtained directly from the hydraulic bulge tests and the extrapolated uniaxial tensile curves. Hydraulic bulging and conventional forming experiments on tailor-welded blanks have also been conducted to validate the predicted results. It has been found out that the predicted limiting dome height of the tailor-welded blanks in conventional forming and hydraulic bulging using extrapolated uniaxial tensile curves is closer to the experimental values when compared to the results obtained by using stress–strain curves obtained from hydraulic bulge tests. It has also been found that using an extrapolated uniaxial tensile curve it is also possible to predict strain distribution and percentage thinning more accurately. It has been observed that with an increase in thickness ratio, the peak pressure increased but the predicted values of peak pressure using flow curves obtained directly from hydraulic bulge tests are closer to the experimental values.

Effect of void nucleation on microstructure and stress state in aluminum alloy tailor-welded blank

The microscopic damage initiation characteristic in welded joint greatly determines the subsequent damage evolution and fracture behavior of aluminum alloy tailor-welded blank (TWB) during plastic forming. In this study, the interactive dependence of void nucleation on microstructure and stress state in the welded joint of a 2219 aluminum alloy TWB was quantitatively explored by in-situ SEM testing. Moreover, a micromechanical model based on actual microstructure was adopted to reveal the underlying mechanisms from the perspective of microscopic heterogeneous deformation. The results showed that three void nucleation mechanisms, including particle-cracking, interface-debonding and matrix-cracking, coexisted in the deformation at different microstructure regions and stress states. The nucleation strain of each mechanism mainly depended on the particle volume fraction, grain size and stress triaxiality. Besides, the proportions of particle-cracking and interface-debonding greatly varied with the grain size and particle volume fraction, and the variation law changed with the stress state. The proportion of matrix-cracking had a weak dependence on the microstructure, while increased with the stress triaxiality decreasing. It made the damage initiation in aluminum alloy welded joint transit from particle-cracking dominance to matrix-cracking dominance with the stress triaxiality decreasing. The micromechanical modeling results suggested that the changes of evolutions and distributions of Mises stress in particle, hydrostatic stress at interface and plastic strain in matrix with microstructure and stress state were responsible for the above effects.

Forming Limit Diagram Prediction of AISI 304–St 12 Tailor Welded Blanks Using GTN Damage Model

Abstract Because of weight and manufacturing cost decrease, tailor welded blanks (TWBs) have great usage in different industries such as the automotive and aircraft industries. Despite the wide use of TWBs in various industries, there are some drawbacks in the formability of these blanks. Using a forming limit diagram (FLD) enables one to prevent necking and fracture of these blanks by correct selection of forming parameters. There are different numerical methods to predict the FLD of sheet metals, but the Gurson–Tvergaard–Needleman (GTN) model is a useful ductile fracture model in this field. In this study, the GTN model was used for FLD prediction of AISI 304–St 12 TWBs. An anti-inference method and a numerical simulation of the tensile test by ABAQUS software (Dassault Systèmes, Vélizy-Villacoublay, France) were firstly used for GTN parameter identification of AISI 304 and St 12 blanks. Proper parameters of the GTN model were imported to the numerical tests of FLD, which was done based on the Nakazima standard test. In the experimental part of this study, carbon dioxide laser welding was used for TWBs welding, which consists of AISI 304 and St 12 blanks with equal thicknesses of 1 mm. The numerical results were compared for FLD prediction, punch’s load-displacement curve, and the fracture position of samples with experimental ones. The results showed that there was a good agreement between the numerical prediction and the experimental results.

Numerical and Experimental Investigation on Hot Stamping of TWB B-Pillar

In order to achieve the targeted crashworthiness performance, the application of Tailor-Welded-Blank (TWB) on the crash-relevant components has become a trend in the automotive industry. This paper aims to investigate the mechanical property and structural performance of the hot stamped TWB B-pillars. After hot stamping, the strength grade for the hard zone is 1500 MPa while the soft zone’s strength grade is 590 MPa. The CAE model shows that the intrusion distance is decreased for the TWB design compared to the monolithic material B-pillar. The three point bending performance could be adjusted by changing the range of the soft zone. It is observed that the weld line has a low crack sensitivity during hot stamping. The transition zone between the hard zone and soft zone is less than 1mm. The ATOS scanning results show that no significant effect on the part’s size deviation for the TWB design compared to the monolithic material B-pillar.

Microstructures and Flow Behavior of Ductibor® 500-AS Steel for a Range of As-Quenched Conditions

Ductibor® 500-AS steel is used in hot-stamping applications within tailor-welded blanks to introduce more ductile, energy-absorbing regions within ultra-high strength structural components. This study aimed to explore the sensitivity of the microstructure and mechanical properties of Ductibor® 500-AS to changes in cooling rate. For this purpose, the microstructures and hardening behavior of Ductibor® 500-AS steel sheet were examined for a range of quench conditions, including austenitization followed by air, die, or water quenching. Optical and scanning electron microscopy investigations revealed a wide range of microstructures, comprising either mostly ferritic, mixed ferritic-martensitic, or mostly martensitic with some tempered martensite/bainite. Tensile and shear tests conducted on the as-quenched samples exhibited a high degree of sensitivity to cooling rate as well as strong mechanical anisotropy. The flow curves of the different material conditions obtained using a shear-conversion technique and fit to a modified Hockett-Sherby model were validated using the finite-element method (FEM) simulations of the uniaxial-tension tests in LS-DYNA, considering isotropic von Mises and/or anisotropic Barlat Yld2000 yield criteria. The predicted load–displacement response and strain localization patterns using the isotropic and anisotropic models were shown to agree with the measured results. However, only the anisotropic model was able to predict the local strain histories consistent with the experiments. Consequently, it is important to account for both of the quench-rate sensitivity and plastic anisotropy of Ductibor® 500-AS in crash-safety simulations of structural components utilizing this steel.

The Effect of Laser Beam Wobbling Mode on Weld Bead Geometry of Tailor Welded Blanks

As a higher weight leads to increased fuel consumption for the automobile industry, the body in white must be lighter to compensate for the weight of additional components. Therefore, tailored blanks are used, which reinforce the body in white only in areas where a higher strength or stiffness is necessary. The applicability of laser welding processes with its numerous advantages, such as low heat input and production efficiency, is often limited when joining imperfect edges steel sheets due to small gap bridging ability. To overcome this limit, recent developments in the laser industry have introduced a novel method to wider the applications of lasers through the utilization of fast beam oscillation techniques, also known as laser beam wobbling. In this study, the effects of the four different amplitudes (0.5 mm, 1 mm, 1.5 mm and 2 mm) of circular laser beam oscillation patterns on the weld bead geometry and microhardness distribution were investigated. The results revealed that the weld bead width increased with the increase of wobble amplitude. Moreover, the tensile strengths of the welded blanks were higher than the AHSS base metal for all amplitude levels.

Comparison between laser beam and gas tungsten arc tailored welded blanks via deep drawing

This paper aims at analyzing the deformation behavior of tailor welded blanks (TWBs), manufactured by laser beam welding (LBW) and gas tungsten arc welding (GTAW), through the deep drawing process. Dissimilar and similar steels with different thicknesses were used in the production of tailor welded blanks. The Nd: YAG laser welding method with nitrogen (N2) as the shielding gas was used to join TWBs. The effects of some significant process factors, namely welding speed, blank holder forces (BHF), material properties of base metals, dry/lubricated condition and laser spot size was experimentally investigated on the weld line movement and drawing depth. Results indicated that using LBW with optimum parameters for the production of dissimilar TWBs caused the control of failure in the weaker base metal. Results showed that the sound welds were produced in similar TWBs with a thickness ratio of 2 when using GTAW, but the weld quality was poor when using LBW. Moreover, it is observed that the critical stresses were taken place outside of the weld zone and rupture due to the high heat input of laser and metallurgical changes of the base metal that occur in the pre-softening zone. In addition, the weld line movement occurred as a result of plastic strain change of the weld joint that caused failure-prone zone creation as well as the adverse wrinkling.

Steel sheets partnered with quenchable sheet in hot stamping of tailor-welded blanks and its application to separation prevention of fractured components

The phase transformation and mechanical properties of non-quenchable steels partnered with the quenchable boron steel in hot stamping of tailor-welded blanks were evaluated to produce tailored components with partially balanced strength and ductility. The effect of the forming start temperature after natural air cooling on the phase transformation and mechanical properties for 270 MPa mild steel, non-quenchable steel, 440 MPa high strength steel, and 22MnB5 steel sheets was examined, and the 270 MPa and non-quenchable sheets had enough ductility after hot stamping. Tailored components having a hardness of about 500 HV1 in the high strength zone and a total elongation of about 30% in the high ductility zone were hot-stamped from a tailor-welded blank composed of 22MnB5 and 270 MPa sheets. It was found that the 270 MPa mild steel sheet is sufficient as a partner sheet of tailor-welded blanks. In addition, the safety of hot-stamped components was heightened by welding a 22MnB5 main blank with a 270 MPa steel patch. Even if the main blank is fractured by a collision, the hot-stamped component is not separated by the 270 MPa patch having high ductility.

Comparison of different welding methods on mechanical properties and formability behaviors of tailor welded blanks (TWB) made from AA6061 alloys

A tailor welded blank (TWB) includes two or more blanks joined together in order to make a single blank. Different welding methods are used to join blanks with different characteristics and form TWBs. In this study, a comparison is made among the effects of three different welding methods namely CO2 laser welding, friction stir welding (FSW), and friction stir vibration welding (FSVW) on mechanical and formability properties of developed TWBs. AA6061 alloy sheets with different thicknesses (1.2 and 0.8 mm) are joined to get TWBs. The forming limit diagram (FLD) and limiting dome height (LDH) are applied to assess the formability. The Taguchi method is applied to find the optimum values of welding parameters. It is concluded that TWBs made by FSVW have higher mechanical properties and formability compared to TWBs made by FSW and CO2 laser welding. The results also indicate that FLD for TWBs made by FSW is higher than FLD for TWBs made by CO2 laser welding and FLD0, for TWBs made by FSVW, increases as vibration frequency increases.

An eave-like model for the welding of 304 stainless-steel tailor-welded blanks with different thicknesses

Due to its excellent corrosion resistance and machinability, stainless-steel material has been widely used in many different areas, such as nuclear power and the aircraft industry. In these applications, the stainless-steel parts often consist of tailor-welded blanks with different thicknesses. It is crucial to keep the tailor-welded blanks of high quality in order to satisfy the demanding requirements. To make the welding process of tailor-welded blanks simple and efficient, a novel welding model for the eave-like structure is proposed in this paper. Based on this model, the butt welding of tailor-welded blanks with a plate thickness combination of 2.0 mm and 1.0 mm are successfully completed by high power diode laser sources. For further inspecting the performance of the welded bead, we analyze the microstructure and evaluate the mechanical strength. The results prove that our tailor-welded blanks can satisfy the industrial requirements. This work gives an experimental guide on the welding of tailor-welded blanks with different thicknesses.

Finite and Numerical Simulations Applied in Tailor Welded Blank

The increase in economic and technological competitiveness means that the automobile industry seeks constant innovation in its production methods and processes, in order to produce lighter, safer and more efficient vehicles. Products with greater mechanical resistance, better conformability, thickness combinations of plates / materials are sought with a focus on reducing mass and increasing the rigidity of the vehicle body. In this scenario, Tailor Welded Blank (TWB), which is a top welding technique (by unconventional processes) of sheets of different specifications (materials, thicknesses and / or coatings), appears as a solution, as it allows localized distribution of mechanical properties, mass, optimizing the relationship between structural rigidity and the total weight of the vehicle body. The great challenge of this technique is to combine two processes with completely different demands, welding and mechanical forming. Due to the complexity of forming TWBs, the use of simulations has been widely adopted. In this review, different results of the numerical simulation methods used for a Tailor Welded Blank are compared, focusing on the details and the influence of the parameters used.

Investigation on Formability of Tailor-Welded Blanks in Incremental Forming

Steel laser tailor-welded blanks (TWBs) are produced by end-to-end joining of base sheets using different welding methods. In this article, the formability of laser TWBs of St12 and St14 with thicknesses of 1 mm and 1.5 in single point incremental forming process were experimentally and numerically investigated. First, the forming limit wall angle was experimentally determined for each of the base sheets. Then, SPIF of TWBs samples was carried out at the thinner sheet wall angle; 67°. For numerical investigation, the mechanical properties of the weld zone were obtained. For one combination of TWBs, the finite element (FE) simulation of incremental forming was performed by the use of ABAQUS/Explicit FE software. The simulation process was validated by comparing the results with those of experiments. Then, the effect of SPIF on thickness, stress and strain distribution of other combinations of TWBs was numerically investigated. The results showed that using the FE model, the SPIF of TWBs without performing high cost experimental tests can be properly investigated. Also, the results revealed that in steel laser TWBs with different thicknesses, the maximum and minimum principal strains are concentrated at the corners and the walls of the thinner sheet of TWBs, respectively. Hence, the maximum amount of effective strain is concentrated at the thinner side of TWBs corners and the weld zone of the two blanks. For the same reason, rupture is observed at these regions.

The interactive effect of microstructure and stress state on the microscopic damage development of aluminum alloy tailor-welded blank

Ductile fracture is the most common defect in plastic forming of tailor-welded blank (TWB). Revealing the damage and fracture characteristics of welded joint is very critical for accurately predicting the fracture defect. In this study, the fracture strain and microscopic damage development of a 2219 aluminum alloy welded joint were systemically investigated by in-situ-SEM testing. The interactive effects of microstructure and stress state on void growth and coalescence were quantitatively explored. Further, a micromechanical model based on actual microstructure was established to reveal the underlying mechanisms. The results show that the prominent void growth rates are affected by the particle size, particle volume fraction and grain size, and the effects vary with the stress triaxiality. The growing voids coalesce through one or both of ligament necking and shearing, which compete with each other dependent on the microstructure and stress state, making the variations of critical void spacing ratio. Attributing to these effects, the fracture strains of different microstructures in welded blank under various stress states are different, and the relationship between the fracture strain and microstructure relies on the stress state. These damage and fracture rules are explained by the microscopic heterogeneous deformation characteristics under different microstructures and stress states.

Welding Deformation of Unequal Thickness Tailor Welded Blanks under Multiple Factors

With the popularity of lightweight requirements, the application of tailor welded blanks with unequal thickness is increasing gradually. The welding deformation of tailor welded blanks with unequal thickness inclined weld is affected by the external constraints and the internal structural parameters of the plates. In this paper, the effect of the external constraints and the internal structural parameters on the multi-layer and multi-pass welding deformation of unequal thickness inclined weld was investigated. The deformation distribution law of butt welding of unequal thickness inclined weld was obtained combined with simulation and experiment results. The results showed that the spring constraint method was similar to the actual welding condition, meanwhile, the control effect of spring constraint on the welding deformation was better. The welding gap had the greatest influence on the welding deformation, followed by the angle of inclined weld, thickness of thick plate and thickness of thin plate. When the thickness difference between two plates was kept at 50%, the control effect of welding deformation was the best.

Laser-based precise measurement of tailor welded blanks: a case study

Precise measurement of tailor-welded blanks is crucial for quality control of laser welding. The difficulty in measuring the seam profile of similar gage tailor–welded blanks lies in lacking of solutions to locate their feature points such as those representing the laser stripe. A laser sensor–based method is proposed to measure tailor-welded blanks based on its laser stripe and texture features, from which the proposed algorithm is employed to extract the feature points for seam profile assessment. The algorithm is evaluated on a laser-based weld seam measurement system, the experiment results show that the proposed method measures the tailor-welded blanks with high accuracy and is suitable for online inspection.

Multi Response Optimization of Parameters in F SW for Tailor Welded Blanks A A 5052 H32 and A A 5083 O u sing Response Surface Methodology

Tensile properties, microhardness, and formability of the tailor welded blank of AA5052-H32 and AA5083-O were investigated. To detect the influence of FSW parameters such as shoulder diameter (SD), rotational speed (RS), and travel speed (TS), a central composite design (CCD) was derived. The response surface methodology (RSM) technique is used to develop the mathematical model and optimization of multiple responses, i.e., ultimate tensile strength (UTS), Yield strength (YS), percentage elongation (TE), dome height (DH), and microhardness (μH). Analysis of variance (ANOVA) technique is used to validate the competency of the established model, and the regression equation is derived to predict the value of output responses. It is found that the welding parameter of FSW plays a significant role in fabricating the joint. It is observed that for the welded combination of AA5052-H32 and AA5083-O, the metallurgically defect-free and sound weld produced. The results are very much significant to a better understanding of the effect of the combination of SD, TS, RS to fabricate the FSW joint. The experimental and predicted result shows a good relationship with each other.