Formability Of Tailor Welded Blanks Research Articles

Effect of medium-speed forming on formability of tailor welded blanks

Despite the widespread use of tailor welded blanks (TWB) in manufacturing auto-body panels and considering that different forming processes are performed at various speeds, it is necessary to examine the forming speed consequences. So, this study aims to investigate the forming speed effect on the formability of TWB and its constituent sheets. TWB consisting of St14 steel sheets of different thicknesses were welded using a fiber laser. Uniaxial tensile tests were conducted at various strain rates, and formability experiments were carried out at the quasi-static and medium-speed forming to construct forming limit curves (FLC). Tensile test results showed that some strain-hardening indicators decreased by strain rate increasing. The flow stress of base metals at different strain rates was successfully predicted by the constitutive model considering variable parameters. At medium-speed forming of base metals, the peak of major strain and fracture moved to the dome center. But, the strain concentration of most TWB samples at two forming speeds occurred in the thin sheet near the dome center. Also, the limiting dome height (LDH) at medium-speed forming decreased. Medium-speed FLC of base metals shifted downward and to the more positive minor strain compared to quasi-static FLC. Medium-speed FLC of TWB was lower than quasi-static FLC, especially on the tension-compression side. The reduction of medium-speed formability was attributed to the strain-hardening lowering, friction reduction, and inertial effects due to increased forming speed.

Experimental and numerical studies on the influence of formability of AISI 316L tailor-welded blanks at different weld line orientations

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.

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.

Review on Sheet Metal Formability

Sheet metal Forming is one of the most important and diverse manufacturing processes and has been an integral part of industries like automotive and aerospace which need high density, lightweight and high strength materials. This paper tries to encapsulate the features related to Formability and its testing. Various parameters like anisotropy and strain rates on which the formability depends are also considered and their impact on the testing. Further, the paper includes study of Formability of Tailor Welded Blanks which is an integral part of the automotive sector. At last the paper concludes with the future developments that can be made in this field along with new modelling techniques and new advancements in testing.

Experimental and Numerical Studies on Formability of Tailor Welded Blanks of High Strength Steel

Abstract Tailor Welded Blanks of high strength steels offer cost effectiveness by weight and parts reduction while maintaining structural integrity and crash performance. However, the potential offered by these steels can only be realized by design engineers if there is proper coordination of material properties, part geometry and process capability. The present study deals with the experimental characterization of tensile properties of parent sheets of high strength steel JSC590RN and their tailor welded blanks with thickness 1.4mm and 1.8mm. Limiting dome height tests were performed using a 100ton hydraulic press on the parent sheets and the tailored blanks to assess formability of the individual parent sheets and the given thickness combination. The increase in strength of these steels lowers the strain hardening exponent which in turn decreases the stretchability of the sheets and results in higher localized thinning. The results obtained by experiments were compared with that of the results predicted by finite element simulations using ABAQUS with incorporation of the weld zone properties. The incorporation of the weld zone properties in the simulations improved the results significantly. The predicted forming limit diagrams of the parent blanks are also plotted. It is observed that the formability of tailor welded blanks are reduced when compared with that of the parent sheets.

Local formability and strength of TWIP-TRIP weldments for stamping tailor welded blanks (TWBs)

The assessment of the local formability and mechanical behavior of weldments in tailor welded blanks (TWBs) made of advanced high strength steels is of crucial importance in the automotive industry, both for the mechanical design of tailored components, and to set up accurate sheet forming numerical simulations. This work investigates the formability of TWBs made of a twinning induced plasticity (TWIP) and transformation induced plasticity (TRIP) steel, determining the local elastoplastic behavior of the different regions of the weldment. To this purpose, several micro-samples were extracted along the weld seam and heat affected zones and then subjected to tensile tests. Tensile tests were also performed on macro-samples to assess the overall mechanical behavior of the TWBs during plastic deformation. A digital image correlation (DIC) technique was used to measure the surface strain field of both micro- and macro-samples, to calculate the plastic strain ratio, through-thickness strain, and to point out possible inhomogeneities in the plastic behavior of the TWB weld beads. The TWB joint exhibited a significant formability of the fusion zone and of the TWIP heat affected zone, whereas it was rather limited at the TRIP side. Locally, an uneven plastic behavior within the fusion zone was observed, with a variable plastic strain ratio (i.e., thinning) in both axial and transverse direction. The other regions of the weld, instead, deformed more homogeneously. Preliminary considerations about the numerical modeling of TWIP/TRIP TWBs and their prospective use in sheet forming operations have been outlined.

Effect of Orientation of Weld Line on Formability of Electron Beam-Welded Dissimilar Thickness Titanium Sheets

Recently, manufacturing industries are looking forward to get insight into the influence of weld orientation on formability of tailor-welded blanks (TWBs) of titanium sheets for design and fabrication of lightweight components. Hence, commercially pure titanium (CP Ti) sheets of 1.0 and 1.2 mm thickness were joined together by electron beam welding process using accelerating voltage of 55 kV, beam current of 14.9 mA and welding speed of 865 mm/min. Two different types of TWBs with weld line perpendicular to the rolling direction (WL ⊥ RD) and weld line parallel to the rolling direction (WL || RD) were fabricated, and subsequently, the tensile test, microstructure and microhardness characterizations were conducted to ensure quality of weld. The limiting dome height (LDH) tests were carried out using laboratory-scale setup to evaluate forming behavior of both the above TWBs in terms of FLD, strain distribution, weld line movement and failure location. It was found that the tensile stress–strain response and formability performance of TWBs were significantly influenced by weld line orientation with lower ductility, ultimate tensile strength and LDH in TWB of WL || RD. Moreover, significant weld line movement and non-uniform strain distribution with necking and subsequently fracture were observed away from the weld line in thinner 1.0 mm CP Ti sheets depending on both sample geometry and weld line orientation.

Simulation Process Deep Drawing of Tailor Welded Blanks DP600 and BH220 Materials in Tool With Elastic Blankholder

Abstract The high-strength steels and tailor welded blanks (TWB) are applied in construction of cars parts to reduction of cars weight [1, 2]. The application of these materials brings possible complicatons during the forming when it proves the considerable influence of stress-strain characteristics differences of of the individual parts of TWB what result in non-constant material flow and consequently a negative movement of the weld interface [3, 4]. One of the ways of elimination of this negative effect is to choose a suitable blankholder system with optimal distribution of blankholder forces by using elastic blankholder with adjustable distribution of blankholder forces. Within the bounds of study the experimental blankholder system with elastic blankholder with adjustable distribution of blankholder forces was used [5, 6]. Finite element methods (FEM) simulation has unsubstitutable role n the study of formability of TWB whereby it is possible to determine the values and points of application of the blankholder forces [7, 8]. The FEM simulations results carried out in simulative LS-Dyna software are presented in this article which is focused on achieving weld interface movement minimalization of tailor welded blanks from DP600 and BH220 materials by optimization of blankholder forces [9, 10].

Optimizacija oblikovanja prilagojenih varjenih surovcev

Optimizacija oblikovanja prilagojenih varjenih surovcev

Comparison of electromagnetic forming of friction stir-welded blanks of dissimilar material AA 5052-AA 6061 with conventional forming process

In this work, studies on formability of Tailor Welded Blanks (TWB) were carried out by means of both quasi-static and high speed forming process. TWBs were manufactured as welded blanks of dissimilar material combination. Welding of AA 5052-H32 to AA 6061-T6 aluminium alloy of 1 mm thickness was done with the help a friction stir welding (FSW) process. Limit dome height (LDH) test was performed by both conventional hydraulic press forming (HPF) and by a high-speed forming process called electromagnetic forming (EMF) process, to investigate the forming behaviour of the TWB. Subsequently forming limit curves (FLCs) were plotted to quantify forming behaviour. Dome heights and FLCs of TWB and base materials are compared. Similar comparison has been made between conventional forming and EM forming process. It is found that the formability of TWB increases considerably with EMF process with base AA 5052 material showed largest increase in formability. Effect of weld line offset on the formability was also investigated. When the weld line was offset by 25 mm towards AA 6061 side of the TWB, the welded blanks showed maximum forming behaviour by EMF process in terms of both dome height and FLC.

Hot stamping of AA6082 tailor welded blanks: Experiments and knowledge-based cloud – finite element (KBC-FE) simulation

A novel hot stamping technique known as ‘Solution Heat treatment, Forming and in-die Quenching (HFQ®)’ was employed to manufacture lightweight structural components from AA6082 tailor-welded blanks (TWBs) of different thickness combinations: 1.5–1.5 and 2.0–1.0mm. A finite element (FE) model was built to study the deformation characteristics during the hot stamping process. The FE model was successfully validated by comparing simulation results with experimental ones. Subsequently, the verified simulation results were analysed through a novel multi-objective FE platform known as ‘Knowledge-Based Cloud – Finite Element (KBC-FE)’. KBC-FE operates in a cloud environment and offers various advanced unique functions via functional modules. The ‘formability’ module was implemented in the current study to predict the limiting dome height and failure mode during the hot stamping process. Good agreements were achieved between the predicted and experimental results, from which studies were extended to predict the forming features of 2.0–1.5mm TWBs. The ‘formability’ module has successfully captured the complex nature of a hot stamping process, featuring a non-isothermal and non-linear loading path. The formability of TWBs was found to be dependent on forming speed and blank thickness, out of which the latter has a dominant effect.

Formability of Tailor-Welded Blanks From Dual-Phase and Bake-Hardened Steels with a Planar Anisotropy Influence

The formability of two types of tailor-welded blanks was analyzed with the concentration on the effects of planar anisotropy on eras forming of deep-drawn parts. The first tailor-welded blank consisted of bake-hardened BH220 steel with different rolling directions, which is applied to the surface car body parts. The second one consisted of dual-phase DP600 steel with different rolling directions, which is applied to supporting parts of automobiles. Stress-strain characteristics of experimental steel sheets were measured using the tensile tests and used in the respective simulations. Simulations via the Dynaform software were compared to the experimental values measured during the deep-drawing process of rectangular boxes.

Experimental investigation of formability of Al-1050 tailor-welded blanks

Tailor-welded blanks (TWBs) are considered one of the important manufacturing methods. By which, a single blank with multi-sheets with different thickness, material, surface conditions, grade, or strength is produced. In this paper, the formability of TWBs is investigated. The base metal used for this study is aluminum (Al-1050) with different thicknesses. A several thicknesses of base metal for instance 0.6, 0.8, 1.0, and 1.2 mm are combined. A different thickness ratio (TR) of sheets combination of TWBs i.e., 1.25, 1.33, and 1.5 is considered. The TWBs are welded using friction stir welding (FSW) technique. A different working condition for instance rotational speed and travel speed is used in this investigation. The TWBs specimens are drawn into flangeless cups. The limiting thickness ratio (LTR) and mechanical properties of base metals are determined. Several experiments are carried out to investigate the optimal working conditions. The experimental results are discussed and presented. A validation of the experimental results using Tagushi approach to verify the optimal welding parameters is presented.

An experimental investigation of the formability of low carbon steel tailor-welded blanks of different thickness ratios

Cold-rolled low carbon steel sheets of thicknesses ranging from 0.8 to 2 mm were sheets welded together to form a single part before the formability tests. In this study, the formability of the tailor-welded blanks (TWBs) was evaluated in terms of three measures which are limited dome height (LDH), forming limit diagram (FLD), and minimum major strain. In addition to the mechanical properties, the welded specimens were analyzed experimentally under the effect of thickness ratios. The influence of welding orientation and its relation with the rolling direction on formability and mechanical properties were also studied. The mechanical properties of the welded specimens were investigated by tensile testing and micro-hardness measurements. The metallographic studies were investigated using optical microscope and scanning electron microscope (SEM). The experimental findings in this study showed that the higher the thickness ratio of the TWBs, the lower the forming limits curve level and the lower formability. The minimum major strain was clearly inversely proportional to the thickness ratio of the TWBs. On the other hand, the results of uniaxial tests clearly illustrated that there was no significant difference between the tensile strengths of the TWBs and base metal. The micro-hardness measurements indicated that the hardness in the weld bead increased by about 55 % of the base metal.

Formability of Friction Stir-Welded Blanks with Different Thickness Ratios

Welded sheets with different thicknesses are one of the interesting types of tailor-welded blanks (TWBs) that are widely used in metal-forming industries. In the present work, the formability behavior of different 1100-aluminum TWBs was studied. In this regard, the TWBs were made with different thickness ratios by using friction stir welding (FSW) at different welding rotational speeds (ω). The thickness ratios of 1.0, 1.3, and 1.7 were investigated where the thinner sheets had 1.5 mm thick for all conditions; i.e., the volume of welded material increased when the thickness ratio increased. Macrostructural observations, mechanical investigations, and sheet-forming limit tests were conducted. The results indicate that increasing ω leads to increasing the weld nugget size up to a maximum level and welding became impossible at higher ω. Furthermore, increasing heat input during FSW, the ultimate tensile strength of welds reduced in comparison with the initial cold-worked base metal. However, the ductility improved by increasing the heat input, which produced the sound welds. Formability studies of the friction stir-welded blanks with equal thicknesses have shown that the forming ratio improves up to 2.8 times the base metal. Forming limit curves also illustrate that increasing the thickness ratio of TWB causes the formability ratio to decrease steadily. Thus, when the thickness ratio becomes 1.7, the formability of TWB decreases approximately to the thinnest base metal.

Theoretical prediction and experimental investigation on formability of tailor-welded blanks

Based on the elastoplastic mechanical properties of the weld and heat affected zone metals obtained by a nanoindentation test, a theoretical calculation model was established for the forming limit diagram (FLD) of tailor-welded blanks (TWBs) on the basis of plastic constitutive relations and Hosford yield criteria. Hemispherical punch bulging tests were performed to verify the FLD theoretical calculation results. The results demonstrated that not only the FLD theoretical calculation of base materials but also that of TWBs had a good agreement with their experiments. Besides, poorer formability of TWBs caused its FLD significantly lower than that of base materials. The theoretical calculation model offers a reliable approach to obtain the specific FLD of TWBs.

Experimental and Numerical Investigations of Constraint Effect on Deformation Behavior of Tailor-Welded Blanks

Tailor-welded blanks (TWBs) have been considered as a productive sheet forming method in automotive industries. However, formability of TWBs is reduced due to different properties or thicknesses of the blanks and is a challenge for manufacturing designers. The plastic capacity of TWBs is decreased even when the material and thickness are the same. The constraint effect of the laser weld (including weld and heat-affected zone) material in the forming process of similar TWBs is a key problem to be solved in the research, development and application of thin-sheet TWBs. In this paper, uniaxial tensile tests with full-field strain measurement by digital image correlation and Erichsen tests are performed to investigate the constraint effect on deformation behavior and explore the mechanism of decreasing formability of similar TWBs. In addition, finite element models are conducted under ABAQUS code to further reveal the phenomenal behavior of the constraint effect. The results of the base material and welded blanks are compared for characterizing the differences. Furthermore, in order to better understand this mechanism, theoretical and numerical investigations are employed and compared to interpret the constraint effect of laser weld on the deformation behavior of TWBs. An index is proposed to quantify the constraint effect. Results show that the constraint effect of laser weld appears in both stretch forming and drawing of TWBs. Strain paths are approaching the plane strain condition as compared to the monolithic blank due to the constraint effect. Constraint effect is a major factor affecting the formability of TWBs when the failure occurs away from the weld seam.

Use of stress based forming limit diagram to predict formability in two-stage forming of tailor welded blanks

In the present work, laboratory scale two-stage stretch forming processes were designed and fabricated where an interstitial free (IF) steel was first pre-strained in biaxial tensile mode, and subsequently it was deformed in a limiting dome height (LDH) test set up in tension–tension and tension–compression modes. Tailor welded blanks (TWB) of dissimilar materials were fabricated by laser welding of dual phase (DP) and IF steels, and these TWBs were subjected to the above two-stage stretch forming processes to characterize the influence of pre-strain, strain path and weld line orientation on formability. A mathematical framework was developed to estimate stress based forming limit diagram (σ-FLD) from strain based forming limit diagram (ε-FLD) using Hill-48 and Barlat-89 anisotropic plasticity theories incorporating three different strain hardening laws. The forming behaviour of pre-strained IF steel material and TWBs was predicted by finite element analysis (FEA) implementing both the ε-FLD and σ-FLD. It was found that the LDH was over-predicted by ε-FLD compared to σ-FLD in case of bi-axial tensile pre-strained IF steel specimens. However, the ε-FLD under-predicted the LDH of circular pre-strained TWBs and similar LDH was predicted by both the FLDs in case of pre-strained longitudinal TWBs. It was observed that the σ-FLD was more robust compared to the ε-FLD, and it was capable to predict formability of TWBs in multi-stage forming processes taking care of deformation histories. Lastly, the predicted thickness distribution, maximum thinning location and load progression curve during the second stage LDH test were validated with experimental results.

Multi‐Objective Genetic Algorithm to Optimize Variable Drawbead Geometry for Tailor Welded Blanks Made of Dissimilar Steels

Formability of a tailor welded blank (TWB) is affected by the strength ratio of the base metals joined. In this paper, formability of TWB with very high strength ratio made by joining twinning‐induced plasticity (TWIP) and low carbon steels is numerically studied using a limiting dome height test. The drawbead geometry at the weaker side is modified to increase the dome height. The design of drawbead is optimized by treating it as a multi‐objective problem with maximum dome height and minimum weldline movement as objectives, which were constructed as metamodels through a genetic algorithms based approach. The necessary data for the metamodeling are generated by finite element (FE) simulation using the commercial solver, LS‐DYNA®. The multi‐objective optimization is carried out using a predator–prey genetic algorithm. The Pareto front estimated using this evolutionary approach is validated using FE simulations and a good correlation is obtained.

Influences of Thickness Ratio of Base Sheets on Formability of Tailor Welded Blanks

The influences of thickness ratio of base sheets on formability of tailor welded blanks were examined based on Erichsen cupping tests. Three-dimensional finite element (FE) models, using Hill’48 yield criterion and iso-hardening rule, were built under the environment of the FE analysis software ABAQUS. The failure onset sites of tailor welded blanks were analysed and the quantitative relationships between the Erichsen index values and base thickness ratio were established. Based on these relationships, the formability of tailor welded blanks made from dissimilar base sheets are evaluated, provided that the Erichsen index values of tailor welded blanks made from identical ones are known and that the above two different types of tailor welded blanks undergo a similar stamping process. The experiments were then carried out to validate this method.