Past GDIS™ Presentations

Sumitomo Heavy Industries developed a new press forming technology Steel Tube Air Forming (STAF) for forming Body-in-White (BIW) parts such as A-pillar reinf., bumper reinf., side frame and so on. The concept of STAF is concentrated on maximum weight reduction and reduction of manufacturing cost with a single process. In the STAF process, a steel tube is processed through “a single step” in the tooling of press machinery. A steel tube is jouel heated (high-speed), air-formed and hardened.

STAF-formed parts have characteristic appearance with optimally designed flanges, TS over 1500 MPa, and continuously varied closed cross-section structure. First of all, STAF-formed parts can significantly improve basic performance against conventional hot-stamped parts due to its closed and flanged geometry. Sumitomo can expect weight reduction by around 30%. More than anything, the most unique part of the process is forming various flanges, which can integrate surrounding parts into STAF, improve joining and enhance performance. STAF’s flanges dramatically reduces part count, thereby reducing manufacturing costs and tooling investments. Furthermore, we puts a compact jouel heating device into practical use, replacing the conventional large heating furnace. The heating process will bring not only super power-saving but significantly reduces CO2 emissions from equipment.

As described above, STAF is the latest technology that can drastically improve performance and reduce weight and manufacturing costs.

Urbanization and Net Zero Emissions policy ambitions are leading contributors to the transportation shift to mobility on demand. Significant growth in Mobility as a Service (MaaS) (ride sharing transportation) is anticipated, and these vehicles will emphasize autonomous vehicle technologies and electrification. This presentation details the development of a new body structure design for a Level 5 fully autonomous vehicle, using the latest Advanced High-Strength Steel (AHSS) grades and fabrication processes.

The vehicle concept was created within the Steel E-Motive project, a collaboration between WorldAutoSteel and Ricardo, the UK-based engineering and sustainability consultancy. The vehicle has been designed with the new mode of transport in mind, with a strong focus on the user, the fleet operator and the vehicle’s operating environment. A change from driver to fully autonomous operation eliminates the requirement for driver interfaces and controls and enables occupants to be seated in unconventional locations and orientations. Legislative requirements such as driver vision and obscuration are also removed, which opens up further freedoms such as the ability to place structure where glazing previously existed. These freedoms have enabled the creation of a unique and spacious transportation environment, while being compact in size and agile around city center.

Despite compact dimensions with short front and rear overhangs, sophisticated engineering and the use of AHSS tailored to the specific vehicle requirements result in compliance to global high-speed crash and safety requirements. This presentation reveals more details of this 2.5-year concept design development program on the Steel E-Motive vehicle and body structure, the steel grades and technologies used and the performance achieved.

The transition to electric mobility (E-mobility) and the resulting changes in the car body structures place new demands on structural components. Especially prismatic, profile shaped components increase in their application. From an economic point of view, however, these new components can only be produced to a limited using the manufacturing processes that have been predominant in the body construction of internal combustion engine vehicles. Roll forming, in contrast, opens up new possibilities for the efficient production of these new types of structural components.
It is – not only for the purpose of crash performance – becoming particularly apparent in the structures for cutting edge electric vehicles that profiles having a multi-chambered cross-section are subject to growing demand. At the same time, the battery masses to be carried increase the need for weight-reducing measures in the body structure, so that high and ultra-high-strength steel (UHSS) alloys with strengths of up to 1700 MPa and more are increasingly being used. As a result of these material requirements or cross-section requirements, numerous manufacturing processes for profile-shaped structures such as extrusion, classic bending processes and deep drawing reach or exceed their capability limits. Roll forming, on the other hand, can meet these requirements and remains as an economical alternative for manufacturing the required multi-chamber profiles from high-strength materials.
In this presentation, we will present current strategies for the production of such profiles by roll forming. In addition to the theoretical presentation of the general suitability of this manufacturing process, we will use concrete examples to discuss the manufacturing strategy as well as how to deal with the specific challenges of high strength materials (including changing material properties). As examples we will use manufacturing lines for components of well-known OEMs, which have been realized by Dreistern in the past years.

The importance of true fracture strain was initially highlighted in the representation of local formability in material selections among various advanced high-strength steels (AHSSs) of similar tensile strength. Inspired by the relative studies, a precedent work compared the true fracture strain results measured via either digital image correlation (DIC) or fracture surface laser scanning on different AHSS tensile test samples. That work concluded that the DIC-based testing results comparatively underestimated the fracture strain. As a continued study, the present work further analyzed the DIC-based testing procedure and attributed such an underestimation mainly to the volume constancy assumption. Furthermore, this work pointed out that also because of the same assumption, the fracture surface laser scanning method to some extent overestimated the true fracture strain results. Nevertheless, it was observed that different AHSS grades were affected discrepantly by such two measurement methods. Therefore, scanning electron microscope (SEM) was applied to inspect the morphology of various micro-voids and dimples on different fracture surfaces to explain such a discrepancy. To bypass the volume constancy assumption, this work proposed two alternative methods, including a DIC-based thinning measurement method and a hybrid method, and discussed their pros and cons. In addition, the effects of DIC-recording frame rate and using different yield functions to derive the effective strain were also studied in this work. Last but not the least, by extending the considerations to damage-fracture modeling for forming and crash simulations, the importance of the true fracture strain accuracy was further highlighted.

Coating Free Press Hardened Steel (CFPHS) is a novel steel grade patented by General Motors Company with improves mechanical properties and surface quality over the current market favorite, AlSi coated 22MnB5. CFPHS has increased tensile strength and improved toughness over 22MnB5, enabling light-weighting of vehicles and improved crash protection for vehicle occupants. To enable vehicle architects to design parts with confidence using this material, it is important to develop computer-aided engineering (CAE) material cards that directly correlate to the actual material performance. This presentation reviews two CAE to trial result correlations demonstrating the compliance of the developed material cards with manufactured parts.

This presentation compares results of bend testing performed via CAE simulation to physical results from two components: a door beam and impact beam. The simulations show a close correlation between expectations from CAE to the physical testing results. This demonstrates that the efforts put into developing the materials cards have resulted in reliable simulation results. These CAE material cards can be utilized going forward to design new components for future programs, or to simulate the functionality of CFPHS in a drop-in application.

A family of new ultra high-strength steel (UHSS) multi-phase (MP) grades has been developed by ArcelorMittal to introduce cold-stamping UHSS products with improved elongation, bendability, flangeability, local formability, and possibly fracture limits, to address unique design challenges posed by automotive structures with very high strength requirements.

Roll forming is a continuous, lengthwise process which progressively bends sheet metal into a desired profile. The gradual nature of the bending enables the forming of ultra-high strength materials. Roll forming is typically applied in vehicle areas where high strength is required, such as bumper systems and rockers. As battery electric vehicles have become more prevalent the demands on those structures have changed; due to the increased vehicle mass, more energy must be absorbed, and in a smaller space to protect the battery system. The MP1300 and 1500 grades developed by ArcelorMittal are presented here as a potential for these applications. The improved bendability will allow for better energy absorption in crash at similar strength levels due to enhanced fracture resistance. The MP grades also help to alleviate challenges in roll forming such as further reducing the radius (R/t) of the section for better packaging, and improving spring-back and part forming operations post roll forming.

Mill trials have already taken place, on both uncoated and galvanized products. The microstructure concept and the characterization of major attributes, including HER and R/t, from sampled coils will be described. Roll forming trials have been conducted with these grades to characterize the bendability, and application specific parts have been produced to validate the improvement in energy absorption; all those results will be disclosed.

After pre-straining and bake treatment, most automotive steels show hardening behavior. In some cases, as the pre-strain increases, the bake hardening effect also increases. This characteristic can be a strong point of advanced high-strength steel (AHSS), especially for crash parts design. Historically, ASTM Standard A653/A653M has been used to evaluate the Bake Hardening Index (BHI). But on high tensile strength and low elongation materials, the BHI often can not be properly evaluated because failure occurs outside the gauge section due to a lack of remaining elongation. Depending on the part design, large strains (over 5%) distributed after forming. The Auto/Steel Partnership steel testing and harmonization team (STHT) concluded that an improved test procedure is needed for large pre-strain and bake hardening effect evaluation. In 2022 the STHT performed two rounds of bake hardening tests on two materials at two labs (POSCO and General Motors Company). The first round utilized the existing ASTM methodology. The second round utilized a modified methodology based on the pre-strain of a larger specimen. The new test procedure has resulted in more accurate BHI values in large pre-strain conditions as compared to the present ASTM test standard.

As the automotive industry gravitates to higher strength steel applications to aid in vehicle light weighting and better safety performance, additional panel springback is encountered using conventional cold stamping processes. To address this, hybrid beads were investigated as an alternate approach to traditional stake beads as a method to induce plastic deformation in the stamping operation and consequently lessen springback. The advantage of hybrid beads, when compared to stake beads, is an improvement in material utilization. To accomplish this, stamping simulations and physical die trials were performed to design and compare different hybrid bead geometries. In all, five different hybrid bead designs were evaluated in laboratory scale die trials and two of these designs were subsequently used in larger production scale die trials. During these production scale die trials, both the robustness of the hybrid beads and the associated forming forces required to engage them emerged as significant issues. However, the hybrid beads proved effective in reducing panel springback and side wall curl when sufficient forming forces were available. Forming simulations were also conducted and agreed with the physical die trials. Additional work is required to further develop alternate hybrid bead geometries for successful implementation.

Accurate characterization of edge fracture of advanced high-strength steel (AHSS) is important for several needs such as material approval, troubleshooting of stamping failures and development of fracture criteria for finite element analysis (FEA) prediction. While the standard hole expansion test has been used for material approval purposes, its use for the other needs of resolving edge fracture issues is hindered by several issues such as test repeatability, and dependence of results on initial hole diameter. In this study, a half-dome test with a spherical punch was employed to perform edge fracture tests on ArcelorMittal’s Gen 3 AHSS, Fortiform®980. For comparison, hole expansion tests were also conducted. Edge fracture strain, strain distribution and strain path in the edge vicinity areas were determined using Digital Image Correlation (DIC). It was found that strain path in the edge vicinity area for half-dome test was closer to uniaxial tension than that from hole expansion test. Furthermore, the half dome test could determine directional dependence of fracture strains with respect to the rolling direction. This study demonstrates that half-dome test could be a valid candidate for comprehensive and accurate edge fracture characterization.

ArcelorMittal and its hot press tooling technology partner, American Tooling Center (ATC), have successfully commissioned a production intent hot stamping B-pillar tool using 1.6 mm Usibor® 1500 AS. The B-pillar tool was designed to represent a reasonably difficult part using a monolithic blank and same gauge laser welded blank (LWB) combinations. The intent is to study stamping conditions and process windows for robust parts, using various press hardened steel grades (Usibor® 1500, Usibor® 2000, Ductibor® 1000, Ductibor® 500), under real world manufacturing conditions. The scope of this presentation focuses on the commissioning activities using monolithic Usibor® 1500 AS and the value of FEA is demonstrated. A final buy-off run was successfully performed along with physical testing of parts, examining part quality and consistency. For example, part strength, part distortion, and manufacturing performance (thinning and wrinkling) were measured on parts sampled throughout the run. Detailed press traces and process data were also logged during the buy-off trial. Key to successful commissioning of the tools was continual communication and collaboration between ATC and ArcelorMittal.

Over the last 20 years the Society of Automotive Engineers (SAE) has supported the Auto/Steel Partnership (A/SP), along with the global automotive and steel industries. The SAE metals technical committee of volunteers provides the avenue for global standards creation through A/SP work and industry development of advanced high-strength steel (AHSS) and Generation 3 steel technology.

Three specifications have been published in the last year, two exciting new, and one critical revision, to support the automotive and steel industries. This review will describe the specifications and the teamwork needed to create these critical documents.

J2947 – Categorization and Properties of Steel Sheet for Automotive Cold Forming Applications
J3215 – Hydrogen Embrittlement Testing of Ultra High-Strength Steels and Stampings by Acid Immersion
J810 – Classification of Common Surface Imperfections in Sheet Steel

Automotive electrification requires many new steel grades; silicon bearing electrical steels have been developed to meet the demanding application requirements of automotive traction motors. Similar to new advanced high strength steel grades developed to meet vehicle architecture, these new electrical steels must be high strength (albeit much lower strength as compared to AHSS) and possess optimized magnetic properties to create efficient motors in serial production. This work will highlight some of the design requirements for electrical steels and show case studies of these grades for application

Laser welded blanks have been widely used to achieve lighter weight with improved structural integrity in automotive BIW structures. However, stamping of laser welded samples have many challenges, one of which is stretch-bending failure. In this study, an experimental methodology is developed to characterize the stretch-bendability of laser welded and monolithic steel blanks. Along with the stretch-bending strain limit criteria, a new global failure criteria is proposed in this study for comparison of stretch-bendability, which helps product design engineers to examine design limits and thus minimize the risk of stretch-bending failure during stamping processes. The results show that the stretch-bendability of the laser welded blanks are less affected by the R/t ratio (radius of the stretch-bending punch / blank thickness) compared to the monolithic blanks.

Increasing automotive requirements for improved corrosion life on frames and chassis components have created a challenge for OEMs and suppliers to improve corrosion resistance. To meet these requirements and improve corrosion resistance, many OEMs are requiring zinc-coated components. The zinc coating adds an additional degree of difficulty to welding as its low vaporization point leads to zinc vapor that can be trapped in the weld metal as porosity.
In response to the aforementioned issue, Lincoln Electric has developed a unique GMAW wire, SuperArc® XLS, that has a marked reduction in porosity compared to conventional GMAW wires on zinc coated steels. Its novel chemistry has shown distinct benefits for minimizing porosity, allowing welds to be made at increased speeds with fewer defects. When combined with a pulsed waveform, this complete process solution provides low spatter and increased process efficiency while maintaining a lower level of porosity when compared to traditional GMAW wires.
The proposed presentation for this conference is as follows: compare end-product porosity defect results and demonstrate the outgassing behavior of zinc vapor in the weld pool. The welding comparison was performed on automotive zinc-coated steels with SuperArc® XLS and standard GMAW wires.
For end-product comparison, X-ray analysis was performed to determine porosity on lap welds completed with constant weld settings and environmental conditions. For outgassing behavior, the movement of zinc vapor was observed via high-speed video of the weld pool surface and via high-speed in-situ X-ray video. This experiment suggested a three region model to discuss the evolution of zinc porosity in GMAW. The results from all testing showcased clear improvement in end-product porosity and markedly different zinc vapor behavior when using SuperArc® XLS compared to standard GMAW wires.

Press-Hardened Steels (PHS) are known to be used in the safety cage of the body-in-white structure of a car owing to their high strength from phase transformation during hot stamping. Resistance spot welding (RSW) of this steel produces a martensitic microstructure in the fusion zone that is brittle and shows minimal energy absorption capability during crash events. In this regard, in-situ post-weld heat treatment (PWHT) has been adopted as a means to improve the toughness of the fusion zone. In this study, in-situ tempering and recrystallization pulses were employed to modify the fusion zone microstructure and improve the energy absorption capability of PHS spot welds. The optimal tempering pulse schedule was obtained by measuring the average hardness of the FZ while the changes in grain size and aspect ratio were used to determine the optimum recrystallization pulse schedule. The results indicate tempering and recrystallization are effective to improve the joint mechanical properties, change the crack propagation path and failure mode after cross-tension test. Similarly, the fractography revealed that the PWHT welds failed in a ductile mode while the as-welded condition showed cleavage features indicating a brittle failure. A comparison between the effectiveness of both tempering and recrystallization will be discussed in this work with an emphasis on the changes in microstructure, joint properties and relevance to the industry in terms of applicability.

Advanced High Strength Steels (AHSS) and New Generation Steels (Gen3), with their unique combination of durability, ductility, and strength, are enabling automakers to meet increasing vehicle weight, safety and performance targets. One of the biggest challenges with these materials is simulating the spot weld separation under impact loading. The Auto/Steel Partnership (A/SP) in collaboration with The University of Waterloo, have developed advanced testing and modeling methods to predict spot weld separation under dynamic loading modes. Novel test methods have been developed to characterize the mechanical properties of the spot welds, which includes the weld nugget, base material and the different components of the heat affected zone (the coarse-grained region above Ac3, the region between Ac3 and Ac1, and region below Ac1). Mini-tensile and mini-shear coupons were extracted from welded coupons for the weld nugget and base metal properties, and HAZ regions. Five test configurations were employed to characterize the plasticity and failure properties of the spot welds, which were uniaxial tensile, shear, notch tension, central hole, and V-bend. To validate the mini-coupon results, larger test coupons were produced using a Gleeble unit to reproduce the representative microstructures of each three HAZ regions. The characterized material properties of the Gleeble produced coupons were compared with the mini-coupons extracted from welded coupons. The mechanical properties were used as input parameters for finite element (FE) simulations. Multiple weld modeling strategies were studied in this project. A meso-scale detailed spot model with a fine FEA mesh was developed to simulate the coupon response to load paths based on microhardness data and the constitutive properties generated from coupon tests. A large-scale industry modeling method was used to study different spot weld failure modes. The next phase of work includes dynamic welded component testing, which is a critical validation step for predicted spot weld energy absorption and strength. Two different dynamic tests are planned for component level validation using CAIMAN Mode 1 and Mode 3 testing.

Third-generation ultra-high strength steels (3G-AHSS) have shown great potential for use in automotive body structures to improve vehicle safety during crash scenarios while simultaneously offering significant light-weighting opportunities. Characterization of material mechanical performance and resistance spot weld joining methods have been completed and must be modeled in CAE simulation software to assist with implementing these materials into automotive structures. Continuous improvement of the weld fracture models used in simulation lead to better prediction of vehicle impacts and helps optimize vehicle design when implementing 3G-AHSS materials. In this work, an optimized single spot-welding schedule was used to weld KS-II single spot weld test samples. The spot welding was optimized to generate a nugget size that matches the electrode face diameter and a nugget size that matches the minimum weld size specified per the AWS D8.9 standard. A unique method of data analysis is employed to improve the simulation boundary conditions and achieve better calibration. The same welding schedule was then used to join structural components with multiple spot weld used in the Caiman Mode I and Caiman Mode III experiments. The Caiman components were tested via quasi-static and dynamic loading conditions. Various common weld material models were calibrated over a range of loading conditions by using the KS-II single spot weld test. The calibrated single spot weld models are then implemented into the component level multi-spot weld CAE model. The simulation accuracy of these weld material models is validated against the experimental data, with a particular focus on the post-weld failure unloading response as weld failure propagates throughout the test component. The results of these weld material model simulation validations highlight that although the peak force of the experiments can be well captured, accurately prediction of the total absorbed energy is an on-going challenge and may indicate a limitation of the current modelling practices. Other material models for joining with finer control over failure behavior are examined as possible alternatives.

This paper discusses a high efficiency 2-cell cross-section roll formed profile in 22MnB5 steel that is subsequently hot formed using the well known Accra® process to result in a front bumper beam with low mass and high performance. Manufacturing and material challenges for the complex blank are discussed. Section optimizations are also reviewed, including corner radii that are tighter than commonly achieved with ultra high-strength steel (UHSS) to achieve higher performance than current state of the art. Hot forming the section to include aggressive and variable section sweeps not normally achievable in UHSS provides for a drop-in replacement of a current production extruded and stretch bent Aluminum bumper. The final assembly is shown to meet similar performance requirements with a very small mass penalty (primarily driven by the drop-in requirement) and a significant cost savings for an upcoming North American OEM SUV mid-cycle enhancement.