Past GDIS™ Presentations

With the ever increasing application of 3rd Gen advanced high-strength steels (AHSS) in the automotive industry, springback control is becoming a very important issue that affects the dimensional accuracy of the stamped panels. A lab-scale die with combination beads (stake beads combined with draw beads) has been manufactured, funded by Auto/Steel Partnership (A/SP), to investigate stamping springback control and reduction. This is done by engineering a combination of draw beads on the binder during draw process together with stake beads on the punch during post-stretching. The finished panel is a U-channel. The investigation is conducted using a next generation AHSS with various bead combinations and depth. Correlations with FEA modeling are conducted using AutoForm which incorporates material models of yield surface and work hardening derived from internal tests. AutoForm Sigma is used to optimize the die actions and bead conditions. It is also used to assist identifying the dominant setup parameters and key material properties in controlling springback.

Laser welded blanks (LWB) have been successfully applied in automotive applications for over 30 years to save weight, reduce cost, consolidate parts, manage crash energy and improve material utilization. Over the last decade, advanced high-strength steels (AHSS) have become commonplace in LWB applications. Dual phase (DP), TRIP, and Multi Phase AHSS steels with tensile strengths up to 1180 MPa are used today in production applications. A 3rd Gen of AHSS will soon be added for their excellent balance of strength and global formability. However, the traditional methods that were originally developed to predict formability of a LWB with conventional steels may not be sufficient to accurately predict formability of a LWB with AHSS. Depending upon the steel chemistry, steel making process and the welding process, AHSS welds may exhibit softening in the heat affected zone or a reduction in ductility. Thus, a new approach to consider these properties in the finite element (FE) model may be needed. In this study, 3rd Gen LWBs were evaluated. To investigate the unique formability characteristics of the LWB, several standard mechanical tests, such as micro-hardness testing and various tension tests under uniaxial, plane-strain, and equi-biaxial conditions were conducted utilizing a digital image correlation (DIC) system. Under equi-biaxial conditions, the 3rd Gen LWB primarily fractures perpendicular across the weld seam, rather than in the parent metal, showcasing a robust welding process. The DIC system was successfully used to characterize the local ductility limit of the weld material. This information can be implemented in FE simulations of the LWB material to predict formability in the weld area. Also, FE simulations with different element types (shell, solid and hybrid) concluded that the weld section and properties should be considered for accurate fracture prediction. These preliminary results will lead to the development of a practice that can be beneficial for the automotive and steel industry to use in characterizing the formability limit of the LWB materials, simulating of stamping of the LWB materials and optimizing the laser weld parameters to improve local

Diode lasers are used in automotive body-in-white (BIW) assembly for more than 20 years. Today, the state of the art method for joining galvanized steel sheets in automotive BIW production is brazing with diode lasers. Due to the introduction of hot-dip galvanized materials through various OEM’ s the well-established brazing process with a single spot started to provide insufficient results. In order to maintain its customer base Laserline had to develop a new solution that would satisfy the quality requirements of the manufacturer. A specific optical module was introduced to target this challenge.

Multi-spot modules make tailor-made spot geometries possible and improve critical joining processes. Since 2016, these modules have been used in series production and have continuously been further developed. Triple-spot modules for brazing hot-galvanized sheets have been used in automobile production worldwide for more than two years now. This was followed by the use of a spot-in-spot module for the optimization of critical welding processes. Automated modules were introduced, and currently a new model has been added: a spot-in-spot module for asymmetric seams that was specifically developed for fillet welds and tailored welded blanks.

This presentation will explore the technology of multi spot modules, their different beam shaping and adjustment capabilities and how it reflects in brazing and welding applications of steel.

To evaluate various weld repair processes and to provide joint test data for use by OEM’s to update approved body repair strategies for coated and uncoated 3rd Gen advanced high-strength steels (AHSS).

This presentation reviews how digital image correlation (DIC) technology has set the metal forming industry up for a game changing revolution in the amount and nature of information that can be gleaned from material testing. The presentation will focus on the benefits of using DIC for the measurement and analysis of the common uniaxial tension test under monotonic loading conditions, providing literally orders of magnitude more information, including new information that not available without DIC.

The expanded and new types of information that DIC enables includes 1) measurement of the stress strain relation and evolution of R Value to strains far beyond maximum load, 2) detection of the onset of localized necking, 3) measurement of the degree of material homogeneity of all of its properties, 4) measurement of the degradation of the elastic modulus with strain, 5) ability to decouple strain and strain-rate effects on the stress-strain behavior, from a single monotonically loaded specimen, without employing jump tests, and 6) the determination of a realistic lower bound for the fracture limit strain and its dependence on strain path.

The unprecedented amount and new information that DIC enables is there for the taking from each and every specimen loaded in uniaxial tension under monotonic loading conditions. Examples of these benefits will be demonstrated for uniaxial tension tests on DP 980 and a DP 1180 steels that were selected for use in the Numisheet 2021 Benchmark Study.

This study introduces a new testing method to evaluate edge formability by emulating production conditions. Production representative conditions include varied shear clearances, a stamping part design other than a simple round hole or straight edge, varied edge shearing speeds with the mechanical press, and applicable forming strain rates during the test procedure. Edge formability of dual-phase (DP) 780 steel from six different steel suppliers was evaluated using the newly developed stamping test using a 300-ton servo press as well as the ISO standard hole expansion testing and the half-specimen dome testing. The edge formability of advanced high-strength steel (AHSS) is significantly influenced by the plastic strain accumulated during the shearing operation. The work-hardening on the sheared edge was quantified with hardness measurements and advanced measurement tools. The concept of Shearing Induced Damage (SID) is introduced to compare the different levels of work hardening and damage on the sheared edges of six different DP780 materials resulting from shearing and punching operations. The SID trends of six DP780 materials show good correlations in both lab-scale testing and stamping results. One of the DP780 steels displayed consistently better performance, while several other DP780 steels showed poor performance in both lab-scale testing methods and stamping testing. Most DP780 steels showed similar formability performance with the machined edge condition for all three different testing methods. Upon shearing, however, the local formability of three of the DP780 steel is significantly reduced, and this results in an earlier onset of edge cracking compared to the best performing DP780 steel in this study. The newly developed testing method is very effective to correlate the lab-scaled standard test data with the edge cracking of the industrial-scale stamping.

OEMs worldwide have announced plans to roll out Battery Electric Vehicles (BEV) in this decade. Depending on regions and market penetration, various OEMs have announced dedicated BEV platforms or updated Internal Combustion Engine (ICE) powertrains to accommodate BEV powertrains. In addition, many OEMs have also announced plans for mild hybrids which would have both ICE and BEV powertrains.

Worldwide standards on battery and occupant protection are not uniform and no clear guidelines are available on how to best integrate the two requirements in future body platforms. Furthermore, many OEMs have scaled back investments on new platform and body assembly updates to funnel their investments to new BEV powertrain developments.

Arcelor Mittal Tailored Blanks (AMTB) Product Development group has developed a novel concept of integrated battery and occupant protection Body-in-White (BIW) concept that showcases way forward for many OEMs. This concept integrates BEV powertrains to ICE body architectures with minimal modifications. Our concepts have intensive use of Press Hardened Steel with Laser Welded or Tailored Blanks in key structural parts to develop an optimized BIW that is lightweight and protects the battery pack while maximizing battery module volume. This is accomplished by a novel central concept of floor ring assembly, optimized front, rear and side crash load paths, and strategic use of press hardened steel and tailored blanks to optimize the weight, cost and performance of the structure.

Concepts from overall dimensions and crash load paths were benchmarked against some recent ICEs and their EV variants that went into serial production in the last two years. Validation of the concept was done using advanced full body crash and stiffness analysis for all major scenarios that would satisfy the most stringent requirements in every region. In addition, the battery box was fully validated for standalone load cases in key regions. In addition, additional load cases were also proposed and evaluated specially to consider new crash modes for battery protection. Forming analysis and weight-cost optimization was also done to ensure manufacturing feasibility of all modified structural parts. Lastly assembly sequence and minimum impact to body assembly sequence was also ensured while ensuring serviceability concepts for battery and body.

Considering above, we see a strong case for steel to remain a material of choice for cost, weight and performance requirements. Tailored Blanks further enhances the position of steel especially with press hardened steel applications. While many OEMs have integrated battery boxes made in alternate materials, steel continues to be a material that could be the way forward, especially if the occupant and battery crash protection are integrated as this concept study demonstrates to maximize value, performance and weight in vehicle architecture.

Currently Mubea uses micro-alloyed advanced high-strength steel (AHSS) to produce shape blanks and formed parts with variable gauges. Two new ideas will be presented to enhance the application of TRB®: 1st, Tailored Properties TRB® and 2nd, Work-Hardened TRB®.

For tailored properties the final TRB® blank will not only have different thicknesses along the part, the highest thickness plateau will also have higher mechanical properties. With this, Mubea can offer higher strength level than previously available, and a new degree of freedom will be achieved by having an additional parameter to vary with two different strength levels.

For the work-hardened solution the general idea is to skip the annealing step after flexible rolling. This opens multiple applications / routes, for parts with simple, limited drawn geometry; at first, this material option, thanks to the saving on the annealing operation, and to the adoption of a lower raw material grade to start from, constitutes a low-cost alternative when compared to regular TRB grades for cold forming. Second aspect, by using higher strength raw material, it’s possible to offer strength levels beyond the current highest material grade (HSLA CR500 grade current limit for TRB®).

AISI has recently completed a comprehensive study to highlight the advantages of steel bumper systems. This proposed presentation will compare the performance and technical cost of (2) efficient steel intensive solutions to a current contemporary aluminum design. In addition, a brief review of benchmarking data will be provided.

Ultra-high strength press hardened steels have quickly become important materials to consider in the vehicle light weighting process due to their superior strength and material down-gauge potential. In this research, the introduction of a hot stamped Usibor® 1500-AS to Ductibor® 1000-AS tailor welded part is considered in a demonstration structure, representative of a sport utility vehicle front end frame module.

The tailor welded hot stamped part is intended to replace the current 590 MPa tensile strength galvanneal coated sheet steel side frame main rails within the vehicle’s front end frame module. In a frontal crash situation the forward portion of the side frame member absorbs crash energy by crumpling along its length, reducing the deceleration felt by the occupant. The aft portion of the side frame member remains sturdy during the crash, protecting the occupant from intrusion of structural members. The proposed side frame main rails are hot stamped from a tailor welded blank (TWB), consisting of a Ductibor® 1000-AS crush tip (crash energy absorption) and a Usibor® 1500-AS high strength rear region (occupant compartment intrusion resistance).

The results of a numerical parametric study will be presented considering the side frame main rail to establish the mass reduction that can be achieved by replacing the 590 MPa strength baseline material with ultra-high strength hot stamped steels. Results from preliminary crash testing of the Ductibor® 1000-AS crush tip will also be presented.

The predominate material used in press hardening processes is AlSi-coated 22MnB5 material in the automotive industry to produce body structure components with tensile strength of approximately 1.5 GPa. The applications of the uncoated 22MnB5 material are very limited due to its surface oxidations during the hot stamping process.

Increasing the tensile strength and bendability of the press-hardened steel (PHS) material will enable lightweighting while maintaining crash protection. Considering the demand of new PHS for better oxidation resistance and further mass reduction, a new uncoated PHS, 20MnCr, is introduced in this paper. 20MnCr materials has slightly reduced carbon level, with chromium and silicon additions for oxidation resistance when compared to the conventional 22MnB5 material. This novel PHS material has an ultimate tensile strength of 1.7 GPa with bending angle above 55° at 1.4mm thickness. This steel is not pre-coated but possesses excellent oxidation resistance property at high temperature, thus eliminating the need for AlSi coating or shot blasting post processing of uncoated 22MnB5 to maintain surface quality.

Microstructural mechanisms used to enhance bendability and energy absorption are discussed for the novel steel. Performance evaluations such as: weldability, component level crush and intrusion testing and corrosion, are conducted on samples from industrial coils and its performances are compared with AlSi coated22MnB5 material.

Increasing automotive requirements for improved corrosion life on frames and chassis components have created a challenge for OEMs and suppliers to improve corrosion resistance of painted welds. This corrosion resistance is linked to the formation of surface silicates or “silicate islands” on the weld surface. These islands consist of multi-component oxides formed during the welding process via chemical reactions between the shielding gas and various deoxidizing elements in the base metal and welding consumable. The impact of these silicate islands on corrosion life stems from their non-conductive nature that interferes with the electrostatic painting process commonly utilized by the automotive industry.

In response to this issue, Lincoln Electric has developed a new solid wire and welding waveform that combine to provide a complete solution for lower surface silicate formation. This new wire, SuperArc® XLS, utilizes a unique mixture of deoxidizing and surface tension modifying elements to minimize surface silicate formation. The new waveform was developed specifically for the unique chemistry of SuperArc® XLS to improve droplet transfer and deliver a high speed, low spatter, low silicate weld for high volume production.

The purpose of this study was to compare paint adhesion and corrosion resistance of welds made with SuperArc® XLS versus welds made with an industry standard GMAW wire. All lap welds were completed with the same weld settings and environmental conditions, after which they were processed using a matrix of three different pre-treatments and two different final coating methods. The 12 distinct combinations of wire/pre-treatment/coating were then subjected to 120 cycles of a cyclical corrosion testing protocol. Results from this testing showcase the improvement in corrosion resistance between SuperArc® XLS and an industry standard GMAW wire.

Laser heat treating (LHT) on automotive stamping and trim dies has resulted in overall cost reductions, shorter processing times, improved quality. These improved results have resulted in multiple advantages for OEMs that use LHT when compared with OEMs treating identical dies with conventional methods. This paper highlights the technical aspects of LHT, cost saving and latest advancements associated with this process.

speed and distance, as well as tool and sheet material, surface finish and coating. The wear over the die radius primarily consisted of a combination of ploughing and galling mechanisms. The ploughing mechanism was found to occur over the entire blank contact region, with two distinct zones observed within the overall contact region. Tool die galling-induced failure occurs more likely at the severe contact pressure/small sliding distance conditions, which take place during the initial portion of the stamping process, showing to be critically important to the overall tool wear response. Therefore, degrees of ploughing- and galling-induced failures seem relevant to the die contacting radius (i.e., die/sheet contacting angles) during the stamping operating transient stage. This work is to develop a table-top inclined sliding tribometer which can change contact angles of die material/metal sheet from 0 to 20 degrees, contact pressure from 0 to 2 GPa and the sliding stroke distance from 0 to 100 mm. The instrument can have an index stage movement so that the sliding wear track is generated on a fresh metal sheet surface in each sliding stroke. A data acquisition system can record contact load, friction force and sliding distance, from which coefficient of friction (COF) and sliding energy can be calculated. Severe wear and galling occur when the COF is significantly increased. The wear behavior of die materials and metal sheets can be observed afterward. Those information is important for better understanding wear behavior at different contact angles and quite valuable for simulation of metal forming.

This presentation will summarize work of the Auto/Steel Partnership (A/SP) project, repairability of advanced high strength steels (AHSS). This project is focused on the evaluation of various weld repair processes and to provide joint test data for use by OEMs. The materials tested were MS1500, MS1700 and press-hardened steel (PHS). The team evaluated the following joining processes; resistance spot welding (RSW), metal inert gas (MIG) welding, MIG brazing and mechanical fastening. Production and service adhesives were also considered. The team utilized coupon test assemblies fabricated from various grades of AHSS. A variety of repair process joints were destructively tested. The test parameters included shear tension and cross tension quasi-static, shear tension fatigue, and cross-sections.

The resulting data can be used by OEMs to update repair process strategies using these advanced high-strength steels.

In conventional high strength steels niobium’s role is very evident: it provides grain refinement and precipitation hardening, both being the main mechanisms for strengthening such low-carbon HSLA steels. Advanced high strength steels, on the contrary, utilize a hard second phase being dispersed in a softer matrix for achieving an attractive combination of high strength and good ductility. Microstructural design on that basis has resulted in dual phase steels, complex phase steels and various forms of TRIP aided steels including 3rd generation steels. Despite that niobium initially has not been regularly alloyed to advanced high strength steels, it is nowadays widely used for optimizing their properties. Essentially, niobium is also refining the microstructure of advanced high strength steels resulting in a better homogeneity of phases, which improves bendability as well as the hole expansion ratio. Besides, niobium boosts the strength especially of the ferritic and bainitic phase by precipitation hardening. In ultra-high strength AHSS, the niobium carbide precipitates can also act as hydrogen traps and thus counteract delayed cracking. The presentation will give an overview of the so-far identified metallurgical effects of niobium in AHSS and will demonstrate the beneficial implications for processing in the mill and properties at the end user.

The Insurance Institute for Highway Safety (IIHS) has been conducting side impact crash tests since 2003. To understand how the side crashworthiness program can be enhanced, an ongoing research effort is focused on understanding the correlation between IIHS ratings and the driver death rate. In addition, the performance of good-rated late-model vehicles has been assessed in higher severity side crash tests. The objective of this study is to summarize the ongoing work and potential next steps toward developing a new crash test procedure or updating ratings criteria to further advance side crashworthiness. Analysis of real-world crashes indicates that tightening the rating criteria can potentially advance vehicle designs. Additionally, adopting a higher severity crash test may address additional real-world injury-causing crashes. Modifications to the IIHS MDB are needed for the 60 km/h test to be more representative of deformation and injury patterns caused by light truck vehicles (LTVs). This presentation will cover concluded research.

Vehicle lightweighting efforts to improve fuel economy require adequate material characterization and simulation tools to improve efficiency without compromising safety. With crash-induced deformation leading to complex stress states on the structural components, we focus the present investigation in the differences in fracture behavior of thin sheets under plane strain states of tension and bending. A numerical analysis is presented to compare the stress-strain response of VDA bending and in-plane notched tensile tests within the localized zone of deformation. The analysis suggests the significant stress state differences in bending and tension are mainly driven by the effects through the sheet’s thickness. These results offer an insight in the fundamental mechanisms contributing to the differences in fracture strain in bending and tension tests. As only one input value is possible for each triaxility level, the consequences of an apparent increase in ductility in bending (with respect to the in-plane tension) in the material characterization are discussed. The effects on the ability to reliably predict fracture in automotive crash and other large structures, commonly modelled using shell elements, are also mentioned.

Keywords: Ductile fracture modeling, material model, crash, shell mechanics, plane strain