Past GDIS™ Presentations

Vehicle mass reduction is a major enabler for supporting MY2025 CAFÉ and reducing CO2 emissions, without sacrificing passenger safety, comfort and vehicle performance. Sheet steel has historically dominated auto body structure manufacturing. However, as the need for more aggressive vehicle lightweighting increases, alternative materials become somewhat more appealing, albeit at a much higher price. In response to the potential inroads by alternative materials, the steel industry has responded by developing classes of advanced high-strength steels (AHSS) which can be thinner and thus lighter than conventional sheet steels while meeting important performance attributes. One potential application for AHSS is for exposed panels such as door outers, fenders and hoods where it might be feasible to use higher-strength steel products in combination with low density reinforcements to meet stiffness, dent resistance and oil canning requirements. Diversitak, along with ArcelorMittal have performed extensive testing that indicates thin layers of strategically placed spray-coated CFRE could improve panel performance with increased dent resistance, reduced oil canning, and increased stiffness, while reducing mass of the panel.

The concept was proven in stages of evaluation including lab samples and panel testing with localized and complete panel coverage. CFRE was applied to stamped sheets of steel with residual stamping oils from the mill, in a time corresponding to automotive processing (~15 secs), following which the samples were processed following automotive e-coat procedures (phosphating + 175-200 C heating), to complete the curing. The data in all cases indicate significant improvement in oil canning and dent resistance. The results of these trials are discussed in this paper.

HITACHI will review current tooling behaviors and common failure modes found when trimming and forming advanced high strength steel (AHSS) components. We will present the current field results that have increased tooling performance for stamping, blanking, forming, punching and piercing AHSS of 890 Mpa and higher. Results will be both Japan based and North American content.
HITACHI will also present advanced die steels as applied to hot stamping tooling when forming A/B Pillar automotive components of 1200 Mpa and higher. Our data will include actual tooling results of conventionally used tool steels compared to newly developed and market available die steels of higher alloy content.
HITACHI will also demonstrate “best practices” for understanding tools steel difference, importance of heat-treatment, post surface coating requirements & general preventive maintenance suggestions.

Increased power density in mechanical power transmission components means greater durability – allowing existing designs to achieve greater capacity, or reduced size and mass for lightweighting. TimkenSteel’s Ultra premium™ certified air-melt technology and Endurance family of ultra-high-strength, high-toughness steels provide affordable solutions for critical, power-dense components. Ultra premium steels combine advanced electric arc melting, vacuum ladle refining and teaming practices with advanced automated scanning electron microscope (SEM)-based steel cleanness evaluation. The result is affordable, certified ultra-clean steels on par with re-melted steel with cleanness metrics that are relevant to component design life. In addition, three new steels in our Endurance family provide yield strengths ranging from 175-210 KSI, ultimate tensile strengths ranging from 230-250 KSI, and Charpy impact energies ranging from 35 to 50 ft.-lbs., allowing these grades to provide longer life, more power and/or lighter weight.

Our measurement techniques compare automated SEM-assessed cleanness data between Ultra premium and vacuum arc re-melted steels to illustrate equivalence, and we illustrate how Ultra premium certification data can be used to assess and estimate fatigue risks using the TimkenSteel virtual component fatigue model. For Endurance grades, we compare their strength, fatigue and toughness properties to a range of common case-carburized gear steel properties. This analysis illustrates the potential to gain 45 percent more horsepower for an existing gear set, or to achieve the same horsepower with a 30 percent lighter gear set.

The Insurance Institute for Highway Safety (IIHS) toughened the safety regulations for small-overlap barrier (SORB) test on the front end crash protection. Vehicles are expected to meet the both passenger and driver side to achieve the top crash ratings. The challenge are to achieve the two-side SORB performance with minimal design change approach with an objective of meeting SORB on both sides and slow speed collisions without any mass addition. Baseline vehicle not designed for the two side SORB performance are considered as the start-up model. The current study focused on using the bumper design space for the optimization achieving the SORB performance on both passenger and driver side. Optimized bumper section was achieved using Meshworks shape morphing and parameterization. The results of the optimization identified the optimized bumper shape which had increased stiffness and minimal mass. Design concept of blockers in the barrier load paths significantly improved the pillar and dash intrusions. Mass savings of 10% were achieved in the given design space in parallel meeting the two side SORB targets and low speed collisions. The investigation concludes that the bumper design space can be used to achieve the SORB performance both on driver and passenger side without any major changes to the front motor compartment.

The automotive industry is adopting increasingly higher strength materials to reduce vehicle weight, while maintaining or improving vehicle crash safety. Often, increases in strength come at the expense of reduced failure strain which mandates greater accuracy in CAE predictions of fracture to support vehicle design. One aspect of material behavior under dynamic (crash) loading that requires further attention is the effect of high rate loading on failure strain. It is common practice in current simulations of vehicle crash to account for the effect of strain rate on constitutive behavior (here, taken as strength as a function of strain and strain rate); however, the effect of strain rate on failure strain is not commonly considered. Indeed, most CAE failure predictions are based on quasi-static characterization methods.

This presentation examines the effect of dynamic loading on the failure loci of a range of ultra-high strength steels (UHSS), including a number of advanced DP980 grades and hot stamped Usibor® 1500-AS as well as Ductibor® 500-AS, a hot stamped advanced high strength steel (AHSS). A range of material strength conditions are introduced by tailoring the Usibor® 1500-AS using in-die heating (IDH) to control the resulting material strength and ductility. High speed tensile experiments using a high-speed hydraulic apparatus and a tensile split Hopkinson bar are used to perform elevated strain rate experiments (strain rates in excess of 1,000 s-1). High strain rate shear, hole tensile and notched tensile experiments are performed to vary stress triaxiality. In situ digital image correlation (DIC) techniques are applied with high speed optical imaging to measure failure strain while high speed thermal measurements are used to characterize temperature rise during elevated rate testing. Measured failure strains are extracted as a function of stress triaxiality for each material condition at quasi-static and dynamic rates.

In the current experiments, elevated strain rate tends to increase failure strain under tensile-dominated triaxiality conditions, whereas significant temperature rise and adiabatic shear localization occur under high strain rate shear loading, leading to earlier onset of failure. The effect of increased material strength on adiabatic temperature rise and the resulting high strain rate failure is examined. Implications for crash CAE are discussed.

Keywords: Dynamic failure, crashworthiness, UHSS

Hard chroming and nitriding are two different commonly-used stamping die surface treatment methods used to reduce die wear during stamping operations. The Auto/Steel Partnership’s Stamping Tooling Optimization (STO) team has completed a study a combined treatment called duplex chroming, a hard chrome layer applied on top of a nitrided surface layer, with expectation of improved die performance. Hard chrome and duplex-chrome coupons were prepared from S0050A substrates (die material). An impact-sliding wear fatigue tester was used to assess the wear of the coupons where a pulsed impact load from 30 N to 160 N was applied to the coupons inclined at an angle to the indenter. This simulates a severe load/wear scenario between sheet metal and inclined die surfaces where a shear force component is added. Coupon wear was characterized through optical and electron microscopy in terms of the degree of wear and, when applicable, cause of premature wear; whether wear was the result of the base material, nitrided layer, nitride layer/hard chrome interface, or hard chrome layer. The test results showed that the duplex-chrome coupons with the nitriding white layer removed performed the best. Hard chrome coupons showed premature wear, where the intender deformed the substrate die material leading to local spalling of the hard-chrome layer. Duplex-chrome surface treatment without the nitriding white layer removed before the hard-chroming provided no benefit due to the brittleness of the white layer weakening the adhesion of the hard-chrome coating. Therefore, both a strong load-bearing substrate and high coating adhesion strength are critical to the duplex-chrome surface treatment anti-wear performance at the high contact stresses.

Tailored tempering is used to produce functional optimized hot formed parts for the automotive industry with regions of increased ductility and higher energy absorption in the event of a crash. There are different methods to accomplish tailored properties, each of them with advantages and disadvantages but there is no concept on the market that meets all requirements. A brief comparison of existing production processes for tailored tempering with advantages and disadvantages will be given.

EBNER as a specialist for heating, cooling, atmosphere control and process development has developed a new technology that is designed to meet all requirements. The new system is integrated directly into the furnace and can run at 900°C in air (for coated blanks) or protective atmospheres (for uncoated blanks). The growing trend towards more complex soft geometries is making new demands on the tailored tempering system. EBNER’s new system allows any shape to be cooled and transformed into a soft zone with uniquely variable mechanical properties and maximum flexibility. Modern additive manufacturing technologies like laser melting are used for the production of this new cooling system.

While customer requirements for the shapes of the soft zones are increasing in complexity, the transition zones between soft and hard zones also need to be adjustable. Test results will be presented showing our ability to obtain very small transition zones and uniform mechanical properties as well as a good surface quality of the Alsip coating.

Since the tailored tempering process is done inside the furnace with this system, a centering device for the blanks is needed. We will also present a unit which allows 4 part batches to be processed.

The Original Equipment Manufacturers (OEM) of the car industries has a standing requirement of more crash efficient products which drives to improve the Crash Management System (CMS) design by utilizing the advantages of new steel qualities.

The subject in the investigation is to find design parameters, obtain material data and understand deformation behavior of latest steel qualities with characteristics increased strength through controlled hot forming. By using Press Hardening 2000MPa (PH2000) and Multilayer Press Hardening (MLPH) material in parts exposed to crash a reduction of weight without loss of performance is possible.

PH2000 and MLPH material qualities are new on the market with special characteristics requiring improved design and background work to prove and promoted the ideas to the OEM´s.

An on the market state of the art CMS was selected as reference. All requirements and overall geometrical limitations applied in this work is governed by this system. Materiel samples was ordered, tensile tests has been performed and material models has been developed.

The main parts exposed for crash energy in a CMS, the crossbar and crash box, has been optimization toward crash using PH2000 and MLPH material qualities. Prototypes has been built and tested through crash.

The use of PH2000 and MLPH material in parts exposed to crash brings lower weight and increased strength compared to today’s state of the art solution.

Press-hardening steels (PHS) have been used in increased amounts in the body-in-white (BIW) structure of vehicles, due to the extreme high-strength (>1500 MPa), thus achieving specific strength (yield strength / density) and with enormous potential to weight savings. However, two main issues have been observed in the applications of PHS, limiting the number of parts designed with this grade: low bindability, related to low toughness, and low resistance to hydrogen embrittlement. The present work shows a systematic comparison of traditional PHS and niobium modified PHS, with regards to both aspects. In relation to bendability, the VDA test was applied to semi industrial specimens, produced with different amounts of Nb and pressed after different times and temperatures. It is shown that standard 1500MPa PHS is very sensitive to those process conditions (different time and temperature combinations), leading to lower bending angle when temperatures or times are exceeded. The robustness of the process, on the other hand, increases when niobium is applied, which is related to a better control of the grain structure, during the step prior to press hardening (prior-austenite grain size). In a separate research, a detail evaluation was performance on the likelihood of hydrogen embrittlement in 1500 through 2000 MPa PHS. It is shown that the presence of fine niobium carbonitrides act as relevant trapping sites for hydrogen, leading to the time to embrittlement is reduced by a factor of 5. The reason for that change is dictated by the physical presence of those nanoparticles in the microstructure but also due to the electronic distribution in of niobium atoms in the carbonitride, attracting hydrogen and decreasing its diffusion. As conclusion, the present paper suggests strategies to improve the main limitation in the application of press hardening steels, leading to important alternatives to the auto industry when using this material.