Past GDIS Presentations
Past GDIS Presentations
To meet regional fuel efficiency and emission standards, vehicle mass reduction has become a major driver for OEMs. Additionally the worldwide shift towards electrification combined with other safety and technology demands will drive automotive manufacturers to aggressively pursue lighter weight vehicles. Increased use of structural adhesives is expected to provide the strength required and the corrosion barrier between traditional and nontraditional materials. In designs where the stiffness of materials or components may be a concern, utilization of structural adhesives can improve noise, vibration and harshness (NVH) and crash performance through a more complete joining surface. New BETAMATE™ Light Weight Reinforcement (LWR) technologies are customizable, highly toughened and range from zero to varying levels of expansion. These new systems are true structural reinforcement solutions available in a range of modulus. BETAMATE™ LWR replaces structural tapes addressing labor and application inconsistencies and enables better gap bridging reliability. They can be used to augment the joining of substrates as well as in areas of the vehicle where weld access may be limited and where design gaps vary. The technology has been successfully implemented in applications to reinforce roof skins and panoramic roofs, and body structural reinforcement to improve crashworthiness. Details on the available adhesive bonding solutions, analysis and characterization will be discussed.
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.
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.
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.
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.
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
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.
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.
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.
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.
Joy Geeraerts and Jeff Sulik from General Motors discussed advanced high-strength steel (AHSS) technologies within the 2019 Chevy Silverado.
Spring-back issues are critical in stamping procedures for advanced high strength steel. The spring-back can be comprehensively controlled by applying a newly designed hybrid bead to effectuate a post-stretching process in a U-channel part forming. Finite element forming simulation is applied in a cross-section to evaluate and optimize the hybrid bead performance, using DP980. A specific post-stretching die with the optimized hybrid bead was manufactured and applied to demonstrate the performances. Excellent spring-back control and material restricting effect were observed in the stamping results. Significant tonnage reduction was achieved. Great correlation was obtained between test and simulation results. An analytical solution was also applied to predict the same process with good correlation.
KEYWORDS: Advanced High Strength Steel, Post-stretching, Hybrid Bead, Bead Optimization, Finite Element Simulation, Analytical Solution
Next generation of advanced high-strength steel (AHSS) with higher strength and ductility in base metal are extensively considered for usage in Body-in-White (BIW) structures with lower thickness to reduce the vehicle weight, and increase fuel efficiency and occupant safety. There have been various technologies under development for mixed materials joining as an alternative joining technology to resistance spot welding (RSW) for BIW assembly. However, limited research has been explored for alternative joining methodology of steel to steel with AHSS. On the other hand, a sustainable eco-friendly manufacturing process capable of joining complex sheet metal assemblies requires more initiatives for development of new joining solutions. Traditional clinching is an accepted method of mechanical cold forming joining process which has been used in BIW for light weight metals and steels with low strength. However, this process is unable to join AHSS with ultimate tensile strength above 980MPa. In the present study, a modified clinching process has been developed with in-situ integration of thermal treatment using class 1 laser technology to soften locally to make feasible the clinching of AHSS. This process has been studied for optimization of temperature control and clinching geometry of Usibor® 1500 and Usibor® 2000 to increase cross-tension and tension-shear strength. The new thermal integrated clinch joining process increases joint strength significantly, this can even reach or exceed the cross-tension strength produced by conventional resistance spot-welding process.
As AK Steel’s NEXMET™ advanced high-strength steel (AHSS) products move from development to commercialization, significant progress is being made to move beyond lightweighting “concepts” to fully functional production intent prototypes that provide not only a “proof” of concept for mass savings, but also provide validation for the FEA models used to predict forming, springback and structural performance. As more of these concepts are proven, a knowledge base is generated to provide OEMs with answers to many nagging questions involving the manufacturing of parts with 3rd Generation AHSS. This knowledge base will allow OEM’s gain the confidence they need to make critical material decisions earlier in the design phase and thus, facilitate further use of AHSS. Several examples will be discussed that demonstrate not only the mass savings of these components but will also provide details of manufacturing.
Lightweighting is critical for reducing fuel consumption levels in future vehicles, and automotive OEMs are striving to use the latest generations of materials with high-strength/density ratios, particularly advanced high-strength steels (AHSS) with complex microstructures. It is well established that the deformation of steels is largely rate dependent; nevertheless, stamping and crash simulations are often performed using data obtained at quasi‐static rates(<~0.1s‐1), which fall below the deformation rates associated with stamping- operations(~0.1 ‐ 10s‐1), and far below the rates experienced during a crash event (~50 ‐ 500s‐1). This is primarily driven by the difficulty in getting experimental data at multi‐ and, rate dependence in many cases is considered insignificant to be accounted for, especially within a narrow window of forming simulations. While this might be acceptable for some steels, it is far from true for the majority of steel grades, particularly the latest generations of AHSS. In this work, detailed experiments are performed over multiple strain rates to fully characterize the flow behavior and fracture behaviors of different steels with various microstructures. The experimental results are used to extract quantitative comparisons between the different rates (in regards to hardening parameters, strength, ductility and fracture strains), and associating those with the different steel types and their micro structures. The differences in rate‐dependence among the investigated steels, and the relationships to the phases present in their microstructures, are discussed.
The need to produce lightweight vehicles has driven the automotive industry to use new advanced steel materials for the vehicle body structure, making the forming processes more challenging for manufacturing engineers. Capturing the behavior of metallic parts during crash events has become very important in determining the structural crashworthiness of vehicles. As the auto industry relies increasingly more on computer simulation for evaluation of crash performance, accurate prediction of material behavior in crash simulation has become a necessity.
The thinning and plastic deformation that occurs during the forming process can influence the energy absorption of a part. There are already established techniques to initialize numerical models for crash analysis using strain and thinning values obtained from forming simulation. Depending upon the amount of plastic strain and the state of stress, damage can also develop during the forming process. This damage may affect the location of failure and the load levels at which failure occurs during a crash event. This project extends the existing methods of initializing crashworthiness models to include damage. The project outlines two approaches of initialization and evaluates the reliability of each of these methods. The first method involves computing the damage directly during the stamping simulation by incorporating a damage law in the material model. This is the most reliable method but requires a change in the standard process of performing forming simulation. The second approach approximates damage using the thinning and plastic deformation computed from a standard incremental forming simulation. The laboratory-scale T-shape panels were formed at different forming depths to achieve different forming statuses, such as with and without necking on the up-front radius. The ex-situ digital image correlation was employed to map the true major and minor strain distribution for the formed T-shape panels, which was considered as a baseline to compare with the forming simulation results. Static crash tests were performed on the T-shape panels with and without necking to determine the crash performance experimentally. In addition, a real production part was also examined analytically to assess effect of forming damage on the crash performance of the part. This project documents direct comparison of the simulation and test results. The work highlights the need for accurate forming simulations at levels of plastic deformation beyond the necking point.
KEYWORDS: Advanced High Strength Steel, Crash, Forming, Damage, Safety
Current methodologies for the experimental and numerical fracture characterization of sheet materials for vehicle crash applications are built upon the identification of a failure locus in proportional loading conditions. These stress-state dependent fracture models require a comprehensive set of experimental tests such as uniaxial tensile and notched-tensile specimens that are analyzed using a fine mesh of solid elements due to the onset of localization where the stress state becomes triaxial and the strain path non-linear. Although commonly used, these test coupons and the inverse-approach to numerical characterization is time-consuming and expensive for automotive applications such as crash events of structural components. A lengthy and convoluted mesh regularization process is required to adapt the three-dimensional failure locus first to plane stress using shell elements and then to larger mesh sizes. Although good predictions can be obtained in the crash simulations, the final failure locus is effectively an exercise in numerical calibration where the numerical fracture strains may have little resemblance to the experimental fracture strains. With the rise of third generation advanced high strength steels (AHSS), an efficient methodology is required that is specifically tailored to industrial crash applications.
In the present study a comprehensive experimental and numerical investigation was performed using three DP980 steels to identify the appropriate test geometries for plane stress fracture characterization in proportional loading. Over ten different test geometries were considered including notched tensile tests, Nakazama domes, tight radius bending and biaxial stretching with miniature punches that promote a strain gradient that suppresses localization. It was observed that an experimental fracture locus can be identified in using only four simple tests that do not require inverse-numerical approaches. A simplified approach to mesh regularization was developed to adapt the experimental locus directly to plane stress models for crash applications. To evaluate the proposed methodology, quasi-static and dynamic axial crush and three-point bend tests were performed for the three DP980 steels using a simplified structural rail geometry. In each of the test cases, the predicted structural response was in very good agreement with the experimental results in terms of the force-displacement, crack locations and energy-absorption.
Keywords: GISSMO, Crashworthiness, DP980, Mesh Regularization
Tailor rolled products are frequently used in the automotive industry as a lightweight solution to meet continuously increasing requirements in crash performance, stiffness, and CAFE standards.
This presentation details the utilization of Tailor Rolled Blanks (TRB ®) for Body-in-White (BIW) automotive parts. Through the flexible rolling process, it is possible to roll different thicknesses into sheets of steel with harmonious transitions. Due to this ability to set a proper material thickness at a specific location of the part, a simple substitution of a monolithic part by a TRB ® part leads to an attractive weight savings. However, when a part design is optimized for TRB ®, the advantages of weight reduction, part integration, and functional improvement can increase significantly.
The applications that will be discussed are tailor rolled products in rear rails with hot formed material, and front rails and crash boxes with cold formed material.
On a part like the rear rail with a complex geometry and “S” bends in different directions, the nesting is often a challenge in combination with the optimized thickness run. When developing a tailor rolled solution for this application the biggest influencing factor is material utilization, which directly influences the production feasibility and cost of the part.
Development on the front rails is concentrated on flexibly rolled cold formed material. Through the utilization of advanced high-strength micro alloyed steels, TRB ® can compete with dual phase steel solutions for similar applications. Since energy absorption during the front impact is the main requirement on the front rail, TRB ® technology is suitable to tune the deformation behavior by having different gauges along the length of the part as well as integration of reinforcements.
The crash boxes need to absorb the energy for the low speed crash test to protect the front rails from damage. At the same time, they introduce the load during the ODB front crash to the front rail. With TRB ® technology it is possible to have a long transition zone between two gauges of constant thickness, so the energy absorption is controllable by gauge and transition zone length to achieve the optimal deformation behavior. Because of this, the cross section can be more compact to release packaging space for powertrain components within the limited space of the front end.
If you have feedback about the GDIS past presentation tool, please email Sarah Burns at sburns@steel.org.