Primary Strategic Areas

As steel continues to be innovative by introducing newer, more versatile grades and manufacturing processes to support vehicle mass reduction, it becomes necessary to construct an industry technology roadmap to help guide technical development activities within each of the following Primary Strategic Areas:

  • Materials
  • Computer-Aided Engineering (CAE) Modeling and Simulation
  • Forming Technologies
  • Tooling Technologies
  • Joining Technologies
  • Other

Addressing technical gaps within each of the preceding areas is key to enabling automakers to adapt quickly and seamlessly to newer AHSS grades with minimal disruption to the existing engineering and manufacturing infrastructure.

Addressing technical gaps within each of the preceding areas is key to enabling automakers to adapt quickly and seamlessly to newer AHSS grades with minimal disruption to the existing engineering and manufacturing infrastructure.

MATERIALS

The North American steel industry’s commitment to support automotive applications of AHSS leads to a number of challenges including the development of higher strength, more ductile and thinner gage steels and the necessary facilities to manufacture these grades. Key initiatives within this particular area can be summarized as follows:

Grade consistency across steel manufacturers and global availability - As advances in microstructure refinement and thermo-mechanical processing become increasingly specialized, same grade consistency across steel makers and global availability of such grades may be impacted. This is contrary to the automotive manufacturers desire to maintain sufficient flexibility to use the same grade for the same part globally with increased confidence. A workable initiative is needed to better align the global needs of both steel manufacturers and OEMs. 

Plasticity fundamentals - Successful modeling of polycrystalline behavior would benefit the understanding and application of new steel grade plasticity properties.

  • Models comprehending the effects of microstructure should also provide grade-based forming information.
  • Models ideally incorporating features of damaged / strengthened constituents could provide information for preformed and intermediate stages of material forming.

Elastic modulus - A key material property playing a very important role in automotive design, engineering and forming.

  • Standardized testing methods are required to accurately measure this property and model the effects of texture and anisotropy directionally on its measurement.
  • Modeling change in elastic modulus for an AHSS material in a typical tension-compression-tension cycle is a difficult challenge for a material exhibiting component phase structure changes. However it would be very beneficial in part forming and performance characterization.
  • A higher elastic modulus would be highly desirable to compensate for gage reduction and avoid loss of part or panel stiffness.

Material Fracture

  • Determination of fracture failure mechanisms of AHSS under complex and high strain rate loading conditions
  • Better the understanding of the effects of deformation mode on shear fracture including the influence of microstructure to aid in designing / refining AHSS products and processing.
  • Standardize testing to measure shear fracture and edge stretchability.

Local formability – Standardize material test methods providing the appropriate material data required to support modeling and prediction of local flow stresses incorporating anisotropy.

Delayed fracture and hydrogen embrittlement – Standardize reproducible test methods to reflect real world conditions.

COMPUTER-AIDED ENGINEERING (CAE) MODELING AND SIMULATION

With the dramatic increases in CAE capabilities over the past three decades, automakers have been increasingly relying on analytical performance validation of their design concepts especially in the pre-production phases. The ability to reliably predict crashworthiness, durability and noise vibration and harshness ahead of hardware builds and physical testing has a profound impact on product development cost and time.

There are three major initiatives to focus on within this area:

  • Advancements in finite element formulations, enhanced modeling, analyses and post-processing techniques will significantly improve the fidelity and speed of the simulations and allow rapid iterations of the design to achieve an optimum balance of performance, mass and cost without compromising safety as the primary objective; 
  • Accuracy and robustness of the material data generated and provided as input to the models to better predict formability (local and global); and
  • Modeling techniques in the future are anticipated to go beyond current simulation of vehicle performance and manufacturing. Additional requirements such as total GHG emissions to reduce the environmental impact as a function of all phases of vehicle life (production, use and end-of-life recycling) may be needed along with other inputs to support technologies such as autonomous vehicles.

These initiatives will require a dedicated collaborative effort between steel manufacturers, OEMs and finite element code developers to ensure analytical assessments and virtual vehicle simulations have the sufficient accuracy and predictive capability to deliver timely product launches with very minimal revisions.

FORMING TECHNOLOGIES

Selection of a particular steel forming technology is subject to multiple factors including: vehicle architectural considerations (e.g., body frame integral versus spaceframe); planned production volumes; tooling investment; piece cost; global applicability across production regions; and compatibility with the manufacturing footprint (i.e., assembly and joining).

Newer steel grades offer improved strength, mass reduction, and environmental sustainability at a higher value. However, they also present additional technical challenges that need to be addressed to ensure seamless applications of these grades with relatively reduced risks. Major challenges requiring attention will be highlighted in the context of the particular technology.

Conventional Stamping - As the most versatile and predominant production process for all steels, stamping and stamping process improvements are critical to expanding the future application of AHSS / UHSS. Arrival of higher-strength, more ductile, thinner-gage steel grades opens up a number of technical gaps such as:

  • Accurate material data to promote proper forming predictions;
  • Correlated and validated forming simulation techniques;
  • Validated material failure models to support forming simulations and improve the analytical predictive capability prior to hardware builds;
  • Springback prediction and control;
  • Phase transformation induced non-linear springback modeling and reduction;
  • General forming guidelines, thinning control and springback compensation, including specific part and die design concessions necessary to ensure first time / high-quality parts;
  • Material handling and blanking techniques (tooling, equipment, volumes);
  • Updated trim and pierce techniques; and
  • Investigation and use of newer press technologies such as servo-presses to improve formability and manage springback.

A key factor in expanding production applications of AHSS is the education and training of stamping and tooling engineers and designers to increase awareness of the unique characteristics of AHSS forming. While this is not a technical challenge, it is a necessary important aspect to ensure successful applications.

Hot Stamping Process - Perhaps one of the most prominent processes under review for forming 1st Gen AHSS is hot stamping. This technology can be direct or indirect and be further refined for softening, hardening and hybrid processing. As the technology continues to mature, there will be a continuing need to address gaps primarily aimed at cycle time improvements and production rate increase, such as:

  • Reducing the time of controlled blank pre-heating through equipment improvements to speed up the direct hot stamping process;
  • Shortening the in-die cooling phase to reduce overall cycle time of the direct hot stamping process;
  • Exploring surface treatments to improve heat transfer and result in reducing the cycle times of direct hot stamping;
  • Reducing the heating and cooling cycle times for indirect hot stamping;
  • Advancing post hot stamping heat treatment practices and equipment (e.g., laser processing or focused induction processing) to tailor component properties and performance characteristics locally within the part; and
  • Accurate prediction of near-net shape blanks for hot stamping.

Hydroforming and Roll Forming - Hydroforming and roll forming processes are mature steel forming technologies widely used within the automotive industry to produce open and closed structural sections. As in the case of stamping, the development of higher-strength, more ductile, thinner-gage AHSS grades opens up technical gaps specific to hydroforming and roll forming needed to be addressed to ensure successful automotive applications. For example:

  • Validated forming simulation techniques and the necessary material properties  required to conduct the analyses; 
  • Updated hydroforming pressure requirements and end seal design;
  • General forming guidelines, thinning control and springback compensation, including specific part and die design concessions necessary to ensure first time / high-quality parts;
  • Updated trim and pierce techniques;
  • Production equipment requirements and updates to existing infrastructure; and
  • Roll size sequencing to best avoiding the possibility of deformed edge micro-cracking.

Other Innovative Forming Technologies - The preceding forming technologies are the most common within the automotive industry. Less common forming processes such as: brake forming; spinning; electro-magnetic forming; electro-hydraulic forming; and explosive forming may be further developed in the future for use in conjunction with stronger, more ductile, thinner gage AHSS grades; especially if some of these technologies can offer tooling and part fabrication cost advantages.

TOOLING TECHNOLOGIES

Regardless of the forming process selected, there is a continuous need to address the capability and adequacy of the existing tooling and equipment technologies to meet the production requirements of current and emerging AHSS grades to achieve part quality at the desired production rates. Technical focus areas include, but are not limited to:

  • Enhanced die modeling, design and optimization methods;
  • Die materials for improved tool life, longer production runs, less maintenance and reduced tooling costs;
  • Die heat treatment to prevent die surface damage and improve impact and wear resistance;
  • Die surface treatment to reduce friction, tool wear and permit operating at higher-surface temperatures for conventional cold forming and potentially improve die heat transfer characteristics in the case of hot stamping;
  • Die lubricant technologies to improve their performance at higher operating pressures and temperatures with stability, improve the cleaning ability with no residue, and corrosion protection; and
  • Press equipment technologies to address higher-tonnage capacity and potentially permit design of AHSS components with fewer hits.

JOINING TECHNOLOGIES

The continuing evolution of AHSS grades demands significant updates to existing joining methods and creative simulation techniques in order to take complete advantage of these new grades and reap the full mass reduction benefits without compromising structural safety, strength or stiffness. In addition, joining steel grades to other automotive grade materials has increased and presented a rising number of applications requiring mixed material joints in the body-in-white, closures and chassis applications. Joining processes can be categorized as:

Welding processes which generally require some form of heat application (with or without filler materials). Examples include: resistance spot welding (RSW); laser welding; gas metal arc welding (GMAW); metal inert gas (MIG); tungsten inert gas (TIG); hot wire welding (HWW); and friction stir welding (FSW).

Mechanical Joining processes not requiring heat application (at least during joining), include: riveting (both self-piercing and blind); threaded fasteners; flow drill screws (FDS); clinching; hemming; impact riveting (Rivtac®); and adhesive bonding.

Welding: Weld strength and durability assurances throughout the life of an automotive body or chassis structure are key considerations in material grade selection. Increased proliferation of current and emerging AHSS / UHSS grades and the development of continuous structural joints in future automotive applications will be boosted significantly by raising the level of confidence in the robustness of the welding processes and the ability to predict, analytically, weld durability as well as weld failure or separation during high-strain rate events. Some of the key considerations are:

  • Developing validated weld fracture / separation models to be used in structure optimization studies and full vehicle simulations.
  • Developing computationally efficient FEA methodology for prediction of weld failure in a large assembly model. 
  • Developing enhanced smart software to guide design and manufacturing engineers through the process of defining weld content and weld parameters as a function of grade and gage combinations, joint performance requirements and steel surface conditions (i.e., coated versus bare).
  • Developing AHSS / UHSS welding best practices defining optimized weld cycles, heat input, clamping pressures and cooling rates for different material grade and gage combinations and stack-ups in order to: 
    • Improve joint fatigue performance;Ensure more uniform and repeatable weld nugget size and composition;
    • Minimize heat-affected zones (HAZ);
    • Minimize micro-cracking in weld zones;
    • Reduce area subject to intergranular coating diffusion in coated AHSS / UHSS; and
    • Address potential post – welding corrosion concerns.
    • Enhancing and updating weld quality assurance practices to reduce variability and increase confidence.

Mechanical Joining: In general, mechanical joining is more versatile since it is independent of the material and grade 

combinations being joined and somewhat independent of the gages. It also has the significant advantage of not altering the microstructure of the joined materials as is in the case of welding. 

Threaded fasteners have been in use within the automotive industry since its inception and guidelines governing their specifications, use and quality assurance are well established. Therefore, these have been excluded from this Roadmap.

Other mechanical joining methods requiring either piercing or deformation (or both) of the joined steel components such as, riveting, flow drill screws, clinching, hemming and Rivtac® will require considerable development especially as automakers start using the newer higher-strength, thinner gage, more ductile AHSS / UHSS grades.

The use of structural adhesives as a primary or secondary joining method is continuing to gain considerable acceptance within the industry as a means of achieving continuous joints without the significant heat input from continuous welding which has unwanted consequences. It is viewed as probably the most efficient method to transfer shear loads. However, since adhesives are typically poor in peel, they are often accompanied by another mechanical joining method (depending on the dominant loading condition) to act as a joint peel stopper.

For the category of mechanical joining, key investigations should include:

  • Developing robust and validated failure models for all joining methods above (including proven adhesive finite element modeling techniques) to be used in structure optimization studies and full vehicle simulations;
  • Developing SPR, FDS and Rivtac® technologies compatible with emerging higher strength AHSS / UHSS grades and suitable for a range of grade and gage combinations and joint stack-ups;
  • Developing best practices to govern the proper arrangement and sequence of AHSS / UHSS grades within a given joint relative to the driving direction of the self-piercing rivets, flow drill screws, Rivtac®;
  • Developing adhesive best practices defining optimized adhesive bead size and placement within a joint for optimum coverage in order to improve joint stiffness and durability;
  • Developing robust, non-destructive methods to detect adhesive presence and appropriate wet-out conditions within a joint; and
  • Investigating structural adhesives compatibility with and sensitivity to existing surface coating technologies to recommend best practices and /or development of new coating chemistries.

OTHER 

Other technical areas driving significant interaction with other automotive related industries and requiring attention as an integral part of the overall technical roadmap include (but not limited to):

  • Corrosion – Increasing standards within the automotive industry will drive the need for a fundamental understanding of different corrosion mechanisms and their interaction with microstructures, surface treatments and surface coatings. This is especially more critical as automakers migrate towards thinner-gage steels for mass efficiency.
  • Paint – One of the hallmarks of a high-quality vehicle execution is the surface quality and appearance of the painted panels. In fact, OEMs are emphasizing the importance of steel surface texture including waviness on paint adhesion and appearance. The ability to leverage stronger and thinner AHSS grades in exposed painted areas of the vehicle body without affecting the appearance will enhance performance and contribute to mass reduction.
  • Repairability – One of the longstanding advantages of steel, when compared to other materials, is the ease of repairability which reduces the cost of ownership to the end customer. With the introduction of stronger, thinner grades of AHSS, it is important to continue to investigate new and improved cost-effective techniques to repair automotive body and chassis components using such grades without compromising their performance or intended function.
  • Recyclability – As newer steel grades with increased alloying emerge on the scene for use by OEMs, it is important to track end-of-life recycling and investigate the potential consequences in order to develop the appropriate action plans in advance of disposal vehicles with these new grades.
  • LCA – A vehicle’s life cycle has three parts (or phases): production, use (driving) and end-of-life (recycling and / or disposal). The manufacturing and disposal of a car or truck can account for a significant portion of the vehicle’s life cycle emissions. While the focus of federal regulations is currently on tailpipe emissions, the true vehicle emissions impact is only evident by considering the entire life cycle. To avoid unintended consequences (overall emission increase) the development of robust, easy-to-use LCA tools will be needed to understand these impacts and direct material selection to support lower total emissions.


Table of Contents | Introduction | Fuel Economy and Emissions | Vehicle Strength | Additional Steel Industry Solutions | Future Steel Solutions | Primary Strategic Areas | Download the full PDF