Search

With the drive towards implementing Advanced High Strength Steels (AHSS) in the automotive industry; stamping engineers need to quickly answer questions about forming these strong materials into elaborate shapes. Commercially available codes have been successfully used to accurately predict formability, thickness and strains in complex parts. However, springback and twisting are still challenging subjects in numerical simulations of AHSS components. Design of Experiments (DOE) has been used in this paper to study the sensitivity of the implicit and explicit numerical results with respect to certain arrays of user input parameters in the forming of an AHSS component. Numerical results were compared to experimental measurements of the parts stamped in an industrial production line. The forming predictions of the implicit and explicit codes were in good agreement with the experimental measurements for the conventional steel grade, while lower accuracies were observed for the springback predictions. The forming predictions of the complex component with an AHSS material were also in good correlation with the respective experimental measurements. However, much lower accuracies were observed in its springback predictions. The number of integration points through the thickness and tool offset were found to be of significant importance, while coefficient of friction and Young’s modulus (modeling input parameters) have no significant effect on the accuracy of the predictions for the complex geometry. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

This paper is concerned with crashworthiness of auto-body members considering the effect of fabrication. Most auto-body members are fabricated with sheet metal forming process and welding process that induce fabrication histories such as the plastic work hardening, non-uniform thickness distribution and residual stress. Crash simulation is carried out for auto-body members with LS-DYNA3D in order to identify the fabrication effect on the crashworthiness. The analysis calculated crash mode, the reaction force and the energy absorption for crashworthiness assessment with the forming effect. The result shows that the crash analysis with considering the forming history leads to a different result from that without considering the forming effect. The analysis results demonstrate that the design of auto-body members should be carried out considering the forming history for accurate assessment of the crashworthiness.. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The “Digital Die Design System” (3DS) international project has been launched following the undesirable lack of reproducibility observed in some Numisheet benchmarks. The main idea behind the project was to repeat the same stamping experiments in different labs or press shops, with exactly the same tools and conditions. In spite of all precautions taken to ensure a good reproducibility of the stamping process, a high level of scatter was found between partners for some geometries and couples of material-lubricant. We discovered that a parameter, not neglected but insufficiently taken into consideration, was responsible for this scatter: it is the ram speed. Thanks to the quantity of recorded data, the examination of results finally drove us to see that, in certain circumstances, small differences of ram speed (i.e. 10 in place of 20 mm/s) were sufficient to strongly modify the level of springback, due to their influence on friction restraining forces. Consequences are discussed in the paper. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]

The article reports on a study to benchmark springback prediction capability of various software and skills of users on an underbody part mostly dominated by bending effect. The simulation process of stamping a cross member panel consists of three operations: forming, trimming and springback. In this benchmark, participants are allowed to use either physical beads or line beads in forming simulation. The information of physical bead geometry and bead centerlines is provided in the Nastran mesh file and IGES file.

The article reports on a study to benchmark springback prediction capability of various software and skills of users on a complex inner body panel. The simulation process of stamping a deck lid inner panel consists of three operations: forming, trimming and springback. Participants during the study are not allowed to move the tooling position in the x-y plane. In this benchmark, participants can use either physical beads or line beads in the forming simulation. The information for the physical bead geometry and bead centerlines is provided in the math files.

Forming Limit Diagram (FLD) has been proved to be a powerful tool for assessing necking failures in sheet metal forming analysis for majority of stamping operations over the last three decades. However, experimental evidence and theoretical analysis suggest that its applications are limited to linear or almost linear strain paths during its deformation history. Abrupt changes or even gradual deviations from linear strain-paths will shift forming limit curves from their original values, a situation that occurs in vast majority of sequential stamping operations such as where the drawing process is followed by flanging and re-strike processes. Various forming limit models have been put forward recently to provide remedies for the problem, noticeably stress-based and strain gradient-based forming limit criteria. This study presents an alternative path-independent forming limit criterion. Instead of traditional Forming Limit Diagrams (FLD) which are constructed in terms of major - minor principal strains throughout deformation history, the new criterion defines a critical effective strain [variant_greek_epsilon]* as the limit strain for necking, and it is shown that [variant_greek_epsilon]* can be expressed as a function of current strain rate state and material work hardening properties, without the need of explicitly considering strain-path effects. It is given by [variant_greek_epsilon]* = f(β, k, n) where β = d[variant_greek_epsilon]2/d[variant_greek_epsilon]1 at current deformation state, and k and n are material strain hardening parameters if a power law is assumed. The analysis is built upon previous work by Storen and Rice [1975] and Zhu et al [2002] with the incorporation of anisotropic yield models such as Hill’48 for quadratic orthotropic yield and Hill’79 for non-quadratic orthotropic yield. Effects of anisotropic parameters such as R-values and exponent n-values on necking are investigated in detail for a variety of strain paths. Results predicted according to current analysis are compared against experimental data gathered from literature and good agreements are achieved. This provides a powerful validation for this approach. The new criterion retains all the advantages of the traditional FLDs since it’s still constructed in the strain space. Its relationship with stress-based forming limit criteria is discussed. It is believed that the approach is especially suitable for production stamping CAE analysis since the strain rate state at any material point during forming deformation is readily available from FEA simulations. It can be easily embedded in forming simulation software or alternatively deployed as a post-processing function for forming simulations. © 2005 American Institute of Physics [ABSTRACT FROM AUTHOR]