“…The determined equivalent n-value depends on the material stress-strain data and manufacturing conditions under which that data was obtained (e.g., cold, or hot stamping conditions). Giving consideration to the n-value during the development of early-stage component design guidelines [8 , 9] therefore enables material and stamping process selection decisions to be made at the onset of a design process. An example of such a design guideline is shown in Fig.…”
“…This in turn has the potential to increase familiarity among industrial designers and therefore reduce the barriers to adoption of new elevated temperature processes such as HFQ. For more information on the development of the design guidelines, the reader is referred to the original paper by Attar, Li and Foster [8] . Fig.…”
“… Fig. 3 An example of a corner design map developed by Attar, Li and Foster [8] , where the feasible and infeasible design regions are mapped out. The corner design map considers the proposed equivalent strain hardening exponent, denoted by Material n-value on the Y-axis.…”
“…Fine tuning of stamping speeds, along with other process parameters, is assumed to take place at the late FE modelling stage of product development. This fine tuning stage will be conducted by HFQ process experts using modern (and often proprietary) state-of-the-art simulation methods, as mentioned by Attar, Li and Foster [8] .…”
“…Such simulations demand material models that are sophisticated enough to account for softening due to damage [3] , effects of biaxial strain states [7] , and prediction of post-form geometry. As mentioned by Attar, Li and Foster [8] as well as Horton et al [9] , accurate forming simulations usually take place late in the product development process, and are not suitable for early-stage concept designers, who lack knowledge in computation and forming processes. Therefore, a simplified approach is needed to approximate the elevated temperature strain rate dependent material behaviour during early-stage design phases.…”
Recently developed elevated temperature metal forming technologies improve material formability and address the springback issues of cold forming. However, the behaviour of alloys at elevated temperatures is viscoplastic and therefore considerably more complex than under cold forming conditions. This complex behaviour creates a barrier for industrial designers when designing for elevated temperature processes, and therefore leads to these processes often being overlooked. To overcome this barrier, a new method is proposed here to determine simpler strain hardening responses that are equivalent to the viscoplastic responses of alloys at elevated temperatures. The equivalent hardening responses are expressed by single material hardening curves and their hardening exponents are taken as parameters to approximate sheet metal viscoplasticity. This method therefore makes it possible to develop early-stage design guidelines that consider different materials and stamping processes. The method was successfully applied to two viscoplastic alloys under hot stamping conditions to determine equivalent hardening responses. The feasibility of the method has been assessed through comparing finite element simulations using the determined equivalent material models with ones using viscoplastic models. The result showed that the thinning distributions obtained were consistent in both cases, providing evidence that the method can be applied to a range of component designs.
The proposed equivalent material models are simpler than existing viscoplastic material models and can be derived directly from experimental stress-strain data.
Creating design guidelines from equivalent hardening exponents enables a straightforward way to compare between cold and hot stamping capabilities. This comparison makes it possible to make manufacturing process and material selection decisions quickly and effectively at the onset of a design process.
Design guidelines enabled by the proposed method are critical resources to encourage the uptake of new elevated temperature metal forming technologies that facilitate lightweighting and improved environmental efficiency.
“…The determined equivalent n-value depends on the material stress-strain data and manufacturing conditions under which that data was obtained (e.g., cold, or hot stamping conditions). Giving consideration to the n-value during the development of early-stage component design guidelines [8 , 9] therefore enables material and stamping process selection decisions to be made at the onset of a design process. An example of such a design guideline is shown in Fig.…”
“…This in turn has the potential to increase familiarity among industrial designers and therefore reduce the barriers to adoption of new elevated temperature processes such as HFQ. For more information on the development of the design guidelines, the reader is referred to the original paper by Attar, Li and Foster [8] . Fig.…”
“… Fig. 3 An example of a corner design map developed by Attar, Li and Foster [8] , where the feasible and infeasible design regions are mapped out. The corner design map considers the proposed equivalent strain hardening exponent, denoted by Material n-value on the Y-axis.…”
“…Fine tuning of stamping speeds, along with other process parameters, is assumed to take place at the late FE modelling stage of product development. This fine tuning stage will be conducted by HFQ process experts using modern (and often proprietary) state-of-the-art simulation methods, as mentioned by Attar, Li and Foster [8] .…”
“…Such simulations demand material models that are sophisticated enough to account for softening due to damage [3] , effects of biaxial strain states [7] , and prediction of post-form geometry. As mentioned by Attar, Li and Foster [8] as well as Horton et al [9] , accurate forming simulations usually take place late in the product development process, and are not suitable for early-stage concept designers, who lack knowledge in computation and forming processes. Therefore, a simplified approach is needed to approximate the elevated temperature strain rate dependent material behaviour during early-stage design phases.…”
Recently developed elevated temperature metal forming technologies improve material formability and address the springback issues of cold forming. However, the behaviour of alloys at elevated temperatures is viscoplastic and therefore considerably more complex than under cold forming conditions. This complex behaviour creates a barrier for industrial designers when designing for elevated temperature processes, and therefore leads to these processes often being overlooked. To overcome this barrier, a new method is proposed here to determine simpler strain hardening responses that are equivalent to the viscoplastic responses of alloys at elevated temperatures. The equivalent hardening responses are expressed by single material hardening curves and their hardening exponents are taken as parameters to approximate sheet metal viscoplasticity. This method therefore makes it possible to develop early-stage design guidelines that consider different materials and stamping processes. The method was successfully applied to two viscoplastic alloys under hot stamping conditions to determine equivalent hardening responses. The feasibility of the method has been assessed through comparing finite element simulations using the determined equivalent material models with ones using viscoplastic models. The result showed that the thinning distributions obtained were consistent in both cases, providing evidence that the method can be applied to a range of component designs.
The proposed equivalent material models are simpler than existing viscoplastic material models and can be derived directly from experimental stress-strain data.
Creating design guidelines from equivalent hardening exponents enables a straightforward way to compare between cold and hot stamping capabilities. This comparison makes it possible to make manufacturing process and material selection decisions quickly and effectively at the onset of a design process.
Design guidelines enabled by the proposed method are critical resources to encourage the uptake of new elevated temperature metal forming technologies that facilitate lightweighting and improved environmental efficiency.
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