Stress development and shape change during press-hardening process using phase-transformation-based finite element analysis

Bok, Hyun-Ho; Choi, Jong Won; Suh, Dong‐Woo; Lee, Myoung‐Gyu; Barlat, Frédéric

doi:10.1016/j.ijplas.2014.11.004

Cited by 24 publications

(8 citation statements)

References 33 publications

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“…Figure 12 shows the part shape with good shape fixability after die release. It should be noted that the stress states during hot-stamping process are unknown in the previous report by Nakagawa et al, 11) or the final stress state is different from the simulation result (compressive stress) reported by Bok et al 10) Thus, we successfully reproduced excellent shape fixability when martensitic transformation occurs.…”

Section: Numerical Analysis Of Changes In the Stress Statementioning

confidence: 45%

“…When martensitic transformation occurs after forming, shape fixability is excellent, as reported in the previous research. 10,11) In IF steel and SUS304 steel, martensitic transformation did not occur during retention at the bottom dead center after forming, springback was present even at a forming start temperature of 800°C, and successive degradation was evident as the forming temperature decreased. This degradation is presumably caused by the reduced shape fixability that occurs when deformation resistance increases with a decrease in forming temperature.…”

Section: Effects Of Forming Start Temperature and Steel Typementioning

confidence: 99%

See 1 more Smart Citation

Mechanism for Excellent Shape Fixability in Hot Stamping Process

2020

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Automobile body parts produced by the hot stamping process exhibit excellent shape fixability with an ultra-high tensile strength of 1.5 GPa. We investigated the effect of flow stress during forming and phase transformation in the hot stamping process. Referring to both experimental and FEM coupled simulation results, we discussed the mechanism behind the excellent shape fixability in the hot stamping process. Steel of 0.2% C was used for hot stamping in this study. IF steel and SUS 304, which have different transformation behaviors, were used for comparison. The forming start temperature varied from 400°C to 800°C. After hot stamping, the springback of the parts was evaluated. The results showed that shape fixability in hot stamping is caused by low flow stress during stamping and martensitic transformation. When martensitic transformation occurs after stamping, excellent shape fixability is obtained regardless of the flow stress during forming. Accordingly, it was concluded that the stress introduced by hot stamping is relaxed and becomes uniform during martensitic transformation. The application of tensile stress due to thermal contraction also contributes to the decrease in springback.

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Section: Numerical Analysis Of Changes In the Stress Statementioning

confidence: 45%

Section: Effects Of Forming Start Temperature and Steel Typementioning

confidence: 99%

Mechanism for Excellent Shape Fixability in Hot Stamping Process

2020

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“…This process is difficult to model because it is time and temperature dependent. This requires a fully coupled thermo-mechanical-metallurgical solution [21,23]. The plastic behavior itself, stress-strain and localization, must be temperature and strain rate dependent.…”

Section: Hot Press Formingmentioning

confidence: 99%

Advanced constitutive modeling and application to industrial forming processes

Barlat

Kim

2016

MATEC Web Conf.

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Abstract. Continuum constitutive descriptions of plasticity suitable for finite element simulations of sheet forming processes are succinctly discussed in this presentation. Although multi-scale approaches allow for a more explicit representation of the physical deformation mechanisms occurring at microscopic scales, they are usually not suitable for industrial applications because of the quick turnaround time needed for process design simulations. Therefore, advances in classical concepts such as plastic anisotropy and strain hardening are still very much in demand. Actual forming simulation examples conducted for the steel industry are presented for illustration purposes.

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“…A characteristic is the sharp gradient of hardness between the different steel grades, which can also be associated with negative effects like notching under certain load paths. If HSLA-steel is combined with boron steel, complex stamping products with a locally high degree of deformation are achievable [29]. Nevertheless, due to the thermal expansion and phase transformation a sequence of tension, compression and tension while quenching occurs, whereby inhomogeneous residual stresses and a complex springback behavior result.…”

Section: Number Of Standsmentioning

confidence: 99%

“…In order to predict the final geometry after cooling and unloading, a numerical analysis with coupled thermo-mechanical-metallurgical effects is suitable to map the stress-strain state in the press hardening process. Based on this model, the stress-strain state during phase transformation and cooling can finally be adapted through adjustment of the temperature-time history [29].…”

Section: Number Of Standsmentioning

confidence: 99%