Springback prediction in sheet metal forming of high strength steels

Lü

Advances in Mechanical Engineering

et al. 2018

The applied straightening moment and the springback after unloading with respect to the straightening process of rectangle-section metal bars have a direct influence on the straightening accuracy and efficiency. In this article, an asymmetrical hardening material model is first proposed to describe the stress-strain curves considering the asymmetrical features of yield stress and plastic hardening stage in tension and compression, and it is also compared with the traditional linear hardening material model. To accurately evaluate the elasto-plastic bending deformation and the springback in the straightening process, an analytical model for the loading and unloading moments is then established. The strain and stress distributions in elastic and plastic regions during the straightening process are also discussed in this article. Finally, the straightening experiments of rectangle-section metal bars under different heat-treated conditions are conducted on the ROSE-JZ50 straightening machine with displacement sensors, force sensors and strain gauges to validate the proposed analytical straightening model.

Section: The Straightening Model Based On Finite Element Methods and Imentioning

confidence: 99%

A novel analytical model for straightening process of rectangle-section metal bars considering asymmetrical hardening features

Lü

Advances in Mechanical Engineering

et al. 2018

“…A schematic of yield surfaces according to the Yoshida-Uemori model was presented in Chongthairungruang et al [17]. The relative displacement of the two yield surfaces in a bounding surface can be defined as follows:…”

Section: Yoshida-uemori Hardening Modelmentioning

confidence: 99%

Effect of Constitutive Equations on Springback Prediction Accuracy in the TRIP1180 Cold Stamping

Seo

Kim

Lee³

et al. 2017

Metals

Abstract:This study aimed to evaluate the effect of constitutive equations on springback prediction accuracy in cold stamping with various deformation modes. This study investigated the ability of two yield functions to describe the yield behavior: Hill'48 and Yld2000-2d. Isotropic and kinematic hardening models based on the Yoshida-Uemori model were adopted to describe the hardening behavior. The chord modulus model was used to calculate the degradation of the elastic modulus that occurred during plastic loading. Various material tests (such as uniaxial tension, tension-compression, loading-unloading, and hydraulic bulging tests) were conducted to determine the material parameters of the models. The parameters thus obtained were implemented in a springback prediction finite element (FE) simulation, and the results were compared to experimental data. The springback prediction accuracy was evaluated using U-bending and T-shape drawing. The constitutive equations wielded significant influence over the springback prediction accuracy. This demonstrates the importance of selecting appropriate constitutive equations that accurately describe the material behaviors in FE simulations.

“…A technique to control the internal stress of the material at bottom dead center of the forming has also been proposed and is close to being made practical 14,15) . Another approach is to analyze the forming method and material behavior by FEM simulation [16][17][18][19][20] , but all of those methods ultimately ensure dimensional accuracy by iterative adjustments of the die through trial and error, and for some product shapes, the dimensional accuracy cannot be ensured.…”

Section: Introductionmentioning

confidence: 99%

Evaluation of the Form-Forming Mechanism for High-Tensile-Strength Steel Plate

2017

Steel plate with tensile strengths of from 440 MPa to 980 MPa is increasingly being adopted for the structural elements of automobile bodies to both reduce weight and increase collision safety. However, the use of such material brings defects in press forming and other problems. The research reported here focuses on the form-forming method, which is effective for forming high tensile strength steel plate. To clarify the features of form-forming, we used eight types of steel plate having tensile strengths of from 270 MPa to 980 MPa in three forming processes, draw-forming, one-step form-forming, and two-step form-forming, to evaluate the shape freezing property. The results showed that the shape freezing property depends on the mechanical properties of the material; speci cally, a correlation with tensile strength, 0.2% proof stress, and elongation was seen. The effectiveness of form-forming for materials of higher strength was con rmed. Improved shape freezing by dividing the form-forming process into two steps was also con rmed. For draw-forming, the entire shaped surface was affected by unbending, so form-forming effectively suppresses unbending. The spatial distribution of unbending was evaluated quantitatively by measuring the residual stress distribution, con rming that residual stress serves as a useful index for clarifying the forming mechanism.