# Study on L-Bending Springback of 45 Steel Leather Cutting Tool Coupled with Local Induction Heating
## 3 Results
### Springback and Stress Analysis at Room Temperature  
Figure 6 illustrates the springback amount and fluctuation rate with the bending angle at room temperature. When the bending angle is 45 degrees, the springback amount turns, first decreasing and then increasing. In the study of V-bending of MART1400 steel, [PERSON] et al. [30] also described this phenomenon. The occurrence of this phenomenon is related to the radius of the mold corner and temperature of the mold; only when the temperature is not more than 375 \({}^{\circ}\)C and the mold corner radius is not more than 2 mm,  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Bending angle (\({}^{\circ}\))** & 15 & 30 & 45 & 60 & 75 & 90 \\
**Maximum bending angle (\({}^{\circ}\))** & 18.71 & 33.59 & 47.27 & 61.62 & 75.75 & 89.83 \\
**Actual bending angle (\({}^{\circ}\))** & 15.48 & 30.97 & 45.05 & 59.31 & 73.38 & 87.31 \\
**Springback (\({}^{\circ}\))** & 3.22 & 2.62 & 2.22 & 2.29 & 2.37 & 2.53 \\
**Springback rate** & 20.80\% & 8.46\% & 4.93\% & 3.86\% & 3.23\% & 2.90\% \\
**Experimental angle (\({}^{\circ}\))** & 15.8 & 29.82 & 43.94 & 56.99 & 71.21 & 84.98 \\
**Error** & 2.06\% & 3.71\% & 2.47\% & 3.91\% & 2.96\% & 2.65\% \\ \hline \end{tabular}
\end{table}
Table 7: Simulation and experimental results at local heating under induction local heating.  
Figure 5: Results from simulations and experiments on sheet bending angles at various temperatures and rotation angles of outer mold.  
the springback amount exhibits a tendency of first reducing and then increasing with an increase in the bending angle. The springback amount tends to rise with the increase in the bending angle when one of these two conditions is not met.  
In this study, the corner radius of the mold is almost zero since the bent sheet is being utilized as a leather cutting tool, which also results in the springback behavior previously mentioned at room temperature. Figure 4 shows that the yield strength of 45 steel at room temperature is around 360 MPa, whereas the forming performance of 45 steel has significantly improved under local heating at 800 \({}^{\circ}\)C, where the yield strength is only close to 60 MPa. The von Mises yield criterion explains the elastic and plastic deformation in the bending area. At room temperature, when the bending angles are 15\({}^{\circ}\) and 30\({}^{\circ}\), the plastic deformation region, as shown in Figure 7, accounts for a relatively small proportion, at which time the elastic deformation area tries to return to its original shape and the springback caused by elastic stress deformation dominates. Figure 8 illustrates how the main influencing element of springback changes from the recovery of the elastic deformation area to the imbalanced compressive and tensile stresses generated by the increasing bending angle when the bending angle is greater than 30\({}^{\circ}\)[25]. With a rise in the bending angle, the maximum tensile stress and maximum compressive stress area become increasingly inconsistent and unbalanced.  
Figure 6: The springback amount and rate of sheet at different bending angles at room temperature.  
Figure 8: The springback amount and rate of the sheet at different bending angles at 800 \({}^{\circ}\)C.  
Figure 7: Stress field in the thickness of the bending area of the sheet before unloading at different bending angles under room temperature.