# Study on L-Bending Springback of 45 Steel Leather Cutting Tool Coupled with Local Induction Heating
## 3 Results  
### Forming Angle Analysis of the Sheet  
It has been proven that process parameters such as temperature and bending angle have considerable impacts on the springback of the sheet. Table 4 illustrates the effects of temperature and the outer mold rotation angle on the bending angle of 45 steel during L-bending. It can be seen that the bending angle of the sheet at room temperature is typically smaller than the bending angle of the sheet at 800 \({}^{\circ}\)C, indicating that the sheet's forming performance has increased at 800 \({}^{\circ}\)C when the rotation angle of the outer mold is the same.  
Tables 6 and 7 show the simulation and experiment results of the bending behavior under different temperatures and bending angles, respectively, where the maximum bending angle and the actual bending angle are the bending angles of the sheets before and after springback under the simulation results, and the springback is the difference between the two. The ratio of the springback to the actual bending angle is known as the springback rate. The inaccuracy in the simulation result is the difference between the real bending angle and the experimental angle. Tables 6 and 7 demonstrate the extremely small difference in the bending angle between the simulation results and the experimental results. The maximum difference in the actual bending angle between the simulation and the experimental results at 800 \({}^{\circ}\)C is just 1.96\({}^{\circ}\), and the corresponding error is 5.78%. The maximum difference in bending angle is 2.32\({}^{\circ}\), and the maximum error between the simulated value and the experimental value at room temperature is 3.91%, indicating that the finite element model has good accuracy.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Bending angle (\({}^{\circ}\))** & 15 & 30 & 45 & 60 & 75 & 90 \\
**Maximum bending angle (\({}^{\circ}\))** & 16.63 & 34.75 & 49.15 & 64.07 & 79.65 & 94.42 \\
**Actual bending angle (\({}^{\circ}\))** & 15.83 & 33.91 & 48.23 & 63.11 & 78.54 & 93.13 \\
**Springback (\({}^{\circ}\))** & 0.81 & 0.84 & 0.92 & 0.95 & 1.11 & 1.29 \\
**Springback rate** & 5.05\% & 2.48\% & 1.91\% & 1.52\% & 1.42\% & 1.39\% \\
**Experimental angle (\({}^{\circ}\))** & 16.68 & 31.95 & 49.90 & 64.01 & 78.55 & 91.64 \\
**Error** & 5.39\% & 5.78\% & 3.47\% & 1.43\% & 0.01\% & 1.6\% \\ \hline \hline \end{tabular}
\end{table}
Table 6: Simulation and experimental results under room temperature.  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Outer Mold Rotation Angle (\({}^{\circ}\))** & 30 & 40 & 50 & 60 & 70 \\
**Bending Angle at 800 \({}^{\circ}\)C (\({}^{\circ}\))** & 9.49 & 45.75 & 73.83 & 93.73 & 105.44 \\
**Bending Angle at Room Temperature (\({}^{\circ}\))** & 7.73 & 42.01 & 68.96 & 88.31 & 100.17 \\ \hline \hline \end{tabular}
\end{table}
Table 4: The bending angle of the sheet corresponds to the rotation angle of the outer mold.  
Figure 5 illustrates the simulation and experimental results of the sheet's bending angle when the outer mold rotation angle from Table 5 is used as input, confirming the inference that the forming performance of the sheet is enhanced at 800 \({}^{\circ}\)C and that the bending sheets at this temperature produce a larger bending angle. This improvement in forming performance is due to the fact that the metallographic structure of 45 steel at room temperature is composed of bulk ferrite and fine lamellar pearlite, and the high temperature of 800 \({}^{\circ}\)C expands the pearlite volume and significantly reduces the grain boundary interface, thereby reducing dislocation motion resistance [23].