## 3 Optimization of Structural Parameters of Steel Bar Hoop Bending Machine
### Finite Element Simulation and Experimental Analysis
#### 3.1.3 Experiment on Springback Angle of Steel Bar Bending  
The experimental equipment is the \"Giant dragon No. 3\" straightening hoop bending integrated machine produced by Hebei Zhijian Machinery Manufacturing Co., Ltd. The company is located in Handan, China. The bending mechanism is shown in Figure 8, and the main technical parameters of the equipment are shown in Table 5.  
Figure 7: Stress cloud diagrams of steel bars with different radii of rotation of crankshaft. The experimental material comprises HRB400 steel bars with a diameter of 10 mm, and the specific parameters are shown in Table 6.  
The angle measurement tool adopts the laser angle measuring instrument, and the specific parameters are shown in Table 7. \begin{table}
\begin{tabular}{c c} \hline \hline
**Projects** & **Parameters** \\ \hline Steel bar grade & HRB400 \\ Nominal diameter & 10 mm \\ Yield strength & \(\geq\)400 Mpa \\ Tensile strength & \(\geq\)570 Mpa \\ Elongation rate & \(\geq\)14\% \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Steel bar material and dimensional parameters. \begin{table}
\begin{tabular}{c c} \hline \hline
**Projects** & **Parameters** \\ \hline Requirement accuracy & \(\pm 0.2^{\circ}\) \\ Display resolution & \(\pm 0.01^{\circ}\) \\ Measuring range & \(4\times 90^{\circ}\) \\ Working mode & Absolute/relative \\ \hline \hline \end{tabular}
\end{table} 
Table 7: Laser angle measuring instrument parameter table. Figure 8: Experimental equipment bending mechanism. \begin{table}
\begin{tabular}{c c} \hline \hline
**Projects** & **Parameters** \\ \hline Equipment dimensions & 12,300 mm \(\times\) 1400 mm \(\times\) 1600 mm \\ Operating voltage & 380 V (50 Hz) \\ Total power & 26 KW \\ Air source working pressure & \(\geq\)0.6 Mpa \\ Maximum feed speed & 60 m/s \\ Production efficiency & 1000\(-\)2800/h \\ Processing range & 4–12 mm (steel bar) \\ Bending angle & 0–180\({}^{\circ}\) \\ \hline \hline \end{tabular}
\end{table} 
Table 5: Parameters of steel bar bending machine. When measuring the angle of the steel bar, the relative measurement mode is selected, one side of the bent steel bar is used as the horizontal line, and the angle of the other side relative to the horizontal line is measured; the measurement method is shown in Figure 9.  
In order to ensure the accuracy of the obtained parameters, data from 20 springback angles were collected for each angle of different structural parameters, and the average of the springback angles measured 20 times was taken. (1) Influence of support shaft diameter on springback angle. The steel bar bending experiment is carried out on the straightening hoop bending machine, and the relationship between the steel bar bending angle and the springback angle is obtained as shown in the figure. Figure 10 shows the steel bar springback angle value corresponding to different support shaft diameters D\({}_{1}\). As can be seen from the figure, when other structural parameters remain unchanged, the rebar springback angle becomes larger with the increase in the support shaft diameter D\({}_{1}\). Combined with the analysis of the simulation results, it can be found that as the diameter D\({}_{1}\) of the support shaft increases, the maximum stress of the steel bar bending becomes smaller, the stress distribution becomes wider, and the springback angle becomes larger. Figure 10: Springback angle values for different support shaft sizes. Figure 9: Steel bar angle measurement. 2. Influence of curved crankshaft diameter on springback angle. Figure 11 shows the steel bar springback angle values corresponding to different bending shaft sizes D\({}_{2}\), and it can be seen from the figure that when other structural parameters remain unchanged, the steel bar springback angle does not change significantly with the increase in bending shaft size D\({}_{2}\).