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A thermal stress forming method for increasing bending angle and improving microstructure and properties

Guo Yankuo, Shi Yongjun, Wang Xiaogang, Fan Kaijun, Wang Qin

Archives of Civil and Mechanical Engineering

2022

Vol. 22, no. 1

art. no. e23, 2022

Thermal stress forming (thermoforming) technology has good advantages in small-batch, complex surface, brittle, and hard material processing. A large bending angle is the main objective of thermal stress forming. However, the problem of small bending angle has always existed. Especially in the case of larger workpiece thickness (h ≥ 1 mm), the bending angle is smaller. To solve the aforementioned problems, a new method (end blocking method, EBM) is proposed. The bending angle and deformation mechanism of this method with different plate thickness and processing parameters are investigated. Finally, the microstructure and properties of the heating zone are observed. The results show that the new method (9.05 deg) can increase the bending angle by 37.71 times with the traditional method (0.24 deg). The reason is that the new method can form a large bending moment in the heating zone and increase the bending angle effectively. Moreover, the method can still achieve a large bending angle (the traditional method: 0.02 deg, the new method: 2.75 deg, increased by 137.5 times), when the plate is thick (h = 1.2 mm). The bending angle obtained by the new method increases with the increment in laser power or the decrement in scanning speed. By contrast, the change in laser diameter has minimal effect on bending angle. In addition, because the new method can produce large compressive stress in the heating zone, the compressive stress can effectively refine the grains and increase the microhardness by 1.22 times. Therefore, this method can effectively improve the microstructure and properties of the heating zone. This method only needs a simple baffle, and the whole process is simple and practical. The new method in this study uses the laser as the heat source and is also suitable for flame thermoforming and high-frequency induction thermoforming.