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1

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

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2022

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Vol. 22, no. 1

art. no. e23, 2022

EN

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.

2

Analysis of the nonstability states during bending processes of metallic tubes at bending machines. P. 1, Derivation of the basic expressions and relationships

Śloderbach Z.

Engineering Transactions

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2016

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Vol. 64, iss. 3

311--330

EN

In this paper the derivation of expressions for admissible values of strains and stresses for vertex points of layers subjected to tension during tube bending at bending machines is presented. The conditions of the dispersed and located loss of stability of the bent tube and the cracking criterion based on the technological index A5 (five fold sample) were assumed as criteria of instability. The original element of this paper is the extension of the criterion of strain location in a form of possible initiation of a neck or furrow (introduced by Marciniak for thin plates [1]) to bending thin- and thick-walled metal tubes at bending machines. Occurrence of loss of stability (especially that in a localised form) during tube bending can strongly reduce the service life. Thus, it is recommended to avoid such states during tube bending for elbows for pipelines or pipe installations.

3

Swivel bending

Moravec J.

Hutnik, Wiadomości Hutnicze

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2015

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Vol. 82, nr 9

604--607

EN

The contribution deals with the issue of bending. The practical part is dealing with developing of design of bending tool for bending of metal sheet parts and made technological processes for manufacturing of non-standard components.

PL

Praca zawiera rozważania badawcze dotyczące procesów gięcia precyzyjnego. Tego rodzaju gięcie stosowane jest w niskoseryjnej produkcji szczególnie odpowiedzialnych elementów. Praktyczna część pracy dotyczy projektowania narzędzi do gięcia elementów z blach i opracowania procesu technologicznego na potrzeby wytwarzania niestandardowych elementów giętych.