Dimensional Effect on Thermo-Mechanical Evolution of Laser Depositing Thin-Walled Structure
WANG Xia1,2, WANG Wei1,2(), YANG Guang2, WANG Chao2, REN Yuhang2
1.School of Mechanical Engineering, Shenyang University of Technology, Shenyang 110870, China 2.School of Mechatronics Engineering, Shenyang Aerospace University, Shenyang 110136, China
Cite this article:
WANG Xia, WANG Wei, YANG Guang, WANG Chao, REN Yuhang. Dimensional Effect on Thermo-Mechanical Evolution of Laser Depositing Thin-Walled Structure. Acta Metall Sin, 2020, 56(5): 745-752.
To accurately predict and effectively control temperatures, stresses and distortions are key problems existing in laser deposition manufacturing technology. The mechanism of thermo-mechanical evolution during the metal depositing process is not yet clear. In order to study the dimensional effect on thermo-mechanical evolution when TC4 single-pass and thin-walled structures are manufactured by laser deposition, finite element simulations and experiments are combined to explore the influence of the structures' length on temperature, stress and distortion of the substrates. The model reliability is validated by thermocouple temperatures and the residual deformations of substrates. The results show that the temperatures of molten pools increase periodically according to the depositing layers. As soon as the laser is terminated, the maximum temperatures of builds decline at high speed, but the minimum temperatures continue to rise in the form of parabola. When the lengths of thin-walled structures increase, the thermal extremes of molten pools are not affected, but the curvatures of cooling curves diminish, the steady cooling rates accelerate, meanwhile the temperature gradients increase. The initial stresses when depositing the first layer are maximum during manufacturing, the stresses decline progressively with the increasing layer numbers, but recover during cooling. While the lengths expand, stresses of the first layer increase. At the same time both low stress regions during depositing and high stress areas during cooling are enlarged which are around the depositing structures, but the lengths of thin-walled structures appear to have a minimal impact on the stress magnitudes. During deposition, the out-of-plane distortions of the substrates oscillate up and down, after cooling the directions of deformations are fixed towards the light source. The out-of-plane distortions are more obvious as the lengths increase. During cooling the substrates' deformations reach equilibrium earlier than temperatures and stresses.
Fund: National Natural Science Foundation of China(51975387);National Key Research and Development Program of China(2016YFB1100504);Open Foundation of Key Lab of Fundamental Science for National Defense of Aeronautical Digital Manufacturing Process of Shenyang Aerospace University(SHSYS2015006)
Fig.1 Sample dimensions and location diagrams of the thermocouples and displacement measuring points
Fig.2 Finite element model and depositing pattern
Fig.3 Measured by thermocouples (Exp.) and simulated (Sim.) temperature history curves of T1~T5 (a), the maximum temperature (Tmax) and the minimum temperature (Tmin) curves of builds with different lengths of thin-walled structures (b)
Fig.4 Peak and valley temperatures of the depositing part on the maximum temperature curves (a), peak and final temperatures of the minimum temperature curves (b)
Fig.5 Distributions of von Mises stress at the end of first layer (a~c) and sixth layer (d~f), and at the time of cooling for 100 s (g~i) when L=20 mm (a, d, g), 30 mm (b, e, h) and 40 mm (c, f, i) (The deformations are scaled by a factor of 6)
Fig.6 Vertical displacement history curves of points D1~D3
Fig.7 Distributions of deformation at the time of 0.25 s (a), 3.75 s (b) and 15.875 s (c) when L=30 mm (The deformations are magnified by a factor of 6)
Fig.8 Simulated (a, c, e) and measured (b, d, f) residual deformations when L=20 mm (a, b), 30 mm (c, d) and 40 mm (e, f)
Fig.9 History curves of temperature, stress and substrate deformation when L=40 mm
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