| FAN Weixin,YAO Zhehe,PAN Chenghao,HONG Jinyuan,LIU Yunfeng,YAO Jianhua.Morphology Evolution of Bending Zone in Laser Thermal Stress Forming[J],53(13):175-186, 197 |
| Morphology Evolution of Bending Zone in Laser Thermal Stress Forming |
| Received:July 10, 2023 Revised:October 07, 2023 |
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| DOI：10.16490/j.cnki.issn.1001-3660.2024.13.017 |
| KeyWord:laser thermal stress forming bending zone specific energy surface tension morphology hardness distribution |
| Author | Institution |
| FAN Weixin |
Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou , China |
| YAO Zhehe |
Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou , China |
| PAN Chenghao |
Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou , China |
| HONG Jinyuan |
Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou , China |
| LIU Yunfeng |
Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou , China |
| YAO Jianhua |
Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou , China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou , China |
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| Abstract: |
| Laser thermal stress forming, as a contactless and highly flexible manufacturing method, is a promising technology in the micro forming field. Due to its high laser power density, thickening phenomenon occurs in the bending zone during the process. During the laser thermal stress forming, the involvement of multiple processes such as melting-solidification and plastic forming, as well as various effects of specific energy and forming mechanisms, constantly changes the temperature and stress state of the material in the bending zone. The flow of the material in the bending zone is affected by various factors including heating methods, bending angles, and forming mechanisms, etc. The evolution law of its morphology is even more complex. In this study, the effects and performance impacts of laser thermal input, bending angles, and forming mechanisms on the macroscopic and microscopic morphology of the bending zone were analyzed, revealing the morphological changes in the bending zone during laser thermal stress forming. The findings provide reference for improving the controllability of the morphology in the bending zone during laser thermal stress forming. The temperature gradient in the direction of sheet thickness and temperature field distribution during the laser scanning were studied by numerical simulation. An experimental setup for laser thermal stress forming was developed. The material of the specimen used in the experiments was 304 stainless steel, with size of 30 mm×30 mm×0.5 mm. A 500 W oscillator continuous fiber laser with 150-250 W laser power and a velocity range of 8-100 mm/s was used. 10-50 times of scanning was conducted with an interval of 5 s. During the process, a high-speed camera was used to capture the morphology of the forming region. After experiments, the bending angle, morphology and roughness of the bending zone of the sample were measured with a confocal microscope (Keyens VK-X1000) and a metallographic microscope (Zeiss Axio Imager2). Furthermore, A Vickers microhardness tester (Nanguang XHV-1000T-CCD) was used to test the microhardness of the shaped sample. With low specific energy, the molten material in the bending zone rapidly solidified after the laser scanning, forming a continuous raised morphology with the increasing of scanning numbers. The macroscopic morphology exhibited convex growth, and the surface roughness increased from 5.5 μm to 37.6 μm with the increase of scanning numbers. With high specific energy, the fluidity of the molten material increased and fully spread under the action of surface tension, resulting in a change in macroscopic morphology from convex to concave. The surface roughness showed an opposite trend, decreasing from 31.7 μm to 5.8 μm with scanning number increasing. In addition, the flow of the molten pool during plastic deformation was still restricted by the sheets on both sides of the forming angle. The effects of laser thermal input, bending angles, and forming mechanisms on the morphology of the bending zone were discussed based on the experimental results. At the same time, as the specific energy of the melting zone increased, the melting morphology changed from round shape into "waist shape", and a massive fine crystal structure was formed at the top region. The heat affected zone was symmetrically distributed around the melting zone, and its width was positively correlated with the specific energy. The microhardness test showed that the hardness of laser thermal stress forming melting zone was slightly higher than that of the matrix, and the hardness of heat affected zone was 40% lower than that of the matrix. In the laser thermal stress forming, the joint action of laser thermal input, bending angles, and forming mechanisms can change the macro/microscopic morphology of the bending zone. As the specific energy and the scanning number increase, the flowability of the material in the bending zone gradually enhances. However, the material flow is restricted by the sheets of the forming angle during plastic deformation. With these effects, the macroscopic morphology of the bending zone grows convexly, and flattens with high specific energy, resulting in a concave morphology, accompanied by corresponding changes in surface roughness. |
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