范伟鑫,姚喆赫,潘成颢,洪锦源,刘云峰,姚建华.激光热应力成形弯折区形貌演变规律研究[J].表面技术,2024,53(13):175-186, 197.
FAN Weixin,YAO Zhehe,PAN Chenghao,HONG Jinyuan,LIU Yunfeng,YAO Jianhua.Morphology Evolution of Bending Zone in Laser Thermal Stress Forming[J].Surface Technology,2024,53(13):175-186, 197 |
| 激光热应力成形弯折区形貌演变规律研究 |
| Morphology Evolution of Bending Zone in Laser Thermal Stress Forming |
| 投稿时间：2023-07-10 修订日期：2023-10-07 |
| DOI：10.16490/j.cnki.issn.1001-3660.2024.13.017 |
| 中文关键词: 激光热应力成形 弯折区 比能 表面张力 形貌 硬度分布 |
| 英文关键词:laser thermal stress forming bending zone specific energy surface tension morphology hardness distribution |
| 基金项目:国家自然科学基金(52175443，U1809220);浙江省自然科学基金(LD22E050013) |
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| Author | Institution |
| FAN Weixin | Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou 310023, China |
| YAO Zhehe | Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou 310023, China |
| PAN Chenghao | Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou 310023, China |
| HONG Jinyuan | Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou 310023, China |
| LIU Yunfeng | Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou 310023, China |
| YAO Jianhua | Institute of Laser Advanced Manufacturing,College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310023, China;Key Laboratory of Special Purpose Equipment and Advanced Processing Technology, Ministry of Education and Zhejiang Province, Hangzhou 310023, China |
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| 中文摘要: |
| 目的 针对激光热应力成形弯折区增厚现象，揭示激光热输入、弯曲角度和成形机制对弯曲过程的影响，以及弯折区域形貌的演变规律，为提高激光热应力成形弯折区域的形貌可控性提供参考。方法 采用高速相机拍摄成形过程中热输入和弯曲角度对弯折区的宏/微观形貌的作用效果，并采用共聚焦显微镜观察试样的宏观形貌，采用光学显微镜分析微观组织，通过维氏显微硬度计测量弯折区附近材料的硬度分布情况，同时结合温度场数值模拟和表面张力理论分析，揭示弯折区形貌的影响因素及形成机制。结果 在低比能作用下，弯折区的熔融材料在激光扫描结束后快速凝固，并在扫描次数逐渐增加的过程中其表面逐渐隆起，并形成凸起状形貌，表面粗糙度随着扫描次数的增加呈现上升趋势，由5.5 μm增至37.6 μm。在高比能作用下，熔融材料的流动性得到提升，并在表面张力的作用下充分铺展，宏观形貌由凸变平，最后呈现凹形形貌，表面粗糙度随着扫描次数的增加呈现相反的变化趋势，由31.7 μm减至5.8 μm。此外，在塑性成形过程中，熔池流动仍受到成形角两侧壁面的限制。硬度测试结果表明，激光热应力成形弯折熔凝区域的硬度略高于基体的硬度，热影响区的硬度比基体的硬度降低了40%。结论 激光热输入、弯曲角度和成形机制会影响弯折区材料表面的挤压、熔化、流动、凝固过程，以及材料内部的温度梯度和界面表面张力，在这些因素的影响下弯折区域的轮廓形貌、成形粗糙度、显微组织和硬度分布发生了变化。 |
| 英文摘要: |
| 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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