【作者】 王鹏飞；

【导师】 孙桂芳；

【作者基本信息】 东南大学 ， 机械制造及其自动化（专业学位）， 2021， 硕士

【摘要】 随着海洋经济的发展,海工设备在开发、利用、保护海洋方面的作用愈加重要。然而海洋装备工作环境恶劣,海工装备出现损坏后若不能及时得到修复,会造成极大经济损失及环境灾难。激光增材技术具有热影响区小、修复质量优异的优势,将水下局部干法激光增材技术应用于海工设备的在线修复及在线表面强化,能够显著提高海工设备的服役安全性及经济性。局部干法需要通过大气流在水下形成局部稳定干区,该大气流下粉末的汇聚行为对修复区质量具有重要影响。另外,海工装备现场修复时不可避免出现对倾斜面的修复。基于理论上水上及水下在倾斜面修复工艺规律上的共通性,本文先研究水平基板激光熔覆工艺参数优化并模拟其温度场及流场分布,然后研究倾斜基板激光熔覆工艺及熔池轮廓演变行为。由于水下局部干法激光熔覆使用的大排水气流对粉末输运汇聚行为影响复杂,本文最后探索大气流及送粉工艺参数对粉末的输运行为影响规律,为后期进一步的水下激光熔覆奠定基础。本文的研究内容主要如下:(1)探究GH3536合金水平面激光熔覆的工艺。首先,通过水平正交实验分析各工艺参数对熔覆层的影响:设计的工艺参数范围内,激光功率与熔高呈反向关系,与宽高比呈正向关系;送粉质流量与熔高呈正向关系,与宽高比呈反向关系。接着,通过数值仿真技术得出熔池内的温度场及流场,并结合工艺参数调整,阐明熔池内流场的物质输运作用在熔池轮廓方面影响的机理(2)在水平面激光熔覆工艺及机理的基础上,研究倾斜基板激光熔覆工艺及熔覆层轮廓演变行为。首先,通过控制变量实验,分析基体倾角、熔覆方向、工艺参数等对熔覆层的影响:基板倾斜会显著降低熔高;同样工况下对比熔高,上坡方向熔覆会略微高于下坡方向;适度增加激光功率可以适度弥补熔高的降低。然后,通过将倾斜导致的重力及激光能量等因素加入仿真模型,进行倾斜熔覆仿真对比实验,阐述倾斜面熔覆时重力影响熔池前后流场的物质输运进而影响熔池轮廓及倾斜导致的激光能量下降引发熔池温度场下降进而熔高下降,并得出熔池流场内前沿流场主导前沿坡角,后流场主导熔高的结论。(3)研究基于送粉的激光熔覆技术在大气流环境下粉末的输运汇聚行为。首先,通过数值仿真结合实验分析粉末流动受工艺参数及侧向气流的影响:增大送粉气流会导致粉末浓度轻微下降,较强的侧向气流则会显著降低粉末浓度及导致粉末浓度分布不均。接着,通过数值仿真技术对不同排水罩及不同工艺参数下的排水性能及内部流场进行分析:排水气与熔覆头较近时排水效果较好,但会干扰粉末汇聚行为;排水气与熔覆头较远时排水效果较差,需要增大送粉气流优化排水效果,但排水气不会对粉末汇聚造成明显影响。最后,综合排水效果及粉末的稳定输送,选择合适的排水罩及相应的工艺参数。更多还原

【Abstract】 With the development of marine economy,the role of marine engineering equipment in the development,utilization and protection of the ocean is becoming more and more important.However,the marine working environment is harsh,and if marine equipment is damaged and it cannot be repaired in time,it will cause great economic losses and environmental disasters.The laser additive technology has the advantages of small heat-affected zone and excellent repair quality.The application of underwater local dry laser additive technology to online repair and online surface strengthening of offshore equipment can significantly improve the safety and economy of offshore equipment.However,the local dry method requires a large air current to form a local stable dry area under water,and the transportation of powder under the high air current has an important impact on the quality of the repair area.In addition,it is inevitable to repair the inclined surface during the on-site repair of offshore equipment.Therefore,studying the transport behavior of powder under strong airflow and laser cladding on inclined surfaces has important theoretical significance and potential practical value.Based on the commonness of the above water and under water repair process rules of inclined plane in theory,the optimization of laser cladding process parameters of horizontal substrate and the simulation of its temperature field and flow field distribution are studied,and then the laser cladding process of inclined substrate and the evolution behavior of weld pool contour are studied.Due to the complex influence of large drainage air flow used in underwater partial dry laser cladding on the powder transport and aggregation behavior,this paper explores the influence of atmospheric flow and powder feeding process parameters on the powder transport behavior,which lays a foundation for further underwater laser cladding.The main research contents of this article are as follows:(1)The process of horizontal laser cladding GH3536 is explored.First,the horizontal orthogonal experiment is used to analyze the influence of various process parameters on the cladding layer: within the range of the designed process parameters,the laser power has a reverse relationship has a positive relationship with the melt height,and a positive relationship with the aspect ratio;the powder delivery mass flow rate has a positive relationship with the melt height and an inverse relationship with the aspect ratio.Then,through numerical simulation technology,the temperature field and flow field in the molten pool are obtained,and combined with the adjustment of process parameters,the mechanism of the influence of the material transport operation of the flow field in the molten pool on the contour of the molten pool is explained.(2)Based on the technology and mechanism of laser cladding on horizontal plane,the laser cladding process of tilted substrate and the evolution behavior of the cladding layer profile are studied.First,through controlled variable experiments,analyze the influence of substrate tilt angle,cladding direction,process parameters on the cladding layer: substrate tilt will significantly reduce the fusion height;the fusion height in the upslope direction will be slightly higher than that in the downhill direction;a moderate increase in laser power can moderately compensate for the decrease in melting height.Then,by adding factors such as gravity and laser energy caused by tilt to the simulation model,a comparative experiment of tilt cladding simulation is carried out,it is explained that gravity affects the material transport in the flow field of the molten pool during the cladding of the inclined surface,which affects the contour of the molten pool,and the laser energy drop caused by the tilt causes the temperature field of the molten pool to decrease and the melting height decreases.It is concluded that the front flow field in the molten pool flow field dominates the front slope angle,and the back flow field dominates the melting height.(3)The powder converging behavior of the laser cladding technology based on powder feeding under the impact of large air currents is studied.First,numerical simulation and experiment analysis are compared: the increase of powder feeding airflow can cause the slight decrease of powder concentration.The strong lateral airflow can significantly reduce the powder concentration and cause uneven powder concentration distribution.Then,numerical simulation technology is used to analyze the drainage performance and internal flow field under different drainage covers and different process parameters: when the drainage gas is close to the cladding head,the drainage effect is better,but the powder transportation behavior is affected;When the cladding head is far away,the drainage effect is poor,and the powder feeding airflow needs to be increased to optimize the drainage effect,but the powder transportation has a good performance.Finally,comprehensive drainage effect and stable powder delivery,select the appropriate drainage cover and corresponding process parameters.更多还原