【作者】 徐玮；

【导师】 刘会霞；

【作者基本信息】 江苏大学 ， 机械工程（专业学位）， 2022， 硕士

【摘要】 近年来,随着工业领域对产品轻量化设计的需求越来越迫切,金属与聚合物材料组合越来越广泛地应用于生产制造当中,因此选择合适的金属与聚合物之间的连接方式是轻量化设计中的关键问题之一。激光连接技术是能实现金属与聚合物的连接并满足轻量化设计行之有效的方法。本文针对聚对苯二甲酸乙二醇酯(PET)与不锈钢SUS304这两种属性存在差异的材料,使用连续激光器进行了激光透射连接聚对苯二甲酸乙二醇酯(PET)与不锈钢SUS304的激光透射连接实验,并对不锈钢SUS304表面微结构预处理来提高PET与不锈钢SUS304的连接强度。论文探究了该材料组合的激光连接性能与机理,对激光透射连接进行了工艺参数优化,并使用基于有限体积法的FLUENT软件对激光透射连接过程进行数值模拟。主要研究工作及成果如下:(1)PET与不锈钢SUS304进行激光透射连接性能与机理研究:分析了激光连接工艺参数(连续激光器电流强度和激光连接速度)对连接接头强度的影响。结果表明,随着连续激光器电流强度的增加,激光连接强度先增大后减少;随着激光连接速度的增加,连接强度先增大后减少;使用超景深电子显微镜对PET与不锈钢SUS304连接界面处进行表征,发现在连接接头处PET熔体流入了不锈钢SUS304表面因粗糙度形成的微凹坑中形成机械铆接;使用X射线能谱仪对剥离后的连接界面进行检测,结果表明,在金属与聚合物之间形成了化学键(O-Fe,O-Cr)。综上所述,在金属与聚合物的连接界面处存在机械铆接效应与化学键合是二者主要连接机理。(2)PET与激光表面微结构预处理不锈钢SUS304激光透射连接性能与机理研究:使用纳秒脉冲激光表面预处理系统在不锈钢SUS304表面制作出微孔微结构。通过单因素实验研究了表面预处理工艺参数(表面微结构预处理功率、扫描次数)与激光连接工艺参数(连续激光器电流强度、激光连接速度)对连接强度的影响。实验结果表明,随着这四个因素的增大,连接强度先增大后减小。PET与经微孔结构预处理强化后的不锈钢SUS304的最高连接强度,相较于未经微孔结构预处理的连接件的最高强度,提高了42.801%左右,这表明微孔结构预处理可以有效提高连接强度。XPS检测结果显示在连接界面也形成了化学键合。总而言之,表面微孔预处理是连接强度增强的主要机理。(3)工艺参数建模与优化研究:对PET与表面微结构预处理的不锈钢SUS304连接工艺参数进行数学建模,分析表面预处理工艺参数(表面微结构预处理功率、扫描次数)与激光连接工艺参数(连续激光器电流强度、激光连接速度)组合对于响应值连接强度的交互式影响。发现预测值与实验值较为吻合,模型具有较好的可靠性。建模结果表明表面微结构预处理功率-扫描次数,表面微结构预处理功率-激光连接速度,扫描次数-连续激光器电流强度,连续激光器电流强度-激光连接速度对于响应值连接强度的交互式影响较大;根据连接强度最大准则进行优化后得到了最优的工艺参数结果。(4)推导了激光透射连接所用到的计算流体力学方程,并使用FLUENT软件建立了激光透射连接PET与不锈钢SUS304的数值模型,对熔池宽度的数值模拟与实验结果对比,发现二者较为吻合,证明了模型的可靠性。分析了PET与SUS304激光透射连接过程中温度场的分布情况,温度场最高温度始终出现在激光热源附近的位置,并且在激光热源前方温度梯度更大。这表明移动热源的局部加热会导致PET急剧温升使得热源前方温度梯度更大;分析了PET与SUS304激光透射连接过程中的熔池形成过程,发现当热量输入增加后形成了较为明显的熔池。在熔池内部出现了熔体流动,熔体受浮力自热源中心向熔池两端循环流动。这表明热输入量是熔池形成的关键因素;分析了激光连接工艺参数(连续激光器电流强度、激光连接速度)对温度场与流场的影响,随着连续激光器电流强度的增加,PET层最高温度增加,流场内最高流动速度增加,熔池宽度变宽,随着激光连接速度的增加,PET层最高温度降低,流场内最高流动速度下降,熔池宽度变窄,随工艺参数变化的影响规律表明激光连接工艺参数是激光连接过程中重要因素之一,工艺参数影响热输入,进而影响在连接过程中的温度场、流场的分布范围。本研究为PET与不锈钢SUS304的激光透射连接的工业领域应用提供了理论基础与技术支持,并且为其他金属与聚合物的异质材料组合的激光连接提供新思路。更多还原

【Abstract】 In recent years,with the increasingly urgent demand for product lightweight design in the industrial field,the combination of metal and polymer materials is more and more widely used in manufacturing.Therefore,selecting the appropriate joining mode between metal and polymer is one of the key issues in lightweight design.Laser joining technology is an effective method to realize the joining between metal and polymer and meet the demand of lightweight design.In this dissertation,aiming at the materials with different properties between polyethylene terephthalate(PET)and SUS304,the laser transmission joining experiment between polyethylene terephthalate(PET)and SUS304 was carried out by using a continuous laser,and the surface microstructure of304 stainless steel was pretreated to improve the joint strength between PET and SUS304.This dissertation explores the performance of laser joining and mechanism of the material combination,optimizes the process parameters of laser transmission joining,and software FLUENT based on finite volume method was used to simulate the process of laser transmission joining.The main research work and results are as follows:(1)The performance and mechanism of laser transmission joining between PET and SUS304 were studied.The effects of laser joining process parameters(continuous laser current intensity and laser joining speed)on the strength of the joint were analyzed.The results show that with the increase of continuous laser current intensity,the laser joining intensity first increases and then decreases;With the increase of laser joining speed,the joining strength first increases and then decreases;The interface between PET and SUS304 was characterized by ultra depth of field electron microscope.It was found that melt of PET flowed into the micro pits formed by roughness on the surface of SUS304 at the joint to form mechanical riveting;The results show that chemical bonds(O-Fe,O-Cr)are formed between metal and polymer.To sum up,there is mechanical riveting effect and chemical bonding at the interface between metal and polymer.(2)Study on the performance and mechanism of laser transmission joining between pet and laser surface microstructure pretreatment SUS304: a nanosecond pulse laser surface pretreatment system was used to fabricate microporous microstructure on the surface of SUS304.The effects of parameters of surface pretreatment process(pretreatment power,scanning times)and parameters of laser joining process(continuous laser current intensity,laser joining speed)on the joining strength were studied by single factor experiment.The experimental results show that with the increase of these four factors,the joining strength first increases and then decreases.The highest joining strength between pet and SUS304 strengthened by microporous structure pretreatment is about 42.801% higher than that of the joint without microporous structure pretreatment,which indicates that microporous structure pretreatment can effectively improve the joining strength.XPS results showed that chemical bonding was also formed at the joining interface.In a word,the surface micropore pretreatment is the main mechanism of strengthening the joining strength.(3)Research on modeling and optimization of process parameter: the mathematical modeling of the joining process parameters between pet and SUS304 with surface microstructure pretreatment is carried out,and the interactive influence of the combination of surface pretreatment process parameters(pretreatment power,scanning times)and laser joining process parameters(continuous laser current intensity,laser joining speed)on the joining strength is analyzed.It is found that the predicted value is in good agreement with the experimental value,and the model has good reliability.The modeling results show that the surface pretreatment power-scanning times,pretreatment power-Laser joining speed,scanning times-continuous laser current intensity,continuous laser current intensity-Laser joining speed have a great influence on the joining intensity;The optimal process parameters are obtained after optimization according to the maximum joining strength criterion.(4)The computational fluid dynamics equation of laser transmission joining is derived,and the numerical model of laser transmission joining between pet and SUS304 is established by using FLUENT software.The numerical simulation of molten pool width is compared with the experimental results,and it is found that the two are in good agreement,which proves the reliability of the model.The distribution of temperature field during the transmission joining between pet and SUS304 is analyzed.The maximum temperature of temperature field always appears near the laser heat source,and the temperature gradient in front of the laser heat source is larger.This shows that the local heating of the moving heat source will lead to a sharp temperature rise of pet and a larger temperature gradient in front of the heat source;The formation process of molten pool in the process of laser transmission joining between pet and SUS304 is analyzed.It is found that an obvious molten pool is formed when the heat input increases.Melt flow occurs in the molten pool,and the melt circulates from the center of the heat source to both ends of the molten pool by buoyancy.This shows that the heat input is the key factor for the formation of molten pool;The effects of laser joining process parameters(continuous laser current intensity and laser joining speed)on the temperature field and flow field are analyzed.With the increase of continuous laser current intensity,the maximum temperature of PET layer increases,the maximum flow velocity in the flow field increases,and the molten pool width becomes wider.With the increase of laser joining speed,the maximum temperature of PET layer decreases,the maximum flow velocity in the flow field decreases,and the molten pool width becomes narrower,The influence with the change of process parameters shows that the process parameters of laser joining are one of the important factors in the process of laser joining.The process parameters affect the heat input,and then affect the distribution range of temperature field and flow field in the process of joining.This study provides theoretical basis and technical support for the industrial application of laser transmission joining between pet and SUS304,and provides a new idea for the laser joining of heterogeneous materials of other metals and polymers.更多还原