【作者】 刘伟；

【导师】 刘会霞；

【作者基本信息】 江苏大学 ， 机械工程（专业学位）， 2017， 硕士

【摘要】 激光透射焊接作为一种新兴的聚合物连接技术,正越来越多地被应用到各行业及各领域中。随着激光透射焊接技术的深入研究,数值模拟在激光透射焊接过程中扮演着越来越重要的角色;在激光透射焊接过程中,上层透光材料的光散射作用使得焊接界面处激光热源的能量分布发生变化;而激光热源在激光透射焊接数值模拟中是影响数值模拟结果的决定性因素。因此,研究激光透射焊接过程中光散射对激光热源的影响对提高激光透射焊接数值模拟的准确性以及更好地指导激光透射焊接工艺具有重要的研究价值和意义。本文选用工业领域广泛应用的聚甲醛(POM)作为研究对象,对激光透射焊接POM的光散射特性进行研究,构建得到了计及光散射的激光体热源模型,并基于此体热源模型,进行数值模拟驱动的激光透射焊接POM实验,采用响应面—遗传算法(RSM-GA)进行实验设计与多目标工艺参数的优化。论文主要研究工作与成果如下:首先,采用刀刃实验法分析半导体连续激光器的光束特性,并描述激光器发射光束沿y方向的归一化激光功率通量分布;此外,将非接触式线扫描实验与激光光束功率通量的数学分析模型相结合,研究上层透光POM的光散射特性,确定POM材料的光散射相关参数,并获得激光光束穿过上层透光POM后在焊接界面处计及光散射的沿y方向的一维线能量密度分布。其次,提出并构建得到了一种能量转换数学模型,该数学模型可将一维线能量密度分布转换为点能量密度分布,并根据转换得到的点能量密度分布拟合得到焊接界面处计及光散射的激光能量密度分布函数;以拟合得到的激光能量密度分布为基础,根据朗伯—比尔定律构建得到了计及光散射的激光透射焊接体热源模型。再次,以该体热源模型作为数值模拟的激光加载热源,进行激光透射焊接POM的温度场数值模拟,在不同功率(P=10W、11W、12W)下,将数值模拟与实验得到的焊缝熔池形貌及尺寸(熔宽、上熔深、下熔深)进行对比;结果表明,模拟结果与实验结果基本吻合,证明了数值模拟模型的准确性,验证了计及光散射的激光体热源模型的准确性与可靠性。最后,基于数值模拟温度场结果的驱动,采用RSM-GA方法进行激光透射焊接POM实验设计与多目标的工艺参数优化;通过旋转中心复合设计法(CCRD)对实验进行设计与规划,采用RSM构建响应(熔宽、上熔深、下熔深、拉伸强度)与各工艺参数(激光功率、焊接速度、离焦量)间的数学分析模型,对模型进行方差分析以评价其合适性,并讨论了各工艺参数对响应的交互影响;将满意度数学函数作为GA的适应度函数,运用MATLAB中的GA工具箱对工艺参数进行多响应目标的优化,并对多目标工艺优化得到的结果进行了验证。本文的研究表明,通过非接触式线扫描实验与能量转换数学模型所构建得到的焊接界面处计及光散射的激光体热源模型具有较好的数值模拟准确性;同时,采用RSM-GA方法的模拟驱动的激光透射焊接实验设计与规划、工艺数学建模以及多响应目标优化是一种有效的方法,为更好地指导激光透射焊接实验、提高焊接质量开辟了新的途径。更多还原

【Abstract】 Laser transmission welding(LTW),as a new kind of polymer bonding technology,is being used more and more in various industries and fields.With the development of LTW technology,numerical simulation plays a more and more important role in the process of LTW.In the process of LTW,the light scattering of the upper transparent material makes the change of the laser heat source energy distribution at the welding interface.Furthermore,the laser heat source is the decisive factor of the numerical simulation results in the numerical simulation of LTW.Therefore,it has important research value and significance for the investigation of the effect of light scattering on laser heat source during the process of LTW,which lays the foundation for improving the accuracy of numerical simulation and guiding the LTW process.In this dissertation,the polyoxymethylene(POM),widely used in the automotive field,is chosen as the research object.And during the process of LTW POM,the light scattering characteristics is investigated.The laser heat source model considering light scattering is constructed,and the LTW POM experiment is driven by this laser heat source.Then,based on the response surface methodology-genetic algorithm(RSM-GA),the LTW experimental design and optimization of multi-objective process parameters are carried out.The main research work and achievements are as follows:Firstly,the beam characteristics of semiconductor continuous laser are analyzed by means of the knife-edge experiment,and the laser beam normalized power flux distribution(NPFD)along y-direction is described.In addition,the light scattering characteristics of the upper transparent POM are studied by combining the non-contact line scanning experiment with the mathematical model of the laser beam power flux.Then the parameters of POM light scattering are determined,and the one-dimensional line energy density distribution along y-direction is obtained at the weld interface when the laser beam transmission through the upper transparent POM.Secondly,a mathematical model of energy transformation algorithm is proposed and constructed,which can transform the one-dimensional line energy density distribution into the point energy density distribution.And using the obtained point energy density distribution,the function of laser energy density distribution considering light scattering at the weld interface is described.Based on the described laser energy density distribution and Lambert-Bill law,the volumetric heat source model considering light scattering is constructed.Thirdly,the temperature field numerical simulation of LTW POM is carried out by using the constructed volumetric heat source as the loaded heat flux for numerical simulation of LTW.Under different laser power(P=10W,11 W,12W),the simulated and experimental molten pool morphology and size(molten pool width,upper depth of molten pool and lower depth of molten pool)are compared.The results show that the simulated results are in good agreement with the experimental results,which approves the accuracy of the numerical simulation model.And the reliability and accuracy of the volumetric heat source model considering light scattering are verified.Finally,based on the temperature field results of numerical simulation,the LTW POM experimental design and the optimization of multi-objective process parameters are carried out by RSM-GA method.The design and planning of the LTW experiment are performed by means of the central composite rotate design(CCRD).A mathematical model was established by using RSM to connect the response(width,upper depth,lower depth,tensile strength)and process parameters(laser power,welding speed,defocus).Then the ANOVA analysis was performed to evaluate the suitability of the mathematical model,and the interactive effects of the process parameters on the response were discussed.Using the desirability function as the fitness function of GA,the GA toolbox is used to optimize the multi-objective process parameters in MATLAB,and the optimized result is verified.The investigated results in this dissertation show that the volumetric heat source considering light scattering at the weld interface,constructed by the non-contact line scanning experiment and the energy transformation algorithm,has high accuracy of numerical simulation.Meanwhile,it is an effective method to adopt the numerical simulation-driven RSM-GA designing LTW experiment,modeling welding process parameters model and optimizing multi-objective.It provides a new way to guide the LTW experiment and improve the welding quality.更多还原