【作者】 张勇；

【导师】 汪小凯；

【作者基本信息】 武汉理工大学 ， 车辆工程， 2019， 硕士

【摘要】 激光焊接是一种先进的制造工艺,是汽车轻量化制造过程中的重要连接技术。随着激光焊接技术的不断发展与进步,激光焊接已广泛应用到了汽车变速箱换挡拨叉、变速器齿轮、离合器、传动轴、车身框架及底盘等汽车零部件的制造中。而激光焊缝的内部质量对于汽车中厚板结构件的安全性有重要影响,因此对汽车中厚板结构件激光焊缝的内部质量进行检测非常必要。目前,针对汽车中厚板结构件激光焊缝内部缺陷的检测方法主要是破坏性切片抽检,但这种方法存在破坏性、滞后性、小样本和检测成本高等缺点,无法满足现代工业生产所需的高可靠性和低成本的检测要求。本文以汽车变速箱换挡拨叉激光焊缝为具体研究对象,开展其焊接质量的超声无损检测研究,具体内容如下:(1)对汽车变速箱换挡拨叉零件进行了介绍,分析了激光焊缝内部缺陷的类型及形成原因,并依据板件焊缝特征,对三种常规超声检测方法进行了讨论,制定了合适的超声检测工艺,并对焊缝内部缺陷的定位与定量分析进行了探讨。(2)在对三种常规超声检测方法进行讨论的基础上,选择并设计了超声水浸聚焦探头,然后进行了水浸聚焦探头的声场仿真与分析,对所选用探头的合理性进行了验证。(3)基于COMSOL软件建立了板件焊缝结构有限元仿真模型,对板件焊缝结构进行声学仿真并进行相应的实验,然后对仿真与实验信号进行处理,并对提取出的信号时域、频域特征值进行分析,证明了超声水浸聚焦检测方法可以检测出激光焊缝中的微小缺陷,超声信号频谱分析可以有效地识别出不同缺陷类型,另外还对焊缝质量进行了评价。(4)介绍了超声相控阵成像理论和超声相控阵成像设备,制定了超声相控阵检测工艺,据此对汽车变速箱换挡拨叉激光焊缝结构进行了超声相控阵成像实验,并与超声水浸聚焦检测实验结果进行了互相验证。本文提出了一种汽车变速箱换挡拨叉激光焊缝常规超声水浸聚焦和超声相控阵成像检测工艺和方法,实现了3-5mm宽激光焊缝内部直径Φ0.2mm当量缺陷的检测,研究结果对于保障汽车关键板类结构件的高质量焊接制造具有重要意义和实用价值。更多还原

【Abstract】 Laser welding is an advanced manufacturing process and an important connection technology in the lightweight manufacturing process of automobiles.With the continuous development and advancement of laser welding technology,laser welding has been widely used in the manufacture of automotive parts such as shifting forks of automobile gearbox,transmission gears,clutches,transmission shafts,body frame and chassis.The internal quality of laser welds has an important impact on the safety of automotive moderate thick plate structural parts.Therefore,it is necessary to detect the internal quality of laser welded joints in automotive moderate thick plate structural parts.At present,the detection method for the internal defects of laser welded joints of automobile moderate thick plate structural parts is mainly destructive slicing,but this method has the defects of destructiveness,hysteresis,small sample and high detection cost,which can not meet the high reliability and low cost inspection requirements required for modern industrial production.In this thesis,the laser welding seam of shifting fork of automobile gearbox is taken as the specific research object,and the ultrasonic nondestructive testing of welding quality is carried out.The specific contents are as follows:(1)The parts of the shifting fork of the automobile gearbox are introduced.The types and causes of the internal defects of the laser welded joint are analyzed.According to the characteristics of the welded joints of the plate,three conventional ultrasonic testing methods are discussed and formulated.Developed a suitable ultrasonic testing process.The location and quantitative analysis of internal defects in the weld are discussed.(2)Based on the discussion of three conventional ultrasonic testing methods,the ultrasonic water immersion focusing probe was selected and designed.Then,the sound field simulation and analysis of the water immersion focusing probe were carried out,and the rationality of the selected probe was verified.(3)Based on COMSOL software,the finite element simulation model of plate weld structure is established.The acoustic simulation of the welded structure of the plate is carried out and the corresponding experiments are carried out.Then the simulation and experimental signals are processed,and the time domain and frequency domain eigenvalues of the extracted signals are analyzed.It is proved that the ultrasonic immersion focus detection method can detect the tiny defects in the laser weld seam,and the ultrasonic signal spectrum analysis can effectively identify different defect types,and the weld quality is also evaluated.(4)Introduced the theory of ultrasonic phased array imaging and ultrasonic phased array imaging equipment,and developed the ultrasonic phased array detection technology.Based on this,the ultrasonic phased array imaging experiment was carried out on the laser weld seam structure of the shifting fork of the automobile gearbox.And verified with ultrasonic water immersion focus test results.This thesis proposes a conventional ultrasonic water immersion focusing and ultrasonic phased array imaging detection process for the laser gear shifting fork of the automobile gearbox,and realizes the detection of the internal diameter Φ0.2mm equivalent defect of the 3-5mm wide laser weld.The research results are of great significance and practical value for ensuring the high quality welding manufacturing of key structural parts of automobiles.更多还原