基于激光散斑图像的焊接缺陷的识别研究

发布时间：2018-07-05 10:49

本文选题：激光散斑 + 激光散斑图像测量法　；参考：《西南交通大学》2017年硕士论文

【摘要】：激光焊接的过程中,会产生不完全焊接,孔隙,裂缝等缺陷,这些缺陷如果没有被检测出来会造成非常大的影响,因此需要针对焊接窄缝进行缺陷检测。可是传统的检测方式针对这种焊接方式不是特别的适用,因此需要一种新型的检测方式来对激光焊接的过程进行监测。激光散斑图像测量法(LSP:Laser speckle photometry)是一种新型的、非接触、快速的光学无损检测方法。它的原理是通过观察和分析热能传过物体或应力拉伸时所引起的物体表面的动态散斑变化来对检测物体进行监测。当热能在传播中或应力拉伸过程中,物体的表面会由于原子细微的变化产生一个肉眼不可见的微小变化,这是由于物体各个局部不同程度的热/机械膨胀引起的。这个微小的变化会使得激光散斑在时间轴上发生变化,也可以说激光散斑的动态变化受到热/机械膨胀的影响。通常情况下这个微小的变化是有规律可循的,但是如果在待检样本的近表面有缺陷,那么这个变化将会无规律,这种无规律的现象是由于缺陷使得样本在局部有着不同于其他地方的热/机械扩张,因而导致了这种不同寻常的现象。在分析视频后,通过记录激光散斑的运动变化,缺陷可以被检出来。通过使用一种特殊的相关函数将散斑强度的变化和局部时间域的空间梯度进行连接,这是激光散斑图像测量法技术原理。在目前的工作中,我们的目标是通过激光散斑图像测量法对于在激光焊接过程中产生的缺陷进行检测。在本文中,第1章介绍了这项工作的目的。第2章介绍了与激光散斑图像测量法及相关技术的发展现状,重点介绍了激光散斑和激光散斑图像测量法的原理。第3章中阐明了当前工作的目标和范围。第4、5、6章对整个实验过程进行详细的描述,给出了实验结果,得到了实验结果,最后对实验的结果进行了分析。本文提出了针对激光焊接检测的新方法,将激光散斑图像测量法与多重激光焊接技术进行结合,通过理论的论证,在大量实验后,证明了检测方法的可行性,将激光散斑图像测量法应用到了新的领域。改进了激光散斑图像测量法的算法,把激光散斑图像测量法从静态测量引到动态测量,通过实验证明了新算法的可行性,从旧算法的不能检测到新算法的可以检测。在目前的研究阶段,通过大量的实验,对整个实验装置进行调整,对实验数据进行分析,证明了激光散斑图像测量法可以对激光焊接的过程进行监测,同时对缺陷进行识别与检测。目前可以通过激光散斑图像测量法可以识别出焊接过程中产生的缺乏融合缺陷和细孔缺陷。
[Abstract]:In the process of laser welding, defects such as incomplete welding, pores, cracks and so on will be produced. If these defects are not detected out, they will have a great impact, so it is necessary to detect the defects of the welding narrow seam. However, the traditional detection method is not especially suitable for this kind of welding, so a new type of detection method is needed to monitor the process of laser welding. Laser Speckle Image Measurement (LSP: laser speckle photometry) is a new, non-contact, fast optical nondestructive testing method. Its principle is to monitor the detected object by observing and analyzing the dynamic speckle changes on the surface of the object caused by the heat energy passing through the object or when the stress is stretched. When the heat energy is propagating or the stress is being stretched, the surface of the object will have a small invisible change due to the subtle change of the atom, which is caused by the different degrees of thermal / mechanical expansion of the body. This slight change will cause the laser speckle to change on the time axis, and it can be said that the dynamic change of laser speckle is affected by thermal / mechanical expansion. Normally, this small change is regular, but if there is a defect in the near surface of the sample to be tested, then the change will be irregular. This irregular phenomenon is due to the fact that the defect causes the local thermal / mechanical expansion of the sample to be different from that of other places, which leads to this unusual phenomenon. After analyzing the video, the defects can be detected by recording the motion changes of laser speckle. The change of speckle intensity is connected with the spatial gradient of local time domain by using a special correlation function, which is the principle of laser speckle image measurement. In the present work, we aim to detect the defects in laser welding by laser speckle image measurement. In this paper, chapter 1 introduces the purpose of this work. In chapter 2, the development of laser speckle image measurement and its related techniques are introduced, and the principle of laser speckle and laser speckle image measurement is emphasized. Chapter 3 describes the objectives and scope of the current work. In chapter 4, chapter 5, the whole experiment process is described in detail, the experimental results are given, and the experimental results are obtained. Finally, the experimental results are analyzed. In this paper, a new method of laser welding detection is proposed. The laser speckle image measurement method is combined with the multiple laser welding technology. The feasibility of the detection method is proved by a large number of experiments. Laser speckle image measurement is applied to a new field. The algorithm of laser speckle image measurement is improved and the laser speckle image measurement method is introduced from static measurement to dynamic measurement. The feasibility of the new algorithm is proved by experiments, and the new algorithm can be detected from the old algorithm. In the current research stage, through a large number of experiments, the whole experimental device is adjusted and the experimental data are analyzed. It is proved that the laser speckle image measurement method can monitor the process of laser welding. At the same time, the defects are identified and detected. At present, laser speckle image measurement method can be used to identify the defect of fusion and fine hole produced in welding process.
【学位授予单位】：西南交通大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TG441.7;TP391.41

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