On-Line Monitoring of Weld Pool Depth with Laser Ultrasound

小行星9622277 当激光能量低于烧蚀水平时，脉冲激光产生是热弹性过程。激光在表面上沉积热量，引起局部膨胀和收缩，这反过来又导致超声应力波。研究人员已经成功地证明了这一原则，在之前的NSF资助的研究中使用相控阵激光器模拟焊接。相控阵列是现有技术中的新奇之处，其允许控制波束宽度、方向和聚焦以及发出的超声波的方向性，以及产生一种类型的波运动，例如表面（罗利）波、剪切波或纵波。在熔化的焊接池的检测中，可以通过使用液体的区别特征来利用最后一个特征，液体不像固体那样携带剪切波。 在目前的研究中，将采用电磁声换能器进行检测。在一个实际的气体保护金属极电弧焊工艺过程中的熔池深度将尝试通过排队的相控激光阵列和电磁声换能器后面的焊枪在一个可编程的自动焊接系统。为了充分了解焊接过程的自动化在线监测，将开发一个分析模型的阵列源，并结合已发表的工作，通过温度梯度的超声波传播的影响。 具有焊接专业知识的工业研究人员捐赠了一套自动化焊接设备系统，并承诺提供现场咨询。工业研究人员与学术人员和学生之间的这种密切的工作关系不仅将技术转移到商业部门，而且在相关的客户拉动制造项目中培训未来的工程师方面都是非常宝贵的。由于焊接过程中的环境非常恶劣（热气体包围的熔融金属飞溅），焊接自动化的当前状态仅限于作为后处理步骤通过监测焊接质量进行开放式控制。这项研究有可能使闭环控制，从而可以实现非常高的焊接质量。这样的制造工艺在焊接工业中在产品质量、返工减少以及因此降低工艺成本方面具有深远的影响。考虑到焊接广泛用于从造船到建筑的各种制造业，对国家基础设施的影响可能是巨大的。

9622277 Ume Pulsed laser generation is a thermoelastic process when the laser energy is below the ablation level. The laser deposits heat on the surface causing a local expansion and contraction which in turn results in ultrasonic stress waves. This principle has been successfully demonstrated by the investigators to simulated welds using phased array laser in a prior NSF funded research. Phased array was the novelty in the prior work which allowed for control of beam width, direction and focusing and the directionality of the emanating ultrasonic waves as well as generation of one type of wave motion, such as the surface (Raleigh) wave, shear wave, or longitudinal wave. In the detection of molten weld pool this last feature can be taken advantage by using the distinguishing feature of liquid, which can not carry shear waves unlike solids. In the current research, the detection will be carried out by electromagnetic acoustic transducer. Weld pool depth during an actual gas metal arc welding process will be attempted by lining up the phased laser array and electromagnetic acoustic transducer behind the welding torch in a programmable automated welding system. In order to understand the process sufficiently to automate the on-line monitoring of welding, an analytical model will be developed for array sources and combined with published work on effects of ultrasound propagation through temperature gradients. Industrial researchers with expertise in welding have come forward with the donation of an automated welding equipment system as well as shown a commitment to provide on-site consulting. This kind of close working relationship between industrial researchers and academic faculty and students should be invaluable not only transferring the technology to the commercial sector but also in training the future engineers in a relevant customer pull manufacturing project. Current state of automation in welding is limited to open control by monitoring the weld quality as a post-processing step bec ause of the very aggressive environment (splattering of molten metals surrounded by hot gases) during the welding process. This research has the potential to make possible closed loop control whereby a very high quality of the weld could be achieved. Such a manufacturing process has far reaching consequences in the welding industry in terms product quality, rework reduction and thus lower process cost. Considering that welding is used extensively in a wide variety of manufacturing from ship building to construction, the impact on the national infrastructure could be enormous.