Characterization of monitor for laser welding.

摘要

This patent-pending robust on-line weld process monitor developed by Argonne National Laboratory is capable of non-intrusively sensing weld surface changes, weld penetration, occurrence of weld spatter, direction of motion of workpiece relative to cover gas flow, and presence of surface impurities like oil on the workpiece. The development of the weld monitor took into account the constraints and operating environment of the factory floor in addition to monitoring needs for quality assurance. The non-intrusive weld monitor is rugged and simple to use, does not require power to operate, is weld spatter protected and low cost. This process monitor is available as a stand-alone monitor with laser pointing suitable as an inexpensive addition to an existing processing system. For constrained configurations, the monitor can be easily integrated into an existing optic module resulting in through-the-optic viewing. The stand-alone monitor's flexibility is suitable for test and evaluation or research and development applications where flexibility in pointing or change in optics is required. A photograph of the monitor is shown in Figure 1. The reproducibility of the monitor's signal output will depend on the accuracy and repeatability in aiming. Laser aiming that comes with the monitor offers the best overall accuracy and ease. Costs can be reduced further with conventional gunsights with loss in accuracy and ease. The reproducibility of the monitor's output will depend on the field of view, the aiming method and the capability to manually aim and lock in position. In practice, even with laser aiming, the accuracy will be compromised by the mechanical system used to allow for aiming adjustments. 10 to 20% changes may be result from using a flexible connector. Improved reproducibility can be obtained at the expense of time taken to aim accurately. The integrated version of the monitor is recommended for process operations. This integrated monitor is available as an option on Spawr Industries reflective optics for high power laser beams or as a modification to the user's beam delivery optics. The advantage of the integrated design is that the monitor is pre-aimed and does not suffer from bumping and space constraints. Excellent reproducibility of the data can then be obtained. Both versions of the monitor are supplied with a BNC connector for detecting the voltage output of the sensor. The standard sensor is optimized for the monitoring of ferrous or steel alloys and other metals that have similar properties. Sensitivity to changes in penetration of < 0.05 mm can be expected. Monitoring of aluminum alloys will require a different sensor that is available as an option. A gas connection is also supplied for the clean gas purge to maintain the cleanliness of the window of the sensor. The gas (air or nitrogen) supplied should be oil and particle free to prevent fogging of the detector window.