A sectional weld micrograph with ICI penetration depth measurements
most common fixed-optic and some scanning-optic heads. ICI makes a time-of-flight measurement with a secondary low- power laser beam, which is immune to blinding by the intense light radiating from the process. This beam is delivered through the same optics as the welding laser, allowing ICI to make direct measurements of the bottom surface of the vapor channel opened by the process laser. This translates into a direct weld penetration measurement. The information produced is similar to the outputs from destructive analysis. Since the measurement occurs during the weld, ICI can be used for automated pass/fail, or even to control the laser power in real time to reach a target depth.
ICI also functions as a leading and trailing in-process measurement. Using a small pair of scanners on the head, the ICI beam can be moved to other regions of the workpiece. This allows collection of seam position and workpiece height data ahead of the welding beam, and imaging of the finished seam surface immediately behind the melt pool. All of these measurements are taken through the head optics, within a few millimeters of the process beam. This suite of quality checks can be performed by a single instrument, by rapidly switching between measurement positions during the weld. The end result is automated pass/fail on any combination of seam position, material height, keyhole depth and finished weld surface, as well as the option to run closed-loop control of laser power and robot motion using the former three measurements. ICI technology provides the most complete automated laser weld monitoring solution to date.
Significant time and cost savings can be realized with advanced in-process sensing. The latest generation of monitoring technology eliminates the need for some downstream tests. The quality assurance for a given weld can often be worked into the existing cycle time. Scrap rates can be cut down through dramatic reduction of destructive tests. Inspection of
18 LIATODAY FOCUS: SCIENCE & RESEARCH SEPTEMBER/OCTOBER 2016
100 percent of production welds means entire batches don’t have to fail when defects are discovered, and the direct nature of latest-generation process measurements lowers the theoretical likelihood of false positives when compared with indirect approaches.
ICI can be used to monitor multiple aspects of the laser weld process at the same time
The ability to keep a complete, accurate record of production parts is allowing manufacturers to change how they approach quality assurance. It’s now possible to think weld-by-weld instead of batch-by-batch, with unprecedented confidence in the quality of the finished product.
Chris Galbraith is the Applications Specialist and Paul Webster is CTO at Laser Depth Dynamics Inc.
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