APPLICATION FOCUS: PROCESS MONITORING COHERENT FEATURED PRODUCT
ExactWeld from Coherent ExactWeld is based on Coherent’s Global Tools Platform and is a turnkey solution for automated, precision laser welding of metal parts. It includes the latest CW or pulsed fibre laser technology with diverse fixed or scanner optics. The high-end version of ExactWeld comes with a granite set up motion module with up to five axes, user friendly software, part clamping, an optional vision system, factory automation capabilities (Industry 4.0/IIoT ready) and reliable process control units. These features combine to maximise weld quality, and
Figure 2: Plasma, laser back reflection and acoustic sensors all show that a rapidly scanned laser welding process was interrupted by the presence of surface contamination
that must be assessed include laser operation, weld geometry, weld metallurgical characteristics, assist gas flow and material surface characteristics (contamination, scratches, etc.). All of these are somewhat interrelated. Laser operation is measured
with tools such as laser power and energy meters, and beam diagnostic cameras. These can measure and flag changes in the laser output itself, drops in delivered laser power (perhaps due to spatter on a protective window), and
“Online process monitoring saves time and money by increasing yields, improving quality, and reducing scrap and rework”
changes in delivered laser power density caused by focal position changes. But, these measurements are only accurately performed off-line, that is, in between process operations. Weld geometry
measurements include seam width and position, and especially a determination of whether the weld has wandered off-seam. Seam gaps or a lack of fusion must also be identified. Additionally, humping, undercut or other undesirable seam properties should be recognised. Measurement of weld depth is also critical. In terms of weld
characteristics, cracks and porosity are key parameters. Other weld quality issues, such as spatter or cosmetic changes (discoloration, etc.), are frequently important as well. There are several diagnostic tools in use for assessing all
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increase production yields, process consistency and operator productivity. ExactWeld is an attractive choice for medical device manufacturing such as endoscope production, as well as the fabrication of precision sensors, jewelry, watch parts and automotive electronics. ExactWeld also incorporates the innovative Coherent
SmartWeld and SmartWeld+ technology for producing complex ‘beam wobble’ patterns, including circular and zigzag paths. This enables bridging of larger gaps, which relaxes tolerances, increases process flexibility, and delivers welds with higher quality and reproducibility. Process monitoring and part control features are key future additions to the ExactWeld platform in order to offer system solutions with maximum customer benefit regarding process quality and yield.
More information:
www.coherent.com/machines-systems/laser-welding/exactweld
these factors. Various camera and machine vision systems are employed for monitoring weld joint and bead geometry, as well as performing seam tracking and checking gap size. Measurements of plasma emissions in the visible spectrum are well-established as a good way to sense weld quality, and can provide an immediate indication if there are problems with the laser focus or shield gas. Problems with weld penetration and the presence of defects also show up in the plasma signature. The back reflection of the infrared light spectrum is
another sensitive indicator of weld pool conditions, particularly its turbulence and temperature. Process temperature is also measured directly using a pyrometer or infrared camera. These sense the thermal (infrared) emission of the melt pool, and are typically monitored at a wavelength much longer than the laser emission wavelength. Temperature measurements provide a particularly sensitive indicator of process conditions, and provide information on penetration depth, surface quality and gaps. Finally, acoustic sensing is a
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Coherent
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