ANALYSIS: WELD MONITORING
ADVANCING NEXT-GENERATION WELD MONITORING
Paul Webster and Chris Galbraith, of IPG Photonics, report on the development of a new inline weld monitoring system based on technology from Laser Depth Dynamics
A
s fibre lasers continue to enable faster and higher-quality welding applications for increasingly sophisticated part designs, manufacturers are pushing for more
complete data regarding weld quality in order to maximise the performance and efficiency from their joining processes. Today’s laser welds commonly include complex geometries or mixed materials. Processing speed and adoption of new applications are increasing quickly as the cost per kilowatt of laser power steadily declines. As these factors place increased demand on traditional quality assurance approaches, such as destructive testing, manufacturers require more advanced monitoring solutions to maximise productivity. Te accurate measurement of laser welding
processes is not an easy task, laser welds produce intense light and heat, which blinds traditional cameras without specialised filtering and illumination. Additionally, important aspects of the laser weld process take place deep beneath the surface of the material, making the complete picture difficult to see. Tere are many process parameters that affect weld quality, and until recently several different types of quality sensor had to be employed to keep an eye on different aspects of a single process. Tis leſt manufacturers to cope with the bulk, expense and complexity of multiple tools pointed at the welding site, while in many cases still not providing enough certainty about the finished product. Te quality assurance holy grail for many
manufacturers in the aerospace, automotive and medical device sectors (among others) would be a single system that can monitor all relevant aspects of the welding process, with tight integration into the welding head, smart soſtware to consolidate results into concise and actionable quality information, and the ability to inspect every weld
14 LASER SYSTEMS EUROPE ISSUE 42 • SPRING 2019
The different monitoring modes of the new LDD system. Inline weld monitoring technology allows a single tool to perform multiple quality assurance tasks during welding
in a production environment. Recent technological advances bring us closer to this.
Seeing potential in start-ups IPG has developed a new inline weld monitoring system, based on technology originally developed by Laser Depth Dynamics – a Canadian start-up launched in 2012, acquired by IPG in late 2017 – that takes full advantage of these recent advances. Te potential of Laser Depth Dynamics’
technology was recognised early on by several industrial players, particularly in the automotive sector, who quickly began to adopt it for production use. Focusing on a single product allowed the company to grow rapidly, culminating in its acquisition by IPG Photonics. Freshly infused with new development resources, the new Canadian branch of IPG has been working with colleagues from our facilities in Massachusetts over the past year to develop the system – the LDD-700. Te new system uses inline coherent imaging
(ICI) to provide an increased level of detail and accuracy for laser weld monitoring. Te regions of interest for monitoring can be categorised into pre-, in-, and post-weld measurements. Te LDD-700 pre-weld monitoring modes include tracking of the seam position, checking the working distance to the material, and looking for incorrect gap or bad fit-up of the joint. In-weld monitoring records the penetration depth of the weld as it’s formed, and post-weld inspection measures properties such as the height of the finished weld surface, the width of the weld bead, or the presence of surface defects such as blowouts. To accomplish weld monitoring in multiple
regions surrounding the process, the system fires a low-power measurement beam through the same optics that deliver the welding laser. Tis beam rapidly switches between different measurement locations on the part, and is capable of recording a swath of metrics, including weld penetration depth, joint position, surface quality and more. By the time the weld step is finished, the system has
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