KEYWORDS: Beam shaping, Laser welding, Copper, Optical coherence tomography, Laser applications, Solid state lasers, Aluminum, Energy efficiency, Disk lasers, High power lasers
Recently, a new laser welding technology called BrightLine Weld has been introduced by TRUMPF. It is based on applying a TruDisk thin-disk solid-state laser with a so called two-in-one fiber delivery optical cable. In combination with a novel system of variable laser power coupling into the inner as well as the outer fiber core, an application-tailored laser power distribution is created. This enables a new degree of freedom through beam shaping for laser keyhole welding. The process benefits are significantly higher achievable feed rates during welding, minimal spatter formation and highest weld seam qualities. This paper presents latest results on welding of steel, aluminum and highly reflective materials such as copper using BrightLine Weld. The welding of gear parts has been performed exploiting the full feed rate performance with highly alloyed steels. Endurance strength tests show that the weld seam characteristics of these novel high-speed welds fulfill state-of-the-art requirements. We also report on results in weld penetration depth monitoring, applying optical coherence topography (OCT) to copper welding samples. Due to the keyhole stabilization in a wide range of feed rates and their respective penetration depths, the keyhole depth monitoring becomes widely applicable and supports the process especially in terms of reliability. Furthermore, an outlook on full penetration welding of tubes and profiles will be given. We will show first application results demonstrating the impact of BrightLine Weld on spatter prevention both on the top and on the bottom side of the weld seam.
Scanning optical coherence topography (OCT) is a 3D imaging technique based on low-coherence interferometry. In recent days, it became a key technology in laser processing. The OCT probe beam is coupled co-axially to the laser beam into the processing optics and provides depth information of the probe. Additional information is obtained when the OCT beam is deflected using a small field scanner attached to the processing optics. This report will present manifold applications for OCT process control, ranging from monitoring the weld depth during the welding process, tracking joints in laser remote fillet welding, or localizing the position of pins in three dimensions for precise positioning of the laser beam.
In laser welding applications optical coherence tomography (OCT) is used to measure the capillary depth for process monitoring and process control. A controlled constant weld depth is expected to run applications closer to their process limits and reduce the number of destructive sample inspections. An essential premise is a reliable weld depth measurement independent from influencing factors. This work analyzes the influence of laser power, beam diameter, feed rate, and work piece material on the weld depth measured using the OCT technology. The results obtained by using fixed laser optics are compared to the corresponding results from scanner optics.
High strength metal alloys and ceramics offer a huge potential for increased efficiency (e. g. in engine components for aerospace or components for gas turbines). However, mass application is still hampered by cost- and time-consuming end-machining due to long processing times and high tool wear. Laser-induced heating shortly before machining can reduce the material strength and improve machinability significantly. The Fraunhofer IPT has developed and successfully realized a new approach for laser-assisted milling with spindle and tool integrated, co-rotating optics. The novel optical system inside the tool consists of one deflection prism to position the laser spot in front of the cutting insert and one focusing lens. Using a fiber laser with high beam quality the laser spot diameter can be precisely adjusted to the chip size. A high dynamic adaption of the laser power signal according to the engagement condition of the cutting tool was realized in order not to irradiate already machined work piece material. During the tool engagement the laser power is controlled in proportion to the current material removal rate, which has to be calculated continuously. The needed geometric values are generated by a CAD/CAM program and converted into a laser power signal by a real-time controller. The developed milling tool with integrated optics and the algorithm for laser power control enable a multi-axis laser-assisted machining of complex parts.
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