This PDF file contains the front matter associated with SPIE Proceedings Volume 10911, including the Title Page, Copyright information, Table of Contents, Author and Conference Committee lists.

Underwater laser ablation with nanoseconds lasers generates high-pressure plasma exceeding GPa, and can be used as a hammer to forge the surface of most metals. This technology is known as laser peening (LP) and has been used in aeronautical and nuclear industries since the late 1990s. Most recently, we have developed a novel LP process without water by using a femtosecond laser, which extends the application to integrated systems with mechanics and electronics incompatible with aqueous environment, and even to components in space. Various applications would be realized by enhancing usability through miniaturization and simplification. In this context, we have developed ultra-compact handheld microchip lasers with passive Q-switch generating sub-nanosecond pulses, which paves the way to a wide range of new applications beyond the horizons posed by current laser systems.

Ultrafast lasers are the ideal tool for a wide range of applications in materials processing. Especially the modification of surfaces of any kind of material like glass, metal and plastics will have huge impact on many high-tech products. Surface structuring is used to generate specific surface properties and as the processes are different and a wide variety of scanning solutions form Galvo with diffractive elements up to polygonscanners are used to distribute the energy onto the surface, the ideal laser source allows to address a broad parameter range. InnoSlab amplification technology is the ideal candidate for that as it is shown in this paper.

We investigate the influence of different laser parameters on Grain-Oriented electrical silicon steels (GO SiFe). The advanced use of ultra-short laser pulses for scribing steel sheets with magnetic domains refinement and loss reduction purpose is proposed. The GO steel samples are commercial ones, commonly used in transformer cores. We compare laser impact on domains refinement obtained by thermal effects (with CW and long laser pulses), with thermal-free ablation produced by an ultrashort source. The laser scribing conditions (power or pulse energy, speed and pattern geometry, size and orientation) are optimized to have minimal deformation on material surface, while maximizing the influence and benefits on the magnetic properties. The steels used for these experiments have got one fixed composition (Silicon Iron alloy with 3% Silicon), the sheets used have got one thickness of 0.23 mm, very big grains size around 3 mm in average and one preferred lamination direction. The effects of the laser on steel samples are studied with different techniques, in order to show the impact on the surface topography, the metal microstructure and on the scalar magnetic properties. The confocal microscopy is used to probe the surface topography. The MFM (Magnetic Force Microscopy) is used to analyze in detail the formation of magnetic domains in the vicinity of laser patterns at the nanoscopic scale. The MOKE microscopy (Magneto-Optic Kerr Effect) is used to get images of magnetic domains at the microscopic scale. The SST (Single Sheet Tester) and the Epstein frame are used to measure the static and dynamic behavior and the power losses with two or one directional flux at the macroscopic scale. The motivation is to find the best laser treatment and patterns to improve the scalar magnetic properties and to reduce the energy consumption of electrical devices made with this steel.

A novel conditioning routine of metallic bonded diamond grinding worms is reported. The competitive manufacturing time is realized by a combination of orthogonal and quasi-tangential laser processes. The introduced quasi-tangential process is only limited by the maximum available laser power of 100W at 10 ps and 800 kHz for roughing. Hence, a maximal ablation rate of 55mm³ min^-1 is reported and the accumulated ablation rate for conditioning is 3mm³ min^-1. Following, the manufacturing of grinding tools within a maximal geometric deviation of 40 μm is shown. The threaded tool is finished by a laser sharpening process exposing the bonded diamonds on the surface for increased cutting characteristics. Thermally induced phase transitions are assessed via Raman spectroscopy and reveal a negligible heat-affected zone.

A novel UV line beam system for large area processing is introduced. The linear beam concept dispenses with movable components such as scanner optics. By using a fixed line beam with ns pulse duration and combining it with a 150 W excimer laser as the beam source a system with optimum reproducibility of the resulting layer modification has been created. Depending on the application, the excimer laser beam can be redirected into a high-resolution mask ablation system with rectangular field geometry. This machine’s modular concept can be used for a wide range of materials and laser-processes, especially for large area applications. Two different laser-material processes, thermal ablation and optical modification, are presented demonstrating the variety of the possible functionality of the system.

Low-chromium ferritic stainless steel that is subjected to a second laser-induced thermal cycle is susceptible to intergranular corrosion. Precipitation of carbides and nitrides depletes the adjacent regions of chromium. For this material, despite its low carbon content of 0.007%, laser transformation hardening has achieved a considerable increase in hardness. For certain thermal conditions during overlapping of tracks the above precipitation mechanism can take place. Numerical modelling was applied to analyse the laser parameters that could be critical for precipitation to take place. The results are compared to experiments that were screened with a standardised test method. Avoiding susceptibility to intergranular corrosion when laser transformation hardening was shown to be difficult during a second thermal cycle of an overlapping pass that passes a critical though narrow temperature range. Based on this, measures to mitigate the susceptibility was introduced, in the form of heating the material above melting temperature. When melting the material, even during the first pass, corrosion behaviour changes. It is shown that the risk of corrosion can be avoided during subsequent passes. Different thermal cycles are analysed to find limits for avoiding susceptibility to intergranular corrosion. By laser treating and mapping the critical thermal cycles, the material can be used in a wider range of applications.

An adequate use of finite resources is one of the greatest challenges of our times. To address this, lightweight concepts based on continuously fiber reinforced composites (FRC) are already being adapted for the transportation industry, especially within the automotive and the aerospace sectors. In order to broaden the use of lightweight composite structures and components, suitable processing, monitoring and control techniques are required for a variety of materials, constituting a prerequisite for economic, flexible and automated high volume production. In this regard, photonic technologies can provide valuable solutions. In this presentation, the latest developments within the field of FRC laser machining are summarized. For the processing of large structures such as resin transfer molding parts, combinations of galvo scanners with robots or axis systems are of particular interest. For this purpose, both high brightness cw fiber lasers and pulsed systems are used. Within the repair chain for valuable FRC parts, pulsed UV and NIR lasers are used for the precise removal of fiber layers in order to generate a defined scarfing. For both applications, disintegration of the fiber matrix interconnection due to thermal impact has to be avoided. Thermoplastic composites are becoming increasingly important for many industrial applications. In contrast to thermoset systems, welding techniques are particularly applicable. In this context, laser welding is not limited to the joining of transparent-absorbing-combinations, as it is required for conventional laser transmission welding processes but can be extended to the welding of structural parts consisting of high-performance carbon fiber reinforcements.

The increasing output power and brilliance of continuous wave (cw) laser sources allows faster material processes but needs novel handling technologies, e.g. beam guiding systems. Current developments like polygon scanner are dissolving consisting restrictions. Finally, physical properties (e.g. primary thermal conduction and heat capacity) will be the remaining limitations for process speed. A brief study should give an outlook what might be possible in the foreseeable future in the field of high speed laser material processing when the above listed technical limitations have been overcome. Therefore, different samples (bulk material as well as layer systems) were mounted on a fast rotating cylinder and treated with a 30 kW (cw) fiber laser. The high circumferential speed of 120 m/s leds to a short beam-material interaction time for each point on the surface and the immense power can be dispersed. The applied laser spot diameter of ~0.2-0.4 mm results in an interaction time about 2-4 μs and an intensity about 10⁸ W/cm². Such parameters are usually known by pulsed laser systems and would be used to enable distinct surface modifications or even single-pulse ablation. The descript test setup should transfer these applications into continuous processes and eliminate losses otherwise caused by duty cycle. Thus it was possible to remove oxide layer or other resistant coatings with an output of several square meters per minute.

Due to the increasing electrification in the automotive industry, materials with a high mass-specific strength are in great demand. In this context, direct thermal joining is an innovative approach to join metals with plastics in the sense of lightweight construction. In order to increase the joint strength, a laser-based surface pretreatment is expedient. The processing with laser radiation generates an inhomogeneous temperature field in the metal, which causes thermal distortion. The deformation can significantly influence the process stability of the subsequent joining process or even prevent its successful execution. Therefore, the thermal distortion in pretreatment was analyzed in order to understand the process behavior and to guarantee excellent joining conditions. For the pretreatment of metal surfaces, infrared continuous wave laser radiation was used. In order to understand the impact of thermal distortion, the metal surface was structured varying the process parameters such as the laser power, the velocity of the laser focal spot, or the applied area energy. Additionally, the structured area size was analyzed. The deformation was analyzed comparing the shape of the metal sheets before and after the processing. Based on the investigations, strategies to reduce distortion were derived and experimentally investigated. Upon the results, it was possible to extract design recommendations for surface structuring using remote ablation cutting. One approach is an oscillating beam guidance which shows significant potential especially in the combination with a high processing velocity.

The demand for marking systems to create durable marks has led to a significant growth of lasers in manufacturing. Qswitched nanosecond pulsed solid state or fiber lasers are used for most of the marking applications today. Manufacturer of marking systems have pushed this growth by providing more powerful or more compact systems. We were able to reduce the overall size of the 3D laser marking head to approx. ½ cubic foot. This reduction in size was possible due to improved pump sources providing higher brightness, improved laser designs, improved electronic design and state of the art packaging technology. The size of approx. 1/2 cubic foot is the most compact full 3D marking system available. In addition, our new laser marking system based on a diode pumped solid state laser shows superior performance compared to laser marking systems based on fiber lasers of the same or even higher average power. We will show marking applications in terms of black engraving, annealing and high quality bitmap marking. Due to the optimized optical layout of the 3D marking system, it is possible to mark 3D shaped objects using the same laser parameters even with objects of different heights. We will present results of a 3D annealing application. Additionally, to achieve high productivity, the laser has to be integrated very easily into the production system in terms of mechanics, optics and software control.

In some applications of Laser Metal Deposition (LMD) the advantages of the utilization of wire instead of powder additives can be used. The use of a wire as a solid additive material eliminates major disadvantages of powder-based LMD processes, namely contamination of the process cell with metal powder, significant material losses during the process, health and safety issues as well as the impact of insufficient powder quality. A closed annularly shaped laser beam surrounding the wire is one of the distinguishing features of the discussed LMD processing head. The laser beam and wire are arranged coaxially to each other, with the wire being fed through the inside of an annularly shaped laser beam without any shadowing. The annularly shaped intensity profile leads to a significant improvement in wire-based LMD. Furthermore, in contrast to lateral wire feeding, two substantial technological advantages, namely the independence of the feed direction and the processing of complex 3D geometries can be identified. Since the angle of incidence on the wire and base material depends on the caustic of the annularly shaped laser beam, the focal length has a significant influence on the LMD process. The results of experiments with different focal lengths are discussed. Material samples from Inconel 718 are built and evaluated metallographically. With the help of a high-speed camera the varying process behavior in dependence of the focal length and laser beam quality is analyzed. Finally, an outlook towards future research will be given.

Laser materials processing, e.g. welding/ additive manufacturing with cw sources or surface modification with short and ultra-short pulsed lasers is a highly dynamic process, requiring a sensor with high temporal and spatial resolution for evaluating the result of the treatment. Especially in the context of Industry 4.0, digitalization and predictive maintenance reliable sensors get much more into focus. A major drawback of this photon-material interaction with respect to the acquisition of trustworthy measurement data from the interaction zone is the presence of intense process emissions and steep temperature gradients. Common devices used as sensors for process monitoring, like CMOS/IR cameras or photo diodes, help to get an idea of the resulting quality but the acquired data is always perturbed by hot vapor emerging from the workpiece surface. Sensors based on OCT/ low coherence interferometry are different to all the other technologies because the measurement is not affected by the process emissions and thus open new horizons in laser materials processing. The use of this method in laser applications has risen in the last years. Since its first appearance in 2008 [1], application examples were shown for laser cutting [2], selective laser melting [3], laser micro machining [4], laser drilling [5] and laser welding [6]. For the latter, a huge potential is foreseen [8].

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 and additive manufacturing, melt pool behavior is directly related to final part quality as instability can lead to pore formation and ejected spatter. In transition and keyhole mode welding of metals, the dynamic balance of forces working to open and close the resulting vapor cavity gives rise to melt pool surface oscillations at frequencies on the order of kHz. Existing process monitoring techniques, such as high-speed video, have been extremely useful to image melt pool boundaries, but are limited in their ability to quantifiably track oscillation amplitudes and monitor high-aspect ratio features. We exploit inline coherent imaging (a through-the-lens technique based on low coherence interferometry) to directly measure melt oscillations through the transition zone (from conduction to keyhole welding). An Yb:fiber laser is used to perform 10ms spot welds on 316 stainless steel with varying laser powers (120-630W). Morphology is measured in situ at a rate of 170kHz. Oscillations are observed starting at the onset of the transition zone (irradiance 0.63MW/cm²) with a frequency of 10.0 ± 0.3kHz. At higher power (keyhole mode, irradiance 1.8MW/cm²), the bottom of the keyhole oscillates with a frequency of 2.5 ± 0.5kHz around a maximum depth of 1mm. This trend agrees with analytic modelling dependent on melt surface tension, density and diameter, as well as complementary experiments that track total laser absorptance using an integrating sphere.

In Laser Material Deposition (LMD), the powder feed into the melt pool is of crucial importance. It has a decisive influence on powder efficiency, geometry and roughness of the layer generated and oxidation by the surrounding atmosphere. For this reason, there is a need to characterize the powder gas jet to ensure process quality. As a solution a machine integrated system was developed, that has the capability to document the particle density distribution. For standardized measurements and comparability of results the procedure is fully automated. In order to measure and capture the required parameters, the powder gas jet is illuminated by a laser line perpendicular to the powder gas stream and observed through the powder nozzle with a coaxially arranged camera. A high frame rate allows the individual powder particles to be captured in number and position. Through step-by-step movement along the powder gas stream, individual layers are recorded in order to reach the particle density distribution with corresponding algorithms. From this distribution, key figures, e.g. position and diameter of the powder focus, can be derived for certification of powder feed nozzles. This information allows the adjustment and wear state of a nozzle to be documented and the processes to be set-up reproducibly. Furthermore the system is used to study the parameters influencing the shape of the powder gas jet. This knowledge can be used for process development, nozzle development and for the production of components with high requirements upon quality.

Laser material processing machines ranging from all kind of applications for different materials face imperfections. Problems such as inhomogeneous raw and focused laser beam diameter and beam mode as well as disturbed caustic along the working area (especially of a flatbed machine) exist in most machines that use or do not use beam expanders. Beam expanders are optic assemblies that are used to collimate the naturally divergent laser beam in order to achieve a more or less parallel propagating beam. Commercially available beam expanders which are supposed to play significant role in maintaining close to perfect beam diameter along the working area quite often do not perform as they are expected, mainly because of misalignment and weak design. Parameters such as beam expander distance from laser beam source, dimensions between the optical components of a beam expander, the tilts and shifts of the beam expander optics should be optimized. A 12m extendible laser testing bench equipped with an in-line raw beam profiler, twin hexapod operated beam expander, in-focus caustic beam profiler and a beam dump are used to adjust the mentioned parameters and observe the changes on the distorted beam. A software controlling the motorized bench is used to change the chosen parameters and display the results. The results will yield an optimization of caustic shape through standard calculation of beam parameters. This unique equipment enable us to optimize CO₂ or fiber laser beams used for the aforementioned applications in relatively short times in comparison to a previously hand operated optic adjustments. Improvements and benefits achieved such as close to perfect material cuts along the working area of a machine are evaluated using CLSM/SEM.

Since the mid-1960s when Kumar Patel invented the 9-10μm CO₂ laser and the 5μm CO laser, the CO₂ laser has experienced tremendous commercial success, while the CO laser has essentially played no role. Until recently, reliable, cost effective, room temperature, long sealed-off lifetime CO laser sources didn’t exist. With the product release of Coherent’s CO laser family, CO lasers are now commercially available with similar performance to CO₂ lasers. Because certain materials have different absorption coefficients at 5μm and 9-10μm, there is a light-material interaction that is wavelength dependent. In addition, the 5μm beam can be focused to a tighter spot size and for the same spot size, it has a longer depth of focus than at 10μm. This finds relevance in the processing of glass and ceramics where 10μm radiation is absorbed near the surface, but 5μm radiation is deposited into the bulk material and does not rely solely on diffusion from the surface. Leveraging this difference, Coherent and other organizations have conducted experiments comparing CO₂ and CO laser processing of glasses and ceramics. Results show that the CO laser provides processing and performance advantages in this important materials processing market. In this paper, we present the performance characteristics of commercially available CO lasers compared to the equivalent CO₂ laser. Application test results include: straight and curved cutting of various glasses, hole drilling, ceramic scribing, and the emerging area of 3-D glass printing. Both successes and remaining challenges are discussed.

In the aviation industry, a major market for carbon fibre reinforced plastics (CFRP), <40.000 drilling operations are performed throughout the assembly process of a small aircraft. Additionally, the drive to minimize costs and time are prevalent in the manufacturing process. The quality requirements in the aviation industry are set to a high level and drilling tools have to be changed frequently, causing considerable costs in terms of tooling and time losses. Laser processing offers benefits such as flexible, and wear free cutting, which contributes to the optimization of processing costs. In this investigation a laser machine, process control, processing strategies and handling equipment adapted to high precision macro drilling and low cycle times were presented. The setup included a novel short pulsed high power laser source by TRUMPF Laser GmbH emitting at λ = 1030 nm integrated in a 5-axis machine. The lab-state laser source provides pulses at t_p = 20 ns, at a maximum pulse energy of E_p = 100 mJ and a maximum average power of P_avg = 1.5 kW, while maintaining a very good beam quality, allowing small focus diameters. Due to a large variety of parameters that have an influence on the process, a test plan based on design of experiments was applied to identify ideal parameter fields. Parameters optimized towards high ablation rates and orthogonal kerf angles were identified. The results revealed a promising industrial processing option for high quality macro boreholes.

Combustion chambers of helicopter engines experience high temperature during combustion of the kerosene spray. Improving the efficiency and reducing the NOx produced by these engines, requires to further increase the temperature within the combustion chamber. However the latter tackles the fusion of the used metallic alloys. Nowadays to sustain such high temperature, the combustion chamber is coated with refractory ceramics and it is drilled with thousands of holes through which compressed air is flowing. Lasers are largely used to drill the holes in the combustion chamber. However drilling sub-millimetric holes with a well-controlled profile in ceramic coated metal alloys with no defects (delamination, formation of cracks…) remains a difficult task. In this presentation, we will detail the technique we developed to drill holes in such ceramic coated combustion chamber using sub-millisecond pulses delivered by high power fiber laser. This technique was made possible thanks to the numerical model we developed using COMSOL. By solving Maxwell’s equations this model account for the propagation of the laser beam within the hole during the drilling process. To test its validity, we drilled a series of holes in 800 µm thick cobalt alloy (KCN22W) coated with a 400 µm thick zirconium oxide (ZrO2) ceramic using an IPG Ytterbium fiber laser (YLS-1200-12000-QCW) and a Precitec drilling head (YK52). Experimental and numerical data are found to be in very good agreement. Moreover, Raman measurements indicate the ceramic alloy is not affected by this drilling process. Further improvements of this technique will be discussed.

The performance of a scalable, compact, Q-Switched CO₂ laser system operating at λ= 9.3μm that is capable of producing over 100 Watts of average power, sub-microsecond pulses with peak powers greater than 10kW and repetition rates as high as 200 kHz is described along with critical design details.

The performance achievable in laser material processing depends not only on the optical power of the source but also on the quality (for example in terms of the beam-parameter-product) of the beam incident on the workpiece. Therefore, to optimize the production yield, flexible laser machines must have the possibility to change the beam quality depending on the specific process in which they are used. A typical example is sheet metal cutting with fiber lasers, as thin and thick sheets require two different beam quality values. The paper reports on a new device that allows continuously and dynamically changing the beam quality of laser beams in the kilowatt range to optimize the performance of laser cutting of sheet metals of different thicknesses. When the device is used with 100 μm input and output fibers, the beam parameter product can be tuned from about 4 mm⋅mrad to 7.5 mm⋅mrad with coupling efficiency always larger than 95%. An even broader beam parameter product range up to 9 mm⋅mrad can be achieved when using 50 μm input and 100 μm output fibers, respectively.

We propose an optical fiber scanner suitable for high-power industrial laser marking systems. The proposed optical scanner enables beam scanning by resonating the optical fiber end with an electric actuator. As our optical scanner is extremely compact and lightweight, high-speed operation can be expected compared with the conventional galvanometer-type optical scanner. In this paper, novel monitoring and compensation techniques of the beam scanning path utilizing a position-sensitive detector in order to compensate for the manufacturing errors of optical fiber scanners are discussed. We demonstrate that the beam can be scanned linearly at a resonance frequency of about 10 kHz by appropriately controlling the amplitude and phase difference of the applied voltage.

Today, fiber reinforced materials are present in a wide field of industrial applications. Short glass fiber reinforced composites are mainly used in automotive, aerospace and medical sectors. In recent years, endless fiber reinforced thermoplastics have gained importance as construction material, especially for lightweight assembly. There are different methods of joining thermoplastic materials such as vibration, resistance and induction welding. Another process is laser transmission welding, which can be characterized by its excellent reproducibility, high flexibility and potential for automation. Typically, laser transmission welding can be applied for joining unreinforced or glass fiber reinforced thermoplastic parts. This welding process was now adapted to heat conduction welding for joining thermoplastic CFRP to itself. The goal of these investigations was to determine the influence of the matrix material on the weld seam quality. The experiments were conducted with a carbon fiber fabric reinforced polyphenylene sulfide with natural matrix material as well as containing carbon black. In the first step, the temperature distribution at the upper joining member, where the heat generation occurred, was evaluated. The heat affected width was determined and correlated to the process temperatures in order to develop a process model. In a next step, lap shear samples were welded and tested. These results were then correlated with previous results.

We present application results of welding copper with multi-kW truly continuous-wave Disk Lasers at the green wavelength of 515 nm. By spatially combining three commercially available 1 kW TruDisk 1020 lasers, 3 kW of green cw laser radiation is provided by a fiber with 200 μm core diameter. We achieved the following highlights by applying this laser source to copper sheets of different thicknesses: Sputter-free full penetration welding of 0.7 mm thickness has been demonstrated with excellent quality and a feed rate of 25 m/min, much faster than comparable IR wobble processes. In deep penetration welding mode, high-quality welds with depths of 1 mm and 2 mm have been obtained with feed rates of 18 m/min and 8 m/min, respectively, even in thick copper sheets, i.e., at maximum heat dissipation. 3 kW of green cw radiation allow welding depths <3.5 mm. Having proven the large potential of multi-kW green cw lasers, we give an overview on the current lab results on the power scaling of the disk laser sources. We demonstrate <2 kW green cw power with a BPP of 2.5 mm·mrad, as well as <3 kW green cw power with a BPP of 5 mm·mrad, both devices being realized with a compact footprint of less than 1 m². Summarizing, our application results prove the high-power green cw disk lasers to be the perfect choice for high-performance welding of copper with an excellent quality.

Spatter formation is a major issue in deep penetration welding with solid state lasers at high welding speeds from 8 up to 20 m/min. One approach to describe spatter formation is based on the assumption of an unstable keyhole. This leads to a temporary constriction of the keyhole due to the melt pool whereby the keyhole pressure increases. Finally, the keyhole collapses and spattering occurs. Therefore, the stabilization of the capillary is a possible way to limit spatter formation. For this purpose, several potential solutions have been tested in the past. However, investigations regarding a precisely local adjustable shielding gas flow on the keyhole stability under the condition of high welding speeds (≥ 8 m/min) is not given in the state of the art yet. To investigate these interactions, a shielding gas supply was developed, which can be adjusted in four axes with a reproducibility of 0.02 mm. Furthermore, the assembly was provided with a coaxial alignment laser for determining the interaction region of the gas. Under the processing of stainless steel (1.4301), different flow rates of argon, helium and nitrogen were tested. Additionally, Schlieren videography was used to visualize the gas flow. The spatial orientation has been varied in angles from 20° up to 48°. The experiments were recorded by means of HV-camera and subsequently analyzed by image processing (number, velocity and trajectory of spatters). Thereby, it was possible to reduce spattering by up to 91 % at welding speeds of up to 16 m/min.

This paper investigates laser welding of AA 6082 by superimposing a pulsed Nd:YAG laser with a continuous wave diode laser in order to reduce the hot-cracking susceptibility. Conventional pulsed laser welds exhibit severe solidification cracking on the application of a conventional rectangular laser pulse shape. Through the superposition of a Nd:YAG and diode laser beam crack-free welds can be realized without the use of an additional filler material in the case of sheet thickness of 0.5 mm. The diode laser beam simultaneously heats the base metal and weld metal during the melt-pool solidification and compensates solidification shrinkage and thermal contraction. Furthermore, the superimposed diode laser reduces the cooling rate during the melt-pool solidification. Hot-cracking can be eliminated by using an additional diode laser with a low output power of approximately 300W. A major impact of the diode laser superposition on the hot-crack suppression is expected to be achieved by reducing the solidification rate during the melt-pool solidification. These thermal changes result in coarser microstructure and therefore enable the easier feeding of liquid into the interdendritic cavities.

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.

Recently along with the advancement of EV shift in the automobile industry and the advancement of lithium ion batteries accompanying the advancement of mobile devices, expectations for laser welding of pure copper are increasing. In the laser welding, although a fiber laser, disk laser and direct diode laser with the wavelength of near infrared ray (IR) are generally, employed, it is difficult for pure copper to weld because of its low light absorption rate to copper. Thus, we have developed a high brightness blue diode laser system with absorption rate about 6 times that of IR laser, and demonstrated for it possible to form a weld bead of pure copper. The intensity of 1.3 × 10⁶ W/cm² on the substrate was easily obtained at the output power of 100 W and the laser spot diameter of 100 μm. In this study, the copper micro bead formation was investigated with respect to the height, penetration depth and contact angle to the substrate by in situ high speed x ray imaging in order to analysis the fusion bonding. As the results, it was found that the bead thickness was depended on the contact angle to the substrate while the laser irradiation. The interfaces between a pure copper and substrate were joined well without cracks or pores.