We report on tool wear and surface roughness for hybrid additive manufacturing of Inconel 718 components. The hybrid additive manufacturing comprises laser powder bed fusion (PBF-LB/M) and an in situ high-speed milling process, i.e., milling is performed within the powderbed, which deteriorates the surface quality by additionally occurring wear mechanisms. Therefore, in this comparative study milling path suction is used to improve tool wear characteristics and thus enhance surface quality. As a result, we quantify the improvement of the maximum tool life according to the flank wear, which is granted by the milling path suction. Additionally, the dominant wear mechanisms are investigated, revealing adherence and abrasion as the main contributing factors to wear. Furthermore, surface analysis shows an improvement of surface quality by the use of the milling path suction. Specifically, a reduction in surface roughness of hybrid manufactured Inconel 718 components down to a minimum of Ra = 0.55 mu m is highlighted.

We report on a novel approach for the monitoring of tangential laser turning with ultrashort laser pulses. By using an ultra-sonic sensor consisting of a membrane-free optical microphone, the current state of the ablation process can be analyzed, potentially enabling a real-time automated regulation. With its high sensitivity, bandwidth, and sampling rate, it is an ideal tool for process monitoring. The material ablation caused by focused femtosecond laser pulses produces distinct sound waves, which can be detected by the optical microphone. The diameter reduction of a rotating cylindrical workpiece during the laser turning process with ultrashort laser pulses results in a variation in the acoustic emissions. From this, properties like the state of the machining progress can be inferred.

A hybrid laser based approach combining ultra-short pulsed laser micro structuring and CO2 laser based polishing has recently been demonstrated to generally meet the requirements of producing complex shaped optical components with the required surface roughness for optical applications. With respect to practical freeform optics, however, the delicate balance between shape accuracy and surface roughness remains a particular task for any free-form optic. We report on such a hybrid laser-based processing approach to realize an afore simulated complex optical geometry for LED-beam shaping with high precision and superior surface quality. To exemplify the function of the freeform optical element having a diameter of 1 inch, it has been developed to convert an initial divergent point source LED into a smiley-shaped profile. The freeform lens was calculated to create a smiley-shaped intensity distribution and is formed by precise 2.5D ultra-short pulsed laser ablation. The optical surface quality is realized by CO2 laser polishing. A particular focus of this contribution is given to a comparative study of the applied polishing laser energy input and polishing strategy with the overall objective to optimize the function of the optical element with respect to the simulated beam profile.

We report for the first time on the realization, comprehensive characterization and application of a 6-axis articulated laser robot using a flexible beam guidance of ultrashort laser pulses via a non-polarization-maintaining hollow-core fiber. Measurements during and after a movement of the fiber-based ultrashort pulsed laser robotic (USPLR) system reveal that fundamental beam characteristics such as transmission, beam pointing and diameter and pulse duration are only marginally affected after passing through the hollow-core fiber. In addition, we studied the application of the USPLR system to laser cutting of brass foils and a printed circuit board (PCB) substrate in a single-path mode and optimize the process with respect to the heat-affected zone and kerf width by varying the applied pulse energy and robot speed. Our findings reveal that heat accumulation plays a significant role for the cutting quality at slow robot speeds of up to 20 mm/s, whereas a reduction of the kerf width down to about 7 µm is feasible. Furthermore, detected vibrations of the USPLR system with varying magnitude at different 3D spatial cutting positions result in oddness of the cutting edges of up to about 200 µm. Nevertheless, optimized process parameters result in a high cutting quality with a small heat-affected zone and a virtually straight and sharp cutting edges in a large processing area of 500 mm × 600 mm × 300 mm, highlighting the substantial potential of the fiber-based USPLR system for flexible and large-area 2D and 3D micromachining.

The actin cytoskeleton in activated T cells undergoes rapid structural changes during the formation of an immunological synapse. Superresolution fluorescence microscopy provides excellent means to visualize such antibody-triggered changes. Here, we use single-molecule localization microscopy (SMLM) enabled by transparent polymer waveguide chips to resolve the filamentous-actin (F-actin) cytoskeleton in activated Jurkat T cells in comparison to nonactivated T cells across a large field of view. Transparent polymer waveguides enable a wide array of imaging modalities. In combination, these modalities reveal the structural differences between lamellipodial and ramified actin networks within the immunological synapse of activated T cells. SMLM images recorded by using narrow-width waveguide total internal reflection illumination resolve the double-stranded helical structure of actin filaments in activated Jurkat T cells. The average crossover length of the filaments is measured to be ~40 nanometers, which corroborates similar observations of isolated actin filaments by electron microscopy.

We report on a method for cutting ultra-thin glass using a novel ultrashort pulsed laser robot system. The systemconsists of a six-axis articulated industrial robot with an ultrashort pulsed laser integrated on the link after robotelbow, while mirrors are used for beam aligning and guiding, as well as a 2D galvanometer scanner and a F-Theta lensmounted on the last robot axis. Due to high flexibility, the system extends the processing scale of ultrashort pulsedlaser to a large scale in 2D, and even in 3D. Combining the movement of the galvanometer scanner and the robot axes,referred as hybrid movement, ultra-thin glass is able to be cut though with a variable cutting edge angle. Ultra-thinglass AF 32 eco is cut using robot movement alone and hybrid movement, with additional axis rotations about thelaser beam focus in two directions. Hybrid cutting is compatible with a wide range of rotation angles, achievingcutting edge angles from 89◦ to 120◦. The influence of cutting edge angles and cutting methods is further evaluatedusing residual stress measurements and three-point bending tests, revealing that the cutting method has a dominantimpact on cutting edge quality. To demonstrate the large scale cutting with defining cutting edge angle, a trapezoid iscut using the hybrid method with extra robot axis rotation, which achieves an average cutting edge angle of 91.9◦.

For the construction of lightweight components, lattice structures are frequently used in additive manufacturing, reducing material consumption, while simultaneously maintaining good mechanical properties. Besides triple-periodic and gyroid structures, double-periodic structures show good mechanical properties in orthogonal directions. Mechanical properties, especially the fatigue behaviour, of laser powder bed fusion (PBF-LB/M) built components are generally diminished by inferior surface quality. Combining PBF-LB/M and a 3-axis in-situ high-speed milling process, a promising hybrid approach is designed. Due to the alternating additive/subtractive build process, the in-situ milling of printed components allows machining of inlaying complex structures yielding an average surface roughness of R-a = 1 mu m, i.e. significantly better as compared to the sole PBF-LB/M-process. To evaluate the advantages of the hybrid manufacturing, we compare the mechanical properties of different lattice structures with different relative densities. In particular, we examine the compressive strength by static load and the fatigue behaviour and endurance limit by cyclic mechanical load. In addition, metallography and surface analysis are employed to substantiate the discussion of the mechanical properties. As a result, we find that the hybrid additive approach yields enhanced static and cyclic load behaviour, that can be assigned to the improved and superior surface quality of the hybrid manufactured components, which excludes sub-surface cracks and micro notches.

Copper(II)-oxide-based femtosecond reductive laser sintering is applied to selectively produce high quality and flexible copper electrodes on ultra-thin glass with thicknesses between 30 and 100 & micro;m. To increase the precursor wettability and the later copper adhesion, the ultra-thin glass substrates are plasma activated. An amplified near infrared femtosecond laser combined with a galvanometric scanner is used to produce two-dimensional copper layers. Different laser and process parameters such as scan speed, laser power and repetition rate are varied to generate these structures with unrestricted design. The metallization rate can be significantly increased by adjusting the repetition rate in a new holistic parameter variation approach. This acceleration is accomplished by increasing the heat accumulation at higher repetition rates to reach the precursor temperature required for chemical reduction and sintering more rapidly. The copper structures are analyzed by optical microscopy, scanning electron microscopy, energy dispersive X-ray spectroscopy and 4-tip resistance measurement, respectively. In an optimized process regime, low electrical sheet resistances down to 117 m Omega/sq are achieved. A hybrid approach combining reductive laser sintering using infrared and laser drilling using ultraviolet femtosecond laser radiation is demonstrated, to produce a functional electrical circuit by employing the fundamental wavelength and the third harmonic of the same laser system.

We report on a study of the mechanical properties of hybrid-additive manufactured Inconel 718 double-periodic lattice structures. For this, a hybrid approach, combining Laser Powder Bed Fusion (PBF-LB/M) and in-situ high-speed milling, is employed. Within this technique, the PBF-LB/M process is interrupted after several layers, as the milling process starts, enabling a machining of inlaying structures. As the surface quality is improved up to R_a = 0.8 µm, in turn, improving the mechanical properties, the static and dynamic behaviour of PBF-LB/M and hybrid built components is compared. Here, in particular, lattice structures, precisely double-periodic arranged hexagonal unit cells, are considered. To evaluate the periodic structures, the compression strength, Young’s modulus, as well as the endurance limit are determined, quantifying the effect of surface improvement by the hybrid approach. With an increase in compressive strength from 95.7 MPa to 142.7 MPa ( ≈ 50

Thermal post processing, such as stress relief, direct ageing or hot-isostatic pressing, are commonly used to alter the structural and mechanical properties of additive manufactured, 3D-printed metal parts. As an alternative approach, in this contribution, we report on combinations of long term deep cryogenic cooling at -196 degrees C of hybrid manufactured Inconel 718 specimen to improve the mechanical properties. Specifically, we compare the static and dynamic mechanical load properties as well as the hardness of as-built components and deep cryogenic treated parts. Additionally, the difference of sole laser powder bed fusion (PBF-LB/M) and hybrid manufactured components is investigated, the latter combining conventional PBF-LB/M and in-situ 3-axis high speed milling, which in turn excludes micro notches and subsurface cracks and improves the surface roughness down to about R-a < 1 mu m. Metallographic analysis is performed to visualize structural changes upon the cryogenic treatment. As a result, we identify microstructural changes, grain migration and closure of porosities upon cryogenic treatment, which lead to a higher ultimate tensile strength and to a significantly higher ability of plastic deformation. Furthermore, for the hybrid additive manufactured components we find enhanced mechanical properties, as the superior surface quality additionally raises the mechanical resistance, in particular the fatigue behaviour and the endurance limit, of the components. Ultimately, the combination of hybrid manufacturing and deep cryogenic cooling yields the best load behaviour.

We report on an evaluation of cutting edge ultra-thin glass processed by a novel ultrashort pulsed-laser robot system. The system consists of a six-axis articulated industrial robot with an ultrashort pulsed laser integrated on the link after the robot’s elbow. Mirrors are used for beam aligning and guiding, and a 2D galvanometer scanner and an F-Theta lens mounted on the last robot axis are used for material processing. Ultra-thin glass AF 32 eco is cut using robot motion only and combined scanner–robot motion, with additional axis rotations about the laser beam focusing in two directions. Hybrid cutting is compatible with a wide range of rotation angles, achieving cutting-edge angles from 88.9° to 119.7°. The influence of cutting-edge angles and cutting methods is further evaluated using residual stress measurements and three-point bending tests, revealing that the cutting method has a dominant impact on cutting-edge quality. To demonstrate the large-scale cutting with defining cutting-edge angles, a trapezoid is cut using the hybrid method with extra robot axis rotation, which achieves an average cutting-edge angle of 91.9°.

We report for the first time on the flexible and large-area 2D laser cutting of ultra-thin glass using an ultrashort pulsed laser robot (USPLR) system emitting at a wavelength of 1030 nm. To optimize the cutting quality of 100 & micro;m thick AF 32 eco ultra-thin glass substrate, experiments were performed with different laser pulse durations, laser pulse energies, laser pulse repetition rates and robot speeds. For the evaluation of the cutting quality, crack formation and induced stresses near the cutting edge were analyzed using imaging polarimetry and digital microscopy. At robot speeds of up to 40 mm/s, crack formation occurs at laser pulse durations greater than 1 ps. Using a laser pulse duration of 1 ps, laser pulse energies of up to 140 & micro;J and a laser pulse repetition rate of 200 kHz, complete cuts are produced in a wide processing window at robot speeds of 15 mm/s to 65 mm/s without crack formation. In addition, when using a laser pulse repetition rate of 400 kHz and a laser pulse energy of 80 & micro;J, the processing window is extremely enlarged due to heat accumulation effects. However, at the high robot speeds of up to 80 mm/s, unevenness and notching of the cutting edges are observed as a result of vibrations of the USPLR system during laser cutting, limiting the potential processing speed. An ultrathin glass component is produced with sharp and rounded cutting edges, demonstrating the high potential of the USPLR system for the flexible and large area 2D laser cutting applications in various industrial sectors.

Despite advances in manufacturing techniques, freeform optics continue to present significant challenges in their production due to their stringent requirements for 3D-precision and surface conditions. The combination of ultra-short pulsed (USP) laser, which enables high accurate processing with minor thermal influence, with a CO2 laser for a secondary thermal polishing step, resembles a promising flexible and fast hybrid laser machining approach. This study focuses on the implementation of a multistage process that utilizes a range of methods for the purpose of generating highly precise and deep-cut 2.5D structures in fused silica. The approach involves deep layer-by-layer USP laser ablation. A comparative study of the applied energy input suggests a two-step alignment process to precisely ablate selected ablation depth per pass. The transfer of predicted processing reproducibility to a deep ablation of multiple 100 mu m is optimized by a refocusing method. The capacity to fabricate deep and low-cut structures is evidenced by the demonstration of an Alvarez-like freeform shape.

Reductive laser sintering using a femtosecond laser and copper(II) oxide nanoparticle precursor is a flexible, vacuum-free and maskless technology for the selective metallization of a variety of materials. We use this technology to fabricate high-resolution micro heating structures on cycloolefin copolymer. The surface resistance is measured using a 4-point method and the morphology is characterized using microscope images. The investigation reveals that scan speeds ranging from 60 to 200 mm/s result in the production of homogeneous Cu surfaces, with surface resistances below 100 m Omega/sq. The optimum value of 66 m Omega/sq is achieved at 120 mm/s. Simple heating structures in the form of meander-shaped conductor tracks are produced. Furthermore, current-voltage characteristics are recorded to ascertain the current carrying capacity of the respective manufacturing parameters. The average temperature of the heating structures is determined and compared using a thermal imaging camera. The performance of the heaters is adjusted so that surface temperatures of over 100 degrees C can be achieved at metallization rates of 2.75 mm/s(2). This constitutes the fundamental basis for the utilization of this technology in prospective lab-on-chip applications.

We report on an automatic laser beam focus monitoring approach for an ultrashort pulsed laser robot system. The system integrates an ultrashort laser mounted on a link of a six-axis industrial articulated robot with a galvanometer scanner and an F-Theta lens mounted on the end of the last robot axis. This enables high precision micromachining using ultrashort pulsed laser over a large 3D processing area. A beam focus monitoring and adjustment method combining a distance sensor and cameras ensures consistent processing quality during extensive robot movement. A conventional beam focus monitoring algorithm based on image processing is compared with a deep learning-based method using YOLO object detection network, where a high accuracy is particularly observed using YOLO network-based method. In addition, the methods are implemented in the system and utilized for the beam focus monitoring for an ablation process of fused silica, with varying the processing surface orientations. Both methods demonstrate the capability for a correct beam focus detecting with surface orientations ranging from -30 degrees to 15 degrees, while maintaining the beam propagating axis parallel to the surface normal.

Ultra-short pulsed (USP) laser technology and its application in laser micro structuring is continuously driven by the availability of higher pulse energies and average laser powers as well as the provision of shorter laser pulses. The latter, in particular, may influences, e.g., the ablation threshold, unwanted thermal impacts, thus the overall quality of any ablation process and, more generally, the fundamental interaction mechanisms underlying the ablation process. Recent technological advancements have made it possible to externally compress the pulses and shorten the pulse duration of existing USP laser systems down to 50 fs in combination with high pulse frequency rates, allowing to foster micro machining processes. We present a comparative study of pulse duration-dependent influences on the quality (surface roughness), repeatability, and efficiency of ultra-short pulsed laser ablation focusing on 400 fs and 50 fs of fused silica using an external pulse compressor and characterize the properties of the compressed pulses.

Reductive laser sintering (RLS) is a novel metallization technology in which a precursor based on copper(II)oxide nanoparticles is used to create conductive copper by means of laser-triggered thermochemical reduction, without the need for costly masks or vacuum techniques. To date, RLS has primarily been used with lasers emitting near-infrared (NIR) radiation, as the precursor exhibits high absorption and Copper is not damaged by laser ablation due to its low absorption. In the present study, identical irradiation conditions are created on a laser machine with two processing stations between the fundamental NIR laser wavelength of 1030 nm and the green laser wavelength of 515 nm generated by a second harmonic module. The objective of this study is to examine the impact of laser wavelength on femtosecond RLS. At a repetition rate of 100 kHz, scan speeds of 10 to 250 mm/s are applied for both wavelengths. Optimal average power densities for homogeneous copper with high conductivities are identified. The surface resistances are determined for a variety of process parameters using 4-point measurements. The employment of a green laser offers two significant advantages. On the one hand, surface resistance of less than 100 mO/sq is achieved, which corresponds to a reduction of 33 % compared to NIR. Conversely, the scan speed can be enhanced, with a potential increase from 30 mm/s to 100 mm/s. The enhancement of this effect by an increase in the repetition rate enables scan speeds of 150 mm/s at maximum conductivity. The experimental findings are corroborated and substantiated by means of optical absorption measurements of the precursor and the copper layers, as well as by microscopic and spectroscopic measurement methods. The copper structures produced with the NIR laser are characterized by a lower copper content than those produced with green illumination.

We report on a hybrid cutting method of ultra-thin glass cutting using an ultrashort pulsed laser robot system. An ultrashort pulsed laser is fixed on the elongation of one axis of a six-axes articulated industrial robot. The laser beam is guided by mirrors along the robot axes into a 2D galvanometer scanner with a telecentric F-Theta lens, the latter being fixed on the last robot axis. The system due to its high flexibility expands ultrashort pulsed laser processing to a large-scale area micromachining toll with true three-dimension capabilities. Furthermore, the combined movement of scanner and robot, here specifically referred to as hybrid cutting movement, extends the system's overall processing abilities. In an experimental study of cutting ultra-thin glass D263, scanner speed as well as laser pulse duration are varied for a continuous robot movement speed at 20 mms-1. The quality of the ultra-thin glass cutting is evaluated in terms of minimal glass chipping and maximum flexural strength of the cut specimen. Applying a three-line scan trajectory, both quality aspects are found to be optimized for a pulse duration of 7 ps and the scan speed of 700 mms-1. To highlight the potential of this new hybrid and true 3D ultra-thin glass cutting, a rectangular is cut from a bent glass sample.

Incomplete cuts during laser fusion cutting result in a closed kerf, preventing the workpiece from detaching from the sheet and resulting in rework or rejection. We demonstrate the approach of a vision transformer, used for image classification, to detect cut interruption during laser fusion cutting in steel and aluminum. With events impending an incomplete cut in steel, we attempt to predict cut interruption before they even occur. To build a data set for training, cutting experiments are carried out with a 4 kW fiber laser, forcing incomplete cuts by varying the process parameters such as laser power and feed rate. The thermal radiation from the process zone during the cutting process is captured with a size of 256 × 256 px2 at sample rates of 20 × 103 fps. The kerf is recorded with a spectral sensitivity between 400 and 700 nm, without external illumination, which enables the melt to be observed in the range of the visual spectrum. The vision transformer model, which is used for image classification, splits the image into patches, linearly embedded with an added position embedding, and fed to a standard transformer encoder. For training the model, a set of images was labeled for the respective classes of a complete, incomplete, and impending incomplete cut. With the trained model, incomplete cuts in steel and aluminum can then be recognized and impending incomplete cuts in steel can be predicted in advance.