The increase in complex workpieces with changing geometries demands advanced control algorithms in order to achieve stable welding regimes. Usually, many experiments are required to identify and ...confirm the correct welding parameters. We present a method for controlling laser power in a remote laser welding system with a convolutional neural network (CNN) via a PID controller, based on optical triangulation feedback. AISI 304 metal sheets with a cumulative thickness of 1.5 mm were used. A total accuracy of 94% was achieved for CNN models on the test datasets. The rise time of the controller to achieve full penetration was less than 1.0 s from the start of welding. The Gradient-weighted Class Activation Mapping (Grad-CAM) method was used to further understand the decision making of the model. It was determined that the CNN focuses mainly on the area of the interaction zone and can act accordingly if this interaction zone changes in size. Based on additional testing, we proposed improvements to increase overall controller performance and response time by implementing a feed-forward approach at the beginning of welding.
Remote laser welding systems can usually focus a laser beam to diameters of 0.1 mm. Therefore, high quality clamping and precise teaching is needed in order to achieve appropriate process tolerance ...for a sound weld. This brings reservation in the field of small series and user-customized manufacturing, where product individualization requires flexible and adaptive systems as workpiece geometry is not exact due to manufacturing tolerances and thermal deformations during welding. The preparation for welding is therefore often time-consuming. To solve this, we have developed an innovative system, which enables in-line adaptive 3D seam tracking. The system consists of an industrial robot (Yaskawa MC2000), a scanning head (HighYag RLSK; working area 200 mm × 300 mm × 200 mm) with optical triangulation feedback and a fiber laser (IPG, YRL-400-AC; 400 W). A feed-forward loop was used to achieve positioning accuracy of under 0.05 mm during on-the-fly welding. Experimental results show that between welding speeds of 25 and 150 cm/min, average tracking deviations are 0.043 mm and 0.276 mm in
y
and
z
directions, respectively. Moreover, teaching times for a specified seam can be shortened for more than 10 times due to the fact that only rough seam teaching is required. The proposed system configuration could be adapted to other classical welding processes.
•Laser power is controlled via triangulation camera in a remote laser welding system.•Relationship between interaction zone's area and process parameters is discussed.•Stable partial penetration is ...achieved for investigated welding parameters.
Remote laser-welding systems are being used more frequently because of their larger working areas, shorter downtimes and ability to weld different seam types with high accuracy at greater speeds in comparison to conventional welding. Therefore, precise process-monitoring methods are needed in order to achieve weld traceability and good process and quality control to accompany different welding situations. This paper proposes the use of optical triangulation feedback on a remote laser-welding system that makes it possible to monitor a larger working area. This configuration means we can monitor the interaction zone itself, analyze the 3D position of the laser beam and key process estimators as a result of laser welding. AISI steel plates were welded in a lap configuration to show that stable partial penetration can be achieved. First, a dependency matrix was constructed for the different welding parameters (material thicknesses, welding speeds and laser powers) in order to describe the change of the weld's penetration depth with respect to the key estimators. An approximation was used to characterize the change of the weld's depth according to the change of the estimators. The experimental results demonstrate that the interaction zone's area can be used to successfully control the laser's power output in order to achieve a stable partial penetration with an error of less than 7 % of the desired target weld depth. Longitudinal macrographies show a significantly more constant weld penetration depth and laser-induced plume reduction during welding.
A method for amplification of high-intensity pressure waves generated with a multi-pulsed Nd:YAG laser coupled with a black-TiOx optoacoustic lens in the water is presented and characterized. The ...investigation was focused on determining how the multi-pulsed laser excitation with delays between 50 µs and 400 µs influences the dynamics of the bubbles formed by a laser-induced breakdown on the upper surface of the lens, the acoustic cavitation in the focal region of the lens, and the high-intensity pressure waves generation. A needle hydrophone and a high-speed camera were used to analyze the spatial distribution and time-dependent development of the above-mentioned phenomena. Our results show how different delays (
t
d
) of the laser pulses influence optoacoustic dynamics. When
t
d
is equal to or greater than the bubble oscillation time, acoustic cavitation cloud size increases 10-fold after the fourth laser pulse, while the pressure amplitude increases by more than 75%. A quasi-deterministic creation of cavitation due to consecutive transient pressure waves is also discussed. This is relevant for localized ablative laser therapy.
•Metal-semiconductor Ti/black-TiOx optoacoustic lens.•Laser-induced pressure wave and acoustic cavitation.•Spatial control of cavitation clouds.•Two-dimensional probability of cavitation induced by ...focused pressure wave.
The optoacoustic (OA) generation of pressure waves above the cavitation threshold causes the rupture of the liquid and the formation of dispersed cavities. The OA lenses involved in this process are generally associated with an ultra-short laser pulse to generate high-frequency ultrasound. OA elements based on carbon nanomaterials or ultrathin metal layers have shown they can deliver high-pressure ultrasound for therapeutic treatments that require high spatial resolution. Secondary processes, induced by a transient pressure, such as cavitation bubbles and shock waves, can lead to a more intense pressure transient. Hence, understanding their dynamics within an OA process and harnessing the spatial localization have become relevant for biomedical applications. Here, we show a single-laser-pulse-induced acoustic wave and the localization of inertial cavitation in an OA process employing a metal–semiconductor Ti/black-TiOx lens as an active component. Detection methods based on Schlieren photography and a laser beam-transmission probe (BTP) were used to study the dynamics. The phenomena were described at different laser-excitation energies (EL), showing an increase in the bubble population confined to the focal region of the lens. The size of the bubbles increases monotonically with the laser’s fluence and their distribution becomes denser and more elongated as a result of the increasing of the pressure-activated nucleation sites and of the bubble–bubble overlapped area. The stochastic nature of the cavities is spatially mapped, showing a probability distribution close to the focal region, which reaches 50% of its value for the cavitation fluence Fcav = 1.2 J/cm2. Our results demonstrate how the spatial distribution and penetration depth of the bubble cloud can be shaped by tuning the EL. The possibility to tailor the localized cavities and secondary ablative effects paves the way for the development of inexpensive technologies based on the photodisruption of localized subsurface tissues.
Remote-laser welding shortens processing times but bring reservations in the field of small series and user-customized manufacturing, where product individualization requires flexible and adaptive ...systems with simplified clamping devices. Also, the workpiece geometry is not exact due to thermal deformations during welding. To solve this, we have developed an innovative system, which enables in-line adaptive 3d seam tracking and laser power control. The system consists of an industrial robot, scanning head with optical triangulation feedback and fiber laser. It enables shorter and easier welding trajectory teaching, laser focus positioning precision of under 0,06 mm and stable partial penetration welding process.
One of the key challenges in robotic remote laser 3D processing (RL3DP) is to achieve high accuracy for the laser’s working trajectory relative to the features of the workpiece. This paper presents a ...novel RL3DP system with an automatic 3D teaching functionality for a precise and rapid determination of the working trajectory which comprises a robot manipulator, 3D scanning head, fibre laser and an off-axis positioned camera. The 3D measurement is based on laser triangulation with laser-stripe illumination using the laser’s pilot beam and scanning head. The experimental results show that the system has a precision better than 70 µm and 120 µm along lateral and vertical direction respectively inside the measuring range of 100 × 100 mm. The teaching time is 30-times shorter compared to a visual teaching procedure. Therefore, such a system can lead to large cost reductions for modern production lines that have constant changes to the products’ geometries and functionalities.
One of the key challenges in robotic remote laser 3D processing (RL3DP) is to achieve high accuracy for the laser’s working trajectory relative to the features of the workpiece. This paper presents a ...novel RL3DP system with an automatic 3D teaching functionality for a precise and rapid determination of the working trajectory which comprises a robot manipulator, 3D scanning head, fibre laser and an off-axis positioned camera. The 3D measurement is based on laser triangulation with laser-stripe illumination using the laser’s pilot beam and scanning head. The experimental results show that the system has a precision better than 70 μm and 120 μm along lateral and vertical direction respectively inside the measuring range of 100 × 100 mm. The teaching time is 30-times shorter compared to a visual teaching procedure. Therefore, such a system can lead to large cost reductions for modern production lines that have constant changes to the products’ geometries and functionalities.
One of the key challenges in robotic remote laser 3D processing (RL3DP) is to achieve high accuracy for the laser's working trajectory relative to the features of the workpiece. This paper presents a ...novel RL3DP system with an automatic 3D teaching functionality for a precise and rapid determination of the working trajectory which comprises a robot manipulator, 3D scanning head, fibre laser and an off-axis positioned camera. The 3D measurement is based on laser triangulation with laser-stripe illumination using the laser's pilot beam and scanning head. The experimental results show that the system has a precision better than 70 microm and 120 microm along lateral and vertical direction respectively inside the measuring range of 100 x 100 mm. The teaching time is 30-times shorter compared to a visual teaching procedure. Therefore, such a system can lead to large cost reductions for modern production lines that have constant changes to the products' geometries and functionalities.
Jedan od bitnih izazova u daljinskoj laserskoj 3D obradi (RL3DP) je postizanje visoke točnosti jer laser radi po rubovima predmeta koji obrađuje. Ovaj rad prikazuje novi RL3DP sustav s automatskom 3D ...nastavnom funkcionalnošću radi točnog i brzog određivanja prijenosa detektiranih rubova koje obrađuje robot sa 3D skenerom, fiber laserom i izvan aksijalno pozicioniranom kamerom. 3D skeniranje se bazira na laserskoj triangulaciji sa pilotskom laserskom trakom. Eksperimentalni rezultati pokazuju da sustav ima preciznost bolju od 70 μm i 120 μm u bočnom i vertikalnom smjeru u mjernom području od 100 × 100 mm. Vrijeme učenja je 30-puta kraće u odnosu na vizualni postupak. Stoga, takav sustav može značajno smanjiti troškove obrade sa modernim proizvodnim sistemima koji se moraju prilagođavati stalnim promjenama geometrije i funkcionalnosti proizvoda.
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