Extreme high-speed laser material deposition, known by its German acronym EHLA, is a new variant of laser material deposition (LMD) with powdered additives. This variant’s process control is unlike that of LMD, where the powder melts as it contacts the melt pool. In the EHLA process, the laser beam melts the powder above the surface of the substrate to deliver a liquid to the melt pool. At a given intensity distribution in a laser beam, the heating of powder particles in the beam path depends largely on the three-dimensional powder particle density distribution (PDD) and the relative position within the laser beam caustic. As a key element of a comprehensive numerical process model for EHLA, this paper presents a statistical/numerical model of the powder-gas jet, as previously published in Experimentelle und modelltheoretische Untersuchungen zum Extremen Hochgeschwindigkeits-Laserauftragschweißen. The powder-gas jet is characterized experimentally and described with a mathematical model. This serves to map the PDD of the powder-gas flow—and particularly the particle trajectories for different grain fractions—as well as the powder mass flows and carrier and inert gas settings, to a theoretical model. The result is a numerical description of the particle trajectories that takes into account the measured particle size distribution with calculations made on the assumption of a constant particle velocity and linear trajectories of the particles.

The Laser as a production tool has gained significant shares in industrial applications today. Laser materials processing is therefore a well established technique, especially in applications like welding, cutting, or surface treatment – benefitting from laser typical features like high processing speed, low heat input into the material, and precise manufacturing technique of high quality. Hence, it is essential to know the quality state of manufactured products. For many application areas this is also formalized through ISO 9000 and other by law enforced regulations. Thus applied quality control is an essential tool in modern manufacturing and necessary in order to keep production results in deterministic boundaries.

Main focus of this contribution is an investigation on process monitoring methods for transparent thermoplastic film laser beam welding. Target is to find feasible approaches to monitor and control the welding process in common industrial applications. The welding process is supported by an IR-absorber between the join partners. The presented work is focused on three different wavelength ranges: Starting from the visible wavelength through near infrared to mid infrared wavelength. In these areas two kinds of sensors are used. The sensors are imaging and integrating systems. The detectors for visible and near infrared are integrated into the beam path.

Laser transmission welding of plastics in industrial applications is expected to be robust against material quality variations and cleanness variations1. The process has to be applicable tolerating all workpiece dimension variations and different assembling positioning within the given tolerances. The inevitable failures of the welding process have to be detected reliably in each part even in large lot sizes.Process monitoring offers an alternative to post-production quality testing which is often destructive, and provides a complete recording of the manufacturing process, as required by official quality standards such as DIN EN ISO 9001.Within the scope of this paper the specific informative capabilities of coaxially spatially-integrated and coaxially spatially-resolved monitoring as well as monitoring of secondary radiation and monitoring by using external illumination are being compared and evaluated. Therefore a welding head is being developed using the already existing modular optical CPC-system of the Fraunhofer ILT. The Coaxial Process Control (CPC) system monitors the machining process in coaxial alignment with the laser beam axis. The welding head allows simultaneous observation using both observation methods.The emitted radiation by the process itself is being detected by a spatially integrating pyrometer and can be spatially resolved by a thermal camera. The visible spectrum is being reflected to a CMOS camera. It allows spatially resolved and spatially integrated monitoring at the same time.The modular system allows also coaxial and off-axis illumination, so coaxial, brightfield and darkfield workpiece illumination is provided and offers different illumination strategies for different materials and welding methods.Laser transmission welding of plastics in industrial applications is expected to be robust against material quality variations and cleanness variations1. The process has to be applicable tolerating all workpiece dimension variations and different assembling positioning within the given tolerances. The inevitable failures of the welding process have to be detected reliably in each part even in large lot sizes.Process monitoring offers an alternative to post-production quality testing which is often destructive, and provides a complete recording of the manufacturing process, as required by official quality standards such as DIN EN ISO 9001.Within the scope of this paper the specific informative capabilities of coaxially spatially-integrated and coaxially spatially-resolved monitoring as well as monitoring of secondary radiation and monitoring by using external illumination are being compared and evaluated. Therefore a welding head is being developed using the already existing modular optical CPC-system of t...

Abstract Das Schweißen mit Laserstrahlung ist ein innovatives optisches Fügeverfahren, das sich gegenüber konventionellen Schweißtechniken durch höhere erzielbare Schweißgeschwindigkeiten und geringere Nahtbreiten bei gleichzeitig gesteigerter Nahttiefe auszeichnet. Wesentliche Qualitätskriterien sind neben erkannten Fehlern der Schweißnaht die Einschweißtiefe und die Nahtbreite, die die Nahtgeometrie bilden. In diesem Beitrag werden optische Sensoren für die Erfassung relevanter Prozessgrößen beschrieben sowie hierauf aufbauend ein prädiktives Regelungskonzept, in dem die Stellgrößen Laserleistung und Fokuslage unter Berücksichtiung der zukünftigen Bahngeschwindigkeit optimiert werden. Bei der Modellierung des physikalisch komplexen, nichtlinearen Prozesses wird ein Neuronales Netz mit externer Dynamik verwendet. Ergebnisse aus der Anwendung des Regelungskonzepts auf den realen Schweißprozess werden vorgestellt.