Macro: Joining 3
2:45pm - 3:00pm
Effects of separately laser-induced metal vapor amounts on the stability of a TIG arc
BIAS-Bremer Institut für angewandte Strahltechnik GmbH, Bremen, Germany
Arc stability during welding can be improved by using a laser process and the associated implementation of a hybrid welding process. Various effects are assumed to be the causes of process stabilization by the additional laser beam. To investigate the metal vapor influence in a more decoupled manner, the metal vapor in this study is generated by a laser beam guided on an external substrate. The laser beam axis is oriented horizontally and thus perpendicular to the simultaneously ignited arc between a TIG welding torch and a counter electrode. The amount of metal vapor is adjusted by varying the laser power. The laser process causes the arc voltage to increase with the amount of metal vapor. This means an increasing electrical resistance and thus effects on the arc stability.
3:00pm - 3:15pm
Laser process manipulation by axial beam shaping
1Luleå University of Technology, Sweden; 2AdlOptica GmbH, Germany
The laser beam is a highly flexible tool, which is used for many material processing applications. However, new beam shaping technologies open even further possibilities and processing options in order to control the heat input into the material. Beam shaping is usually done by manipulating the spatial intensity distribution in one layer to create. A new beam shaping device offers the possibility to create up to four focal spots in axial direction, which enables an extended depth of focus and tailoring the distribution of the energy along the beam axis. In this work, the impact of different axial beam shaping settings on process behaviours during laser material processing is shown. At low processing velocities, the amounts of measured spatters at the bottom side of the processed sheets show a reduced number compared to higher speeds. It is assumed that a stable keyhole opening is achieved that prevents the spattering.
3:15pm - 3:30pm
Spatter formation in high-speed laser processing of high-alloyed steel
Technische Universität Ilmenau, Production Technology Group, Germany
Balancing processes require highly precise mass corrections especially in case of high-speed turning rotors. In order to hold profitable cycle times, these mass corrections have to be carried out in a short time. The application of cw-mode laser radiation represents a novel approach for these balancing processes. Thereby, spatter formation was identified as the primary removal mechanism. It is necessary to characterize the processing zone sufficiently to provide a deeper understanding of spatter formation at processing speeds beyond 60 meter per minute. In this study, a glass plate was used for flanking the processing zone to realize high-speed videography in a half section setup. This approach allows to perform measurements directly in the processing zone regarding melt pool dimensions, keyhole front and their interaction. In combination with image processing, precise weighings and metallographic examinations, a classification of certain process regimes referring to the processing speed is given.
3:30pm - 3:45pm
High-speed synchrotron X-ray imaging of the formation of wedge-shaped capillaries during laser beam welding at high feed rates
1Universität Stuttgart, Institut für Strahlwerkzeuge, Pfaffenwaldring 43, 70569 Stuttgart; 2Chair for Laser Technology LLT, RWTH Aachen University, Steinachstraße 15, 52074 Aachen; 3Fraunhofer Institute for Laser Technology ILT, Steinbachstraße 15, 52074 Aachen
Especially in case of high feed rates, the geometry of the capillary elongates in feed direction. At certain feed rates it might suddenly change to a wedge-shaped geometry. For the determination of the capillary-geometry during welding high-speed-X-ray imaging was performed at the IFSW X-ray-facility and at the synchrotron at DESY. The investigations addressed the transition of the capillary-geometry from a high aspect ratio to a wedge-shape geometry. In order to access the melt flow during welding, the movement of tungsten carbide particles was analyzed in the image sequences. The comparison of different laser spot diameter from 100 µm to 1360 µm and feed rates of up to 2 m/s resulted in the identification of the critical feed rate for the transition to the wedge-shaped capillary for each spot diameter. In the talk, the phenomena occurring during the transition will be presented and possible reasons for the transition will be discussed.
3:45pm - 4:15pm
Invited Talk: Melt-track merging and instabilities in multi-laser additive manufacturing
Princeton Institute for the Science and Technology of Materials, Princeton University, United States of America
Control over laser beam shape can enable precision control over the resulting materials properties in any laser processing application. One simply way to control the intensity profile of the material illumination is through the use of multiple laser sources or beamlets. However the use of multiple beams can introduce unexpected phenomena and instabilities that can create undesired effects in the material. In this work, we use synchronized laser beams to create two molten pools running parallel to each other in a powder bed fusion system where the beams are separated by a controlled spatial and temporal offset. Through varying the offset, results reveal that besides the completely merged and completely separated regimes, there exists a third regime in which periodic coalescence occurs between the two molten pools. We examine the instability that leads to this periodic structure as well as how to control its formation.