Laser welding
The laser beam welding (EN ISO 4063: Process 52) is a welding process . The energy is supplied via a laser . It is mainly used for welding components that have to be joined at high welding speeds, with narrow and slender weld seams and with little thermal distortion. The process, which is often called laser welding , is usually carried out without an additional material.
Process description
The laser radiation is focused using optics. The workpiece surface of the joint edge, i.e. the joint joint of the components to be welded, is in the immediate vicinity of the focus of the optics (in the focal point). The position of the focus relative to the workpiece surface (above or below) is an important welding parameter and also determines the welding depth. The focal spot has a typical diameter of a few tenths of a millimeter, which results in very high energy concentrations if the laser used has the typical power of a few kilowatts of laser power. The absorption of the laser power causes an extremely rapid rise in temperature on the workpiece surface beyond the melting temperature of metal, so that a melt is formed. Due to the high cooling speed of the weld seam, it becomes very hard, depending on the material, and usually loses its toughness. To protect the welding point from oxidation , it is constantly flushed with high-purity argon (1 l / min), which is heavier than air and thus displaces oxygen. The purity of the argon gas should be at least "4.6" (99.996%).
Deep laser welding
With high beam intensities in focus (as with steel materials approx. 4 MW / cm² depending on the travel speed; at a speed of 1 m / min, about 2 MW / cm² may be sufficient) a vapor capillary forms in the melt in the direction of the beam (with metal vapor or partially ionized metal vapor filled, tubular cavity, also called keyhole ) in the depth of the workpiece. As a result, the material is also melted in depth, the melting zone can be deeper than it is wide. The vapor capillary increases the absorption of the laser radiation in the material due to multiple reflections on the walls, which means that a larger melt volume can be generated compared to thermal conduction welding. The quality of the weld can be determined online by assessing the keyhole using appropriate optics.
Thermal conduction welding
If radiation intensities of up to 100 kW / cm² are used, heat conduction welding is usually involved. Since metals for laser beams can have a reflectivity of up to 95% , depending on the irradiated wavelength, the intensity is not sufficient to generate a vapor capillary ( keyhole ). The radiation does not penetrate, the heat and thus the weld pool penetrate less deeply, which is why mainly thin material is welded with it.
Replacement for resistance spot welding
A new method of laser welding can partially replace resistance spot welding . No continuous path is welded, only individual clip-shaped welding lines. These can be adapted to the load on the component and are more stable than conventional resistance-welded points.
Laser beam MSG hybrid welding
The laser beam MSG hybrid process is the combination of a laser beam with a MSG welding process in a common process zone. The advantages of both methods are used. Extremely deep penetrations with a good flank bond are achieved. This creates a very narrow heat-affected zone with less distortion and the escaping metal plasma additionally stabilizes the MSG arc. The process allows very high welding speeds, which leads to lower energy per unit length. The main reason for high profitability is the reduction in weld preparation. Entire work steps can be omitted. The number of welding beads can also be reduced. By combining the two processes, a large number of additional parameters can be set and the process can be ideally adapted to the task.
Laser welding in a vacuum
Main article: Laser welding in a vacuum
The laser welding in a vacuum or laser beam welding in vacuum (short lava or LasVak) is a method of modification of the laser beam welding. It combines vacuum technology, which is normally used in electron beam welding , with the established joining technology of laser beam welding. The process is usually used in a pressure range of 1 - 100 hPa and is characterized by a very high weld seam quality and, above all, freedom from pores and weld spatter. The weld seams produced with LaVa welding are similar in design to electron beam weld seams.
Laser transmission welding
Laser transmission welding of plastics mostly takes place in the overlap process. Two different welding partners are used for this. The upper one is transparent to the laser wavelength used. The laser shines through this almost unhindered. Due to the transparency , it hardly heats up. The lower welding partner must absorb the radiation . The addition of absorbent particles (approx. 0.3 % by weight of carbon black) can contribute to this. This substance absorbs the energy, begins to melt and transfers the resulting heat to the upper partner through thermal conduction. In order for the energy transfer and material contact to take place, both partners often have to be pressed together, or at least fit together perfectly. A weld seam can be produced by the merging of the two substances. The welding energy should be selected so that the laser only penetrates about 60% of the workpiece. If you then laser from both sides, complete welding is guaranteed. Too high a power should be avoided as it can damage the metal.
Efficient diode lasers are often used for this purpose ; with the required low powers (5–150 watts), they have a beam quality that is sufficient for this welding process .
Laser welding of plastics
Only thermoplastics can be used for laser welding of plastics - only these can form a melt.
Laser welding of ceramics
Researchers at the University of California in San Diego have succeeded in 2019, using ultra-short pulse lasers hermetic welds between ceramic manufacture -Werkstücken. So far, the process has not been suitable for the permanent insertion of electronic components, but it does promise use in various fields of application of technical ceramics . Previously were injection molded been referred to as "ceramic welding".
Advantages and disadvantages
A major advantage of laser-welded components is the lower, concentrated energy input into the workpiece compared to other welding processes. The consequence is, among other things, a lower thermal distortion. This welding process is therefore often used to join components to form prefabricated parts (e.g. gear wheel and synchronizer body → gear wheel ).
This often outweighs the disadvantage of the low level of radiation absorption during heat conduction welding of metals.
Another advantage is the large working distance (welding up to a distance of 500 mm or in hard-to-reach places) and the free choice of the ambient atmosphere.
A special feature of laser welding is that all seam geometries can be produced (butt welds, overlap welds or fillet welds). However, large gap widths cannot be bridged, in which case additional materials may be used. The disadvantage is the high system costs.
equipment
A laser welding system usually consists of the laser, a movement unit and an optical system for guiding the laser beam, at the end of which the processing and focusing optics are located. The movement system either moves the laser beam over the workpiece or the workpiece under the laser beam. Structures in which both the workpiece and the laser beam are moved are rarer. The laser beam can also be moved over the workpiece with a mirror scanner after focusing. Scanner systems consist of a combination of rotating facet mirrors or tiltable deflection mirrors (see galvanometer ), which can reflect the laser beam to different locations via the adjustable angle of the mirror. The main advantage is the very high possible speed of positioning the laser beam. This technique requires that the laser provides a laser beam very high beam quality at a comparatively high laser power ( fiber laser , disc laser , slab laser , CO 2 -laser o. Ä.). This type of laser welding is also known as remote welding .
In the case of remote welding, a distinction can be made between two different approaches: The remote heads (also called scan heads) and the large-scale remote systems. While the large-scale systems are permanently installed and can process very large work areas (> 4 m²), the scan heads are i. d. Usually mounted on a moving mechanism (linear axis or robot). Scan heads only have a small working area (generally <0.5 m²). By moving the scan head to different positions, however, a larger work area can be achieved. If the movements for positioning and welding take place one after the other, one speaks of step-by-step welding , and when both movements take place in parallel, of "welding on the fly".
Frequently used beam sources for laser welding of metals are the Nd: YAG laser ( wavelength 1.06 µm) and the carbon dioxide laser (wavelength approx. 10.6 µm). Recently, diode lasers have also been used more and more frequently , since semiconductor lasers in the high-power range (several 1000 W) can now be produced. Their significantly higher efficiency compared to Nd: YAG and carbon dioxide lasers is advantageous. The beam of the Nd: YAG laser and the diode laser is fiber-permeable, i. In other words, it can be fed into the laser welding optics via a fiber optic cable or a fiber optic cable . This consists of glass lenses. The CO 2 jet, on the other hand, can only be guided through air and must be guided to the processing optics via mirrors. In the case of CO 2 lasers, this consists of lenses made of single-crystal zinc selenide or often of a focusing mirror (usually made of copper).
Trivia
The Return of the Jedi Knights is a short story written by the German travel writer Stephan Thiemonds during a professional stay in Map Ta Phut . The European welding specialist (DVS EWS) was inspired by the first practical confrontation with the technology of laser welding. The story, written in the style of magical realism , first appeared in 2015 as part of his Querweltein Unterwegs book series in volume 7, Welding connects . Under the same book title, a revised and expanded new edition with new laser welding stories was published in January 2020, published by the media department of the German Association for Welding and Allied Processes . The profundity of this modern industrial history lies in answering the question why the globally operating DSI laser service team from Germany can be seen as the industrial Jedi knights of the 21st century: because they are similar to those equipped with laser swords Star Wars Jedis, united with their laser welding machines fighting for the good power.
literature
- Ulrich Dilthey (Ed.): Laser beam welding - processes, materials, production, testing. Manual for the BMBF project association “Qualification of Laser Processes” within the framework of the Laser 2000 funding concept. DVS-Verlag, Düsseldorf 2000, ISBN 3-87155-906-7 .
Individual evidence
- ↑ laser welding. technolix.net, July 8, 2007, archived from the original on January 15, 2008 ; Retrieved July 8, 2007 .
- ↑ Simon Olschok: Laser beam arc hybrid welding of steel in the thick sheet area. In: U. Dilthey (Hrsg.): Aachener Reports Fügetechnik. Shaker Verlag, 2008, p. 20 f.
- ↑ Shaker Verlag GmbH .: Laser beam welding in a vacuum Extension of the process limits for thick-walled sheet metal . 1st edition. Herzogenrath 2015, ISBN 978-3-8440-4032-6 .
- ↑ EH Penilla et al .: Ultrafast laser welding of ceramics. In: Science. American Association for the Advancement of Science, August 23, 2019, accessed September 14, 2019 .
- ↑ Dirk Eidemüller: materials research. Laser welding with ceramics. In: Golem.de. IT news for professionals. Golem Media GmbH, September 10, 2019, accessed on September 14, 2019 .
- ↑ Ulrike Rockland: Can you weld ceramics? BAM researchers at the Hanover Fair. BAM press release 4/2011. In: Informationsdienst Wissenschaft (idw). Federal Institute for Materials Research and Testing (BAM), April 1, 2019, accessed on September 14, 2019 .
- ↑ Stephan Thiemonds: Welding connects . 1st edition. DVS Media, 2020, ISBN 978-3-96144-078-8 .