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Minimization of distortions during laser welding of ultra-high strength steel
University West, Department of Engineering Science, Research Enviroment Production Technology West. Swerea KIMAB, Joining Technology, Kista, Sweden . (PTW)ORCID iD: 0000-0001-8933-6720
Volvo Cars, Torslanda; XPRES, KTH Royal Institute of Technology.
Volvo Cars, Torslanda.
Swerea KIMAB, Joining Technology, Kista; XPRES, KTH Royal Institute of Technology, Stockholm.
2014 (English)In: ICALEO 2014 Congress proceedings, 2014, 1-10 p.Conference paper, Published paper (Refereed)
Abstract [en]

Ultra high strength steels are frequently used within the automotive industry for several components. Welding of these components is traditionally done by resistance spot welding, but to get further productivity and increased strength, laser welding has been introduced in the past decades. Fusion welding is known to cause distortions due to built-in stresses in the material. The distortions result in geometrical issues during assembly which become the origin of low joint quality due to gaps and misfits.

U-beam structures of boron steel simulating B-pillars have been welded with laser along the flanges. Welding parameters and clamping have been varied to create different welding sequences and heat input generating a range of distortion levels. The distortions have been recorded dynamically with an optical measurement system during welding. In addition, final distortions have been measured by a digital Vernier caliper. The combined measurements give the possibility to evaluate development, occurrence and magnitude of distortions with high accuracy. Furthermore, section cuts have been analyzed to assess joint geometry and metallurgy.

The results shows that final distortions appear in the range of 0-8 mm. Distortions occur mainly transversely and vertically along the profile. Variations in heat input show clear correlation with the magnitude of distortions and level of joint quality. A higher heat input in general generates a higher level of distortion with the same clamping conditions. Section cuts show that weld width and penetration are significantly affected by welding heat input.

The present study identifies parameters which significantly influence the magnitude and distribution of distortions. Also, effective measures to minimize distortions and maintain or improve joint quality have been proposed.

Finally, transient FE simulations have been presented which show the behavior of the profiles during the welding and unclamping process.

Place, publisher, year, edition, pages
2014. 1-10 p.
Keyword [en]
Welding, laser, steel
National Category
Production Engineering, Human Work Science and Ergonomics Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-7262OAI: oai:DiVA.org:hv-7262DiVA: diva2:778177
Conference
ICALEO – 33rd International congress on applications of lasers & electro-optics
Funder
VINNOVA
Available from: 2015-01-09 Created: 2015-01-09 Last updated: 2015-01-28Bibliographically approved
In thesis
1. Laser welding of boron steels for light-weight vehicle applications
Open this publication in new window or tab >>Laser welding of boron steels for light-weight vehicle applications
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Laser beam welding has gained a significant interest during the last two decades. The suitability of the process for high volume production has the possibility to give a strong advantage compared to several other welding methods. However, it is important to have the process in full control since various quality issues may otherwise occur. During laser welding of boron steels quality issues such as imperfections, changes in local and global geometry as well as strength reduction can occur. The aspects that need to be considered are strongly depending on alloy content, process parameters etc. These problems that can occur could be fatal for the construction and the lowest level of occurrence is wanted, independent of industry.

The focus of this study has been to investigate the properties of laser welded boron steel. The study includes laser welding of boron alloyed steels with strengths of 1500 MPa and a recently introduced 1900 MPa grade. Focus has been to investigate weldability and the occurrence of cracks, porosity and strength reducing microstructure that can occur during laser welding, as well as distortion studies for tolerances in geometry. The results show that both conventional and 1900 MPa boron alloyed steel are suitable for laser welding.

Due to the martensitic structure of welds the material tends to behave brittle. Cracking and porosity do not seem to be an issue limiting the use of these steels. For tolerances in geometry for larger structures tests has been done simulating laser welding of A-pillars and B-pillars. Measurements have been done with Vernier caliper as well as a more advanced optical method capturing the movements during the welding sequence. Results from the tests done on Ushaped beams indicates that depending on the geometry of the structure and heat input distortions can be controlled to give distortions from 1 to 8 mm, at a welding length of 700 mm. This means that important geometry points can be distorted several millimeters if the laser welding process not is controlled.

Place, publisher, year, edition, pages
Trollhättan: University West, 2015. 100 p.
Series
Licentiate Thesis: University West, 1
Keyword
Laser welding; boron steel; high strength steels; strength reduction; brittle behavior; crack susceptibility; distortions; light-weight; quality
National Category
Production Engineering, Human Work Science and Ergonomics Manufacturing, Surface and Joining Technology Metallurgy and Metallic Materials
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-7263 (URN)978-91-87531-04-0 (ISBN)
Presentation
2015-01-22, C118, Högskolan Väst, Trollhättan, 10:15 (English)
Opponent
Supervisors
Available from: 2015-01-12 Created: 2015-01-09 Last updated: 2016-04-19Bibliographically approved

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