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Resistance Nut Welding: Improving the Weldability and Joint Properties of Ultra High Strength Steels
2007 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 51, no 3-4, 28-36 p.Article in journal (Refereed) Published
Abstract [en]

This study covers resistance projection welding of three different M6 and M8 weld nut types to high- and ultra high strength thin sheet steels ranging up to 1 500 MPa tensile strength. Static tensile testing, torsion testing and fracture evaluation as well as metallographical examinations were used to evaluate the suitability of the selected nut types for applications in high and ultra high strength steels. Different resistance welding equipment were compared and both alternating current and direct current were evaluated. A new etchant was used for examining the fusion zon ein the nut joints, which indicated that no significant melting of the interfaces had occurred. This was evident for all the weld nut types welded to the galvanized thin sheet steels. The electrical characteristic of the power source plays an important role for the weld result. A rapid current build-up during the first period (AC) of weld time increased the initial heating of the weld nut projections that improved the joint strength. Significant differences in pull-out strength were recorded in joints welded with different AC power sources. Current curve modification for MFDC welding machines is a promising way of increasing the joint strength. A welding cycle with an initial high peak current pulse followed by a current plateau improved the pull-out strength by more than 100 %

Place, publisher, year, edition, pages
Springer-Verlag, 2007. Vol. 51, no 3-4, 28-36 p.
National Category
Materials Engineering
Research subject
Materials Science and Engineering
Identifiers
URN: urn:nbn:se:kth:diva-167983DOI: 10.1007/BF03266557OAI: oai:DiVA.org:kth-167983DiVA: diva2:813649
Note

QC 20150526

Available from: 2015-05-25 Created: 2015-05-25 Last updated: 2017-12-04Bibliographically approved
In thesis
1. Challenges in Resistance Welding of Ultra High Strength Steels
Open this publication in new window or tab >>Challenges in Resistance Welding of Ultra High Strength Steels
2015 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Increasing the use of Ultra High Strength Steels (UHSS) in vehicle bodystructures is important for reducing weight and cutting CO2 emissions. This thesis investigates challenges in resistance welding that can be a barrier to implementing UHSS as a replacement for low strength steels in vehicle structures. Empirical research has been performed to offer new approaches for improved joint strength and to increase knowledge on cracking mechanisms in resistance projection welding and resistance spot welding of UHSS. By optimising the current build-up phase and peak current during the first milliseconds of weld time, it was shown that the strength could be improved by up to two-fold for projection welded joints. An approach to improve the ductility and strength of resistance spotwelds in UHSS using reduced cooling time was unsuccessful. The reduced cooling rate after weld metal solidification did not fully create the desired softened microstructure. The study on the surface cracking mechanism in resistance spot welded dual-phase UHSS showed that cracking is linked to the galvanization method. It is proposed that formation of aluminium oxide layers on the electrode tips increases the surface temperature and thereby increases the probability for liquid metal embrittlement and surface cracking.

Place, publisher, year, edition, pages
Stockholm: KTH Royal Institute of Technology, 2015. xvii, 59 p.
Series
TRITA-IIP, ISSN 1650-1888 ; 15:02
Keyword
Resistance welding, spot welding, surface cracks, nut welding, UHSS, projection welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
Materials Science and Engineering
Identifiers
urn:nbn:se:kth:diva-167985 (URN)978-91-7595-577-3 (ISBN)
Presentation
2015-06-03, M311, Brinellvägen 68, KTH, Stockholm, 10:00 (Swedish)
Opponent
Supervisors
Funder
XPRES - Initiative for excellence in production research
Note

QC 20150526

Available from: 2015-05-26 Created: 2015-05-25 Last updated: 2015-05-26Bibliographically approved

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