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Characterization of cold lap defects in tandem arc MAG welding
University West, Department of Engineering Science, Research Enviroment Production Technology West. (PTW)
University West, Department of Engineering Science, Division of Production Engineering. (PTW)ORCID iD: 0000-0003-2560-0531
University West, Department of Engineering Science, Division of Production Engineering. (PTW)ORCID iD: 0000-0001-7787-5444
University West, Department of Engineering Science, Division of Production Engineering. (PTW)ORCID iD: 0000-0002-9578-4076
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2012 (English)In: Welding in the World, ISSN 0043-2288, E-ISSN 1878-6669, Vol. 56, no 9/10, 20-25 p.Article in journal (Refereed) Published
Abstract [en]

The objective of this investigation was to classify and characterize the small lack of fusion defects, called cold lap, located at the weld toe. Since the defects are very small (0.01–1.5 mm) and difficult to detect by NDT methods, a better understanding of the formation mechanism is required to be able to avoid their formation. The investigation consisted of two parts. Firstly, a study was made on the type and frequency of cold laps. Three types were identified, namely “spatter cold lap”, and “overlap cold lap” and “spatter-overlap cold lap”. No relation between type or frequency of cold laps and the welding parameters could be established. Secondly, the interface between spatter and the base material was investigated using optical and scanning electron microscopy, to better understand the cold lap formation mechanism. Manganese-silicate particles were found in the interface located in such a way that they may assist cold lap formation.

Place, publisher, year, edition, pages
2012. Vol. 56, no 9/10, 20-25 p.
Keyword [en]
GMAW, oxides, cold lap
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-4659DOI: 10.1007/BF03321377ISI: 000309080800003Scopus ID: 2-s2.0-84878458620OAI: oai:DiVA.org:hv-4659DiVA: diva2:556185
Projects
LOST and WIQ
Available from: 2012-09-24 Created: 2012-09-24 Last updated: 2016-02-12Bibliographically approved
In thesis
1. Cold lap formation in Gas Metal Arc Welding of steel: An experimental study of micro-lack of fusion defects
Open this publication in new window or tab >>Cold lap formation in Gas Metal Arc Welding of steel: An experimental study of micro-lack of fusion defects
2013 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Cold laps are defined as micro-lack of fusion defects at the weld toe more or less parallel to the surface of the parent plate. These defects are known to negatively influence the fatigue properties of weldments. Previous studies suggest that cold lap formation can not be avoided completely in Gas Metal Arc Welding (GMAW). Therefore, a better understanding of formation mechanisms is imperative to be able to minimize the number and size of these defects. The main objective of this work has been to provide a more comprehensive understanding of cold laps, including categorising, characterisation and defining the most significant factors for formation. GMAW was used to produce welds that were investigated by metallographic methods using light optical microscopy, scanning electron microscopy and energy dispersive spectrometry. A novel classification of cold laps was introduced and three types of cold laps were identified: spatter cold laps, overlap cold laps and spatter-overlap cold laps. It was shown that cold laps are partially or fully filled by oxides. The most common oxides are manganese silicon oxides which were concluded to be formed primarily by oxidation of droplets. The presence of oxides was found to significantly increase the tendency to form spatter cold laps as well as overlap cold laps. Particularly for overlap cold laps, it was found that the depth (in transverse direction of weld) is reduced when welding in a non-oxidising environment. Welding on blasted surfaces increased the cold lap formation by entrapment of gas. The droplet and base metal temperatures were also found to be significant factors in cold lap formation. For overlap cold laps the occurrence frequency decreased with increased preheating temperature of the base metal. Mechanisms of overflowing resulting in overlap cold laps were discussed based on an extensive literature review. Several phenomena are believed to contribute to overflow including Rayleigh instability, the balance of forces, transfer of lateral momentum by droplets and an outward Marangoni fluid flow of the weld pool.

The present studies suggest that cold lap formation can be suppressed by ensuring that the welding process (arc) is as stable as possible and by welding on a preheated work piece in a non-oxidising environment.

Place, publisher, year, edition, pages
Trollhättan: University West, 2013. 54 p.
Series
PhD Thesis: University West, 2
Keyword
Tandem GMAW, old laps, lack of fusion, Spatter, Overlap, Overflow, Manganese, Silicon, Oxides, Temperature
National Category
Mechanical Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5596 (URN)978-91-977943-6-7 (ISBN)978-91-977943-5-0 (ISBN)
Public defence
2013-09-24, C118, Högskolan Väst/University West, Trollhättan, 11:10 (English)
Opponent
Supervisors
Available from: 2013-09-17 Created: 2013-09-17 Last updated: 2015-10-02Bibliographically approved

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