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Cold lap formation in Gas Metal Arc Welding of steel: An experimental study of micro-lack of fusion defects
University West, Department of Engineering Science, Division of Mechanical Engineering. (PTW)
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 [en]
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: urn:nbn:se:hv:diva-5596ISBN: 978-91-977943-6-7 (print)ISBN: 978-91-977943-5-0 (print)OAI: oai:DiVA.org:hv-5596DiVA: diva2:648916
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
List of papers
1. Study on temperature influence on lack of fusion formation in spatter/base metal interface
Open this publication in new window or tab >>Study on temperature influence on lack of fusion formation in spatter/base metal interface
2014 (English)In: Advanced Materials Research, ISSN 1662-8985, Vol. 875 - 877, 1421-1428 p.Article in journal (Refereed) Published
Abstract [en]

In the development of modern welded structures with longer life-time and/or higher load-carrying ability, fatigue properties are becoming more and more important. A lot of researches have been done to investigate which factors can elongate the fatigue life of weldments. Cold lap defects, were found to be important initiation sites of the fatigue failure in 1990s. In the ISO standard, cold lap is referred to as a type of micro-lack of fusion. Previous study found that most of the cold laps in GMAW process are formed in spatters. In this paper the interface of spatter/base metal was cut, polished and investigated by conventional metallographic methods. The aim is to reveal the influence of temperature on cold lap formation. In the experiments, different pre-heating temperatures of the parent plate were used in tandem GMAW. Results showed linear empirical relationship between the temperature of the parent plate and the amount of lack of fusion in the spatter/base metal interface.

Place, publisher, year, edition, pages
Trans Tech Publications Limited, 2014
Keyword
Cold Lap, EDS, GMAW, Lack-of-Fusion (LOF), Manganese, Oxides, SEM, Silicon, Spatter, Temperature
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4665 (URN)10.4028/www.scientific.net/AMR.875-877.1421 (DOI)
Conference
International Conference on Frontiers of Mechanical Engineering,Materials and Energy(ICFMEME 2012)
Projects
WIQ and SUMAN
Available from: 2012-09-24 Created: 2012-09-24 Last updated: 2016-02-11Bibliographically approved
2. Factors influencing fusion of spatter to the base metal during tandem GMAW
Open this publication in new window or tab >>Factors influencing fusion of spatter to the base metal during tandem GMAW
2012 (English)In: Proceedings of The 5th International Swedish Production Symposium: 6th-8th of November 2012 Linköping, Sweden / [ed] Mats Björkman, Linköping, Sweden, 2012, 233-239 p.Conference paper, (Refereed)
Abstract [en]

Tandem gas metal arc welding (tandem GMAW) is, as a high productivity welding method of manufacturing process, utilized broadly in modern Swedish industry. Spatter is more or less an inevitable flaw in GMAW, especially for the high efficiency processes. Recently, spatter was found as a potential source of cold laps, which negatively influences fatigue life. The main objectives of this paper are to investigate the spatter/base metal interface and identify the primary factors for formation of cold laps.

Tandem GMAW was performed in a sealed chamber filled with either pure argon or pure dioxide. Cross sections of spatter and base metal were prepared and evaluated by Light optical microscopy and Scanning Electron Microscopy (SEM) with an attached Energy Dispersive Spectroscope (EDS).

Mn-Si oxides were found to enhance the lack of fusion occurrence in the spatter/base metal. The oxide of Mn and Si mostly came from oxidation of the droplets in the welding process. Spatter diameter and spatter distance was evaluated with respect to lack of fusion in spatter/base metal interface for welds using pure Ar shielding gas. From this it was concluded that temperature is another important factor for lack of fusion formation in the spatter/base metal interface.

Place, publisher, year, edition, pages
Linköping, Sweden: , 2012
Keyword
tandem GMAW, cold lap, spatter, lack of fusion, SEM, EDS, oxide
National Category
Engineering and Technology Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4664 (URN)978-91-7519-752-4 (ISBN)
Conference
5th International Swedish Production Symposium, SPS12
Available from: 2012-09-24 Created: 2012-09-24 Last updated: 2016-02-11Bibliographically approved
3. Influence of oxides on cold lap formation in tandem GMAW
Open this publication in new window or tab >>Influence of oxides on cold lap formation in tandem GMAW
2012 (English)In: Science and technology of welding and joining, ISSN 1362-1718, E-ISSN 1743-2936, ISSN 1362-1718, Vol. 17, no 8, 643-648 p.Article in journal (Refereed) Published
Abstract [en]

The connection between the formation of cold laps and the presence of Mn‐Si oxides was studied. The underlying purpose is to understand the fundamental mechanisms of cold lap formation and to avoid it. Tandem gas metal arc welding (GMAW) was used to produce welded specimens in two different shielding gases (pure Ar and pure CO2) with base metal S355 MC (EN-10149-2) and wire G3Si1 (EN ISO 14341-A). Cross-sections of welds in the cold lap location were evaluated by light optical microscopy and scanning electron microscopy combined with energy dispersive spectroscopy. The results showed that the Mn‐Si oxides significantly enhanced cold laps formation, especially the overlap type cold lap formation. The Mn‐Si oxides originated from oxidation of the droplets. These oxides transfers to the surface of the weld pool at the weld toe, where they contributed to the formation of the cold laps.

National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-3826 (URN)10.1179/1362171812Y.0000000057 (DOI)000309661300006 ()2-s2.0-84867507729 (Scopus ID)
Available from: 2011-10-31 Created: 2011-10-31 Last updated: 2016-02-11Bibliographically approved
4. Influence of preheating temperature on cold lap formation in tandem GMAW
Open this publication in new window or tab >>Influence of preheating temperature on cold lap formation in tandem GMAW
2013 (English)Conference paper, (Refereed)
Abstract [en]

A cold lap is defined as a type of micro-lack of fusion in ISO standard (ISO 6520-1:2007) and have been found to influence fatigue properties of welds significantly. In the present study, the main purpose was to investigate the influence of preheating temperature on cold lap formation in tandem GMAW, both with respect to dimensions and occurrence probabilities.

Three different preheating temperatures were applied and cross-sections of welds were evaluated by light optical microscopy. The results showed that the cold lap occurrence frequency is a function of base metal temperature. However, the base metal temperature does not have a significant influence on cold lap depth.

Place, publisher, year, edition, pages
JOM-Institute, 2013
Keyword
Cold lap, GMAW, temperature, overflow, formation, overlap, lack of fusion, Work-integrated learning, WIL, AIL
National Category
Manufacturing, Surface and Joining Technology
Research subject
Work Integrated Learning; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5561 (URN)87-89582-21-7 (ISBN)
Conference
JOM-17 - International Conference on Joining Materials. Helsingör, Denmark 5-8 May 2013
Projects
SUMAN SVETS
Available from: 2013-07-24 Created: 2013-07-24 Last updated: 2016-02-11Bibliographically approved
5. Characterization of cold lap defects in tandem arc MAG welding
Open this publication in new window or tab >>Characterization of cold lap defects in tandem arc MAG welding
Show others...
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.

Keyword
GMAW, oxides, cold lap
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-4659 (URN)10.1007/BF03321377 (DOI)000309080800003 ()2-s2.0-84878458620 (Scopus ID)
Projects
LOST and WIQ
Available from: 2012-09-24 Created: 2012-09-24 Last updated: 2016-02-12Bibliographically approved
6. Cold laps - micro-lack of fusion defects in steel arc welds: a review
Open this publication in new window or tab >>Cold laps - micro-lack of fusion defects in steel arc welds: a review
(English)Manuscript (preprint) (Other academic)
Keyword
Review, cold lap, micro defect, lack of fusion, oxides, formation, NDT, magnetic field, weld pool, arc, welding
National Category
Mechanical Engineering
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-5613 (URN)
Available from: 2013-09-25 Created: 2013-09-25 Last updated: 2016-02-11Bibliographically approved

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Citation style
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Output format
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