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Temperature measurements during friction stir welding
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0003-3261-9097
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0001-9553-7131
University West, Department of Engineering Science, Division of Production Systems. (PTW)ORCID iD: 0000-0002-1869-232X
2017 (English)In: The International Journal of Advanced Manufacturing Technology, ISSN 0268-3768, E-ISSN 1433-3015, Vol. 88, no 9-12, p. 2899-2908Article in journal (Refereed) Published
Abstract [en]

The increasing industrial demand for lighter, more complex and multi-material components supports the development of novel joining processes with increased automation and process control. Friction stir welding (FSW) is such a process and has seen a fast development in several industries.This welding technique gives the opportunity of automation and online feedback control, allowing automatic adaptation to environmental and geometrical variations of the component.Weld temperature is related to the weld quality and therefore proposed to be used for feedback control. For this purpose, accurate temperature measurements are required. This paper presents an overview of temperature measurement methods applied to the FSW process. Three methods were evaluated in this work: thermocouples embedded in the tool, thermocouples embedded in the workpiece and the tool-workpiece thermocouple(TWT) method. The results show that TWT is an accurate and fast method suitable for feedback control of FSW.

Place, publisher, year, edition, pages
2017. Vol. 88, no 9-12, p. 2899-2908
Keywords [en]
Friction stir welding, TWT method, temperature, aluminium, thermocouples
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-9531DOI: 10.1007/s00170-016-9007-4ISI: 000394323600047Scopus ID: 2-s2.0-84973646335OAI: oai:DiVA.org:hv-9531DiVA, id: diva2:947429
Funder
Region Västra Götaland, RUN 612-0254-15
Note

Funders: Swedish Agency for Economic and Regional Growth through European Regional Development Fund, 20200328

Available from: 2016-07-08 Created: 2016-07-08 Last updated: 2020-02-26Bibliographically approved
In thesis
1. Thermo-electric temperature measurements in friction stir welding: Towards feedback control of temperature
Open this publication in new window or tab >>Thermo-electric temperature measurements in friction stir welding: Towards feedback control of temperature
2016 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Friction Stir Welding has seen a fast uptake in many industry segments. Mechanical properties superior to fusion welding, the ability to weld "unweldable" aluminium alloys and low distortion are often described as the main reasons for the fast industrial implementation of FSW. Most existing applications consist of long straight welding joints. Applications with complex weld geometries, however, are rarely produced by FSW. These geometries can induce thermal variations during the welding process, thus making it challenging to maintain a consistent weld quality. In-process adaptation of weld parameters to respond to geometrical variations and other environmental variants allow new design opportunities for FSW. Weld quality has been shown to be reliant on the welding temperature. However, the optimal methodology to control the temperature is still under development.The research work presented in this thesis focuses on some steps to take in order to reach the improvement of the FSW temperature controller, thus reach a better and consistent weld quality. In the present work different temperature methods were evaluated. Temperature measurements acquired by the tool-workpiece thermocouple (TWT) method were accurate and fast, and thereby enhanced suitable for the controller. Different environmental conditions influencing the material heat dissipation were imposed in order to verify the controller effect on the joint quality. In comparison with no controlled weld, the use of the controller enabled a fast optimization of welding parameters for the different conditions, leading to an improvement of the mechanical properties of the joint.For short weld lengths, such as stitch welds, the initial plunge and dwell stages occupy a large part of the total process time. In this work temperature control was applied during these stages. This approach makes the plunge and dwell stages more robust by preventing local material overheating, which could lead to a tool meltdown. The TWT method was demonstrated to allow a good process control during plunging and continuous welding. The approach proposed for control offers weld quality consistency and improvement. Also, it allows a reduction of the time required for the development of optimal parameters, providing a fast adaptation to disturbances during welding and, by decreasing the plunge time, provides a significant decrease on the process time for short welds.

Place, publisher, year, edition, pages
Trollhättan: University West, 2016. p. 62
Series
Licentiate Thesis: University West ; 13
Keywords
FSW, Robotic, Temperature, TWT, Plunge, Control
National Category
Robotics
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9982 (URN)978-91-87531-43-9 (ISBN)978-91-87531-42-2 (ISBN)
Supervisors
Available from: 2016-11-09 Created: 2016-10-12 Last updated: 2019-12-04Bibliographically approved
2. Thermoelectric Measurements for Temperature Control of Robotic Friction Stir Welding
Open this publication in new window or tab >>Thermoelectric Measurements for Temperature Control of Robotic Friction Stir Welding
2020 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Friction stir welding (FSW) has undergone a rapid expansion in several industrial sectors such as in the aerospace, marine, railway and automotive sectors. Current industrial applications are mainly simple long straight welds, but there is a growth of interest in components with higher geometric complexity. However, welding of geometrically complex components represents a challenging task due to the resulting uneven induced thermal dissipation along the weld, but especially due to the need for suitable equipment, able to accurately follow a complex 3D path under high mechanical loads, while managing the machine deflection. This is the case for robots, where the high process forces result in deflections, which affects robots' compliance, leading to weld failures and poor consistency in mechanical properties.

In the presented approach, the rotational speed is controlled during welding in order to maintain the set temperature value along the weld. An innovative method to measure the process temperature, the tool-workpiece thermocouple (TWT), which offers a temperature estimation from the whole tool-workpiece interface (TWT-data), is set as the controlled variable. The overall aim of this thesis is then to demonstrate the industrial applicability of TWT temperature control for joining geometrically complex components using robotic friction stir welding.

The TWT-data signal is demonstrated to be fast, repeatable and representative of the welding temperature. Moreover, TWT-data supplies online information during the whole weld procedure, especially during plunging. The shoulder contact with the workpiece is identified by TWT-data, providing for an improved plunging operation, which was demonstrated to significantly improve the use of robotic FSW, overcoming the lack of stiffness inherent to this equipment type at this welding stage.

Improved joint performance, low tensile strength variation along the weld path and a reduced number of failed welds were achieved by welding under temperature control. As a result, such a welding approach simplifies the development of a welding procedure, allowing for a decrease in time and material. The concept was successfully validated by performing two welds consisting of two dissimilar materials in a two-dimensional weld path on a geometrically complex component by using robotic equipment. The temperature control approach is not limited to robotic equipment, but also suitable for standard FSW equipment, being of interest to a various range of applications where quality and/or time is an important factor.

Abstract [sv]

Friktionsomrörningssvetsning (FSW) genomgår en snabb industriell utveckling inom bland andra flyg-, marin-, järnvägs- och fordonssektorn, speciellt i aluminium. Aktuella industriella tillämpningar har hittills huvudsakligen varit enkla långa raka svetsar, men intresset för komponenter med högre geometrisk komplexitet ökar. Sådana komponenter utgör en utmanande uppgift på grund avvarierande inducerad termisk spridning längs med fogen, och särskilt på grund av behovet av lämplig utrustning, som kan följa en 3D-svetsbana. Detta gäller speciellt när verktyget monteras på en industrirobot, där höga processkrafter resulterar i böjning, vilka kan leda till svetsfel och sämre mekaniska egenskaper. Utgångspunkten i detta arbete är att temperaturen i verktygets kontakt med materialet har störst betydelse för fogkvaliteten.

I det presenterade tillvägagångssättet styrs rotationshastigheten under svetsningen för att bibehålla önskad temperatur längs svetsen. En innovativ temperaturmätmetod baserad på termoelektrisk effekt mellan verktyg och arbetsstycke (TWT) erbjuder en skattning av temperaturen från hela gränssnittet mellan verktyg och arbetsstycke (TWT-data). Denna temperaturskattning används som den styrda variabeln. Det övergripande syftet med denna avhandling är att visa att styrning baserad på TWT-data är industriellt användbar för att bibehålla fogegenskaper vid fogning av geometriskt komplexa komponenter med hjälp av friktionsomröringssvetsning.

TWT-data visar sig vara ett snabbt, repeterbart och genomförbart sätt att få en representativ realtidsskattning av fogens temperatur under hela processen. Som sådan är den lämplig för skattning av processtemperaturen och styrning av processen. TWT-data tillhandahåller information även under startskedet och identifierar när verktyget pressas mot arbetsstycket, och speciellt när verktygets skuldra får kontakt med arbetsstycket. Denna information ger en förbättrad startprocedur, vilket är viktigt speciellt vid robotisering, eftersom robotens vekhet påverkar verktygets z-position.

Svetsning under temperaturreglering gav förbättrad fogprestanda, låg draghållfasthetsvariation längs fogen och ett reducerat antal misslyckade svetsar, och förväntas förenkla utvecklingen av en svetsprocedur, vilket möjliggör en minskning av tid och material.

Konceptet validerades framgångsrikt genom att svetsa en komponent bestående av två olika fogar med en tvådimensionell svetsbana i en geometriskt komplexkomponent med hjälp av robotutrustning. Tillvägagångssättet för temperaturstyrning är inte begränsat till robotutrustning, utan också lämpligt för standard FSW-utrustning, vilket är av intresse för olika applikationer där kvalitet och tid är viktiga faktor.

Place, publisher, year, edition, pages
Trollhättan: University West, 2020. p. 110
Series
PhD Thesis: University West ; 33
Keywords
Friction stir welding, Aluminium, Temperature measurements, Process control, Robotics, Geometrically complex components, Friktionsomrörningssvetsning, Aluminium, temperaturmätning, Processstyrning, Robotik, Geometriskt komplexa komponenter
National Category
Manufacturing, Surface and Joining Technology
Research subject
Production Technology; ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-14982 (URN)978-91-88847-48-5 (ISBN)978-91-88847-47-8 (ISBN)
Public defence
2020-02-25, Albertssalen, 09:00 (English)
Opponent
Supervisors
Available from: 2020-02-26 Created: 2020-02-26 Last updated: 2020-02-26Bibliographically approved

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Silva, AnaDe Backer, JeroenBolmsjö, Gunnar

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