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In-situ temperature measurement in friction stir welding of thick section aluminium alloys
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0003-3261-9097
University West, Department of Engineering Science, Division of Production Systems. TWI Ltd. Cambridge, UK. (PTW)ORCID iD: 0000-0001-9553-7131
TWI Ltd. Cambridge, UK.
Linnaeus University, Växjö, Sweden.
2019 (English)In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 39, p. 12-17Article in journal (Refereed) Published
Abstract [en]

Friction stir welding (FSW) is a reliable joining technology with a wide industrial uptake. However, several fundamentals of the process such as the temperature inside the stirred zone of the weld and its influence on mechanical properties, are not yet fully understood. This paper shows a method for accurate temperature measurements in multiple locations around the tool, to identify the location of the peak temperature, the temperature variations between the advancing and the retreating side of the tool and its relation to the tool geometry. Both standardised thermocouples in the FSW tool and the novel "tool-workpiece thermocouple" method were used to record temperatures.Bead-on-plate welds in 20 mm thickness AA6082-T6 were produced while the temperatures were measured in three locations on the FSW tool: at the shoulder outer diameter, at the transition from shoulder to probe and at the probe tip. It was found that the hottest point in the stirred zone was 607 °C and was located at the transition between the shoulder and probe, on the retreating-trailing side of the tool. The lowest temperature was found at the probe tip on the retreating-leading side of the tool.The results offer a better understanding of the temperature distribution around a FSW tool. The method presented can be applied to verification of thermal simulation models, tool design optimization, quality assurance and temperature feedback control.

Place, publisher, year, edition, pages
Elsevier, 2019. Vol. 39, p. 12-17
Keywords [en]
Friction stir welding, Temperature measurement, Aluminium alloys, Thick section, Thermocouple, TWT
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-13705DOI: 10.1016/j.jmapro.2019.02.001ISI: 000464296700002Scopus ID: 2-s2.0-85061529967OAI: oai:DiVA.org:hv-13705DiVA, id: diva2:1294088
Funder
Region Västra Götaland, RUN 612-0254-15Knowledge Foundation, 20140130Swedish Agency for Economic and Regional Growth, 20200328Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2020-02-26Bibliographically approved
In thesis
1. 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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Ferreira Magalhães, Ana CatarinaDe Backer, Jeroen

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