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Thermoelectric Measurements for Temperature Control of Robotic Friction Stir Welding
University West, Department of Engineering Science, Division of Welding Technology. (PTW)ORCID iD: 0000-0003-3261-9097
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 [en]
Friction stir welding, Aluminium, Temperature measurements, Process control, Robotics, Geometrically complex components
Keywords [sv]
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: urn:nbn:se:hv:diva-14982ISBN: 978-91-88847-48-5 (print)ISBN: 978-91-88847-47-8 (electronic)OAI: oai:DiVA.org:hv-14982DiVA, id: diva2:1396346
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
List of papers
1. Temperature measurements during friction stir welding
Open this publication in new window or tab >>Temperature measurements during friction stir welding
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.

Keywords
Friction stir welding, TWT method, temperature, aluminium, thermocouples
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-9531 (URN)10.1007/s00170-016-9007-4 (DOI)000394323600047 ()2-s2.0-84973646335 (Scopus ID)
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
2. In-situ temperature measurement in friction stir welding of thick section aluminium alloys
Open this publication in new window or tab >>In-situ temperature measurement in friction stir welding of thick section aluminium alloys
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
Keywords
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:nbn:se:hv:diva-13705 (URN)10.1016/j.jmapro.2019.02.001 (DOI)000464296700002 ()2-s2.0-85061529967 (Scopus ID)
Funder
Region Västra Götaland, RUN 612-0254-15Knowledge Foundation, 20140130Swedish Agency for Economic and Regional Growth, 20200328
Available from: 2019-03-06 Created: 2019-03-06 Last updated: 2020-02-26Bibliographically approved
3. Analysis of Plunge and Dwell Parameters of Robotic FSW Using TWT Temperature Feedback Control
Open this publication in new window or tab >>Analysis of Plunge and Dwell Parameters of Robotic FSW Using TWT Temperature Feedback Control
2016 (English)In: Proceedings of 11th International Symposium on Friction Stir Welding, Cambridge, UK, 2016, p. 1-11Conference paper, Published paper (Other academic)
Abstract [en]

Friction stir welding (FSW) and variants of the process have generated high interest in many industries due to its several advantages such as low distortion, superior mechanical properties over arc welding and the possibility of joining dissimilar materials. Increased complexity of industrial applications require a better control of the welding process in order to guarantee a consistent weld quality. This can be achieved by implementing feedback control based on sensor measurements. Previous studies have demonstrated a direct effect of weld temperature on the mechanical properties of FSW joints, [1], and therefore, temperature is chosen as primary process variable in this study.A new method for temperature measurement in FSW referred to as the Tool-WorkpieceThermocouple (TWT) method has recently been developed by De Backer. The TWT method is based on thermoelectric effect and allows accurate, fast and industrially suitable temperature monitoring during welding, without the need for thermocouples inside the tool [2].This paper presents an application of the TWT method for optimisation of the initial weld phases, plunge and dwell, operation in conventional FSW, which can also be applied to friction stir spot welding (FSSW). An analysis of the operation parameters by using feedback temperature control is presented aiming to better control of the initial weld phases through temperature feedback.

The introduction of the TWT temperature sensor provides additional process information during welding. Fast data acquisition gives opportunity to differentiate different process phases: contact of probe tip with workpiece surface; plunge phase; dwell phase. This would be followed by tool retraction for FSSW or tool traverse phase for FSW.The effect of the plunge parameters on weld temperature and duration of each phase were studied for the purpose of optimising the process with respect to process (i) robustness, (ii)time, (iii) robot deflection and (iv) quality. By using temperature feedback, it is possible to control the plunge phase to reach a predefined weld temperature, avoiding overheating of the material, which is known to have a detrimental influence on mechanical properties. The work presented in this paper is an important step in the optimization of robotic FSSW and FSW.

Place, publisher, year, edition, pages
Cambridge, UK: , 2016
Keywords
Plunging, Friction Stir Spot Welding, Temperature, TWT, Robot
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-9530 (URN)
Conference
11th International Symposium on Friction Stir Welding, Cambridge, UK, 17-19 May, 2016
Available from: 2016-07-08 Created: 2016-07-08 Last updated: 2020-02-26Bibliographically approved
4. Thermal dissipation effect on temperature-controlled friction stir welding: [Efeito da dissipação térmica inducida durante soldadura por friçcão linear sob controlo de temperatura]
Open this publication in new window or tab >>Thermal dissipation effect on temperature-controlled friction stir welding: [Efeito da dissipação térmica inducida durante soldadura por friçcão linear sob controlo de temperatura]
2019 (English)In: Soldagem & Inspeção, ISSN 0104-9224, E-ISSN 1980-6973, Vol. 24, article id e2428Article in journal (Refereed) Published
Abstract [en]

During Friction Stir Welding (FSW) of complex geometries, the thermal dissipation, induced by geometric features or the surrounding environment, may strongly affect the final weld quality. In order to guarantee a consistent weld quality for different conditions, in-process welding parameter adaptation is needed. This paper studies the effect of thermal dissipation, induced by the backing bar thermal conductivity, on the weld temperature and the temperature controller response to it. A new temperature sensor solution, the Tool-Workpiece Thermocouple (TWT) method, was applied to acquire online temperature measurements during welding. An FSW-robot equipped with temperature control, achieved by rotation speed adaptation, was used. AA7075-T6 lap joints were performed with and without temperature control. The cooling rate during welding was register plus macrographs and tensile tests were assessed. The controller demonstrated a fast response promoting the heat input necessary to maintain the set welding temperature. The results demonstrated that temperature control using the TWT method is suitable to achieve higher joint performance and provides a fast setup of optimal parameters for different environments. © 2019, Universidade Federal de Uberlandia. All rights reserved.

Keywords
Aluminum alloys; Controllers; Cooling; Friction; Research laboratories; Temperature control; Temperature measurement; Temperature sensors; Tensile testing; Thermal conductivity; Thermoanalysis; Thermocouples; Welds, Cooling rates; Friction stir welding(FSW); Online temperature measurement; Surrounding environment; Temperature controllers; Thermal dissipation; TWT method; Welding temperatures, Friction stir welding
National Category
Manufacturing, Surface and Joining Technology
Identifiers
urn:nbn:se:hv:diva-14999 (URN)10.1590/0104-9224/SI24.28 (DOI)000510209200001 ()2-s2.0-85078163111 (Scopus ID)
Funder
Region Västra Götaland, RUN 612-0254-15European Regional Development Fund (ERDF), No. 20200328
Available from: 2020-02-22 Created: 2020-02-22 Last updated: 2020-02-26
5. Robotic Friction Stir Welding of complex geometry and mixed materials
Open this publication in new window or tab >>Robotic Friction Stir Welding of complex geometry and mixed materials
2018 (English)In: 50th International Symposium on Robotics, ISR 2018, VDE Verlag GmbH , 2018, p. 35-41Conference paper, Published paper (Refereed)
Abstract [en]

Friction stir welding (FSW) is a solid state process for joining materials which has demonstrated advantages compares with other methods which include joining of mixed materials, hard to weld alloys and consistent and high quality. This paper presents a study of robotic FSW initiated by Volvo Skövde plant to join an insert workpiece of extruded aluminium with a cylinder block of aluminium casting. A three-stage procedure was decided to determine the feasibility to apply robotic FSW. The stages included study of welding the mixed materials, weld along the complex joint line with holes and channels close to the joint, and finally welding the cylinder block. The results based on preliminary analysis indicate that the final tests were successful and the process is feasible for the challenging case study. However, further studies are recommended in order to identify the operating parameters window, tool design, and control of the process in order to optimize productivity and quality. © VDE VERLAG GMBH

Place, publisher, year, edition, pages
VDE Verlag GmbH, 2018
Keywords
Aluminum castings, Cylinder blocks, Cylinders (shapes), Die casting inserts, Friction, Joining, Quality control, Research laboratories, Robotics, Welds, Complex geometries, Friction stir welding(FSW), Joining materials, Mixed materials, Operating parameters, Preliminary analysis, Robotic friction stir welding, Solid-state process, Friction stir welding
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
urn:nbn:se:hv:diva-13431 (URN)2-s2.0-85059384869 (Scopus ID)978-3-8007-4699-6 (ISBN)
Conference
50th International Symposium on Robotics, ISR 2018; Messe Munchen East EntranceMunich; Germany; 20 June 2018 through 21 June 2018
Available from: 2019-01-21 Created: 2019-01-21 Last updated: 2020-02-26Bibliographically approved
6. A Friction Stir Welding case study using Temperature Controlled Robotics with a HPDC Cylinder Block and dissimilar materials joining
Open this publication in new window or tab >>A Friction Stir Welding case study using Temperature Controlled Robotics with a HPDC Cylinder Block and dissimilar materials joining
Show others...
2019 (English)In: Journal of Manufacturing Processes, ISSN 1526-6125, Vol. 46, p. 177-184Article in journal (Refereed) Published
Abstract [en]

The automotive industry is going through a radical transformation from combustion engines to fully electric propulsion, aiming at improving key performance indicators related to efficiency, environmental sustainability and economic competitiveness. In this transition period, it is important to continue the innovation of combustion engines for e.g. plug-in hybrid vehicles. This led Volvo Cars to pursue radically new manufacturing processes such as Friction Stir Welding (FSW). The work presented in this paper is a case study whereby feasibility of using FSW to join a reinforcement element into the aluminium casted Cylinder Block was studied. The complex geometry of the joint required a flexible five-axis manipulator, i.e. an industrial robot, as well as advanced process control, i.e. temperature feedback control, in order to maintain a consistent weld quality throughout the whole component. The process was successfully demonstrated in a lab environment and offers a cost-efficient solution while maintaining the durability and higher efficiency. The outcome of this study shows the great potential of implementing the FSW process in combination with High Pressure Die Casted components, such a Cylinder Block. © 2019 The Society of Manufacturing Engineers

Place, publisher, year, edition, pages
Elsevier, 2019
Keywords
Aluminum; Automotive industry; Benchmarking; Casting; Combustion; Competition; Cylinder blocks; Dissimilar materials; Efficiency; Friction; Friction stir welding; Industrial manipulators; Intelligent control; Manipulators; Plug-in hybrid vehicles; Research laboratories; Robots; Sustainable development; Temperature control, Advanced Process Control; Automotive; Economic competitiveness; Environmental sustainability; Friction stir welding(FSW); Key performance indicators; Manufacturing process; Radical transformation, Process control
National Category
Manufacturing, Surface and Joining Technology Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering; Production Technology
Identifiers
urn:nbn:se:hv:diva-14487 (URN)10.1016/j.jmapro.2019.08.012 (DOI)000493221100017 ()2-s2.0-85072050179 (Scopus ID)
Available from: 2019-10-01 Created: 2019-10-01 Last updated: 2020-02-26Bibliographically approved

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Ferreira Magalhães, Ana Catarina

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