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Surface Quality and Strength in Robotic Friction Stir Welding of Thin Automotive Aluminium Alloys
University West, Department of Engineering Science, Division of Automation Systems. (PTW)ORCID iD: 0000-0001-9553-7131
University West, Department of Engineering Science, Division of Automation Systems. (PTW)ORCID iD: 0000-0001-5608-8636
2011 (English)In: The 4th International Swedish Production Symposium / [ed] Jan-Eric Ståhl, The Swedish Production Academy , 2011, 554-562 p.Conference paper (Refereed)
Abstract [en]

Friction Stir Welding (FSW) is a novel method for joining materials without using consumablesand without melting the materials. It uses a rotating tool that creates frictionalheat and mixes the materials mechanically together. Robotic application of FSW allowsthree-dimensional welding of light-weight metals in e.g. the automotive industry. TheStiRoLight project is driven by Saab Automobile AB and performed at University Westfor investigation of robotic FSW of three-dimensional welding seams. It aims to introduceFSW in the automotive production line. This paper describes the effect of penetrationdepth of the FSW tool during force controlled robotic welding of thin (< 2 mm) aluminium inoverlap configuration. The influence of pin length on strength of welded aluminium sheetsis investigated using tensile and peel tests. The main limiting factor for penetration depthis the surface quality on the backside of the weld, which often is important in automotiveapplications. Further, the roughness of the plates on the backside is measured and relatedto pin length and backing bar properties. This paper shows a relation between penetrationdepth and tensile strength, and suggests an optimal pin length to guarantee a good weldquality while maintaining an acceptable surface quality. The influence of sheet thicknesstolerance is also discussed. Knowledge is fed back to designers and manufacturingengineers to facilitate for use in production with guaranteed product quality.

Place, publisher, year, edition, pages
The Swedish Production Academy , 2011. 554-562 p.
Keyword [en]
Robot, Friction Stir Welding, Surface Quality, Automotive, Aluminium
National Category
Manufacturing, Surface and Joining Technology Robotics
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-3711OAI: oai:DiVA.org:hv-3711DiVA: diva2:444015
Conference
Swedish Production Symposium. Lund, Sweden, 3rd to 5th of May 2011
Projects
StiRoLight (Vinnova-FFI)
Available from: 2011-09-27 Created: 2011-09-27 Last updated: 2016-02-08Bibliographically approved
In thesis
1. Robotic Friction Stir Welding for Flexible Production
Open this publication in new window or tab >>Robotic Friction Stir Welding for Flexible Production
2012 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Friction Stir Welding (FSW) is a modern welding process that joins materials by frictional heat, generated by a rotating tool. Unlike other welding processes, the material never melts, which is beneficial for the weld properties. FSW is already widely adopted in several industries but the applications are limited to simple geometries like straight lines or circular welds, mostly in aluminium. The welding operation is performed by rigid FSW machines, which deliver excellent welds but puts limitations on the system in terms of flexibility and joint geometries. Therefore, several research groups are working on the implementation of the FSW process on industrial robots. A robot allows welding of three-dimensional geometries and increases the flexibility of the whole system. The high process forces required for FSW, in combination with the limited stiffness of the robot brings some extra complexity to the system.  The limitations of the robot system are addressed in this licentiate thesis.

One part of the thesis studies the effect of robot deflections on the weld quality. A sensor-based solution is presented that measures the path deviation and compensates this deviation by modifying the robot trajectory. The tool deviation is reduced to an acceptable tolerance and root defects in the weld are hereby eliminated. The sensor-based method provided better process understanding, leading to a new strategy that uses existing force-feedback for path compensations of the tool. This method avoids extra sensors and makes the system less complex. Another part of this work focuses on the extra complexity to maintain a stable welding process on more advanced geometries. A model is presented that allows control of the heat input in the process by control of the downforce. Finally, the robot’s limitations in terms of maximal hardness of the materials to be welded are investigated. Parameter tuning and implementation of preheating are proposed to allow robotic FSW of superalloys.

Abstract [sv]

Friction Stir Welding eller ”friktionsomrörningssvetsning” är en svetsprocess som kräver ett roterande verktyg som genom friktionsvärme får materialet att mjukna. Verktyget blandar runt det plastiska materialet mekaniskt och skapar en fog av hög kvalité. Processen fungerar utan gas, utan rök, utan tillsatsmaterial och utan att smälta materialet. Alla dessa fördelar skapar stort industriellt intresse inom flera branscher. Idag används tekniken nästan uteslutande i styva maskiner som svetsar raka eller cirkulära fogar och framförallt för aluminium. Eftersom processen kräver stora krafter mellan material och verktyg är det svårt att implementera processen på en robot. En robot möjliggör svetsning av tredimensionella geometrier och ökar dessutom flexibiliteten.  Flera forskargrupper runt i världen har tagit fram en fungerande FSW robot som kan svetsa tunn lättviksmaterial som aluminium med hög kvalitet. Användningen i industrin av FSW robotar är däremot obefintlig och det finns ett antal anledningar till det. Först är roboten vek vilket gör att verktyget kan missa svetsfogen i hårda material och svetsdefekter kan uppstå. En annan anledning är at det inte finns en användbar automatiserad processtyrning tillgänglig, mest för att FSW är en robust process och inte kräver en avancerad styrning vid svetsning av raka fogar.

De praktiska arbeten som redovisas i denna licentiatuppsats är huvudsakligen utförda i en robotiserad FSW-demonstrator på Högskolan Väst. FSW-roboten är en modifierad industrirobot som är försetts med spindel och kraftåterkoppling för att styra kraften som roboten applicerar på arbetsstycket.

Detta arbete har identifierat ett antal problem som behöver lösas för att få en robust robotiserad FSW process i en flexibel produktionsmiljö. I denna licentiatrapport beskrivs en lösning hur en typ av svetsdefekter kan förhindras genom en sensorbaserad bankompensering. Både en kamera- och lasersensor-baserad mätmetod presenteras. En annan bankompenseringsstrategi är beskriven, som använder kraftsensorn från befintlig kraftåterkoppling istället för att lägga till extra sensor. Denna strategi kan utvecklas till en komplett utböjningsmodell på roboten i hela arbetsområdet. Robotens begränsningar gällande svetsbarhet av hårda material har undersökts och med hjälp av parameteroptimering och förvärmning kan även hårda nickelbaserade legeringar svetsas med roboten.

Place, publisher, year, edition, pages
Lund: Lund University, 2012. 141 p.
Keyword
Friction Stir Welding, Automation, Robotics, Aluminium, Lightweight design
National Category
Mechanical Engineering Robotics Control Engineering Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Industrial engineering; ENGINEERING, Mechatronics
Identifiers
urn:nbn:se:hv:diva-4429 (URN)978-91-7473-342-6 (ISBN)
Presentation
2012-06-15, C118, Högskolan Väst, Trollhättan, 17:10 (English)
Opponent
Supervisors
Projects
StiRoLight
Available from: 2012-06-27 Created: 2012-06-18 Last updated: 2016-02-08Bibliographically approved

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