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Analysis of Plunge and Dwell Parameters of Robotic FSW Using TWT Temperature Feedback Control
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0003-3261-9097
University West, Department of Engineering Science, Division of Production System. (PTW)ORCID iD: 0000-0001-9553-7131
University West, Department of Engineering Science, Division of Production System.ORCID iD: 0000-0002-1869-232X
2016 (English)In: Proceedings of 11th International Symposium on Friction Stir Welding, Cambridge, UK, 2016, 1-11 p.Conference 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. 1-11 p.
Keyword [en]
Plunging, Friction Stir Spot Welding, Temperature, TWT, Robot
National Category
Manufacturing, Surface and Joining Technology
Research subject
ENGINEERING, Manufacturing and materials engineering
Identifiers
URN: urn:nbn:se:hv:diva-9530OAI: oai:DiVA.org:hv-9530DiVA: diva2:947425
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: 2016-10-14Bibliographically 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. 62 p.
Keyword
FSW, Robotic, Temperature, TWT, Plunge, Control
National Category
Robotics
Research subject
Production Technology
Identifiers
urn:nbn:se:hv:diva-9982 (URN)978-91-87531-43-9 (Printed version) (ISBN)978-91-87531-42-2 (ISBN)
Supervisors
Available from: 2016-11-09 Created: 2016-10-12 Last updated: 2016-11-10Bibliographically approved

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Silva, AnaDe Backer, JeroenBolmsjö, Gunnar
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