Heated Friction Stir Welding: An Experimental and Theoretical Investigation into How Preheating Influences Process Forces

Friction stir welding between plates of unequal thickness, which are made from similar or dissimilar materials, finds wide range of applications in the aerospace and automotive sectors. Friction stir welding of plates made from dissimilar materials having unequal thicknesses is challenging. One of the major challenges is the control of rapid tool degradation which occurs during welding. This work reports a maiden study on tool degradation of high thickness ratio unequal thickness dissimilar material joints made between 6.3 mm thick AA2024-T3 and 2.5 mm thick AA7475-T7 plates. The degradation of friction stir welding tool made of T4 tool steel having tapered cylindrical pin and scrolled shoulder was analyzed. The geometry of tool (before and after welding) was compared; the degradation was categorized, characterized, and analyzed in the light of measured welding temperature, process forces, and process parameters. It was found that the pin undergoes significant degradation in the form of wear and deformation compared to the tool shoulder. The experimental results demonstrated that lower flow stresses caused by higher process temperature leads to lower tool wear and deformation, and vice versa. In addition to temperature and process forces, the surface tilt angle was found to significantly affect the pin deformation. The higher surface tilt angle caused an increase in tool wear and deformation.

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Flow, process forces and strains during Friction Stir Welding: A comprehensive First principle approach

Proceedings of the Institution of Mechanical Engineers Part B Journal of Engineering Manufacture ◽

10.1177/0954405420970087 ◽

2020 ◽

pp. 095440542097008

Author(s):

Dhruv Bajaj ◽

Arshad Noor Siddiquee ◽

Noor Zaman Khan ◽

AK Mukhopadhyay ◽

Sohail M A Khan Mohammed ◽

...

Keyword(s):

Friction Stir Welding ◽

Shear Strain ◽

Material Flow ◽

Large Scale ◽

Defect Formation ◽

First Principle ◽

Flow Process ◽

Maximum Shear Strain ◽

Friction Stir ◽

Process Forces

Friction stir welding is recent yet spectacular process, which assumes accrescent expanse to evolve as a multi-purpose process. Its potential is greatly being tapped through large-scale experimental and computer simulation-based investigations. Several simulation and empirical models have been proposed but exact fundamental analyses on forces, material flow and strain are still absent. Complexities associated with the process are perhaps the main reason that a fundamental analysis is difficult. A comprehensive analysis of this kind is critical for understanding the evolution of microstructure, mechanical properties of joint and defect formation. This study presents an analysis of material flow, process forces and strains using first principle approach. Results have been presented as exact mathematical expressions in terms of material properties and process parameters. It was demonstrated that the material during stirring experiences direct and shear strains both when it moves from advancing side to retreating side in front of the tool and after rotation deposits behind the tool. It was also demonstrated that the strain significantly reduced from advancing to retreating side; for a typical case the shear strain greater than 10,000% prevails in advancing side and the maximum shear strain on retreating side is of the order of 6000%.

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Process forces during friction stir welding of aluminium alloys

Science and Technology of Welding & Joining ◽

10.1179/136217108x372540 ◽

2009 ◽

Vol 14 (2) ◽

pp. 141-145 ◽

Cited By ~ 29

Author(s):

N. Balasubramanian ◽

B. Gattu ◽

R. S. Mishra

Keyword(s):

Friction Stir Welding ◽

Aluminium Alloys ◽

Friction Stir ◽

Process Forces

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Tool Downscaling Effects on the Friction Stir Spot Welding Process and Properties of Current-Carrying Welded Aluminum–Copper Joints for E-Mobility Applications

Metals ◽

10.3390/met11121949 ◽

2021 ◽

Vol 11 (12) ◽

pp. 1949

Author(s):

Aristide Tchouaha Tankoua ◽

Tobias Köhler ◽

Jean Pierre Bergmann ◽

Michael Grätzel ◽

Philip Betz ◽

...

Keyword(s):

Friction Stir Welding ◽

Spot Welding ◽

Pure Aluminum ◽

Thin Sheet ◽

Similar Process ◽

Friction Stir ◽

Research Activities ◽

Process Forces ◽

Force Reduction ◽

Tool Diameter

According to the technical breakthrough towards E-Mobility, current-carrying dissimilar joints between aluminum and copper are gaining an increasing relevance for the automotive industry and thus, coming into focus of many research activities. The joining of dissimilar material in general is well known to be a challenging task. Furthermore, the current-carrying joining components in E-Drive consist of pure aluminum and copper materials with relatively thin sheet thickness, which are thermally and mechanically very sensitive, as well as highly heat and electrically conductive. This results in additional challenges for the joining process. Due to their properties, friction stir welding and especially fiction stir spot welding (FSSW) using pinless tools—i.e., as hybrid friction diffusion bonding process (HFDB) is more and more attractive for new application fields and particularly promising for aluminum–copper joining tasks in E-Mobility. However, the feasibility is restricted because of the relatively high process forces required during friction stir welding. Thus, to fulfill the high process and quality requirements in this above-mentioned application field, further research and process development towards process force reduction are necessary. This work deals with the application of the tool downscaling strategy as a mean of process force reduction in FSSW of thin aluminum and copper sheets for current-carrying applications in E-Mobility, where the components are very sensitive to high mechanical loads. The tool downscaling approach enables constant weld quality in similar process time of about 0.5 s despite reduced process forces and torques. By reducing the tool diameter from 10 mm to 6 mm, the process force could be reduced by 36% and the torque by over 50%. Furthermore, a similar heat propagation behavior in the component is observable. These results provide a good basis for the joining of E-Drive components with thermal and mechanical sensitive sheet materials using the pinless FSSW process.

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Microstructural and Mechanical Behaviour Evaluation of Mg-Al-Zn Alloy Friction Stir Welded Joint

International Journal of Automotive and Mechanical Engineering ◽

10.15282/ijame.17.3.2020.08.0612 ◽

2020 ◽

Vol 17 (3) ◽

pp. 8150-8159

Author(s):

Kulwant Singh ◽

Gurbhinder Singh ◽

Harmeet Singh

Keyword(s):

Heat Treatment ◽

Friction Stir Welding ◽

Magnesium Alloys ◽

Mechanical Performance ◽

Fuel Efficiency ◽

Research Work ◽

Grain Structure ◽

Tensile Fracture ◽

Friction Stir ◽

The Impact

The weight reduction concept is most effective to reduce the emissions of greenhouse gases from vehicles, which also improves fuel efficiency. Amongst lightweight materials, magnesium alloys are attractive to the automotive sector as a structural material. Welding feasibility of magnesium alloys acts as an influential role in its usage for lightweight prospects. Friction stir welding (FSW) is an appropriate technique as compared to other welding techniques to join magnesium alloys. Field of friction stir welding is emerging in the current scenario. The friction stir welding technique has been selected to weld AZ91 magnesium alloys in the current research work. The microstructure and mechanical characteristics of the produced FSW butt joints have been investigated. Further, the influence of post welding heat treatment (at 260 °C for 1 h) on these properties has also been examined. Post welding heat treatment (PWHT) resulted in the improvement of the grain structure of weld zones which affected the mechanical performance of the joints. After heat treatment, the tensile strength and elongation of the joint increased by 12.6 % and 31.9 % respectively. It is proven that after PWHT, the microhardness of the stir zone reduced and a comparatively smoothened microhardness profile of the FSW joint obtained. No considerable variation in the location of the tensile fracture was witnessed after PWHT. The results show that the impact toughness of the weld joints further decreases after post welding heat treatment.

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