OCTOBER 19-20, 2012 - YMCA University of Science & Technology

Proceedings of the National Conference on
Trends and Advances in Mechanical Engineering,
YMCA University of Science & Technology, Faridabad, Haryana, Oct 19-20, 2012
A STUDY OF RECENT TRENDS IN FRICTION STIR WELDING
Rajan 1 , Shailesh S. Sengar 2 , Jitender Kumar
1. Department of Mechanical Engineering, YMCAUST Faridabad
2. Department of Mechanical Engineering, YMCAUST Faridabad
3. Department of Mechanical Engineering, YMCAUST Faridabad
Abstract
This paper deals with the fundamental understanding of friction stir welding process. Friction stir welding is
one of the most economical and highly efficient methods in joining similar and dissimilar metals. Most
commercial FSW applications use simple butt joint like circular cross section and alternative designs such as
T-sections, ɪ-section, triangular Geometry and corner welds are very rarely welded. The focus of this paper is on
mechanism of FSW, influence of parameters, heat generation in the process, understanding the deformation,
microstructure and the properties of similar and dissimilar welded materials. This review paper will cover
relevant published work conducted to date on FSW.
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Keywords: FSW, LSW, FSSW, ERHAFW
1. Introduction
Friction stir welding (FSW) is a solid state process for joining materials, especially dissimilar materials, which
involves generation of heat by the conversion of mechanical energy into thermal energy at the interface of the
work pieces without using electrical energy or heat from other sources during rotation under pressure.As a highquality,
precise, high-efficiency, energy-saving and environmental- friendly technique, FW has been widely used
in the aerospace, shipbuilding, automobile industries and in many applications of commercial importance. Some
of the advantages over the conventional welding techniques are very low distortion, no fumes, porosity or
spatter, no consumables, no special surface treatment and no shielding gas requirements. Two important types of
friction welding is explained as follows:
2. Spin welding
Spin welding systems consist of two chucks for holding the materials to be welded, one of which is fixed and the
other rotating. Before welding one of the work pieces is attached to the rotating chuck along with a flywheel of a
given weight. The piece is then spun up to a high rate of rotation to store the required energy in the flywheel.
Once spinning at the proper speed, the motor is removed and the pieces forced together under pressure. The force
is kept on the pieces after the spinning stops to allow the weld to "set". This technique is also known as inertia
welding, rotational welding or inertial friction welding.
3. Linear friction welding
Linear friction welding (LFW) is similar to spin welding except that the moving chuck oscillates laterally instead
of spinning. The speeds are much lower in general, which requires the pieces to be kept under pressure at all
times. This also requires the parts to have a high shear strength. Linear friction welding requires more complex
machinery than spin welding, but has the advantage that parts of any shape can be joined, as opposed to parts
with a circular meeting point.
4. Mechanism of joint formation
In most of cases three stages are identified in friction welding. First stage occurs as the surface contact is made
at localized regions especially at surface irregularities and asperities. Due to the high local pressure during
rotation, surface films are broken down to reveal the parent metal and local hot spots are continuously formed
and destroyed. The second stage is characterized by steadily increasing power demand. At the start of this stage,
the temperature reaches its operating value and plastic deformation begins at the interface as indicated by ‘burn
off’ at the joint area. The third stage of the process begins when the rotating component is brought to rest and the
applied pressure is maintained or decreased to consolidate the weld. Rapid material displacement in joint region
causes diffusion at the interface, recrystallization and grain growth. During deceleration stage, the interface
undergoes hot working as identified by the rise in torque. This continues until such a point when the shear
strength of the interface equals to that of the material adjacent to it. The absolute value of the torque developed is
governed by the adjacent material, applied pressure and the speed of rotation.
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