1. ABSTRACT
In general, Forming Limit Diagrams (FLDs) are considered as a convenient
and often used tool for the evaluation of the forming process of sheet materials.
Forming limit diagrams (FLD-s) deliver quantitative, graphical information
concerning the ultimate ductility of the material and display under various strain
conditions and boundary criterion of material failure during deep drawing process.
FLD also indicates the limiting strains that the sheet metal can sustain over a wide
range of major to minor strains ratios. In fact, during the design stage of any new
sheet metal component, FLD is used extensively to design the final component and
tooling shape and to optimize the forming process parameters. Therefore in order
to attain successful forming process, FLD analysis must be done.
Friction Stir Welding (FSW) is a collection of a series of friction-based solid
state joining processes, in which the frictional heat is generated through a relative
movement between two components when force is applied to soften the interface
material. These techniques show considerable advantages when compared to
traditional fusion welding techniques, such as the absence of solidification defects,
ability to weld dissimilar materials, lack of consumables, and ease of automation,
limited energy requirements and high ecocompatibility. Therefore, Friction stir
welding has been attracting increasing attention in many applications, such as
aerospace, automobiles, railway and nuclear industry.
In the present work, an attempt has been made numerically to construct the
FLD of bare aluminium plate (Al-5052) and friction stir welded plates with
constant spindle speed 1500 rpm and at different welding speeds ranging between
0.25 mm/s to 1.25mm/s. Forming limit diagram of base metal Al-5052 and a
Friction stir welded Al-5052 plates were compared numerically using ABAQUS

2. finite element software and justified by conducting experiments. The effect of
material imperfections on FLD of aluminium plates was also studied.
It is observed that, the forming limit diagram (FLD) of Friction stir welded
plates of 1 mm/s and 1.25 mm/s has shown improved formability when compared
to other friction stir welded plates. Numerical FLD of base metal (Al-5052)
showed better correlation with experimental results. Due to lack of provisions for
material modeling in numerical method, moderate correlation was noted for FLD
obtained through numerical and experimental methods. Due to finer grain size at
the weld region, improved formability was observed for the welded plates.
Key words: FLD, formability, friction stir welding process, welding speed,
material imperfections