Abstract
In friction stir welding, lesser tool life restricts the usage of non-circular pin in friction stir welding tool eventhough it delivers comparatively better weld joints than circular pin. Process peak temperature during the process affects the shear strength of the flowing material around the tool pin. Maintaining the process peak temperature as low as possible improves the properties in heat affected zone but on the other hand it increases the stress on the tool pin.Especially on the usage of non-circular pin, the pin surface experiences uneven stress distribution and causes premature tool failure. In this paper, optimum thermal environment through proper selection of process parameters and dwell period with respect to the pin geometry are analysed. A comparative analysis is also made to understand the impact of increase in flat surfaces in the pin surface on weld quality in the view of developing a suitable thermal environment that can improve tool life without compromising joint strength. Apart from this, optimum dwell period for the chosen tool pin geometry is analysed based on the empirical softening temperature of the material.
Highlights
Friction stir welding, being a completely solid state joining process, eliminates major problems associated with other molten state joining processes
The friction stir welding flow of material around the tool depends on the major process parameters like axial force and tool rotational speed, apart from that the tool pin profile plays a key role on propelling the material behind the tool in the stir zone during the forward motion of the tool
Experimental study was carried out to correlate the relationship between pin geometry, process temperature and weld quality in the view of observing optimum thermal conditions to use flat-faced tool pin in the friction stir welding of AA2024-T3 plates
Summary
Friction stir welding, being a completely solid state joining process, eliminates major problems associated with other molten state joining processes. Venkatarao et al.[13] attained better weld strength with the usage of hexagonal tool pin profile in the joining of AA2219 Al-Cu alloy-plates These facts reveal that along with the pin geometry, the optimization of process parameters with respect to the chosen pin geometry should be done in order to create an efficient thermal environment which assists the material flow rate along with less property degradation in the heat affected zone. Joining with lower process temperature causes insufficient material flow around the tool which develops weld defects From these factors it can be understood that the process thermal environment has to be optimised according to the pin geometry as every pin shape has different flow inducing ability. Temperature rise in the dwell period is analysed to obtain an optimum dwell period for the chosen pin geometry
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