Friction Stir Processing on Two Overlapping (side by side) Metal Beads of Wire Arc Additive Manufacturing

Kotturu, Sridath and Chinthapenta, Viswanath (2019) Friction Stir Processing on Two Overlapping (side by side) Metal Beads of Wire Arc Additive Manufacturing. Masters thesis, Indian institute of technology Hyderabad.

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Abstract

The Wire Arc Additive Manufacturing(WAAM) is the best method for manufacturing large metal additive parts due to its high deposition rates, less buy to fly ratio, low production costs and the ability to produce parts of large build volume. However, like any other process, the WAAM process too has got its own drawbacks/limitations. The localized heat input in a particular direction in this WAAM process for that matter in any welding process leads to thermal gradients which inturn leads to residual stresses and finally distortions. So predicting thermal cycles, working on mitigating residual stresses and improving the mechanical properties of deposited material on each layer is very much essential to build the components of large build volume. Thus to use WAAM for large production we need a mechanism that should be incorporated in the WAAM machine so that the stresses developed after each layer are reduced and the mechanical properties of each layer are improved. In this project, the work is concentrated on using Friction Stir Processing(FSP) to achieve the above things. Friction stir processing(FSP) is a method that is generally used to alter microstructure according to the requirement of mechanical properties like Ductility, Strength, Fatigue life, e.t.c on welded joints. It is also the only method to manufacture surface composites, which represents the capability of the process for altering the microstructure. In this undertaking, I Considered working with two overlapping(side by side) metal beads so that this layup can be used as a way for building large parts with superior properties. So in this process, I have started with the analysis of two overlapping metal beads predicting the thermal cycles, stresses and the distortions produced in base plate due to weld deposition using finite element package in Abaqus. Also, the stresses and distortions produced in the deposited weld beads can be analyzed. After obtaining the analysis results of deposited layers, the analysis of Friction Stir Processing on this two overlapping metal beads is performed, again using Finite Element package in Abaqus. This is done in order to get an idea about the temperature histories of the material points so that the phase transformations if any can be predicted. Experimental Study of Thermal cycles, Residual Stresses and the Distortions produced in the workpiece due weld deposition is performed. The Simulated results matched well with performed experimental results. This study also suggests the optimal Tool rotation speed of the tool in Friction Stir Processing so as to get the required microstructural properties on the overlapping metal beads. In this study, the parameteric study of only Rotational speed of the tool is considered keeping all the other parameters constant. In this study we have observed that,using Friction Stir Processing one can alter the microstructure thus mechanical properties on two overlapping metal beads using only the tool rotation speed as the varying parameter, and this was proved here by doing simulations and performing experiments.

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