Finite Element Analysis and Experimental Investigation on Effect of Process Parameters in Plasma-Assisted Friction Stir Welding of Low Carbon Steel

Nowadays, hybrid friction stir welding of high strength/melting point alloys like steels is an emerging technique to improve the material flow and reduce the welding forces. This work carried out the experimental and numerical investigations on friction stir welding (FSW) and plasma-assisted hybrid FSW (P-FSW) of AISI 1018 low carbon steel plates. A three-dimensional finite element (FE) transient thermal model based on the DFLUX subroutine was developed using the FE software package ABAQUS 6.14. The moving coordinate-based surface heat flux distribution for the tool shoulder and volumetric heat distribution for the tool pin was considered. The Gaussian distribution of heat flux was applied in the P-FSW to model the preheating source. The transient thermal profiles and stir zone isotherms of the FE models were correlated fairly well with the experimental results of the FSW and P-FSW. The influence of tool rotational speed, traverse speed, plasma radius, and the gap between tool shoulder and plasma preheating source on comparative thermal history was investigated. It was observed that the plasma assistance in FSW significantly enhanced the heat generation than the normal FSW. Furthermore, the temperature in P-FSW increased by enhancing the plasma radius and reducing the gap between the tool shoulder and the plasma preheating source. The plunging force was reduced by around 20-25% using the plasma preheating ahead of the FSW tool. P-FSW joint experienced a comparatively higher weld strength, which can be attributed to the more grain refinement in P-FSW than the FSW under the higher heat generation.