Coupled thermomechanical analysis of friction stir welding process using simplified models

Abstract

It is widely recognised that the fundamental mechanisms associated with the weld formation process and their relationships with welding parameters are complex and remain to be fully understood. The present paper reports a series of general findings based on a set of simplified numerical models that were designed to elucidate various aspects of the complex thermomechanical phenomena associated with friction stir welding. The following phenomena were investigated in separate numerical models: (i) coupled friction heat generation; (ii) plastic flow slip zone development; and (iii) three-dimensional heat and material flow. The friction induced heat generation model was used to quantify the contributions of coupled thermomechanical friction heating, including non-linear interfacial phenomena between the tooling (e.g. stir pin) and material being welded. The plastic work induced heating effects were also examined. The plastic slip formation mechanisms were then investigated by considering contributions from various heating mechanisms. Finally, a simplified three-dimensional heat and material flow model, based on the observations from the coupled friction heat generation model, was used to establish some initial insight regarding the heat and material flow. The results from the three subproblem areas were then generalised in the form of a simple parametric relationship between welding variables (i.e. travel and rotating speeds) and weld formation conditions. A series of assumptions were made in constructing these individual models since there exists little information on actual material behaviour under friction stir welding conditions. However, the findings from the present study not only illuminate some of the important weld formation mechanisms in friction stir welding, but also provide an effective framework for more focused investigations into some of the fundamental phenomena identified in the three subproblem areas: such investigations will be reported separately in a future publication.

Recent advances in friction-stir welding – Process, weldment structure and properties

“…Generally this state is reached before strain drops to a low value, ǫ = 1, and since the strains involved in FSW are much larger, it may be assumed that a single set of material constants corresponding to steady-state deformation can be utilised with the assumption that they are independent of strain. Most of the recent studies have considered the temperature dependent thermal conductivity, specific heat and yield stress for the work-piece [39][40][41][65][66][67]. The tool material commonly used for the FSW of aluminium alloys, steels and Ti-6Al-4V are tool steel and tungsten, respectively.…”

A Comparison of Different Finite Element Methods in the Thermal Analysis of Friction Stir Welding (FSW)

“…In the model, a transient thermal condition in which the power was recorded experimentally and defined in the model as a constant value was used. Dong et al [84] and Chao et al [85] compared the experimental and the numerical results of the generated heat energy during FSW using the Lagrangian method. In Chao's model, a steady state condition was employed for the tool and a transient condition was used for the plates.…”

A Semianalytical Thermal Model for Fiction Stir Welding

“…Dong et al developed a work [6] in which they reported a series of general findings based on a set of simplified numerical models that were designed to elucidate various aspects of the complex thermomechanical phenomena associated with FSW. A friction-induced heat generation model was used to quantify the contributions of coupled thermomechanical friction heating, including nonlinear interfacial phenomena between the tooling (e.g., stir pin) and material being welded.…”