Ti6Al4V alloy is very hard to flowform at room temperature due to its limited ductility. However, it retains excellent adiabatic heat trapping and thermal softening abilities, which can play an important role in improving the formability. In this paper, a 3-D finite element model of backward flowforming with three staggered rollers has been developed in Abaqus/explicit to study the thermomechanical behavior and the residual stress evolution. The model has been validated via flowforming experiments. The role of the heat generation due to plastic deformation is highlighted by comparing a thermomechanical analysis to a purely mechanical analysis without incorporating the additional heat input due to the plastic work. The maximum predicted temperature rise during cold flowforming is 911 °C, which significantly reduces the flow stress in the deformation zone. The two most important factors, which affect the temperature rise in the deformation zone, are friction coefficient and coolant heat transfer coefficient. Hence, a study has been done to assess the sensitivity of the thermomechanical behavior and the residual stresses towards these factors. The friction between the mating surfaces is helpful, but a friction coefficient higher than 0.1 causes through-thickness strain heterogeneity. An increase in the friction coefficient reduces the residual stresses, while an increase in the convective heat transfer coefficient causes a transition from compressive to tensile residual stress along the thickness of the tube.
Ti6Al4V alloy Flowforming process Thermomechanical behavior Finite element model Residual stresses Heat transfer
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Seshacharyulu T, Medeiros SC, Morgan JT et al (2000) Hot deformation and microstructural damage mechanisms in extra-low interstitial (ELI) grade Ti–6Al–4V. Mater Sci Eng A 279:289–299CrossRefGoogle Scholar
Ericsson, T (2002) The effect of final shaping prior to heat treatment, handbook of residual stress and deformation of steel. ASM Int., pp 150–158Google Scholar
Mahdi M, Zhang L (1997) Applied mechanics in grindingis—V. Thermal residual stresses. Int J Mach Tools Manuf 37:619–633CrossRefGoogle Scholar
IIT Kharagpur NPTEL Web Course (2012) Finite element formulation for 3 dimensional elements, NPTEL: National Programme on Technology Enhanced Learning. Available at: https://nptel.ac.in/courses/105105041/31[Accessed 10 Jan. 2019]