Gradient thickness-dependent distribution of residual stress and springback of thin-walled TC4 titanium alloy sheet with variable thickness in collaborative manufacturing process of pre-plastic forming and milling

Abstract

Thin-walled sheet components with variable thickness and complex curved surface are expanding considerably in the advanced manufacturing field of aerospace industry due to its aerodynamic shape and light-weight characteristics, and collaborative manufacturing method of pre-plastic forming and milling was used to solve the problems of low rough milling efficiency and large milling difficult of such components. However, the structural characteristics of thin-walled and variable thickness brought the problems of residual stress and springback after pre-plastic forming, which impacted the milling quality and increased milling allowance in subsequent milling. In this work, based on three-point bending tests of thin-walled TC4 titanium alloy sheets with different ratio of thickness variation (ζ) and its Finite Element Analyze (FEA), gradient thickness-dependent distribution of residual stress and springback after pre-plastic forming was systematically studied. The results showed that with the ζ increasing from 1 to 6, difference of residual stress (Δσres) between both sides increased from 0 to 356.81 MPa, difference of springback (ΔS) between both sides increased 0 to 0.23 mm, and Springback Angle (SA) increased from 11.02 ° to 11.88 °, which was due to the increasing of stress component along the breadth direction and the decreasing of strain component along the thickness direction, and specimen #5 (ζ = 3) had more uniform distribution of residual stress. In addition, through considering the decay of elastic modulus (E) after plastic deformation, absolute error of SA of specimen #6 (ζ = 6) was reduced from 1.98 ° to 0.95 °.