Precise Machining Based on Ritz Non-uniform Allowances for Titanium Blade Fabricated by Selective Laser Melting

Abstract

Selective Laser Melting (SLM) is an increasingly concerned trend in Ti-6Al-4V blade manufacturing, while the SLMed Ti-6Al-4V blade cannot be used directly because of poor surface integrity and high residual stresses. Precise machining after SLM is a feasible solution but also a challenge. The low rigidity of the blade will lead to deformation when machining. The deformation can lead to surface error and may make defect parts. Two-steps machining processes to address the problems were proposed in this paper. First, a non-uniform allowance distribution was allocated and optimized in semi-finishing based on Ritz solution to elastic deformation. The blade was simplified as a cantilever thin plate with various thickness, and the thickness of finishing allowance was designed and optimized on the premise of ensuring the thin-wall stiffness of the blade, so as to realize the design of Ritz non-uniform allowance. Then, finishing machining was conducted to achieve precise parts. A blade deformation model was established to evaluate surface error with cutting force moving and changing. Finite element analysis and experimental validation in ball-end milling of a blade were conducted. FEA results and experimental results showed dimensional errors have been reduced up to 50%. Further surface tests demonstrated that the mean surface roughness reduced from 7.88 μm to 0.815 μm. And the residual surface stresses of the SLM samples changed after semi-finishing machining due to the residual stress relaxation and redistribution. The results demonstrated that the proposed method enhanced the surface quality of blade fabricated by SLM.