Precise machining based on Ritz non-uniform allowances for titanium blade fabricated by selective laser melting

Bo Zhang,Juntang Yuan,Zhenhua Wang,Xi Li

doi:10.1007/s00170-022-08701-7

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-step machining processes to address the problems were proposed in this paper. First, a non-uniform allowances 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 thicknesses, and the thicknesses of finishing allowances were 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 allowances. Then, finishing machining was conducted to achieve precise parts. A blade deformation model was established to evaluate part distortions with cutting force moving and changing. Finite element analysis (FEA) 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 to 0.815 μm. And the residual surface stresses of the SLM samples changed after semi-finishing machining due to the residual stresses relaxation and redistribution. The results demonstrated that the proposed method enhanced the surface quality of the blade fabricated by SLM.

Highlights

Additive manufacturing (AM) is a rather new type of metal parts manufacturing technology developed in recent years
The results demonstrated that the proposed method enhanced the surface quality of blade fabricated by Selective Laser Melting (SLM)
Blade parts fabricated by SLM have poor surface integrity and high residual stresses

Summary

Introduction

Additive manufacturing (AM) is a rather new type of metal parts manufacturing technology developed in recent years. Selective laser melting (SLM) is a typical common AM technology. It is a powder layer fusion technology that can produce complex structures with relatively good surface quality [1]. The surface quality and the manufacturing tolerances of Ti-6Al-4V parts built with SLM still require finishing processing to produce the final products. The cutting forces in the process of machining tend to produce unnecessary deformation, resulting in surface error of machined parts (see Fig. 1). The post machining accuracy must be considered for SLM forming components. The surface error prediction is necessary before machining. For different methods to improve the machining accuracy, modeling and simulations to predict the machining surface error are useful in verification before expensive experimental tests [3]. Some strategies are listed for improve the final surface topography [4]:

Methods

Findings

Discussion

Conclusion