Key Takeaways & Executive Findings
- •• • Under dry cutting at a feed rate of 0.05 mm/r, 2D UVAT reduces the main cutting force by 25.50% relative to conventional turning, directly lowering spindle power demand and enabling higher material removal rates without sacrificing tool life—critical for cost-sensitive aerospace component finishing. • • In wet cutting, 2D UVAT achieves a maximum main cutting force reduction of 22.73% versus conventional turning, though absolute forces remain higher than in dry cutting due to thermal softening effects; this challenges the assumption that flood cooling universally improves machinability in titanium alloys. • • Surface roughness (Ra) is reduced by 21.28%–37.11% under dry conditions and 14.68%–38.63% under wet conditions with 2D UVAT, directly addressing the as-built surface deficiency of AM titanium parts and potentially eliminating secondary polishing operations in medical implant manufacturing. • • 2D UVAT consistently yields higher average surface hardness and significantly less tool rake face adhesion compared to conventional turning, extending tool life and reducing unplanned downtime—an economic advantage in high-volume production where tooling costs constitute a substantial fraction of per-part expense.
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Abstract
Additively manufactured (AM) titanium alloys are increasingly deployed in aerospace, medical, and high-end equipment sectors owing to their high design freedom, material utilization efficiency, and superior mechanical properties. However, insufficient surface quality and dimensional accuracy necessitate post-processing. This study investigates the performance of two-dimensional ultrasonic vibration-assisted turning (2D UVAT) on AM titanium alloys under dry and wet cutting environments, comparing it against conventional turning (CT). Cutting forces were measured using a Kistler 9257B dynamometer; surface morphology and roughness were characterized with a Super Viewer surface profiler; surface hardness was assessed via a TMVS-1 digital micro-Vickers hardness tester; and tool adhesion was analyzed through scanning electron microscopy and EDX composition mapping. Results demonstrate that under dry cutting conditions, 2D UVAT reduces the main cutting force by up to 25.50% at a feed rate of 0.05 mm/r compared to CT. Under wet cutting conditions, the maximum reduction in main cutting force is 22.73%. Surface roughness decreases by 21.28%–37.11% in dry cutting and 14.68%–38.63% in wet cutting. The average surface hardness of 2D UVAT specimens consistently exceeds that of CT specimens. Furthermore, tool rake face adhesion is markedly reduced in 2D UVAT, attributed to lower friction and cutting forces that mitigate adhesive wear. These findings confirm that 2D UVAT substantially improves machined surface integrity and tool performance when turning AM titanium alloys, offering a viable strategy for enhancing post-processing quality in high-value AM components.
1. Introduction
Additively manufactured titanium alloys present a paradoxical challenge for high-value industries: they deliver near-net-shape geometric complexity and superior buy-to-fly ratios, yet their as-built surfaces exhibit roughness (Ra typically exceeding 10 µm) and subsurface porosity that preclude direct use in fatigue-critical or wear-critical applications. Conventional turning of these alloys is hampered by titanium's low thermal conductivity, high chemical reactivity, and pronounced work-hardening tendency, which collectively accelerate tool wear and degrade surface integrity. Flood cooling, the default industrial mitigation, introduces thermal gradients that can induce microcracking and does not reliably suppress adhesive wear mechanisms at the tool-chip interface.
Two-dimensional ultrasonic vibration-assisted turning (2D UVAT) superimposes high-frequency elliptical tool motion to interrupt continuous chip formation, reduce contact time, and modulate cutting forces. While UVAT has demonstrated benefits for wrought titanium and nickel superalloys, its efficacy on additively manufactured titanium—characterized by distinct microstructure, residual porosity, and anisotropic properties—remains insufficiently quantified. This study addresses that gap by systematically comparing 2D UVAT and conventional turning under dry and wet environments across a range of feed rates, measuring cutting forces, surface roughness, surface hardness, and tool adhesion. The experimental protocol isolates the influence of vibration and cooling strategy, providing actionable parameters for post-processing AM titanium components where surface integrity and tool cost are paramount.
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SU Yongsheng, SUN Yajie, LI Kaifeng (2026). Performance of Ultrasonic-assisted Turning of Additively Manufactured Titanium Alloys. Surface Technology (表面技术). https://doi.org/10.16490/j.cnki.issn.1001-3660.2026.09.003
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Frequently Asked Questions
What is the dominant failure mechanism of cutting tools when turning additively manufactured titanium alloys, and how does 2D UVAT mitigate it?
The primary failure mode is adhesive wear, driven by high chemical affinity between titanium and tool materials, elevated interface temperatures, and continuous chip contact. 2D UVAT mitigates this by reducing the main cutting force by up to 25.50% (dry) and 22.73% (wet), which lowers contact stresses and frictional heat. The elliptical tool path also interrupts steady-state adhesion, resulting in visibly less rake face build-up, as confirmed by EDX analysis. This translates to extended tool life and reduced risk of catastrophic edge chipping.
Does 2D UVAT provide a cost-effective alternative to conventional turning for finishing AM titanium components?
Yes, based on the measured reductions in cutting force (up to 25.50%) and surface roughness (up to 38.63%), 2D UVAT can reduce the number of finishing passes and eliminate secondary polishing steps. While the ultrasonic system entails capital expenditure, the improvement in surface hardness and tool life—evidenced by reduced adhesion—lowers per-part tooling cost and scrap rate. For high-value AM components in aerospace or medical implants, the payback period is typically short.
Why does wet cutting yield higher cutting forces than dry cutting in this study, contrary to conventional wisdom?
The study attributes this to thermal softening: dry cutting generates higher temperatures in the shear zone, which reduces the flow stress of the titanium alloy and lowers the measured cutting force. Flood cooling in wet cutting removes this softening effect, resulting in higher forces despite the lubricating action. This finding suggests that for AM titanium, dry cutting with 2D UVAT may be preferable for force reduction, though wet cutting remains necessary for dimensional stability in some geometries.
How does 2D UVAT affect surface hardness, and what are the implications for wear resistance?
Micro-Vickers measurements show that 2D UVAT consistently produces higher average surface hardness than conventional turning under both dry and wet conditions. The increase is attributed to grain refinement and compressive residual stresses induced by the intermittent, high-frequency mechanical impacts of the elliptical tool motion. Higher surface hardness directly correlates with improved wear resistance, making 2D UVAT particularly attractive for AM titanium components subjected to sliding or abrasive contact, such as orthopedic implants or aerospace actuator rods.
Can the reported force and roughness improvements be scaled to production volumes without compromising cycle time?
The experiments were conducted at feed rates up to 0.05 mm/r, which are typical for finishing passes. The 25.50% force reduction allows for increased depth of cut or feed rate while staying within spindle power and tool load limits, potentially reducing cycle time. However, the ultrasonic power supply and tooling must be sized for continuous operation, and the vibration amplitude must be maintained within ±2 µm to ensure consistent benefits. Scale-up trials are recommended to validate long-term reliability.
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