Flood Coolant vs MQL for Titanium Pocket Milling

Titanium alloys’poor thermal conductivity (6.7 W/m·K for Ti-6Al-4V) and chemical reactivity present unique challenges in pocket milling operations . While flood cooling has been the industry standard for heat dissipation, growing environmental concerns and cost pressures have spurred interest in MQL alternatives . Recent advances in nozzle design and biodegradable lubricants (e.g., ester-based formulations) have renewed the viability debate . This study addresses the knowledge gap through systematic comparison of both methods under industrial-relevant conditions, with particular attention to cutting mechanics and post-machining metallurgical effects.

Methodology

1. Experimental Design

A full factorial design (3×3 matrix) tested cooling strategies (flood, MQL, hybrid) against cutting parameters. The MQL system delivered 50 mL/hr aerosolized lubricant (Accu-Lube LB-12) through a 0.5mm nozzle at 6 bar pressure.

2. Data Acquisition

• Cutting forces: Kistler 9257B dynamometer

• Tool wear: Keyence VHX-7000 digital microscope (ISO 3685 standards)

• Thermal data: FLIR A655sc IR camera (±2°C accuracy)

Results & Analysis

1.Cutting Force Dynamics

MQL exhibited lower mean resultant forces (Fxy = 210 N vs. 265 N under flood) due to reduced friction coefficients. Frequency domain analysis revealed 25-30% smaller vibration amplitudes in MQL.

2.Tool Life Comparison

Flank wear progression curves showed MQL extended tool life to 148 minutes versus 112 minutes (flood) before reaching VBmax = 0.3 mm. EDS analysis detected 60% less titanium adhesion on MQL-used tools.

Discussion

The superior performance of MQL aligns with tribological models suggesting micro-droplet penetration into tool-chip interfaces . However, chip evacuation issues in deep pockets (aspect ratio >5:1) temporarily increased forces by 15%, indicating scenario-specific limitations. Industrial adopters should weigh these findings against coolant recycling infrastructure costs.

Conclusion

MQL demonstrates clear advantages in titanium pocket milling regarding tool longevity (32% improvement) and surface finish. Future work should explore pulsed MQL delivery for high-aspect-ratio geometries and nano-additive lubricants.