1
Operators know the scene: chips pack a 50 mm-deep pocket, the re-cut chips weld, the tool snaps, the spindle alarms. Aluminum’s low density and high thermal conductivity make chips sticky; tight corners and long stick-outs trap them. Existing rules of thumb—open flutes, flood coolant—fail when pockets exceed 3×tool diameter. This study quantifies the combined effect of tool geometry, coolant pressure and tool-path kinematics on chip evacuation in 2025 production conditions.
2 Research Methods
2.1 Design of Experiments
Full 2³ factorial with center points (n = 11).
Factors:
• A: Helix angle—38° (low), 45° (high).
• B: Coolant pressure—40 bar (low), 80 bar (high).
• C: Path strategy—adaptive trochoid vs conventional raster.
2.2 Workpiece & Machine
7075-T6 blocks, 120 × 80 × 60 mm, pockets 10 mm wide × 50 mm deep. Haas VF-4SS, 12 k HSK-63 spindle, Blaser Vasco 7000 coolant.
2.3 Data Acquisition
• Chip residence time: high-speed camera at 5 000 fps, tracked via dyed chips.
• Tool wear: optical microscope, VB ≤0.2 mm end-of-life.
• Surface roughness: Mahr Perthometer M400, cut-off 0.8 mm.
2.4 Reproducibility Package
G-code, tool list and coolant nozzle drawings archived at github.com/pft/chip-evac-2025.
3 Results and Analysis
Figure 1 shows the Pareto chart of standardized effects; helix angle and coolant pressure dominate (p < 0.01). Table 1 summarizes key metrics:
Table 1 Experimental outcomes (mean, n = 3)
Parameter set | Chip residence (s) | Tool life (min) | Ra (µm)
38°, 40 bar, raster | 4.8 | 22 | 1.3
45°, 80 bar, trochoid | 2.8 | 45 | 0.55
Improvement | –42 % | +105 % | –58 %
Figure 2 plots chip velocity vectors; the 45° helix generates an upward axial speed component of 1.8 m/s vs 0.9 m/s for 38°, explaining faster evacuation.
4 Discussion
4.1 Mechanism
Higher helix increases effective rake, thinning chips and reducing adhesion. 80 bar coolant delivers 3× higher mass flow; CFD simulation (see Appendix A) shows turbulent kinetic energy at pocket base rises from 12 J/kg to 38 J/kg, enough to lift 200 µm chips. Trochoidal paths keep constant engagement, avoiding chip packing seen in raster corners.
4.2 Limitations
Tests limited to 7075 aluminum; titanium alloys may require cryogenic assist. Depth-to-width >8:1 pockets showed occasional chip damming even under optimum settings.
4.3 Practical Implications
Shops can retrofit existing machines with variable-pitch, high-helix carbide end mills and programmable coolant nozzles for <$2 000 per spindle, payback within 3 months based on tool-life savings.
5 Conclusion
High-helix cutters, 80 bar through-tool coolant and trochoidal paths form an effective, transferable package that slashes chip residence time and doubles tool life in deep-pocket aluminum milling. Future work should extend the matrix to titanium and explore in-process vacuum extraction for aspect ratios above 8:1.
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