30-Second Summary: Aluminum alloys are inherently easy to machine, but chip tangling and surface quality are the biggest challenges in deep hole drilling. High speed, high feed, and adequate lubrication are the keys to success. Use polished, uncoated carbide tooling to prevent aluminum adhesion. For high-silicon cast alloys (>10% Si), PCD tooling is recommended for production volumes.
Key Machining Points
- Vc: 80-160 m/min (can be 2-3 times higher than steel). For high-speed production, 100-220 m/min is achievable with carbide tooling on rigid machines.
- Feed: 0.07-0.28 mm/rev (D=10mm), prioritize higher feed to produce thicker chips that break more readily. Low feed (below 0.04 mm/rev) produces thin continuous ribbons that tangle.
- Tooling: High helix angle gundrill, polished chip flutes, uncoated K-grade carbide (prevents aluminum adhesion on rake face). For high-silicon alloys, PCD-tipped or diamond-coated tooling for production runs.
- Coolant: Emulsion or synthetic fluid, 30-60 bar, focus on lubrication and chip evacuation. Maintain stable coolant temperature (20-22°C recommended) — aluminum's high thermal expansion coefficient (23 μm/m·K, roughly twice that of steel) makes dimensional stability sensitive to coolant temperature fluctuations.
Common Alloy Comparison
| Alloy | Type | Machinability | Typical Vc | Notes |
|---|---|---|---|---|
| 6061-T6 | Wrought, general-purpose | Good | 100–160 m/min | Clean cuts, good surface finish, excellent for general deep hole drilling |
| 7075-T6 | Wrought, high-strength | Moderate | 80–120 m/min | Abrasive, tool wear higher than 6061. Zinc content causes adhesive tendency at high speed |
| 2024-T3 | Wrought, aerospace | Good | 100–150 m/min | Stringy chips, needs aggressive chip breaker geometry |
| A356-T6 | Cast, automotive | Moderate-Good | 80–130 m/min | Silicon content abrasive, use K10 grade; eutectic Si particles accelerate flank wear |
| AlSi10Mg | Cast, high-silicon | Fair | 60–100 m/min | ~10% Si causes abrasive wear. PCD tooling recommended for high-volume production. Expect 3-5× longer tool life vs. carbide |
| AlSi12 / 390 | Cast, hypereutectic | Poor | 50–80 m/min | >12% primary Si particles extremely abrasive. PCD mandatory for production. Use coolant ≥50 bar to flush abrasive debris |
Chip Breaking Strategies
- Feed rate control: Higher feed produces thicker chips that curl and break naturally. Target ≥0.10 mm/rev for D=10mm holes.
- G73 chip-breaking cycle: Uses a small retract (0.1-0.5mm) without full withdrawal, breaking chips by interrupting the cut. Effective for moderate depth-to-diameter ratios.
- G83 peck drilling: Full retraction to clear chips. Preferred for depth-to-diameter ratios above 15:1 or when chip tangling is severe.
- Chilled coolant: Reducing coolant temperature by 10-15°C below ambient produces shorter chips (20-30% reduction in chip length observed in studies), as lower temperatures reduce thermal softening that promotes continuous chip formation.
Common Problems
- Chip tangling: Long ribbon chips wrap around the tool — increase feed, add chip breaker geometry, or switch to G73/G83 cycle.
- Surface scoring: Chips scratch the machined surface during evacuation — increase coolant flow for flushing, verify coolant filtration (<20 μm recommended for gundrilling).
- Built-up edge (BUE): Aluminum adheres to the cutting edge at moderate speeds (40-80 m/min range). Stay above 100 m/min or use polished uncoated carbide to avoid BUE.
- Dimensional deviation: Aluminum's high thermal expansion coefficient (23 μm/m·K) — maintain stable coolant temperature within ±2°C for tight tolerances.