Nickel and cobalt-based superalloys are the most difficult materials for deep hole drilling. Hot hardness, severe work hardening, and low thermal conductivity combine. Low Vc, high rigidity, and aggressive cooling are mandatory. Coolant pressure is the single most important tool life factor.
| Alloy | Wear Mode | Vc (m/min) | Pressure | Tool |
|---|---|---|---|---|
| Inconel 718 | Notch + work hardening | 15–30 | ≥100 bar | AlTiCrN carbide |
| Inconel 625 | Adhesion + abrasion | 20–35 | ≥80 bar | AlTiCrN / TiAlN |
| Hastelloy X | Oxidation + crater | 15–25 | ≥100 bar | AlTiCrN superlattice |
| Waspaloy | Work hardening + chipping | 12–22 | ≥100 bar | PCBN / AlTiCrN |
| Monel 400 | Severe adhesion | 20–35 | ≥80 bar | Sharp TiAlN, polished rake |
| Rene 88/95 | Plastic deformation + oxidation | 10–20 | ≥100 bar | PCBN or ceramic-coated |
| Study | Condition | Key Result |
|---|---|---|
| Aerospace thrust actuator (dgflex) | Inconel 718, Ø2.5mm × 12×D, 36 holes | 300 PSI + TiAlN = 3–5 holes. 1000 PSI + AlCrN + optimized = 36+ holes. 10× improvement. |
| Cryogenic gundrilling, 2024 | Inconel 718, Ø10mm, LN&sub2; vs oil | Ra 29–55% better. Wall temp 18–28% lower. Circularity 12–22% better. |
| SLM vs wrought, 2025 | Vc 25, f 0.04, LCO&sub2; cryo | LCO&sub2; reduced tool wear 68% for SLM Inconel 718. |
| Nano-MQL, 2025 | Nanofluid MQL drilling | Ra 45% better vs flood. Temp 34–56% lower. |
| Coolant pressure vs flow (CFD) | Internal cooling, Inconel 718 | Higher pressure (not flow) improves edge cooling and tool life — dead zones persist at the edge regardless of flow rate. |
| Uncut-chip-to-edge-radius ratio | t₀/r₁ < 1 (thrust-dominated) | Thrust force and straightness deviation rise up to 3× vs cutting-dominated conditions — keep feed×f above the edge-radius limit. |
| Hybrid EDM guide hole + gundrill | Sequential EDM hole then gundrill | Thrust 800→250 N, straightness 48.65% better, uniform wear at 80 mm depth. |
Confirm ≥100 bar and kidney-shaped through-tool delivery; a standard 50-bar machine will not do.
Short tool overhang, tight spindle, solid workholding — serrated chips will excite any compliance.
Start at the low end of Vc with feed 0.01–0.03 mm/rev, continuous engagement, no dwell.
Peck 0.5–1×D with full retract; partial retracts leave serrated chips in the bore.
Steady coolant pressure and smooth spindle load = healthy. Spikes mean chip jamming or edge failure.
Tool life and parameters vary run to run — log holes per edge and adjust upward methodically.