Machining Inconel 718 on a CNC lathe is notoriously difficult due to its high work-hardening rate, low thermal conductivity, and abrasive nature. However, with the right cutting parameters, tooling, and coolant strategy, you can achieve consistent results and acceptable tool life. This guide focuses on practical tips for production turning.

1. Cutting Parameters – Start Conservative

For rough turning of Inconel 718 (solution treated and aged), use the following starting points:

● Cutting speed (Vc): 35–55 m/min (115–180 SFM) for uncoated or PVD-coated carbide. Do not exceed 60 m/min for roughing.

● Feed rate: 0.10–0.25 mm/rev (0.004–0.010 in/rev). Avoid feeds below 0.08 mm/rev to prevent rubbing and work hardening.

● Depth of cut: 1.0–2.5 mm (0.040–0.100 in). Light depths (under 0.5 mm) cause excessive edge wear.

● Constant surface speed (G96) is mandatory to maintain consistent chip load as diameter decreases.

For finishing passes: reduce feed to 0.05–0.12 mm/rev and depth to 0.2–0.5 mm, but keep speed similar or slightly lower.

2. Tooling – Substrate, Geometry & Coating

Use ISO S-class carbide (fine grain or ultra-fine grain) with a sharp but honed edge (T-land 15–25 µm). The best coatings for Inconel 718 are:

● AlTiN (Aluminum Titanium Nitride) – high hot hardness and oxidation resistance.

● TiAlN + MoST – adds lubricity to reduce built-up edge.

● Avoid TiN or TiCN – they degrade quickly at high temperatures.

Insert geometry: positive rake, open chipbreaker (e.g., “MF” or “MS” chipbreaker from major brands). For internal turning (boring), choose inserts with through-coolant holes.

3. Coolant & Chip Control – High Pressure Is Key

Flood coolant is not enough. For reliable machining of Inconel 718 on a CNC lathe, you need high-pressure coolant (HPC) at 300–1000 PSI directed precisely at the cutting zone.

Benefits of HPC:

● Breaks stringy, hazardous chips.

● Reduces thermal softening of the cutting edge.

● Prevents re-cutting of work-hardened chips.

If your lathe does not have HPC, consider through-tool coolant adapters and increase pecking cycles for drilling operations. Also, use a chip conveyor with strong flushing because Inconel chips are abrasive and can damage the machine bed.

4. Toolpath & Programming Strategies

To minimize work hardening and edge notching, follow these CNC programming rules:

● Avoid dwell (G04) unless absolutely necessary. Any stop while in cut will cause a hard spot.

● Use constant engagement – modern CAM can produce dynamic or trochoidal turning paths that distribute thermal load.

● Climb turning (tool moves from large to small diameter on a OD turn) helps reduce built-up edge.

For deep holes: use peck drilling cycles with short pecks (2–3 mm) and full retract to clear chips.

● Set max spindle speed (G50 S1200) to prevent centrifugal issues at small diameters.

Example turning cycle start:

G96 S55 M03

G50 S1200

G99 (feed per rev)

G01 Z-10.0 F0.15

5. Troubleshooting Common Problems

6. Summary & Best Practices

To successfully machine Inconel 718 on a CNC lathe:

● Use S-class carbide with AlTiN coating.

● Run Vc 35–55 m/min, feed 0.10–0.25 mm/rev, depth 1–2.5 mm.

● High-pressure coolant (≥500 PSI) is non-negotiable for tool life.

● Program constant surface speed and avoid dwell.

● Monitor tool wear every 15 minutes; replace insert at 0.3 mm flank wear.

Following these parameters and tooling tips will turn Inconel 718 from a nightmare into a manageable high-value material.

For custom turned parts made from Inconel 718. feel free to request a quote from Dongguan Start Precision Technology Co., Ltd.