Considerations when milling titanium

Milling titanium is challenging due to its material properties, including high strength, low thermal conductivity, and chemical reactivity at elevated temperatures. These factors necessitate specialized tooling, machine parameters, and process planning. Below is a concise guide outlining key considerations:

1. Tooling

Material: Use high-performance carbide tools, preferably with coatings like AlTiN or TiAlN to improve wear resistance and reduce heat buildup.

Geometry: Sharp cutting edges and positive rake angles minimize cutting forces. Use tools with variable helix angles to reduce vibration and chatter.

2. Cutting Parameters

Speed: Titanium has low thermal conductivity, so heat concentrates at the tool tip. Use low cutting speeds (typically 30–60 m/min for carbide tools).

Feed: Moderate to high feed rates (0.05–0.2 mm/tooth) help maintain chip load and prevent rubbing, which causes work hardening.

Depth of Cut: Keep axial depths small to moderate. Radial engagement should be limited to <30% of tool diameter in high-speed strategies.

3. Coolant & Lubrication

Use high-pressure, high-flow coolant (typically water-soluble) to evacuate chips and control temperature. Flood cooling is often preferred; MQL is sometimes viable in controlled environments.

Avoid recutting chips—chip evacuation is critical due to titanium’s tendency to produce long, stringy chips.

4. Machine Tool

High-rigidity machines with vibration damping are essential. Titanium amplifies chatter due to its elasticity and work-hardening behaviour.

Spindle power must be sufficient to handle high loads at low RPMs.

5. Workholding

Ensure rigid fixturing; any micro-movement can rapidly increase tool wear or cause tool failure.

Consider thermal expansion—titanium expands differently than steel or aluminium, and heat can cause distortion in the workpiece.

6. Tool Wear and Monitoring

Tool wear occurs rapidly due to high cutting temperatures. Monitor for signs of crater wear and edge chipping.

Use tool life management and possibly in-process monitoring if tolerances are tight or machining is unattended.

7. Strategies

Consider trochoidal (adaptive) milling for roughing to keep engagement consistent and reduce heat concentration.

Minimize dwell time—titanium work-hardens quickly if the tool lingers.

Use climb milling to reduce tool wear and improve surface finish.