Machining Characteristics of Medical Titanium
1. Processing Challenges Due to Material Properties
Low Thermal Conductivity
Thermal conductivity (~7 W/m·K) causes heat concentration in cutting zones, rapidly increasing tool temperature (>800°C) and accelerating tool wear.
Solution: High-pressure cooling (>70 bar) with specialized cutting fluids.
High Chemical Reactivity
At high temperatures, titanium readily reacts with tool materials (e.g., carbide), forming built-up edge (BUE).
Typical issue: Titanium adhesion to tool edges leads to coating delamination.
Low Elastic Modulus
Approximately 50% of steel's modulus, causing elastic deformation during machining and compromising dimensional accuracy (especially in thin-walled components).
Work Hardening Tendency
Cold-worked hardened layers (up to 0.1mm deep) increase subsequent machining difficulty.
2. Critical Machining Parameters
| Process | Recommended Parameters | Tool Selection |
|---|---|---|
| Turning | Cutting speed: 30–50 m/min (roughing) | Diamond-coated inserts / ultrafine carbide |
| Milling | Feed per tooth: 0.05–0.1 mm/z (finishing) | Sharp edges (rake angle ≥15°) |
| Drilling | Speed: 500–800 rpm (Φ5mm drill) | Cobalt HSS (HSS-Co) or solid carbide |
| Grinding | Wheel speed: 15–20 m/s | Green silicon carbide (GC) or CBN wheels |
3. Medical-Specific Requirements
Surface Integrity
Implant surface roughness must be ≤0.8μm (ISO 7206), typically requiring electropolishing or sandblasting.
Contamination-Free Machining
Lead/cadmium-containing coolants are prohibited; vegetable-based coolants are recommended.
Microstructure Control
β-phase content affects biocompatibility; overheating must be avoided to prevent grain coarsening.
4. Specialized Techniques
Cryogenic Machining: Liquid nitrogen cooling suppresses heat generation for precision components.
Laser-Assisted Machining: Localized preheating reduces cutting forces in Ti-6Al-4V ELI.
Ultrasonic Vibration Cutting: Minimizes burr formation in dental abutments.
