Introduction
You need a titanium part that is stronger than Grade 2 but still weldable, formable, and corrosion-resistant. You do not need the extreme strength of Grade 5 (Ti-6Al-4V) or its complex heat treatment requirements. What you need is Grade 4 titanium—also known as TA4—the strongest of the unalloyed titanium grades.
Grade 4 sits in a unique position. It offers tensile strength up to 655 MPa, significantly higher than Grade 2, while maintaining the excellent corrosion resistance and biocompatibility of commercially pure titanium. It is the go-to material for applications requiring more strength than lower grades but without the added complexity of alloyed titanium.
But machining Grade 4 is not like machining Grade 2. Its higher strength and hardness demand more powerful equipment, more durable tools, and more careful parameter selection. At Yigu Technology, we machine TA4 for aerospace, medical, and industrial clients. This guide covers the material’s properties, machining strategies, and quality control methods that deliver consistent results.
What Makes Grade 4 (TA4) Titanium Unique?
A High-Strength Unalloyed Titanium
Grade 4 titanium is the strongest of the commercially pure (CP) titanium grades. It achieves its strength through controlled oxygen and iron content rather than alloying elements.
| Grade | Tensile Strength (MPa) | Yield Strength (MPa) | Hardness (HB) | Typical Use |
|---|---|---|---|---|
| Grade 1 | 240 | 170 | 80 | High formability |
| Grade 2 | 345 | 275 | 95 | General purpose |
| Grade 3 | 450 | 380 | 110 | Moderate strength |
| Grade 4 | 485–655 | 415–550 | 120 | Highest strength CP |
| Grade 5 | 895–965 | 830–900 | 330–370 | High-strength alloy |
Key difference: Grade 4 achieves its higher strength through tighter control of oxygen (up to 0.40%) and iron (up to 0.30%). These elements strengthen the material without the need for vanadium or aluminum, keeping it weldable and formable.
Mechanical Properties
| Property | Value | Implication for Machining |
|---|---|---|
| Tensile Strength | 485–655 MPa | Higher cutting forces than Grade 2 |
| Yield Strength | 415–550 MPa | Resists deformation; requires rigid setups |
| Hardness | 120 HB | More abrasive; accelerates tool wear |
| Elongation | 15–20% | Still ductile; forms chips |
| Modulus of Elasticity | 105 GPa | Stiff; less deflection than lower grades |
Physical Properties
| Property | Value | Implication |
|---|---|---|
| Density | 4.51 g/cm³ | Lightweight; excellent strength-to-weight |
| Thermal Conductivity | 16 W/(m·K) | Low; heat concentrates at cutting zone |
| Melting Point | 1660°C | High; no thermal softening during machining |
| Electrical Resistivity | 0.55 μΩ·m | Poor conductor; not for electrical applications |
Corrosion Resistance
Grade 4 titanium offers excellent corrosion resistance, comparable to other unalloyed titanium grades. It resists:
- Seawater and marine environments
- Chlorides and many acids
- Industrial atmospheres
- Biological environments (biocompatible)
This makes it suitable for marine components, chemical processing equipment, and medical implants.
How Does Grade 4 Compare to Other Titanium Grades in Machining?
| Factor | Grade 2 (TA2) | Grade 4 (TA4) | Grade 5 (Ti-6Al-4V) |
|---|---|---|---|
| Strength | Moderate | High | Very high |
| Machinability | Good | Fair | Poor |
| Tool wear rate | Baseline | 25% higher | 50–100% higher |
| Cutting speed | 80–120 m/min | 60–100 m/min | 40–70 m/min |
| Recommended tool | Carbide | Coated carbide | Coated carbide, ceramic |
Real-World Example:
A comparative milling test found that TA4 caused 25% more tool wear than Grade 2 when using the same cutting tools and parameters. The higher hardness and strength require adjusted strategies.
What Machining Strategies Work Best for TA4?
Cutting Tools
Tool selection is the most critical factor in machining TA4. The material’s higher strength and low thermal conductivity demand tools that resist wear and manage heat.
| Tool Material | Suitability | Notes |
|---|---|---|
| Carbide (micro-grain) | Best for production | High hardness; wear-resistant |
| Coated carbide (TiAlN) | Extended tool life | Reduces friction; heat-resistant |
| High-speed steel (HSS) | Limited | Acceptable for low-volume; wears quickly |
Tool life test: TiAlN-coated carbide tools lasted 30% longer than uncoated carbide when machining TA4 under equivalent conditions.
Tool Geometry
| Feature | Recommendation | Why |
|---|---|---|
| Helix angle | 40–45° (end mills) | Reduces cutting forces; improves chip evacuation |
| Rake angle | Positive (5–10°) | Lowers cutting forces; prevents work hardening |
| Edge preparation | Sharp but honed | Sharp enough to cut; honed to prevent chipping |
| Flute count | 4-flute for finishing; 2-3 for roughing | Balance chip clearance and surface finish |
Cutting Parameters
Milling
| Parameter | Recommended Range | Notes |
|---|---|---|
| Cutting speed | 60–100 m/min | Lower than Grade 2; manage heat |
| Feed per tooth | 0.08–0.15 mm/tooth | Moderate; avoid rubbing |
| Depth of cut (rough) | 0.5–2 mm | Light cuts manage heat |
| Depth of cut (finish) | 0.1–0.3 mm | Light passes for surface finish |
Turning
| Parameter | Recommended Range | Notes |
|---|---|---|
| Cutting speed | 50–80 m/min | Slower than milling |
| Feed rate | 0.1–0.2 mm/rev | Moderate |
| Depth of cut | 0.5–2 mm | Avoid heavy cuts |
Drilling
| Parameter | Recommended Range | Notes |
|---|---|---|
| Cutting speed | 30–50 m/min | Significantly slower |
| Feed rate | 0.05–0.1 mm/rev | Peck frequently |
| Tool | Carbide with through-coolant | Essential for deep holes |
Coolant Strategy
Flood coolant is essential for machining TA4. The low thermal conductivity means heat builds up quickly. Coolant:
- Cools the cutting zone
- Reduces tool temperatures
- Flushes chips away
- Prevents work hardening
High-pressure coolant (30–50 bar) is recommended for drilling and deep cuts. Through-coolant tools are particularly effective.
What Quality Control Measures Are Needed?
Tolerances
Grade 4 titanium can achieve tight tolerances with proper equipment and process control.
| Feature | Achievable Tolerance | Conditions |
|---|---|---|
| Small parts (<50 mm) | ±0.005 mm | Rigid setup; carbide tools; controlled environment |
| Medium parts (50–200 mm) | ±0.01 mm | Good fixturing; in-process inspection |
| Large parts (>200 mm) | ±0.02–0.05 mm | Thermal management; careful setup |
Surface Finish
| Application | Typical Ra Requirement |
|---|---|
| Aerospace components | ≤1.6 μm |
| Medical implants | ≤0.8 μm |
| Industrial parts | 1.6–3.2 μm |
| Sealing surfaces | ≤0.4 μm |
Achieving good finish:
- Sharp tools (replace before dull)
- Light finishing passes (0.1–0.2 mm)
- Adequate coolant
- Rigid setups to prevent chatter
Inspection Methods
| Method | Purpose | Typical Accuracy |
|---|---|---|
| CMM | Dimensional verification | ±0.001 mm |
| Optical profilometry | Surface finish measurement | ±0.01 μm |
| Ultrasonic testing | Internal defects | Detects voids, inclusions |
| Eddy current testing | Surface cracks | Detects micro-cracks |
| Visual inspection | Surface defects | Burrs, scratches, tool marks |
What Are the Common Challenges and Solutions?
Tool Wear
Challenge: TA4’s higher hardness accelerates tool wear. A comparative test showed 25% more wear than Grade 2.
Solutions:
- Use TiAlN-coated carbide tools
- Reduce cutting speed (60–100 m/min for milling)
- Maintain constant engagement; avoid dwell
- Replace tools based on cutting time, not failure
Heat Buildup
Challenge: Low thermal conductivity (16 W/m·K) concentrates heat at the cutting zone.
Solutions:
- Flood coolant (essential)
- High-pressure coolant for deep cuts
- Avoid excessive depth of cut
- Use tools with high positive rake angles
Work Hardening
Challenge: Like all titanium grades, TA4 work-hardens if the tool rubs instead of cuts.
Solutions:
- Maintain consistent feed (do not dwell)
- Use sharp tools
- Climb milling (tool moves with rotation)
- Avoid interrupted cuts where possible
Chip Control
Challenge: TA4 produces stringy, difficult-to-break chips.
Solutions:
- Use chip breaker geometries
- Maintain adequate feed to promote chip breaking
- Flood coolant to flush chips away
- Peck drilling for hole operations
Where Is Grade 4 Titanium Used?
Aerospace Components
TA4’s strength-to-weight ratio and corrosion resistance make it suitable for:
| Application | Why TA4 |
|---|---|
| Structural brackets | High strength; lightweight |
| Hydraulic system components | Corrosion resistance; pressure integrity |
| Fasteners | Strong enough for structural joints |
| Airframe parts | Weight savings without alloy complexity |
Medical Devices
Grade 4 titanium is biocompatible and used in medical applications:
| Application | Why TA4 |
|---|---|
| Orthopedic implants | Stronger than Grade 2; biocompatible |
| Surgical instruments | Corrosion-resistant; sterilizable |
| Dental fixtures | Biocompatible; strong |
| Prosthetic components | Lightweight; durable |
Industrial Applications
| Application | Why TA4 |
|---|---|
| Chemical processing equipment | Corrosion-resistant |
| Marine components | Seawater resistant |
| High-performance fasteners | Strength with corrosion resistance |
| Heat exchangers | Thermal conductivity adequate; corrosion-resistant |
Consumer Products
| Application | Why TA4 |
|---|---|
| High-end watches | Durable; aesthetic |
| Sporting goods | Lightweight; strong |
| Bicycle components | Weight savings |
| Jewelry | Biocompatible; attractive finish |
How Does TA4 Compare to Other Titanium Grades?
| Property | Grade 2 (TA2) | Grade 4 (TA4) | Grade 5 (Ti-6Al-4V) |
|---|---|---|---|
| Tensile Strength | 345–550 MPa | 485–655 MPa | 895–965 MPa |
| Machinability | Good | Fair | Poor |
| Weldability | Excellent | Excellent | Good (requires filler) |
| Corrosion Resistance | Excellent | Excellent | Excellent |
| Cost | Low | Moderate | High |
| Typical Applications | General purpose | Higher-strength CP | Aerospace, high-performance |
Choose Grade 4 when:
- You need more strength than Grade 2
- You require excellent weldability and formability
- The application does not require the extreme strength of Grade 5
- Corrosion resistance and biocompatibility are important
- Cost is a factor (Grade 4 is less expensive than Grade 5)
Yigu Technology's Perspective
At Yigu Technology, we have extensive experience machining Grade 4 titanium across aerospace, medical, and industrial applications. Our approach is built on understanding the material’s unique characteristics:
- Higher strength requires more rigid setups and more durable tools
- Lower thermal conductivity demands aggressive coolant strategies
- Work hardening tendency requires consistent feeds and sharp tools
Our standard practice for TA4:
- TiAlN-coated carbide tools for all production runs
- Cutting speeds: 60–100 m/min for milling; 50–80 m/min for turning
- Flood coolant with high-pressure option for deep cuts
- Rigid workholding to handle higher cutting forces
- CMM inspection for dimensional verification
- Surface finish measurement to ensure Ra values meet specifications
We have found that with proper parameter selection and tooling, TA4 machines predictably and reliably, delivering parts that meet the demanding requirements of aerospace, medical, and industrial applications.
Conclusion
Grade 4 (TA4) titanium occupies a unique position among titanium grades. It offers the highest strength of the unalloyed grades while retaining the excellent corrosion resistance, biocompatibility, and weldability of commercially pure titanium.
Machining TA4 requires understanding its characteristics:
- Higher strength and hardness than Grade 2
- Lower thermal conductivity concentrates heat
- Work hardening tendency demands consistent cutting
Success comes from:
- TiAlN-coated carbide tools for wear resistance
- Reduced cutting speeds (60–100 m/min for milling)
- Flood coolant for heat management
- Rigid setups to handle higher cutting forces
- Sharp tools to prevent work hardening
When these practices are followed, Grade 4 titanium machines reliably, delivering components that perform in the most demanding applications.
FAQ
What makes Grade 4 (TA4) titanium different from other titanium grades in terms of machining?
Grade 4 titanium has higher strength and hardness (120 HB vs 95 HB for Grade 2) and similar low thermal conductivity (16 W/m·K). This combination makes it more challenging to machine than lower grades. It causes more tool wear—approximately 25% more than Grade 2 under equivalent conditions—and requires lower cutting speeds (60–100 m/min for milling vs 80–120 m/min for Grade 2).
What are the typical tolerance levels achievable when CNC machining TA4?
With proper equipment and process control, ±0.005 mm tolerances can be achieved for small parts. For most parts, ±0.01 mm is consistently maintainable. Factors affecting tolerance include:
- Machine rigidity
- Tool sharpness and wear
- Thermal management
- Workholding stability
Achieving tight tolerances requires rigid setups, carbide tooling, and careful thermal control.
What inspection methods are most effective for ensuring the quality of TA4 machined parts?
A combination of methods ensures comprehensive quality verification:
- CMM (Coordinate Measuring Machine) : Dimensional accuracy, ±0.001 mm
- Optical profilometry: Surface finish measurement, Ra values
- Ultrasonic testing: Internal defects, voids, inclusions
- Eddy current testing: Surface cracks and micro-defects
- Visual inspection: Burrs, scratches, tool marks
For critical aerospace and medical components, all methods may be required.
What are the best cutting parameters for machining Grade 4 titanium?
Recommended starting parameters:
- Milling: Cutting speed 60–100 m/min; feed 0.08–0.15 mm/tooth; depth 0.5–2 mm
- Turning: Cutting speed 50–80 m/min; feed 0.1–0.2 mm/rev; depth 0.5–2 mm
- Drilling: Cutting speed 30–50 m/min; feed 0.05–0.1 mm/rev; peck frequently
These parameters should be adjusted based on specific machine capability, tooling, and part geometry. Flood coolant is essential.
Can Grade 4 titanium be welded after machining?
Yes. Grade 4 titanium has excellent weldability. It can be welded using:
- TIG welding (gas tungsten arc)
- MIG welding (gas metal arc)
- Electron beam welding (for precision applications)
Unlike alloyed grades like Grade 5, TA4 does not require specialized filler metals or complex post-weld heat treatment. However, proper inert gas shielding (argon) is essential to prevent contamination and embrittlement.
Contact Yigu Technology for Custom Manufacturing
At Yigu Technology, we specialize in CNC machining of Grade 4 (TA4) titanium for demanding applications. Our capabilities include 5-axis milling, CNC turning, and multi-process manufacturing with a focus on precision and quality.
We serve the aerospace, medical, and industrial sectors with components that meet the highest standards. Our TA4 machining expertise includes:
- TiAlN-coated carbide tooling for extended tool life
- Optimized cutting parameters for heat management
- Rigorous quality control with CMM inspection
- Documentation including material certifications and inspection reports
Whether you need aerospace brackets, medical implants, or industrial components, we deliver TA4 parts with precision and reliability.
Contact us today to discuss your Grade 4 titanium machining project.
