Machining Titanium Grade 5 (Ti-6Al-4V)
Ti-6Al-4V (Grade 5, AMS 4928) is the most widely machined titanium alloy in the world — and one of the most demanding. Its unique combination of high strength (130 ksi / 896 MPa UTS), low density (0.160 lb/in³), and excellent corrosion resistance makes it the default choice for high-performance structural parts. This guide walks through every parameter you need to machine it successfully.
Cutting speed: 80–150 SFM (24–46 m/min) with carbide · Coolant: 500–1,000 psi (35–70 bar) flood · Chip load: ≥0.002 in./tooth (0.05 mm) · Tolerance: ±0.001 in. (±0.025 mm) achievable
Before You Machine Ti-6Al-4V: What You Need to Know
Ti-6Al-4V is the engineering default for titanium — not because it is the easiest to machine, but because its properties justify the challenge. At 130 ksi (896 MPa) UTS and 0.160 lb/in³ density, it delivers structural performance that aluminum and steel cannot match at the same weight. When a design requires lightweight, high-strength, and corrosion-resistant, this alloy is the answer.
Machining it requires understanding why it behaves the way it does. Ti-6Al-4V has a thermal conductivity of 6.7 W/m·K — roughly 25× lower than 6061 aluminum and ~6× lower than 4140 steel. Heat that would normally dissipate into a chip or the workpiece instead concentrates at the cutting edge. Without aggressive coolant, this heat softens the carbide, initiates BUE (Built-Up Edge, where titanium chemically welds to the tool), and can trigger work hardening if chip load drops too low.
This guide provides the specific parameters that address each of those failure modes. If you are new to Ti-6Al-4V, read the material overview and speeds/feeds sections first. If you are debugging a specific problem, jump directly to the relevant section using the table of contents above.
Key Takeaway
The three numbers that matter most when starting a new Ti-6Al-4V job: (1) 80–120 SFM (24–37 m/min) for roughing, (2) 500+ psi (35+ bar) coolant pressure, (3) chip load ≥ 0.002 in./tooth (0.05 mm/tooth). Get these right first. Fine-tune from there.
Ti-6Al-4V Material Properties and Specifications
Ti-6Al-4V is an alpha+beta titanium alloy — a two-phase microstructure created by adding 6 wt.% aluminum (which stabilizes the alpha, hexagonally close-packed crystal phase) and 4 wt.% vanadium (which stabilizes the beta, body-centered cubic phase). This dual-phase structure is what makes the alloy heat-treatable and provides its high strength-to-weight ratio. The table below lists the key properties you will reference during process planning and drawing review.
| Property | Value | Condition | Standard |
|---|---|---|---|
| UTS | 130 ksi (896 MPa) | Annealed | AMS 4928 |
| UTS (STA) | 150–165 ksi (1,034–1,138 MPa) | STA | AMS 4967 |
| 0.2% Yield Strength | 120 ksi (827 MPa) | Annealed | AMS 4928 |
| Elongation | 10% min | Annealed | AMS 4928 |
| Density | 0.160 lb/in³ (4.43 g/cm³) | — | ASTM B348 |
| Elastic Modulus | 16 Msi (110 GPa) | — | AMS 4928 |
| Poisson's Ratio | 0.342 | — | — |
| Thermal Conductivity | 6.7 W/m·K | — | AMS 4928 |
| CTE | 4.8 µin./in./°F (8.6 µm/m/°C) | 68–392°F (20–200°C) | — |
| Max Service Temp | 600°F (315°C) | Sustained | ASM Handbook |
| Beta Transus | ~1,830°F (999°C) | — | ASTM B265 |
| Hardness | 302–340 HB | Annealed bar | AMS 4928 |
Ti-6Al-4V Speeds, Feeds, and Depth of Cut
These parameters are validated for Ti-6Al-4V per AMS 4928 with high-pressure flood coolant (500+ psi / 35+ bar). All values assume PVD TiAlN-coated solid carbide tooling unless otherwise noted.
| Operation | SFM (m/min) | Feed ipt/ipr (mm) | DOC (in.) | Radial Engagement | Notes |
|---|---|---|---|---|---|
| Rough Milling (3-flute) | 80–100 (24–30) | 0.003–0.005 ipt (0.08–0.13 mm/tooth) | 0.050–0.100 | 25–35% cutter dia. | Trochoidal path preferred; reduces peak load |
| Semi-finish Milling (4-flute) | 100–120 (30–37) | 0.002–0.003 ipt (0.05–0.08 mm/tooth) | 0.020–0.050 | 30–40% | Maintain coolant; watch tool wear |
| Finish Milling (4-flute) | 120–150 (37–46) | 0.001–0.002 ipt (0.025–0.05 mm/tooth) | 0.005–0.020 | 10–20% | Fresh insert only; Ra 32 µin. (0.8 µm) achievable |
| Rough Turning | 100–120 (30–37) | 0.010–0.015 ipr (0.25–0.38) | 0.050–0.150 | — | Positive rake insert (+10° to +15°) |
| Finish Turning | 140–180 (43–55) | 0.004–0.008 ipr (0.10–0.20) | 0.010–0.030 | — | Ra 16–32 µin. (0.4–0.8 µm); spring-back offset required |
| Drilling (solid carbide) | 80–100 (24–30) | 0.002–0.004 ipr (0.05–0.10) | — | — | 130° drill point; peck every 1–2D |
| Thread Milling | 60–80 (18–24) | — | Full thread depth per pass | — | Preferred over tapping for Ti-6Al-4V |
| Reaming | 40–60 (12–18) | 0.005–0.010 ipr (0.13–0.25) | 0.005–0.010 stock | — | Flood coolant; spiral flute carbide reamer |
Trochoidal Milling for Ti-6Al-4V Pockets
For slotting and pocket roughing, trochoidal milling (circular arc tool path, 20–30% radial engagement) reduces peak cutting forces by 40–60% vs. conventional full-width slotting. This allows higher axial depths (0.100–0.500 in. or 2.54–12.7 mm) and reduces tool deflection on long reaches. Supported in CAM: Mastercam Dynamic Milling, Fusion 360 Adaptive Clearing, hyperMILL Trochoidal.
Key Takeaway
If your Ti-6Al-4V program uses the same speeds as aluminum, it will fail. Start at 80–100 SFM (24–30 m/min) for roughing and verify tool life after the first 5 parts. If flank wear (VB) exceeds 0.012 in. (0.30 mm), reduce SFM by 10% or verify coolant pressure. Never reduce chip load below 0.002 in./tooth to compensate — that causes work hardening.
Tool Selection for Ti-6Al-4V
Tooling for titanium comes down to three decisions: coating (what prevents the titanium from bonding to the tool), geometry (how many flutes, what rake angle, what edge prep), and holding (how the tool is gripped in the spindle). Each decision directly affects tool life and surface quality. The cards below cover specific recommendations — if a term is unfamiliar, here is the context you need.
PVD TiAlN is a thin coating applied by Physical Vapor Deposition. Despite containing “Ti” in the name, it works on titanium because the aluminum in the coating oxidizes at cutting temperature to form an Al₂O₃ barrier that physically prevents diffusion between the tool and the workpiece. K-class carbide refers to an ISO classification for tungsten carbide grades optimized for non-ferrous and difficult-to-machine materials — the “K” indicates a cobalt binder with fine-grain WC structure designed for abrasion resistance and toughness at lower cutting speeds.
Solid Carbide Endmills (Milling)
- Coating: PVD TiAlN — first choice. AlTiN acceptable. Avoid TiN.
- Helix angle: 35–45° for better chip evacuation and shear angle
- Number of flutes: 3–4 for roughing (chip clearance); 4–5 for finishing
- Edge prep: slightly honed (5–10 µm) — sharp enough to cut, not sharp enough to chip
- Diameter: maximize to fit geometry — larger tool = more rigid = less chatter
- Tolerance: h6 shank tolerance for shrink-fit or hydraulic holders preferred
Turning Inserts
- Grade: K-class (WC/Co) with PVD TiAlN or uncoated for coolant-intensive ops
- Rake angle: +10° to +15° positive — reduces cutting force, temperature
- Nose radius: 0.015–0.031 in. (0.38–0.79 mm) for finish turning
- Edge condition: sharp or very slight hone — never strong land or T-land geometry
- Insert shape: round (RCMT) for interrupted cuts; CCMT/VCMT for general turning
- Wear limit: replace at VB = 0.012 in. (0.30 mm) flank wear — do not exceed
Drill Selection
- Material: solid carbide with TiAlN coating — no cobalt HSS in Ti-6Al-4V
- Point angle: 130–135° — reduces thrust and improves centering in gummy material
- Flute form: parabolic or 3-flute for deep holes — better chip evacuation
- Through-spindle coolant: required for holes > 3× diameter
- Peck cycle: retract every 1.0–1.5× drill diameter for hole depths > 3D
- Split point: reduces walk-out; important for hole location tolerance
Tool Holding
- Shrink-fit holders: best runout (<0.0002 in. / 0.005 mm TIR) — preferred for finishing
- Hydraulic chucks: excellent vibration damping — good for roughing
- ER collet: acceptable for tools < 0.500 in. (12.7 mm) dia.; ensure collet is clean and unworn
- Side-lock holders: avoid for long reaches — excessive runout amplifies chatter
- BT40 vs. CAT40: equivalent; HSK-A63 preferred for high-speed spindles (>10,000 RPM)
- Minimum stick-out: maximize rigidity — excess overhang amplifies chatter in Ti-6Al-4V
Coolant Strategy for Ti-6Al-4V
High-pressure flood coolant is not optional for Ti-6Al-4V — it is the most critical process parameter. The table below compares three coolant tiers from prototype-level (50–150 psi / 3.4–10 bar) through production high-pressure (500–1,000 psi / 35–70 bar) to cryogenic LN₂.
| Parameter | Standard | High-Performance | Cryogenic (LN₂) |
|---|---|---|---|
| Pressure | 50–150 psi (3.4–10 bar) | 500–1,000 psi (35–70 bar) | N/A (delivered at -196°C / -321°F) |
| Flow rate | 2–5 GPM | 5–15 GPM | 0.5–2 L/min LN₂ |
| Coolant type | Water-soluble oil 5–8% | Water-soluble oil 8–12% | Liquid nitrogen |
| Nozzle placement | Standard flood | Multiple directed nozzles at cut zone | At cutting edge, not flood |
| Tool life vs. dry | +50–100% | +200–400% | +400–800% |
| Capital cost | Low (<$5K) | Moderate ($5K–$30K) | High ($30K–$100K+) |
| Typical use | Low-volume, prototype | Production structural/medical | High-volume production |
Achievable Tolerances for Ti-6Al-4V Parts
| Feature | Standard | Precision | Requirement |
|---|---|---|---|
| Turned OD | ±0.005 in. (±0.13 mm) | ±0.001 in. (±0.025 mm) | Fresh insert, light finish pass, spring-back compensation |
| Bored ID | ±0.005 in. (±0.13 mm) | ±0.001 in. (±0.025 mm) | Spring-back offset: test cut + measure + correct |
| Reamed hole | ±0.001 in. (±0.025 mm) | ±0.0005 in. (±0.013 mm) | Carbide reamer, flood coolant, 0.005–0.008 in. (0.127–0.203 mm) stock |
| Milled flat | ±0.005 in. (±0.13 mm) | ±0.002 in. (±0.05 mm) | Rigid workholding; stress-relieve after roughing |
| Thread pitch dia. | ASME B1.13M 6H/6g | 5H/5g achievable | Thread mill preferred — see DFM rules |
| Flatness (6 in. / 152.4 mm span) | ±0.003 in. (±0.08 mm) | ±0.001 in. (±0.025 mm) | Stabilization anneal at 1,000°F (538°C) before finish |
| Surface finish (mill) | Ra 63 µin. (1.6 µm) | Ra 32 µin. (0.8 µm) | Finish pass 0.005 in. (0.127 mm) DOC, fresh insert |
DFM Rules Specific to Ti-6Al-4V
Minimum wall: 0.060 in. (1.5 mm)
Below 0.060 in. (1.5 mm), wall deflects under cutting forces causing chatter. Support thin walls with fixturing where unavoidable.
Corner radii ≥ 0.060 in. (1.5 mm)
Allows endmill ≥ 0.120 in. (3.05 mm) diameter. Larger endmills run faster and more rigidly, reducing cycle time 20–40%.
Pocket depth-to-width ≤ 4:1
Deeper pockets require excessive endmill stick-out, amplifying deflection and chatter in Ti-6Al-4V's difficult-to-cut material.
Thread mill ≥ M6 threads
Ti-6Al-4V spring-back causes tap breakage in blind holes. Thread milling is more reliable for M6 (1/4-20) and larger.
Hole depth ≤ 5D without through-spindle coolant
Standard peck drilling handles ≤5D. 5–10D requires through-spindle coolant callout on drawing.
Specify condition on drawing
"Ti-6Al-4V per AMS 4928, Condition Annealed" — not just "titanium." Drawing must reference the applicable AMS or ASTM specification.
Review Ti-6Al-4V Sourcing Before Release
MakerStage routes Ti-6Al-4V RFQs to shops with AMS 4928 material cert capabilities, high-pressure coolant, and PVD-coated tooling. Upload your STEP and 2D drawing to get engineer-reviewed pricing first; after order confirmation, DFM can flag machining risks before production.
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