How Do We Treat Titanium Alloys on CNC Machines
Titanium is not hard to cut because it is strong. It is hard to cut because it keeps heat in the cut. This guide shows the sequence we use for TA1, TA2 and TC4 (Ti-6Al-4V): tool choice, coolant pressure, cutting parameters, workholding and inspection. Read it and you can tell whether a titanium part belongs on a 3-axis mill or a 5-axis center with through-spindle coolant.
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Key takeaways
Why How Do We Treat Titanium Alloys Starts With Heat
Titanium has roughly half the thermal conductivity of 304 stainless and about a tenth of aluminium. Heat generated at the cutting edge has nowhere to go. It builds in the chip, the tool and a thin layer of the part surface. Tool life drops fast once edge temperature passes the coating limit, and the part can move after machining because the heat gradients are uneven.
The second issue is chemical. Titanium is reactive at high temperature. At around 500–600 °C it starts to pick up oxygen and nitrogen from the air, and it will weld to tool material under pressure. That is why a dull edge is worse than a broken one: it rubs, welds, then tears a chip out of the workpiece.
The third issue is elasticity. TC4 has a low modulus compared with steel, roughly 110 GPa. Thin walls and long unsupported sections deflect away from the cutter, then spring back. The tool rubs instead of cutting, the surface work-hardens, and the next pass is harder than the first.
Put together, these three points explain almost every titanium problem on the shop floor. If you treat the operation as a heat and rigidity problem rather than a hardness problem, the parameter choices stop being mysterious.
- 1Low conductivityMost cutting heat stays in the edge and part, not in the chip.
- 2Chemical reactivityThe surface absorbs oxygen and welds to tool material above roughly 500 °C.
- 3Low modulusAround 110 GPa for TC4, so thin sections deflect and work-harden.
Tool Selection for Titanium Alloys
Use micro-grain tungsten carbide with 6–10% cobalt. Fine grain gives a sharper edge and better resistance to chipping than coarse grades. Avoid titanium aluminium nitride-only coatings that break down early; AlTiN and TiAlN coatings work well because they hold hardness at high temperature and act as a diffusion barrier.
Geometry matters more than grade. A positive rake angle of 8–15°, a sharp honed or lightly polished edge, and a generous flute space for chip evacuation all reduce cutting pressure. For roughing, a variable helix end mill breaks the harmonic that causes chatter in deep pockets.
For drilling, use a 135–140° point with a split point or a four-facet grind, and through-coolant holes. For reaming, a straight-flute reamer with a left-hand helix pushes chips forward. For tapping, use a spiral-flute tap with a larger pitch diameter, because titanium tends to close in on the tap.
Do not use the same tool you run on aluminium. The geometry is too aggressive and the edge is too sharp in the wrong way. A dedicated titanium tool set is cheaper than the scrap it prevents.
- 1Carbide gradeMicro-grain, 6–10% cobalt, uncoated or AlTiN coated.
- 2Rake anglePositive 8–15°, sharp edge, large chip room.
- 3Drills135–140° split point with through-coolant holes.
- 4AvoidAluminium-style high-helix tools and dull edges.
Coolant Pressure and Cutting Parameters
Flood coolant is not enough on deep cuts. High-pressure through-spindle coolant at 70–150 bar does two jobs: it cools the edge and it blasts the chip out of the flute before it can be re-cut. Re-cutting a chip is the fastest way to chip a titanium edge.
Surface speed for TC4 is usually 30–60 m/min with coated carbide, and 60–90 m/min with sharp uncoated carbide in light finishing. Feed per tooth runs 0.05–0.15 mm depending on radial engagement. Keep radial engagement low, around 5–10% of tool diameter, and axial depth high. This keeps the chip thin and the heat generation low.
Roughing with a trochoidal path at 10% radial engagement lets you run a deeper axial cut without stalling. The tool stays in the cut longer and the feed stays constant. If the feed stops, the edge rubs and hardens the surface.
For finishing, take a light spring pass. Titanium deflects, so the first finish pass may not clean the wall. A second pass at the same setting removes the spring-back material without adding much time.
- 1CoolantThrough-spindle, 70–150 bar, aimed at the cutting edge.
- 2Surface speed30–60 m/min for TC4 with coated carbide.
- 3Radial engagement5–10% of tool diameter, high axial depth.
- 4FinishingLight spring pass to clean deflected walls.
Workholding, Distortion and Inspection
Titanium moves after machining because residual stress releases when material is removed. For thin plates and rings, stress-relieve the blank before the final cuts. Rough the part, let it sit, then finish. The pause lets the part settle.
Support the workpiece as close to the cut as possible. Use soft jaws, expanding mandrels or a vacuum fixture for thin walls. For 5-axis work, a dovetail or a cast fixturing block gives a rigid base and a clean exit for the tool.
Measure at room temperature. A part that came off the machine warm can read 0.01–0.02 mm large. If a tight tolerance matters, wait for the part to cool, then check with a temperature-compensated CMM.
In-process probing catches drift before the part is finished. On a long run, probe one critical feature every few parts and adjust the offset. That is cheaper than sorting finished parts.
- 1Stress reliefRelieve the blank before final cuts on thin parts.
- 2SupportSoft jaws, mandrels or vacuum close to the cut.
- 3Measure coolWarm parts can read 0.01–0.02 mm large.
Mistakes That Scrap Titanium Parts
The most common mistake is running too fast with too little coolant. Titanium rewards a slow, steady cut. If the chip comes off blue and thin, you are burning the edge. Drop the surface speed and raise the feed per tooth.
The second is using a long, slender tool because the pocket is deep. Tool deflection is the root cause of chatter, poor finish and broken edges. If you cannot shorten the tool, use a smaller diameter with a higher spindle speed, or change the setup so the feature is closer to the holder.
The third is measuring too early. A warm titanium part reads large. If you adjust the offset on a warm part, you will cut the next part undersize. Let it cool first.
The fourth is re-cutting chips. In a deep pocket, chips pile up at the bottom, and the tool cuts them again. That is how a good edge chips in the middle of a light pass. Add coolant pressure and a program that lifts the tool clear between passes.
- 1Too fast, too dryBlue powdery chips mean the edge is overheating.
- 2Long tool, no supportDeflection causes chatter and edge chipping.
- 3Measuring warmOffset changes on a hot part produce undersize parts.
Step by Step: How Do We Treat Titanium Alloys in the Shop
Follow this order. Skipping a step is how titanium parts get scrapped.
- 11. Confirm the alloy and temperAsk for the mill certificate. TA1 and TA2 are commercially pure and cut easier. TC4 (Ti-6Al-4V) is the common high-strength grade and is the hardest to machine. Annealed TC4 is more forgiving than aged TC4. If the drawing does not state the condition, ask before quoting.
- 22. Relieve stress in the blankFor thin plates, rings and long parts, rough machine, then stress-relieve or let the blank normalize before finishing. Leaving 0.5–1.0 mm on critical surfaces for the final pass gives the part room to move.
- 33. Set up for maximum rigidityShorten the tool overhang to no more than 3× diameter. Use a shrink-fit or hydraulic holder, not a collet, for long reach. Support the part close to the cut. Check the fixture for any movement with a dial indicator before cutting.
- 44. Choose the tool and coatingMicro-grain carbide with 6–10% cobalt, AlTiN coated for roughing, sharp uncoated or lightly coated for finishing. Positive rake 8–15°. Do not reuse a tool that has run steel; the edge geometry and coating are different.
- 55. Start with conservative parametersSurface speed 30–60 m/min, feed per tooth 0.05–0.15 mm, radial engagement 5–10% of diameter, high axial depth. Run a test cut, listen to the sound and check the chip. A silver, curled chip is good. A thin, blue, powdery chip means too much heat.
- 66. Turn on high-pressure coolant70–150 bar through-spindle. Aim the stream at the cutting edge, not at the top of the part. On deep pockets, add a second external nozzle to clear chips. Never run dry in a pocket.
- 77. Keep the feed movingNever dwell in the cut. If you must stop, retract the tool first. A stopped edge rubs, welds and work-hardens the surface. Restarting into a hardened patch is what breaks tools.
- 88. Inspect after the part coolsLet the part reach room temperature, then measure critical features. Use a CMM or a micrometer with a light touch. Titanium is springy, so heavy gauge pressure can give a false reading. Record the numbers and adjust the offset on the next part.
Which Titanium Grade and Setup Fits Your Part
Match the grade and machine to the feature, not the other way around.
| Grade / feature | Typical use | Machine setup | Watch out for |
|---|---|---|---|
| TA1 / TA2 (commercially pure) | Chemical parts, heat exchangers, gaskets | 3-axis mill, flood coolant | Gummy chips, built-up edge |
| TC4 (Ti-6Al-4V) annealed | Aerospace brackets, medical implants | 4-axis or 5-axis, through-spindle coolant | Work hardening, tool wear |
| TC4 thin wall under 2 mm | Housings, covers, surgical trays | 5-axis with vacuum or soft jaws | Deflection, chatter, spring-back |
| TC4 deep pocket over 3× D | Manifolds, valve bodies | 5-axis, trochoidal roughing, 70–150 bar | Chip packing, edge chipping |
| TC4 tight bore ±0.005 mm | Bushings, hydraulic fittings | Mill-turn or jig bore, spring pass | Heat growth, gauge pressure |
| TC4 long part over 500 mm | Structural rails, shafts | 4-axis with steady rest or tailstock | Sag, vibration, thermal drift |
Treat titanium as a heat problem, not a hardness problem
If you control the heat and keep the setup rigid, TC4 cuts predictably. If you fight it with speed, you will burn tools and scrap parts.
Titanium Machining Questions We Hear
Can titanium be machined without high-pressure coolant?
Yes, on light cuts and shallow features. Flood coolant works for TA1 and TA2 with a sharp tool and a conservative feed. But for TC4 pockets deeper than about 2× diameter, you need pressure to clear chips and cool the edge.
If your machine has no through-spindle option, use a high-volume external nozzle aimed at the cut and reduce the radial engagement. Run a test part and check the chip color before running the batch.
What surface finish can we hold on TC4?
As-machined TC4 usually lands around Ra 1.6–3.2 μm with a good setup. With a sharp finishing tool, a light spring pass and a rigid holder, Ra 0.8–1.6 μm is realistic. Below Ra 0.8 μm we usually add a finishing operation or a secondary process.
Finish depends more on rigidity and tool condition than on the machine's top spindle speed. A worn edge will tear the surface no matter how slow you run.
Why does titanium work-harden during machining?
Work hardening happens when the tool rubs instead of cutting. The surface deforms, the grain structure changes, and the next pass meets a harder layer. It is caused by a dull edge, a dwell in the cut, or too little feed per tooth.
The fix is to keep the edge sharp, keep the feed moving, and take a cut deep enough to get under the hardened layer. A spring pass at the same depth often cleans it up.
Do we need to stress-relieve titanium blanks before machining?
For thin plates, rings and long parts, yes. Residual stress from rolling or forging releases as material is removed, and the part moves. Stress relief before final machining reduces that movement.
For thick, compact parts, the risk is lower. We still rough, let the part settle, then finish, which costs little and protects the tolerance.
Which titanium grades do you machine?
TA1, TA2 and TC4 (Ti-6Al-4V) are the grades we see most. TA1 and TA2 are commercially pure and are used for corrosion resistance and formability. TC4 is the workhorse high-strength grade for aerospace, medical and motorsport parts.
We also machine Inconel and magnesium AZ31B / AZ91D on the same 5-axis centers, but those need different parameters and tooling.
How do you keep titanium parts within ±0.005 mm?
Rigid setup, sharp tools, controlled heat, and measurement after the part cools. We rough with plenty of stock, let the part settle, then finish with light passes. Critical features are probed in-process so the offset can be adjusted before the run ends.
Every part gets a final inspection before shipment, and we can send the report with the parts on request.
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