GR5 (Ti-6Al-4V) machined parts are bought against two documents at once: a material specification that fixes the alloy and its condition, and a drawing that fixes geometry, tolerance and finish. Because titanium is expensive to cut rather than expensive to buy, the drawing package, not the bar price, decides part cost.
Why Machining, Not Metal, Dominates the Cost of a GR5 Part
Bar stock is the smaller line item; cutting time, tool wear and scrap dominate, and all three are worse in titanium for reasons that come from the metal:
- Faible conductivité thermique — around 7 W/m·K typical, so heat stays at the cutting edge instead of leaving with the chip. Tool life collapses once the edge rubs.
- Low elastic modulus — roughly 110 GPa, half that of steel. Thin walls and long overhangs spring away from the tool, producing chatter, taper and tolerance drift.
- Galling and work hardening — titanium smears onto the edge, builds up and then tears the surface. A dull tool does not cut slowly; it ruins the part.
The answer is slower speeds, heavier feeds, rigid setups, generous coolant and frequent tool changes — a shop quoting GR5 at aluminium cycle times is a warning sign, not a bargain.
What Belongs on the Drawing and the Purchase Order
Machined parts fail on incomplete specification far more often than on bad cutting, so each line below should be explicit:
| Item | Why it matters | Typical entry |
|---|---|---|
| Alloy and UNS | Fixes chemistry and trade name | GR5 / UNS R56400, or Grade 23 / UNS R56407 for implants |
| Material specification | Sets the test regime behind the certificate | AMS 4928 for bar and forgings, ASTM B348 for general bar, ASTM F136 for ELI |
| Condition | Drives strength, ductility, machinability | Mill annealed, or solution treated and aged (STA) |
| Tolerances | Separates general and critical features | General ±0.1 mm; critical features called out |
| Surface finish | Fatigue life and sealing | Ra 1.6 µm typical, finer on seal faces and fillets |
| Inspection | Defines what is measured and recorded | First article, CMM report, PMI, penetrant where specified |
| Traceability | Ties the part back to the melt | Heat number on the part or bag, EN 10204 3.1 report |
Condition: Mill Annealed or Solution Treated and Aged
Annealed GR5 is the default for structural parts needing ductility and damage tolerance; STA trades elongation for strength and suits loaded fittings, fasteners and airframe hardware. Figures below are typical or per-standard reference values, not a guaranteed supply spec — your drawing governs.
| Condition | Tensile / yield | Where it is used |
|---|---|---|
| Mill annealed | 895 MPa min tensile, 828 MPa min yield, 10% min elongation per ASTM B348 | Brackets, housings, general structural parts |
| Solution treated and aged | Typically around 1,100 MPa tensile, lower elongation | High-strength fittings, fasteners, loaded hardware |
STA is not a substitute for Grade 23 where fracture toughness governs. On cyclically loaded, safety-critical parts, extra-low-interstitial stock to ASTM F136 is the usual route, with strength and toughness agreed together.
Machining Titanium Without Damaging the Part
Most rules that keep a GR5 part inside tolerance are process discipline, not machine capability:
- Sharp, correctly ground cobalt high-speed steel or carbide tooling with positive rake and a honed edge.
- Slow surface speed, heavy feed per tooth, climb milling where the setup allows — cut under the hardened layer instead of rubbing through it.
- Rigid fixturing, minimum overhang, and support thin walls so the part cannot deflect from the cutter.
- High-pressure coolant and chlorine-free lubricants; chloride residue is a risk on hot titanium.
- Never let the tool dwell; stopping in the cut work-hardens the surface and worsens the next pass.
One safety point for any machine shop: fine titanium chips are flammable, need dedicated housekeeping, and a chip fire must be smothered with dry sand or salt — never water or CO2.
Inspection and Documents to Expect
For machined parts the certificate package is part of the product. A complete set carries an EN 10204 3.1 mill test report tied to the heat number, a dimensional report against the drawing, and positive material identification where grade mix-ups are a real risk — GR5 (Ti-6Al-4V) is easily confused with GR9 (Ti-3Al-2.5V) and GR2 (commercially pure titanium) in a shared warehouse. Add hardness, finish and penetrant records only where the drawing calls for them, and specify protective packaging: a scratch is a fatigue initiation site, not a cosmetic defect.
Sourcing GR5 Machined Parts
As an integrated titanium supplier we machine GR5 and Grade 23 parts from bar, forging and plate stock, and pass the grade, condition and specification on your order through to production rather than paraphrasing it. Tolerances are agreed before the first chip is cut and inspection scope is confirmed against your RFQ. MOQs run from prototypes to production releases, lead time is quoted with the offer, and one accountable contact owns the order from drawing review to dispatch. Buyers fixing the input stock first will find forms and conditions in our titanium bar and rod range; the ASTM B348 and AMS 4928 comparison for bar and billet covers the certificates that travel with it.
Frequently Asked Questions
Is Grade 5 titanium difficult to machine?
Yes. Low thermal conductivity keeps heat at the cutting edge, the low elastic modulus lets thin sections deflect, and titanium galls onto tooling. It is machined daily, but at slower speeds, heavier feeds and more frequent tool changes.
What tolerances can be held on titanium machined parts?
Typical practice holds turned diameters to ±0.05 mm and milled features to ±0.1 mm, tighter where grinding is specified and the part is rigid enough. Thin walls and long bores are the exceptions, so call critical features out individually rather than relying on the general tolerance block.
Should implant parts be Grade 23 rather than Grade 5?
Most implant designs specify Grade 23 (Ti-6Al-4V ELI) to ASTM F136, because tighter oxygen and iron limits raise fracture toughness and improve fatigue crack growth behaviour. Plain GR5 remains acceptable for instruments and non-implant hardware; ASTM F1472 covers wrought Ti-6Al-4V for implants where invoked.
What documents should arrive with the parts?
At minimum an EN 10204 3.1 mill test report tied to the heat number and a dimensional report against the drawing. PMI, hardness, surface finish and penetrant records are added when the drawing requires them, and the full inspection scope should be settled in the RFQ so nothing is discovered at goods-in.
Send a Drawing for a Machined Part Quote
Email the drawing, alloy and condition, quantity and inspection requirements to FDtitanium and we will return an offer with the material specification, tolerance review, certificate scope and lead time stated up front.
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