Waterjet Cutting Titanium

Why waterjet for titanium

Titanium is reactive at elevated temperatures. Laser cutting titanium produces a heat-affected zone where the material absorbs oxygen and nitrogen from the air, forming a hard, brittle alpha-case layer that must be removed by chemical milling or machining. Plasma cutting is worse — the HAZ extends deeper and the cut edge is metallurgically compromised.

Waterjet avoids all of this. The abrasive waterjet stream cuts at ambient temperature. There's no HAZ, no alpha-case, no residual stress, no microstructural change. The cut edge is the same material as the parent plate, ready for welding, bending, or use as-cut. For aerospace and medical titanium applications where material integrity is non-negotiable, waterjet is the default cutting process.

Cut speeds by thickness

60,000 PSI pump, 0.015" mixing tube, 80-mesh garnet abrasive, Grade 5 (Ti-6Al-4V):

Quality 1 (rough separation, Ra 250+ µin):

0.125" thick: 12–18 IPM. 0.250" thick: 6–10 IPM. 0.500" thick: 2.5–4.5 IPM. 1.000" thick: 1.0–1.8 IPM. 2.000" thick: 0.3–0.6 IPM. 4.000" thick: 0.08–0.15 IPM.

Quality 5 (fine finish, Ra 60–120 µin):

0.125" thick: 4–7 IPM. 0.250" thick: 2–4 IPM. 0.500" thick: 0.8–1.5 IPM. 1.000" thick: 0.3–0.6 IPM. 2.000" thick: 0.08–0.18 IPM.

Titanium cuts approximately 40–50% slower than mild steel and 20–30% slower than stainless steel at the same thickness. The hardness and toughness of Ti-6Al-4V requires more energy per cubic inch of material removal. Grade 2 CP titanium cuts 15–20% faster than Grade 5 due to lower hardness.

90,000 PSI hyperbaric pumps (Flow, KMT, OMAX HyperJet): increase cut speed 30–50% over 60,000 PSI systems. The higher pressure produces a more coherent jet with better energy transfer. A 90K pump cutting 0.500" Ti-6Al-4V at Quality 3 runs 1.8–2.8 IPM vs 1.2–2.0 IPM at 60K. The tradeoff is higher pump maintenance cost and consumable wear.

Edge quality and taper

Waterjet cut edges on titanium show the same quality characteristics as other metals, but the striations are more pronounced because titanium is tougher and deflects the jet more at the exit side:

Top edge: Clean and sharp at all quality levels. The jet enters the material with full energy.

Bottom edge: Quality depends on speed. At Quality 1 (fast rough cut), the bottom edge has visible striations and 0.010–0.020" of taper — the kerf is wider at the top than the bottom. At Quality 5 (slow fine cut), striations are minimal and taper is 0.002–0.005".

Taper compensation: Modern 5-axis waterjet heads (Flow Dynamic Waterjet, OMAX Tilt-A-Jet) tilt the cutting head 1–3° to compensate for taper. This produces near-zero taper (< 0.002") on the finished surface while allowing the opposing surface to carry all the taper. Specify which surface is the quality surface in the nesting — the taper-compensated side will be perpendicular; the scrap side will show the taper.

Achievable tolerances

Standard waterjet (no taper compensation): ±0.005" on thin material (under 0.250"). ±0.008–0.010" on 0.500–1.000". The taper itself doesn't affect positional tolerance — it affects edge perpendicularity.

With taper compensation (5-axis head): ±0.003" on material up to 1.000". ±0.005" on 1–2" thick. This is adequate for most near-net-shape titanium blanks that will be machined to final dimensions on a CNC mill.

For tighter tolerances: Waterjet to +0.010–0.020" oversize, then machine to final dimensions on a CNC mill. This is the standard workflow for aerospace titanium plate parts — waterjet produces the near-net blank (saving 60–80% of the CNC roughing time), then the 5-axis mill finishes to print tolerances.

Nesting and material savings

Titanium plate is expensive — $30–80/lb for Ti-6Al-4V plate depending on thickness and quantity. The waterjet kerf is 0.030–0.045" wide (depending on mixing tube diameter), which is wider than laser (0.010–0.015") but narrower than plasma (0.060–0.100"). Tight nesting with 0.060–0.080" web between parts minimizes scrap.

Common tab: leave 0.020–0.030" tabs holding the part in the sheet, snap them out after cutting. Tabbing prevents parts from shifting in the water tank during cutting, which would cause the jet to cut into an adjacent part. On titanium, use 2–3 tabs per part — titanium is stiff enough that fewer tabs are needed compared to aluminum.

Scrap titanium has value — $3–10/lb for clean Ti-6Al-4V turnings and scrap plate. Keep titanium scrap separate from other metals. Contaminated titanium scrap (mixed with steel or aluminum) is worth significantly less.

Stack cutting

Stacking multiple sheets of thin titanium and cutting them together doubles or triples throughput. This works well for material under 0.125" thick. Stack 2–4 sheets with double-sided tape or clamps between layers. The waterjet cuts through all layers simultaneously.

Limitations: tolerance degrades on the bottom sheet due to jet spread through the stack. The bottom sheet may have 0.003–0.005" more taper than the top sheet. For non-critical blanks, this is acceptable. For precision work, cut single sheets.

Waterjet vs other processes for titanium

Waterjet vs laser: Laser can cut thin titanium (under 0.250") faster than waterjet, but the HAZ and alpha-case formation make laser cutting unacceptable for most aerospace and medical titanium applications. If HAZ doesn't matter (decorative, non-structural), laser is faster and cheaper on thin stock.

Waterjet vs wire EDM: Wire EDM produces tighter tolerances (±0.0005" vs ±0.003–0.005") and better surface finish. But wire EDM is dramatically slower — a 20" profile in 1" Ti-6Al-4V takes 8–12 hours on wire EDM vs 30–60 minutes on waterjet. Use EDM for precision features and tight-tolerance details; use waterjet for near-net blanks and profiles where ±0.005" is adequate.

Waterjet vs band saw: For straight cuts in titanium plate (squaring blocks, cutting bar to length), a band saw is faster and cheaper. Waterjet wins when the cut profile has any curves, angles, or features.

Cost

Waterjet cutting titanium runs $75–150/hr shop rate (the higher end reflects the abrasive consumption — titanium uses more garnet per inch of cut than steel). A typical aerospace titanium blank with 40" of cut in 0.500" Ti-6Al-4V at Quality 3: approximately 25–40 minutes of cut time plus 15 minutes of setup = $50–100 per part.

Compare this to CNC-machining the profile from a rectangular billet: 1–3 hours at $125–175/hr = $125–525. Waterjet near-net blanking typically saves 40–70% of the CNC roughing cost on titanium plate parts.