What material can sink the ultra-high pressure water jets

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  Key takeaways
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  How sink the ultra-high pressure water jets actually remove material
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  Which materials the jet cuts well, and which it does not
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  Thickness, taper and kerf: where the process stops being accurate
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  When to switch from waterjet to CNC milling
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  Waterjet versus CNC milling by part requirement

Two mechanisms share the same nozzle. Pure water at 3,000–4,000 bar exits a sapphire orifice 0.1–0.4 mm wide at roughly 900 m/s. On soft goods such as rubber, foam, gasket sheet and food, the jet erodes the material by shear and pressure alone. No grit, no dust, a kerf around 0.2–0.3 mm.

Hard materials need help. An abrasive waterjet feeds garnet grit of 80–120 mesh into the mixing chamber, where the water accelerates the particles to 200–300 m/s. Cutting now happens by micro-abrasion. The grit chips away grains of metal, stone or composite rather than melting or shearing them.

That distinction decides your answer to what material can it sink the ultra-high pressure water jets. If a material responds to erosion or micro-abrasion, the jet cuts it. If it delaminates, spalls or shatters under point load, the jet may still break it, but not cleanly.

Cutting is also cold. Measured temperature rise at the kerf stays under roughly 100 °C for most jobs, and often much less. There is no heat-affected zone, no recast layer and no micro-crack ring around the edge. Hardened tool steel at 58 HRC cuts without losing temper.

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  Pure waterSoft, low-density materials; kerf 0.2–0.3 mm.
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  Abrasive waterMetals, stone, glass, composites; kerf 0.8–1.2 mm.
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  Cold cutNo heat-affected zone, no recast layer.
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  No contactThin or flexible parts do not deflect under tool force.

Metals are the easy case. Aluminum 6061, 7075 and ADC12; stainless 304, 316L and 17-4PH; carbon steel 1018, 4130 and 4140; copper C110 and brass C36000; titanium TC4 and Inconel all cut to a square edge. Thickness is rarely the limit below 100 mm. Hardness matters less than you would expect, because the grit does not care about temper.

Stone, tile and glass are common waterjet work. Marble, granite, porcelain tile and borosilicate glass cut cleanly with abrasive. Laminated safety glass is the exception. The interlayer holds the two panes together, and the jet tends to wash out the plastic instead of severing it, leaving a rough, cloudy edge that usually needs rework.

Composites split into two groups. Carbon fiber and glass fiber laminates cut well, with a kerf around 1.0 mm and no fiber pull-out if feed rate is kept moderate. Honeycomb and foam-core panels are different. The thin skins cut, but the low-density core can crush or fill with grit slurry, and the panel may need a sacrificial backing plate.

Plastics, rubber and foam cut with pure water. ABS, PC, PMMA, POM, PEEK and polyethylene all behave. So do gasket sheet, silicone and most elastomers. Thick PMMA above roughly 40 mm can craze along the cut if the jet stalls, so keep the nozzle moving and do not dwell.

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  Cuts cleanlyAluminum, stainless, titanium, tool steel, granite, carbon fiber.
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  Needs careLaminated glass, honeycomb panels, thick PMMA, ceramics above 20 mm.
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  Poor fitThin single-pane glass, brittle ceramic tile under 5 mm, soft-core sandwich panels.

The jet loses coherence as it travels. Every extra millimeter of depth lets the stream spread, so the kerf widens toward the bottom of the part. On a 20 mm steel plate the top edge may measure 0.9 mm and the bottom 1.1 mm. On 100 mm stainless the bottom kerf can reach 1.6 mm or more.

That spread produces taper. A typical abrasive cut leans 0.1–0.3 mm over the part height, and the lean grows with thickness and speed. If your drawing calls for a square edge on a 60 mm part, expect to slow the feed, use finer grit, or plan a secondary machining pass.

Accuracy follows the same curve. On thin sheet under 10 mm, waterjet holds roughly ±0.1 mm on position. On thick plate, ±0.25 mm is realistic, and the edge quality drops from a smooth matte to a rougher surface. We quote ±0.005 mm only for CNC milling, not for waterjet.

Piercing is the other boundary. The jet must drill through before it can cut, and on brittle or laminated material that pierce can chip or delaminate the top surface. Starting off the part edge, or pre-drilling a 6–8 mm start hole, avoids most of that damage.

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  Kerf0.2–0.3 mm pure water; 0.8–1.2 mm abrasive.
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  Taper0.1–0.3 mm lean over part height.
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  PositionAbout ±0.1 mm thin sheet, ±0.25 mm thick plate.
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  PierceStart off-edge or pre-drill to avoid chipping.

Waterjet is a 2D process. It cuts a profile through a flat plate and it does that extremely well. The moment your part needs pockets, threads, counterbores, tight corner radii under 1 mm or a flat bottom, the jet cannot help. That is milling work.

Tolerance is the second trigger. Waterjet holds around ±0.1 to ±0.25 mm depending on thickness. If the drawing calls for ±0.005 mm, or a surface finish of Ra 0.8–1.6 μm, the part goes to a machining center. Many shops waterjet the blank and then mill the critical features, which saves material and cutter wear.

Small holes are the third trigger. The jet can drill holes down to roughly 1.5 times the kerf width, which is often 1.5–2 mm. If you need a Ø1.0 mm hole or a dense hole pattern, drilling or milling is faster and cleaner.

Cost follows volume too. For one prototype plate, waterjet is quick and cheap. For a 10,000-part run with tight tolerances, CNC milling with the right fixture usually wins on cycle time and repeatability. We run both, so we can tell you where the crossover sits for your part.

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  Stay with waterjetFlat 2D profiles, thick plate, heat-sensitive alloys, stone and composites.
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  Switch to milling3D features, threads, ±0.005 mm tolerance, holes under 2 mm.
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  HybridWaterjet the blank, mill the critical features.