Cutting Metal With Water
An abrasive waterjet pushes water through a jeweled orifice at around 60,000 psi, accelerating it past Mach 2, then entrains garnet abrasive in a mixing tube. What leaves the nozzle is a supersonic slurry roughly 0.03 to 0.05 in (0.8 to 1.3 mm) across that erodes through almost anything. No flame, no arc, no melting: the part is cut by controlled abrasion. Pure waterjet without abrasive is used for soft materials such as foam, rubber gaskets, food, and insulation, but most industrial work is abrasive.
The Real Advantage: No Heat-Affected Zone
This is the whole argument. Laser and plasma cut by melting and vaporizing, leaving a heat-affected zone at the edge a few thousandths to a few hundredths of an inch deep, where hardness, grain structure, and residual stress differ from the parent material. Usually that does not matter. Sometimes it matters enormously.
- Hardened and heat-treated materials. A laser locally re-tempers the edge of hardened tool steel. Waterjet does not, so parts can be cut after heat treatment instead of fighting distortion.
- Fatigue-critical parts. A heat-affected zone plus recast layer is a crack initiation site, which under cyclic loading interacts directly with material fatigue in product design.
- Titanium, Inconel, and reactive alloys. Thermal processes create oxidation and alpha case that must be removed; waterjet leaves clean parent metal.
- Reflective metals. Copper, brass, and bright aluminum trouble older laser sources. Waterjet is indifferent to reflectivity.
- Composites, stone, and glass. Carbon fiber delaminates and burns under a laser and glass shatters; waterjet cuts both routinely.
- Low-melt plastics. Acrylic lasers beautifully, polycarbonate yellows and gasses. The distinction is in acrylic vs polycarbonate, and waterjet is the standard answer for polycarbonate and most engineering thermoplastics.
The Second Advantage: Thickness
Waterjet cuts thick material that other sheet processes cannot touch. Practical capability runs to 6 in (150 mm) in steel and further in softer materials, with some shops cutting 8 in and beyond. Fiber lasers are strong to about 1 in in steel and fall off sharply after that. Plasma reaches 2 in with a rapidly degrading edge.
The catch is speed. Cutting rate is roughly inversely proportional to thickness, and a jet that crosses 0.25 in aluminum at 20 inches per minute may crawl through 2 in steel at under an inch per minute. Thick waterjet work is capable, not fast, and the price reflects it.
What It Costs and How Jobs Are Priced
Shops quote machine time plus consumables plus setup, and the dominant variable is inches of cut path times material thickness. Rates land in the $100 to $250 per hour range including abrasive, which runs $0.25 to $0.45 per pound at 0.7 to 1.5 lb per minute of cutting.
Practical consequences for how you design and quote:
- Perimeter drives price, not part area. Intricate internal cutouts cost far more than a solid blank of the same footprint.
- Every internal feature needs a pierce. Piercing is slow and abrasive-hungry, especially in thick or brittle material. Twenty holes cost real money; consider drilling them instead.
- Nest your own parts and share cut lines. Submitting a full sheet layout cuts material waste and setup charges, and adjacent parts sharing a cut path halve that path's cost.
- Setup is a fixed hit. Usually $50 to $150 per job, which is why a one-off is expensive per part and fifty are not.
Accuracy, Edge Quality, and Limits
Standard tolerance is about plus or minus 0.005 in on a typical part, tightening to plus or minus 0.003 in on machines with dynamic heads and loosening in thick sections. Two effects define the edge. Taper: the jet is wider entering than leaving, so cuts come out slightly V-shaped, typically 0.002 to 0.010 in across the thickness, which tilting dynamic heads compensate for. Stream lag: the jet trails behind the nozzle and leaves a curved striated pattern on the bottom edge, which is why fast cutting striates and slow finish passes come out near-satin. Shops quote edge quality on a numbered scale, and the machine-time difference between the roughest and finest can be threefold on the same geometry, so specify only what you need.
Real limits: waterjet cuts two-dimensional profiles through a sheet, so no pockets, counterbores, blind features, or threaded holes. Minimum internal radius is set by stream diameter, roughly 0.03 in, so sharp internal corners are impossible. Thin sheet under about 0.02 in can distort, and parts come out wet and must be dried immediately to avoid flash rust on carbon steel.
When Laser, Plasma, or Something Else Is the Better Call
For thin sheet metal in production quantities, fiber laser is faster and cheaper, often by a large margin, and the design rules for those parts are in the sheet metal design guide. For thick structural steel where edge quality is secondary, plasma is cheaper still. For precise internal features, pockets, and holes with tight tolerance, the answer is milling, priced as described in CNC machining cost. For very fine detail in hardened material where even waterjet's radius is too large, EDM machining is the fallback.
Waterjet's sweet spot is the overlap zone: thick material, heat-sensitive material, exotic alloys, mixed materials in the same shop, and low to medium quantities where the process needs no tooling at all.
Where It Fits in a Product Program
Because waterjet needs zero tooling and accepts a DXF directly, it fits prototypes, brackets, mounting plates, gaskets, and low-volume structural parts, alongside the options in rapid prototyping techniques. Many programs run waterjet for the first few hundred units and switch to stamping or laser later, which is the reasoning behind choosing a manufacturing process by volume.
Get the Right Cutting Process on Your Part
Projects House specifies cut process, edge quality, and tolerances for metal and composite parts, and quotes the alternatives side by side so you are not paying waterjet rates for a laser job. Send a DXF or STEP file with material and quantity through our contact form.