Waterjet Cutting: Abrasive and Pure-Water Cutting Basics

What the work looks like

Waterjet cutting uses a high-pressure stream of water (pure waterjet, for soft materials) or water plus abrasive garnet (abrasive waterjet, for metals, stone, glass, and composites) to cut any material up to several inches thick. Pressures run 60,000 to 90,000 psi at the intensifier pump. The jet exits a diamond or carbide orifice, mixes with garnet in the mixing tube, and cuts a kerf about 0.040 inch wide. Flow International, OMAX, KMT, and WARDJet are the main brands.

Waterjet's advantages over laser and plasma:

• No heat-affected zone (HAZ). Material does not change metallurgically.
• Cuts anything: stainless, titanium, glass, stone, composites, cardstock, food.
• Thick cuts (up to 10 inches and more) that no laser can match.
• No fumes, no flammable gases.

Disadvantages: slower than laser on thin steel, abrasive cost ($0.30 to $0.50 per pound and a typical cut uses 1 to 2 lb/min), tapered edge on the far side of the cut (compensated by software).

Job titles: Waterjet Operator, Waterjet Programmer, Fabrication Technician. Pay $20 to $35 per hour for operators.

Safety and tools

Waterjet hazards:

• The jet itself is a lethal cutting tool. Never point, insert a body part, or cross the jet with any part of you. An abrasive jet cuts bone instantly. Medical literature on "waterjet injection injuries" is grim.
• Noise: 100 to 110 dB at the head. Hearing protection (dual protection, earplugs plus muffs) for prolonged work.
• Abrasive dust: respirable garnet, which is not particularly toxic but creates a dust nuisance. Dust collection or spray mist is standard.
• Splash: water and fine abrasive spray. Safety glasses or a face shield, waterproof coat or apron during maintenance.
• Slip hazard: the area around the cutting tank is always wet. Slip-resistant boots, squeegee the floor.
• Ultrahigh-pressure lines: a leak can cut skin. Never tighten a fitting under pressure. Bleed down before any wrench work.

Daily operation checks:

• Water supply clean and soft (filtered, demineralized; hard water damages the orifice).
• Garnet hopper full (typically 80-mesh HP garnet, or 120-mesh for fine-finish work).
• Orifice and mixing tube condition: a worn orifice flares the jet, a worn mixing tube steepens the taper.
• Tank water level and abrasive removal system.
• Pump pressure and seal condition.

Tools: the machine itself, orifice change kit, mixing tube change kit (carbide tubes last 40 to 80 hours), garnet scoop, pressure gauge, calipers to verify kerf width, nesting software (OMAX IntelliMAX, FlowPath, Bystronic ByJet CAM).

Your first exercise

If you have waterjet access, shadow an operator through a startup: power on pump, warm up, run a test pierce on scrap, check kerf and taper, then start the production file. If no access, read the OMAX or Flow operator manual (both have PDFs online). Learn the names: intensifier pump, jeweled orifice, mixing tube, nozzle, focusing tube. Learn the pressure path from pump to nozzle.

Where to go next

Build on Waterjet Cutting with Laser Cutting (Introduction to Laser Cutting), Oxy-Fuel Cutting (Introduction to Oxy-Fuel Cutting), Plasma Cutting, Press Brake Operation (Introduction to Press Brake), Blueprint Reading, and Precision Measurement (Introduction to Precision Measurement). Safety: High-Pressure Hydraulics, Hearing Conservation, Workplace Safety.