In our shop we’ve three laser cutting machines and one waterjet machine. We view them as complimentary metal cutting tools rather than competitor processes. Rather like Batman and Robin, and not Batman versus Superman. Our waterjet and laser machines are part of one team, and like every member of a successful team, they have different yet complimentary skills.

Laser can’t do everything

For small quantity work laser cutting is our “go-to” process. The machines are fast and flexible tools for metal cutting, but they can’t do everything. Copper makes a good example of their limitations. Not only is it reflective, but it has a reddish color. That makes it an excellent mirror for CO2 laser light. Instead of vaporizing, as most metals do, copper bounces the beam back, creating a safety hazard and possibly damaging the machine. (To a lesser extent, brass and aluminum present the same challenge.)

There are some other limitations to consider too. Lasers cut by heating, which is an issue with non-metallic materials like plastics and rubber as well as stone. (Not that we cut a lot a lot of stone, but if we needed to, it wouldn’t be done on a laser.)

Textured surfaces can challenge laser cutters because they tend to reflect the beam around rather than absorbing the energy. And lasers can’t cut really thick material because of how the beam focuses to a point. (The beam intensity diminishes as you move away from that focus.)

Cutting these “difficult” materials is where our waterjet cutter comes in. Like laser cutting, waterjet cutting is a non-contact process, so there’s no distortion put into the metal. It also means minimal loads go into the machine structure, which helps ensure high accuracy and repeatability.

Lots in common

Waterjet and laser cutting machines have other things in common. These are gantry-style machines that move a cutting head over the sheet of material. The motion axes are under computer control, which lets them cut complex 2D shapes. Part programs can be created on the machine or directly from CAD files, which means minimal setup and no tooling results in very fast changeovers between jobs. In short, both technologies are great for cutting small quantities of metal blanks for fabrication.

The differences

Laser cutting machines use a tightly focused beam of light to vaporize metal. They can cut steel up to 5/8” thick at speeds of 3”/second or more and accuracy is around +/-0.002”. The cut edge is square and generally smooth, although there may be a very small heat affected zone (HAZ). Some dross and spatter will occur when cutting thicker materials, which requires a bit of clean-up.

A waterjet machine cuts with water pressurized to 60,000psi and traveling at supersonic speeds. To cut harder materials an abrasive grit – we use garnet – is added to the stream. There’s nothing a waterjet can’t cut and it can handle material up to 12” thick. Cutting speeds are lower though – half what the laser can do, or less depending on material – but accuracy is comparable. The cut edge is smooth and square, and there’s no HAZ.

We’ve got options

To summarize, laser and waterjet cutting are similar ways of producing complex 2D shapes. Laser works well for thinner sheet metals like stainless and carbon steel, but waterjet is better for cutting reflective metal and nonmetallic materials, especially if they’re thick. As metal fabricators, most of our work is with ferrous metals, which is why we have three laser machines, but like Batman’s Robin our waterjet is there when we need it.