An operator offloads a sheet of cut parts. Aside from the small parts tabbed in place, the cut pieces lift out of the nest to reveal clean edges, ready for the next operation. That’s the ideal, at least.
Quite often, of course, burrs (or dross) remain. Such imperfections may seem like par for the course, but many times operators can avoid them by making the right adjustments to the cutting parameters. To uncover them, operators need to know exactly what has to happen when the laser cutting beam, assist gas, and workpiece interact to create the perfect cut edge.
So what are these parameters? To find out, The FABRICATOR spoke with Charles Caristan, PhD, a technical fellow and global market director, fabrication and machinery, at Air Liquide’s Conshohocken, Pa., office. A longtime expert in laser cutting, Caristan is the author of Laser Cutting Guide for Manufacturing, published by SME.
So what’s the secret to burr-free laser cutting? There is no “one” secret, of course, but Caristan described some strategies that revolve around one element of laser cutting that’s largely under the operator’s control: the gas flow dynamics, or how the assist gas flows through the kerf.
Knowing Which Parameter to Change
For the most part, modern machines control the laser beam characteristics: specifically, the beam power (usually at the maximum) and beam profile. The beam focus, based on the focusing optic used, is set for particular material grades and thicknesses.
Technicians (and on modern systems, the machines themselves) may check myriad parameters, from beam alignment through the beam delivery system (in CO2 lasers) to centering the nozzle, to calibrating the focus position to ensure that the focus position commanded on the CNC matches the true focus position on the workpiece for every lens diameter used.
For certain applications, having that focus spot too high in the cut can leave spiky dross; focusing too low in the cut yields slower cutting speeds and can leave beads, a telltale sign of “overflushing.”
The focus position usually is saved as part of a cutting program table. The remaining parameters include the gas pressure, nozzle standoff, commanded laser power-frequency duty, and cutting speeds for various cut contours.