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Best practices for laser cutting call for matching the right assist-gas nozzle diameter to the laser output power and assist-gas type and pressure, based on workpiece material type and thickness. Fail to do so and not only will cutting speed suffer, but—more importantly—so will cut quality and, ultimately, customer satisfaction. Typical nozzle diameters range from 0.8 to 3 mm.

Nozzle Diameter for Laser Cutting Mild and Stainless Steels

From “Facts About Laser Cutting,” Linde AG

Mild Steel--Oxygen Assist Gas
Thickness (mm)	Laser Power (W)	Nozzle Dia. (mm)
1.0	800	0.6-0.8
2.0-4.0	1000	0.6-1.2
6.0	1000	1.0-1.5
8.0-12.0	1500	1.2-1.5
18.0	2000	1.2-1.5
25.0	4000	1.5-2.0
Stainless Steel--Nitrogen Assist Gas
1.0	1500	1.2-1.5
4.0	3000	2.0-2.5
6.0	3000	2.5-3.0
9.0-12.0	4000	2.5-3.0

As custom sheetmetal fabricators expand their customer base and begin to take on a greater variety of metal alloys and sheet/plate thicknesses, the unproductive time spent making nozzle changes can quickly add up. Faced with just that scenario, Republic Sales & Manufacturing added automated nozzle changing to its shopping list when it acquired its latest 4-kW CO2 laser-cutting machine (a Trumpf TruLaser 3030), early in 2012. The Dallas, TX firm, primarily an OEM manufacturer of blowers and related accessories, also operates a 2008-vintage 4-kW Trumpf laser-cutting machine. Both machines, which feature a 60- by 120-in. sheet capacity, are used to cut mild- and stainless-steel work from 16 gauge to 3⁄8 in. thick.

“We cut a lot of material 1⁄4 in. and thicker,” says engineering manager Noel Torres, explaining why, after careful consideration, the firm opted for CO2-laser-based cutting machines rather than fiber-laser-equipped machines.

“The two Trumpf cutting machines give us a competitive advantage as we look to grow our custom sheetmetal-fabrication business,” Torres says. Custom fabrication represents about 20 percent of the firm’s business, the remainder comprising fabrication and assembly of blowers and enclosures for the food and waste-processing industries, among others.

“Our strategic goal for the last several years,” says Torres, “has been to grow our custom-fabrication business. That’s why we’ve invested in more sophisticated fabrication equipment, including the two laser-cutting machines. They elevate our capabilities above many of the shops we’re competing with.”

Targeting Bigger Customers, Bigger Orders

Republic Sales & Manufacturing installed this Trumpf TruLaser 3030 early in 2012. The machine’s technology package boasts three key features: automatic nozzle changer, a beam-alignment unit and automatic lens-status inspection. Also helping to justify the new-laser purchase is Republic’s ability to operate the machine unattended, thanks to Trumpf’s LiftMaster automated load/unload system.

The Republic Sales campus encompasses three buildings; sheetmetal fabrication lives in a 10,000-sq.-ft. building housing the lasers, four CNC press brakes, and paint and welding departments, and 20 production employees. Anywhere from 10 to 20 orders move through the shop per day, comprising part volumes ranging from one to as many as a few thousand.

“We typically process, in custom fabrication, a lot of really small orders,” Torres says. “We’re expecting that our expanded capacity with the new cutting machine will help attract larger orders from big OEM customers.”

The TruLaser 3030 represents what Trumpf called, when introduced a few years ago, a “new design concept—one cutting head for all sheet thicknesses.” The machine’s technology package features lens and nozzle automation, designed to optimize laser-beam-on time and cut edge quality. The technology package’s three key features: automatic nozzle changer, a beam-alignment unit and automatic lens-status inspection. Also helping to justify the new-laser purchase is Republic’s ability to operate the machine unattended, thanks to Trumpf’s LiftMaster automated load/unload system.

An Extra Hour of Cutting per Day

Nozzle size simply becomes one more process parameter in the cutting program downloaded to the machine control as part of a job number. “To cut the full range of material types and thicknesses, we use six different nozzle diameters,” says Torres, “from 0.8 to 2.7 mm. The automated nozzle changer gets the job done in less than a minute, while manual nozzle changes take 5 min. or more. That feature alone provides about an hour of added production time every day.”

Republic laser-cuts mild- and stainless-steel work from 16 gauge to 3⁄8 in. thick, using six different assist-gas nozzle diameters. Thanks to the automated nozzle changer on the firm’s new cutting machine, it gains an extra hour of production time per shift.

In addition to using the right-sized nozzle, laser-cut quality depends on an accurately aligned beam. And during production, a beam can move out of alignment numerous times per shift, says Torres, especially troubling when customers are specifying dimensional tolerances in the neighborhood of 0.005 in.

“Inspecting and adjusting beam alignment can take 30 to 40 min. when done manually,” Torres says, referring to the firm’s 3-yr.-old cutting machine, which lacks automatic beam alignment. “If we performed that task multiple times per shift we’d never get any work done. So, we specify that our operators inspect and adjust beam alignment twice per shift, or every 4 hr. As a result, we have to deburr some parts coming off of the machine.”

With the new cutting machine and its automated beam-alignment feature, Torres notes a significant improvement in cut quality and a corresponding reduction in cut-edge deburring. “We find that the machine’s alignment-inspection process very briefly interrupts production several times per shift, on average,” he says, “as it detects and corrects for minor beam misalignment. Each interruption lasts for just 2 or 3 min., and the resulting improvement in edge quality easily makes up for the lost beam-on time.” MF