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When smaller is better

Oct. 1, 2003
Compact laser-machining systems pack just the right power for cutting thin sheetmetal.

Compact laser-machining systems pack just the right power for cutting thin sheetmetal.

By Dan Popescu, Haas Automation Inc.,
and David Clark, Coherent Inc.

Edited by Patricia L. Smith

Cutting thin sheetmetal is the specialty of the Haas Z4-500 lasercutting system.

The 4th-axis capability of the Haas Z4-500 laser-cutting system enables precision radial machining of parts, including thin-walled tubing.

The Z4-500 Laser Cutting System from Haas Automation incorporates a compact sealed CO2 laser and lets Laser Cutting Corp. cut, drill, engrave, and weld thin sheetmetal quickly and efficiently.

Maintenance-free, sealed CO2 lasers provide up to 21/2 years of continuous operation.

High-power CO2 laser-cutting systems, while ideal for cutting thick metal plates, often fall short when it comes to cutting thin sheetmetal. That's because these lasers generally can't run at full power or speed without damaging thin material. However, a new class of low-cost, compact laser-machining stations — built around a sealed CO2 laser and machiningcenter platform — promises to process thin sheetmetal parts more efficiently and economically than their massive counterparts.

For the most part, shops must reduce power more than 50% to cut thin material with a high-power laser-cutting system. Doing so minimizes dross (re-cast molten metal). Running at reduced power is also important when cutting around corners, because the metal on each side of the laser focal spot is in the heat-affected zone (HAZ) and easily melts when the laser beam moves into this preheated region.

To avoid overshoot, the cutting speed of high-power CO2 lasers is usually limited to approximately 100 in./min, although the machines can cut thin sheets up to 30 that rate. Unfortunately, shops won't get a maximum return-on-investment by operating these high-power lasers at less than 50% power and at only 3% of their maximum cutting speed.

Sealed CO2 systems, on the other hand, are built around a lower average power — below 500 W. These systems complement high-power systems by processing thin sheetmetal more economically, leaving highpower systems free to efficiently cut thick metal plates. This makes them perfect for jobshops such as Laser Cutting Corp., Middletown, Del., a laser jobshop specializing in highprecision fabrication of components and the processing of exotic materials.

Laser Cutting needed an inexpensive system that was easy-to-use and versatile enough to tackle drilling, engraving, and welding. The laser also had to meet customer requirements for ever-tightening levels of dimensional control, finer features, better quality, and greater cleanliness of finished products fabricated from thin sheetmetal and thin-walled tubing.

According to Mark Kreshock, company president and co-founder, high-power CO2 laser systems (over 1 kW of output power) didn't fit the bill. Besides their inefficiency at cutting thin metal sheets, these systems take up a good deal of floorspace and have high capital and operating costs. The company found what it needed with a compact Z4-500 laser-cutting system from Haas Automation Inc. The machine employs a 500-W Diamond K-500 sealed CO2 laser from Coherent Inc.

Sealed CO2 lasers have qualities that make them well suited for thinsheetmetal processing. They feature slab-discharge technology and offer the benefits of compact design, easeofuse, maintenance-free operation, and low operating costs. Laser heads can also operate up to 25,000 hr without needing scheduled maintenance. This translates to over 21/2 years of continuous operation. Two further advantages of sealed lasers are their fast pulsing — up to 100 kHz — and high peak-power qualities of 1.5 kW/pulse.

The slab-discharge technology used in these lasers produces highfrequency pulses with extremely fast rise-and-fall times relative to the duration of the pulse. Therefore, metal is efficiently cut or drilled rather than merely heated. The result is a clean cut or hole with little heatinduced damage. This efficiency, coupled with fast pulsing, allows slab lasers to process metals quickly.

A feature of the Diamond slab laser from Coherent is a 50% on/off-mode of operation that delivers a peakpower of 1.5 kW/pulse. High peakpower results in faster material removal, because the "off" time allows the material to cool and minimizes the HAZ. "The Haas Z4-500 has more value for us, because the pulsed 500-W sealed laser inside the Haas unit can effectively do the work of a 1,000-W system," says Kreshock.

The small size and low-maintenance needs of sealed CO2 lasers allow the laser, its power supply, and the focusing optics to be fully enclosed within a compact machining station, as with the Z4-500, which has a footprint of 140 110 in. Because the Z4-500 is based on the Haas VF-4 VMC, it is mechanically similar to a milling machine. Therefore, the cutting bed moves, while the laser head remains stationary.

"The system holds tolerances well, because it is based on a mill design," explains Kreshock. "It operates at speeds up to 500 ipm, with a positioning accuracy of up to ±0.0002 in. and a repeatability of ±0.0001 in." Laser Cutting's unit also has 4th-axis capability for radial cutting of tubing.

In addition to their other benefits, compact laser-machining systems won't blow a shop's budget. For example, a laser-machining station using a 500-W sealed laser, and with 4th-axis capability for radial cutting, costs less than $200,000. An additional 5th-axis option can also be added to a machine later, if necessary.

For Laser Cutting, the Z4-500's software control was a major factor influencing its selection of the machine. "Since programming is also based on the Haas VF-4 VMC, 90% of the software is the same, except for the laser options. Because we were familiar with the Haas software, switching to lasers was easy," explains Kreshock.

The advanced, but simple-to-use software accurately controls both the amount of energy delivered by the laser and the location to which it is delivered. In this way, hard tools are replaced with virtual laser tools. This feature provides the flexibility and speed for Laser Cutting to handle several different processes, including cutting, engraving, and drilling, on the same sheet of material in one setup.

The shop imports customer designs in a variety of software formats, including IGES, DXF, DWG, DXB, ACIIS, SolidWorks, and even a design-drawing format, into the system. These are automatically converted into a cut program. "By eliminating the hard-tooling process, we can fabricate products in as little as 15 min," observes Kreshock. "This means we can provide our customers with fast prototype turnaround times — in less than a week and sometimes in just one day."

Adding to the shop's flexibility is the laser-welding capability of the Z4-500. According to Kreshock, "We have applications that require us to weld materials, such as molybdenum, Kovar, stainless steel, and nickel." Up to four gases, including nitrogen, oxygen, and a mixture of the two, can be connected to the system for gas-assisted welding. The choice of welding gas is then selected through software that's controlled by the operator.

Cutting molybdenum
Laser Cutting recently exploited the advantages of laser machining by cutting parts from molybdenum sheets. Its customer wanted a variety of holes, slots, and notches machined in the thin material for use in an industrial furnace.

Molybdenum has a high melting temperature but is brittle at room temperature. Mechanical punching, stamping, and drilling systems can easily fracture and delaminate the material if it's not preheated. "Some shops don't work with molybdenum," explains Kreshock, "but we work with it regularly because the laser is ideal for this material."

The molybdenum sheets were 0.020-in. thick and required holes between 3/8 and 5/8 in. in diameter. Slots were 1/4 1-in.

The laser's "soft-tooling" approach eliminated the need for hard tooling, allowing Laser Cutting to quickly produce prototypes. And because of the nature of laser machining — plus the fact that a laser is a noncontact tool — the finished molybdenum parts were precision-machined without fractures or delamination.

According to Kreshock, laser machining provided economic benefits to the customer. "The parts were cheaper for our customer because there was no hard-tooling cost," he comments.

Mr. Popescu is laser product manager with Haas Automation Inc., Oxnard, Calif., and Mr. Clark is business development manager of the Materials Processing Business Unit, Coherent Inc., Santa Clara, Calif.

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