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Getting on the beam with lasers.

Some tips on avoiding the "neat stuff syndrome" when choosing a laser system.

Lasers for metalworking. Gee whiz, high-tech. For specialized applications. Wrong. "We've always thought of lasers as just a tool to do a job," says Terry Feeley. "We didn't get our customers interested in doing business with us because we had lasers. They became interested because we could cut, weld, drill, or mark materials they couldn't normally work with, or we could do it more cost-effectively than they could do it conventionally."

Mr Feeley is president of HGG Laser Fare, a Smithfield, RI, laser job shop. In business since 1980, Laser Fare uses both solid-state (Nd:YAG) and gas (C|O.sub.2~) lasers with 3-, 4-, and 5-axis capability to provide cutting, welding, drilling, and marking services for a variety of customers.

Laser Fare purchases laser equipment every year, says Mr Feeley, and he advocates a practical approach--avoiding what he calls the "neat stuff syndrome"--to laser machine selection. "Most of the suppliers now are less caught up in the technology and more interested in delivering real value, and I think that's a very healthy sign," he says.

Carl Nilsen, president of PRC Corp, a manufacturer of C|O.sub.2~ lasers based in Landing, NJ, agrees. "Potential customers should be careful of looking at laser as a technology," he says. "It should be looked at as a machine tool. They should use all the usual industry standards to evaluate its reliability and its cost and not get into the 'technical tourism' so common among laser suppliers."

The main question is: will the system do the job you're buying it to do, for the price you're expecting to pay?

To figure that out, you'll need to know something about the laser portion of the system as well as about the machine tool systems associated with the laser, operating costs, and your expectations as far as part quality and throughput.

On the beam

When it comes to evaluating the laser itself, important factors are power and beam quality. Both are potential sources of confusion.

Discussions of power can be tricky because lasers operate in different ways. Continuous wave lasers deliver uninterrupted power. Pulsed devices deliver short bursts of power to the workpiece. Both modes have their place; pulsed operation, for example, is beneficial in ejecting material in drilling operations.

Conrad "Connie" Banas, chief scientist, United Technologies Industrial Lasers (UTIL), South Windsor, CT, explains that a pulsed laser may generate peak powers many times greater than its average power rating, while a continuous wave device is providing a constant power output.

As an example of the difference, he compares welding 1" thick steel with a 3-kW pulsed YAG laser and a 25-kW C|O.sub.2~ continuous wave device. "You can take a 3-kW pulsed YAG and demonstrate full weld penetration, because in pulsing you get a 30-kW peak, and a 30-kW peak will penetrate through that thickness of steel. But welding speed is determined by the average power of the device. With the pulsed laser, speed would be a fraction of an inch per minute. With a 25-kW continuous wave device, you'd probably do that weld at 40 ipm," he says.

Beam quality is "something the industry has wrestled with how to characterize for some time, and I think we've got a long way to go in fully understanding all the factors involved," says Terry VanderWert of Laserdyne Div, Lumonics Corp, Eden Prairie, MN.

Right now though, in the US, the most important measure of beam quality is called |M.sup.2~, which is a ratio of the actual divergence of a laser beam compared to that of an ideal beam. Divergence implies how well the beam can be focused and is determined by factors including the wavelength of the light and the energy distribution within the beam.

Technology may be changing the accepted thinking with regard to energy distribution within the beam, where a normal (gaussian) distribution has been considered ideal. Mr VanderWert says fiber optic beam delivery for YAG lasers may offer advantages beyond configuration flexibility, providing a round beam with good energy distribution. "Because you're imaging the end of the round output fiber, the effect of out-of-roundness on beam profile seems to be eliminated. We're looking at using fiber optic delivery to give a more perfectly round beam," he says.

PRC, meanwhile, is working with researchers at Rutgers University on a waveguide system that would do for C|O.sub.2~ lasers what fiber optics have done for YAG beam delivery. The waveguide system consists of a hollow-core sapphire fiber that is just as flexible as a fiber optic cable. The system currently can handle 1300 W of continuous power, and Mr Nilsen says the eventual goal is a fiber that can withstand 3000 W. The system will be installed in beta test sites by the end of the year, he adds.

Regardless of how the beam is delivered, "customers don't have to know the technical details of beam quality," says Mr Nilsen. "But they should be aware of its importance."

Mr VanderWert agrees. "Beam quality is important, but it's most important to us as machine tool designers. In most of our systems, we're moving the beam above the workpiece in some number of axes, and we have to have a good understanding of what the beam looks like in space," he says.

Back to basics

According to Mr Feeley, things in the area of systems integration have changed quite a bit since 1980, when Laser Fare built its own machines by purchasing a laser here, a positioning table there, and controllers somewhere else and integrated them into a metalworking system. "There are a number of integrator now who have done a respectable job of putting the pieces together," he says.

"Again, what potential users ought to be looking for are solutions to specific manufacturing problems," advises Laserdyne's Mr VanderWert. "The factors that are important in selecting a laser system are in principle the same as you might use in selecting any machine tool."

First, he says, look at programming. How are you going to program the parts? What form is the part data in? The number of businesses using CAD systems is growing, but there are a number of applications, like automotive prototyping, where the design data don't exist or are being changed faster than the files are being updated.

When it comes to the machine tool portion of the system, all the factors that apply in evaluating conventional machine tools should be considered, including static and dynamic positioning accuracy. Also important is the basic system configuration. Although some multi-axis systems are hybrids, there are basically two choices when it comes to getting around the workpiece: either move the laser or move the work.

"Moving beam versus moving table design is an issue, particularly for two-axis cutting," says Mr VanderWert. "With a moving beam design, you're positioning a constant mass. It's not affected by the mass of the workpiece, and you can fine-tune the servo system to get optimum performance. If you're moving a workpiece around, you have performance trade-offs to handle a range of part sizes, from sheet to heavy plate," Mr VanderWert says.

Finally, try to evaluate the machine's capabilities in the context of your expectations for part quality and throughput. Important part quality requirements include dimensional and position tolerances; presence of burrs, heat-affected zones, and recast layers; and cleanliness (spatter resulting from cutting or welding).

Operating costs

PRC's Mr Nilsen says it's important for potential users to try to take into account all the costs involved in operating the laser system over its expected life cycle. "The issue is cost--not just capital cost, but floor space and operating costs. Capital costs are probably the minimum expense, because you're doing that once. You can either afford it or not. But the real hidden costs are what it's going to take to operate the system over ten years," he says.

The main driver of laser operating costs is the gases used. Carbon dioxide lasers actually use a relatively small amount of C|O.sub.2~ mixed with helium and nitrogen. Both C|O.sub.2~ and YAG lasers use assist gases such as nitrogen, oxygen, and argon for cutting and welding operations.

Although prices of gases in the US right now are relatively low, Mr Nilsen believes that could change fairly quickly over the next few years. "Gas consumption has to become more of an issue here in the US. The more gas that's used, the more electricity is consumed somewhere in the US to produce it. In Europe, the cost of industrial grade gases is about twice as much as here. Laser purity gases may be four times the price we pay. So any customer who buys a laser that requires specialty gases, either a mixture or in purity, may find during the next few years that they can't afford to operate the laser any more," he says.

The bottom line

So what's Mr Feeley's ultimate advice for prospective laser users?

"The proof is in the pudding. Our days of believing brochures are basically long past," he says.

Laser products: emphasis on practicality

Given the current focus (no pun intended) on the "steak" of laser metalworking equipment as opposed to the "sizzle" of technology, here's a selection of laser products designed to increase productivity, cut costs, and enhance the value of laser systems.

Many metalworking lasers are still programmed by "teaching," which involves the operator manually following scribe lines indicating part features. Laserdyne has developed TeachVision, a vision-based programming system for its largest multi-axis laser machines. The patent-pending system uses a high-resolution video camera to image scribe lines, trim lines, or other features to be laser-cut in five or more axes. A hand-held remote control provides full operator control for program development or editing. An LCD built into the hand-held control displays text, graphics, and the camera image of the line defining the feature to be cut.

The device includes a feature called Auto Normal, which automatically orients the laser head perpendicular to the part surface. This saves time and increases accuracy and consistency of the angle of the cut relative to the surface.

Also from Laserdyne is a right-angle nozzle available as an option on the company's 780 BeamDirector multi-axis C|O.sub.2~ or YAG laser systems. The right-angle head provides easy access to the tube IDs for contour cutting or trimming and allows deep-hole drilling of severe angled holes and welding of hard-to-reach areas. The system also features 135 deg of tilt motion, providing part processing capability in areas above horizontal.

Rofin-Sinar Inc, Plymouth, MI, is putting the emphasis on beam quality and versatility with its RSY 150 P, a 150-W YAG laser for welding, cutting, drilling, and marking applications. The versatility is made possible by precise focus and full pulse shaping capabilities, which deliver high peak powers and provide the ability to cut, weld, and drill faster than conventional lasers in the same power range.

The compact system is sold complete with power supply unit, beam delivery, cabinet, microprocessor control, and cooling system, and can be equipped with a fiber optic beam delivery system for added processing versatility.

Trumpf Inc, Farmington, CT, has added accuracy to its Lasercat compact laser cutting center with the Cat Eye, a probe that uses a light beam to monitor and measure distances between pre-punched holes and the sheet edge.

Designed for mounting alongside the machine's laser cutting head, the Cat Eye focuses a beam of light onto the pre-punched workpiece material. The focused beam finds and measures the distances between holes and locates the sheet edge, giving fast, accurate calculation of coordinates. Trumpf says the probe is especially useful for recalculating coordinates when repositioning carts are used to accommodate large workpieces.

To maximize cutting rates for a variety of materials, a tunable 1-kW C|O.sub.2~ laser has been developed by PRC Corp. The device uses a tunable resonator to provide continuous rated power at four wavelengths between 9.1 and 10.6 ||micro~meter~. Other wavelengths in the range are available at lower power ratings, and the tunable laser also can operate in a variety of pulse modes.
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Title Annotation:includes related article
Author:Destefani, James D.
Publication:Tooling & Production
Date:Sep 1, 1993
Previous Article:Non-contact metrology.
Next Article:Building on quality.

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