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Parts without Machining & Lasers without Lamps: New Developments for Advanced Manufacturing

Is it possible to build parts and dies with metal without traditional cutting or forming techniques? Can you do laser material processing with a laser that doesn't have a flash lamp? The answer is in the affirmative for both.

It's entirely possible that metal parts will be manufactured and there won't be any cutting tools involved, nor will there be presses or other conventional equipment—at least not conventional with regard to cutting and forming. Rather, these parts, even complex, contoured items, will be produced through the implementation of laser technology.

For example, out at Sandia National Laboratories(Albuquerque, NM and Livermore, CA), they're working on what they are calling "free-form fabrication," a process that is being performed with what is being called "Laser Engineered Net Shaping" (LENS). This is a process wherein the researchers are going straight from a CAD model and producing, from metal powers like Inconel 625 and 316 stainless steel, bona fide, full-blown, 3D parts. Sandia researcher John Smugeresky remarked, "We can envision making parts from materials that can't be machined or deformed."

DMD
This setup for Direct Metal Deposition (DMD) may look fairly simple, but once it is fully developed, it has the potential to produce highly complex parts - both in terms of geometry and of tailored material properties-in short order without metalcutting or metalforming equipment. (Drawing courtesy: Center for Laser Aided Intelligent Manufacturing, University of Michigan)

Fundamentally, the process is similar to the fairly common rapid prototyping (RP) technologies that are being used throughout the auto industry. But there are differences. The similar part is that a laser is being used to create a defined object from an undifferentiated mass of materials. In the case of more common RP, this mass is typically a liquid or powdered polymer; sometimes there are metallics involved. But typical RP isn't in the Inconel range. What's more, conventional RP is performed with a fairly low-power laser; given the type of material that needs to be melted in order to create the part, anything more would be overkill. But in the case of LENS, the lasers being used are of a higher power, such as with a 1.8-kW CW Nd:YAG laser. This power is needed to produce the metal parts, as the powder is melted in order to build up the parts.

But like the RP approach, the processing is guided by digital information: the CAD model is converted into an STL file, which, in turn, is used to control both the build-up and the axes orientation required to build a part from the powder which is first made molten, then which solidifies in order to result in a part.

laser diode
The downside of the laser diode is the shape of the output. This leads to a comparatively large spot size and reduced power density. Still, there are good applications for the equipment. (Drawing courtest: Rofin-Sinar)"

LENS is a CRADA—a cooperative research and development agreement. It was established late last year. It is funded for $3-million over the next two years, with monies coming from both the government, and private industry. One of the CRADA members is Optomec, which is based in Albuquerque. It is working toward developing standard LENS machines which are estimated to cost on the order of $300,000 to $500,000.

Meanwhile, similar work is proceeding at the Fraunhofer Institut Werkstoff- und Strahltechnik in Dresden. It's program is called "laser-induced liquid phase sintering of composite powders." The rationalization for the program is a simple one. Product development time is always under increasing pressure, so they would like to have the technical means by which prototypes can be quickly produced with materials that have properties that are similar to those of the real product. In addition to parts, Fraunhofer researchers are also working at producing die casting molds.

Closer to home, there is an aggressive program at the University of Michigan in Ann Arbor, at the Center for Laser Aided Intelligent Manufacturing. The process there is called "Direct Metal Deposition" (DMD). According to Dr. Jyoti Mazumder of the center, the DMD process is a synthesis of the laser, a powder deliver system (fundamentally a cladding system), machine tool numerical control, CAD/CAM, and a feedback device that keeps everything working right. Mazumder emphasizes the importance of the feedback system to the effective operation of the DMD system. "This helps assure that the stresses involved won't interfere with the product," he observes.

Other considerations, also being worked on at the university, are software that will allow for on-the-fly changes of material layer thickness levels and the ability to change materials on the fly. (One interesting aspect of the DMD method is that it allows parts to be made with different materials in different areas, thereby allowing the tailoring of part properties.)

Tools You Can Use:
Welding Roofs or Cutting Rails

Although laser roof welding is not yet a common practice in the U.S. car industry, European manufacturers—including Volkswagen and Volvo—have embraced the practice in a big way. So in the event that it gets transferred to the U.S., the HL 4006D Nd:YAG laser from the Trumpf Laser Div. (Plymouth Twsp., MI) is a unit worth knowing about. Roof welding—as well as transmission component welding, which is a common domestic practice—is one of the application areas where it is a performer, whether the parts in question are steel or aluminum.

High-powered YAG
High-powered YAG
from Trumpf.

The laser provides 4 kW at the workpiece. A quality, focused beam means narrow welds and a minimal heat-affected zone. As it is a YAG laser, the power is transmitted to the workpiece via an optical fiber; up to three fiber optic cables can be attached to the HL 4006D which means, of course, beam delivery to three workstations.

More interested in cutting? Trumpf is also launching the HL 1003D, which is also a CW Nd:YAG laser. This unit, which is designed to be coupled with a robot, puts 1 kW at the workpiece for cutting. One supplier, an early user of the equipment, is using it to cut heavy-gage sections of hydroformed rails.

Like the work at Fraunhofer, they're working on developing dies with DMD. For example, they've produced a die with H13 tool steel that measures 3.3 × 6.5 × 5 in. The laser power: 1.8 kW. The total time the laser was running to produce the part is 24.3 hours.

The question of production cost is always an issue. Mazumder says that it is about a wash when the comparison is made between die machining and DMD. But he suggests that the big advantage can be found in the minimized amount of time involved in part production.

Is it possible for there to be a situation where a company might have a series of DMD machines instead of conventional metalcutting machines? Mazumder suggests that it is conceivable, but the likelihood of this happening in the near term isn't exactly so high that manufacturers of machining centers ought to start getting nervous. Still, it does indicate that there is, long term, at least, the distinct possibility that this approach to part making will become sufficiently robust for short-run production without tooling, fixturing and metalcutting or forming equipment to be employed.

Going Solid-State

Typically, if you think about a laser system, you figure that there is some sort of crystal or gas that lights up inside a cabinet like something on The X-Files before it is optically transferred into a visible or invisible beam. It is easy to wrap your mind around the notion of working with light energy because there are, in effect, light bulbs involved.

But when you start thinking about diode lasers, things become incredibly different. In this case, instead of having flash lamps doing the pumping, solid-state devices are doing the work. Diodes have been used for the past several years to do things like play compact discs, but they are now becoming available with sufficient power to go beyond pumping out Celine Dion's latest.

What's happening is that the individual diodes—which measure about 10 × 0.15 × 0.6 mm (this is a silicon slice that's about the size of a penny—are being stacked up. Put about 40 of these little bars in a stack and, with an output of approximately 30 W per bar, you end up with on the order of 0.8 to 1.0 kW. Arrange a couple of stacks together, and you arrive at 1.5 to 1.8 kW—enough power to do some work.

Tools You Can Use: Is It Right?

PRC Laser (Landing, NJ) specializes in CO2 lasers and accessories. It has established what it is calling the OEM Referral Service. The stated objective is not to have people buy PRC lasers, but, instead, to help engineers and managers determine, by talking with an applications engineer at PRC, whether a laser would be right for their particular application and if so, to make recommendations—and not necessarily of PRC equipment.

One company that's offering high-power diode lasers is Rofin-Sinar Inc. (Plymouth, MI), which, last year, acquired dilas Diodenlaser GmbH, which is said to be the first laser manufacturer to provide commercially viable diode pumped lasers for material processing.

Richard Walker, general manager of Rofin-Sinar, ticked off some of the advantages of high-power diode lasers:

  • Compact laser head size. The head is about the size of a toaster oven (e.g., a 1.6-kW head measures 254 × 135 × 130 mm). What's more, added to the system are a 19-in. rack-mounted power supply and a 6-kW chiller.
  • High wall-plug efficiency. One of the issues that is a concern with lasers is that more power goes in through the wall plug than comes out the working end (to be sure, what comes out the end is in a highly concentrated form). The efficiency of a typical CO2 laser (taking the amount of electrical excitation power and comparing it to the laser power) is about 5 to 10%. For Nd:YAG it is 1 to 4%. High-power diode lasers have an efficiency of 30 to 40%.
  • Maintenance-free. Remember, this is a solid-state device. There are no lamps. No reflectors. No deionized water.
  • Long-life. A diode may last as long as 10,000 hours. Yes, that's may. But Walker noted that these things last a whole lot longer than flash lamps regardless of how long they're in service.

So, will this mean that there will be a stampede toward diode lasers and away from the more conventional types? Probably not. For one thing, they are comparatively new, so there's a whole lot that remains to be learned about their applicability for industrial applications.

Tools You Can Use: Precision Work

If you're looking for a unit that can cut with kerfs as narrow as 30 microns, drill holes 60 microns in diameter in material 1 mm thick, or make welds just 0.2-mm thick, check out the KLS 246 250-W Nd:YAG system from Lasag Corp. (Arlington Heights, IL). Among its features are a swing-out cavity that permits quick lamp changes without the need for realignment, a hand-held terminal for programming and operation, and an overall compact design.


Precision processing 
unit from Lasag.



Tools You Can Use: New Cutting & Welding Gear

Messer Cutting and Welding (Menomonee Falls, WI) is entering the U.S. market with laser and combination laser/plasma systems. The company will be launching, in 1998, its TopLine family of machines, which includes three models, the Ecolas, Easylas, and Multilas. Each of these sheet metal processing machines uses a Fanuc CO2 laser, ranging in power from 2 to 3 kW.

A design study of the 
Multilas from Messer.

The Ecolas has a 1,500 x 3,000-mm table and a 60 m/min-speed. The Easylas has a 1,250 x 2,500-mm table and a speed of 80 m/min. The Multilas, which will be introduced later this year, will offer a 2,000 x 6,000-mm table and a speed of 100m/min.

What's more, there is, Walker pointed out, a drawback: Divergence. Or, more plainly, the beam quality isn't very good. Essentially, there are a series of stripe emitters—10 or more—on the surface of each of the bars. Each emits an oval-shaped output. This needs to be focused in some manner because what it looks like, in effect, is a series of overlapping oval ice cream cones. Even handled, the result is a focused spot on the order of 1.4 × 3.5 mm at 1.6 kW, which is much bigger than the spots provided by either a CO2 or conventional YAG laser. Which means that the resultant power density is lower. Which means that the standoff distance (i.e., between the laser and the workpiece) is less.

That said, where can the high-powered diode lasers find use? First of all, it is worth noting that the wavelengths (808 and 940 nm) are good for both metals and nonmetals. In the area of welding, for example, 0.8-mm thick mild steel can be welded with a 3.5-mm wide weld by 1.4 kW at a rate of 1 m/min. Where the welding ability really shines, however, is in the area of plastic welding, where a small high power diode laser, with an output power of no more than 60 W, can weld a variety of plastic components, from electronic keys to plastic gas tanks at a rate of up to 10 m/min.

In the area of metals, heat treating and hardening are good ones, as are brazing and soldering.

This is really just the beginning of diodes for industrial use. One can only assume that the laser manufacturers are going to be working the disadvantages out, or at least minimizing them to the greatest extent possible. Given that, the opportunities provided by these compact devices could greatly extend the application of lasers.

British Steel laserA Big One for British Steel

"The main driving force for the use of lasers in industry is lower fabrication cost, resulting from high cutting and welding speeds and minimum distortion during welding. The SR-25 will be used to develop new, laser-friendly steels to complement existing products and to supplement the work of job shops for economical special welded assembled and steel fabrications using heavy plate and coil. British Steel may also produce long beams and other small volume profiles in custom arrays, fabricated by special section rolling mills," said British Steel's Dr. Alan M. Thompson, principle welding engineer at its Mooregate, Rotherham facility. He's talking about a 25-kW laser fromConvergent Energy (Sturbridge, MA) that will be installed later this year in one of the company's facilities. It is thought that the laser will be the most powerful one in Great Britain. The laser features a gantry system measuring 5 × 3 × 1 m; it provides five axes of controlled motion. It can weld or cut steel up to 1-in. thick at speeds of 40 ipm or more.