Laser Fabrication | Laser Software

Lasers and the job shop fabricator

Terry VanderWirt

There is a growing trend among job shops to invest in multi-axis laser systems. With a need for flexibility from project to project and their willingness to challenge this non-contact manufacturing technology, job shops are finding new ways to get jobs done. In fact, part designs that were never before possible are rapidly developed as laser processing permits these companies to innovate in surprising ways.

The software advancement of lasers--plus the ability of contract manufacturers to get the most out of this software--is really at the heart of why these job shops are increasingly successful with laser.

Good examples of these trends can be found at Meco, Inc., of Paris, Illinois, a precision metal fabricator who uses two laser systems along with an array of other CNC equipment, and at laser system manufacturer, Laserdyne, the laser systems division of Lumonics, of Minneapolis, Minnesota. Meco is a 200-employee job shop and specializes in manufacturing parts like turbine engine combustors for leading aerospace manufacturers. Laserdyne designs and builds standard laser systems and performs in-house contract laser machining and welding.

Laser's Real Worth Is Doing The Difficult

Meco began its experience with laser systems in 1984. As a specialized fabricator of turbine engine parts for major aerospace and turbine manufacturers, it regularly experienced heavy trim-die maintenance costs as high as $150,000. Laser processing was the logical solution to reducing these costs. Moreover, Meco began envisioning what it could do with a multi-axis system beyond simple trimming operations.

As it turned out, it did a lot beyond flat-trimming and this is the heart of the real story behind both Meco's success and Laserdyne's. It has also been the key to the growth of laser systems in many job shops. Meco looked beyond the obvious application and provided input to Laserdyne for development of multi-axis laser system features which it needed for its aerospace projects and which later became a standard in the aerospace and automotive industries.

Meco's first system was a five-axis Laserdyne 780 BeamDirector. They used the five-axis laser system to work with complicated contoured metal shapes--from trimming edges, cutting holes and welding sections of formed, thin-metal parts made of stainless steel as well as other materials. The system provided flexibility and speed for both production and prototype runs, requiring only the simplest tooling so setups were very fast and tooling costs were small. But this is the old news--Meco has been doing this kind of laser processing work on three shifts now for over eight years.

More interestingly, a recent development in turbine engine combustor design created a need for development of new laser system hardware and software. The old methods would work for this new part design.

The new combustor design allows for more laminar air flow to create more efficient cooling. However, Meco had no effective production method for producing the hundreds of small (0.019-inch) holes set at shallow angles over the entire contoured surface with the required precision. Conventional methods and standard user techniques were unreliable and inconsistent.

A solution to the small hole-drilling problem didn't come easy. The combustors were roll-formed and welded out of 0.04-inch and 0.06-inch thick high-temperature, oxidation-resistant alloy. Holes were 0.019-inch diameter ([+ or -]0.001 inch) and set at a 15-or 20-degree angle to the contoured surface. The imprecise nature of the roll-form process resulted in parts that were out-of-round by 0.01 inch to 0.02 inch, enough to create major difficulties in controlling both hole diameter and hole location. Besides these obvious positioning difficulties, the existing C[O.sub.2] laser wasn't capable of drilling small holes at shallow angles.

Laserdyne and Meco set out to solve this hole drilling problem with a new generation five-axis Laserdyne 550 BeamDirector equipped with a Lumonics JK704 Nd:YAG laser. Through an intensive development process, Laserdyne designed new hardware and software to go with the system.

Because the surface variations in combustor parts were not consistent from one combustor to the next, automatic focus control allowed the beam focal point to be maintained at a constant location relative to the surface. Meco found very quickly that without focus control, the focal point would change, resulting in variation in hole diameter. Hole location would also vary. The latter phenomenon is called "Abbe Error."

Since the holes were cut at 15- or 20-degree angles, the positioning error was compounded. For example, with a hole cut at 45 degrees, the error in hole location when offsetting along the axis of the beam would be approximately 1:1. In other words, the error would be equal to the amount the part deviates from its ideal surface. On the other hand, when holes are angled at 15 degrees, the error in hole location is nearly four times the surface deviation. (Actual error is one/tangent of the angle or 3.7 times the deviation in the surface location.) The result was that a 0.01-inch deviation in the location of the part surface would result in a 0.037-inch hole position error.

To correct this Abbe Error positioning problem, Laserdyne designed a new feature for its automatic focus control, known as "Selectable Seek." This provides the ability to define the direction of the offset of the system, within the part program, responding to any deviation in the gas assist/automatic focus control nozzle which targets the laser beam. This was made possible by locating part features independent of part distortion.

With Selectable Seek, the system is programmed to offset in a direction parallel to the reference plane of the workpiece. Like earlier Laserdyne systems, the nozzle moves along the beam line when cutting holes perpendicular to the workpiece surface. When cutting angled holes, the software enables the system to distinguish the correct axis for compensating motion. When special cases arose, Meco changed the direction through the software.

Meco quickly found more than enough work to justify the new laser, much like it did with its first system, not just in the manufacture of new generation engine combustors but also in other aerospace parts it produces which require high-volume hole drilling.

The pressure Meco was getting from its customers brought about by shorter production leadtime requirements--nothing new in the job shop industry--was relieved by its laser system processes. Because tooling was either unnecessary or relatively simple with the laser system, there were fewer tool development delays. Some of the more routine operations done with Meco's laser systems were also speeded up. Trimming went from 30 to 200 inches per minute. Edge finish was burr-free and consistent. With fewer "secondary operations" needed, there were fewer part setups needed and fewer errors.

According to Will Magers, Executive Vice President of Meco, all of these features made Meco more competitive in its bidding for work. The laser systems' flexibility gave them an extra way to be creative in their problem-solving processes.

Meco found other bonuses with their laser systems, too. One of these was the ease with which in-process gaging could be handled and changes could quickly be made in the software programs when needed. Statistical process control (SPC) was made a lot easier over old handchart methods. Data could be gathered electronically on a real-time basis, not some time after the fact. Meco says the documentation improvements alone have saved their company and customers thousands of dollars. It's facilitating an important part of their ISO 9000 effort, according to Mr. Magers, and helped them survive in a number of vendor base reduction efforts by their aerospace customers.

According to Mr. Magers, "For us, laser machining is not just a new manufacturing process, it is leading all of our manufacturing processes because we're able to produce new part designs because of it." It's been pretty good for Laserdyne too. Laserdyne sold its 130th system earlier this year and over 65 percent of the machines have been purchased by aerospace manufacturers and aerospace suppliers like Meco.

For more information on laser systems from the Laserdyne Div. of Lumonics Corp., circle 36 on the Postpaid Card.

Laser Cutting Thicker Materials

Laser machining is not limited to thinner materials as proven by Aero-Fab, an Indianapolis-based manufacturer of aerospace components. Pictured here is a cutaway of one Aero-Fab part--a 17-inch long by 14-inch high by 1-inch thick (432 x 356 x 25 mm) cooling frame made of Nimonic and used in General Electric land-based turbine engines. It presented manufacturing difficulties because of the material hardness and thickness. The part required 194 0.060-inch (1.5-mm) diameter holes drilled at 12-degree angles, each with a tolerance of [+ or -]0.003 inch ([+ or -]0.075 mm).

Aero-Fab originally produced the part by hand-drilling the holes, a costly and time-consuming process that caused frequent and expensive tool breakage, plus required substantial part rework. Typical processing time for one handdrilled part was 16 hours.

Laserdyne then began producing the parts in its job shop on a contract basis, on a 550BeamDirector laser. Once the process was proven, Aero-Fab bought the same model, and moved the process in house, saysDaryl Grubb, Laser Department Manager at Aero-Fab.

The process involves laser piercing into the part, trepanning or contour cutting the 0.060-inch diameter holes, and then forcing the minute slug through the exit hole. This process provides much straighter and cleaner holes than percussion drilling.

Mr. Grubb says the laser operates at 50 joules-per-pulse with a 250-mm focal length lens, which allows easy and fast deep-hold penetration of the part. Repeatability has been a consistent [+ or -]0.003 inch ([+ or -]0.075 mm) and part production increases have been recorded at up to 200 percent.

Aero-Fab's Laserdyne 550 Beam-Director is equipped with a Lumonics JK704 Nd:YAG laser. The system has axis travel of 25 by 25 by 24 inches (635 x 635 x 610 mm). It has a 360-degree continuous rotary table and [+ or -]135 degrees of full motion using the Laserdyne Beam-Director as an alternate to using conventional tilt tables. The direct drive Beam-Director axis provides precise point-to-point or contouring motion, and speeds as high as 32 rpm. The system is capable of processing a 29-inch diameter by 24-inch high (737 x 610 mm) cylindrical part.