A 5-axis laser and a CAD/CAM program and helping to reduce the lead time on producing contoured sheet metal components for the aerospace industry and cut costs associated with it by as much as 25 percent.

CONTOURED SHEET METAL components in the aerospace industry have traditionally been formed and cut to final dimensions in stamping presses. But tooling the componets can take weeks--or even months--and costs can run up to $100,000.

Dynamic Metals Products Inc., an aerospace manufacturer that fabricates sheet metal components for aircraft engines, reprocesses these parts using a hydroform press that forms material up to 10 inches deep. Last year, the company purchased a 5-axis laser machine to finish and trim parts. Previously, this was done manually.

The process reduces lead time on a typical aerospace engine component, such as a manifold tube, from about three months to one month and cuts costs by a much as 25 perceent, according to Dynamic Metals, whose customers include Pratt & Whitney, Allison Gas Turbine, the U.S. government and Textron Lycoming.

The most difficult part of coverting the trimming operation to the laser was programming the laser in five simultaneous axes. It was necessary to select CAD/CAM software that can program the 5-axis laser machine. Dynamic Metals selected the Mastercam, CAD/CAM program from CNC Software of Tolland, Conn, CNC Software wrote a program that met the requirement of the application using the 4.11 version of its Mastercam program, which provides a C language programming interface. (Programs that are written to this interface are called C-hooks.) Dynamic Metals used a Mastercam C-hook called CURV5AX that generates 5-axis code from contours and a 3-D surface.

The programming process followed the same steps normally taken with Mastercam: first producing a wireframe model of the part from a blueprint with the program's CAD tools or by importing a file from another CAD program; then defining the surfaces of the part using the software's surfacing tools. On the manifold tubes, the programmer primarily used the ruled surfaces option, which defines a surface based on a linear connection between cross sections. More-complicated areas were defined with the Coons patch function, which generates a surface mesh blending together either three or four boundaries. Once the surfaces were defined, the programmer accessed the CUR V5AX function, which prompted them to select with a mouse the boundaries to be cut.

At that point, Mastercam automatically generates the laser paths required to produce the part. The surface being cut is constantly changing in orientation. The resulting laser path is plotted onto the screen for examination. When the programmer is satisfied, the G-code (the code readable by the laser machine) is sent over the network to the CNC machine. CNC Software is currently working on an upgrade to the CUR V5AX function that will incorporate the machine head and tooling geometry, making is possible to see it on the screen to void the possibility of crashes between the machine head and the piece being machined.

Learning to use the Mastercam tool took only a few weeks. Now that the process is learned, a manifold tube can be programmed in about three hours.

FROM BRACKETS TO AUGMENTER LINERS

Dynamic Metals began laser cutting using a 2-axis laser that cuts 60-inch by 96-inch sheet stock in seconds without any tooling, thus reducing cost and lead time. Between 200 and 300 inches can be cup per minute, depending on the metal. Within three months, the laser was working at 100 percent capacity. Engineers at Dynamic Metals then realized that the same opportunity existed in the production of contoured parts.

The 5-axis laser was put in use to provide the additional capability of trimming all around a part. The 5-axis laser eliminates the need to build trim dies that range in cost from $10,000 to $100,000 and take weeks or months to design and build. Programmers at Dynamic Metals can now generate a typical 5-axis program in about 3 hours. The lasers, like the other machines in the plant, are programmed via a Lantastic network, with each machine having its own 33-MHz 80486 Digital Equipment Corp. personal computer at its side.

Products range from brackets to augmenter liners. Augmenter liners, which comprise the opening at the rear of a jet engine, range from 5 to 6 feet long and are typically 42 inches in diameter. Recently, Dynamic Metals began fabricating and machining parts such as seals, bearing housings, and brackets. Because of the high volume of laser work, the company installed a 1200-gallon high-pressure liquid nitrogen bulk tank. The nitrogen gas in the tank clears the vaporized material from the part that is being lasered.

The mainfold tubes produced by Dynamic Metals are bent in the middle like an elbow joint and are manufactured from flat Inconel sheet stock in different configurations and sizes. The stock in sheared to a rectangular shape. Then it is formed into half-segments on a hydroform press that uses hydraulic pressure up to 15,000 psi. The press uses a male die corresponding to the shape to be formed and a female called a draw ring thast is surrounded by a bladder that fills with oil.

The advantage of this technique is that forms up to 10 inches deep and of almost unlimited shape can be produced. The segments are annealed for stress relief and then restruck in the hydroform press to complete the form.

The next procedure, trimming, is critical to achieve a perfectly circular shape. In the past this was carried out with a manual operating called scribe sanding. This method involves producing layout dies, scribing the parts, rough sawing, and hand sanding. The complete process takes about 20 minutes for each half-section; a typical 50-piece lot would take about 2000 minutes, or 33 hours, to finish. Additional time was required for hand-fitting each section prior to the final welding operation.

The cutting machine is a TLC-105 2-kilowatt laser from Trumpf Inc. of Farmington, Conn. The laser has cutting and welding heads and uses flying optics, which means the part stands still while the head moves. The machine offers 81 inches of x-axis travel, 40 inches of y-axis travel, 16 inches of z-axis travel, [+ or -] 120 degrees of b-axis travel and unlimited c-axis travel. Dynamic Metals also purchased a rotary table that provides unlimited a-axis travel.

The tube is mounted on a fixture on the rotary table at a 90-degree angle, exposing bogth edges that need to be trimmed. To avoid distortion caused by stress relief, a male and female fixture are used to clamp the part while it is being cut. The part is further constrained by a tailstock at the center of the rotary table, and the material is flipped up into the vertical position. Cutting takes place in this position and takes one to two minutes, including loading and unloading.

In addition to applying the machine, another important process innovation was developing tooling for the job on the 2-axis laser machines using 1/8-inch sheet stock. The tooling is laid out in flat patterns with female slots and matching male tabs cut into them, fitting together like an erector set. Using this method, male and female clamps fpor manifold tubes or virtually any other laser tooling are produced in an hour or two.

These methods have reduced the costs of these components by approximately 25 percent. Lead time has been reduced from 10 to 12 weeks to 2 and 4 weeks. Quality has also been substantially improved. Each piece is now perfectly consistent with everty other one, avoiding the need for matched pairs. The laser also provides substantially higher dimensional accuracy than the manual approach. In addition, the 5-axis laser provides similar advantages on a wide range of other work that requires geometry that is cut true to a surface.