For the aerospace industry, one of the more exciting innovations to spring out of this machine tool technology revolution has been the evolution of high-speed machining (something that couldn't have happened without the software and hardware innovations that came along with the faster machines). Not only are spindles and guideways capable of going faster more accurately, but also better controls and CAM software ensure the machining program can keep up with the machine.

Alan Levine is Director, Computer-Aided Manufacturing, at Concepts NREC. The company produces its own line of CAD/CAM/CAE software and also designs and develops turbomachinery components for several companies. He reinforces the impact that high-speed machining has had on the industry.

"I have seen a customer reduce machining time up to 55 percent over the past four years using high-speed milling," says Levine. He goes on to point out that the advantages of that 55 percent reduction go beyond the more obvious savings of cost-per- part and return-on-investment. The company also had to outsource less work to finish jobs on time—a significant bottom-line enhancer.

The impact of these high-speed, extremely capable machines does not stop at producing quality parts quickly, however. There is also great potential machining smaller components from block material instead of a casting (which can be much less costly in some cases), or taking previously separate components and combining them, as is the case with blisks or IBRs (integrated blade rotors).

According to Levine, it was not so long ago when blisks or IBRs were not often used in the aerospace industry. "Blisks could not be made large enough or accurately enough, and they were too expensive. They also greatly reduce the number of parts in an engine, simplifying assemblies and balance procedures."

However, technological advancements have made blisk manufacturing more than possible. According to Levine, the combination of advanced high-speed machining, advanced CAM software and better block processing speeds from controls are making it possible to work blisks along the order of 40 inches to 50 inches in diameter.

Concepts NREC's MAX- series of CAM software tools is specialized for turbomachinery and aerospace applications. The MAX-series generates toolpaths that take into account the materials used to make blisks (like aluminum and titanium), the thin walls of the blades, machining the tight quarters between blades, and the ultra-high tolerances and quality requirements.

The MAX- series comprises three modules:

• MAX-5, for flank milling complex parts,
• MAX-AB for point milling complex parts, and
• MAX-SI for generating cutter paths for integrally shrouded components.

The modules can work in tandem or separately, and they contain turbomachinery- specific features such as:

• The ability to immediately interact with all five-axis machine tools via a set of customized postprocessors engineered by the company;
• Unique parameters and instruction sets for splitter blades, leading and trailing edges (point specified, radiused, or elliptical), twist undercuts, machinability verifications, and blade indexing;
• Cutting methodologies that allow for less slotting when cutting hard materials;
• Pre-programmed cutter path templates that are specific to turbomachinery components;
• The ability to anticipate cutter path and cutter orientation direction changes, and to integrate well with machine control systems.

These features enhance the generation of toolpaths nonetheless. For example, the MAX- modules are analytically, and strategically based, so it is creating a series movements strung together by G-code, it is creating the best possible path to create the part. This eliminates unnecessary reversals and reduces radical accelerations and/or decelerations. Good CAM programs also keep an eye out for extreme velocity and acceleration by using prescribed limits, and can override programmer-created commands where a high velocity rate could affect the cutter path and mar the part.

CAM packages like the MAX- series complements well the advanced high-speed machining centers like the Makino V55-5X. The V55-5X maximizes techniques like Flush Fine, a machining process that combines a shallow depth of cut to keep heat away from the part with high spindle speeds and cutting speeds. Flush Fine works well on the blades of the blisk since the low heat means the thin walls are much less likely to distort. Super Geometric Intelligence (SGI) software is another innovation in the V55-5X that maximizes the original CAM program. The servo control software is sort of a watchdog, looking ahead of where the program is at, and making corrections on the fly. SGI analysis monitors parameter settings to reduce excessive accelerations and to maintain an accurate path at high feedrates. And the system works even better when the CAM software produces NC instructions with good position, velocity and acceleration characteristics.

The V55-5X also has a five-axis table with a dual tilt mechanism, which brings the part to the spindle from more angles, so the spindle does not move as much, keeping chatter and undesirable conditions at bay.

Another feature that is important to machining good blisks is the rigidity and robustness of the machine itself. This may go without saying, but if you were machining a thin blade wall, vibration and chatter would translate into an unusable part and wasted metal. To eliminate the likelihood of this as much as possible, the V55-5X (and all Makino machines, for that matter), feature an integrated construction with rigid castings, a heavy and vibration reducing base and a stiff spindle.

While the V55-5X has many features that lend themselves well to blisk manufacturing, it certainly is not the only machine in Makino's line of machines capable of blisk manufacturing. Machining of monolithic parts can also be accomplished with Makino's line of five-axis machining centers—like the MC1516-5X, MC1816-5X and MC1013-5X—as well as horizontal machining centers like the A55E, A88E and MAG4.

As important as the CAM software capabilities and the high-speed machining center capabilities are, there are a few other details that should not really be overlooked. The postprocessing of the CAM program, for example, is extremely important. So important, in fact, that Concepts NREC offers an array of customized postprocessors for most machine tools to ensure the integrity of the CAM program remains in tact.

The machine also needs to have a robust control that can handle all of the events that need to take place during blisk machining. A pause from the control could mean a hesitation on the tool level that will gouge and ruin the blisk.

Last but not least, the right cutting tool is essential for blisk operations. Not only does it need to pull heat away from the part to prevent distortion of the blades, but it also needs to be hearty enough to last through an entire machining cycle (or as close to it as possible) for faster cycle times. Several innovations have occurred in the past five years, including new geometries and advanced coating materials. Also, a collaborative effort on the part of spindle makers, toolholder manufacturers, and cutting tool makers to create more robust tooling systems all contribute to the advent of cutting tools more capable of the unique machining conditions present in blisk manufacturing.

Copyright © 2001 - 2008 by Makino, Inc. All rights reserved.