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Five-Axis Machining

 

Adding a fifth axis can cut machine setups, and improve quality and productivity

 
By Patrick Waurzyniak
Senior Editor

  
 
   

Machining with five-axis equipment can offer manufacturers many advantages, including dramatically reduced setup times, lower costs per part, more accurate machining, and improved part quality.

For certain applications, particularly in aerospace, five-axis machining helps manufacturers enhance productivity with far fewer setups on a smaller number of machines. Automotive manufacturers and die/mold applications also can realize substantial payoffs from five-axis machining, especially as costs for the latest five-axis gear have declined.

Aerospace demands five-axis for highly contoured aircraft components. The reasons for going with five-axis equipment vary, but the benefits of deploying multiaxis machines center on improved productivity, higher machining accuracy, reduced in-process inventory, and improved operator and machine usage.

"In aerospace, it's primarily to eliminate the need for form cutters, because there are very few, if any, parts in aircraft structures that have straight lines on them," notes Randy Von Moll, technical product manager for the HyperMach line of five-axis machining centers from Cincinnati Lamb (Hebron, KY). "Everything has contour to it, and typically it's a compound contour because of the shapes of aerodynamic structures. Airplanes, especially modern fighters and bombers, are getting stealthier. That means they have more contour, more curvature than ever before, and they must be machined on five-axis equipment."

Standardized tooling saves money and lead time for manufacturers, he adds. "If you can stock multiple tools on your shelves, just standard solid carbide end mills versus having special tools ground with different angles on them to produce the contours, it reduces cost and lead-time." 

Five-axis configurations vary widely depending on the application, but in aerospace machining, both rotary axes are on the spindle, notes Von Moll, as in Cincinnati's HyperMach, a 70' (21-m) long high-speed five-axis linear motor profiler recently demonstrated cutting at 4000 ipm (102 m/min). In Cincinnati's demo for its aerospace customers, aluminum parts were milled from solid billet stock with spindle speeds to 18,000 rpm while exceeding 130 hp (97 kW) and 450 in.3/min (7374 cm3/min) metal removal rate. The system will be used this summer by aerospace supplier Brek Manufacturing Co. (Gardena, CA) to machine large structural sections of Boeing's (Seattle) C-17 Globemaster transport plane.

"Typically on a large aerospace machine, both rotary axes are on the spindle," Von Moll says. "In our case, the fifth axis is applied as a tilting spindle, to give you full five-axis contouring capability. Other people do a rotary tilting table and put both the rotary motions under the part. Our design has the tilting spindle."

With larger structural parts for aerospace, gantry-type machining systems like the HyperMach also are needed to handle the sheer size of airframe components. "The parts are typically getting larger, not smaller," notes Von Moll, "because the trend is toward monolithic structures. You used to have multiple sheet-metal components that were manufactured and then fastened together mechanically, which demanded a lot of additional assembly tooling and assembly labor."

Programming complexity, aside from high cost, has posed the biggest barriers to widespread adoption of five-axis machinery. "Five-axis machines continue to get faster and more accurate, so it's a technology that's emerging," Brett Hopkins, senior application engineer, machining centers, at Makino (Mason, OH). "It has its applications, but it is certainly not a mature, fully functional technology yet. CAM systems are still very weak. The learning curve for a CAD/CAM operator to become very good with five-axis is a challenge for shops."

Since Makino focuses on high-cost, high-precision five-axis applications, the company's offerings for die/mold haven't been widely received by the industry based on cost, Hopkins says. "Among the European builders, there's a huge push in the five-axis machining centers for die/mold, and they're doing a fairly good job of marketing that philosophy. There are benefits to the five-axis approach, in terms of being able to hit multiple sides of the parts and being able to shorten your tool length on side walls.

"There are some significant limitations to full five axis right now," he adds. "Very few CAM systems can give you good data for full five-axis machining. They are almost all capable of giving you good data for 3+2-axis machining. PowerMILL by Delcam for the machining center area is probably second to none, and then Unigraphics and Open Mind are the other leaders."

"For die/mold, anytime that we can machine in a 3+2 manner, you've got significant benefit to the accuracy and surface finish of your part," says Hopkins. "Full five axis is something to be done when other options are not allowed based on the geometry--you've got to do that in full five axis. And the only industry where we've seen that happen at the moment is in the aerospace industry, like with blisk work, which is a combination of blade and disk. Die/mold can take advantage of three-axis or 3+2."

Competing with Asia and Eastern Europe has led European manufacturers to embrace five-axis technology. CAM software and the sheer cost of five-axis machine tools are now less of an issue than in recent years, notes Mark Forth, PowerMILL product manager for Delcam plc (Birmingham, UK). "The key is that it needs to be easy to use and it absolutely has to do the job," Forth says.

In Europe, manufacturers readily accepted five-axis machining as a way to help compete with lower-cost labor centers in Asia and also in Eastern Europe. Forth notes that Delcam's research showed that more than 50% of Delcam's European customers went into five-axis machining in 2003, while in North America five-axis accounted for about 20% of its sales.

"Because labor's so cheap in other markets, companies that want to remain competitive have to start machining smarter," Forth notes, "which doesn't mean just machining faster or working longer hours. It means looking really closely at your current processes, focusing on your application, and investing in new technology, training, correct tooling, and a host of other factors to cut down lead times, so we can remain competitive.

"It's a really complex issue, and there are many different reasons why adoption of the technology has been slow," he adds. "First, these machines aren't cheap. It's all right if you're a Boeing or another large manufacturer, but for the tooling guys that are thinking of investing in this technology, it's a big chunk of money."

For smaller tool-and-die shops, five-axis equipment ranging from $100,000 to $1 million is a major investment, particularly in a down economy. "There's been inertia because the cost of that technology has historically been so high, but what's happened over the last few years is that we're definitely getting to the stage where these machines are more affordable for these smaller shops."

Smaller shops are now seeing advantages to using five-axis and 3+2 technology, he says. In the tool-and-die industry, 90% of the jobs can be machined extremely efficiently using 3+2 technology, he explains, because it provides greater flexibility to cut the part, reduce tool length, improve surface finish, and we can still employ high-speed, high-efficiency machining techniques.

"Previously when you had a part with a very deep cavity, using long-reach tooling, you would run at very slow feeds and speeds to reduce tool deflection," Forth says. "The manufacturing process is taking far longer because you're having to use a work-around, if you like. An ideal scenario would be to go in with a much shorter tool length to achieve optimum cutting conditions, but to be able to angle the head in such ways that it doesn't collide with the job."

Programming for simultaneous five-axis machining is complex. "The progression's gone from three to 3+2-axis machining, where I can shorten my tool length and run my machine at high speeds as well," Forth says. "With simultaneous five-axis, all axes move at the same time, I'm not just considering what's happening at the end of my tool and the part that I'm machining, I must consider what's happening at the other end of the tool which is attached to the holder, spindle, and the machine tool head, because we're introducing additional parameters to control the tool axis vector, as well as the tool's X, Y, and Z position."

Programming for five-axis requires much more consideration than for 3+2 machining, he adds. "Part geometry, workpiece orientation, and entry and exit conditions are extremely important," Forth states. "Good collision detection is absolutely essential. You need to make sure you know what's happening and that the head of the machine isn't colliding with the part, clamps, or fixturing."

With the latest PowerMILL version 5.5 announced in May, Delcam added machine-tool collision detection to its simulation module functionality that offers users complete verification of toolpaths prior to machining. "Many CAM software packages claim provision for 'gouge-free' toolpaths which are verified against the tool and the holder but not for the machine itself, which is essential for five-axis programming."

Advanced controls geared for aerospace enable manufacturers cut the complex shapes frequently encountered with aircraft designs. At Westec, Siemens' Sinumerik 840D controller added a new motion-control program in which both the toolpath and the orientation are determined by separate spline curves, which reduces the machining time while simultaneously improving surface quality, especially for five-axis machining of sculptured surfaces.

Many aerospace manufacturers use the Siemens 840D to perform complex cutting motions including transformation orientation (TRAORI). "TRAORI is very powerful, and I think an absolute requirement. We pretty much standardized on 840D for the five-axis aerospace product," notes Cincinnati's Von Moll, "but we do offer alternatives, if it's absolutely required. Typically most people are satisfied and will go with the 840D."

The TRAORI helps manufacturers with hybrid kinematics-type machines, systems that don't have conventional axis orientations, he adds. "These are link-style machines, hexapod-style machines. With hybrid kinematics, the twin ballscrew rotary axis head, the V5 head that we use on HyperMach and on the entry-level V5 machines, actually is a transformation of linear ballscrews into rotary motion. Siemens worked closely with us in the development of the control--with the conversion of linear ballscrew motion to rotary motion. These are things that they do routinely, and it's not to say that you can't do that with GE Fanuc's products, it's just that Siemens makes it more user-friendly, and is willing to take on the types of applications a little more aggressively than others."

High-speed machining also plays a key role in manufacturers deploying five-axis systems to speed up their manufacturing processes. "In the past, machining in five-axis was seen as a specialty requiring a great deal of skill along with expensive software tools," notes Gary Zurek, applications engineering manager, Mikron Bostomatic Corp. (Holliston, MA).

To apply five-axis machining techniques effectively, users need to find the proper solutions for their particular application, Zurek adds. "There are many solutions on the market today, and users should seek out credible experts in five-axis machining. It can be quite confusing to new users entering this field, which can lead to discouragement and a loss of return on the investment."

Speed, accuracy, and flexibility combined with manufacturing knowledge and experience can help users find the right tools for their needs, he adds. Zurek notes that Mikron's HSM400U HS five-axis machine offers 1.7-G acceleration on the combined linear axis, 40 m/min. feed rates with rotational rates of 150 rpm on the B axis and 250 rpm on the C axis. "This gives our customers the tools to be highly competitive with our machines," Zurek says, "and by combining our machine tool technology with our software tools, we commonly see our customers achieving reduced cycle times, improved quality, and the flexibility to run unattended."

Faster five-axis machining aids just about any manufacturing operation, where metalcutting efficiencies lead directly to increased productivity. "Just as in three-axis machining, machine-tool speed is the greatest advantage," notes Kurt Nishimura, Manager, High Speed Machinery, Mori Seiki USA Inc. (Dallas and Nara, Japan). "With five-axis machines, in the past the limiting factor was the speed of the rotary tables, but today's five-axis machines possess faster rotary tables."

With Mori Seiki's Supermiller 400 five-axis VMC, the B-axis table speed is 200 rpm, and the machine's B-axis can also be used for turning, at a table speed of 1500 rpm. Mori Seiki also offers the GV-505/5AX five-axis VMC, which like the Supermiller has full five-axis contouring capabilities and 12,000-rpm spindle speeds, notes Nishimura. The Supermiller features fast rotary tables and the ability to pass 4" (102-mm) bar through the table. It uses a Fanuc CNC while the GV-503/5AX has a Mitsubishi control.

"Cost of the machine seems to be one of the larger hurdles that I see today. These machines are much more expensive than their three-axis counterparts," Nishimura adds.

Automotive applications for five-axis equipment have stayed strong as the aerospace market remains relatively soft, notes Joe Kraemer, Variaxis product manager, Mazak Corp. (Florence, KY). Mazak's recently announced Variaxis 730-5X VMC features a high-precision table with 150 degrees of tilting range and a 50-taper spindle. "Aerospace is our top field, particularly for large machines machining structural components like large wing spars and floor beams," Kraemer notes. "Five-face machining is a smaller market."

Much of Mazak's current lineup has sold well into high-production machining applications, particularly into engine manufacturing, where five-axis equipment helps reduce setups. "By reducing setups, it cuts down on your work in process," Kraemer says. "We're doing well with jet engine components, prismatic parts, and engine components in automotive. We have several machines geared strictly for the jet engine market, and it's growing tremendously, where we used to sell only one five-axis machine a month."

Fast, single setups often make five-axis machining more efficient than three-axis equipment. "The true beauty of the five-axis machine is the quick setups, for low-volume work," notes Doug Gale, vice president and general manager, Handtmann CNC Technologies (Buffalo Grove, IL).

With the Handtmann PBZ NT 800 five-axis machining center, aerospace customers can mill, drill, tap, and saw parts to length in one setup, eliminating the need for any other machine or material handling system, notes Gale. "Our five-axis machines are very strong in aerospace and automotive applications," he adds. "The key to these five-axis machines has a lot to do with how you hold the part. We have quite a few machines in the automotive sector, such as the Audi space frames that are being machined on our five-axis machines."

 

This article was first published in the June 2004 edition of Manufacturing Engineering magazine. 


Published Date : 6/1/2004

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