Cutting Tool Engineering
February 2011 / Volume 63 / Issue 2

Turning Vertical

By Bill Kennedy, Contributing Editor

MEGATURN_P3 copy.tif
Courtesy of Mazak

The Megaturn Nexus 900 VTL from Mazak turns large parts in a comparatively compact machine envelope.

Turning a lathe vertical can be a productivity turn for the better—for large and small parts.

The most familiar configuration for a lathe involves a horizontal spindle turning a workpiece usually supported by a tailstock. However, turning the horizontal arrangement on its end can be beneficial—most often when turning large parts. That’s because there’s no need to fight gravity when handling the workpiece because the part’s weight helps anchor it on the machine’s rotating table. Positioning the part relative to the cutting tool requires only simple X-Y adjustments. Clamping and off-axis forces on the part are minimized, facilitating machining of thin-walled or delicate parts.

Traditional examples of vertical turret lathes are massive, manual Bullard or Giddings & Lewis machines. Today, machine tool builders are offering technologically advanced versions of vertical lathes for turning large parts. But in addition to processing of large parts, vertical lathes also can expedite high-volume production of smaller parts by combining an inverted spindle with integrated automation.

Handling Big Parts

Rick Ware, vice president, sales and marketing for Mazak Corp., Florence, Ky., said the market for large traditional-style vertical lathes shrank through the late 1990s and early 2000s, a trend he attributed to declining demand for very large parts. In addition, “People were beginning to do machining on multitasking-style platforms, and just didn’t buy the big machinery,” he said. However, large part making is growing again, including components for wind turbines and other energy-related applications, as well as big parts for marine, railroad, construction and agricultural equipment, he noted.

Regarding parts best suited for a vertical lathe, heavier and bulkier parts with large swing (diameter clearance) requirements are typically machined on a vertical rather than horizontal lathe. A key consideration is ease of part handling and setup.

“You don’t have to chuck a large part horizontally; you just drop it down on the table and clamp it,” Ware said. “Part loading and unloading is much easier. Loading a large part on a horizontal is a little more exciting for the operator, but not nearly as safe, and I tend to prefer safe more than exciting.”

According to Ware, machines like the Mazak Megaturn Nexus 900 are appropriate for large-part machining. The vertical lathe enables turning relatively large parts in a comparatively compact machine envelope. The Megaturn 900 features a moving, rather than fixed, column supporting the cutting head. With a fixed column machine, the head moves on a cross-rail, and the swing capacity of the machine is limited to the cross-rail’s length. Overhead interference with the cross-rail also limits the height of parts being machined.

To maximize the part size a Megaturn machine can handle, the turret head is mounted on a column, instead of a cross-rail, that moves left and right in the X-axis. That enables the machine to handle larger-diameter and taller parts by avoiding turret interference that would occur with a fixed column/cross-rail in a comparably sized machine. Mazak says the machine is appropriate for parts up to 920mm in diameter and as tall as 800mm.

VDM1000H_HobbingHead.tif
Courtesy of MAG IA

The hobbing head of a MAG VDM 1000H VTL has a swivel range of ±30º and works simultaneously with the two servodrives of the main spindle to permit skiving of hardened gears up to 800mm in diameter.

Even for much larger parts, manufacturers are seeking new capabilities for the traditional large VTL. For machining very large parts, MAG IAS LLC, which acquired VTC builder Giddings & Lewis in Fond du Lac, Wis., offers its VTC series with swings as large as 9,000mm and Z-axis travel of 2,500mm.

The big machines offer advanced technologies, including rigid hydrostatic rams that enable heavy cuts with acceptable surface finishes, and linear-scale rail leveling and locating. Modular construction allows the machines to be configured for specific applications. Helene Nimmer, global product leader, pointed out that the venerable large VTCs often lacked CNCs, but “there is additional functionality on machines today.” Options include a C-axis, live spindles, grinding capability, pallet shuttles, gear cutting and right-angle heads to boost productivity and throughput.

A machine MAG introduced in October 2010 has an even higher level of functionality, Nimmer said. The VDM 1000 H is a variation of the VDM 1000 VTL, which machines workpieces up to 1,150mm in diameter and 1,000mm in height. Engineered to enable complete machining of gears—including turning, drilling, milling, tapping and hobbing—the VDM 1000 H has a B-Y axis and a motorized tilt-angle hobbing head. With a swivel range of ±30°, the hobbing head works simultaneously with the two servodrives on the main spindle to permit skiving (hard hobbing) of hardened gears up to 800mm in diameter. “The advantage in incorporating the gear cutting on the lathe is that you are able to turn the gear as well as cut the teeth,” Nimmer said.

Throughput Specialists

In contrast to a focus on facilitating the turning of large components, an inverted vertical spindle lathe can maximize throughput when turning parts of nearly any size. Inverted vertical spindle machines generally do not require additional automation to run higher volumes. In an inverted spindle machine, the part does not rest on a table but rather is gripped in a movable overhead spindle. That spindle can pick up parts and replace them in a conveyor or chain, making the VTL a self-contained machining system. For processing low-profile parts such as brake rotors and transmission components, the arrangement produces high throughput and consistency.

3240.tif
Courtesy of EMAG

EMAG VTLs have a recirculating conveyor chain to transport workpieces to and from the pickup station located behind the machining area. The chain is fitted with what EMAG calls “carrier prisms” that adapt to different workpieces.

An example is the VL5i series of VTLs from EMAG LLC, Farmington Hills, Mich. The machines are part of EMAG’s Platform 250 offering, where “250” represents the 250mm-dia. size of the machines’ chucks. The machine tool family also includes customizable VSC250 units and VLC250 multifunction VTLs.

The VL5i can handle a maximum workpiece diameter of 220mm, provides 300mm of Z-axis travel and, depending on the workpiece, can load a part in 2 to 4 seconds. The machine has a 360mm-dia., 12-station turret, which accommodates turning and driven tools for drilling and milling.

According to Peter Loetzner, CEO of EMAG, the VL5i VTLs are manufacturing systems for small- and medium-sized companies. However, he said, the machines’ simplicity and flexibility have prompted even Tier 1 manufacturers to implement groups of VL5i machines to support high-volume production.

The VL5i’s automation system includes a recirculating conveyor chain to transport workpieces to and from the pickup station, located behind the machining area. The recirculating chain enables the machine’s inverted spindle to release a finished part and pick up a blank. The chain is fitted with what EMAG calls “carrier prisms” that adapt to various workpiece shapes and sizes.

The system allows an operator to remove completed parts and load raw stock, but, according to Loetzner, some end users also use robots to load the conveyor.

Loetzner said the machine is being applied by Tier 2 and Tier 3 companies, such as forging suppliers, that previously supplied only blank parts to heavy equipment manufacturers. The system allows manufacturers to perform initial machining on the blank, Loetzner said. “They add value to the blank before they ship it to their customer, which increases profits.”

Vertical turret lathes are a specialized product and aren’t right for every application, but they can be the right choice when part features and volume requirements fit their singular capabilities. CTE

About the Author: Bill Kennedy, based in Latrobe, Pa., is contributing editor for CTE. He has an extensive background as a technical writer. Contact him at (724) 537-6182 or by e-mail at billk@jwr.com.


QM1.tif
Images courtesy of B. Kennedy

Lou Botti of Quality Mould enters machining parameters at the control of the shop’s Doosan Puma VT 900 VTL.

QM3.tif

QMI was able to cut processing time more than 50 percent when it moved roughing of a 34 "-dia. forged steel gear blank from a horizontal lathe to a Doosan Puma VT900 VTL. QMI employed modified specials, such as this extended holder (inset), to enable large forged-steel rings to be roughed in one setup.

Gearing up vertical

Quality Mould Inc., Latrobe, Pa., a mold designer and manufacturer, used to generate as much as 80 percent of its business from making specialty glass molds, but after that market changed, the shop diversified into prototype and production manufacturing for various industries.

For a manufacturer of agricultural and construction machinery, QMI had been rough machining 34 "-dia., 9 "-tall, 2 "-thick forged steel rings for drive gears. The process included removing a flange, cutting a taper and turning the diameter, in all removing about 1 " of material per side from the 500-lb. ring.

The shop machined the blanks on a horizontal lathe. “We were doing two setups because we had to flip the part,” said QMI President D.J. Danko. The lathe chuck gripped only about 0.800 " of the edge of the part, so machining parameters were conservative: a DOC of 0.150 " to 0.200 " and feed of 0.008 to 0.010 ipr at 500 sfm. “You really couldn’t rip into it; you’d tear the part out of the machine,” Danko said. Including rechucking to machine the second side, it took about 2 hours to rough one part.

QMI thought a VTL would make the process more productive by simplifying and solidifying part positioning and clamping. The shop acquired a Doosan Puma VT 900 VTL with a 60-hp spindle, 40 " table and 12-position turret. Shop personnel developed workholding to grip the part on its ID and also developed special tooling and process parameters that enabled roughing the ring in one setup.

The shop now can rough a part in 50 minutes. The part runs at a 0.300 " DOC and 0.012 to 0.015 ipr at 500 sfm. Chucking the part vertically, Danko said, enables the shop to “run it a lot faster because we are cutting downward and are pushing all the force into the chuck, where before we were hanging there with the weight suspended.”

Because a heavier cut is possible, the shop now uses 632-size inserts instead of the 432-size used previously. Danko noted that tools last longer on the vertical machine because chips fall away during OD turning, rather than piling up on the insert as they did on the horizontal machine.

Lathe Department Manager Lou Botti said he still considers the cutting parameters to be conservative, but that helps ensure the reliability of a mostly untended operation. “We put that machine over on one side of the shop. The guy puts the part in, and an hour later walks over, pulls it out, puts another one in, hits the button and walks away.” Botti added that the Doosan machine is a “workhorse,” and said it routinely holds tolerances of ±0.001 " on big parts.

Danko said vertical turning is relatively new to QMI, “but it seems like more people are going that way.” The company has turned bearing races for wind power applications, and is quoting jobs for other gear manufacturers. Considering the state of the economy, investing in new equipment took some courage, but “we got it up and running and now we can really pursue these customers,” Danko said. “We are looking at hundreds of parts a month for this machine.”

—B. Kennedy



VTC1.3_pinchturn 2.tif
Courtesy of MAG

When roughing large workpieces such as this 56,000-lb. A36 steel casting for a rock crusher bowl, Busch Precision uses the twin rams of its MAG VTC 3500 VTL simultaneously to perform pinch turning.

Milwaukee's best for big parts

Large components, typically ranging from 10 " to 20 " in diameter and as large as 180 " in diameter, are a mainstay for Busch Precision Inc., Milwaukee. The job shop manufactures and repairs machinery components and performs subcontract and on-site machining, as well as machine rebuilding.

According to Matt Pettigrew, production supervisor, the shop’s vertical lathes are good for machining large, heavy parts. “You’re not fighting gravity, and that facilitates part holding and part handling,” he said. However, he added, a horizontal boring mill, with its large work envelope, is a better choice for some very large parts, especially long ones. “With the horizontal boring mill, you can have stuff hanging off the table; it doesn’t matter. It won’t get in your way.”

The vertical machine is the right choice for large parts that fit because setup is easier. “You can set the part down on the table,” said Pettigrew. “On a horizontal lathe you have to hang it in the air and get everything perfect, but on a vertical you are basically setting it on the floor. If it’s a little crooked it’s not going to kill you; you can finesse it to where you want it a little easier.”

The shop’s newest VTC is a VTC 3500 from MAG. The machine has a 3,500mm table with a maximum swing capacity of 3,700mm, Z-axis travel of 1,250mm and X-axis travel of ±2,060mm. It is fitted with two 250mm-square rams to enable pinch turning (cutting with both rams simultaneously).

The shop doesn’t always perform pinch turning because taking the time to program two tools where one can do the job is not cost-effective. “However, we try to do it whenever we can, usually for roughing,” Pettigrew said. “Instead of trying to rough with one ram at one depth of cut, if it is real hard material I can divvy up the DOC to take half and half. I am still removing the same amount of material because the machine is taking two cuts at once. That saves on chip load.”

For roughing big parts, the shop typically uses inserts in a mid-range 433 size. “But we also go all the way up to 866, which is 1 "-wide carbide,” Pettigrew said. “That’s for roughing cuts with interruptions; it’s a real big brute of an insert.”

Despite the large dimensions of the parts it handles, the shop holds tight tolerances, he added. “I just finished a 118 "-dia. part that was +0.002 ", minus nothing.”

—B. Kennedy


Contributors

Busch Precision Inc.
(414) 362-7300
www.buschprecision.com

EMAG LLC
(248) 477-7440
www.emag.com

MAG IAS LLC
(920) 921-9400
www.mag-ias.com

Mazak Corp.
(859) 342-1700
www.mazakusa.com

Quality Mould Inc.
(724) 532-3678
www.qualitymouldinc.com

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