Turning Vertical

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.

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.

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