Verticle Lathes | Lathe Turning

Turning turning on end

Destefani, Jim

Verticals put a productive twist on machining of round parts

Chances are, you haven't given much thought to vertical turning. But flipping your typical horizontal lathe on end has multiple advantages compared to conventional turning machines, including a relatively small footprint, easy chip disposal, and a gravity boost for loading of large, heavy parts. The configuration also facilitates automation and has excellent spindle accuracy.

The market for vertical turning machines consists of two distinct segments. Inverted verticals are chucker machines that are primarily aimed at relatively mid- to high-volume, automated applications in the automotive and other industries.

On the heavy-duty end of the market, large vertical turret lathes (VTLs) feature high-horsepower spindles and tables that can handle workpieces weighing thousands of pounds. Traditional applications for VTLs include production of components for jet engines, oil and gas exploration, military and off-road vehicles, pumps, and compressors. Suppliers report that current applications are about the same, but the customer base has evolved from OEMs to their first and second-tier suppliers.

The machines have evolved, as well. Most VTLs now feature toolchanging and live tooling capability. Becoming more common are four-axis machines, which allow complete machining of components such as railroad wheels in a single setup. Some machines are also equipped with pallet changers that allow operators to set up the next part while the current job runs.

Exemplifying the current crop of VTLs is the VTC series of machines from Giddings & Lewis (Fond du Lac, WI). Four models cover a size range from 1700 to 2700 mm maximum swing and from 1250 to 2500 mm table diameter.

All the machines feature a 75-kW AC motor coupled to a two-speed table drive. The system generates torque of 24,550 N*m for the two smaller machines and 41,144 N*m for the larger models. All also use a hydrostatic ram.

Perhaps more important, all have been re-engineered to reduce part counts and eliminate parts that are prone to failure such as limit switches. A 50% reduction in part count has improved reliability and allowed G&L to offer the machines at about 2/3 the price of previous generation.

VTC machines also use the company's proprietary Wedge-Lock modular tooling system, which is based on a taper system much like a boring mill or machining center. Rather than pulling the tool in from the rear like on a conventional tapered tool, the system uses hydraulic wedge assemblies on each corner of the ram that force the tool into the tapered socket. G&L says the system allows placement of electrics, hydraulics, and coolant through the tool, and is relatively easy to manufacture compared to a Hirth coupling or cross keys.

A relatively new player in the heavy-duty vertical market is Haas Automation (Oxnard, CA). Introduced in 2002, the company's Vertical Turning Center (VTC) allows single-setup turning and live-tool milling of parts to 48'' (1220 mm) diam, 28'' (710 mm) tall, and weighing up to 10,000 lb (4500 kg). Features include a 48'' diam T-slot table and 50-taper milling head. The table is powered by a 30-hp (22.5-kW) drive system through a two-speed gearbox for turning and a servomotor for C-axis positioning and interpolation with accuracy of + or -30 arc-sec.

Live-tool operations are via a 50-taper spindle with 30-hp vector drive system that yields 450 lb-ft (610 N* m) of torque and speeds to 5000 rpm. The machine features a 30-station side-mount toolchanger that can hold 21 milling and drilling tools, two turning tools, and one boring tool. Additional turning and boring tools may be added, but require empty adjacent pockets.

Inverted vertical turning machines feature a spindle that also serves as part of the machine's material handling system. The spindle grabs workpieces from an external conveyor system, takes them to the machining area, and presents them to a fixed tool turret. After machining, the spindle returns the finished part to the conveyor, which moves the next workpiece into position.

The arrangement has advantages over conventional turning machines, which require full-time operator attention, and over machines equipped with gantry robots and other external operator's role is reduced to loading blanks on the conveyor and removing finished parts. The operator's role is reduced to loading parts on the conveyor and removing finished components. Depending on parts and cycle times, this may be every couple of hours or even only once or twice per shift.

Eliminating an external robot or gantry reduces cost and floor space requirements. Users save not only the initial cost of the robot, but also the cost of programming and tooling. The conveyor arrangement also simplifies setups, although at the cost of some of the flexibility of a robot or gantry system.

Typical of the breed are VL series machines from Hardinge Inc. (Elmira, NY), which are built in Germany by Hardinge-Emag GmbH, a joint venture with German machine builder Emag Maschinenfabrik. The VL3 features a 21-hp (15.6-kW), 7500-rpm spindle; storage capacity for 20, 3.1'' (79-mm) or 14, 5.1'' (130-mm) diam workpieces; and a 6'' (152-mm) chuck capacity. The VL5 uses a 29.9-hp (22.3-kW), 4500-rpm spindle, a circular parts conveyor that can accommodate up to 28 workpieces, and a chuck with either 8 or 10'' (204 or 254-mm) capacity.

Both machines have spindle Z-axis traverse rate of 1181 ipm (30 m/min) and X-axis rate of 2362 ipm (60 m/min). Both feature rigid disk-type, 12-station VDI 40 bidirectional tool turrets that can handle live tooling in any position. GE Fanuc's 21-iT control is standard; machines with live tooling and C axis get Fanuc's 18i-T control.

Inverted machines also lend themselves to cellular manufacturing arrangements. Simple part conveyors can link units to create flexible transfer lines that can be reconfigured to handle changing production requirements. And, the machines' small footprint means cells based on inverted turning take up less floor space than horizontal turning cells.

Mazak Corp. (Florence, KY) markets its IVS 200 inverted vertical machine as a solution for medium to high-volume production of automotive and similar parts. The company has displayed two of the two-axis machines set side by side, with connecting automation to allow machining of opposite sides of a turned part. The machines are said to have a very small footprint, and feature an automatic tool presetting arm. When the tool tip is brought into contact with the Tool Eye, the machine control automatically registers offset and other tool characteristics. The device also monitors and compensates for tool wear.

Also touted as an expandable platform for cellular applications is the CTV 250 from DMG America Inc. (Schaumburg, IL). The machine features a linear motor drive for the X axis, which results in 1-g acceleration and rapid traverse rates of 3936 ipm (100 m/min) in X. A 33.5-hp (25-kW) motor drives the spindle at speeds to 5000 rpm. A 10" (254-mm) chuck, Y axis for eccentric drilling and milling operations, and Siemens 840D control round out the package.

Forgings and castings are commonly used workpiece forms for all types of machining processes, and variability in workpiece dimensions and geometries can be a challenge to process automation. Mori Seiki's latest inverted machine, the Pick-up Turn CS200B, was developed specifically to handle short castings and other low length-to-diameter ratio parts such as brake rotors, motor housings, and compressor rotors.

With spindle speeds to 5000 rpm and peak power output of 15 hp (11.2 kW), the machine can handle workpieces up to 15.7" diam x 5.9" long. Machine ballscrews and linear guide-ways are permanently lubricated using phenolic pads impregnated with mineral oil, eliminating the need to add oil. Doing away with oil lubrication also helps keep coolant free from problems caused by tramp oil.

An example of how productive vertical turning can be-and how the technology can replace not only horizontal turning but also perform milling, drilling, and other operations-is provided by applications at a couple of European automakers.

The job involves complete machining of differential cases. Advantages of the turning-based approach include single source for machines and simplified tooling and workholding requirements, according to machine supplier Hessapp Div., Cross Huller (Port Huron, MI).

Relationships between key machined features of the nodular cast iron parts are critical. For example, the tolerance on concentricity and position of an inner machined spherical surface to cross holes is 60 [mu]m. Perpendicularity between bored and reamed trunnion IDs and the cross holes also is 60 [mu]m. C^sub pk^ requirement was 1.33 for all dimensions.

The first operation happens on a Hessapp DVT 300 machine with dual spindles, cross slides, and tool turrets. After the part is chucked on the body OD, the first spindle roughs the trunnion ID and flange OD. For operations on the second spindle, the part is chucked on the machined flange OD and located off the machined face for semifinish boring of cross holes and reaming of the trunnion ID.

Next, the part is transferred to a Hessapp VDM 300-12L with a vertical spindle for machining the internal sphere and a horizontal reaming spindle. The part sits horizontally on the chuck with the window facing up to allow boring bars to enter, then moves on the machine cross slide (X axis) to allow semifinish and finish machining of the inner sphere.

This operation is followed by reaming of trunnion IDs and finish boring/reaming of cross holes. Machining all these features in a single chucking assures that the critical dimensional tolerances and relationships between the holes and the inner sphere are held.

A single-spindle VDM 250R machine with cross slide and horizontal turret completes machining and establishes critical dimensions on the part OD. The part is chucked on the finished trunnion ID using an arbor and a tailstock. Then three tools finish-turn all critical OD dimensions, which also have a specific relationship to the inner sphere and trunnion ID.

Longest cycle time in the cell is 2.5 min, so the process is capable of producing 20 parts/hr at 85% efficiency. All the machines are built using modular Hessapp components and are connected by a palletized conveyor. Hessapp has delivered half a dozen of the cells in Europe, and has quoted the process to tier suppliers in the US.

Jim Destefani

Senior Editor