More than a lathe with live tooling

July 1, 2001
One machine tool builder explains the essentials for true multitasking.

One machine tool builder explains the essentials for true multitasking.

Large Y-axis strokes are what make it possible for Millturns to do two-point part probing for more accurate multitasking operations.

With sufficient power and maneuverability, Millturn machines handle basic machining operations and then some on tough workpiece materials.

Millturn multitasking machines accommodate long, heavy tools using a dovetail holding system.

Mention multitasking and most likely the vision of a lathe with live tooling comes to mind. It is this live tooling that lets these machines turn, mill, bore, drill, and tap parts. But is that really all multi-tasking is? According to one machine tool builder, it takes more than live tooling to make a "true" multitasking machine.

The ultimate goal of multitasking is to chuck a part once and complete it from start to finish. Having to take a part off the machine for gaging or to do long bores, for instance, defeats that purpose. This is why WFL of Linz, Austria, believes a multitasking machine is complete when it includes accurate built-in gaging, sufficient spindle torque/power for various other machining operations, and the ability to not only handle long tools but to also change them automatically. According to Kurt Steyrleuthner of WFL, one of the things that separates multitasking machines is Y-axis travel and B-axis capability. Large Y-axis strokes are what give WFL's Millturn machines the ability to perform two-point probing for more precise part gaging. And powerful milling spindles with B axes let the machines do such operations as gear hobbing, 5-axis machining, and turnmilling on large workpieces with hardness ratings as high as 60 Rc. In addition, machine size and a special dovetail toolholding system accommodate and automatically change boring bars measuring up to 6 1 /2-ft long.

Two-point probing
Millturns, available in the U.S. through the Motch Corp. of Cleveland, are slant-bed-style turn/mill machines with single-tool carriers. On the M100 and M120 models, the Y-axis strokes are 19.685 and 25.590 in., respectively. With these larger strokes, the Millturn's Mar-poss probe system can reach two opposite sides (two-point probing) of a 24-in.-diameter part, for example, and gage using an axis other than the one doing the turning.

With the Millturn, shops can load parts at random, and through probing, the machine "finds" the part and does a zero offset on the program. It basically orientates itself to the part's position in the machine to establish zeros radially, axially, and diametrically. "What takes conventional gaging and part-orientation methods hours to accomplish, the Millturn does in minutes," comments Steyrleuthner.

On a machine with a short Y-axis stroke, shops have to gage one side of a part or a part feature that is reachable and then relate all other dimensions to it. "The problem," says Steyrleuthner, "is the reference feature may be slightly off-center, or the part itself is hanging down. This creates different readings from one end to the other."

He says, "probing in the machine for part orientation, size, and machining accuracy is a vital element for multitasking." This is why the Mill-turn's gaging system also includes Heidenhain glass scales on the Y axis, a programmable probe, and special software that tracks such things as thermal expansion of workpieces and forces at the machine's spindles and axes.

The software compensates for thermal expansion of the workpiece during machining. All measuring data is stored and printed. The software also continuously monitors and controls forces at the machine's spindles and axes, and displays these values if so desired.

More power
According to Steyrleuthner, multitasking machines must provide machining-center-like capabilities for complete part processing with normal milling tools. But in addition to this, they need sufficient power to handle heavy cuts and today's tough materials. Not all parts are 3-in. 2 and made out of aluminum.

With this in mind, WFL equips its M100 with a 34-hp milling spindle and an 80-hp main spindle, while the M120 packs 75 hp in its milling spindle and 120 hp in the main spindle. Both machines have a B-axis swiveling range of 110° to +90°, along with a rigid turn/mill-unit construction for I.D. and O.D. work. Having power and maneuverability, the Millturns can perform — besides basic turning, milling, and drilling — such operations as circular milling, turnmilling, active B-axis turning, shaping, and gear hobbing, along with simultaneous 5-axis interpolation using the machine's B, C, X, Y, and Z axes.

In B-axis turning, a clamped insert cuts while being oriented around the various part contours. This turning technique eliminates blending lines in parts by using the same insert for completing different radii.Turnmilling, on the other hand, is turning part diameters using a milling tool, quite effective on parts with interrupted cuts and multiple large radii. And it neutralizes the influence of an unbalanced mass while turning.

Millturns can shape the inside gear patterns found on numerous types of drive shafts and hob outside gears as well. And the interpolation of its B axis makes helical gear cutting possible at any angle.

Added to the Millturn's various machining operations is a feed-optimization function, which is based on a programmable "adjustment curve." This lets shops set a higher basic feed, which is then scaled down, within defined limits, along the part characteristic curve, taking into account the actual load on the milling spindle. As the cutter enters further into the material, and both the cutting volume and the absorbed power increase, the feedrate for all interpolating axes along the cut path automatically reduces to a programmable minimum. This ensures a favorable chip load, and the machine travels faster in sections where little or no material is being removed.

Dovetail system
Part of multitasking is lathe work, and lathe work invariably involves deep bores in long parts, says Steyrleuthner. So it is important for a machine to not only have the room for long tools but also have the ability to change them automatically, which increases a machine's utilization rate.

Heavy-duty boring bars, vibration dampening bars, ejector drills, and other special tools up to 6.5-ft long are changed automatically from a pickup station on top of machine head-stocks. For longer and heavier tools, the MT100 and 120 store 8.202-ft-long, 330-lb boring bars in 18-station magazines and automatically change bars via a separate tool loader. An extra boring-bar slide is available that supports 8.5-in.-diameter bars up to 6.5-ft long.

What makes it possible to wield these monstrous tools is the Millturn's robust head and special dovetail holding system. The combination provides a diameter-to-length tool ratio of 1:16, in addition to ample tool rigidity and stability for maintaining bore-wall thicknesses and eliminating any variations.

The holding system grips tools with a longer clamping length as compared to short-taper systems. With it, shops can incorporate into their manufacturing processes not only conventional boring bars but also large drills, rotating deep-hole drilling tools, and driven tools for inside machining.

Millturn lands aerospace work

SP uses a special bottle-bore contouring tool with inserts that feed in and out for cutting the various I.D. contours of a helicopter trailing arm.

Large parts, such as aircraft landing-gear housings and helicopter trailing arms, that require multiple machining operations are perfect candidates for SP's Millturn machine from WFL.

SP Aerospace and Vehicle Systems in the Netherlands designs, develops, and manufactures landing-gear components for airplanes and helicopters. One of the company's more recent projects is the trailing arm for the NH-90 naval utility helicopter. It's a multinational project involving the Netherlands, Italy, Germany, and France, and SP is the main contractor.

The NH-90 project is also noteworthy because it is the first part SP is running on its new WFL Millturn M65, which is similar to an M100 and 120 but smaller. With the M65, the company reduces part manufacturing steps/setups from as many as 40 down to four. All milling and turning, both I.D. and O.D., is done on the M65, including a special contour-boring operation.

Main landing-gear struts are anywhere from 3 to 6-ft long and solid before machining. After which, they are practically hollowed out, and SP accomplishes this using a series of 5-ft-long line tools.

Starting with a 2-in.-diameter gun drill and then progressively opening up the I.D. with a few other tools, the shop then finishes the center with a bottle bore, or contouring boring bar. This tool actually follows the different I.D. contours as it cuts. While clamped in the Millturn's dovetail system and powered by the machine's milling drive, the bottle bore's independent inserts automatically feed in and out to follow the different diameters. The action is similar to that of a CNC boring head.

WFL supplied SP with a complete turnkey system. The two companies worked together to develop the NC programming for the trailing arms and designed all necessary fixturing. However, the machine is not dedicated to one type of part per se. SP plans on doing as much as it can with the Millturn, says Ton Staassen, manager of business development at SP.

"Our current equipment can produce the necessary part tolerances," he says, "but at a cost. Mainly because of the inherent rework involved when using multiple machines and setups. The Millturn makes the machining process more reliable with less chance of human error. Reducing lead times and part setups are the two main benefits of the Millturn."