VMCs Fill in the Lines
Users benefit from a wide range of value choices
By Jim Lorincz
Manufacturers are in for a steady diet of innovation by machine tool builders in their VMC product-line offerings. The reasons are not too difficult to see as builders seek to stretch their muscles across the board covering entry level, mid-range, and high-end offerings. Some are looking to establish new beach heads in niches that fit their particular technology strengths.
Whatever approach is taken, manufacturers, from job shops and contract manufacturers to production houses, are benefiting from choices that are value-driven, i.e. more machine at a lower price. Said another way, users can buy just the machine and technology that they want to pay for—no more, no less. Builders are intent upon making it possible for users to buy up to the next level of technology—the builder's next level of technology—as growth in their customer's business requires.
MAG Fadal (Chatsworth, CA) offers a range of VMCs starting from 22 x 16" to 65 x 35" (559 x 406 mm to 1651 x 889 mm) X, Y. "That's what customers look for, a wide variety in the Y axis," explains Dr. J. Manjunathaiah, vice president-engineering.
"At the smaller [size] end of the market, we offer the FX series of machines, which have job shops and contract manufacturers as their key customer base. The FX features high axis performance, quick acceleration, and spindles capable of speeds from 8000 to 15,000 rpm and torque from 70 lb-ft [95 Nm] to more than 200 lb-ft [270 Nm] for cutting harder metals such as hardened steel, and small titanium parts," Dr. J says.
"The box-way design gives a lot of vibration dampening, especially for rough heavy machining," he says. Two CNC controls are offered, the Fadal CNC and the Fadal GE Fanuc Oi-MC. The Fanuc 0i is a digital control with fully integrated digital drives and motors for up to four-axis machining.
For machining titanium and other hard metals that require high torque, MAG Fadal has introduced its VMC 6535HTX. "For machining titanium you need very slow spindle speed and big depths of cut to achieve productivity. The machine must be very rigid with a lot of torque at the low-end spindle speeds. The HTX delivers 500 Nm at speeds to 575 rpm," Dr. J says.
It is important that the machine structure has the rigidity to support the loading, especially twisting forces, during this heavy machining. Dr. J explains: "This machine is specifically designed with heavy castings for base, column, and head, a large 63-mm ball screw to handle high axial thrust, the Fanuc 18i CNC, and drives and motors capable of high torque.
"Cincinnati Machine [a sister MAG IAS company] has accumulated a lot of experience and data over the years at Boeing machining titanium with large machines. This includes the processing knowledge for cutting speeds, coolant pressures, and what sort of cutters to use. The beauty of the VMC 6535 HTX is that it delivers that same machining capability in a smaller machine at a considerably lower price point," he adds.
Since acquiring Bridgeport Machines in late 2004, Hardinge Inc. (Elmira, NY) has integrated its legacy line of midrange VMCs with Bridgeport's range of high-performance VMCs, HMCs, and five-axis machining centers. In doing so, Hardinge has positioned these products to ensure that the user purchases the right tool for the right use.
"Bridgeport had a line of products that were pointed directly into the mid to high-end range of machines; whereas Hardinge was already building low to mid-range products, so the distinction was clear from the beginning as to how these two lines would complement one another, under the Bridgeport brand," explains Andy McNamara, milling product manager-North America.
As this process of integration developed, Hardinge realized that Bridgeport needed additional products to fill the yet to be addressed "entry-level" VMC market. Here's what the Bridgeport lineup looks like today.
At the high-end is the XR-Series, which includes VMCs, HMCs, five-axis and high-speed machining centers designed for high-performance and high-production needs. In the middle, are the soon to be launched GX-Series, which represents a range of general-performance VMCs from the GX 480 to the GX 1600. The third range is the XV line, which includes the XV 710 and XV 1000.
The three ranges offer users the ability to choose the machine performance they require. McNamara explains, "Today the Bridgeport brand features platforms that are built around the market segment for which they are intended, enabling our customers to purchase the machine that best fits their individual need without compromise. That's to say, we don't want customers forced into investing more for a level of performance or capability that exceeds their requirements. At the same time, we want customers to be able to obtain all the features required to machine complex parts or any production level that may be needed."
Hardinge continues to expand the Bridgeport product offerings. The GX-Series was recently beefed up to include a few models that feature boxways, rather than linear ways. And soon, the XR-Series will include more horizontal and five-axis models to extend the machine solutions available.
The route to expanding VMC product offerings at Haas Automation Inc. (Oxnard, CA) follows a path of technology innovation that has managed to uncover whole market opportunities where, perhaps, none were thought to exist. Two of the most recent examples can be found in a class of VMC, the SS or Super Speed machines, which were introduced in 2002. A second was the introduction in 2001 of toolroom mills and lathes, followed by so-called office machines.
"We've had SS models available for five years," explains Robert Burrows, Haas Automation product manager for VMCs. "The competitive impetus for designing the SS VMCs was to reduce our customers' cost per part. One of the easiest ways to do this is by reducing cycle times and increasing throughput. The SS machines accomplish this through high spindle speeds, fast rapids, and quick tool changes," Burrows explains.
"Basically, we took our standard machine and changed the pitch of the ball screws from 8 mm and bumped them up to 12 mm for increased rapids to 1400 ipm [35.5 m/min]. The second thing we did was change the tool changer. We put a servo motor on it instead of the regular DC motor. That allowed us to increase our tool change time considerably, also reducing cycle time.
"The third thing was that we changed the spindle configuration. With the SS models we introduced 12,000-rpm spindle in an in-line direct-drive version. There's a coupling that goes between the motor shaft and the spindle. Without a belt, there is less heat generated. The net result has been better finishes and better accuracies, as well as reduced cycle times, faster tool change, and faster rapids," Burrows says.
In effect, Haas went from full-featured VMC machines back to entry-level types of machines with the toolroom machines and then to the office machines, though in this case into segments that really hadn't existed before.
With development of its Nexus line of VMCs, Mazak Corp. (Florence, KY) recognized that job-shop owners demand more than simple milling functions. They are looking for faster turnaround, a discounted price, and tighter tolerances, and must have reliable equipment, with reduced setup time and maximum spindle utilization, to survive.
The success of the Nexus line of machines has led to continued expansion at Mazak's HQ manufacturing plant in Kentucky. In fact, the Nexus line of machines that is manufactured and assembled in Florence is the first line of Mazak's global machines that are being built in Mazak's Japan and UK facilities using its Cyber Factory production system.
The Nexus machine line has expanded to include a 40-taper spindle, 40-taper high-speed version, 50-taper spindle, 50-taper high-torque version, and a two-pallet changer system. Designated VCN 510C-HS, a high-speed version of the VMC, combines a wide machining envelope with a high-speed, 30-kW, 15,000-rpm spindle and 1968 ipm (50 m/min) rapid-traverse rate.
The Nexus line has added a five-axis version with the addition of a tilting rotary table for five-face machining. The VCN510C-II/5X features a 30 hp (22.4-kW), 6000-rpm integral spindle/motor with 206 lb-ft torque (278 Nm). A 30 hp, 4000- rpm 310 lb-ft (418 Nm) spindle with a 1:3 fixed gear reducer is an option that is available for heavier cutting requirements.
CNC control is provided by Mazak's new Mazatrol Matrix Nexus with a capacity of registering 4000 tools and their related offsets in the control. Programming and simulation can be performed on-machine in conversational mode, or off line in EIA/ISO format while the machine is cutting. Feed rates are said to be two times faster for cutting complex part geometries than the previous-generation CNC.
For high-speed machining of large die/mold applications, Makino Inc. (Mason, OH) has extended its VMC line with the introduction of the V99 and V99L (extended table and travel) VMCs. "Because of the positioning accuracies, repeatability, and tight tolerances for geometric relationships of squareness and straightness, the V99 and V99L machines can also be used for broader applications," explains William Howard, VMC product manager.
"They represent the extension of Makino's V series line of products that includes the V22, V33, V56, and the recently introduced V77 and V77L models," he says. The V99 has X, Y, Z axes of 1500 x 1000 x 800 mm with rapid traverse and cutting feed rates of 20 m/min. The large 1800 x 1000-mm worktable accepts a maximum workpiece 650-mm high weighing 8800 lb (4000 kg).
"To get an idea of workpiece size, this machine can handle a work load larger than a four-door Hummer, which weighs in at about 8100 lb [3674 kg]," says Howard. The V99L is 2 m in the X axis, 1 m in the Y and 800 mm in the Z axis.
Both machines come with a 40-taper, 20,000-rpm or a 50-taper, 12,000-rpm spindle, and can accommodate a maximum tool size of 120 mm in diam by 400-mm long, and weighing 8 kg on the 40-taper spindle, or 145 mm in diam by 400-mm long and weighing 20 kg on the 50-taper spindle. Available as options are a 40-taper, 30,000-rpm HSK-63F spindle and a 50-taper, 18,000-rpm HSK-100A spindle.
The V99 and V99L models incorporate 0.05 µm scale feedback on all axes, providing positioning accuracy of ±0.0015 mm and repeatability of ±0.001 mm positioning and contouring accuracy during continuous machining of large workpieces.
"When you are dealing with large workpieces, stiffness and rigidity can make a huge impact," says Howard. "Finishing times can last several days. The workpieces can be very heavy and hard to set up, and eliminating steps like stress relieving, or having the ability to hard mill, can save time and money."
Hurco Companies Inc. (Indianapolis) designs and manufactures a broad line of machining centers and turning centers to meet a variety of applications in job shops. Machines are characterized by flexible Hurco controls. The control allows the user to determine the best way to approach each job whether by G-Code, Hurco's shop-floor conversational programming, or direct to the control using the DXF Transfer feature.
Hurco's entry-level VM series of machines typically feature 20-station, swing-arm ATCs and 8000-rpm and 10,000-rpm spindles. The company continues to expand its flagship VMX series with the addition of two new machines, the VMX60 and VMX84 models. The VMX series are designed to use digital drives, larger ball screws, larger linear rails, and heavier servo drives to increase metal removal, and higher feed rates to reduce part cycle times.
Later this year, Hurco will launch the VMX42SR five-axis machine with a swivel head and rotary table. It will join Hurco's VTXU traveling-column machine that relies on a heavy-capacity, integrated trunnion table for its complex machining.
With the introduction of the NMV5000 DCG five-axis VMC, Mori Seiki USA Inc. (Rolling Meadows, IL) combines three of its technology innovations: DCG (Driven at the Center of Gravity), DD (Direct Drive) motors, and the octagonal ram. DCG technology and box-in-box construction minimize vibration by pushing moving structural parts along their simulated centers of gravity. The DD motors on the B and C axes transmit power directly without gears, eliminating backlash and ballscrew wear for greater accuracy over the life of the machine.
The newest of the three developments is the octagonal ram. "In some ways, it's the most exciting," says Greg Hyatt, vice president and chief technical officer of the Mori Seiki Machining Technology Laboratory (MTL). "The octagonal ram addresses the relative benefits of boxways and linear guideways, each of which has distinct advantages in specific applications," says Hyatt.
"The octagonal ram is a hybrid that combines the superior damping capacity of boxways with the high rapid traverse speeds and accuracy possible with linear guideways," Hyatt says. "By putting the boxways on the octagonal ram closest to the cutting tool we gain the damping without the loss of accuracy due to the heat normally generated by boxways. Because the ram is symmetrically supported, there is no displacement of the spindle centerline."
There are two categories of users that benefit the most from the inherent stability of the NMV5000 DCG. The first group is small-lot production, where the box way machine can be counted on to make the first part a good part. "The superior damping makes the machine more forgiving in making the first part right," Hyatt says.
The second group of applications are those that would push any machine to instability, such as cutting high-temperature alloys like Inconels, Udimets, or other materials where high-force machining tends to produce chatter. Typical applications in the turbomachinery side of aerospace include machining the hot turbine section of jet engines, and in the oil patch, machining difficult alloys for critical performance for downhole applications, or for medical implants.
This article was first published in the June 2007 edition of Manufacturing Engineering magazine.