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Basic VMC Platform is a Proven Workhorse

Jim Lorincz
By Jim Lorincz Contributing Editor, SME Media

VMCs have had a productive past, present and the future looks promising

The iconic three-axis vertical machining center ranks right up there with the two-axis CNC lathe as one of the two fundamental building blocks of any machine shop. Or quite possibly every start up in a garage where the fledgling shop owner is machining parts by night while holding down a day job.

In their most basic configuration, these single-table machines with automatic tool changers (ATC) typically hold a minimum number of tools, enough to machine large, flat workpieces that require basic milling and drilling operations. Machining more complex workpieces calls for more tools, pallet changers, and other time and labor-saving devices. Pallet changers for VMCs in both automated (APC) and manual styles are able to match operator setup time to production requirements. In fact, it would be difficult to visit any shop with the latest CNC technology and not see tucked away in some out-of-the-way place, older legacy bare bones VMCs with familiar nameplates still filling a much needed secondary machining function for their employers.

VMCs Evolution Includes Innovative Hybrid Machining

According to Scott Walker, president, Mitsui Seiki (USA) Inc. (Franklin Lakes, NJ), the VMC is on an evolutionary path that began with adding fourth and fifth-axis machining capability and one that Mitsui Seiki is continuing by creating hybrid machines that add innovative technologies to standard VMC and HMC platforms. At IMTS later this year, Mitsui Seiki will introduce its hybrid additive/subtractive machine and the innovation won’t stop there. Mitsui Seiki is currently developing GE’s Blue Arc technology for machining hardened metals in a hybrid combination with conventional machining.

“Once we started adding fourth and fifth axes with table on table and trunnion configurations, pallet changers, more tools, and high-speed spindles, the VMCs became very productive,” said Walker. “Today, our trunnion-style Vertex five-axis machine has become very popular for machining integrally bladed rotors [IBR] for jet engines, turbine blades for power generation, or for tool and die work. At IMTS, we’re going to introduce a VMC with additive manufacturing capability using a powder feed so that we can operate in both the additive and subtractive machining environment. The next logical step will be to slide that capability over into our trunnion-style horizontal machining center platform which would open up capability to handle 2-m workpieces,” Walker said. “For example, if you are manufacturing a big valve body and you want to add some kind of boss or feature to it you can additively manufacture it right on the component inside the machine. Also, because the VMC makes a good platform for other applications, we’re developing special applications like cam grinding and high-speed turning because really there’s a lot that can be done inside the work envelope of a VMC.”

Mitsui Seiki is developing Blue Arc technology that can be added to its vertical and horizontal machine platforms. “Blue Arc technology uses a low-voltage electrode that we can burn hardened materials at very high stock removal rates, of 300+ cc/min. The problem with the big, heavy-duty, high-torque machines that are typically used for roughing titanium, some Inconels, and Waspaloys is that they don’t have the agility and high traversing rates for five-axis motion, holding the tolerances that are required after roughing,” said Walker. “Blue Arc technology gives you the ability to achieve high stock removal rates on an agile machine because burning metal off doesn’t put a load on the machine like pushing a cutter through metals at high metal removal rates like 300+ cc/min.”

According to Walker, the potential applications for Blue Arc technology include large castings for jet engine housing or power generation where the gates on the castings can be literally burned off. “For the power generation market, let’s say you have a 3–4’ [0.91–1.2-m] long stainless steel forged turbine blade. The two ends of the blade have blocks on them that need to be machined or ground into a Christmas tree shape and fitted into a turbine wheel. With Blue Arc, you could take a Christmas tree-shaped electrode and burn that shape into the material in seconds rather than several minutes and then go to finishing. Other applications include burning material out of titanium or Inconel integrally bladed rotors replacing the expense of carbide cutters or for large structural components, forgings or tool and die workpieces where material can be burned off faster than machining considering the amount of metal that has to be removed to get a functional component.

VMCs Morph To Handle Complex Workpieces

Today, vertical machining centers from Mazak Corp. (Florence, KY) include three, four, and five-axis machining capabilities with MX hybrid roller guides for durability and long-term accuracy, on-board probing for part location and feature inspection, and user-friendly CNC controls that simplify programming. The Vertical Center Universal 5X VCU features a five-axis rotary/tilt table with high-speed roller gear cam technology for production of small complex parts. It is equipped with a CAT 40-taper 10,000-rpm spindle for machining steel, aluminum, and cast iron (12,000 and 20,000 rpm optional). Part sizes up to 15.74 × 15.74 × 12″ (400 × 400 × 304 mm) can be produced; the machine’s high-speed rapid traverse rates in all three linear axes is 945 ipm (24 m/min).

For precise five-axis machining, the VCU 400 5X’s trunnion-style rotary/tilt table features durable high-speed gear cam drive technology for high torsional rigidity and positioning accuracy. The table tilts +95°-45° in the B axis and rotates 360° in the C axis and can handle workpiece weights up to 440 lb (200 kg). Mazak’s MX hybrid roller guide system is designed to deliver high levels of durability and reliability, resulting in long-term accuracy. The innovative way system increases vibration dampening, extends tool life, and handles high load capacities, eliminating tramp oil in the coolant by utilizing a greener grease-based lubrication system.

The new Matrix 2 CNC control is optimized specifically for five-axis machining. Performance of the control is said to be much faster with higher processing speeds for small increment operation. A five-axis spline interpolation function included in the control’s software provides smooth toolpaths from long block-by-block programs, easy tool vector control, and shorter cycle times, resulting in superior five-axis surface finishes.

Hand-Scraped VMC Box Ways Achieve High Speed

Kitamura Machinery USA Inc. (Wheeling, IL) remains committed to the traditional construction-based process of hand scraping of its induction-hardened ways. The argument used to be that box ways were too slow for anything other than heavy-duty machining, but advances in Kitamura’s technology have achieved rapid traverse rates of 2362 ipm (60 m/min) on box ways. The combination of geared spindles and Meehanite cast iron construction provide optimum damping capacity and vibration absorption, resulting in dependable and accurate long-term performance required for high-precision machining. In addition gear head spindles are offered with high-speed 20,000-rpm, four-step geared spindles.

The high level accuracies of ±0.002 mm (full stroke) achieved through hand-scraping and solid box way design is said to produce superior abrasion resistance and vibration absorption for heavier cutting ability, better surface finishes and longer tool life. As a result, it isn’t surprising that Kitamura VMCs are being used in a variety of industries from smaller high-precision medical parts to larger, heavier mold machining. In addition, Kitamura is in the process of adding larger travel machines in smaller footprints (really small) in its VMC line because floor space at its customers is at such a premium. Both its double-column machine line-up, as well as its five-axis VMC lines are being expanded.

CNC Control Sets Five-Axis Machine Apart

For Hurco Companies Inc. (Indianapolis), it’s the CNC part of the VMC that it believes sets it apart from every other machine tool builder. Historically, its customers have manufactured parts for the automotive, aerospace, medical equipment, energy, injection tool and molding, transportation, and computer equipment industries—all of which are under global competitive pressure. While Hurco is known for conversational programming, which its founder invented and developed, the NC side of its control is said to be as good as any in the industry with complete compatibility with the most commonly used CAM systems and comprehensive FANUC integration.

Hurco’s VMCs are designed to give customers the ability to eliminate process steps and increase efficiency during the 60% of non-cut time that accompanies most jobs, especially helping customers efficiently produce a high mix of parts at lower volumes profitably. The Hurco VMX42SRTi five-axis machine, for example, features direct drive C-axis rotary table, making it valuable for most applications, but with specific benefits for the aerospace industry. The design of the VMX42SRTi features a flush rotary torque table that provides a larger workcube and manufacturing flexibility.

For the five-axis parts, the embedded C-axis rotary table supports taller parts due to more than 3.5 additional inches (76.2 mm) in Z. For three-axis work, the increased table size supports parts up to 42 × 24″ (1066 × 610 mm). Basic specifications of the VMX42SRTi include X-Y-Z travels of 42 x 24 × 24″ (1066 × 610 × 610 mm), a 12,000-rpm spindle standard, a 40-station swing-arm ATC and, X-Y-Z rapid traverse speeds of 1378 × 1378 × 1181 ipm (35/35/30 m/min). The integrated Hurco CNC control includes both conversational and NC programming modes in addition to Hurco’s exclusive NC/conversational merge feature. The VMX 42SRTi is equipped with UltiMotion, the motion control system of Hurco’s own invention that simultaneously reduces cycle time and improves surface finish quality due to sophisticated software algorithms.

New Generation of Fully Digital VMCs

The new generation Bridgeport Conquest V Series vertical machining centers from Hardinge Inc. (Elmira, NY) are fully digital, high-quality machine tools, designed to achieve maximum capacity and performance in the job shop, OEM, aerospace, automotive, and power generation industries, among many other manufacturing sectors. Manufactured to the highest industry standards, the Bridgeport Conquest V1000 is designed with features to meet and exceed the requirements of the demanding metalcutting market. This machine provides fast rapid traverse of 1692 ipm (43 m/min) on X and Y axes and 1417 ipm (36 m/min) on the Z axis and a highly sophisticated yet user-friendly Mitsubishi M70V control with NAVI MILL Programming and 10.4″ (264-mm) LCD.

The machine features a direct-drive 20-hp (15-kW), 10,000 rpm (12,000 and 15,000 rpm optional) 40-taper spindle motor with 110 ft-lb (149 N•m) of torque, and a 30-tool swing-arm automatic tool changer. The machine is designed for rigidity with large, robust 45-mm ballscrews on all axes and 35-mm linear guides standard on the X axis with 45 size guides on the Y and Z axes. The V1000 weighs in at 15,400 lb (7000 kg) and takes up 105 × 120 × 112″ (2673 × 3048 × 2850 mm) floor space. Working surface is 47.2 × 23.6″ (1200 × 600 mm) X-Y-Z travels are 40.16 × 24 × 24″ (1020 × 610 × 610 mm).

For applications that require speed as well as accuracy, the Bridgeport’s Conquest V480 APC VMC features an integrated automatic pallet changing capability. The V480 APC is a fast extremely compact yet rugged machine, developed for applications that require speed as well as accuracy. The V480 APC is manufactured from grey cast iron to the highest standards and levels of reliability. The machine is fully digital with a X-Y-Z rapid traverse rates of 1417 ipm (36 m/min) and acceleration rates of 4.8 m/sec² providing a fast and accurate response to all machining needs.

Turnkey Advanced Five-Axis Solution Ready To Go

A turnkey machining solution that gets businesses up and running faster in five-axis machining is being offered in North America through a partnership between CAMWorks CNC machining software from Geometric Ltd. (Scottsdale, AZ) and Ganesh Machinery Inc. (Chatsworth, CA). The partnership brings together a leading CNC machine manufacturer and a global leader in 3D CNC machining software that is offering a ready-to-use five-axis CNC machine that will enable manufacturing organizations to implement advanced machining capabilities more quickly and cost-effectively. This advanced machining solution is offered in a Ganesh VFM 5X-8 five-axis vertical machining center, bundled with CAMWorks 3D CNC machining software, and a certified postprocessor.

Because CAMWorks is bundled with the Ganesh five-axis machine, the postprocessor is pre-programmed and certified, reducing the learning curve and time to productivity. State-of-the-art training has also been prepared specifically for this bundle, further reducing challenges often arising when implementing advanced multiaxis machining solutions. “As Ganesh enters the five-axis CNC machining world, we realize that helping our customers become productive with our machines as quickly as possible demands the use of quality software with a clean postprocessor,” said Ganesh owner, Harvinder Singh.

“We wanted to package our machine with modern, easy-to-use CAM software that minimizes the learning curve and facilitates fast, successful implementation. We are familiar with CAMWorks software because we use it internally and believe it will help our customers get up and running more quickly,” said Singh. The fact that CAMWorks software utilizes the Solidworks CAD modeler as its geometry engine is regarded as a huge plus.

“As part of this bundle, we’ve developed a CAMWorks postprocessor specifically for the Ganesh five-axis machine, as well as a virtual machine simulation add-on for proving our complex toolpaths,” said Jim Foster, vice president-global channel sales and marketing at Geometric. “Deploying five-axis machining in a production environment is challenging, and many unforeseen delays related to software, postprocessors, and training can occur. By partnering with Ganesh, we are helping businesses take five-axis machining to production faster and without costly pitfalls,” Foster said.

This article was first published in the June 2016 edition of Manufacturing Engineering magazine. 

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