VMC Technology Stretches Applications, Productivity
Smart Manufacturing Magazine June 2019
By Jim Lorincz
Advanced models continue to expand VMC reach on the shop floor.
Vertical machining centers with advanced features and functions are earning their stripes as more productive members of machine shops’ CNC equipment arsenal. Today’s VMCs are challenging the notion that they have to be consigned to some seldom visited dark corner of the shop, or limited to secondary machining. VMCs have traditionally been lower priced compared with horizontal machining centers but without the production capability.
To some extent, the most recent additions of advanced technology have enabled VMCs to close the productivity gap and secure a competitive edge in high-speed, high-precision applications as diverse as aerospace, medical, energy and similarly demanding industries. The functionality of VMCs has been significantly increased with the addition of fourth- and fifth-axis table-on-table and trunnion configurations, multiple pallet changers, more tools, and high-speed spindles. VMCs are capable of machining the most complex workpieces, such as bladed rotors for jet engines, turbine blades for power generation, large aerospace components, and precision mold and die work.
Mold and Die VMC Case Study
Werkzeugbau Leiss GmbH is considered one of the world’s leading and most successful producers of extrusion blow molds and stretch blow molds. In close cooperation with its customers, the company from Ludwigsstadt, Upper Franconia, Germany, develops new packaging designs for the food, pharmaceutical, chemical, automotive and cosmetic industries, as well as dies and molds are that designed and manufactured by some 65 skilled Leiss employees.
“As a service provider in tool design and construction, we see ourselves as a partner for our customers,” said Daniel Leiss, explaining the company’s strategy. He manages the company together with his father Fritz Leiss. The close partnerships with customers often begin with the development of new packaging designs. “The earlier we help the process with our experience, the more economical the manufacturing of the dies are for all those concerned.”
This makes it possible for Werkzeugbau Leiss to manufacture 250 new dies per year with a total of around 1,000 cavities, as well as periphery components, such as blow pins, masks/punchings or dies/pins.
Werkzeugbau Leiss manages its high-volume production in its large and modern facilities. Precision machining is done by a powerful fleet of machines, including ten CNC machines from DMG Mori. In addition to two CTX turning machines, the fleet of machines includes five vertical machining centers from the DMG Mori DMC V series. This includes the DMC 1150 V, the DMC 1450 V and also the new DMC 1850 V.
The machines work to full capacity, machining the high-precision extrusion blow molds, which make up 80 percent of Leiss’ production. Their manufacturing processes range from drilling and milling the cooling systems to roughing and finishing. “We benefit from the high stability and accuracy of the machines, which has enabled us to reduce finishing work to a minimum, especially in the field of large molds for long-stroke machines,” said Daniel Leiss, referring to the subsequent polishing of the molds.
The largest model of the DMC V series was installed in July 2018 as a field test machine, which Daniel Leiss considers to be the perfect addition: “With the DMC 1850 V, DMG Mori has adapted a tried-and-tested machine concept to the increasing quality requirements when machining larger and heavier components.” The vertical machining center expands to 1,850 mm travel paths in the X axis, and 700 mm and 550 mm respectively in the Y axis and Z axis. The maximum load capacity is 3,000 kg.
According to Daniel Leiss, the DMC 1850 V ideally matches the mold and die maker’s requirements. “Machine stability applies both to 2.5D machining and drilling as well as to 3D roughing. With its accuracy and dynamics, the machine is also impressive for 3D fine finishing and is therefore suitable for use in all phases of tool production,” he said. After only a few months of field testing, the DMC 1850 V was being used in a two-shift operation and has been performing reliably since.
VMC with Tilt Table
Mazak Corp., Florence, Ky., continues to expand its Kentucky-designed and built VMC line with the VC-500A/5X Vertical Machining Center that features a trunnion-style tilt table. The VMC is designed for accurate, cost-effective processing of small, complex parts via full five-axis machining. The VC-500A/5X joins Mazak VMCs that include three-, four- and five-axis machining capabilities with onboard probing for part location and feature inspection. The VC-500A/5X features the Mazatrol SmoothX CNC, making it easy to generate programs for complex parts production.
Advanced functions of the VC-500A/5X allow it to ensure the shortest possible machining cycle times, especially in fine increment programs for simultaneous five-axis operations and free-form die-mold machining, the company said. These functions include high-gain feed forward control, fast rotary axis speeds, variable acceleration control, and intelligent pocket milling. Special gear design software and a metrology unit can be integrated into a closed-loop gear machining process.
Axis travels of the VC-500A/5X accommodate part sizes up to 19.88″ (505 mm) in diameter and 12″ (305 mm) in height. Rapid traverse speeds for these three linear axes are 1,181 ipm (30 m/min). The VC-500Z/5X is equipped with a high-performance 12,000-rpm CAT-40 spindle for machining all common materials, including steel, aluminum, and cast iron. Optional spindle speeds of 15,000 rpm and 20,000 rpm are available.
A 60-tool ATC helps reduce set-up time, allows for redundant tooling and provides increased unmanned, uninterrupted operations. This process gives job shops a high-precision and cost-effective option to machine small to medium batch gears with standard tooling.
Single Machine Automation
With shop floor space at a premium, small footprint machines are widely valued, as is automation that can optimize available floor space. Single-machine automation systems for vertical machining centers offer a productive solution for small shops with the ability to meet changing production demands with expandable, cost-effective systems. They require minimal floor space and provide lights-out operation, keeping machine spindles in the cut while operators are free to load new parts, perform quality control checks or tend to various other shop tasks.
When it comes to automation, machine tool OEMs, such as Mazak, realize that one size does not fit all and continue to develop scalable automation systems. Such systems are scalable in size, cost, and capability, yet provide the typical benefits of any form of automation—increased output from machines and labor—essentially doing more with less.
Here’s how Mazak sizes up the benefits of single-machine automation. Compared with more expansive automation systems, single-machine automation systems have dramatically smaller footprints, and in many job shop cases that is all that is needed.
Today’s single-machine automation systems are typically standardized solutions, yet flexible and expandable. For instance, Mazak’s Multi Pallet Pool (MPP) automation system gives shops the option of three different configurations, holding 6, 12 or 18 pallets. The system works across different production methods and the operator can set the MPP system to run low-mix/high-volume parts or short-run parts with frequent changeovers.
Initially, a shop could start with a six-pallet MPP com-posed of two rows of three pallets. This two-level system could expand to six pallets on each row for a total pool of 12 pallets. For an 18-pallet system, the MPP would grow to three rows of six pallets. Regardless of configuration, the MPP’s size in terms of footprint remains small, saving valuable shop floor space.
An MPP six-pallet changer paired with a Mazak Variaxis i-600 five-axis VMC, for example, uses 29 percent less floor space than a six-pallet linear-type system while providing the same capacity. Compared with a 12-pallet system, the MPP reduces floor space requirements by 44 percent. And when used with a Mazak Variaxis i-700 five-axis VMC, a six-pallet MPP is 44 percent smaller than a six-pallet linearly arranged system, and the MPP’s 12-and 18-pallet systems need less than half the space.
In contrast to other automation systems, the MPP uses actual machine pallets instead of additional ones placed on top of a machine’s existing pallet. The Variaxis i-600’s MPP features a 400 sq-mm pallet that holds a 300 kg maximum load at dimensions up to 600 mm in diameter and 425 mm in height.
The Variaxis i-700 MPP pallet is 500 mm square and has a load capacity of 400 kg. The MPP operates with the same pallet clamping system as would a typical two-pallet changer installed on a machine tool. Within the MPP, a servo-driven robot picks and places pallets in and out of the machine.
The MPP uses the same Smooth PMC software that controls Mazak’s extensive, multi-machine Palletech Automation System. The machine tool’s control displays the software that runs on a separate cell controller unit. Smooth PMC software makes it easy to monitor the automated machining system from almost anywhere using a smartphone, PC or tablet. The software also lets shops change schedules on the fly, manage part program files, track tool life/breakage as well as issue instructions to the shop floor.
Getting from Print to Part Faster
You would expect that Hurco Companies Inc., which invented conversational programming, would be a leader in streamlining the process of getting from print to part faster with CNC machining centers. And it is.
Hurco VMCs run the gamut, from the VM CNC VMC compact footprint value model to VMX five-axis series machines, and for the largest aerospace parts the DCX series of double-column machining centers with 2- and 3-m X axes. Hurco’s VMCs are used to manufacture parts for the automotive, aerospace, medical equipment, energy, injection tool and mold, transportation and electronics industries.
On its higher-end CNC machining centers, Hurco offers dual-screen control for faster, easier processing. A Data Block Search helps operators edit a part program to correct a feature, for example. Instead of searching through lines of code, the programmer uses the graphics screen to select the part feature that needs to be edited and the corresponding line of code appears on the other screen so that the change can be made quickly.
Hurco’s Concurrent Programming feature is enhanced with the dual-screen control. While the machining center is running one part, the operator can program the next part without interrupting the machining cycle.
DXF Transfer allows the operator to import the CAD image, select the desired features, and the WinMax CNC control automatically creates the program. The part program can be checked on the screen with Hurco’s verification graphics system, which includes 3D solid rendering of the toolpath with dynamic rotation and real-time tool display so that the part can be viewed from any angle without being forced to re-draw it.
Recent Hurco control and software features are designed to streamline everything from optimizing cycle time to capturing tooling information. UltiMotion reduces cycle time by up to 30 percent which, according to Hurco, significantly increases surface finish quality.
UltiMonitor allows remote monitoring of the machine from any web browser, or it is possible to see the control screen or video from a USB camera at the machine. Absolute Tool Length allows tool setup to be independent from the part and machine. As a result, tool information only needs to be captured once, allowing the tool to be used on other machining centers, facilitating the use of an offline tool presetter. In addition, Tool Change Optimization analyzes the part program and automatically reduces the number of tool changes by rearranging the program for optimal efficiency.
Full-Fledged VMC Capability
The familiar FANUC RoboDrill mimics a vertical machining center’s ability to perform milling, drilling, tapping, facing, pocketing and slotting—everything that a VMC can do, said Ken Corklin, RoboDrill product manager, Methods Machine Tools Inc., Sudbury, Mass.
“The RoboDrill competes very well with 20 x 30″ and 20 x 40″ VMCs and can do the same amount of work as a 40-taper 20 x 30″ VMC and do it 15-50 percent faster. Reasons are fast tool change, fast spindle on and off, and high acceleration rate motors. Even if a 40 taper can do some heavier roughing, the RoboDrill beats them in slotting, tapping, drilling, pocketing and circular interpolation. With roughing, the RoboDrill is usually 15 percent faster; without roughing as much as 20-40 percent higher,” he said.
There are over 7,000 RoboDrills installed in North America, with about half in job shops and half in industry-specific shops. Applications include high-speed machining of aluminum for aerospace parts, titanium and cobalt chromes for medical parts and gun parts as well as general engineering.
“BIG Plus spindle technology has given the 30-taper C-frame style RoboDrill the surface contact area that enables it to take heavier, high-quality cuts and do it at lightning speeds—something that 40-taper machines have trouble matching,” said Corklin. “For example, RoboDrill is able to do typical mold and die work or medical applications with a high-speed ball end mill with feed rates of 200 ipm (50 m/min) or more because of its fast acceleration/deceleration rates.”
RoboDrill is available in three sizes: short bed, medium bed and long bed with the latest FANUC 31i-B5 Nano CNC control. X/Y/Z travels in the short bed model are 300 x 300 x 300 mm; 500 x 400 x 330 mm in the medium model; and 700 x 400 x 330 mm in the long bed. Rapid traverse rates are 2,125 ipm (54 m/min) in all three models. BIG Plus spindles are 10,000 rpm and 24,000 rpm with a 21-tool ATC.
The newest additions to the RoboDrill include a servo motor for the turret, which reduces cycle time, as well as features like Ai Overlap, which allows arc radius moves in the Z axis for reduced cycle time instead of 90º corners requiring a stop. A touchscreen iHMI control from FANUC allows for growing use of apps, such as Renishaw’s Go Probe.
RoboDrills are designed to match seamlessly with FANUC robots for standard automation packages or for customized automation solutions. Methods has a number of standard “bolt-on” automation solutions in the new Plus Series, including the Plus K.
The Plus K allows the RoboDrill to run unattended through an extended automatic tool changer and an automated pallet changer. Custom automation solutions have been a focus of Methods Automation for years, according to the company.
With the FANUC 31iB5 control, the RoboDrill is five-axis capable. Options such as AICCII and thousand block lookahead make it capable of high-speed contour-ing and machining. Its size and 1.5 g acceleration make it highly maneuverable and capable of cycle time reductions of 15-50 percent compared to standard VMCs, according to Corklin.
Linear and Box Way VMCs
Many machine tool builders now lean exclusively toward linear guideway machines. But Doosan Machine Tools America, Pine Brook, N.J., offers both linear and box way VMCs, providing a wide range of machining options.
The DNM Series features linear guideways, BIG Plus 40- and 50-taper spindles (which come standard on Doosan VMCs), and spindle speeds from 8,000-15,000 rpm. The S model is equipped with 15,000 rpm and faster rapids. X-axis travels range from 20.5″ to 85″ (520-2,160 mm) in the model lineup.
For heavier machining in harder materials, the Mynx Series features box way design, BIG Plus 40- and 50-taper spindles with either geared head or direct drive, depending on the model, and 6,000 to 12,000 rpm range.
For production shops, models include the VC Series with rotary pallet changers, and the DMP 500/2SP with twin spindles and two tool changers. The DMP has a 47.2 x 20.5″ (1,200 x 520-mm) table and an up to 40-tool magazine accessible by each spindle in about the same footprint as a single-spindle machine. Each spindle can be adjusted slightly with the W axis to avoid the need for perfect alignment of workholding or fixture heights.
Doosan’s five-axis verticals include the DNM with two-axis trunnion tables integrated into the machine platform. With a rotary table paired with a direct drive, 40-taper, 12,000 rpm spindle, the machine offers a step up from a standard VMC.
Finally, DVF five-axis machines offer a more fully integrated solution, with either a cantilever-style five-axis or a trunnion-style table. VCF Series five-axis fixed table VMCs offer more in part range since the machine travels and table size are larger. The additional axes are in the B-axis rotating head spindle or in the built-in, above-table rotary axis.
Checklist for Evaluating Advanced VMCs
The latest vertical machining center models coming to market have advanced features, construction attributes, and components that contribute to reliability and efficiency levels never thought possible on a VMC. According to Ellison Technologies, a provider of machining solutions to North American metal-cutting operations and their global affiliates, here are some of the newer characteristics and capabilities that you’ll want incorporated into your next VMC.
For discussion of favorable VMC characteristics, refer to “New Generation VMCs Are More Productive and Efficient Than Ever,” Manufacturing Engineering, June 2017, which includes this information: “Review how the machine is constructed so that in 10, 15 perhaps even 20 years, it’s still running as accurately as the day you installed it. Check that the manufacturer uses finite element analysis (FEA) to design the castings for its spindle head, base, column, and saddle. The idea is to get the natural harmonics of the structure outside of the operational range of the machine.
“Also make sure that the casting method used is licensed by the Meehanite Worldwide organization. This patented process demands the highest quality iron-producing procedures, providing long-term rigidity, heavy-duty cutting capability and proper vibration dampening over the life of the machine.
“Other construction highlights of a quality machine include an arched pyramid column that is hand-scraped to the bed, making the two castings behave almost like one, also ensuring tight machine geometry that reflects in part accuracy. High-quality ceramic spindle bearings, double-anchored pre-tensioned ballscrews, and linear roller motion guides are among other construction aspects to consider. Roller guides have three times the rigidity and twice the life of ball bearing motion guides.
“Upon a sound structure, scrutinize additional components, such as spindles, the coolant system and chip conveying mechanism. All of these contribute to efficiency. Look for features like a dual-contact spindle (taper/face) such as BIG Plus, tool load monitoring, through-spindle coolant and adaptive feed rate control for optimal tooling application and cycle time. Further, understand how the machine is designed to handle heat. Arguably the greatest advancement in recent years is the application of a variety of thermal stability improvements.”