Horizontal machining center technology—a long-time mainstay of OEMs and Tier One contract manufacturers—has morphed into space efficient, versatile machining platforms that any high-mix job shop can benefit from. Today’s HMCs have earned their reputation for performance and productivity in multiple-machine cellular and flexible manufacturing configurations. Automation ranges from on-machine twin pallets to pallet pools, with as many as eight pallets, to flexible manufacturing systems (FMS) servicing as many as ten machining centers. Automatic tool changers (ATCs) deliver hundreds of tools to flexible manufacturing systems that have relegated dedicated transfer line technology in the automotive industry to an inflexible manufacturing past. The latest trends in HMC technology include on-machine, multiple-function machining to extend processing capabilities, twin-spindle technology to meet high-volume flexible production needs, and continued reliance on automation to achieve production goals.
As one machine tool executive put it succinctly, “you’ll never see the stuff that’s really cool that I’m working on until it’s part of our product offering.” With that in mind, here’s what some leading machine tool builders can talk about.
Mitsui Seiki USA Inc., Franklin Lakes, N.J., has extended the machining capabilities of its HMC platform, creating multifunction machines by incorporating different machining and processing functions. “What’s happening today in HMCs is happening inside the machining envelope in front of the spindle,” said Bill Malanche, COO. “There’s a trend in the market today toward adding different machining processes in the machine envelope. Typical examples would be grinding or using additive/subtractive [processes] for repair of workpieces like turbine blades and blisks, or even initial inspection or machine verification,” Malanche said.
To meet its focus on technology for machining difficult-to-machine materials, Mitsui Seiki offers HMC models that have been adapted with GE’s Blue Arc electro-erosion metal removal technology for higher metal removal rates compared to conventional milling of difficult-to-machine materials. Industries like aerospace, defense, power generation and energy—using metals like nickel alloys, stainless steel, titanium and other hard metals—are good targets for multifunction machines.
“In most cases, adding a new function to the HMC is as simple as replacing cutter technology,” said Malanche. In one example he cited, an aerospace landing gear manufacturer is using a Mitsui Seiki HMC with trochoidal/planetary grinding capability to finish-grind precision bosses and bores rather than having them finished on a specialty machine. In another, a machine tool builder was able to eliminate the need for scraping and fitting for its gear shaving and hobbing machines because of the tight tolerances of straightness and squareness achieved with its Mitsui Seiki HMC, Malanche said.
Mitsui Seiki is seeing more inquiries from its customers for machinery verification, especially in automated systems, rather than relying simply on CMM parts inspection. “One of our customers is verifying their machines on a regular basis for production. Parts are held in a zero-point workholding fixture and measured to a standard that is in both the machine and the CMM. Part accuracy is correlated between CMM and machine, creating a history for the process,” Malanche said.
There are two good reasons to do it that way, he said. First, CMMs can be bottlenecks on the production floor and, secondly, the part can be qualified for the next production step, such as premachining or heat treating, if needed. Mitsui Seiki is currently working with a Japanese company that has developed a universal test coupon for five-axis machines that can measure both the CMM and the machine with results traceable to NIST standards. The coupon is mounted on the pallet and periodically inserted into the machine to confirm data with a CMM. “It makes sense, especially for high-cost components like a $50,000 or $65,000 integral rotor blade or for a $25,000 structural component,” Malanche said.
Automotive manufacturers depend on the flexibility that the latest machining center technology can provide to meet manufacturing requirements for powertrain components, structural parts and the latest e-mobility components, according to Maxime Paulet, PCI/TT Group. The French company’s PCI/Tongtai Meteor machines, which are distributed in North America by Absolute Machine Tools Inc., Lorain, Ohio, are used in the automotive industry for high-volume production.
“A few years ago, we saw a change coming in requirements for automotive structural parts and powertrain components that required manufacturers like us to adapt our technology to those new parts,” said Paulet. “Because of PCI’s relationship with Absolute Machine Tools and Tongtai Group, we are able to provide our customers with turnkey production line engineering and installation for the most technologically advanced machining solutions.”
PCI/Tongtai Meteor machines include single- and double-spindle machining centers for powertrain parts. Meteor HMCs process internal combustion engine parts, such as gearbox housings and cylinder blocks, as well as electric motor housings and battery tray components for hybrid and fully electric vehicles. The machines can produce structural and suspension components, including steering arms and knuckles, in addition to aluminum parts for nearly any automotive application, according to Paulet.
Meteor twin-spindle machines feature fully independent spindles with their own work zones. Paulet explained that two very different parts can be made on the machine at the same time; one spindle on one part and the second spindle on another part, each with its own machining envelope. If one spindle should go down, the second spindle continues to run. “The two fully independent work zones can equate to a 30 percent or more cost savings when compared to buying two individual single-spindle machines,” said Paulet, and “floor space is maximized with one machine versus two, allowing for increased throughput and ROI.”
Twin-spindle Meteor TS630V machines feature X-axis travel of 630-1300 mm and Y- and Z-axis travels of 630 mm. Part size capacity is 800 mm rotation diameter and 1,275 mm length. Single-spindle Meteor 630 machines, which are designed for machining cylinder heads on standard powertrains, have X-, Y-, and Z-axis travels of 630 mm and part size rotation diameter of 800 mm and 960 mm length. The single-spindle, 1,800-mm machine features extended X-axis travel of 1,805 mm and can process parts up to 1,275 mm long. Gantry, robotic and manual loading/unloading systems are available.
“As a turnkey supplier of machining systems, it’s important for us to alert the user when something goes wrong with the machine. We have introduced an intelligent spindle with power monitoring and vibration signal analysis that measures vibrations between the tool and the spindle in real time. The technology enables the manufacturer to detect if anything is going wrong in the process, like a broken tool, and will stop the machine before bad parts are made,” Paulet said.
Manufactured in DMG Mori’s Davis, Calif. plant, NHX 4000 and NHX 5000 HMCs are designed for high-production environments that require heavy cutting and high accuracy. Industries as diverse as energy, aerospace, industrial equipment and contract manufacturing want to make as many chips as possible, as fast as possible, according to Derek Miller, product manager.
DMG Mori, with U.S. headquarters in Hoffman Estates, Illinois, has optimized the evacuation of chips by rigorously studying machine interaction with these chips to solve production issues. Miller explained that NHX4000 HMCs with center-drop conveyors allow chips to fall straight onto the conveyor. They aren’t flushed down a slope into a conveyor outside the machine. The machines have expansive and adjustable coolant flow to knock chips out of corners, single-piece axis protectors to eliminate wear, and pallet skirts to keep chips out of the pallet clamping area.
HMCs are especially useful for parts that require more than one face to be machined. “Some people think that simple machining operations (like drilling and tapping) can be done easily on a vertical, but oftentimes these parts can be more effectively machined on an HMC, especially when more than one face needs machining. On a vertical, every time you re-fixture a part, the spindle stops moving. On a horizontal, there’s an external setup station that allows you to load the next part while the machine continues to cut the current part, never stopping the spindle,” Miller explained.
There are two default speedMASTER spindles for the NHX series: a 20,000-rpm spindle with 50 hp and 163 ft-lb of torque that will cut materials from alloy steel to aluminum with ease, and a 15,000-rpm, high-torque, 50 hp (37 kW) spindle with an 184 ft-lb (249 Nm) option for machining difficult-to-machine materials. Every NHX is equipped with Magnescale magnetic linear scales that measure true location of the part rather than the location calculated by the encoder on the servo motor. The linear scale method ensures the same positioning accuracy of the machine over its entire life, avoiding the wear and maintenance costs associated with maintaining encoder accuracy.
Two primary forms of automation are available: part handling and pallet handling. According to Miller, part-handling automation is primarily robotics based. “This is for customers who make thousands or hundreds of thousands or more of the same part or parts, year over year. Part-handling automation is specifically intended for that customer who has high-volume, repeat work.” For customers who make a wide range of parts in quantities ranging from single digits to hundreds or thousands, it becomes very difficult to find a common feature to grab on all of the parts, said Miller. “Especially for horizontals, that’s where pallet-handling automation comes into play. In HMCs, parts are mounted to a pallet or to a tombstone, which is then mounted to a pallet, which means the standard feature is going to be the pallet.”
The most popular of DMG Mori’s pallet handling options is the Linear Pallet Pool, a flexible, multi-level, multi-machine, high-production cell. Standard configurations range from one machine, one setup station, and 12 pallets; to eight machines, five setup stations, and 99 pallets. According to Stuart Luper, software product specialist, linear pallet software (LPS) can create production schedules by taking into account basic criteria like part quantities, due dates, and cycle times, and also detailed criteria such as tooling by machine, company holidays, and even the skill level of operators by shift. “This kind of scheduling was previously done by a person or a group of people, and even the best scheduling team could never guarantee the absolute optimal schedule like LPS can,” Luper said.
OKK’s lineup of machine tools includes more than 60 models of horizontal, vertical and five-axis machining centers that are represented in North America by Methods Machine Tools Inc., Sudbury, Mass. OKK large-capacity HMCs are regarded as an ideal addition to Methods’s machining solutions for industries such as aerospace, automotive, energy and die-mold, among others.
According to Bob Meier, technical sales engineer for Methods Machine Tools, who had previously been with OKK for 24 years, the reasons to adopt HMC technology are pretty obvious. “Shops that want to grow recognize that HMCs offer advantages over VMCs, in some cases. An HMC keeps the spindle running while hitting all four sides of a part, for example. One HMC takes up less space than several VMCs and is often able to reduce the number of operations, depending on the complexity of the part,” he said.
As for learning to use an HMC, Meier said, “Programming for automotive parts, for example, is generally well known. On the other hand, aerospace parts can be extremely complex and challenging to program, and that is where our engineers can provide guidance.” OKK HMCs are equipped with a FANUC F31i-B control, which facilitates user-friendly programming as well as high-accuracy machining.
OKK’s four- and five-axis HMCs provide solutions to a diverse customer base, ranging from OEMs with their own products to job shops that have a high mix of parts machined in small-batch quantities.
“Automation starts right on the HMC with OKK’s twin-pallet technology and can be extended with pallet pools, robots or linear rail systems for a single machine or multiple-machine cells. Sophisticated material handling and storage systems are available. Through Methods Automation, customers have the ability to work with a team of experts to decide on the right solution for their business,” Meier said.
For applications where parts or families of similar parts are being machined from materials with only minor changes from one part to another, robots are very effective, according to Meier. “For these applications, stationing a robot in front of the machine or multiple machines makes a lot of sense as long as the robot can keep up and match the takt times of the machining centers. Robots can be rail-mounted as well as pedestal-mounted, and cells can be configured to include inspection with a CMM,” Meier explained. When shops that run a high mix of products need to switch over to run different products, robots can change grippers and quick-release fixtures can facilitate changeover.
Robot actuators can be permanently plumbed to the machine, Meier said. “Sometimes the robot tells the machine it has the part. Sometimes the machine controls the fixture, which is tracked with information about the batch read from sensors embedded in the fixture plate,” Meier said.
OKK HMC users benefit from Methods Machine Tools’ applications engineering, service and turnkey engineering and automation capabilities, according to the company. Methods’ Automation department has more than 30 automation engineers, including specialists in design, control, fluids, integration/assembly, installation, and electrical/mechanical. It also has experts in machining. The applications engineering department has more than 60 engineers nationwide who develop turnkey solutions, if required, and facilitate problem solving and solutions for customers. Methods applications engineers help clarify and simplify operations by providing help with machine tool selection, NC programming, test cuts, process design, project management, installation and support of its product lines.
Knowing spindle utilization rates on HMCs and other machine tools on the factory floor can be a valuable aid to decision-making that can improve productivity. In fact, according to Brad Klippstein, controls product specialist, Okuma America Corp., Charlotte, N.C., data collection can be one of the easiest paths to higher profitability. Klippstein is referring to the vision of a smarter factory that is being realized in factories with Okuma’s Connect Plan Software.
“The software is a complete package, offering both data collection and artificial intelligence (AI). Connect Plan Software can look at the data collected on machine tools running on the factory floor, indicate where the problem areas, if any, lie and show how to improve productivity,” said Klippstein. The software-based system collects machine tool data and provides detailed information that can be used to fine-tune processes and improve productivity.
“Connect Plan offers a wide array of compatibility across various Okuma machine tools, legacy Okuma products, and other builders’ control systems. It offers a very open path to shop floor data collection and analytics, driving our customers toward smarter manufacturing environments,” said Klippstein.
The Factory Monitor in the Connect Plan Software provides a layout of the factory floor and a summary of each machine’s current status. Critical data are collected from machines in the network and presented in graphs through a standard web browser. Data are automatically archived for future analysis, and users can access information such as machine status, maintenance status, machining reports, alarms and operation history.
Klippstein explained that by looking at the Factory Monitor, shop personnel can get a snapshot of machine stoppages and maintenance notifications, helping them to prevent breakdowns by performing machine maintenance.
It’s possible to journal down into specific machine status reports to benchmark equipment and compare production results against historical records. Users can view uptime and downtime of the shop floor.
Connect Plan allows users to trace the conditions that led to a machine stoppage and identify what contributed to the issue, including offsets made, axial load, operator log-in ID, tool life remaining, feed rate override, alarm detail, and machine operating condition. Charts aid users in identifying reasons behind machine idle states, potentially reducing setup and non-cutting times, according to Klippstein.
Reports can be exported from the system and used for customized viewing and additional analytics.
There is an active market in 40-taper 400- and 500-mm horizontal machining centers, according to Jared Leick, product specialist, Mazak Corp., Florence, Ky. “Smaller machines offer the kind of flexibility that’s required for a lot of components. Applications can cover a wide range of products, from manifold blocks to radar systems to medical instrumentation,” he said. “Job shops are always looking to expand their range of part machining capability which horizontal machining centers offer.”
He believes job shops benefit from having the ability to run machines using Mazatrol CNC conversational as well as EIA/ISO programming. “Mazatrol gives the flexibility of quick and easy setups for short runs or when not running complex parts. For complicated parts and contouring, EIA/ISO programming is valuable for running large lot sizes and optimizing the process,” Leick explained.
HMCs can accommodate a variety of productive workholding devices, depending on the product diversity that production strategies require. “We see everything from two- and four-sided fixtures to tombstones and vises (ranging from manual to hydraulic and pneumatic) as well as articulated robots positioned overhead or in front of machines.”
For high-volume applications, Mazak’s PALLETECH system can accommodate a large number of machines in an FMS configuration. Also available is Mazak’s Multi-Pallet Pool (MPP) single-machine automation system for 400- and 500-mm HMCs. An MPP offers the convenience of a larger PALLETECH system while taking up to 30 percent less space. Mazak’s MPPs are designed to expand as a manufacturer’s production requirements grow. The system’s standard 10-pallet stocker can be reconfigured to handle 16 pallets.
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