Automation by Machine Design
Systems deliver the flexibility shops require
By Jim Lorincz
Buying a stand-alone machining center is one thing. Buying one without the prospect of enjoying the flexibility that automation can bring to low-volume, high-mix production, especially at the job shop level, is quite another. Single stand-alone machines, from this point of view, can be viewed as a dead end when it comes to meeting competitive requirements for increased throughput of high-value, complex parts of the highest quality produced with minimum setup and handling. The stand-alone might generate profit today, but how long will the customer be willing to pay for under-utilized labor or missed opportunity due to lack of flexibility. The configuration of machines purchased today can put manufacturers on the fast track to a competitive future.
Machining-center design increasingly emphasizes the ability of machines, whether HMCs, VMCs, multitasking machines, or, more recently, five-axis platforms, to accept automation. Machines and their interfaces are being developed according to the dictum that "the days of one machine–one operator" are, or should be, over. The objectives of automation are well accepted, and include higher spindle utilization rates, higher throughput, reduced labor, process consistency, and flexibility to redeploy machines for future production needs.
There are a number of important trends in machine design:
- Machining centers, multitasking machines, and five-axis machines are being designed to be integrated with pallet pools, robots, and RGVs, and can accept barfeeders, gantry loaders, and other advanced devices.
- Robots are being positioned away from the front of machines so that operators have access, and machines can be accessed from the sides or overhead by railmounted gantry robots.
- Single and multiple-machine cells are being created with robots on board, while retaining the ability to run machines manually, if so desired.
With the growth and acceptance of multitasking and five-axis machines accelerating, Palletech systems from Mazak Corp. (Florence, KY) are automating a mix of dissimilar machine models, as well as lines of similar machines. "In addition to untended load/unload, from stockers from one to three levels high, and robot loading from overhead rail-mounted robots, the next steps in automation are aimed at increased throughput of quality, complex, high-value parts with minimum part handling," says Mike Kerscher, machining center product group manager, Mazak's Cybertec division.
Once strictly the province of high-volume, low-mix part production, robots are successfully being used by low-volume, high-mix contract manufacturers. Reliability of robots as measured by longer mean time between failure (MTBF) is unquestioned, and repeatability as seen in the diversity of applications, whether in high or low-volume applications, is filtering down the supply chain to lower automotive-tier shops. The impact of robots on machine tools can be seen in the "Made for Machine Tools" Web site that Fanuc Robotics America Inc. (Rochester Hills, MI) has launched as a resource for machine-tool OEMs, integrators, machine shops, and other contract manufacturers considering using robots to automate a machine-tending operation.
The site (www.fanucrobotics.com/machinetool) includes a wide range of application videos that provide real-world examples of how robots can be used to automate machining processes, including turning, grinding, boring, cutting, milling, drilling, EDM, deburring, and metal fabrication. Robots are available ranging from a lightweight six-axis parallel-link robot, to the ubiquitous LR Mate series for welding apps, and in sizes up to that of the M-2000iA robot capable of handling workpieces weighing from 900 to 1350 kg. Robots are fitted with iRVision for 100% inspection, repeatability in the chuck, and finding parts on belt conveyors (2-D) or pallets (3-D).
Automation solutions from Makino Inc. (Mason, OH) range from simple cells with a single machine and robot loader to larger systems consisting of machining centers, parts conveyors, robot and gantry loading, automated assembly and inspection equipment, and parts washers. David Walton, project engineering manager, outlines their scope: "We offer customized automation solutions for high-volume, high-production applications like automotive where a number of parts are run over and over again for a total of several hundred thousand parts a year. For contract manufacturers and shops where there is a high mix of parts going across the machining centers, our pallet-handling system delivers fixtures to the machining center under the control of the cell controller." Makino's MMC palletizing system is designed to enable contract manufacturers to run lean and realize more uptime on their machines for a mix of parts, without having to qualify the fixture every time it is removed, stored, and reintroduced to the machining center. The latest version is the MMC-R automation system for fixture-plate distribution with a six-axis robot for tending four and five-axis HMCs and VMCs in high product mix, low-volume production applications. An optional seventh-axis floor track can support additional machines and storage capacities.
"Automation objectives are in line with lean running. Manufacturers are able to increase spindle utilization and reduce setup times through accurate and reliable machine loading, unloading, and part storage," Walton says. "By transporting fixture plates in place of a complete machine pallet, manufacturers benefit from reduced part-fixture costs."
Most observers agree that the use of robots has progressed beyond just having two robots standing between two machines. "Obstacles to integration into automation systems haven't been the robots, but the machining process itself," according to Gregory A. Hyatt, vice president and chief technical officer, DMG/Mori Seiki USA (Hoffman Estates, IL). "Machining processes that were adequate for manual operation sometimes may not be robust enough for automation with robots. The most common problem is chip control, especially for lathes, or in drilling operations on machining centers, but basically for any operation that produces a long stringy chip."
A second parallel area of concern is quality control in automated operations. "You don't eliminate cost if you still have to have a man there doing quality inspection checks. You may make his job easier, but the cost is still there," says Hyatt. DMG/Mori Seiki has developed a method of monitoring the quality of workpieces with its Hydrogage. The principle of the Hydrogage is the same as that for an air gage. Hyatt explains: "We measure the back pressure as the fluid escapes between the plug and the bore or between the C frame and the shaft. Instead of using air to measure, we use the machine tool's coolant at 1000 psi [6.9 MPa], and measure pressure throughout the fluid. Hydrogage can be used equally well on lathes or machining centers. On machining centers, it can be used on critical bores where we have to maintain a bore size by adjusting the boring bar as needed or replacing it with a redundant tool."
"RGV palletizing systems are moving toward the job shop," says William Vejnovic, vice president of engineering, Toyoda Machinery (Arlington Heights, IL). "We have focused on low-volume, high-mix of part numbers going through the RGV systems, turning multiple jobs with lot sizes of 20 or less parts per month around, typical, for example, of aerospace jobs shops. Our HMCs are completely modular, designed so that if you buy a stand-alone machine, you can simply change-out a kit on the front end pallet changer to turn it into an RGV-ready machine. All of our spindles, pallet changer, and tool magazines are independent modules that can be swapped out during installation of the machine."
The orientation of Toyoda HMCs toward automation in its 450, 550, 630, 800, and 1050-mm machines is seen in the compatibility of the locating surfaces of its pallet systems. "If you buy a machine with an RGV, new or previous machine models from different generations as long as they are of the same pallet size will fit into the system," Vejnovic explains. "Most typical configuration of the RGV system was two to four HMCs with the larger systems having ten machines. Pallet buffer storage is typically in the 20–30 pallet range. Regardless of how many buffer pallets are in the system, we incorporate a chip into the pallet so that another 300 pallets can be stored off line."
Flexibility for the RGV system is provided by design characteristics of the HMCs. "For untended operation, an inductive broken-tool detection system, inspection with a Renishaw probe, which are typically utilized for in-process inspection not intended for first article or final part buyout, and Renishaw laser-tool measurement are available. The software has real-time tool checking. Before a pallet is brought into the machine, the software will check to see that the machine has all the right tools in the ATC for the job, matching tool numbers in the job to the machine. In addition, the software has a first-tool flag function that ensures that only a brand new tool in the magazine will be measured, saving noncutting time," explains Vejnovic.
"When considering an HMC, it's always important to look at the machine's design to see how readily it will accept automation," says Gisbert Ledvon of GF Agie Charmilles (Lincolnshire, IL). "Some machines are not designed for automation, putting automation in front of the machine, making them inaccessible to the operator for manual operation. Look to see how easy it is to change-out the automation, and whether there is access to the front and side and the worktable," Ledvon. "Another consideration is the machining center itself. We have developed Smart Machine modules with features that enable the HMCs to deliver consistent performance results, which are especially important in running untended."
GF Agie Charmilles' Smart Machine modules put intelligence into the milling process by providing communications between the operator and the machine to optimize processes. Modules include APS (Advanced Process System), a vibration monitoring system that makes vibration caused by interrupted cuts, poorly balanced tools, and the like visible as g-load. The latest version of the ITC (Intelligent Thermal Control), the ITC-5x, was developed for five-axis machines with a rotary tilting table or a tilting head and a rotary table. ITC-5x addresses heat drift where mechanical construction is simply not the answer. In spite of exact compensation between tool and workpiece, the position of the rotation axis stored in the control can change, especially in the swiveled levels.
To complete the automation process, Ledvon advises automating report notification with a capability like MT Connect to monitor processes, errors, stoppage, tool breakage, and the like.
"About 60% of the VMCs we sell are cellular and automated for the flexibility that today's shops need," says Cris Taylor, CEO, Chiron America (Charlotte, NC). "We automate our machines in two basic ways, with robots and with bar or extrusion feeders. In our Flexcell Uno flexible manufacturing system with one VMC, we create an off-the-shelf cell by integrating a robot and a pallet system with one VMC. The robot is on one side of the machine so it can also be used as a manual machine. The cells are compact, can be shipped on a truck, installed, and moved around the shop."
The Flexcell Duo takes the robot and VMC combination a step further. It integrates two FZ 08 W or FZ12KW machining centers on 11 m2 of floor space with a workpiece changer and robot with part magazine to form a manufacturing system for flexibility in six-sided machining of complex parts. The two high-performance machining centers can operate independently of one another. Each machine can have two spindles so that one robot can tend four spindles. It is possible to set up on one of the machines while the other is machining. Loading and unloading of one of the machines can take place during machining with either identical or different workpieces. Workpieces are stored on 15 individual pallets.
"Our customer base ranges from larger job shops with batch work to tier one automotive suppliers, and machines can run materials ranging from plastics to steel, gold, aluminum, and copper," says Taylor.
When Methods Machine Tools Inc. (Sudbury, MA) introduced its RoboDrill Med Cell, it represented the latest progression of the concept which integrates a high-speed six-axis Fanuc LR Mate 200iC robot with the RoboDrill VMC for five-axis machining of medical parts and devices. The initial combination was found in the Job Shop Cell, which was tweaked to simplify and speed changeover to running a different part.
"We designed a universal conveyor with tracks that can be made narrower or wider to handle different-sized workpieces in a minimum amount of time," explains Steve Bond, RoboDrill product manager. "That made it possible for the shop to adjust the infeed and outfeed of the cell, changeover a gripper, and be ready for another job." Typical parts machined on the Job Shop Cell include automotive-specific components, valves, and brake components for the RV industry.
Still, another step was needed to meet what the company felt could be an effective machining option for the medical-device industry. "We took the idea a little further and said, if we are going to palletize with some kind of off-the-shelf EDM-style tooling like that available from System 3R, Erowa, or Hirschmann, the workpiece could be mounted and loaded onto the five-axis machining center used by medical device manufacturers," explains Bond. As a result, the Med Cell features an integrated macro chuck that enables different parts to be mounted on the same universal chuck base. Any part that will fit in its 6" (152-mm) vise or chuck can be palletized. Because the workpiece is pallet-mounted, parts remain perfectly aligned when moved through other production operations. Typical medical parts that can be machined include bone plates, knees, hip stems, and polymer cups that hold the ball used in the artificial hip.
Erowa Technology Inc. (Arlington Heights, IL) has broadened the reach of its EDM-style palletizing systems to include chip-making applications for HMCs and VMCs, from graphite milling to steel cutting, including five-axis machining. "Our automation isn't aimed at the high-production markets. It is designed more for mold and die, aerospace, medical or general machining, typically shorter-run production," explains Erowa's Chris Norman, COO.
"The whole idea is to get the operator out of setting up inside the machine, to let him set up off line so that the spindle running time is maximized. Repeatability of our system is 2µm. For palletization of large parts, a dashboard cavity, or a wing spar, for example, that can be moved by palletized fixturing, the MTS system offers repeatability of better than 5µm. Our MTS system allows us to build customized baseplates that cover the table of a large machine with chucks onto which pallets of different sizes can be moved quickly so that setup time is reduced. It isn't uncommon for palletization to allow an operator to do in minutes something that would take hours otherwise," Norman explains.
This article was first published in the June 2010 edition of Manufacturing Engineering magazine.