By Jim Lorincz
Machine tool builders have adopted advanced designs and used computer-aided modeling to develop machine technology that meets requirements of manufacturers from one-off applications to production runs in the thousands or many times greater. The challenges they face are complicated by customer requirements to meet higher degrees of accuracy, increased throughput, improved reliability, and safety and lower cost. This continuing effort to achieve "lean" production has challenged the machine builders to rethink their product offerings. They are taking into account the innovative capabilities of multitasking machines in combination with standard HMCs and four and five-axis machining centers, as well as VTCs and integrating these into cellular configurations.
It matters which industry is being targeted for these product developments. For one thing, "lean" operation can mean very different things to manufacturers from job shops to aerospace to high-volume automotive operations. The days of batch production to economic order quantities to build inventories are receding into the past. The requirement today is for flexibility to produce on demand and move readily from one family of parts to another, or within families of parts for high-mix, low-volume manufacturing.
Over the years, Kennametal Inc. has employed many manufacturing methodologies to achieve its production goals. Recently, management challenged engineering to create a workflow that reduced lead times and cost and increased customer service levels—all while manufacturing in lot sizes of six or fewer pieces per production run across a large offering of products. In addition, management wanted to reduce the manufacturing footprint.
Jim Stanko, engineering manager, explains that Kennametal’s original plan called for purchasing six to eight turn-mill systems to produce semi-finished blanks with KM, HSK, or steep-taper back ends in economical lot sizes with at least 50–100 pieces per run. Finished blanks would then be stored in a supermarket by blank style, with each style servicing about 30–40 different line items in Kennametal’s catalog. A second set of turn-mills would serve primarily to create the front-end features of the part, whether it was to be a thermo tool, TG/ER collet chuck, end mill adapter, shell mill adapter, cutting unit, or milling cutter. To fill an order, the operator would simply pull the required number of blanks from the supermarket for the order, which might range from one to twenty pieces per order.
Advanced Manufacturing Cell Solution
Methods Machine Tools Inc. (Sudbury, MA) proposed an alternative solution that created what Stanko calls "an advanced manufacturing cell," comprising just two multitasking and two turn-mill systems instead of the six or eight turn-mill systems Kennametal had originally planned to buy. Methods recommended two Nakamura Tome Super NTX turn-mills with robotic material handling to produce the blanks. The Super NTX features a tool spindle on the upper side, B-axis ATC capability, and two turrets on the lower side. The machine configuration allows three tools to be engaged in the cut simultaneously. The NTX has a tool-to-tool time of 0.2 seconds, and by using the two lower turrets during the ATC tool change, idle time could be reduced even further.
The Super NTX systems have an integrated management system that allows the operator to program and save a new style of blank by specifying the diameter, length, and end connection. Blanks can be quickly and easily recalled later when needed to fill an order, and machined into final products by the Matsuura Cublex 42 and Cublex 25 mill-turn systems. The Cublex multiprocess technology provides five-axis milling, vertical and horizontal turning, and optional grinding capabilities.
Each of the Cublex systems used by Kennametal has a pallet hive attached to the machine tool and at least 180 tools in the tool chain. A series of fixtures within the pallet hives allows the operator to set up orders for KM, HSK and steep-taper products. "It has been a big time saver," says Stanko. "While one order is being run, multiple other orders are loaded, queued, and scheduled to run. The only time the machine shuts down is to change pallets. In addition, having a large tool chain along with the pallet hives, externalizes setup time and doesn’t create additional downtime."
Once the systems are set up, they run with minimal operator involvement. Through the use of vision and laser measurement, a robotic material handling system ensures the proper raw materials are presented. One operator services two systems, performing quality audits, feeding material, and removing finished blanks.
"The cell has allowed us to decrease lead times for operations prior to heat treat from up to 14 days to a matter of hours," says Stanko. "Many times we have been contacted by one of our customers experiencing an emergency need. We can now literally walk over to the supermarket, pull a blank, set the blank in a fixture, schedule the part to run next and have the part ready for heat-treat in less than one hour, something that would have been impossible in the past."
Stanko credits the cell with significantly reducing cost. Previously Kennametal had 14 operators and 12 machine tools. Now, with the cell, Kennametal only needs one operator per shift and uses just four mill-turn systems, while producing more than twice the production rate.
According to Mike Kerscher, product specialist, Mazak Corp. (Florence, KY), demand for multitasking solutions with automation are being met by combining Mazak’s HMCs, Variaxis five-axis machining centers, and e-Vertical multitasking machines into its Palletech systems. "With more than 1300 spindles in Palletech systems currently in operation, our customers are familiar with the potential that this automation represents," says Kerscher. Multitasking with automation is identified as the highest of five levels of multitasking that Mazak’s product portfolio delivers.
The Right Combination of Machines
"The challenge always is to identify what combination of machines is the best fit for the customer’s requirements. Our multitasking machines with pallets are well-suited for applications where the principal machining requirement is machining center-based with some turning. It can make a lot of economic sense to combine a multitasking machining center with the right combination of conventional machining centers if turning is a smaller percentage of the work the customer needs done," says Kerscher. The alternative, of course, would be using multitasking machines with chucks that emphasize turning, which are also a staple of Mazak’s product offering.
"Applications for Palletech systems configured with these machine combinations are component driven," says Kerscher. "As manufacturers become more familiar with the unique capabilities of multitasking machines, they are able to be more creative in their part designs. For example, the Orbitec 20-valve production center, which is able to generate turned features on a stationary workpiece, could be paired in the same cell with one or two conventional HMCs, depending on machining requirements," Kerscher points out.
Mazak has employed a multitasking FMS system at its Florence, KY, plant for a number of years. It is now configured with four FH-8800 HMCs and an Integrex e-1060V/8 five-axis multitasking machining center. A headstock for one of its large Quick Turn Nexus models is machined on the e-1060V/8, which has saved cycle time by 11% and reduced three operations to two. "The headstock has some machining center features on it, as well as turned features in the bore. We put it up on its end and turn it and then we’ll send it to one of the conventional machining centers to do some milling of the mounting surfaces and drilling holes where it bolts onto the bed," says Kerscher.
Kerscher believes that as machine tools become more sophisticated, shops are getting more utilization out of the spindles they have, enabling them to get parts through the shop more quickly and be more responsive to their customers. "Higher mix, lower volume production is well within their reach," says Kerscher. "Manufacturers can make any quantity they need and have setups immediately available to them without losing time due to machine setup. They don’t need to make a batch of parts anymore. The challenge is for process engineers to think in nonconventional ways. Programming isn’t difficult. It’s more of an attitude thing for the process engineer to see that there are other ways to produce the same parts."
Mega Parts Machined in Large Cells
Cellular machining of mega-sized parts, particularly with regard to material handling, pose their own special challenges, according to Ken Wichman, application engineering manager, MAG IAS (Erlanger, KY). "One of the things that we’re seeing is a trend toward larger standard machines in cells rather than custom machines. We are configuring cells with large machining centers, boring mills, and VTCs with material-handling systems that typically handle net loads of 7000 kg and up," says Wichman.
"We’re seeing the re-emergence of big machining and boring mills. MAG’s offering includes three large classes of machines: the HMC 1250 and 1600 horizontals, the MC 1250 boring mill, and the VTC 1600. All have net load capacity of 7000 kg and up and can be mixed in the same cell." And on MAG’s drawing boards is a material handling system for even larger machines including the MC1600 and VTC 2000 and 2500-mm models.
"Manufacturers are really beginning to think about automating these larger machines, something that wasn’t thought of too much in the past," says Wichman. "It comes down to keeping spindles turning. Smaller parts have shorter cycle times so you want to exchange them quickly. Big parts have long cycle times, but handling them outside the machine and having something ready to go really is a benefit. It may look like the material handling is hardly ever running, but it’s keeping the spindles busy and that’s important in large-part cells. The challenge, of course, is moving a huge weight around in a controlled and safe fashion."
MAG is using standard machines that require very little modification rather than custom-built machines. The idea is to have a standard machine that you modify very little, if at all, and then integrate a material handling system with it. "It’s a standardized, modularized package. The basic system moves a single pallet at a time. There is an option for a vehicle that carries two pallets at a time, replacing queuing at the machine which saves a lot of floor space," Wichman says.
Large parts require crane loading so operator safety and ergonomics are important considerations. "One thing that we’ve done is lower the pallet into the floor so basically the top of the pallet is at floor level. For example, with a 1250-mm or 1600-mm machine the top of the pallet is 48–54" [1.2–1.3 m] off the floor. With a work envelope that extends almost two meters above the top of the pallet the operator can’t reach very much of it from standing on the floor. Platforms are one answer, but nobody likes going up and down stairs. So hydraulic lift stations to raise and lower loads are an option that we offer to keep the operator in a comfortable position relative to the pallet’s work envelope."
With a reputation earned in the automotive industry, Enshu offers other industries a proven production machine with high reliability and outstanding accuracy. Automotive judges their suppliers based upon the uptime, output and accuracy of the parts coming off a line of machines. To survive in this demanding environment, Enshu designs their machines to a 5000-hr mean time between failure [MTBF] and a 60-min mean time to repair [MTTR] criteria. "Regardless of the industry served, everyone benefits greatly from consistent high output and flawless reliability," according to Mike Germann, national sales manager, Enshu USA Corp. (Schaumburg, IL).
Enshu, a major supplier to Japanese and Korean auto transplants here in North America, celebrated its 90th anniversary last year and with it introduced its new global spec GE Series horizontal machining centers.
Enshu’s horizontals feature the Fanuc 31iMB control, temperature-controlled and refrigerated spindles, ballscrews, and servomotor mounts. Horizontals are shipped with 40-taper 15,000-rpm 29.5-hp (22-kW) spindles and 50-taper 10,000-rpm 40.2-hp (30-kW) spindles. The GE Series features 2-micron positioning full-stroke, with 1-micron repeatability, even with rapid traverse feed rates of 3543 ipm (90 m/min).
In addition to automotive, principal markets for Enshu’s horizontals are aerospace, electronics, firearms, fluid power and medical. "The 31iMB control allows us to use nano interpolation with five places to the right of the decimal point [four in metric]. We introduced cross roller LM guideways back in 2003 and expanded them across the entire GE Series for superior stiffness and rigidity while maintaining the same low coefficient of friction as ball bearings LM guides. All electronics, sensors, and pneumatic components are global spec quick change automotive-type to minimize repair time," Germann points out.
"In general, our evolution is to higher productivity, more accuracy, and thermal stability to obtain an extended operating range for life-long quality output. Because of our automotive experience, we offer customers a higher Cpk and a six sigma capable machine right out of the box. In automotive, we get judged on downtime for an entire line if one machine is down, so we have to extend process control and monitoring beyond the machine itself. Enshu integrates a micro-fine rolling filter conveyor with a magnetic separator and a through-spindle coolant system directly to the control so they can be monitored and controlled just as the machine itself. We are monitoring pressure on the through-spindle coolant and put the machine into a feed hold as the pressure falls outside the limits, plus or minus, before a drill breaks or process control is lost. Same thing holds true for the chip conveyor we are monitoring motor load, chain tension and coolant levels because if you starve a tap of coolant you could break the tap or blow the thread fit," Germann explains.
"A lot of process control and advanced fault recovery are built into our machines, so that manufacturers keep coloring between the lines and don’t run bad parts. If you run bad parts the process stops and downtime is incurred, just as if the machine were to fault out. Process control is everyone’s business, regardless of the industry you serve," Germann concludes. ME
This article was first published in the June 2012 edition of Manufacturing Engineering magazine. Click here for PDF.