Metalcutting: Milling, Boring, and Drilling
Process improvements key to boosting manufacturing productivity
Faster, more efficient metalcutting these days often means improving the process, not just lower cycle times. Manufacturers today face intense competition, increasing the need for better, more cost-effective solutions to manufacturing problems.
"Today's major trend is moving away from the focus on individual part cycle times," says Jim Endsley, product manager for milling, DMG America (Charlotte, NC). "Manufacturing has traditionally 'squeezed' every second possible out of the actual machining process for each part. Advancements in cutting tools, higher speeds and feeds, and machine tool technology with reduced idle times, have aided this effort, but only to a certain level.
"In the end, engineers are still faced with the same manufacturing bottlenecks as in the past," Endsley notes. "Once a cycle time is achieved, the only alternative left to increase or maintain production quantities is to add more machine tools into the process. This solution adds costs to the process in many additional areas beyond simply the machine tools--costs that are direct 'overhead' and cannot be engineered out of the process."
To boost efficiency, more and more manufacturing is now turning to new processing methods. "Starting with a 'clean sheet of paper,' engineering staffs are now discovering the Universal Machining Method of manufacturing," Endsley notes. "This method simply allows the processing of piece parts without multiple handlings and machine setups. Thus, it greatly reduces the need for adding expensive machine tools to the overall manufacturing process.
"This alternative method combined with the newest machine tool and cutting tool technologies, allows manufacturing flexibility, processing speed, and an overall cost effectiveness that they can rely upon. This mindset is the solution to the problems that US manufacturing is facing in today's global economy."
At IMTS, DMG America will showcase its new milling machines including the Deckel Maho DMC75V milling machine featuring 3500 ipm (88.9 m/min) rapid rates, an 18,000-rpm spindle, and accuracy to 0.0004" (0.01016 mm) anywhere in the working envelope, Endsley notes, with linear-drive technology in all axes.
Boring mill performance has increased as many customers demand the higher throughput expected from many other machine tools. "With boring mills, we're seeing a migration to the performance characteristics of machining centers," notes Ken Campshure of Giddings & Lewis (Fond du Lac, WI). "Even for large part manufacturing, customers are expecting faster traverse rates, acceleration, and spindle speeds. As a result, we're starting to see a shift from box ways on boring mills to the various antifriction way systems such as roller ways or hydrostatics in order to gain more speed.
"Many manufacturers, particularly moldmakers, are requesting spindles that are able to run at high speeds for finishing work," Campshure adds. "They want this in conjunction with a four-speed head offering the low-end torque needed for roughing."
While reduction in maintenance and lifecycle costs is not confined to boring mills, this is also a trend in most product areas, he notes. "One example is the use of better wiring systems, like Profibus. Some of the ways Giddings & Lewis has made life easier for maintenance personnel is the consolidation of gages and fluid levels on one floor-level panel. We also use distance-coded referencing for positioning, which eliminates the need for limit switches. Timing belts, of course, have been known to break. We've replaced some timing belts with gear sets on axis drives. The push for easy maintenance has also reduced the use of hydraulics."
Using high-performance heads adds machining flexibility and has become particularly strong in Europe and in the mold industry here, he adds. "With these types of heads, manufacturers optimize their tooling and reduce the number of setups."
At IMTS, G&L will introduce its new generation of boring mills, a line featuring three types of boring mills including the PT Series (plain table), RT Series (rotary table), and MC Series (palletized boring mill), with a total of six new models available. G&L will demonstrate its RT 1250, 1250-mm rotary table boring mill at the show.
"In developing the new generation, we used a design technique we call Modular Standard," Campshure says. "There are two important benefits with this technique--customers have choices and we are able to offer machines at competitive prices. Among the options manufacturers may choose are various tables, travels, spindles, and controls. The new models incorporate many of the trends we've discussed, including higher traverse, acceleration, and spindle speeds."
Maintenance simplification and reduction was a key design criterion for the new boring mills, he adds. "In addition to consolidation of the gages and fluid levels on the floor-level panel, the gages are marked with nominal operating ranges and lubrication frequencies. The new boring mills have robust protection of important subsystems, including the power tracks and linear feedback."
In addition, a new technique for maintaining ballscrew preload adds axis stiffness. Preload is held constant regardless of a change in the ballscrew length due to temperature. "A proprietary G&L thermal compensation system is important to the accuracy of our boring mills. Without compensation, we've seen spindle displacement of nearly 0.25 mm in our tests. G&L's compensation software dynamically mitigates this spindle growth."
Synchronous feed tapping has become the most popular method of producing threads on CNC machining and turning centers, according to Mark Johnson, president of Tapmatic Corp. (Post Falls, ID). "Its only limitations have been caused by each individual machine's ability to move mass in response to electric impulse," Johnson says. "The laws of physics still apply and every machine has its limits. If the feed rate does not match the thread pitch perfectly throughout the entire tapping cycle extra wear occurs on the tap."
Some manufacturers have addressed this problem by making rigid tap drivers less rigid through the use of soft plastic components or Belleville washers, Johnson notes. "Tap life was improved but durability and tool life were unpredictable. Tapmatic developed SynchroFlex based on a patented, computer-generated, precisely machined double flexure. It compensates both axially and radially for the unavoidable discrepancies between each machine's programmed RPM, feed and traverse, and the exact thread pitch and precise hole location. It's predictable and consistent throughout the life of the tool.
The MDC-500 mill/drill center provides high-speed drilling and tapping, as well as full milling capabilities, in an affordable package. The machine features dual fixture stations that allow the operator to load and unload parts on one fixture while the machine mills, drills, and taps parts on the other. A servo-powered, gear-drive indexer swaps the fixture stations in 4.7 sec. The machine's work cube is 20 X 14 X 20" (510 X 355 X 510 mm), and it uses a 7500-rpm (10,000 and 15,000-rpm optional), 40-taper spindle powered by a 20-hp (15-kW) vector drive system. Other features include high-pitch ballscrews and high-torque servos on all axes, side-mount toolchanger (24+1 tools), 40-gal (150-L) coolant tank with high-volume pump, and Haas CNC.
Milling and Tapping
Milling/tapping centers are available with three working envelopes from 10 X 16 X 10" (254 X 405 X 254 mm) to 16 X 24 X 18" (405 X 610 X 455 mm). Features include rapids of 1900 ipm (48 m/min), maximum spindle speeds of 15,000 rpm, tool changes of 0.8 sec, and a rigid cast-iron frame. Available in 30-taper or 40-taper with either a crown-type turret or a tool magazine with toolchanger arm, the machines have a Fanuc 0i MB CNC.
Tong Tai Seiki U.S.A. Inc.
Company will display its new Agile Oil Hole Drill, a six-axis machine for drilling oil holes in crankshafts or other deep holes in shafts at various positions, angles, and depths. With three linear, three angular, and one spindle drive, the drilling machine can also ball-nose mill or chamfer parts at entry and at exit holes. The design uses servo-fed rack and pinions and/or pivots, providing all positioning while a servo-fed ballscrew feeds the cutting tools. The digital spindle drive provides more than 5 kW of power for two spindles, and individual spindle drives also are available.
Ingersoll CM Systems
The new Romicron fine boring system is designed for finishing high-precision bores by adjusting the tip of the boring tool in a fast, accurate fashion. Unit permits adjustments of 1.0µm on the tool radius without removing the tool from the machine; system is suitable for production applications demanding SPC with 1.33 Cpk or greater. Boring range is 4.0 to 326 mm, and units come in five modular versions for applications with 50-mm diam and larger. System's clearing marked, graduated dial makes it easy to see each adjustment. Definite stops include clicks that allow operator to hear adjustments.
Romi Machine Tools Ltd.
Versatile Trak DPM V Series bed mills feature the ProtoTRAK VM CNC controller and are suitable for small parts, but are said to also possess the mass and weight needed to handle heavy workpieces. The controller allows users to transition freely between manual and CNC operation. Features of the machine include Windows operating system, inverter-duty spindle, electronic handwheels, and AC brushless servomotors.
Southwestern Industries Inc.
Horizontal Boring Mills
Company will demonstrate its next-generation line of horizontal boring mills, replacing its G, H, and PC series machines with new lines including the PT Series, or plain-table boring mill, RT Series with built-in rotary table, and the MC Series featuring additional automation including pallet shuttle and toolchangers. PT Series consists of three models with tables from 1500 X 3000 to 1800 X 4200 mm. Two RT Series models have built-in rotary tables from 1250 X 1600 to 1600 X 2500 mm. The new models are modular in design, with various table styles and sizes, headstocks, controls, attachments, and X-Y-W-axis travel options.
Giddings & Lewis Machine Tools
Machining with Micro Tooling
Featuring a 60,000-rpm spindle and designed for tooling 0.250" (6.4-mm) and under, the VelociRaptor features feed rates to 1000 ipm (25 m/min) and integrated workholding. To ensure X, Y, Z location repeatability, Quick-Pallets registers pallets using a beveled-boss-in-cavity system. A vacuum pump holds the pallet in place during machining. Working envelope is 40 X 30 X 6" (1016 X 760 X 152 mm), and the machine has a 30-tool Automatic Tool Management System. Options include spindles to 4.5 kW, and fourth and fifth axes.
Compact Machining Center
The new compact five-axis DMC 60 T universal machining center offers high dynamics, fast pallet changer, short chip-to-chip times, and optimized work-area design. Company will display productivity improvements with this new machine that features a successful monoblock design with overhead traversing column and has five axes in the standard configuration. Machine's toolchanger provides a chip-to-chip time of 4 sec. Universality is ensured by the milling head with a high-performance 37.5 hp (28-KW) spindle operating at speeds to 12,000 rpm (optionally 18,000 rpm), and with a B axis that can be interpolated with a swivel range of 30º in each direction, beyond the horizontal or, respectively, vertical axes, allowing machining with negative angles.
DMG America Inc.
This article was first published in the August 2004 edition of Manufacturing Engineering magazine.