One-Hit Wonder Takes Off
Every cycle produces a part machined complete
By Jim Lorincz
In major league baseball, a one-hitter is almost always a sure winner. Unfortunately, there are a lot of ways for the other team to score runs. A one-hit masterpiece can be pitched in a losing cause. In multitask machining, also referred to as done-in-one and one-setup clamping, a part is machined complete with each cycle.
The one-hit multitasking process produces a winner every time.
That's why multitasking is one of the hottest machine concepts for producing quality complex parts for industries as diverse as aerospace, oil and energy, medical, and off-highway, construction, and farm equipment, as well as general engineering.
"Multitasking machines [MTM] consolidate operations in one setup, make more efficient use of a company's resources, realize the pursuit of done-in-one and one-pass machining, minimize tolerance stack-up, and eliminate repetitive fixturing and dead transportation time, as well as accelerating throughput time," explains industry consultant Bert P. Erdel, technology advisor to DMG America Inc. (Schaumburg, IL).
Multifunction machines began with slant-bed CNC lathes with turrets for live tooling and turning tools, and have evolved into two general classes of multitasking machines. The turret-type is more closely identified with the lathe for turning workpieces on-centerline. Tooling in single or multiple turrets enables multifunction processing with milling, drilling, tapping, hobbing, and boring functions, among others.
The second type of multitasking machine is more closely related to machining centers with turning capability. They have powerful milling spindles, which are capable of B-axis off-center machining of workpieces. The B axis allows rotation around the Y axis for drilling at an angle or contour milling.
Trends in multitasking processes follow advances in technology:
- Larger parts are being processed on machines with beds to 6—8-m long with longer, often programmable, vibration-damped boring bars.
- On-machine probing monitors tools and workpieces to minimize human intervention and ensure quality production.
- Simulation software is available to prove out possible machine interference issues before programs are run, and on-machine crash avoidance software ensures real-time, uninterrupted operation.
- Tooling is being developed to minimize change time and maximize available use of positions in turrets and magazines.
"Nowhere have multitasking processes taken hold more than in aerospace, where costly part material and workpiece complexity find fertile ground for multitasking/multi-axes machines," Erdel says. "For example, the DMG GMX linear multitasking turn-mill centers offer finish-machining of turbine blades with accuracy, speed, and productivity. This is made possible by the simultaneous drive of the angular B-axis range of 30—120° in combination with precision part clamping and counter holding. The result is complete six-side machining of the blade, including finishing blade roots and grooves."
Typically, the largest markets for WFL Millturn Technologies (Novi, MI; Linz, Austria) have been aerospace both in jet engines and in landing gears. "Last year may have been an exception to that as we sold over 19 machines just for large crankshafts worldwide," says WFL's Ben Baggerly. "That's a big market now, not just for engines, but also for pumps and compressors. The energy market overtook aerospace as our biggest market." Oilfield applications include tubing hangers, well-completion tools, and components for wind turbines, and for applications such as control rods, pumps, and motors for nuclear power generation.
WFL has extended the bed of its large M150 machine from 6.5 to 8 m, enabling it to machine workpieces 60" (1.5-m) in diam that weigh up to 33,000 lb (14,968 kg). "For multitasking to be really productive, on-machine probing is something that is too often underutilized. We have developed more than 100 probing cycles in our machines for such things as accurate true position on bolt-hole patterns or measuring crankpins on a crankshaft," Baggerly says. Also, WFL has added simulation software that enables the user to have a 3-D model on a PC to test programs before they get to the machine. The company's CrashGuard option provides real-time on-machine collision prevention.
"The aerospace industry, which generates complex shapes for blades and blisks and some of the larger parts such as landing gears, is benefiting from longer machine beds and the availability of long boring bars," says Mark Mohr, VP, Mori Seiki USA Inc. (Rolling Meadows, IL). Typical materials being machined include grades of titanium, Inconel, Hastelloy, and Waspaloy.
"We have developed machines such as the NT 6600 with its 6-m bed with multiple steady rests and long boring bars that are carving out applications in other industries, such as the printing and roll industry, because of the machine's ability to run large parts and utilize multiple tools," says Mohr. The NT series of integrated machines combines turning and milling functions with simultaneous five-axis control and employs DCG (Driven at Center of Gravity) technology and box-in-box construction, along with the turret with a built-in milling motor, and direct drive B axis.
The difficulty of finding skilled operators for multitasking machines has been addressed by Mori Seiki by developing a training module for its NT series available through the online curriculum of the company's training enterprise, Mori Seiki University. "In this way, the operator has been exposed to the initial learning needed, and can go to class and learn about the machine tool with some background and knowledge of the processes involved," says Mohr.
Training is important because multitasking machining requires a different approach to processing parts and programming. "The mentality which assumes that the same sequence of operations that works on conventional machines will work on a mill turn couldn't be further from the truth," says WFL's Baggerly. "With a mill turn, you have to step back and re-think how the part is processed. The real challenge is to think of the best way to utilize the capabilities of the mill turn, and write the program that way."
No one doubts that programming is not as straightforward as that for conventional turning and milling. "In our view, a multitasking machine is any machine capable of doing more than one different machining operation, usually milling and turning, concurrently. This separates multitasking machines from traditional four-axis lathes, multispindle milling machines, or single-tasking mill/turn machines," according to Bill Hasenjaeger of CGTech (Irvine, CA).
"A multitasking machine often has more than one workholding station, such as a main part spindle and a subspindle. The spindles often have unique configurations, maybe the subspindle is actually mounted on one of the toolstations or turrets. Multitasking machines tend to cram many tool and part-mounting stations on different axes into a relatively small space. The motion complexity is high, with several things moving at once, making the chance for collisions between machine components, tools, and parts very high. Hence, off-line simulation prior to committing the NC program to the machine is practically mandatory," Hasenjaeger explains.
Auxiliary components such as programmable tailstocks, steadyrests, parts catchers, or exchange mechanisms, and automatic head or tool-attachment changers that are likely to be encountered add to the complexity. "These can all be simulated in Vericut, including complex behavior such as the mechanical advancement of the tailstock or steady rest until it touches the workpiece. Simulation of the spindle status is also important in these machines: knowing when the part spindle is spinning, or when it is indexing or stopped, when the tool spindle is spinning, checking if they spin in the correct direction for proper cutting, etc."
Bill Gibbs, president/founder, Gibbs and Associates (Moorpark, CA), points to the fact that due to the complexity of programming multitasking machines, they were often relegated to large-volume production. "When using them, it was just too costly to program these devices and not get a reasonable return through production volume." However, the lot size of these machining runs are starting to get smaller and smaller. "Manufacturers are beginning to view multitask machining as a way to improve overall part quality and do so cost effectively in small-lot sizes. In addition, parts being machined on MTM devices are becoming less and less axially oriented. This highlights the multitask machine tool's versatility, and only continues to increase market demand for these devices," Gibbs explains.
GibbsCAM now has a five-axis option that supports B-axis live tooling, and the software's Machine Simulation module can simulate and validate programs prior to running them on the shop floor. Machine Simulation also allows machine tools to be virtually set up, proving out setup parameters and making machine time more productive.
Cutting tool manufacturers have taken up the challenge of multitask machining and adopted several approaches to optimizing tooling. "We started with turning tools to use the B axis on a 45° angle that grew into the CoroPlex TT, the dual-point turning tool with 180° index to have another cutting edge," explains James Grimes, Sandvik Coromant Co. (Fairlawn, NJ). "We introduced two styles. The 45° style could be used to shorten the length of the tool and get the B-axis spindle closer to the workpiece to avoid interference with chuck jaws or tailstock, or some other peripheral item. The 90° style would be a longer tool that could be used for turning or boring."
For multitasking, Sandvik Coromant's CoroPlex MT is a combination tool that has two turning inserts 180° apart, across from two milling inserts so that the tool can be a two-flute 390 cutter or a two-edge turning tool. Simply indexing the tool 90° changes the process from milling to turning, or vice versa. The CoroPlex SL line allows the user to build a mini-turret, creating a station with four different cutting heads. "It's especially important for end users who have a limited number of pods in the tool magazine. The user can save four pods by using two different turning tools, a threading tool, and a grooving tool on one miniturret. It also reduces tool change time and allows loading redundant tools," Grimes explains.
Rather than running MTM machines with standard tooling that would take up more space and indexing time, Iscar Metals Inc. (Arlington, TX) works with its customers to produce a semi-custom tooling solution. Michael J. Gadzinski, national training manager, explains: "We would rather make a semi-custom tool for them that can use standard inserts. In the long run, that's the most cost-effective approach. We try to provide a tool that will make their part faster and more accurately, with faster cutting speed and feed rate to reduce their cycle time."
Iscar begins by working with the end user right from the beginning. "We prefer to do a process layout based on the parts the customer intends to make on the machines," Gadzinski explains. "We'll take a part print as an example, and ask how many different ways can we combine tools into one station. Although most of these machines have quite a few different tools that are available in the turret, we try to come up with something that can do threading, facing, OD turning, boring, and drilling—all in one setup."
Multitasking machining continues to make inroads in small-parts machining, especially for medical applications. Mazak Corp. (Florence, KY) has introduced the Integrex i-150 multitasking center for one-clamping machining of small complex parts, such as those typically found in medical device manufacturing, or for high-precision component machining involving round, square, or angular features.
The i-150 configuration consists of a single horizontal 15-hp (11-kW) main spindle for turning, and C-axis control with a 6" (152.4-mm) through-hole chuck. Bar capacity is 2.56" (65 mm). Machining center capability is provided through an integral 100-hp (74.6-kW), 12,000-rpm milling spindle mounted on the vertical rotating B axis. The B axis features a roller cam, non-coupling design, and an absolute feedback scale for high-accuracy positioning, and five-axis contouring through a -10 to +190° range.
The i-150's internal workholding system is said to allow more operations in one setup, more consistent accuracy, and the opportunity for untended operations over longer periods. The workhandling device acts both as an NC tailstock and a workholding vise to pick the part from the spindle, index it to 45° or 90° for angled or backside operations, and then unload finished parts onto a conveyor. A front-loading tool magazine houses either 36 or 72 tools that are within reach of the operator, even while the machine is cutting.
Multitasking is especially beneficial with large parts where a part may be too large or awkward to rotate. According to Ken Campshure of MAG Giddings & Lewis (Fond du Lac, WI), spindle utilization can be maximized and the number of required setups reduced in machining large parts through the use of attachments or options.
Campshure outlines the process: "Horizontal boring mills [HBM], for example, use programmable boring bars or contouring heads to add turning capabilities to the traditional milling and drilling operations. The Z-axis movement of the spindle, actuated by the CNC control, moves the cross slide of a contouring head or programmable boring bar. The rotation of the HBM's live spindle turns the tool. The W-axis table movement provides the axial feed of the workpiece.
"Because the attachment is a programmable axis, it is possible to produce part features of varying sizes. A part with several different bore diameters may be machined with one attachment. This approach saves not only cycle time but tooling costs as well, since fewer tools are required. Other part features possible with attachments include tapers, grooves, threading, back-spot facing, contours, chamfers, facing, recessing phonograph finishes, and profiles."
These attachments can be automatically changed. For example, MAG Giddings & Lewis' HBMs, including the latest floor-type boring mills, the FT and FTR series, achieve this with a standard toolchanger or attachment rack, depending on the attachment size.
Okuma America Corp. (Charlotte, NC) has introduced its Multus 400, which consolidates turning, milling, and material handling operations into a single machine. The Multus 400 is designed to hand the part from one spindle to the other to complete milling and turning operations without removing the part from the machine. The Multus 400 features Collision Avoidance System software that can run the entire machining simulation and catch potential collisions before they create scrap in combination with Okuma's THINC-OSP control.
The RatioLine series of multitasking mill-turn centers from Index Corp. (Noblesville, IN) takes a modular approach to produce different configurations, ranging from production turning to turn-mill centers for processing large and complex workpieces. The model G250, equipped with a heavy motor spindle as a tool carrier in conjunction with a tool changer, allows complex parts to be produced from bar. The G250 has a 27.5-kW motor milling spindle that takes heavier work than typical live tools. The heavy milling spindle allows a much larger tool capacity (maximum 80) and higher-speed milling. The G250 can handle diam to 150 mm.
This article was first published in the April 2008 edition of Manfacturing Engineering magazine.