Production Mission Evolving
Small lot sizes, parts gain focus
By Jim Lorincz
Multitasking technology offers the ability to tailor production of parts machined complete in one chucking to better match manufacturer's shipping, and therefore, cash flow. "Instead of shipping all the parts at the end of the month, Done In One allows shops to make partial shipments at the end of every week, to manage their cash flow," says Chuck Birkle, vice president, Mazak Corp. (Florence, KY).
It's still another plus for a technology that includes machines from the simplest mill-turns to the most ambitiously equipped multispindle and multiturret versions with Y and B axes that are able to put multiple tools in the cut simultaneously.
Multitasking machines can bring multiple tools to bear on workpieces, often simultaneously, for done-in-one machining. Turning and milling are, by far, the most common cutting processes. Increasingly, they are being joined by other processes including grinding, hobbing, polishing, and inspection.
The benefits of multitasking technology are well known:
- Done-in-one machining
- Reduced setup time
- Increased accuracy
- Untended operation potential
- Minimal operator handling
- Better throughput
- Leaner operation (less waste, less WIP)
Multitasking technology is based most often on lathe or milling platforms, each with its own production strengths and limitations. Bar feeding readily automates CNC lathes. Machining centers benefit from fixturing with trunnions and rotary tables.
"There are a number of trends that we see," says Birkle. "Customers are coming to us and wanting multitasking machines that are small with a compact footprint with the accuracy for machining complex precision shapes typical of medical parts. The majority of these parts are machining-center-type parts with high-rpm milling requirements."
At the other end of the spectrum, the energy industry is asking for machines that can handle the largest components for components for wind turbines. Birkle explains: "Multitasking machine technology can be used for parts that you can hold in your hand or parts that are the size of an office."
For machining small complex precision medical parts, Mazak introduced its compact-footprint i-150 multitasking machine. For the largest wind turbine parts, Mazak has introduced the new Integrex e-1850 single-table machine for machining parts with a maximum diam of 3.5 m and weighing up to 15 tons (13.6 t).
"Once customers accept multitasking, they start asking up to help with other functions, such as hobbing, grinding, polishing, and the like. A function like hobbing isn't going to replace gear-cutting machines, but for some features, it's nice to have," says Birkle.
The grinding and hard-turning combination in machines from United Grinding (Miamisburg, OH) is effective in both high-volume applications and conventional general engineering work.
"Our hard turning/grinding machines have the flexibility to produce high precision parts by preparing parts for finish grinding with hard turning. Hard turning can access areas of parts that are typically not accessible to grinding wheels," says Hans Ueltschi, vice president, United Grinding (Miamisburg, OH).
For high-volume automotive applications, the Schaudt CombiGrind with high-speed spindles is available in two versions, vertical and horizontal. The horizontal version is similar to the Studer S242, and performs inner and outer diam grinding, hard turning, drilling, brushing, and gaging in one setup of automotive components and subassemblies like gearshafts, shaft drives, motor shafts, and turbochargers.
For conventional applications, the Studer S242 machine is capable of turning various shapes and forms, minimizing setup times for complete machining of parts. Combined processes include external grinding, internal grinding, turning, grooving, thread cutting, milling, drilling, and back and front-end facing. Typical applications include transmission shafts, HSK or ISO toolholders, and pump gears.
"The challenge is to recognize appropriate workpieces for these machines," says Ueltschi. "We can reduce setup time, and, because of the flexibility of the programmable tailstock, we can handle a variety of workpiece sizes, especially when machining very small lot sizes."
Ueltschi cites the example of toolholders: "In the case of high-precision bores, for example, toolholders, which are long workpieces with small-diam bores, can be precisely preturned and then finish-ground to achieve more accurate cylindricity than you could get by grinding alone."
The Matsuura Cublex machines from Methods Machine Tools Inc. (Sudbury, MA) provide five-axis milling, turning, and grinding. "Cublex technology addresses industry demand for multiprocess machining capabilities in a single workcenter that is tailored for the small-lot production of highly complex parts," explains Vice President Dave Lucius.
The two Cublex models are the Cublex 25 PC 40 with a maximum work size of 9.8" diam x 9.8" high (249 x 249 mm), 5.2" (132-mm) pallets, a field expandable 40-pallet changer, and a 15,000-rpm spindle. The larger Cublex 42 PC 24 has a work envelope of 16.7" diam x 13.7" high (424 x 348 mm), a field expandable 24-pallet changer with a 12" (305-mm) round pallets, and a 12,000-rpm spindle.
"Our customers began to realize the big advantage of the Cublex platform for processing smaller lot sizes. You can think of the Cublex as a B-axis lathe that can automatically change up to 40 different chucks with expandable tool capacity. It also offers the full five-axis high-speed machining capability of a machining center," says Lucius.
The B200 is the latest addition to the line of Multus Multitasking machines (joining the larger B300 and B400 models) from Okuma Corp. (Charlotte, NC). "The B200 is designed for smaller complex components like medical and small aerospace parts. Parts are typically hand-held size, and standard workholding is a 6" [152-mm] chuck," explains Rod Tojdowski, applications engineer.
The B200 Multus can be configured in a variety of ways: main spindle on left-hand side and subspindle on the right-hand side. "If the majority of your work needs support and you don't need a right side spindle, you can get the machine with a right side tailstock. For those choosing two spindles, the left and right spindles can be configured to meet the customer's requirements."
Spindles available are standard bore and big bore with each side specific to the needs. The Multus line has an upper H1 turret that can accommodate turning tools and rotating tools which includes a toolchanger behind it. In addition, a Renishaw tool probe tool can be used for in-process gaging.
"The Okuma OSP 200 CNC control is the basis for all Thinc applications. The Thinc control supports the Partners in Thinc alliance with more than 30 suppliers of auxiliary equipment ranging from coolant management, automation for loading and unloading parts, monitoring communications, in-process and postprocess gaging, tooling presetter, tool storage management, among many others.
"Complex surgical tools, implants, and other medical apparatus can be machined with a reduction in part processing time of up to 70%, with superior quality, finish, and cost efficiencies by employing a Model MC 726 MT five-axis CNC milling/turning center from Stama America (Itasca, IL). The reason is the MC 726 MT's ability to provide continuous precision production from bar stock of a mix of parts, including machining of the sixth side.
In bar-feeding applications, the material stock is fed directly to the rotating/swiveling positioning trunnion. Drilling, milling, and turning operations are performed on both vertical and horizontal spindles.
In application, the 9-axis MC 726 MT cuts the bar in one clamping, including milling, turning, and swiveling the part to machine the sixth side. Other machines in the Stama System 7 series can perform six-sided machining with a secondary, CNC-integrated counter-spindle that allows reaching any dihedral angle in a hemisphere. Models are also available with tailstock or jaw-chuck assemblies.
The new CTX beta TC and CTX gamma TC series of turning/milling centers from DMG America Inc. (Itasca, IL) are designed for complete machining of workpieces from 49.2 to 78.8" (1250–2000-mm) long, turning diam up to 24.8–(630 mm), and a bar capacity to 3" (76-mm) diam. Throughput and versatility are ensured by the integrated disk magazine with a fast toolchanger and space for 24 tools on the CTX beta TC model, or 36 tools on the CTX gamma TC.
The heart of the DMG mill-turn machines is the integrated moving column with a turning/milling spindle and interpolating B axis. Machines features a mobile column horizontally fitted on the Z axis for best application of force.
The NC-controlled B axis swivels in the range of ±100° for five-axis simultaneous milling. Programming is supplied via either a Siemens 840D CNC with ShopTurn programming or the Heidenhain PLUS iT with DinPlus or TurnPlus (optional) software.
For production turn-mill applications, Index Corp. (Noblesville, IN) has introduced its C200 series production turn-mill center in two spindle sizes for 65 and 90-mm bar capacity for main and counterspindles. "Three driven tools form the machine's 42-tool complement can be on the work simultaneously," explains Lars Hermann, vice president.
Typical applications for the C200 include automotive components, fittings, fluid-power parts, and medical devices produced in small-to-medium lot sizes. The C200 features three 14-position tool turrets, 160-mm chuck sizes, and identical main and counterspindles with 25/33 kW and 23/31 kW (100%/40%) for the 65 and 90-mm models, respectively. Each of the 14-station turret positions is equipped for driven tools.
Up to three tools can be at work simultaneously with both Y axes and backworking at the same time. The counterspindle with a driven Z axis can be synchronized with the travel of turret three. Counterspindle pick-up from the main spindle is accomplished in 1.5 sec.
"Simultaneous machining with two Y axes, one at the main spindle and one shared between the main spindle and the counterspindle, gives users the option to divide machining operations for the best machining efficiency and flexibility," Hermann points out.
Mori Seiki USA is introducing two multitasking machines for machining small precision parts, one based on the lathe model and one on the milling-machine model. "The two new machines build on our success with the NT line of multitasking lathes and the NMV line of multitasking machining centers," explains Detlef Streichert, application engineer.
"The NT1000 is the smallest of Mori Seiki's integrated NT Series machines, providing exceptional compact multitasking machining. With a footprint of only 58 ft2 [5.4 m2], the NT 1000 is ideal for high-precision medical workpieces.
"For Mori Seiki's customers that feel more confident with a milling-type machine or where small delicate parts cannot be bar-fed, the NMV 3000DCG based on the milling model is being introducedand has X-axis travels of 19.69" [500 mm] and can accommodate workpieces up to 220 lb [100 kg]," says Streichert.
The MX1600/2100ST multitasking series from Doosan Infracore America (West Caldwell, NJ) has been redesigned for increased performance, reliability, and ease of maintenance for machining aerospace, automotive, defense, medical, environmental, and general engineering parts.
For speed and accuracy, machines feature 100% roller-type linear guide-way. Horsepower and torque specifications have been increased on both milling and turning spindles, and the milling work envelope is larger with Y-axis stroke of over 9" (203-mm). The B-axis tilting head components are larger to provide more rigidity and driving torque.
New features include innovative thermal error compensation and electronic "air-bag" function. In the event of collision, the control instantaneously reverses the movement of the axes to mitigate damage.
Multitasking Retires Multiple Machines
One of the real promises of multitasking technology is its ability to do complete machining on one machine—work that has been done on multiple dedicated machines.
Richard Parenteau of Methods Machine Tools relates how one hand-tool manufacturer increased its production of a spindle shaft used in one of its products from 60,000 pieces to 85,000 pieces per year to meet increased demand, without purchasing additional dedicated machines. "For many years, the manufacturer had run two 10-hr shifts per day to produce the spindle shaft. The part had three operations: blanking and qualifying on a bar-fed turning center; milling on a VMC with a fourth axis; and finish milling and turning on a mill-turn. Total cycle time was 5 min, 10 sec. Takt time for the VMC was 3 min, 20 sec.
"To meet production demands, we determined that the VMC—with the longest cycle time—was the area to pursue. The latest mill/turn, the Nakamura-Tome NTY-3 multitasking turning center was selected. This machine features opposed twin spindles with three turrets and 9.5-hp (7-kW) milling on all turret stations, all with Y axis capability.
The part is now produced on one machine that is capable of all three operations. A part is made complete in 2 min, 15 sec, a 50% reduction in cycle time. There is a bar feed main spindle with two turrets simultaneously milling the vane shape. The second spindle is for finish turning and milling the drive square at the same time on the machine.
This article was first published in the May 2009 edition of Manufacturing Engineering magazine.