Finding the Right Strategy
Processing on multitasking equipment boosts throughput and can reduce tolerance stackup
By Jim Lorincz
There's enough history with the by-now familiar mill/turn and multitasking machining processes for manufacturers to recognize the potential impact on their manufacturing strategies.
Multitasking, multifunction machines operate in single machine, single setup processing. They can also be combined with other machine capabilities such as five-axis machining, or integrated by various forms of automation into cellular configurations with standard machines.
Mill/turn machining and multitasking capability are characterized by increasingly sophisticated software and advanced developments in tooling. At the heart of these choices lie some important concepts:
- At the heart of multitasking is multifunction machining with milling, turning, drilling, boring, and—increasingly—grinding being performed in one setup.
- Multitasking capabilities offer the flexibility to perform complex machining in small-lot and medium-lot size production.
- The measure of success in multitasking is not necessarily reducing cycle time, but rather accelerating throughput.
"Multitasking is a term that can be better understood as a 'start a part, finish a part' approach to manufacturing," explains John M. Judge, executive vice president, Cincinnati Machine (Hebron, KY). "Parts that might sit in queue or in a tote pan waiting for the next operation or operations can be handled by putting them on a machine that can do milling and turning. As a result, multiple handlings, multiple setups, and multiple fixtures are eliminated."
Judge says that multitasking is an enabler of lean, which in turn is an initiative of start-a-part finish-a-part. "It all gets down to how we approach designing solutions for our customers. We look for the best possible solution that Cincinnati Machine and other MAG brands offer whether they are multitasking, vertical, horizontal, or a specific platform."
The objective, Judge points out, is "to get users thinking about the least cost per piece with emphasis on the total life-cycle cost of that part."
To Judge's way of thinking, experience with traditional ways of processing parts is the best teacher. "When you configure operations with multitasking in the lineup, you have to begin thinking in a very different way," Judge says.
"You have to throw away all the conventional wisdom and experience about feeds and speeds and fixturing. The workholding is going to be different. The feeds and speeds are going to be different. In a multitasking machine, you have to be very aware of the dynamics of the part. Processors and programmers have to be very aware of thermals, which in traditional ways of processing parts may have been masked while parts waited in queue to be processed in multiple setups on dedicated machines."
For this reason, Judge says that it is essential that both machine builders and users be aware of the importance of doing runoffs of parts using new multitasking processing techniques. "Machine cycle times, the actual cut time, may be longer, but the real throughput time is going to be significantly reduced. Inventory will be reduced, the total cost per piece will be reduced, and the total cost of ownership of those part families will be reduced," he points out.
Developments in machines and tooling follow a pattern of leap frogging one another that often finds one out in front of the other, says Gerald Owen, national application manager, Mori Seiki USA Inc. (Rolling Meadows, IL). "Machine tools, especially multitasking machines, have leaped ahead and led to development of cutting tools that give users a wider choice of manufacturing strategies," Owen says.
"When you start talking about reducing setups, it generally involves doing the part complete in a single operation. If I can set up a number of parts in a greatly reduced amount of time, the actual cycle time for a part completed becomes less important. I don't have to worry about cycle time. I want a good part first time, every time, and that takes everything, setup, programming, and tools all working together," Owen points out. The important thing is reducing the time from when the order hits the shop floor to the time that the part comes off a machine complete, ready for assembly or shipping, not just reducing cycle time.
"One of the things we are doing is trying to learn how to use these newly developed tools more effectively by adapting them for use on more standard machines. We are doing this by cutting in the Y-axis plane rather than the traditional X-axis plane. We also do this by rotating a turning insert so that we are always entering and leaving the cut and never in the cut for more than a fraction of a second to get better tool life," Owen explains.
Similarly, Mori Seiki is doing something similar with milling tools. "We're taking what's normally a face mill or an end mill and programming it as a turning tool. That allows us to utilize all the horsepower from the milling motor, rotate the tool, the same direction based on specific calculations and drive the horsepower from the milling motor into the turning spindle itself. By doing this we can use the lower turret simultaneously and take a heavier cut than we normally would because we have more available horsepower in the cut.
"By the same token on a Y-axis lathe with a subspindle we can do a lot more with these machines because of advances in control technology like coordinate rotation. Tools like multiheaded tooling stations are designed for an integrated-type machine such as our NT series machines. On a machine with a standard turret such as a Y-axis lathe, the cutting plane is actually indexed or rotated to different orientations through coordinate rotation so that you are then moving in the plane that the cutting edge is designed in. This allows us to use these new tools in a nonstandard way and increase productivity," Owen says.
"We've been successful doing ID work with a tool with multiple stations, typically with a drilling insert, boring insert, and threading insert, each one in a different plane. We use the drilling insert sitting on center like we normally would and drill the part. Since this is a fixed turret machine we rotate the coordinate system so that the X plane is in line with the tip of the boring insert. We rotate the coordinate system around so that even though this is at some odd angle, 120° or 30° off 90°, for example, we're moving in that plane and will touch the part geometry on centerline again. So we rotate the coordinate system instead of the tool. It enables us to use a single tool to drill, bore, and thread and do the same things we would normally do on a multitasking machine."
Mazak Corp. (Florence, KY) has integrated multitasking capability up and down its product lines. It's not just limited to high-tech, high-ticket machines for prismatic or complex parts, such as impellers for the aerospace industry or even pump parts for the oil patch, though those certainly have been good growth areas for Mazak's e-machines.
The Integrex IV series of multitasking machines are in their fourth generation; while the Nexus line of vertical and horizontal machines are taking on multitasking capabilities. The Nexus VCN 510C has a tilting rotary table that gives it a five-axis machining capability, while on the turning side the QTN Nexus 450 MSY will be shown at Mazak's June Energy Expo at its Energy Services Technology Center in Houston with a 2-m boring bar that will drill 1-m holes in shafts.
Integrex advanced multitasking machines marry turning-center and full-function machining center capability to eliminate multiple setups, fixtures, tools, handling, and waiting time. They are known for their ability to machine round parts with secondary operations, fully prismatic parts from solid or castings, or sculptured parts such as aerospace components and molds.
Mazak describes the many benefits of multitasking machining. They include:
- Compress leadtimes from days to hours,
- Reduce lot sizes with no cost penalty, even to lot sizes of one,
- Reduce part costs by requiring fewer fixtures, tools, and labor,
- Reduce non-value-added time,
- Improve part accuracy by eliminating tolerance buildup,
- Reduce shop burden by using fewer machines, space, and utilities,
- Run untended to increase cutting time, and increase throughput and profitability.
The Mazak multitasking lineup of machines includes: Quick Turn Nexus for turning mainly smaller parts with secondary operations front and back; Integrex IV series machines for small to medium range, turn, mill, drill, and tap cylindrical prismatic and sculptured parts; the Integrex e-Series horizontal machines for medium to large range complex part machining in one setup, milling and turning; and the Integrex e-Series vertical for large-range vertical turning plus prismatic, angular, and sculptured-shape machining, as well.
The Nexus machines, which originated in the Florence, KY, plant, are now taking on the mantle of global machine for Mazak, and are being built in its UK, Singapore, and Minakomo II (Japan) plants.
Also new to the lineup is the Cybertech turn Series for large, heavy-duty multitask turning for oil service and other demanding applications. Other machines in the series include: Multiplex/Dual Turn machines with dual spindle and dual turret that can finish all faces of production parts in one setup; Super Quadrex four-axis turning, designed for high-volume shaft work with secondary operations; and IVS Series for production turning with vertical spindle.
It wasn't too long ago that Cessna Aircraft Co (Wichita, KS), a subsidiary of Textron Inc. invested in a combination of multitasking Integrex machining center technology, HMCs, and a Palletech Manufacturing System, to achieve world-class production for its landing gears, primarily consisting of trunnions, trailing links, and barrels.
Trailing links, milled out of steel forgings, required processing on two different machines with a total of five different setups, and took about 40 hr to produce. The five-axis, multitasking Integrex e-1060V machining centers, using standard cutters and running the same processes, produce training links in 6 hr on a single setup.
Single setups are possible on these complex, five-axis parts because the e-1060V's milling spindle can tilt 150° for both horizontal and vertical machining operations as well as angle boring and milling on multiple faces. The main table can turn large diam workpieces in the same setup, further reducing throughput time. The e-1060V is connected to a double-stack Palletech Manufacturing system for automatically shuttling pallets in and out of the machining center, and keeping the spindles turning untended.
Multitasking capability can help manufacturers expand capacity for a diverse range of products, as well as reduce throughput and productivity for a family of products. John G. Wilson Machine Ltd. (Princeton, ON, Canada) machines and fabricates some 3000–4000 different types of parts a year, including urns for cremation, parts for school buses, park benches, cooking woks, and V-belt pulleys. Their primary product is package-strapping dispensers, and they are the world's largest producer of them, turning out 50,000 units a year.
Recently, shop management determined the need to add production capability and had initially considered purchasing several machine tools to handle the existing and anticipated workload. Just as important as capacity, however, was creating a machining solution that not only met production goals, but business goals as well. The Okuma distributor, EMEC Machines Tools (Mississauga, ON, Canada) recommended that the shop consider an Okuma MacTurn multifunction machine.
MacTurn machine technology from Okuma America Corp. (Charlotte, NC) has enabled John G. Wilson Machine to improve the machining throughput of complex parts on a single machine.
The MacTurn Series machines have options such as an expandable ATC, subspindle, lower turret with optional milling, and nine-axis machining/turning functions. At John G. Wilson Machine, the MacTurn machine provided flexibility to produce a wide variety of parts with an ATC with 44 tools in the upper turret, and allowed the addition of untended operation in the third shift.
The shop purchased a MacTurn 250 machine and began to transfer jobs to it. One of them is a 8620 high-carbon steel bearing stud used in a lift-truck application. The part required a varying taper along the full length of its outside diam, and along the length of a hole hollowed in its center.
"We produce 30,000 of these parts per year, and we were producing them using multiple operations on existing machines. It was costly and time-consuming," explains Reg Henry, manufacturing operations manager. The shop saved one and a half minutes per piece by switching the part to the MacTurn. The B axis allows the cutting tool to be positioned at any angle. This, in addition to the full milling capability of the B axis (15–20 hp or 11.1–14.9 kW), gives the shop the ability to produce a wide range of part geometries, even from hardened materials.
Perth Precision (Stratford, ON, Canada) produces some 10,000 chuck bodies annually for wood-turning lathes manufactured by its sister company, Oneway Manufacturing, and other lathe manufacturers. To help reduce machining-cycle time and improve the overall dimensional accuracy of the chuck bodies, Perth management looked for a more-efficient method of production in multifunction machining, to benefit from producing finished parts using one continuous turning, milling, and drilling operation on a single machine.
Perth's experience prior to acquiring the MacTurn-250 had been with traditional forms of two and four-axis machining rather than multifunction machining. Using multiple machines and multiple machining operations, it took about 23-min cutting time to produce one chuck. With the MacTurn, it takes about 11 min to produce one chuck. Also Perth is using an Okuma gantry to load and unload parts, reducing the need for human intervention and reducing the number of operators from four to one.
In addition, Perth Precision has been able to manufacture chuck bodies closer to print specifications. By machining parts in a continuous operation on a single machine, the elimination of multiple setups has reduced error build up during part handling and re-fixturing. "We are able to hold very tight tolerances of 0.0004–0.0005" [0.010–0.013 mm]," says Glenn Voyce, machine operator.
This article was first published in the May 2007 edition of Manufacturing Engineering magazine.