Turn up productivity with turn/mill machines

This article was supposed to be about all the things you wouldn't want to do on a turn/mill machine. A prime example: you wouldn't want to try to produce

That may have been true in the early days of the technology. "The rule of thumb for years was that milling and drilling should be no more than about 15*20% of total cycle time," says Tim Thiessen, lathe product manager, Okuma America (Charlotte, NC).

But, he notes, that rule applied (and still does) for lathes with live tooling capability, not the current crop of turn/mill machines that feature multiple spindles, multiple turrets, and milling capability comparable to that of some machining centers. Some machines with high-speed spindles are used for grinding; others incorporate operations as unusual as laser welding. All the machine builders contacted for this article told stories of users who make parts with essentially no turning content.

Typical is one from Yusuf Venjara, general manager, engineering, Hitachi Seiki USA (Con gers, NY). He tells of a customer machining small, disposable medical parts from forgings on a VMC with a pallet changer. The operation was switched to a turn/mill machine with a magazine-style bar feeder, and now runs 6-7 hours at a clip untended. "The turning component of cycle time on this part is really limited to feeding the bar," Venjara says. "Everything else is machining center-- type work. They even use a slitting saw for cut off."

Given this blurring of the distinctions between conventional turning and milling machines, Venjara now employs a purely functional definition to answer the question of whether a particular unit is a turning machine or a milling machine. "I base it on how the machine is being used. When the spindle is turning, it's a turning machine. But, when the spindle is stopped, it becomes a fourth axis. So it's all relative."

What's driving machine builders to develop more capable and more complex multitasking machines is the desire of many users to produce on a single machine parts that might previously have required both turning and milling operations.

"The big attraction of these machines is, customers can feed raw material in one end of the machine, and take finished parts out the other end," says Brian Ferguson, lathe product manager, Hardinge Inc. (Elmira, NY). "With the right workholding and handling systems, customers can pick parts out of the machine and place them on conveyors. With a magazine barfeeder, these machines can run untended for hours at a time."

And, making parts complete is naturally more accurate than moving parts from machine to machine or from fixture to fixture. "You have built-in accuracy," says Chuck Birkle, VP, Cybertech Div., Mazak Corp. (Florence, KY). "Whenever you can move the machine around a fixed workpiece, you're on one common datum for turning, milling, drilling and other operations."

Klaus Voos, VP, Index Corp. (Shelton, CT) says the all-in-one machining ability of turn/mill machines can provide a major advantage in an era of small lot sizes and just-in-time delivery schedules. "You can go from raw material to a finished part in a relatively short time compared to multistep processes," he says. "When you have to go through several machines, it can take days to add another operation on the part."

Amplifying this point is Birkle, who urges manufacturers to rethink their definition of cycle time. "Many people believe the primary measure of machining productivity is measured by the time between start and stop on the machine," he says. "But if you take a step back and look at the bigger picture, cycle time is not just the time between the green button and the red button; it's the time between when raw materials are ordered to the time that material is converted into a product for the customer."

According to Birkle, turn/mill machines can help streamline production by promoting a more even flow of components through a shop. "Is machining cycle time lower than it would be on a machining center? Maybe not, but the fact that I can get these parts complete, in ship sets, and I can ship in smaller quantities, is a real key point. It gives many smaller shops better cash flow, and it allows them to fulfill just-in-time deliveries with smaller lot sizes."

But Voos points out that operating such sophisticated machines places a premium on both process development and having the right manufacturing infrastructure in place. "In terms of process development, it's important to find the right sequence of operations, the right tools, speeds and feeds, chip control-all these things are important, and it's more challenging than a conventional process, because you're looking at a lot more tools," he says.

"Operating one of these machines is a bigger challenge for an operator than running a small machine that's just part of a sequence of operations," he continues. "The programmer has more demands placed on him, and procedures for tool preparation, material flow, and other support issues need to be solid."

Programming also remains an issue for turn/mill machines. In fact, as the machines become more complex, programming becomes an even bigger key to productivity, according to Hanan Fishman, vice president, IMCS Inc. (Fort Washington, PA). He claims the company's PartMaker software was the first CAM system developed "from the ground up" for programming turn/mill applications.

"Other CAM systems focus largely on two-axis turning and milling," Fishman says. "But turn plus mill does not equal turn/mill. A turn/mill machine has a number of different coordinate systems at work for performing different types of milling operations. Users of turn/mill machines know which coordinate system they want to use, but they need an intuitive means of handling them."

IMCS's patented Visual Programming capability "lets users literally `divide and conquer' a part," Fishman says. "On these kinds of parts, you may have some turning work, some drilling of off-center holes, some polar interpolation [rotational indexing of the spindle], and milling on the part OD. When you program a part in PartMaker, you break down the part into its most basic elements. In one window, you perform all turning operations, in another window, you program all polar interpolation in another window, you program all your OD work, and so on."

The software then lets users resequence operations using what the company calls a Process Table, which shows all operations and lets users point and click to reshuffle them to get the optimal cutting sequence. The table tracks both the time needed for each operation and total machining time, giving users a reliable picture of cycle time before they cut the first part.

Another difficulty when programming the increasingly common twin-spindle and/or twin-turret machines is synchronizing the simultaneous operations, according to Fishman. "These machines can essentially do the work of two machine tools, but it's not as if you have two separate machines," he says. "The programs need to be linked through synchronization ["sync"] codes. Our software uses Visual Synchronization, which lets users click on a picture to choose the kind of synchronization they want to perform. The most common type of synchronization is where one turret is cutting on the main spindle and one is cutting on the subspindle."

One user getting a lot of mileage out of PartMaker software is Slabe Machine Products (Willoughby, OH). The 100-person shop has invested in turn/mill technology for some time with the goal of machining parts complete in a single setup. Slabe's lineup currently includes twin-turret, twin-spindle machines from Hardinge and Nakamura-Tome.

With the complexity of its machines on the rise, Slabe realized it had to address programming, according to VP Brendan Slabe. "As more and more jobs go to the turn/mills, PartMaker greatly simplifies programming so we really can 'drop them complete.'"

The software's visual approach lets Slabe programmers handle the live-tooling capabilities of the turn/mill machines, and supports simultaneous machining capability by giving them the ability to perform process synchronization in an intuitive manner. The program automatically inserts "Wait" or "Sync" codes into the NC code it generates.

PartMaker may be the first software developed specifically for CAM on turn/mill machines, but the field is becoming more crowded. Just introduced at last month's Detroit Advanced Productivity Exposition-an SME-- sponsored trade show-is the latest version of GibbsCAM. Developed by Gibbs and Associates (Moorpark, CA), the package provides all-new support of mill/turn programming. But development of the new capability wasn't easy, according to company founder and CEO Bill Gibbs.

"The minute you step across the turn/mill line, you kind of go through the looking glass," he says. "Before, everything was either a mill or a lathe; everyone understood what they were and what they did. But when you cross that turn/mill line, suddenly no two manufacturers build the same thing. Each builder has a spin on what's more effective and more marketable. And while there are some general groupings of popular features, it's dangerous to get hung up on a rigid machine definition."

Gibbs overcame this problem by developing a piece of software that lets the person setting it up define the machine in terms of the number of turrets, slides, and spindles it has, where these components are all located in space, and a variety of parameters such as rapid traverse rates and feeds. This machine definition document (MDD) is the first thing users select, so the software knows up-front which machine is being programmed.

Machines with subspindles and multiple turrets also create what Gibbs calls "significant process management issues." To address these concerns, the company developed what it calls utility operations. "Normally, we define an operation as a tool cutting something," Gibbs says. "But a utility operation doesn't cut; instead, it allows the programmer to take discrete control graphically over things in his machine that don't cut metal-for example, a tailstock or a subspindle, or a barfeed, or part loading/unloading. The programmer needs to have discrete ways to represent these things in the program flow as he generates the program.

Finally, GibbsCAM addresses the issue of synchronizing simultaneous operations using a drag-anddrop interface called a Sync Dialog, which gives programmers the ability to see the program with every operation represented in real time. Users click on the items they want to start and end at the same time, then resequence operations to optimize the job.

"Our typical user sits down and draws some shapes, places them on the screen where his spindles would be, and creates some milling and turning operations as he would on a simple machine," Gibbs says. "Then, as a final step, when he has the components of his program, he can optimize the job in terms of time and flow, and see a full graphic visualization of what the machine is doing."

Users of NC verification also now have new capabilities for turn/mill simulation and visualization. VeriCut 5.1 software from CGTech (Irvine, CA) can simulate and verify turn/mill machines, including simultaneous display of the entire machine tool and cut stocks. The package supports multiaxis, synchronized machining with multiple tools, according to the company's Bill Hasenjaeger.

In the new release, all machine components attached to the machine spindle automatically spin during turning operations. Thus, when the spindle is turned on, nonsymmetric components such as three-jaw chucks, fixtures, and nonsymmetric stocks become realistic "spun" models. During mill/turn machining, the turning operations dynamically update the milled stock, and milling operations update the "spinning" stock used in turning operations to provide what Hasenjaeger says is the most accurate turning and mill/turn production machine simulation available.