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Tasked with Success

Kip Hanson
By Kip Hanson Contributing Editor, SME Media

Machinists have long recognized that the most efficient way to make parts is to complete them in as few operations as possible—preferably just one. Doing so eliminates the need for downstream fixtures and other types of workholding, thus decreasing costs. And, as clamping parts for secondary operations introduces positioning errors (not to mention potential damage), accuracy improves when they’re “done in one.”

A PUMA SMX -2600ST multitasking lathe cutting a helical gear. (Provided by DN Solutions)
A PUMA SMX -2600ST multitasking lathe cutting a helical gear. (Provided by DN Solutions)

In addition, there’s no work in process with parts finished in a single operation, nor is there a risk of scrapping a job that took weeks to move through the shop. And multitaskers take up less shop floor real estate than the multiple machine tools that would otherwise be required to complete most parts.

Other benefits of multitasking CNC lathes, include:

  • Once set up, multitasking changeover times typically are measured in minutes rather than hours.
  • With capabilities such as gear cutting, metal deposition, laser machining and additive, shops can bid on work that might otherwise be a no-quote.
  • Unattended/lights-out machining is much more feasible with a multitasking lathe and its array of cutting tools.

Multitask systems have set a new standard in CNC turning. Parts come off the machine ready to wash, pack and ship. But becoming a multitasking shop requires careful planning. To better understand the complexities, benefits and requirements of multitask lathes and turning centers, Manufacturing Engineering (ME) queried six industry experts.

Two is Less Than One

We started by asking Joe Wilker, product manager at Florence, Ky.-based Mazak Corp. (owner of the trademarked “Done in One” term), a fundamental question about the growing popularity of multitasking.

ME: Some might balk at a multitasking machine’s high price tag, arguing that they can buy two or even three machines for the same amount. What do you tell them?

Wilker: I would counter by asking, “How can you afford not to buy a multitasker?” The traditional approach of processing parts through three or four different machines is costly. You have multiple programs, multiple setups and multiple operators, each of which adds expense and presents a potential failure point. With a multitasking machine, you load a chunk of raw material and come back to a finished part, ready to ship. Cash flow improves, and because you can complete so many operations in one machine—turning, drilling, five-axis milling, gear cutting and more—the flexibility is unbelievable compared to more conventional machines.

The MULTUS U3000 multitasking machine from Okuma is said to improve accuracy and decrease total cost of ownership in a more compact footprint. (Provided by Okuma)
The MULTUS U3000 multitasking machine from Okuma is said to improve accuracy and decrease total cost of ownership in a more compact footprint. (Provided by Okuma)

ME: What kinds of work are most of your customers doing with multitasking?

Wilker: It depends on the type of part, but I can tell you that job shops will typically load the machine up with all the tools and programs needed to run a bunch of different jobs and just leave them set up. Changeover is then a matter of swapping out the workholding, calling up the program and hitting cycle start. It’s for this reason that I usually recommend customers buy the biggest tool magazine they can afford, because it allows them to run more jobs without interruption.

ME: Are you suggesting that multitaskers are limited to the low-volume, high-mix jobs typical of most job shops?

Wilker: Not at all. I just worked with a customer who invested in one of our HQR machines, which is a twin-turret, twin-spindle configuration. They’re running a family of six parts with bar stock coming in one end, a robot packing parts on the other, completely unattended. Multitaskers are also becoming quite popular with many of the large OEMs, which are replacing their multi-machine cells with a single multitasking lathe, robot, wash station and a CMM.

Tooling Up

As the application engineering manager at DN Solutions America, Pine Brook, N.J., Robert Appleton offers similar advice. He begins by suggesting that shops take a hard look at tooling needs when purchasing a multitask unit.

ME: Investing in high-quality tooling is good advice on any new machine purchase. How are multitaskers different?

Appleton: When a customer moves from a machine with CAT or BT tooling to one with CAPTO or HSK, there’s an investment they should be made aware of, especially if they’re trying to maximize productivity. This is why we offer discounts on tooling packages with new machine purchases. And because multitaskers are so productive, shops should also plan on using high-quality cutting tools designed for this type of work, even though these might cost a bit more.

ME: Are there any large investments other than tooling, training and the machine itself?

Appleton: An offline tool presetter helps reduce downtime on any machine, but considering the higher burden rates of a multitasker, it’s even more significant. First-timers should also plan on a fairly lengthy ramp-up period. I’ve seen many customers over the years go from a manual lathe or knee mill where they’re cranking handles to a twin-turret, live-tool machine that is completely automated. It can be overwhelming, and in my experience, takes about three months or so until they get comfortable. That said, I think multitasking is getting much easier than it once was. Not only are the younger people less intimidated with advanced technology like this, but the controls are friendlier than they once were.

ME: I’ve heard that multitaskers—at least those with an ATC—are slower than traditional CNC machines, making them less effective on smaller parts with short cycle times.

Appleton: There’s some truth to that, but you have to look at the big picture. Yes, the smaller the part, the faster you can make it on a single opportunity machine. But unless you can drop it in complete, you’re back to secondary operations with their additional fixturing costs, work-in-process, loss of accuracy, reduced flexibility, increased handling and all the other arguments for multitasking. And on larger parts where the cycle time is long, you can stick a robot in front, load it up for the night and go home. It’s hard to compete with that.”

Milling True

David Fischer, lathe product specialist at Okuma America Corp., Charlotte, N.C., notes that automatic-tool-changer-type (ATC) machines with a true milling spindle (such as Okuma’s Multus series) are best for high-mix, low-volume work, while a twin-spindle live-tool lathe with two or even three turrets is often preferred for high production machining.

ME: How would you define a “true milling spindle.”

Fischer: A true milling spindle is just like it sounds—the same type of spindle you’d find in a machining center. In our case, that means speeds of 12,000 rpm and higher, as well as an automatic tool changer equipped with Capto tooling. But because the spindle head rotates in the B-axis, you can perform five-axis milling, or index and lock the spindle in up to 12 positions and use it for turning operations. That’s what we call the M-axis.

Gear hobbing is but one of the many operations possible on a multitasking machine. (Provided by Mazak)
Gear hobbing is but one of the many operations possible on a multitasking machine. (Provided by Mazak)

ME: How does that compare to the traditional bolt-on milling attachments found on a mill-turn lathe?

Fischer: There are numerous advantages to this configuration. Perhaps the biggest is that it opens the door to the ATC I just mentioned. Aside from having far more tools, this means you can swap them out while the machine is making parts, rather than pausing operation as you would with a traditional turning center. Swapping tools is also much faster, due to the fact that you have Capto rather than stick tooling—everything in the tool magazine is quick-change. Nor is there a need to spend a few thousand dollars each for bolt-on milling attachments, which not only require routine maintenance but also have far less torque than a multitasking spindle. In addition, there are fewer problems with tool interference when you’re not mounting a whole bunch of tools onto a turret, as with a traditional CNC lathe.

ME: What advice do you have for anyone considering an investment in multitasking technology?

Fischer: I tell people that multitasking is like an onion, in that there are multiple layers that must be addressed. The tooling’s a big part of it, but there’s also the programming software and especially the post-processors. Ask anybody what the biggest headache they have with their CAM software and they’ll probably tell you it’s developing the post.

Getting good code is critical, which is why Okuma Japan has developed a factory-approved post-processors program with our software partners. And going back to the tooling for a minute, shops should keep an open mind to the possibilities that the B-axis and Y-axis bring. A number of providers have developed multi-function toolholders and cutting tools that take advantage of these capabilities.

Mastering the Path

Nick Nikolov, an applications engineer at Mastercam-maker CNC Software LLC, Tolland, Conn., has a lot to say about the need for CAM systems.

ME: Is programming more difficult on a multitasker?

Nikolov: I wouldn’t say it’s all that difficult, but it’s definitely different than programming a regular lathe or mill. People tend to get confused at first with the different planes and axes, so it’s essential to get a solid grasp on all that early on. They should also take the time to accurately define their chuck, toolholders, stock extents, machine boundaries ... as this will help reduce any chance of interference or collision while making the programming process easier to visualize.

ME: If you had to pick a lathe or a mill programmer for your new multitasking machine, who would you choose?

Nikolov: Good question. Because the part spins on a multitasker, I’d have to say a lathe person would be my first choice, but it really depends on the types of parts you’re making, whether there’s a lot of five-axis simultaneous vs. 3+2 machining, and, most importantly, the available skill level. Regardless, a robust CAM system makes it much easier, no matter what department you started out in.

Accurate toolpath simulation is critical when machining complex parts like this landing gear. (Provided by CGTech)
Accurate toolpath simulation is critical when machining complex parts like this landing gear. (Provided by CGTech)

ME: What about some of the more advanced programming features, like superimposition, pinch turning and other synchronized axis motion? Any struggles there?

Nikolov: It makes everything easier when you have full simulation, so you understand what’s going to happen and make the necessary program adjustments before pushing the green button. It’s a lot like Swiss-style turning in this respect, because you have all these different operations taking place simultaneously and can’t always see what’s going on in there. It can get complicated, but, at the same time, I feel that we and some of the other CAM providers have done a good job with the different wait codes and specialty cycles, making the programming process much easier.

Seeing Clearly

Gene Granata seconds the need for robust simulation. The director of product management at CGTech of Irvine, Calif., he points out that the company’s VERICUT software brings several crucial capabilities to the multitasking party.

ME: If CAM offers simulation, why do I need VERICUT?

Granata: Mastercam has excellent graphics, as do many other CAM systems. But VERICUT is one of the few software packages that reads and simulates the actual post-processed G-code the control uses. This is necessary on any CNC machine tool, but is crucial with multitaskers, mill-turn machines, five-axis machining centers and other machinery where the risk of interference is high.

ME: Others have suggested that multitaskers are somewhat less crash-prone than, say, a Swiss-style lathe, which has many tools in close proximity to one another. Thoughts?

Using Mastercam Mill Turn’s Backplot function, programmers can make sure the tool is positioned correctly before considering collision possibilities. (Provided by CNC Software)
Using Mastercam Mill Turn’s Backplot function, programmers can make sure the tool is positioned correctly before considering collision possibilities. (Provided by CNC Software)

Granata: It depends on how you run the machine. Oftentimes, shops don’t multitask in a way that’s the most efficient. They’re kind of handpicking the routines and lining them up in a linear fashion—they’ll do some turning and grooving, then stop using the turret and engage the milling head, then go back to the turret and drill the backside of the part on the sub-spindle. They’re not using the machine’s capabilities to the fullest. If you have accurate simulation of the post-processed code, there’s far less trepidation about utilizing the wait codes and synchronization functions.

ME: Let’s say you have a solid post-processor, and a dozen repeat jobs. Is toolpath simulation still needed?

Granata: Maybe not at that point, but you might still need toolpath optimization. That’s something that many users don’t understand. They’ve mastered multitasking’s advanced functions and are making parts faster than ever, so they assume that’s as good as it gets. They’re optimized, in other words. But from my side, there’s still a lot more on the table if you would just let the experts guide you further down the path. I’m talking about our Force optimization product, of course, but there’s more to it than that. Shops that take the time to investigate new cutting tool technologies and machining techniques—many of which are ideal for multitasking machines—stand to make the most of what is admittedly a significant machine tool investment.

The Yellow Coat

As a turning product specialist at Sandvik Coromant, Mebane, N.C., John Winter is a cutting tool expert. He’s a big fan of multitasking’s benefits; the toolchanger is another matter.

Amortize toolchange time by fitting two tools into a single holder, one of the many tools from Sandvik Coromant’s multitask machining lineup. (Provided by Sandvik Coromant)
Amortize toolchange time by fitting two tools into a single holder, one of the many tools from Sandvik Coromant’s multitask machining lineup. (Provided by Sandvik Coromant)

ME: Tell us about multi-functional tools.

Winter: I think multitasking is the way of the future because it has all the capabilities of a lathe and mill combined in a single machine. That’s great for all the reasons you’ve listed, never mind that you can complete so many different functions in one clamping of the part.

The downside is the automatic tool change—it’s relatively slow compared to a conventional machining center or lathe. This is why we developed the CoroPlex family of tools, which are designed to reduce the number of tool changes by ganging up several tools into a single body. For example, the CoroPlex TB is basically a double-sided boring bar that supports OD and ID turning, or the CoroPlex SL, which is like a four-sided mini turret that can do grooving, threading and turning just by indexing the milling spindle.

ME: Some of these tools look like they’re hanging out quite a way. Isn’t rigidity a concern?

Winter: The CoroPlex SL has a fairly long stick-out and side pressure would be a concern with most machines. But that’s one of the beauties of multitaskers in that you can orient the milling head perpendicular to the cutting forces and drive them toward the spindle, similar to what you do when plunge milling on a machining center. So there are ways to combat any loss of rigidity, depending on how aggressively you want to remove metal.

ME: Does that mean I can take what would normally be a negative lead-angle tool, say an 80° diamond, and tip it forward, thus utilizing the chip thinning effect?

Winter: Well, you have to be careful because the insert geometry and chip breaker aren’t necessarily designed for that, and you can start to lose chip control and tool life. If you want to take that approach, I would probably move to our Prime Turning solution. As with our Y-axis cutoff, it takes advantage of multitasking’s immense capabilities.

For instance, some customers have found great success by tipping the B-axis head, laying down that five-degree lead on the Prime tool to create what is essentially a very large wiper. This allows very high feed rates without any loss of surface finish. Granted, tricks like this add to the programming complexity, but can also serve as key differentiators between your shop and the competition.

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