This tool disk (upper) sports a generic setup for part families. Hardinge's ESA tool disk eliminates having to re-set tools when they are removed and reinstalled.
The relationship between a lathe's chuck and its tool disk dictates the part sizes a shop can run before seeing tool interference.
Tool-interference diagrams are designed to help shops avoid tool interference problems.
FOR EVERY MINUTE A SHOP SPENDS SETTING up tooling, a lathe's spindle is not working. And, when spindles are idle, shops do not make money. However, there are ways to reduce lathe-tooling-setup time. Fast tooling setups start by grouping lathe work into part families based on certain criteria. For instance, all parts that fit within the size of a 4 4-in. cube and require drilled holes no larger than 1.000 in. in diameter would run on a lathe tooled for those requirements. It does not matter if the parts are from different jobs or that they have different run times, as long as they meet the job criteria. The idea is to establish set arrangements on the tool disk for each part family so that time is not wasted wondering what tools will work and having to completely break down disk setups between every job.
These disk arrangements include common tooling, such as stick tools for I.D. and O.D. work, that may never have to be removed, but they also include tools that will change, such as drills and boring bars. In any event, shops should strive to change as few tools as possible per setup, and when tools need to be changed, the process should be done as quickly and as accurately as possible. One way to accomplish this is to use quick-change tooling, such as the KM system available from Kennametal (www.kennametal.com).
The KM system is modular in design, and secures tools in holders that load into receptacles bolted on lathe tool disks. It provides toolchanging repeatability within 0.0001 in. and allows shops to develop what Kennametal refers to as tool-kitting assemblies.
For tool kitting, shops load tools into KM holders and preset lengths off-line using a presetter unit or height gages. This ensures that tools are ready when needed and eliminates setup time wasted on running test cuts or touching tools off part surfaces to determine offsets after loading a new tool.
While quick-change systems are popular, some shops have issues with the rigidity and cost of such systems. "The KM system provides as much rigidity as standard stick tools because it incorporates a three-point-contact design that delivers high clamping power and rigidity using low activation forces, along with ten-to-one tapers," says Curt Rellick, product manager for systems tooling at Kennametal.
He also says that the majority of rigidity problems occur when shops exceed boring bar and drill length-to-diameter specifications. For instance, steel boring bars typically handle ratios of 4:1, while carbide bars have between 6 and 8:1 ratios. The key is to stay within a tool's recommended ratios, says Rellick.
To make quick-change tooling more affordable, Kennametal offers its KM-25 system with interchangeable heads and shanks similar to other quick-change systems. To accommodate different tools, shops only need to purchase heads that cost under $100. The system also eliminates the need for removing wedges to change a tool and touching off on workpieces for offsets. Instead, shops can establish tool lengths with height gages on tables located near lathes.
Besides quick-change tooling, shops can speed lathe tool-disk setups with special preset sleeves/adaptors. Machine tool builder Hardinge Inc. (www.hardinge.com) offers such sleeves and incorporates them, along with a part-family tooling program, into its own manufacturing processes. Using a part-family tooling program has helped Hardinge to slash its average lathe-tooling setup times from more than an hour to 10 to 15 minutes.
Hardinge markets its preset sleeves under the HDZ name. The HDZ sleeves hold drills, end mills and boring bars as preset tools. That speeds tool changes and eliminates the need for physically touching tools off on workpieces. In addition, shops do not have to mount indicators on machine spindles to ensure that boring bars are in-line and running with a machine's Z axis.
Another way shops speed tool setups is through repeatable, rigid and high-accuracy lathe turret tool disks, such as Hardinge's ESA units. These disks let shops set tools once and remove and reload them without having to relocate or readjust settings because ESA disks hold repeatability stack to within 0.0002 in.
"Small shops often incorporate VDI-type disks and tooling to speed tool setups. While VDI may be an established standard, it is not always the most repeatable for resetting tool centers," says Mark Tuccio, senior design engineer at Hardinge
For flexibility to accomplish more operations, shops usually want as many stations on a tool disk as they can get, but this spurs problems that involve the number of tools that a shop can mount before tool interference develops.
Ed Danzer, chief technology officer at Danzco Inc. in Tenino, Wash., always sets up his turret tool disks with as much fixed tooling as possible and changes only a few tools from job to job. He says the practice works for 80 percent of his parts, but for some jobs he has to remove certain tools from the disk because they hit the machine's chuck.
Ray Gieling Sr., president of Rayco Precision Machine in Mentor, Ohio, says his company also removes tools from the disk to prevent crashes, and running six tools in a 10-station disk or four in a 12-station one is not out of the ordinary.
"What happens is that, when working with short workpieces using a turning tool located next to a boring bar in the tool disk, the boring bar sticks out so far that it hits the chuck," explains Gieling. "For instance, if my boring bar is sticking out 3 in. and I'm machining a 1 1 /2-in. part, I have to waste time playing 'musical tools' to ensure the setup works," he says.
Interference happens most for jobs that require a lot of tools, and what looks like it would work during programming does not always work when you actually setup the tool disk, says Gieling. So he and Danzer say they rely on their years of experience to speed tooling setups and avoid interference problems.
However, Glenn Pedersen, turning products manager at Daewoo (www.infracore.com), says there are other ways to avoid tool interference. "The first and most-effective thing a shop can do is to review a lathe's tool-interference data/diagram before purchasing the machine," he says. These drawings typically show maximum diameters in which various tools can operate without interference. As long as these diameters are larger than workpieces and machine chucks, shops will not experience interference.
"The key is the relationship between chucks and tool-disk sizes — certain size chucks match up with certain size disks on certain size machines to prevent tool interferences. Change one or the other, and a shop has problems," says Pedersen.
Deawoo's Puma 240 Series lathes have 12-station tool disks that are designed to work around 8-in.-diameter chucks for interference-free operation when running workpieces up to 8 in. in diameter. The company also makes the same machine with a larger through-hole and 10-in.-diameter chuck, so if a shop outfits that machine with a 12-station disk, they will experience tool interference.
"It's a matter of selecting the proper machine. If a shop runs 20-in.-diameter parts in a 15-in.-diameter chuck on a machine with a 12-station tool disk, they will have to deal with tool interference," says Pedersen. "In that particular 15-in.-diameter chuck, they should be running part diameters no larger than 13 in. to prevent interference." But running parts smaller than a machine's chuck is not always the rule-of-thumb because shops can use different chuck sizes on different size machines, he says.
Does having fewer stations, meaning more room between tools, on a tool disk cure interference problems? It appears so.
Putting a 12-station disk on a machine with a 10-station tool disk that is interference-free for a 15-in.-diameter chuck requires switching to a 13-in.-diameter chuck to re-main interference free. And equipping the same machine with an 8-station disk could provide virtually interference-free operation for part diameters up around 20 in. "The tradeoff is between tool interference and the number of tool stations a shop wants," Pedersen says, adding that most shops want more than eight tool stations on a disk."
Turrets Don't Hold Tools
What many people refer to as a lathe's turret is actually the machine's top plate or tool disk. Turret mechanisms drive a lathe's top plate, which is what holds tooling. "It is important to remember this because some turret mechanisms are better than others," says Jeff Ervay, turning product manager at Hardinge.
A machine tool builder may offer a high-quality top plate, but mounting it on a subpar turret would deliver no performance gains whatsoever, he says.
Shops also should realize that not all turret mechanisms are created equal. Hardinge, for example, builds crash-protection features into its turrets. In the event a shop crashes a tool or tool disk, these turrets sustain little, if any, damage, and realignments are quick and accurate.