January 2008 Edition

swiss turning

Automatic lathe can boast some all-American touches

Two engineers from Rem Sales, the North American importer of Tsugami machine tools, approached the OEM a year ago with some customer feedback. The goal was to design a new Swiss-turn automatic lathe for the North American market. From that feedback evolved the SS-20.

"There were several items on our list of machine design parameters, and these were based on first-hand feedback from our customers," says Ron Gainer, head engineer on the project.

"Item number one was a roomy work area. It's typical to see a gang-type Swiss machine with a very small interior. The tooling is cramped, and often the first thing I hear from an operator is, 'I can't get my hand in there.'"

"And the first thing I hear from people when they look at this machine is, 'Look at the amount of space between the main and sub-spindle!' An operator can get his hands and shoulders in there, too, which is important when you are maneuvering around, changing tools, and so on."

Flexible tooling

In addition to roominess, tool modularity is another leading-edge strategy with new Swiss technology. As shorter runs pervade, machine operators need to change part runs quickly. Sometimes the parts are vastly different from each other, requiring completely dissimilar tool setups.

The SS-20's standard main spindle configuration includes seven turning tools, five cross-rotary tools, and five ID tools, while the standard sub-spindle setup includes four ID stations, two face drills, and two cross-rotary tools. Quick changes can be made to the configuration of main and sub-spindle cross rotary, ID, and turning tools, allowing for efficient machining of a greater variety of parts.

Thread whirling, polygon turning, and angular face-drilling operations are possible with an adjustable face-tool attachment.

"The modular concept allows removing a tool and replacing it with a different kind of tool," says Gainer. "The user can take a whole spindle out and insert a totally different spindle in a completely different position; so, for example, he has face-drilling capabilities instead of cross-tooling capabilities. Live tools can replace stick tools. Tools can come out of the back slide and go into the front slide. It actually functions more like a turret machine in that way, which significantly expands capability."

Beefier

The nomenclature for the SS-20 indicates 20mm diameter capability; however, the machine is built on a 32mm frame – another American suggestion – providing the added robustness to hog out a healthy amount of metal and provide milling capabilities on the cross slide.

The ability to remove ample material on each pass contributes to cycle time reduction. Another user request that was incorporated: a longer 350mm sub-spindle stroke to allow longer workpieces to be discharged from the front side. Likewise, the rotary guide bushing corresponds to longer workpieces with a 220mm stroke. The rule of thumb is 10-to-1, so a 20mm machine would normally have a 200mm stroke. The belt-driven guide bushing itself is a new design, featuring front-adjust and a larger bearing.

Two in one

Adding even more flexibility, the SS-20, like some other Tsugami models, can also operate as a chucker machine by removing the guide bushing and inserting a chucker kit.

The nomenclature for the SS-20 indicates 20mm diameter capability; however, the machine is built on a 32mm frame – another American suggestion – providing the added robustness to hog out a healthy amount of metal and provide milling capabilities on the cross slide.

Even though today's Swiss machines with their milling and other rotary tool capabilities are also effective for stubby parts, there are still times when running without the guide bushing makes sense; for example, for parts made out of unground, expensive, and malleable materials such as copper. Another case in which using a chucker would make sense is when users need to chuck on the ID, such as die cast parts that are pre-manufactured on an ID mandrel.

"Working as a chucker machine, users can make parts just as fast or faster than in Swiss mode, and the spindle stroke doesn't dictate the remnant," says Dan Dean, a member of the American engineering team with Gainer. "In a Swiss machine, you have a collet and a guide bushing and a little bit of stroke in between there so you're typically going to get an 8-12" remnant. When you take that guide bushing out, the main spindle collet goes up into the work area.

"Now the remnant is only the length of the collet pad. For guys who are running copper that's $8 a foot or so, that's a giant savings. They can get more parts out of what used to be irreclaimable remnants that they sold for a fraction of their worth. We have jewelry customers that could run gold and silver, platinum, and magnesium in this machine."

Further, in chucker mode, the material doesn't have to be perfectly precision-ground because the material spins around the centerline of the machine collet.

In a collet, an operator can insert a piece of material that has 0.005" runout and if the spindle bearings are good, a 10μ" round part can result. So another benefit of that chucker kit is the improved roundness of the part. When stock is placed in a guide bushing, if the material is egg-shaped, the resulting workpiece is egg-shaped because the part is turned around the centerline of the material rather than the collet. The rule of thumb is that chucked parts should be within a 4-to-1 length to diameter ratio; however, for very small diameters, the ratio changes to 3-to-1 and even smaller.

"With guide bushings, we generally advise that the operators will get 60 percent better parts than the original material," says Dean. "For example, if you put in a piece of material that has a thousandths of runout on a guide bushing, you're going to get a four ten-thousandths runout on the part itself."

A toolchanger?

Other compelling advancements in Swiss technology include Tsugami's TMU1 which is a 1.5" dia. capacity Swiss-type machine with a unique feature – a fully automatic 60-station (118 optional) toolchanger serving its independent 7.5hp milling spindle. The main 15hp spindle is a sliding headstock Swiss-type with an adjustable guide bushing. A 16-station front turret accepts two ID tools. Other features include full front and rear C-axes, and a B-axis on the tool spindle with 210 degrees of positioning.

The 16-tool turret services both the main and sub-spindle for the backworking functions. The sub-spindle has a stroke of 800mm allowing it to pickoff work from the main spindle. Its power and rotation speeds match the main spindle, essential for such operations as threading.

Opposite the turret, and mounted on the compound slide, is a milling spindle that uses an integrated 2.2kW motor providing 10,000rpm for the milling and drilling operations. The live tool spindle's B-axis indexes from 15 to 195 degrees in 0.0001-degree increments. It is this spindle that is serviced by the machine's automatic tool changer. A double-arm mechanism accesses the tool storage unit.

In addition to the productivity benefits surrounding the agility of storing tools for a host of jobs and the ability to complete jobs in one setup, the TMU1's automatic toolchanger has a direct impact on tooling costs. Toolholders on a conventional CNC Swiss can cost as much as $3,500 each, particularly for the milling heads. Toolholders on the Tsugami cost about $150 each. Rem Sales, www.rsleads.com/801tp-188 .

What do you think?
Will the information in this article increase efficiency or save time, money, or effort? Let us know by e-mail from our website at www.ToolingandProduction.com or e-mail the editor at dseeds@nelsonpub.com.