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A riveting tale of hardturning

A riveting tale of hardturning

Speed and superior surface finishes abound as a result of one shop's quest for production control.

Speed and superior surface finishes abound as a result of one shop's quest for production control.

No more grinding for Orbitform. It now roughs and finishes hardened parts on a Midas CLT-160HD lathe from Somerwill Engineering.

Orbitform, using an offset fixture, turns the six recesses in this CPM 10V part that has a hardness of 66-70 Rc.

Orbiting describes the tool's motion as it forms the head of a rivet on an Orbitform assembly machine.

These M2 steel parts, with harnesses of 62-64 Rc, form the various rivet-head shapes on Orbitform's assembly machines. The machines are then incorporated into semi or fully automated assembly systems consisting of dial indexers, pallets systems, automatic parts feeding, machining, gaging, load monitoring, vision systems, and more.

Once upon a time, a company known as Orbitform would pack up its parts and send them out to be ground. But the Jackson, Mich., shop disliked the idea of outsiders controlling the crucial stage of surface finishing parts, not to mention the cost and time involved. So why didn't the company get its own grinder? Because

Orbitform found a different type of machine that finishes parts in half the time it would take to grind them. The company now hardturns on a Midas CLT-160HD lathe, designed specifically for that purpose, from Somer-will Engineering .

According to Alex Lisachenko, partner and vice president of operations at the Twinsburg, Ohio, machine tool company, four main design features make its CLT-160 lathe exceptional for hardturning.

These are a rigid base, cast iron major components, a finely tuned servo system, and heavy-duty parts in the cutting loop.

The machine's base is a fabricated steel weldment, and its spindle housing, way block, carriage, and slide are cast iron. All this provides structural stiffness and damping. Lisachenko says the base is stable because of its low profile. "Everything is down close to the ways and tight," he says, "including the linear gang-style tooling." This tooling is nothing new, he adds, but this style is best suited for hard-turning machines.

Most hardturning operations deal in microns. Because of this, CLT-160s sport Fanuc AC digital servo drive systems tuned to reduce motion frequency changes or vibrations. These vibrations may be minute, says Lisachenko, but they can definitely affect part surface finishes. In addition to the servo system, the machine's heavy-duty components, such as bearings, ballscrews, and linear bearings, also dampen vibration.

It's more than riveting
Orbitform, which manufactures forming, fastening, and assembly systems, gets its name from orbit forming. It's a cold-forming operation in which an orbiting tool held at a fixed angle, typically 3° to 6°, progressively moves malleable material into a desired, predetermined shape. The process is commonly used in fastening and assembly to produce a high quality form on rivet heads.

A hardened, rod-shaped tool, called a peen, does the actual rivet-head forming, and every custom fastening and assembly system Orbit-form builds includes one. Peens are perishable tooling, so the company gets a lot of orders for them. These parts are now hardturned on the Somerwill lathe. Most jobs consist of five or six pieces, and peen sizes vary in O.D. from 3 /16 up to 2 in., with lengths between 1.165 and 7.000 in.

Orbitform makes its peens from such hard materials as M2, Rex 76, and M4. Machinists rough cut parts before heat treat, leaving between 0.010 and 0.015 in. of stock for hardturning of the finished shape. At that stage, peens are as hard as 60 to 68 Rc.

Most of the hardturning is face work at one end of the peen. While the overall part shape lends itself well to hardturning, these end shapes can be complicated and difficult to cut. Operators finish parts in two passes, using separate cutters for roughing and finishing. For all peen configurations, Orbitform uses 1 /8-in.-wide CBN cutters with inserts from Sumitomo and Sandvik. Most of the face tooling lasts through 60 to 70 parts, says Phil Teremi, peen manufacturing support leader at Orbitform.

The CLT-160 runs at 600 sfm and 0.0015 in. of feed for the final hardturning pass, which produces a surface finish between 8 and 12 µ. According to Gary Hanson, a manufacturing engineer at Orbit-form, these results are as good as, if not better than, the former ground surfaces. And the Somer-will takes less time, he adds.

What impressed both Hanson and Teremi, though, was Somerwill's willingness to prove its machine could hardturn Orbitform's parts. The machine tool builder actually supplied all the tooling and set up a machine at its own facility, says Hanson. For the demonstration, Somerwill actually hardturned complete peens from heat treated blanks, doing both the roughing and finishing.

Machine specs

Somerwill Engineering's Midas CLT-160HD CNC gang tooling lathe features a 12.6-in. maximum swingover with an A2-5 spindle nose taper and 1.57-in. through hole. A six-in. Kitagawa B-series power chuck — with a hydraulic cylinder and actuator with controls — easily accommodates the machine's maximum bar capacity of 1.50 in. The spindle turns work at speeds between 60 and 6,000 rpm using its 7.5-hp continuous and 10-hp (for 30 min duration) drive motor.

The X and Z axes rapid traverse as fast as 787 in./min and feed at 394 in./min. Programmable travel, via Fanuc OTD CNC, covers 14.6 in. in X and 9.05 in. in Z. With an over-all weight of 4,409 lb, the CLT-160HD's footprint measures 8954.368.5 in.

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