Look Ahead: Fibrous alloys: General Industry Coverage

Steel is an alloyed material that has long been considered the go-to metal for toolholders and boring bars. Suprock Technologies is trying to change that, having developed prototype toolholders and boring bars made of composites.

Composites are analogous to metal alloys in that component designers can mix different fibers, orientations and ratios of fiber and resin to achieve the desired properties, explained Christopher Suprock, the company’s principal/founder. Suprock uses various composite types, including ones reinforced with carbon, aramid and glass fibers.

“For instance, in an application where stiffness is paramount, you can have a high concentration of carbon fibers at a large radius in the cross section,” Suprock said. A composite designed for stiffness can have a modulus of elasticity up to 379 GPa compared to 200 GPa for steel, he noted. That enables a composite tool to experience nearly twice the cutting force and have the same deflection as steel, thereby allowing users to increase chip loads.

Courtesy of Suprock Technologies

Suprock Technologies has developed composite boring bars and toolholders, where the body is composite while the front end remains steel, as alternatives to entirely steel ones.

Composite tooling also helps reduce vibration and chatter more effectively than steel tooling when machining, according to Suprock. That’s because the polymer bond between the individual fibers is effective at damping energy and dissipating that energy as low-level heat. “Racecars and heavy machinery often utilize carbon-fiber driveshafts to prevent transmission damage,” he said.

Suprock added that composites are generally four to five times lighter than steel, depending on a composite’s composition, and the lower a tool’s mass and the higher its stiffness, the higher its natural frequency. “That’s good because it means we can control chatter more easily,” he said.

By improving the natural frequency, Suprock added that a boring bar with an 8:1 depth-to-diameter ratio, for example, can be replaced with one having a 10:1 ratio without sacrificing performance. “A 10:1 composite bar has a higher natural frequency than an 8:1 steel bar,” he said.

For tunable boring bars, a higher natural frequency dramatically improves performance. “If the bar is lighter, it’s easier to tune,” Suprock said.

The thermal properties of composites are also beneficial for tooling. A composite’s thermal expansion can be controlled to near zero and the material often contracts, Suprock noted. For example, a carbon-fiber composite with a high modulus of elasticity has a thermal expansion on the order of -1×10-7 in./in. ° F, whereas steel is 6×10-6 to 7.3×10-6 in./in. ° F. “This means if the machining envelope warms up during an operation, a composite tool maintains its dimensions 60 times better than steel and does so in a conservative direction—contracting instead of expanding,” he said.