Flute polishing boosts surface integrity

END USER: Niagara Cutter LLC, (800) 861-6111, www.niagaracutter.com.
CHALLENGE: Improve cutting edge integrity and flute faces of cutting tools.
SOLUTION: A flute finishing process that uses a fine-grit, hybrid resin-bond flute polishing grinding wheel, special truing wheels and fine-grit dressing sticks.
SOLUTION PROVIDER: Norton/Saint-Gobain Abrasives, (254) 918-2313, www.nortonindustrial.com.

---

Manufacturers of round carbide cutting tools are continually seeking ways to improve their flute finishes. Finer surface finishes produce superior cutting edges, extend tool life, enhance workpiece finish, provide faster metal-removal rates and enable more efficient chip evacuation when machining ductile, nonferrous materials.

Courtesy of Niagara Cutter

Niagara Cutter uses the Norton flute polishing process for imparting mirror finishes on its cutting tools, such as this endmill.

Niagara Cutter LLC, Reynoldsville, Pa., was one such toolmaker seeking to improve the cutting edges and flute gullets of its standard round carbide tools for machining aluminum alloys, as well as some of its specials, noted Jim Lundy, the company’s grinding technology manager.

He added that the flutes weren’t polished or loose abrasive media was applied. Polishing with loose abrasive, however, is a labor-intensive, manual process that requires skilled operators and often causes “edge dumping,” or rounding the cutting edge.

In addition to the media, the company applied a fine-grit grinding wheel, but was not achieving the desired results, Lundy noted.

A fine-grit wheel forms small chips during grinding, imparting fine grinding marks and minimizing surface and subsurface damage. The challenge, however, is to properly true and dress the wheel for the task.

Courtesy of Niagara Cutter Courtesy of Niagara Cutter

The flute face and cutting edge of a cutting tool before (Figure 1) and after (Figure 2) applying a Norton fine-grit, hybrid resin-bond grinding wheel during the flute polishing process.

To achieve the desired results, Niagara Cutter contacted Norton/Saint-Gobain Abrasives, Worcester, Mass., to develop a wheel and process for polishing flutes. The grinding wheel manufacturer responded with a fine-grit, hybrid resin-bond wheel and specific truing and dressing requirements.

According to Kenneth Saucier, senior corporate applications engineer for Norton/Saint-Gobain, who developed the Norton flute polishing process, a flute surface has three major components: aesthetics, surface roughness (as measured in R_a) and surface integrity. “It is possible to get a very appealing finish but a poor cutting edge,” he said. “Using a fine-grit grinding wheel will allow you to achieve all three attributes.”

Niagara Cutter applies 1,000-grit wheels for flute polishing to enhance surface—and therefore cutting edge—integrity and aesthetics by imparting a mirror finish, although it does not target a specific R_a value. “A jagged cutting edge is typical without the Norton process on standard tools,” Lundy said.

The polishing wheel requires special truing wheels for rounding and profiling and 800-grit aluminum-oxide dressing sticks for exposing fresh diamond particles. Lundy emphasized the importance of maintaining open truing and grinding wheels when truing, a condition determined by operator touch during setup. “A standard operator is not going to experience success without some help,” he said. “The process has to be perfect.”

Although Lundy estimated that truing times increased about 20 percent with the Norton process, he doesn’t consider the additional 2 to 3 minutes significant.

In addition, the process, which Niagara Cutter performs both attended and unattended, adds a finish-pass step to the polishing cycle. For Niagara Cutter, the additional step increased cycle time for the polishing operation 5 to 10 percent, but that operation represents only about 10 percent of the overall cycle time, according to Lundy.

Lundy added that there was no spindle load for the polishing pass. Spindle load is equivalent to heat generation—carbide’s enemy—and, therefore, the additional polishing step does not compromise tool quality or integrity.

Having highly polished flutes, however, provides benefits to Niagara Cutter’s customers. “For drills, the polishing process adds lubricity,” Lundy said. “It’s a smooth surface and the chips are able to exit more freely.”

In addition, Lundy noted the flute polishing process not only extends tool life, but provides more consistent tool life.