Deburring Difficult-to-Machine Materials

Not only are hard materials more difficult to machine, they can also pose challenges in other processes, like deburring and surface finishing. Wheel brushes are often good solutions for surface finishing, polishing, deburring, edge blending and removing contamination such as paint and rust. But on harder materials, a wheel brush’s wire filaments can break off or deform, even if they are crimped. Knotted wire options are available for more aggressive deburring, but these still may not be sufficient for today’s hardened steels and alloys. However, wheel brushes with abrasive nylon filaments made of silicon carbide are strong enough to handle aggressive deburring and surface finishing. A diamond grit can also be used for the hardest metals and alloys. 

Deburring 4140 Steel

JR Precision & Welding, a Houston, Texas, machine shop specializing in three- and five-axis CNC machining, 3D printing and welding, was having difficulty deburring parts machined from hard material. Specifically, the shop needed to remove large burrs from 4140 steel alloy, a 1% chromium and molybdenum steel alloy that is generally hardened and tempered to a tensile strength of 850 to 1,000 megapascals.

The part that needed deburring was a muzzle break, or compensator, which is connected to the barrel of a rifle or pistol. There are different forms of muzzle brakes, but most consist of a small length of tubing approximately 5 centimeters long. Muzzle brakes have features such as slots, vents, holes and baffles to redirect a portion of propellant gases to counter recoil and unwanted muzzle rise.

However, when machining these holes, large burrs were forming at the oval-shaped gas ports. The company was machining the part on a five-axis machine in an elliptical path, which increased the size of the burrs. “The burrs that were created were razor sharp and thicker than we wanted them to be on each of the four main ports in the part,” says James Mawazeb, director of operations and lead engineer at JR Precision & Welding.

This led Mr. Mawazeb to reach out to a local tooling representative from Bass Tool & Supply for wheel brush options that could remove the burrs in one automated operation. The rep, in turn, suggested he contact Los Angeles, California-based Brush Research Manufacturing. Brush Research manufactures an array of wheel, cup and end brushes in a variety of sizes, filaments and grits.

Choosing the Best Deburring Brush

Based on the geometry, location of the burrs and the hardness of the metal alloy, it wasn’t immediately clear what the best solution would be. So, the engineers at Brush Research suggested Mr. Mawazeb send in several sample parts for testing in the lab.

At its surface finishing laboratory, Brush Research engineers analyze customer parts that require finishing, then select and test the tools that will provide the best solution according to customers’ parameters. “After testing out disc brushes with different depths and speeds, we decided to try an abrasive nylon wheel brush,” says Elysha Cole, product support specialist at Brush Research. “It was able to easily get into the slots, push the burrs out and remove them.”

The abrasive-filled nylon filaments are set into molded cores, allowing higher filament densities and putting more cutting tips at the point of attack. In addition, the filaments are durable and self-sharpening, providing excellent performance and wear life. As the brushes come in contact with the work surface, the filament grit wears off, exposing new cutting particles. This keeps the brush sharp, even after repeated use. And unlike the bristles of metal brushes, the abrasive nylon fibers are not prone to deforming or breaking off.

The product used to prove the concept was a 6-inch diameter tool with silicon carbide filaments. Because the burrs were a bit heavier and the customer was not concerned about the final surface finish, the machine shop opted for 80 grit. The tool can be automated on CNC equipment or offline as a secondary deburring operation.

According to Mr. Mawazeb, the abrasive nylon brush met all his requirements, including its fit in the five-axis machine’s magazine holder and existing toolholders. However, he was skeptical about how much material the brush would remove. “We didn’t want the brush to affect the outer diameter measurements in a way that affected the performance of the ports,” he says. But after testing the abrasive nylon brush, Mr. Mawazeb was impressed. In addition to removing the large burrs, the brush provided a soft edge break to the four ports without affecting the surface finish. “The abrasive nylon brush removes just the right amount of material,” he adds. “The surface finish actually matched what the customer wanted as well.”

After proving the concept in the lab, JR Precision & Welding ultimately decided to purchase a smaller 3-inch diameter version of the wheel brush. The shorter trim fill has less give, delivering an even more aggressive action than the 6-inch brush. According to Mr. Mawazeb, the machine shop has installed the abrasive nylon brushes, and the equipment is programmed for the next order muzzle breaks scheduled for production.

Brush Research Manufacturing | 323-261-2193 | brushresearch.com