Cutting the coolant when making gears

When it comes to hobbing auto gears, dry machining dominates. “There are no new automotive applications that are being done wet,” said Tom Ware, product manager for gear tools at Star SU Co. LLC, Hoffman Estates, Ill. “There are a few tier suppliers that have not updated to new equipment and are still running some wet applications, but all the major manufacturers have gone dry.”

Two factors contributing to the dry scenario are enhanced machine rigidity and advanced chromium-based tool coatings. The vast majority of new hobbing machines are direct-drive, CNC ones, Ware said. “You don’t have any gear trains anymore in the machines, so you get a very rigid cut.”

The chromium-based tool coatings include Alcrona Pro and Balanit Altensa from Oerlikon Balzers, he added. The coating composition has a high aluminum content to improve heat resistance.

“If everything is right, the part comes out of the machine and you can hold it in your hand,” Ware said. He noted how the sense of touch is still an effective way to gage a machine process, even with the vast array of high-tech measuring devices on the market. “The cooler the part is, the better off you are.”

In addition to resisting heat, chromium-based tool coatings are fairly easy to remove when resharpening hobs made of K-grade carbide without leaching cobalt, Ware said.

Some applications require coated carbide hobs to run at only 250 to 300 m/min. for performance consistency considerations. However, Ware said, the tools can run as fast as 400 to 450 m/min.

The complete article will appear in the Industry Briefs section of the August 2018 issue.