A combination tool for thread forming

Engineers at German carmaker Audi AG and toolmaker Emuge-Franken, with help from the Institute of Machining Technology at Dortmund (Germany) Technical University, have put a new spin on the way that threads are formed in materials such as aluminum. They call the process “helical thread forming.”

The punch-tap helical thread-forming tool was developed by Audi and Emuge-Franken. Image coutesy of Emuge.

Their “punch-tap” tool differs from a conventional or cold-forming tap. Instead of a continuous thread profile, the tool has two twisted rows of teeth that are offset 180° to each other. The tool head has two broaching teeth. When the tool punches—quickly—into a predrilled tap hole, it simultaneously turns on a steep helical path, and the broaching teeth generate spiral grooves on opposing sides of the hole. Then the spindle turns another 180° while the axial feed axis moves half a pitch, causing the teeth lining the sides of the tool to cut all of the threads at once. That 180° turn lines the broaching teeth back up with the helical grooves they cut, and the tool is retracted along that same path—which, if you are making a standard M6 thread that’s 0.59″ (15mm) deep, is about 15 times shorter than the thread path itself would be. The entire process takes less than half a second, reducing threading time about 75 percent compared to cold forming, said Emuge.