Push-pull concept for precision broaching - STENHOJ - #1

MVS Metform, a division of MacLean Vehicle Systems, has recently installed a new type of broaching machine for high volume machining of internal splines in gear blanks. Located in Savanna, IL, Metform expects this technology, from Stenhoj Hydraulik of Denmark, to help it control the lead error on its parts, a critical factor in keeping its auto industry customers happy.

Most modern broaching machines are designed to pull the broach tool through the part. In some cases, broach tools may be pushed through the workpiece. But this new machine, Stenhoj's SDZ model, uses a simultaneous push-and-pull technique designed to help keep the broach tool perpendicular to the part.

"The key unique factor of the machine is the push-and-pull bayonet collet system that actually very firmly controls the cutting action and the path of the broach tool," says Ken Nemec, president of Broachman LLC, Stenhoj's North American representative. "No other broaching machine has a system like this."

According to Nemec, the broach tool is held both top and bottom during cutting in hydraulically clamped collets. Those collets are mechanically linked so they move in unison.

"They're firmly being held and pushed and pulled simultaneously through the part, distributing all the power very evenly and keeping the broach on a firm, rigid path," Nemec says.

On a typical vertical broaching machine, Nemec says, nothing holds the top end of the broach, which can lead to tool movement on some parts.

For Metform, controlling such movement was a critical factor in deciding on a broaching process.

"The most important feature of the Stenhoj Hydraulik broach machine is that the cutting force and drive mechanism

According to Nemec, the machine controls lead so well that even after heat treating, parts don't need any subsequent finishing operations. Often with other technologies, parts have to be hard turned or re-broached after heat treating. "This application makes both of those unnecessary," Nemec says, "because the lead error can be held so close."

Metform has been using the technology for more than a month. "So far, we have seen excellent results," Collier says.

Another important feature of the Stenhoj technology is that it helps increase tool life, says Nemec. The SDZ

are in alignment," says David Collier, product development engineer at Metform. "The push-pull feature helps maintain alignment of the tool to the part locator, for the full length of the cutting stroke. This helps hold the spline perpendicular to the locating face, which is a critical feature for our customer."

Controlling the lead error is critical for many broaching customers, Nemec says. "If the splines are straight up and down, the lead is good. If they have a tilt to them or an angularity to them, then it creates gearbox noise and premature wear in a gear, and that's what we're trying to avoid."