Indexable-insert broaching tool technology for lathes

Modern Machine Shop, August, 2007 by Derek Korn

Shops can benefit in a number of ways by broaching on a CNC lathe. Locking a lathe's spindle and driving a broaching tool in and out of a workpiece to create keyways and slots increases the number of operations that can be performed in a single chucking on a single machine. This improves feature-to-feature accuracy, reduces the amount of time for handling and setup, and eliminates the need for specialized broaching equipment.

Tools with brazed or replaceable carbide inserts are commonly used for such broaching operations. The latter version offers an advantage in that the insert--not the entire tool--can be replaced after it becomes worn. That way, the tool body can remain installed in the lathe's turret during insert replacement, making it unnecessary to re-zero the tool after a new insert is installed.

Razorform Tools (Playa Del Rey, California) has a new twist on the replaceable insert concept for broaching tools. Its Razorform tool system is said to be the industry's first indexable-insert-style broaching tool, providing two cutting edges per TiN-coated, micro-grain carbide insert. Once one insert edge becomes worn, a machine operator removes two screws securing the sizeable insert to the tool body and flips the insert around to the present the second cutting edge. This design not only decreases tooling cost, but also increases tool life and performance, the company says.

The size and proprietary geometry of the Razorform insert, in addition to the support provided by the tool body, offer stability during the cut to reduce chatter. The force of each longitudinal cut is directed through the middle of the insert and the heat-treated, 4140-steel tool body, which also contributes to overall system rigidity. The inserts are currently available in sizes to create slots from 1/8 to 5/16 inch wide. Custom widths are also available.

The company recommends using coolant during broaching operations primarily to wash chips out of the slot during machining. A typical depth of cut is 0.0015 inch per pass, but smaller depths may be necessary when broaching extremely hard materials.

One early adopter of this broaching tool system for CNC lathes is Baldor Electric, located in Fort Smith, Arkansas. The manufacturer of electric motors had been using brazed-insert tools to machine keyways in 4140 steel workpieces. The company was able to machine 20 to 30 parts per brazed insert. The tool would then have to be removed from the machine and re-sharpened. Now, using the Razorform tool, it is possible to machine 100 parts per insert cutting edge and then index the insert to machine another 100 parts. Because the tool body remains installed in the machine during insert change, the company claims to save 10 to 15 minutes of downtime because it isn't necessary for an operator to re-zero the tool.

For more information from RazorformTools, call 310-822-2810 or search MMSOnline.