… Don’t forget about the geometry!

Bill Tisdall, Development and Turning Products Manager

The geometry of a turning insert provides two major benefits, it forms and breaks the chip coming off the component and provides edgeline strength for the carbide cutting material. Our goal is to apply an insert that will give us the best balance of tool life and productivity versus toughness and process security.

The geometry of the insert is key to achieving this goal. In finishing applications, where cutting forces are low, grade and geometry combinations are of little matter in terms of edge strength. Usually, the criteria for this area are tool life, chip control and surface quality and because the cutting forces are low, a harder grade can generally be applied without sacrificing process security.

However, moving into medium and roughing applications harder grades can fail due to the heat and mechanical pressure the insert is exposed too. There are various choices of turning geometries in each application area – finishing, medium, and roughing. Each of these geometries provide various edge strength and chip breaking characteristics.

A good rule of thumb is to match harder grades with stronger geometries while maintaining acceptable chip breaking. Another simple way to increase process security, tool life and productivity is to use the largest nose radius as possible. Many times we rough and finish with the same tool; for instance, a CNMG 432. This is simple, reduces tool costs, and saves space in the turret of the turning center. However, these cost savings pale in comparison to the money we can make by using a CNMG 433. Using the larger nose radius allows us to increase the feed rate – getting more parts out the door in shorter period of time. The larger nose radius usually results in a large jump in tool life sometimes up to 40%.

Finally, the larger radius gives the insert edge more strength to handle mechanical pressure and more area to dissipate heat. So when you are looking at new grades don’t forget to look at the insert geometry. By doing so you will insure that your process yields the highest productivity and reliability.