by Kevin Burton
A simple, but incredibly effective principle
The Y axis option has broadened the possibilities to use rotating tools in multi-task machines and turning centres. Now this capability has inspired a great innovation in one of the original missions of these machine tool types: Y axis parting. Implementing this new tool and method brings significant machining improvements in potentially any parting operation.
Adding rotating tools to turning centres means you can combine several setups in a single machine for a more streamlined and productive machining process. To accomplish this, turn-mill machines were introduced in the 1990s. The initial idea was to enable driving a milling cutter, drill, or threading tap on one or more tool positions in the turret to eliminate limitations of polar interpolation and other related programming difficulties. To improve reach, an extra set of ways was added to move the rotating tool across the spindle face. This was accomplished by mounting the tools on revolver sides or on its face by installing the Y axis ways on a slanted bed or by using an independent milling head. Both machine tool makers and manufacturers soon recognized the benefits of integrating both milling and turning operations. Today, the Y axis option has become a standard feature in most multi-task machines and optional in many new turning centres.
As potential tool breakage risks leading to costly machine downtime or scrapped components, parting-off is a stage of the machining process where manufacturers don’t compromise on security. To meet the high demands put on these type of tools, the CoroCut QD system was developed by Sandvik Coromant in 2013. While considering how to improve this system even further, tool developers started looking at modern machines with Y axis capacity. This resulted in an innovation that involved more than just the tool design but also a completely new method: Y axis parting.
The Y-axis Parting Principle
The principle behind Y axis parting is incredibly simple. While conventional parting-off tools align with the X axis of the machine tool, the Y axis tool has been rotated 90° counterclockwise to align with the Y axis. In a conventional tool configuration, the relatively long and slender parting blade and holder are fed at a 90° angle into the rotating workpiece. The largest cutting force is generated by the cutting speed, and the rest by feed motion. The consequence is a force vector that is directed diagonally into the tool at an angle of roughly 30°, across a very weak section of the blade. To avoid tool breakage, this is compensated by reducing the blade overhang and increasing the blade height, which in turn sometimes compromises the usability of the tool. By turning the tip seat 90° and utilizing the Y axis, the tool can cut its way into the workpiece, essentially with its front end, which nearly aligns the resulting cutting force vector with the longitudinal axis of the blade. FEM analyses confirmed the new solution eliminates critical stresses and increases the blade stiffness by more than six times compared to conventional blade designs.
In short, when switching to parting in the Y axis plane, you get a beneficial direction of the cutting force, resulting in less instability and vibration. This means you can ramp up the feed rate without losing stability or breaking the tool for an extremely secure and productive parting process. Simple as that.
Kevin Burton is product and industry turning specialist at Sandvik Coromant Canada. SMT
