For CNC Multitasking Machines, Why Part Along Y?

B-axis turn-mills and many live-tool CNC turning centers offer Y-axis motion perpendicular to the Z axis. This third linear axis enables cutters to traverse across the spindle center line to perform operations such as milling, drilling and slotting, the goal being to machine parts complete in one setup.

Sandvik Coromant has found a way to further take advantage of that motion to more effectively perform parting-off operations compared to the traditional X-axis process on lathes without a Y axis. It achieved this by redesigning its CoroCut QD tool rotating the insert seat 90 degrees and engaging the workpiece in the Y axis so that cutting forces are directed toward the strongest portion of the tool’s blade.

“This would really benefit the customer who wants to shave seconds off cycle times with higher feed and lower noise,” says Staffan Lundström, product manager, Sandvik Coromant. “You don't have to live with noise and vibration if you have a Y axis. For the customer, it means both saving some time and adding possibilities to have unmanned production.”

Lundström had the idea of parting-off using the Y axis for a couple years until he developed a prototype with the help of a small team at Sandvik Coromant. The first tool test did not go well, resulting in rattling noises and vibrations coming from the machine tool and finally a broken insert.

“It was a major setback for us,” Lundström explains. “I didn't really understand what was wrong.”

Then, the team reviewed what had happened, decided to add internal, through-tool coolant and modified the adapter design. When it tested the new prototype on a different machine, this alternate parting-off method proved to be successful.

With the current design, at a 60-mm (2.36-inch) blade overhang, the blade bending stiffness is said to be more than six times that of a conventional tool parting-off in the X axis, providing a more stable cutting process, enabling the use of longer tools and achieving higher feed rates and faster cycle times.

In one test comparison, a shop serving the aerospace industry noted the differences between parting off a 35-mm bar of Inconel 718 on a multitasking machine using the Y-axis method with the CoroCutQD tool and the standard X-axis method with another tool. The Y-axis method achieved a cutting speed of 40 m/min and feed of 0.12 mm/rev yielding a tool life of 35 parts. The X-axis method achieved a cutting speed of 30 m/min and feed of 0.05 mm/rev yielding a tool life of only 10 parts.

Tool length can be measured using an offline presetter. The tool length becomes the tool center height when parting off, and it is important to have the center height correct, especially when parting-off to center, the company says. If it is difficult to see the cutting edge, there is a gage plane on the tool.

The tool accommodates workpiece diameters up to 180 mm (7 inches) and cutting widths of 3 to 4 mm (0.118 to 0.157 inch).