New B-Axis Contouring for Multitasking Machines

In late June 2007, a test cut was performed successfully at the Los Angeles office of the Mori Seiki machine tool company. Olivier Thenoz, DP Mill Turn Product Manager, performed the test cut in cooperation with Randy Felten, Manager, Applications, for Mori Seiki. The pair performed a B-axis contouring operation on a Mori Seiki NT3150. The result was a part produced with outer profile with a single tool rotating smoothly about the B-axis, demonstrating the unique capabilities of the new operation. The coordinates in the NC code were output for the tool nose center using the RTCP (rotate the center point) function of the Fanuc control. The RTCP function makes the tool rotate about its control point instead of rotating about the B-axis pivot point. The RTCP function must be used for this cycle. “If you’re using one tool instead of three, you could be saving as much as 20 seconds,” said Thenoz. “If you multiply that by the number of parts you’re producing, the results can be very interesting.” Thenoz added that, while ESPRIT 2008 offers comprehensive improvements for all users, the addition of the B-axis contouring capability is an industry first.

“The axis control is amazing,” Felten said of the B-axis contouring, following the test cut. “I’ve never seen this before, though the possibility has been discussed. There are people who have wanted to do this, but there was no one who did.”

• Maintain a constant lead angle between the tool and the surface
• Minimize the tool rotation, tilting the tool only when necessary

The “Minimize change of Lead Angle” strategy maintains the initial lead angle of the tool in relation to the profile being cut. The initial lead angle is a function of the original tool orientation in the turret and the orientation of the first element in the profile. As the slope of the profile changes, the tool tilts accordingly to maintain the same lead angle relative to the surface being cut. The total tilt of the tool is limited by a user-defined range of lead angles and by the automatic detection of a collision between the tool and the surface.

This strategy produces the best cutting conditions by keeping the best angle between the tool and the surface being cut, but it produces almost constant movement in the B-axis which can generate over-travel motion. The “Minimize change of Orientation Angle” strategy maintains the initial tool orientation until the tool reaches a surface that cannot be cut while the tool is in its current orientation. Only then does the tool tilt as much as necessary to cut the surface within the user-defined B-axis angle limits. This strategy minimizes the rotation of the B-axis to areas that cannot be cut with a traditional tool angle. This strategy was used for the test cut mentioned earlier.

Both strategies are easily verified and users can display useful tool axis vectors on the screen in order to choose the best strategy for any part geometry.

During the entire cut, the user has full control over the range of B-axis rotation. The angle of the tool can be limited in two ways. First, user-defined minimum and maximum B-axis angles define the total allowable range of B-axis motion on the head during the cut. The tool angle will never exceed these limits. Second, for even tighter control, user-defined minimum and maximum lead angles define the allowable range of the local lead angle of the tool.

Built-in collision detection prevents a collision between the part and the tool when the toolpath is calculated. Instead of relying solely on the geometric definition of the tool, collision detection uses a silhouette of the tool that can be controlled by the user. The shape of the tool silhouette depends on the actual tool geometry and user-defined clearance values for the front and back of the tool. Extra clearance can be added to the front and back of the tool to avoid the possibility of the tool dragging on the material as the tool cuts areas that have a similar angle to the front or back of the tool.

By basing the new B-Axis Contouring cycle on ESPRIT’s standard SolidTurn Contouring cycle, users gain productivity quickly within a familiar environment. Programming time is reduced because users can fully leverage the B-axis capabilities of their machine tool within a single operation. With traditional turning cycles, the B-axis is first rotated into position at the beginning of the cut and maintains that position throughout the cut. The new B-Axis Contouring cycle allows for dynamic, continuous rotation of the B-axis to fully leverage the capabilities of the machine tool.

Programmers no longer need to create several programs using traditional methods. Instead, a single B-axis contouring operation will finish an entire profile without stopping for tool changes. Eliminating tool changes saves precious seconds in the overall cycle time and also eliminates the possibility of witness marks where one tool finishes and another begins. By forming close relationships with machine tool manufacturers, DP Technology is able to offer their customers the latest technology to get the most from their machine tool investment.