This application is based on and claims the benefit of priority from Japanese Patent Application No. 2019-181437, filed on 1 Oct. 2019, the content of which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

Field of the Invention

The present invention relates to a numerical controller, a machine tool system, and a numerical control method. The present invention particularly relates to a numerical controller, a machine tool system, and a numerical control method each causing a machine tool to perform thread cutting while shredding chips.

Related Art

Such a numerical controller for a machine tool that performs thread cutting while shredding chips has been described in WO2016/056526, for example. WO2016/056526 describes such a controller for a machine tool that avoids, when thread cutting is performed on a workpiece, long extended chips from wrapping around a workpiece or a cutting tool, as well as avoids a machining surface of the workpiece from being damaged. Specifically, WO2016/056526 describes the controller for a machine tool, which is provided with vibration setting means that sets, during thread cutting through which a workpiece and a cutting tool are allowed to rotate relative to each other, to feed-move relative to each other in a machining feed direction, and to vibrate relative to each other in radial directions of the workpiece to helically perform cutting-in processes a plurality of times, a pattern of vibration during each of the cutting-in processes involving the vibration in such a manner that a part already machined by a different cutting-in process is partially present in a part to be machined by a predetermined cutting-in process.Patent Document 1: Pamphlet of PCT International Publication No. WO2016/056526

SUMMARY OF THE INVENTION

To improve machining accuracy when a machine tool performs thread cutting on a workpiece, it is desirable to suppress as much as possible the workpiece being rotated from being influenced by relative vibration between a cutting tool and the workpiece. On this point, in the controller described in WO2016/056526, since a cutting tool is vibrated only on one axis in radial directions of a workpiece, core misalignment would likely occur on the workpiece being rotated. Therefore, it has been demanded to suppress core misalignment from occurring due to relative vibration between a cutting tool and a machining target, to improve accuracy of a finished shape, and to suppress a tip of the cutting tool from being influenced.

(1) A first aspect of the present disclosure is a numerical controller that causes a machine tool to perform an operation for performing thread cutting through which a cutting tool and a machining target are allowed to move relative to each other to perform cutting-in processes a plurality of times on the machining target to form a thread on the machining target, the numerical controller including: a driver that controls a spindle that rotates the machining target, and drive axes having three axes;

a vibration superimposing unit that superimposes vibration to be applied to two axes or more among the three axes on the relative movement between the cutting tool and the machining target so that the cutting tool and the machining target vibrate relative to each other along a thread groove; and a thread cutting vibration adjusting unit that shifts, by a vibration phase shift amount set beforehand, a phase of the vibration relative to a phase of the spindle per each of the cutting-in processes to be performed the plurality of times.

(2) A second aspect of the present disclosure is a machine tool system including:

the numerical controller according to (1) described above; and a machine tool that allows a cutting tool and a machining target to move relative to each other to perform cutting-in processes a plurality of times on the machining target to form a thread on the machining target.

(3) A third aspect of the present disclosure is a numerical control method for a numerical controller that causes a machine tool to perform an operation for performing thread cutting through which a cutting tool and a machining target are allowed to move relative to each other to perform cutting-in processes a plurality of times on the machining target to form a thread on the machining target, the numerical control method including:

controlling a spindle that rotates the machining target, and drive axes having three axes;

superimposing vibration to be applied to two axes or more among the three axes on the relative movement between the cutting tool and the machining target so that the cutting tool and the machining target vibrate relative to each other along a thread groove; and
shifting, by a vibration phase shift amount set beforehand, a phase of the vibration relative to a phase of the spindle per each of the cutting-in processes to be performed the plurality of times.

According to the aspects of the present disclosure, where, in thread cutting on a machining target by a machine tool, vibration is applied to two axes or more among an X axis, a Y axis, and a Z axis, it is possible to suppress core misalignment from occurring due to relative vibration between a cutting tool and the machining target, to improve accuracy of a finished shape, and to suppress a tip of the cutting tool from being influenced.

