Numerical control device and numerical control method

A numerical control device for a machine tool, the machine tool including:

• a first drive shaft to move a first tool or a machining target, the first tool performing a first machining process;
• and a second drive shaft to move a second tool or the machining target, the second tool performing a second machining process, the numerical control device controlling the first drive shaft and the second drive shaft such that a movement of the second drive shaft is superimposed on a movement of the first drive shaft to allow the second machining process to be executed relative to the first machining process, the numerical control device comprising
• a control computer to, in response to a superimposition control command to superimpose the movement of the second drive shaft on the movement of the first drive shaft, perform control on the first drive shaft, the second drive shaft, and a main shaft by
• changing at least one of a first vibration rate, a second vibration rate and a main shaft rotation speed on a basis of a first vibration command, a second vibration command and a main shaft rotation speed command such that the first vibration rate stays constant and the second vibration rate stays constant, and
• changing a second amplitude such that the second drive shaft is vibrated with a third amplitude, the second amplitude being included in the second vibration command and being for vibrating the second drive shaft, the third amplitude being based on a difference obtained by subtracting a first amplitude from the second amplitude, the first amplitude being included in the first vibration command and being for vibrating the first drive shaft,
• the main shaft being a rotation axis of the machining target, the first vibration rate being the number of times that the first drive shaft vibrates per rotation of the main shaft, the second vibration rate being the number of times that the second drive shaft vibrates per rotation of the main shaft, the first vibration command being to vibrate the first drive shaft, the second vibration command being to vibrate the second drive shaft, the main shaft rotation speed command being directed to the main shaft, the main shaft rotation speed command being a command on the main shaft rotation speed per unit time.