Cutting tool and cutting method
A cutting tool for cutting a hard brittle material is formed from a light-transmittable material through which laser light can pass and is provided with a rake angle, the laser light is propagated through the cutting tool, the cutting tool and the hard brittle material are brought into contact with each other, the laser light is incident to at least a contact part where the cutting tool and the hard brittle material are in contact with each other and a part with the rake angle, the laser light except for Fresnel reflection light on an end surface of the cutting tool is incident to the hard brittle material through the contact part and the rake angle part to soften the hard brittle material, and the softened hard brittle material is cut.
1. A cutting method comprising:
providing a cutting tool for cutting a hard brittle material, the cutting tool being made of a commercially-available square diamond prism, and providing the square diamond prism of the cutting tool with a rake angle;
propagating laser light from a laser light source through an optical fiber to a convergence lens and then into and through the cutting tool, and bringing the cutting tool and the hard brittle material into contact with each other to irradiate, with the laser light, at least a contact part of the cutting tool where the cutting tool and the hard brittle material are in contact with each other and a rake angle part of the cutting tool where the rake angle is provided;
irradiating the hard brittle material through the contact part and the rake angle part with the laser light propagated through the cutting tool except for Fresnel reflection light reflected on an end surface of the cutting tool to soften the hard brittle material; and
cutting the softened hard brittle material,
wherein the laser light, which is propagated through the cutting tool except for the Fresnel reflection light reflected on the end surface of the cutting tool, is incident, through the contact part and the rake angle part, to the hard brittle material perpendicularly to a planar direction of a surface of the hard brittle material that is in contact with the cutting tool.
2. The cutting method according to claim 1 , wherein
the hard brittle material is formed from a material causing metal phase transition by coming into contact with the cutting tool, and
a contact load between the cutting tool and the hard brittle material is set to a load causing the metal phase transition in the hard brittle material.
3. The cutting method according to claim 1 , wherein the laser light propagating through the cutting tool is parallel light.
4. The cutting method according to claim 1 , wherein
the end surface is formed in an arc shape as the cutting tool is seen along a cutting direction of the hard brittle material, and
the end surface has a radius R as expressed by Equation 4:
R >[ r /sin(θcrt)] [Equation 4]
wherein
a diameter of light flux of the laser light emitted from the end surface of the cutting tool as seen along the cutting direction is 2r, and a critical angle at which the laser light is totally reflected at an angle normal to the end surface of the cutting tool at the time of emission of the laser light from the inside to the outside of the cutting tool is θcrt°.
5. The cutting method according to claim 1 , wherein
the end surface is formed in a V shape as the cutting tool is seen along a cutting direction of the hard brittle material, and
the end surface has a V-shaped opening angle φ under a total-reflection condition, as expressed by Equation 6:
φ>2×(90°−θmax) [Equation 6]
wherein
the total-reflection condition is expressed by Equation 5:
θmax=sin −1 ( n 2/ n 1) [Equation 5]
a refractive index of the cutting tool corresponding to a wavelength of the laser light is n1 and a refractive index of atmosphere outside the cutting tool is n2.