Chamfering apparatus and chamfering method

A chamfering apparatus includes: a laser beam transmissive member allowing a laser beam to be transmitted therethrough and contacting one surface of a workpiece, the laser beam transmissive member including an inclined surface that is inclined in an opposite direction to a chamfering direction relative to the one surface in a state where the laser beam transmissive member is in contact with the one surface; and a laser machining head configured to emit an ultrashort pulse laser beam for forming a laser filament inside an edge portion to the inclined surface of the laser beam transmissive member. The ultrashort pulse laser beam is transmitted through the laser beam transmissive member, incident on the one surface of the workpiece from the laser beam transmissive member, transmitted through the edge portion in the chamfering direction, and forms a laser filament inside the edge portion, the laser filament extending in the chamfering direction.

TECHNICAL FIELD

The present invention relates to an apparatus for and a method of chamfering an edge portion of a workpiece.

BACKGROUND ART

In the manufacturing of a glass plate product, a workpiece is obtained by cutting it out of a raw material, such that the workpiece is in a size that matches the size of the product, and then chamfering is performed on edge portions of the workpiece. Generally speaking, it is desirable that the chamfering angle be about 45°.

Conventionally, chamfering has been performed mainly by a mechanical method using grinding stone. However, in such a mechanical method, cullet is generated and adheres to the workpiece during the chamfering. Therefore, it is necessary to clean the workpiece after the chamfering.

Patent Literature 1 proposes chamfering edge portions by forming laser filaments inside glass (see, in particular, FIGS. 4 and 5). This chamfering technique indicates a possibility of overcoming the drawbacks in conventional chamfering methods.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

However, it is considered that in order to obtain a desirable chamfering angle through actual application of this chamfering technique, it is necessary to diagonally emit a pulse laser beam onto the surface of the workpiece. In such a case, the incidence angle at the surface of the workpiece may become excessive great, and accordingly, there is a risk of great reflection loss at the surface of the workpiece. Thus, in this case, it is considered that forming laser filaments inside the workpiece is difficult, and for this reason chamfering cannot be realized.

An object of the present invention is to provide an apparatus for and a method of chamfering an edge portion of a workpiece at a desirable chamfering angle by forming laser filaments inside the workpiece.

Solution to Problem

A chamfering apparatus according to one aspect of the present invention is a chamfering apparatus for forming a tapered surface on an edge portion formed by two surfaces of a workpiece, the workpiece allowing a laser beam to be transmitted therethrough, the tapered surface extending in a chamfering direction that is inclined relative to one of the two surfaces. The chamfering apparatus includes: a laser beam transmissive member that allows a laser beam to be transmitted therethrough and that contacts the one surface of the workpiece, the laser beam transmissive member including an inclined surface that is inclined in an opposite direction to the chamfering direction relative to the one surface in a state where the laser beam transmissive member is in contact with the one surface; and a laser machining head configured to emit an ultrashort pulse laser beam for forming a laser filament inside the edge portion to the inclined surface of the laser beam transmissive member, such that the ultrashort pulse laser beam is transmitted through the laser beam transmissive member, incident on the one surface of the workpiece from the laser beam transmissive member, transmitted through the edge portion in the chamfering direction, and forms a laser filament inside the edge portion, the laser filament extending in the chamfering direction.

According to the above configuration, the inclined surface of the laser beam transmissive member is positioned on the optical path of the ultrashort pulse laser beam, and forms an interface between a medium through which the ultrashort pulse laser beam emitted from the laser machining head propagates (i.e., incidence side) and the laser beam transmissive member (i.e., transmission side). The one surface of the workpiece is positioned on the optical path of the ultrashort pulse laser beam, and forms an interface between the laser beam transmissive member (i.e., incidence side) and the workpiece (i.e., transmission side). Assume that the incidence angle at the one surface is i2, and the inclination angle of the inclined surface relative to the one surface is φ. In this case, the refraction angle r1at the inclined surface satisfies the following equation: r1=i2−φ. In order to increase the incidence angle i2at the one surface for the purpose of adjusting the chamfering direction to a direction corresponding to a desirable chamfering angle, the inclination angle φ may be set to a value close to the incidence angle i2based on the following equation: r1=i2−φ. In this manner, the refraction angle r1at the inclined surface can be reduced. As a result, the incidence angle i1at the inclined surface can also be reduced. This makes it possible to suppress the reflection loss of the ultrashort pulse laser beam at the inclined surface.

As described above, the ultrashort pulse laser beam is incident on the surface of the workpiece through the laser beam transmissive member including the inclined surface, which is inclined in the opposite direction to the chamfering direction. This makes it possible to make the incidence angle i2at the surface of the workpiece great and allow the ultrashort pulse laser beam to be transmitted through the workpiece while making the incidence angle i1at the inclined surface small to suppress the reflection loss at the inclined surface. As a result, necessary beam intensity for forming the laser filament inside the edge portion can be obtained, and the chamfering of the edge portion of the workpiece can be performed at a desirable chamfering angle.

The chamfering apparatus may include a machining head scanning device configured to move the laser machining head in an extending direction of the edge portion. The laser beam transmissive member may extend in the extending direction in a state where the laser beam transmissive member is in contact with the one surface. The laser machining head may emit the ultrashort pulse laser beam to the inclined surface of the laser beam transmissive member while being moved by the machining head scanning device in the extending direction relative to the laser beam transmissive member and the workpiece.

This configuration makes it possible to readily keep the state where the laser beam transmissive member is in contact with the surface of the workpiece. As a result, the reflection loss at the surface is suppressed.

The chamfering apparatus may include a machining head scanning device including: a machining head holder configured to hold the laser machining head; and a transmissive member holder configured to hold the laser beam transmissive member, the machining head scanning device moving the laser machining head and the laser beam transmissive member in an extending direction of the edge portion relative to the workpiece in a state where the laser beam transmissive member held by the transmissive member holder is in contact with the one surface. The laser machining head may emit the ultrashort pulse laser beam to the inclined surface of the laser beam transmissive member while being moved by the machining head scanning device together with the laser beam transmissive member in the extending direction relative to the workpiece.

The chamfering apparatus may include a workpiece conveying device configured to move the workpiece parallel to an extending direction of the edge portion. The laser machining head and the laser beam transmissive member may be not conveyed by the workpiece conveying device. The laser beam transmissive member may contact the one surface of the workpiece while the workpiece is being moved by the workpiece conveying device in the extending direction. The laser machining head may emit the ultrashort pulse laser beam to the inclined surface of the laser beam transmissive member.

The chamfering apparatus may include a workpiece conveying device configured to move the workpiece parallel to an extending direction of the edge portion. The laser machining head may be not conveyed by the workpiece conveying device. The laser beam transmissive member may be moved by the workpiece conveying device together with the workpiece in a state where the laser beam transmissive Member is in contact with the one surface. The laser machining head may emit the ultrashort pulse laser beam to the inclined surface of the laser beam transmissive member while the laser beam transmissive member is being moved by the workpiece conveying device.

The laser beam transmissive member may include: a contacted surface that makes surface contact with the one surface; and a prism including the inclined surface.

The laser beam transmissive member may be a liquid member. The chamfering apparatus may include: a transmissive member reservoir configured to store the laser beam transmissive member; and a workpiece holder configured to hold the workpiece in a state where the edge portion is immersed in the laser beam transmissive member stored in the transmissive member reservoir. A liquid surface of the laser beam transmissive member in the transmissive member reservoir may form the inclined surface. The workpiece holder may hold the workpiece in a state where the one surface of the workpiece is inclined relative to the liquid surface.

A chamfering method according to another aspect of the present invention is a chamfering method of forming a tapered surface on an edge portion formed by two surfaces of a workpiece, the workpiece allowing a laser beam to be transmitted therethrough, the tapered surface extending in a chamfering direction that is inclined relative to one of the two surfaces. The method includes: bringing a laser beam transmissive member that allows a laser beam to be transmitted therethrough into contact with the one surface, such that an inclined surface of the laser beam transmissive member is inclined in an opposite direction to the chamfering direction relative to the one surface; emitting an ultrashort pulse laser beam for forming a laser filament inside the edge portion to the inclined surface of the laser beam transmissive member, such that the ultrashort pulse laser beam is transmitted through the laser beam transmissive member, incident on the one surface of the workpiece from the laser beam transmissive member, and transmitted through the edge portion in the chamfering direction; and forming a laser filament inside the edge portion by the ultrashort pulse laser beam, the laser filament extending in the chamfering direction.

Advantageous Effects of Invention

The present invention makes it possible to chamfer an edge portion of a workpiece at a desirable chamfering angle by forming laser filaments inside the workpiece.

DESCRIPTION OF EMBODIMENTS

Hereinafter, embodiments of the present invention are described with reference to the drawings. In the drawings, the same or corresponding elements are denoted by the same reference signs, and repeating the same detailed descriptions is avoided below.

As shown inFIG. 1, a chamfering method of the present embodiment is suitably performable in the manufacturing process of a plate-shaped product90, such as a glass substrate for liquid crystal, a cover glass for a liquid crystal display or organic light-emitting diode display, or an architectural plate glass. In the manufacturing of the product90, first, a plate-shaped workpiece81is obtained by cutting it out of a plate-shaped raw material80, such that the workpiece81is in a size that matches the size of the product90. It should be noted that the method of cutting the workpiece81out of the raw material80is not particularly limited. For example, mechanical cutting or laser cutting is used.

The workpiece81includes, as its surfaces, a pair of flat surfaces82aand82bspaced apart from each other in the thickness direction of the workpiece81and side surfaces83connecting between the flat surfaces82aand82b. The workpiece81includes, as its edge portions84, first edge portions85and second edge portions86. The first edge portions85are formed by the first flat surface82aand the side surfaces83. The second edge portions86are formed by the second flat surface82band the side surfaces83. When seen in a plan view, the first edge portions85form a closed loop along the sides of the first flat surface82a. The same is true of the second edge portions86. The flat surfaces82aand82bare substantially congruent with each other. The side surfaces83are substantially perpendicular to the flat surfaces82aand82b. Each edge portion84forms a substantially 90° sharp edge.

Next, chamfering is performed on these edge portions84. As a result of the chamfering, chamfered portions91are formed on the respective edge portions84. The chamfered portions91include first chamfered portions92and second chamfered portions93. The first chamfered portions92are formed on the respective first edge portions85, and the second chamfered portions93are formed on the respective second edge portions86. The chamfered portions91include respective tapered surfaces94. Each of the tapered surfaces94connects between two surfaces that form a corresponding one of the edge portions84. Each tapered surface94is inclined relative to the two surfaces, and extends in the extending direction of the corresponding edge portion84. The tapered surfaces94include first tapered surfaces95of the respective first chamfered portions92and second tapered surfaces96of the respective second chamfered portions93.

One of the purposes of the chamfering is to reduce external impact shock (i.e., to prevent damage to the product90when an external object hits the product90, and prevent damage to the external object at the time). In the chamfering method of the present embodiment, each chamfered portion91is formed such that the angle formed between the tapered surface94and one of the two surfaces forming the edge portion84, i.e., the chamfering angle, is about 45°.

As one example, the workpiece81is rectangular When seen in its thickness direction (i.e., when seen in a plan view). The side surfaces83include: a first long side surface83aconnecting between first long sides of the respective two flat surfaces82aand82b; a second long side surface83bconnecting between second long sides of the respective two flat surfaces82aand82b; a first short side surface83cconnecting between first short sides of the respective two flat surfaces82aand82b; and a second short side surface83dconnecting between second short sides of the respective two flat surfaces82aand82b.

In this case, the first edge portions85include: a first long edge portion85a, which is formed by the first flat surface82aand the first long side surface83aand which extends in the extending direction of the first long side (perpendicularly to the thickness direction); a second long edge portion85b, which is formed by the first flat surface82aand the second long side surface83band which extends in the extending direction of the second long side (in parallel to the extending direction of the first long side); a first short edge portion85c, which is formed by the first flat surface82aand the first short side surface83cand which extends in the extending direction of the first short side (perpendicularly to the extending direction of the first long side and perpendicularly to the thickness direction); and a second short edge portion85d, which is formed by the first flat surface82aand the second short side surface83dand which extends in the extending direction of the second short side (in parallel to the extending direction of the first short side). Reference signs92ato92dinFIG. 1denote a first long chamfered portion, a second long chamfered portion, a first short chamfered portion, and a second short chamfered portion corresponding to the edge portions85ato85d, respectively, and these chamfered portions are first chamfered portions92. Reference signs95ato95ddenote a first long tapered surface, a second long tapered surface, a first short tapered surface, and a second short tapered surface corresponding to the chamfered portions92ato92d, respectively, and these tapered surfaces are the first tapered surfaces95.

The same applies to the second edge portions86, the second chamfered portions93, and the second tapered surfaces96. Similar to the edge portions85ato85d, reference signs86ato86dinFIG. 1denote a third long edge portion, a fourth long edge portion, a third short edge portion, and a fourth short edge portion, which are the second edge portions86. Reference signs93ato93ddenote a third long chamfered portion, a fourth long chamfered portion, a third short chamfered portion, and a fourth short chamfered portion corresponding to the edge portions86ato86d, respectively, and these chamfered portions are the second chamfered portions93. Reference signs96ato96ddenote a first long tapered surface, a second long tapered surface, a first short tapered surface, and a second short tapered surface corresponding to the chamfered portions93ato93d, respectively, and these tapered surfaces are the second tapered surfaces96.

In the chamfering method of the present embodiment, laser filaments F (seeFIGS. 2Band3A) are formed inside the edge portions84of the workpiece81. Each laser filament F is a hollow portion formed inside the workpiece81when an ultrashort pulse laser beam L (seeFIGS. 2A, 2B, and 3A) is transmitted through the inside of the workpiece81. The laser filament F extends linearly along the optical path of the ultrashort pulse laser beam L. In the present specification, the description of the details of the formation principle of the laser filament F is omitted.

The ultrashort pulse laser beam L is a pulse laser beam whose pulse duration is set to a short time of, for example, several femtoseconds to several hundred picoseconds. Other various parameters of the ultrashort pulse laser beam L (e.g., energy, beam intensity, wavelength, and focal length) are set such that the laser filaments F are formed inside the edge portions84. The wavelength is, for example, set to be within the range from the green light region to the near-infrared region. Alternatively, the wavelength may be set outside the range. The focal length is set such that the focal point is positioned inside each edge portion84.

The workpiece81is made of a material that allows the ultrashort pulse laser beam L to be transmitted therethrough and that has such brittleness that laser machining is performable thereon. Suitable examples of the material of the workpiece81include glass (e.g., soda glass, quartz glass, LCD glass, hybrid glass, tempered glass, etc.), single crystal corundum (e.g., sapphire glass), and ceramic.

FIGS. 2A and 2Bshow a chamfering apparatus1of Embodiment 1. The chamfering apparatus1includes: a holding stand2; a laser beam transmissive member3; a laser machining head4; a laser oscillator5; and a machining head scanning device6. The machining head seaming device6includes: a machining head holder7configured to hold the laser machining head4; and a movement actuator8configured to move the machining head holder7. Operations of the laser oscillator5and the movement actuator8are controlled by a controller10.

The holding stand2holds the workpiece81. The holding stand2includes a horizontal top surface2a, in which a large number of vent holes (not shown) are formed. The holding stand2may be of a suction type or a floating type. The holding stand2may suck air through the vent holes to suck the workpiece81onto the top surface2a, or may blow air out of the vent holes to make the workpiece81float slightly above the top surface2a. In either case, the holding stand2holds the workpiece81in such an orientation that the first flat surface82aor the second flat surface82bextends horizontally directly on or slightly above the top surface2a.

The laser beam transmissive member3allows the ultrashort pulse laser beam L to be transmitted therethrough. The laser beam transmissive member3contacts one of the two surfaces forming each edge portion84. The laser beam transmissive member3includes inclined surfaces13, each of which is inclined relative to the one surface when the laser beam transmissive member3is in contact with the one surface.

FIGS. 2A and 2Bshow a state where chamfering is being performed on the first edge portions85(including the first long edge portion85a, the second long edge portion85b, the first short edge portion85c, and the second short edge portion85d). Of the two surfaces forming each first edge portion85(i.e., the first flat surface82aand the side surface83), the first flat surface82afaces the top surface2aof the holding stand2. The laser beam transmissive member3is made of an optical glass prism, and includes contacted surfaces11, each of which makes surface contact with the side surface83, which is one of the two surfaces forming the first edge portion85.

As shown inFIG. 2A, when seen in a plan view, the top surface2aof the holding stand2is larger than the workpiece81, and the edge lines of the workpiece81are positioned inward of the edge lines of the top surface2a. As shown inFIG. 2B, the laser beam transmissive member3includes a supported surface12, which is supported on the top surface2aoutside the edge lines of the workpiece81. The laser beam transmissive member3is held by the holding stand2in a state where the contacted surfaces11are in contact with respective surfaces (the side surfaces83) of the workpiece81. The side surfaces83stand upright perpendicularly to the first flat surface82a. The laser beam transmissive member3has a right-triangle cross section. Each contacted surface11forms a right angle with the supported surface12, and each inclined surface13forms the hypotenuse of the right triangle. The contacted surfaces11contact the respective side surfaces83in a state where the contacted surfaces11stand upright perpendicularly to the supported surface12and the top surface2asupporting the supported surface12. The inclined surfaces13are inclined such that the closer the inclined surfaces13are to the top surface2a, the more distant the inclined surfaces13are from the contacted surfaces11and the surfaces being in contact therewith (i.e., the side surfaces83).

As shown inFIG. 2A, the laser beam transmissive member3extends in the extending directions of the edge portions84when the laser beam transmissive member3is in contact with the surfaces of the workpiece81. Specifically, the laser beam transmissive member3includes: a first long transmissive member3a, which extends in the extending direction of the first long edge portion85a(i.e., the extending direction of the first long side) and which is in surface contact with the entire first long side surface83ain the extending direction; a second long transmissive member3b, which extends in the extending direction of the second long edge portion85b(i.e., the extending direction of the first long side) and which is in surface contact with the entire second long side surface83bin the extending direction; a first short transmissive member3c, which extends in the extending direction of the first short edge portion85c(i.e., the extending direction of the first short side) and which is in surface contact with the entire first short side surface83cin the extending direction; and a second short transmissive member3d, which extends in the extending direction of the second short edge portion85d(i.e., the extending direction of the second short side) and which is in surface contact with the entire second short side surface83din the extending direction. These four transmissive members3ato3dmay be formed as separate members. Alternatively, the four transmissive members3ato3dmay be partly or entirely integrated together. As one example, the first long transmissive member3aand the first short transmissive member3cmay form a transmissive member that is L-shaped when seen in a plan view, and also, the second long transmissive member3band the second short transmissive member3dmay form a transmissive member that is L-shaped when seen in a plan view. As another example, the four transmissive members3ato3dmay form a transmissive member that is in the shape of a rectangular window frame when seen in a plan view.

The laser machining head4emits the ultrashort pulse laser beam L, which is intended for forming laser filaments F inside the edge portions84, to each inclined surface13of the laser beam transmissive member3while being moved by the machining head scanning device6in the extending direction of the corresponding edge portion84relative to the holding stand2, the laser beam transmissive member3, and the workpiece81. The laser oscillator5oscillates the ultrashort pulse laser beam L. The laser machining head4may include an objective lens (not shown) for adjusting the focal length, such that the ultrashort pulse laser beam L focuses inside the edge portion84. The laser machining head4may be provided with a fine adjustment mechanism configured to cause the laser machining head4to make micromovements, such that the laser light is precisely emitted to machining positions based on glass end surface information that is obtained through measurement by a glass end surface measuring device. In this case, the operation of the fine adjustment mechanism may be controlled by the controller10.

The laser machining head4moves along the extending direction of each of the first edge portions85, which form a closed loop when seen in a plan view. While the laser machining head4is moving from one end to the other end of the first long edge portion85ain the extending direction of the first long edge portion85a(i.e., the extending direction of the first long side), a large number of laser filaments F are formed inside the first long edge portion85a,such that the laser filaments F are arranged in the extending direction of the first long edge portion85a. A large number of laser filaments F are also formed inside each of the other edge portions85bto85dof the first edge portions85in the same manner. The machining head scanning device6may be configured in any form. For example, the machining head holder7may be realized by a linear motion mechanism that is programmed to move along predetermined moving paths, and the movement actuator8may be an electric motor that drives the linear motion mechanism.

FIG. 3Ais an enlarged view ofFIG. 2B, andFIG. 3Bshows a comparative example. The laser beam transmissive member3is absent in the comparative example. In such a case, the ultrashort pulse laser beam L needs to be directly incident on the side surface83of the workpiece81after propagating through air. The incidence angle i at the side surface83is the arc sine of a value that is obtained by multiplying the relative refractive index n of the workpiece81relative to the air by the sine of the refraction angle r (i=arcsin (nsinr)). The refraction angle r at the side surface83is the complementary angle of the chamfering angle θC(r=90−θC).

As one non-limiting example, assume that the relative refractive index n of the workpiece81relative to the air is 1.45. In this case, if the refraction angle r is 43.6°, then the incidence angle i is 90° (sin90°≈1.45sin43.6°). In the first place, reflection of the ultrashort pulse laser beam L on the side surface83becomes obvious around when the incidence angle i exceeds 18°. If the incidence angle i is set to 17.5° as indicated by a light beam (1) in order to allow the ultrashort pulse laser beam L to be sufficiently transmitted through the workpiece81, then the refraction angle r is 12.0° (r=arcsin (sin17.5°/1.45)). In this case, the chamfering angle θCis 78.0°, which is far from a desirable value (e.g., 45°). Even if the incidence angle i is increased as indicated by a light beam (2) in order to bring the chamfering angle θCcloser to 45°, most of the ultrashort pulse laser beam L reflects on the side surface83, and thus the ultrashort pulse laser beam L is hardly transmitted through the workpiece81. As a result, necessary beam intensity for forming the laser filaments F inside the edge portion84cannot be obtained.

FIG. 3Ashows the optical axis of the ultrashort pulse laser beam L by one-dot chain line. As shown inFIG. 3A, in the present embodiment, the ultrashort pulse laser beam L emitted from the laser machining head4propagates through air, and is incident on the inclined surface13of the laser beam transmissive member3to be transmitted through the laser beam transmissive member3. The ultrashort pulse laser beam L is transmitted through the inside of the laser beam transmissive member3from the inclined surface13and reaches the contacted surface11without exiting from the laser beam transmissive member3to the air. The ultrashort pulse laser beam L is then incident on the surface of the workpiece81(the side surface83) from the contacted surface11, and transmitted through the first edge portion85from the side surface83. The ultrashort pulse laser beam L is transmitted through the inside of the first edge portion85in a chamfering direction. The “chamfering direction” is a direction in which the tapered surface94(the first tapered surface95) to be formed as a result of irradiation with the ultrashort pulse laser beam L is inclined relative to one of the two surfaces forming the edge portion84(the first edge portion85), which is irradiated with the ultrashort pulse laser beam L, the one surface being in contact with the laser beam transmissive member3(i.e., the side surface83).

The inclined surface13is inclined in the opposite direction to the chamfering direction by an inclination angle φ relative to the contacted surface11and the surface of the workpiece81(the side surface83), which is in contact with the contacted surface11. The wording “inclined in the opposite direction” herein means being inclined with respect to an axis that extends in the same direction as the extending direction of an axis with respect to which the chamfering direction is inclined, but being inclined in the opposite direction to the chamfering direction. The chamfering direction is inclined (clockwise inFIG. 3A) in one direction with respect to an axis that extends in the extending direction of the first edge portion85(i.e., the direction perpendicular to the plane ofFIG. 3) relative to the surface of the workpiece81(the side surface83), which is in contact with the laser beam transmissive member3, by the chamfering angle θC. On the other hand, the inclined surface13is inclined (counterclockwise inFIG. 3A) in the opposite direction to the chamfering direction with respect to another axis that also extends in the extending direction of the first edge portion85relative to the surface (the side surface83) by the inclination angle φ. The chamfering angle θCand the inclination angle φ herein are both acute angles.

The inclined surface13forms an interface between the laser beam transmissive member3and a medium (the air) through which the ultrashort pulse laser beam L emitted from the laser machining head4propagates. The contacted surface11and the surface (the side surface83) being in contact therewith form an interface between the laser beam transmissive member3and the workpiece81. Hereinafter, it is assumed that the incidence angle of the ultrashort pulse laser beam L at the inclined surface13of the laser beam transmissive member3is i1; the refraction angle thereof is r1; the incidence angle of the ultrashort pulse laser beam L at the surface (the side surface83) of the workpiece81is i2; and the refraction angle thereof is r2. It is also assumed that the absolute refractive index of the air for the ultrashort pulse laser beam L is nA; the absolute refractive index of the laser beam transmissive member3for the ultrashort pulse laser beam L is nB; and the absolute refractive index of the workpiece81for the ultrashort pulse laser beam L is nC. It is further assumed that the incidence position of the ultrashort pulse laser beam L on the inclined surface13is P1; the incidence position of the ultrashort pulse laser beam L on the surface (the side surface83) is P2; and the intersection point of the inclined surface13and the contacted surface11is V.

Based on the Snell's law, the incidence angle i1and the refraction angle r1satisfy the following equation: sini1/sinr1=nB/nA. Also, the incidence angle i2and the refraction angle r2satisfy the following equation: sini2/sinr2=nC/nB. The refraction angle r2is the complementary angle of the chamfering angle θC, and satisfies the following equation: r2=90−θC. The sum of the inner angles of ΔVP1P2is 180°; ∠VP1P3=90+r1; and ∠VP2P1=90−i2. Accordingly, the inclination angle φ(∠P1VP2) satisfies the following equation: φ=i2−r1.

In order to set the chamfering angle θCto 45°, which is one example of a desirable value, it is necessary to increase the refraction angle r2to 45°, and it is also necessary to increase the incidence angle i2in accordance therewith. In the present embodiment, by bringing the inclination angle φ close to the incidence angle i2, the refraction angle r1and consequently the incidence angle i1are allowed to be small (r1=i2−φ). This makes it possible to suppress the reflection loss at the inclined surface13and allow the ultrashort pulse laser beam L to be transmitted through the laser beam transmissive member3. In particular, if the inclination angle φ is equal to the incidence angle i2, the ultrashort pulse laser beam L can be made incident on the inclined surface13perpendicularly. In this case, there is substantially no reflection. It should be noted that if the inclination angle φ is greater than the incidence angle i2(i.e., if the refraction angle r1is a negative value), then the ultrashort pulse laser beam L is incident on the inclined surface13from the opposite side to the incidence direction shown inFIG. 3Awith respect to the normal line to the inclined surface13.

As one non-limiting example, assume that the incidence angle i1is 17.5°; the relative refractive index nB/nAof the laser beam transmissive member3to the air is 1.45; and the relative refractive index nC/nBof the workpiece81to the laser beam transmissive member3is 1.00. In this case, in order to obtain the chamfering angle θCof 45°, the refraction angle r1needs to be 12.0° (r1=arcsin (sin17.5°/1.45)), which is the same as the refraction angle r in the comparative example, while the refraction angle r2needs to be 45°. At the time, the chamfering angle θCof 45° can be realized if the inclination angle φ is 33°, because in this case the incidence angle i2is 45°, and the incidence angle i2and the refraction angle r2follow the Snell's law (sini2/sinr2=1.00).

As previously described, various materials are applicable as the material of the workpiece81. The workpiece81is a brittle material that allows the ultrashort pulse laser beam L to be transmitted therethrough (e.g., transparent ceramic, polymer, transparent conductor, various glass, rock crystal, quartz, diamond, sapphire, etc.) The laser beam transmissive member3is a prism, and a laser beam transmissive material such as optical glass is selected as the material of the laser beam transmissive member3. When the material of the workpiece81and the required chamfering angle θCare determined, the inclination angle φ of the laser beam transmissive member3can be determined, accordingly.

The ultrashort pulse laser beam L propagates in the chamfering direction inside the first edge portion85. As described above, the ultrashort pulse laser beam L reaches the inside of the first edge portion85with suppressed reflection loss. This makes it possible to keep the beam intensity high inside the first edge portion85. Consequently, a laser filament F is formed extending in the chamfering direction. The laser filament F is formed inside the first edge portion85, that is, formed between the two surfaces forming the first edge portion85(i.e., the side surface83and the first flat surface82a). It should be noted that since the focal length of the ultrashort pulse laser beam L is adjusted as previously described, the laser filament F is not formed inside the laser beam transmissive member3. The ultrashort pulse laser beam L transmitted through the inside of the first edge portion85exits the workpiece81from the other one of the two surfaces forming the first edge portion85(i.e., exits from the first flat surface82a).

Returning toFIG. 2A, as a result of irradiating the inclined surface13with the ultrashort pulse laser beam L while moving the laser machining head4, a large number of laser filaments F are arranged in the extending direction of the first edge portion85at minute intervals. After the laser filaments F are formed over the entire first edge portion85in the extending direction, by lightly hitting the corner of the first edge portion85, the tip side of the first edge portion85can be separated from the workpiece81, such that the separation is made at the positions where the laser filaments F are formed. It should be noted that in a case where the workpiece81is made of non-tempered glass, it is possible that the corner portion cannot be separated by merely forming the laser filaments F. In this case, the corner portion can be separated by additionally applying heat to the cut positions with a heat source, such as a laser. As a result, the first chamfered portion92is formed, which includes the first tapered surface95, which is inclined by the chamfering angle θCrelative to the surface (the side surface83).

As described above, by irradiating the workpiece81with the ultrashort pulse laser beam L through the laser beam transmissive member3including the inclined surface13, which is inclined in the opposite direction to the chamfering direction of the chamfered portion to be formed (i.e., the first chamfered portion92), a desirable chamfering angle θCcan be obtained even when the incidence angle i1at the inclined surface13is made sufficiently small. Moreover, during the formation of the chamfered portion (the first chamfered portion92), cullet is not generated from the workpiece81. Therefore, a large cleaning device for cleaning the workpiece81after the chamfering is not required. Since the concern about the adhesion of cullet to the workpiece81is reduced, quality inspection at the end of the process can be simplified.

In the present embodiment, in a state where the laser beam transmissive member3extends in the extending direction of the edge portion84and is in contact with the surface of the workpiece81(the side surface83), the laser machining head4emits the ultrashort pulse laser beam L to the inclined surface13of the laser beam transmissive member3while being moved by the machining head scanning device6in the extending direction of the edge portion84relative to the laser beam transmissive member3and the workpiece81. This makes it possible to readily keep the laser beam transmissive member3in surface contact with the workpiece81, and readily prevent the reflection of the ultrashort pulse laser beam L on the surface of the workpiece81.

FIGS. 4A to 4Cshow one example of a method of performing chamfering on one of the second edge portions86. As shown inFIG. 4A, after the chamfering of the first edge portion85is ended, the workpiece81may be turned over and supported on the top surface2aof the holding stand2. Then, chamfering may be performed on the second edge portion86in the same manner as the chamfering of the first edge portion85. As shown inFIG. 4B, the laser beam transmissive member3may contact the second flat surface82b, which is one of the two surfaces forming the second edge portion86. In this case, the chamfering direction is the direction in which the second tapered surface96to be formed is inclined relative to the second flat surface82b, and the inclined surface13is inclined relative to the second flat surface82bin the opposite direction to the chamfering direction. It should be noted that the chamfering of the first edge portion85may also be performed such that the laser beam transmissive member3is brought into contact with the first flat surface82ain such a manner as shownFIG. 4B. However, it is highly likely that the first flat surface82aand the second flat surface82bserve as design surfaces of the product90, which are visible while the product90is in use. By bringing the contacted surface11into contact with the side surface83, which is the less visible one of the two surfaces during the use of the product90, as shown inFIGS. 3B and 4A, laser filaments F can be formed by using the laser beam transmissive member3without having a concern about possible damage to the design surfaces. Further alternatively, as shown inFIG. 4C, the contacted surface11of the laser beam transmissive member3may be brought into contact with the side surface83, and then the inclined surface13may be irradiated with the ultrashort pulse laser beam L from below. It should be noted that the chamfering of the first edge portion85may also be performed in such a manner as shown inFIG. 4C.

As shown inFIGS. 5A and 5B, in a chamfering apparatus201of Embodiment 2, a machining head scanning device206includes: a machining head holder207configured to hold the laser machining head4; and a transmissive member holder221configured to hold a laser beam transmissive member203. Similar to Embodiment 1, the laser beam transmissive member203is also made of an optical glass prism, and includes: a contacted surface211, which contacts one of the two surfaces forming the edge portion84of the workpiece81(in the illustrated example, the side surface83forming part of the first edge portion85); and an inclined surface213, which is, when the contacted surface211is in contact with the one surface, inclined relative to the contacted surface211and the one of the surfaces of the workpiece81, the one surface being in contact with the contacted surface211. The inclined surface213is inclined relative to the one surface in the opposite direction to the chamfering direction of the chamfered portion91to be formed.

The machining head scanning device206moves the laser machining head4and the laser beam transmissive member203in the extending direction of the edge portion84relative to the workpiece81in a state where the laser beam transmissive member203held by the transmissive member holder221is in contact with one of the two surfaces forming the edge portion84of the workpiece81. The laser machining head4emits the ultrashort pulse laser beam L to the inclined surface213of the laser beam transmissive member203while being moved together with the laser beam transmissive member203by the machining head scanning device206in the extending direction of the edge portion84relative to the workpiece81.

In the present embodiment, the laser beam transmissive member203moves together with the laser machining head4. For this reason, it is not necessary for the laser beam transmissive member3to be long in the extending direction of the edge portion84. This makes it possible to make the laser beam transmissive member3compact. The machining head holder207is fixed to the transmissive member holder221or integrally formed on the transmissive member holder221. As a result, the laser machining head4is held by the machining head holder207in such a manner that the position of the laser machining head4relative to the laser beam transmissive member203held by the transmissive member holder221does not change. This makes it possible to keep constant the incidence angle i1of the ultrashort pulse laser beam L at the inclined surface213and the focal position of the ultrashort pulse laser beam L.

As shown inFIGS. 5A and 5B, the edge lines of a top surface202aof a holding stand202are positioned inward of the edge lines of the workpiece81. Since the holding stand202is thus positioned inward, even when the transmissive member holder221is moved close to the holding stand202to bring the laser beam transmissive member203into contact with the workpiece81, interference of the transmissive member holder221with the holding stand202can be avoided.

As shown inFIG. 6, in a chamfering apparatus301of Embodiment 3, a laser beam transmissive member303is a liquid member, and the chamfering apparatus301includes a transmissive member reservoir322configured to store the laser beam transmissive member303. The workpiece81is held by a workpiece holder323in a state where the edge portions84are immersed in the laser beam transmissive member303stored in the transmissive member reservoir322.

In this case, the liquid surface313of the laser beam transmissive member303in the transmissive member reservoir322is horizontal. The liquid surface313forms the inclined surface of the laser beam transmissive member303. The workpiece holder323holds the workpiece81in a state where one of the two surfaces forming the edge portion84of the workpiece81(in the illustrated example, the first flat surface82a) is inclined relative to the liquid surface313. Since the edge portion84is immersed in the laser beam transmissive member303, the laser beam transmissive member303is in contact with the first flat surface82a,and the first flat surface82aforms an interface between the laser beam transmissive member303and the workpiece81. The liquid surface313of the laser beam transmissive member303is inclined relative to the first flat surface82aby the inclination angle φ. The chamfering direction of the chamfered portion91to be formed (i.e., the direction in which the tapered surface94is inclined relative to the first flat surface82a) is inclined in the opposite direction to the liquid surface313with respect to the first flat surface82a.

The ultrashort pulse laser beam L emitted from the laser machining head4propagates through air, and is then incident on the liquid surface313of the laser beam transmissive member303. The ultrashort pulse laser beam L is refracted at the liquid surface313, transmitted through the laser beam transmissive member303, and incident on the first flat surface82a. The ultrashort pulse laser beam L is refracted at the first flat surface82a, and transmitted through the inside of the edge portion84in the chamfering direction.

The laser beam transmissive member303is water, for example. A laser beam whose attenuation coefficient in water is small is used as the ultrashort pulse laser beam L. As one example, the attenuation coefficient of the ultrashort pulse laser beam L in water may be set to 10% or less. The attenuation coefficient is correlated with the wavelength of the ultrashort pulse laser beam L, and becomes a minimum value at a particular wavelength. Therefore, the wavelength may be set within a range that contains a wavelength value at which the attenuation coefficient becomes the minimum value. By setting the wavelength of the ultrashort pulse laser beam L in accordance with the laser beam transmissive member303in this manner, necessary beam intensity for forming laser filaments F inside the edge portion84of the workpiece81can be kept, and thereby the laser filaments F can be formed inside the edge portion84.

As one non-limiting example, assume that the relative refractive index of the laser beam transmissive member303(which is water) relative to the air is 1.33, and the relative refractive index of the workpiece81relative to the laser beam transmissive member3is 1.09. In this case, in order to obtain the chamfering angle θCof 45°, the refraction angle r2needs to be 45°, and the incidence angle i2needs to be 50.4° (i2=arcsin (1.09sin45°)). If the workpiece81is held such that the inclination angle φ is equal to the incidence angle i2, the chamfering angle θCof 45° can be obtained by causing the ultrashort pulse laser beam L to be perpendicularly incident on the liquid surface313. If the incidence angle i1is 17.5°, the refraction angle r1is 13.1° (r1=arcsin (sin17.5°/1.33)). Therefore, if the workpiece81is held such that the inclination angle φ is 37.3° (φ=50.4−13.1), the chamfering angle θCof 45° is obtained.

FIG. 7shows one variation of Embodiment 3. As shown inFIG. 7, a transmissive plate303b, which allows a laser beam to be transmitted therethrough, may be held by a transmissive plate holder324, and part of the transmissive plate holder324may be submerged under the liquid surface of a liquid laser beam transmissive member303a. As one example, the transmissive plate holder324is cylindrical. The transmissive plate303bis held at one end of the transmissive plate holder324; the lower surface of the transmissive plate303bis in contact with the laser beam transmissive member303a; and the upper surface of the transmissive plate303bis in contact with the inner space of the transmissive plate holder324, i.e., in contact with air. The upper surface of the transmissive plate303band the surface of the workpiece (the first flat surface82a) form the inclination angle φ. The ultrashort pulse laser beam L propagates through the air. Then, the ultrashort pulse laser beam L is incident on the upper surface of the transmissive plate303b, transmitted through the transmissive plate303b, and exits from the lower surface of the transmissive plate303bto be incident on the liquid laser beam transmissive member303a. Thereafter, the ultrashort pulse laser beam L is transmitted through the laser beam transmissive member303a, incident on the surface of the workpiece81(the first flat surface82a), and transmitted through the inside of the edge portion of the workpiece81. Also in this variation, similar to Embodiment 3, laser filaments F can be formed inside the edge portion85(the first edge portion85). In particular, compared to a case where the laser beam is directly incident on the liquid surface, a concern about reflection of the laser beam due to bubbling at the liquid surface is eliminated. This makes it possible to keep necessary beam intensity for forming the laser filaments F inside the workpiece81.

As shown inFIGS. 8A and 8B, in Embodiment 4, the shape of a workpiece481when seen in a plan view is different from the shape of the workpiece in the foregoing embodiments. The workpiece481is rounded rectangular when seen in a plan view. At each of the four corners of the workpiece481, when seen in a plan view, a quarter arc-shaped rounded corner portion481ais formed. In this case, side surfaces483of the workpiece481include curved side surfaces483e, each of which connects between one of two long side surfaces483aand483band one of two short side surfaces483cand483d. Similar to Embodiment 1, a laser beam transmissive member403of a chamfering apparatus401is supported by the top surface2aof the holding stand2together with the workpiece481. The laser beam transmissive member403includes: transmissive members403ato403dsimilar to the four transmissive members3ato3dof Embodiment 1 (seeFIG. 2A); and curved transmissive members403e, which are in contact with the respective curved side surfaces483e. Each curved transmissive member403eincludes: a contacted surface411, which is curved so as to make surface contact with the corresponding curved side surface483e; and an inclined surface413, which is inclined relative to the contacted surface411. The laser machining head4emits the ultrashort pulse laser beam L to the inclined surface413of each curved transmissive member403ewhile moving along the arc of the corresponding rounded corner portion481a, and thereby laser filaments F can be formed inside the rounded corner portion481asimilar to the foregoing embodiments.

As shown inFIGS. 9A and 9B, in Embodiment 5, a chamfering apparatus501includes, instead of the head scanning device, a workpiece conveying device configured to move the workpiece81in the extending direction of the edge portion. In the present embodiment, the laser machining head4and a laser beam transmissive member503do not move. The chamfering apparatus501includes a running truck509configured to run on a floor surface. A holder502is provided on the running truck509. The holder502includes: clamp portions502aprovided at both ends of the running truck509and configured to support the workpiece81from below; and a support portion502bconfigured to support the workpiece81from below between the clamp portions502a. The running truck509moves parallel to the extending direction of the edge portion85, thereby conveying the workpiece81in the extending direction of the edge portion85. At the time, the workpiece81moves relative to the laser machining head4and the laser beam transmissive member3while keeping one of the two surfaces forming the edge portion85(the side surface83) in surface contact with a contacted surface511of the laser beam transmissive member503. Also in the present embodiment, similar to the foregoing embodiments, laser filaments F can be formed inside the edge portion85of the workpiece81, and thereby chamfering can be performed on the edge portion85.

As shown inFIGS. 10A and 10B, the contacted surface511and an inclined surface513of the laser beam transmissive member503do not intersect. The laser beam transmissive member503has such a roughly conical shape that it is tapered from the inclined surface513toward the contacted surface511. Such a shape allows the laser beam transmissive member503to be compact. Owing to such a shape, the area of contact between the workpiece81and the laser beam transmissive member503is small, which makes it possible to reduce damage to the surface of the workpiece81and/or the contacted surface511of the laser beam transmissive member503even when the workpiece81and the laser beam transmissive member503are slid against each other.

As shown inFIG. 11, a laser beam transmissive member603of Embodiment 6 has a roughly right-triangle shape similar to Embodiment 1. However, a contacted surface611of the laser beam transmissive member603is short in the thickness direction, and is in contact with only a part of the side surface83. The contacted surface611is continuous with a recessed surface614via a step. In a state where the contacted surface611is in contact with the surface of the workpiece81(the side surface83), the recessed surface614is away from the surface of the workpiece81. A spacer625is provided between the surface of the workpiece81and the recessed surface614. In this case, even when the workpiece81and the laser beam transmissive member603are slid against each other, since the contacted surface611is small, damage to the surface of the workpiece81and/or the contacted surface611of the laser beam transmissive member603can be reduced. While the contacted surface611is made small, the recessed surface is supported by the surface of the workpiece81via the spacer625. This makes it possible to stabilize the orientation of the laser beam transmissive member603relative to the workpiece81. For example, the spacer625is made of a material that is more brittle than the material of the workpiece81, such as synthetic resin. Therefore, even when the workpiece81slides against the spacer, the workpiece81will not be damaged. This makes it possible to improve the quality.

Although the embodiments of the present invention have been described above, modifications, additions, and deletions can be suitably made to the above-described configurations without departing from the scope of the present invention.

Although the details are not shown, in a state where the laser beam transmissive member is in contact with one of the surfaces of the workpiece, the laser beam transmissive member may be moved by the workpiece conveying device together with the workpiece in the extending direction of the edge portion. Also in this case, the head scanning device can be eliminated, and the laser machining head need not be conveyed by the workpiece conveying device. The laser machining head is only required to emit the ultrashort pulse laser beam to the inclined surface of the laser beam transmissive member while the laser beam transmissive member is being moved by the workpiece conveying device. As a result, a plurality of laser filaments arranged in the extending direction of the edge portion can be formed in the edge portion of the workpiece. This variation is also applicable to chamfering of an edge portion formed by two surfaces that intersect and form a non-right angle, and also applicable to a case where it is desired to obtain a chamfering angle of not 45°. The plan-view shape of the plate-shaped workpiece is not particularly limited. Although the embodiments have been described by taking the chamfering of a plate-shaped workpiece in the manufacturing process of a plate-shaped product as one example, the present invention is also applicable to the manufacturing of a product having a different shape and to the chamfering of a workpiece having a different shape. For example, chamfering may be performed on the edges of the raw material80.

REFERENCE SIGNS LIST

3,203,303,403laser beam transmissive member

6machining head scanning device

7,207machining head holder

82afirst flat surface

82bsecond flat surface

221transmissive member holder

322transmissive member reservoir

L ultrashort pulse laser beam

F laser filament

i1incidence angle at the inclined surface of the laser beam transmissive member

r1refraction angle at the inclined surface of the laser beam transmissive member

i2incidence angle at the surface of the workpiece

r2refraction angle at the surface of the workpiece