JPH0912327A - Method and apparatus for cutting glass - Google Patents

Abstract

PROBLEM TO BE SOLVED: To increase the cutting speed without deteriorating the cutting precision and cut face at the time of forming a crack with a laser beam to cut a glass sheet by specifying the power distribution of the laser beam.

SOLUTION: A cut or a notch is formed along the one end of a glass sheet 10 to form a crack starting point 19 on one end of the sheet 10. The point 19 is then used to form a crack 20 by moving a laser beam 16 across the sheet 10 along a desired cutting line. The sheet 10 is effectively heated by the laser beam 16 at a local region along the cutting line. Consequently, a stress to expand the crack is developed along the laser beam path due to the temp. extension of the sheet 10 in the local heated region. In this method, a laser beam having a specified power distribution consisting of the mixed component of the TEM₀₁* mode and TEM₀₀ mode which is of higher order than TEM₀₀ mode.

COPYRIGHT: (C)1997,JPO

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a method for cutting a glass sheet, and more particularly to a method for protecting a glass sheet during a glass cutting operation.

[0002]

2. Description of the Related Art Conventionally, a laser has been used to divide a glass plate. PCT patent WO93 / 20015 describes the use of laser light in propagating so-called blind cracks across a glass sheet in order to divide the glass sheet in two. In one specific form of this patent, small cuts or cuts are made on one side of the glass sheet and then laser light is used to form cracks through the glass sheet to widen the cuts or cuts. The sheet is then split into two smaller sheets by mechanical cutting along the laser score line. In order to make such a method effective, the laser light is brought into contact with the glass sheet in the area of the cut or incision to move the laser and the glass sheet relative to each other, and two small sheets at the desired path of the cut line. A laser beam is propagated to form the.
It is desirable to direct the stream of fluid coolant to the heated surface portion of the glass downstream of the laser so that the glass sheet cools quickly after the laser light heats the glass sheet. Thus, the heating of the glass sheet by the laser and the cooling of the glass sheet by the aqueous coolant distort the glass sheet and spread the cracks in the direction in which the laser light and the coolant pass.

[0003]

Problems to be Solved by the Invention PCT Patent No. PCT /
One problem with methods such as those described in GB 93/00699 is that they do not provide sufficient production rates to match the types of conventional glass cutting methods.

Furthermore, when a conventional laser having a Gaussian intensity distribution is used, the working range in which the laser works well is narrowed. Therefore, there is an advantage in extending this working range.

[0005]

SUMMARY OF THE INVENTION The present invention is directed to a method of cutting a glass sheet, in which a laser beam (and cooling) is conducted in a desired path across the glass sheet to induce cracks along the path of the laser beam. Agents are optional). The resulting thermal gradient creates a tensile stress in the surface layer of the material, and when this stress exceeds the tensile strength of the glass, the material will cause blind cracks to descend into the region of compression and enter the material. become. When the laser light then traverses the glass, the crack follows the laser light. The depth, shape, and direction of the crack are determined by the stress distribution, and the power density, size, and shape of the beam spot, the relative velocity of the beam spot and the material, the properties and characteristics of the coolant supplied to the heating region, It depends on several factors, including the thermophysical and mechanical properties of the material being cracked and its thickness. The intensity profile of the laser spot on the glass has also been found to be an important factor in determining the maximum speed that can be used. In the present invention, the laser has a non-Gaussian intensity profile. In one embodiment, the laser beam intensity operates in a bi-peak mode, namely TEM _{01 *} mode or TEM ₁₀ mode. It is desirable to direct a suitable coolant flow to the region of material along the direction of travel of the beam spot in order to cause a very localized cooling of the surface layer along the cutting line.

[0006]

According to the present invention, as compared with the known technique,
In the glass cutting step, it is excellent in that an improved cutting speed can be achieved without impairing the cutting accuracy and the cut surface of the glass.

[0007]

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a system for cutting glass sheets along desired cutting lines using laser cutting techniques. As shown in FIG. 1, in the glass cutting system of the present invention, a glass sheet 10 has an upper surface 11 and a lower main surface 11. Since the glass sheet 10 first forms the crack starting point 19 at one end of the glass sheet 10, a cut line or a cut line is made along one end of the glass sheet. This crack initiation point 19 is then used to move the laser beam 16 across the glass sheet in the path of the desired cutting line to form the crack 20. The laser light effectively heats the glass sheet in localized areas along the desired cutting line. The resulting temperature expansion of the glass sheet within the locally heated region causes stresses that spread the cracks along the path traveled by the laser. It is desirable to add water coolant by means of the water jet 22 to enhance the stress distribution and thereby promote crack propagation. By using this laser cutting method, rather than the conventional method using a mechanical cut, many glass chips caused by the mechanical cut are removed.

The laser beam 16 used in the glass cutting process must heat the glass surface to be cut. Consequently, it is desirable that the emitted light of the laser be of a wavelength that the glass absorbs. In order for this to occur, it is desirable that the emitted light is infrared light having a wavelength of 2 μm or more, for example, a CO ₂ laser having a wavelength of 9-11 μm and a wavelength of 5-.
Beams such as a 6 μm CO laser, a 2.6-3.0 μm wavelength HF laser, and an erbium YAG laser with a wavelength of about 2.9 μm are desirable. When the material surface is heated, its maximum temperature should not exceed the melting point of the material. If the melting point of the material is exceeded, residual thermal stress will occur after the glass cools and cracking will occur.

Cracks 20 are formed in the glass towards the interface of the heating and cooling regions, which are the regions of maximum thermal gradient. The crack depth, shape, and direction are determined by the distribution of thermoelastic stress, and are mainly based on the following multiple factors.

The power density, size and shape of the beam spot; the relative velocity of the beam spot and the material; the thermophysical properties, the quality, the supply conditions of the coolant to the heating area; the thermophysical and mechanical properties of the cracked material. In order to optimize the cutting cycle for materials with different physical properties, their thicknesses and surface conditions, it is necessary to establish an appropriate relationship between the main parameters and the variables of the cutting process. International Patent No. WO93 /
As described in US Pat. No. 5,015,095, the velocity V of the relative displacement of the laser 16 across the glass 10 depends on the size of the beam spot 18 and the distance from the region where the cooling water flows.
And the depth d of the crack 20 are expressed by the following equation.

V = ka (b + 1) / d where V is the relative velocity between the beam spot and the material, and k
Is a proportional coefficient depending on the thermophysical properties of the material and the power density of the beam, a is the width of the beam spot, b is the length of the beam spot, l is the distance from the near end of the beam spot to the front end of the cooling region, d is the depth of the blind crack 4.

In determining the maximum power density of the laser beam used in cutting the material, the maximum temperature of the material surface layer should not exceed its melting point. Therefore, at low heat splitting rates, about 0.3 for low solubilities of thick glasses.
A minimum power density of × 10 ⁶ W / m ² is acceptable. When dividing high melting quartz glass, corundum, or other materials having a high melting point or high thermal conductivity, for example, 20 × 10 ⁶ W
A laser beam with a higher power density of / m ² can be used. Most of the experiments used a CO ₂ laser with a power of 150-300 watts, but it seems more successful with a higher power laser.

The laser operates by lasing occurring in a resonator defined by mirrors at each end. The concept of a stable resonator can be best clarified by tracing the optical path of a ray through the resonator. The stability threshold is reached when a ray parallel to the axis of the laser cavity is permanently reflected back and forth between two mirrors without loss.

Resonators that do not reach the stability criterion are called unstable resonators because the light rays deviate from the axis. There are many types of unstable resonators. One simple example is the type of convex spherical mirror versus flat mirror. Others include concave mirrors of different diameters (light reflected from a large mirror escapes around the edges of a small mirror) and a pair of convex mirrors.

The two types of resonators have different advantages and different mode patterns. A stable resonator concentrates light along the laser axis and efficiently extracts energy from that region, but not from the peripheral region away from the axis. The resulting beam has an intensity peak in the center and the intensity diminishes Gaussian away from the axis. This is the standard type used with low gain continuous wave lasers.

Unstable cavities tend to spread the light inside the laser cavity over a larger volume. For example, the output beam may have an annular shape with a ring-shaped intensity peak around the axis.

There are two types of different modes in the laser cavity: the transverse mode and the longitudinal mode. Transverse modes exist in the cross-sectional shape or intensity pattern of the beam. Longitudinal modes correspond to different resonant modes due to the laser cavity length occurring at different frequencies or wavelengths within the gain band of the laser. Single transverse mode lasers that oscillate in a single longitudinal mode oscillate at a single frequency, while those that oscillate in two longitudinal modes are at two independent wavelengths (usually in close proximity).
It oscillates at the same time.

The electromagnetic field "shape" within the laser cavity depends on the curvature of the mirror, the spacing, and the cavity diameter of the discharge vessel. Even if the arrangement and spacing of the mirrors and the wavelength are slightly changed, the "shape" (electromagnetic field) of the laser beam is greatly changed.
A special term was developed in describing the "shape" and the spatial energy distribution of the beam, but here the transverse modes are classified according to the number of local minima appearing in the bidirectional beam cross section.
The lowest order mode, the fundamental mode, has an intensity peak in the center and is known as the TEM ₀₀ mode. This is Figure 3
It is a laser that has been conventionally used and has a Gaussian intensity distribution as shown in FIG. The modes with one local minimum along one axis and no local minimum along its vertical axis are TEM _{01 *} or TEM ₁₀ , which are determined by their orientation. An example of the intensity distribution of the TEM _{01 *} mode is shown in FIG. 2 (beam intensity I for distance d across the beam). For most laser applications, the TEM ₀₀ mode is considered the most desirable. However, non-Gaussian modes such as TEM
_{It has been found that a 01 *} mode or TEM ₁₀ mode beam can be used to deliver the laser energy more uniformly to the glass surface. As a result, it was found that higher laser cutting speeds can be achieved with lower power than if the laser has a Gaussian intensity distribution. Further, the laser power can be used in a wider range due to the expanded operation range of the laser cutting process. This is probably because the non-Gaussian laser beam can further improve the uniformity of energy distribution over the entire beam.

The laser beam shown in FIG. 2 has a ring shape. As described above, the power distribution shown in FIG. 2 is a cross section of the power distribution of the ring-shaped laser beam. A non-Gaussian beam in which at least one pair of intensity peaks are located at the outer periphery of the central region having a lower power distribution is desirable in the present invention. Thus, it is desirable that the center of the laser beam has a power intensity lower than the power intensity of at least a plurality of outer peripheral regions of the laser beam. This low power center region may be completely zero power level, in which case the laser beam will have a T% of 100%.
EM _{01 *} Power distribution. However, the laser beam has a two-peak mode, ie, as shown in FIG.
It may be a combination of one or more mode levels such as a combination of TEM _{01 *} mode and TEM ₀₀ mode in which the power distribution in the central region is simply lower than the power distribution in the outer peripheral region. When the beam is in the two-peak mode, it is desirable that the beam has a combination of 50% or more in the TEM _{01 *} mode, more preferably 70% or more in the TEM _{01 *} mode, and the rest in the TEM ₀₀ mode.

Since the surface temperature of the glass 10 depends directly on the time of exposure to the laser beam, by using an elliptical beam instead of a circular cross section, at the same relative speed, the glass surface of the glass surface along the cutting line is changed. The heating time at each point can be extended. Thus, at the specified power density of the laser beam 16, the distance from the laser beam spot to the front edge of the cooling spot, which is important for maintaining the depth required to heat the glass 10, is the same. However, the laser beam spot spreads more in the moving direction,
And again, it will make the relative velocity of the laser beam spot and material more acceptable.

In the present invention, the laser spot has an extremely elongated shape, for example, an elliptical shape, and the long axis of this elongated shape is 20 mm or more, more preferably 30 mm or more, and further 40 mm to 100 mm or more. desirable. The long axis of the laser beam spot is in the direction of propagation of the desired cutting line across the glass sheet. For thin sheets of glass (1.1 mm or thinner), the optimum length of the long axis of the laser beam spot is related to the desired propagation velocity, with the long axis b being greater than 10% of the desired laser cutting speed per second. Larger is desirable. in this way,
Laser cutting rate of 5 with 0.7mm thick glass
At 00 mm, the long axis of the laser is preferably at least 50 mm long.

As a preferred specific embodiment of the present invention, it is desirable that the crack 20 spreads only in the depth direction of the glass sheet 10. The final division of the glass sheet into smaller sheets is preferably done by applying a bending moment to the cracks 20.
The bending can be accomplished by conventional bending equipment (not shown) and techniques such as those used to cut glass in the process of using conventional mechanical surface cutting methods. Since crack 20 uses a laser cutting technique rather than a mechanical incision, the formation of glass chips during the mechanical cutting process can be minimized as compared to conventional techniques.

As a preferred specific embodiment of the present invention, a system controller (not shown) such as a digital computer is incorporated in a system for controlling the movement of a laser, a glass sheet, and other movable parts on the system. Connecting. The system controller uses conventional machine control techniques to control the movement of various parts of the system. The system controller uses various manufacturing operating programs stored in its memory, each of which is suitable for moving a laser or glass sheet (and other moving parts if necessary) for a particular size glass sheet. It is desirable to be designed to control the

The following example demonstrates the method according to the invention.

Example 1 This example is a comparative example showing the operation of a CO ₂ laser having a Gaussian power distribution.

Laser 16 was a Model 1200 axial-flow two-beam CO ₂ laser manufactured by PRC Corporation. The beam was positioned about 2 meters from the glass surface with a spot size of about 12 mm (laser beam diameter at the laser emission point). A pair of cylindrical lenses was placed in the optical path of the laser between the laser and the glass surface to deform the laser spot. As a result, the laser spot that hits the laser on the glass is about 45-5
An elongated elliptical beam having a width of 0.1-0.15 cm at a center point of 0 mm. The fundamental mode of the cavity of this laser is TEM ₀₀ . When this is the only mode in which the resonator can oscillate, the resonating 00-mode laser will propagate with as little divergence as possible and be focused with the smallest spot size. In Example 1, the laser power distribution is "planar" at the laser front facet with a small internal aperture.
Gaussian (TEM ₀₀
It works in mode).

The glass sheet 10 has a crack initiation point 19
The edges of the glass sheet were manually scored to form the. As a result, approximately 8 mm is
A crack starting point 19 was created by forming a small score line having a depth of about 0.1 mm. Glass sheet 10
Is placed so that the laser 16 contacts the crack initiation point 19 and causes the glass sheet 10 to travel along a straight path across the glass sheet at the power and speeds listed in Table 1 below. I moved it.

Table 1 Laser velocity Peak power (W) Success probability (%) 400 mm / sec 120 100 420 mm / sec 120-165 100 465 mm / sec 165-175 100 475 mm / sec 165-179 100 480 mm / sec 168-179 66 The 500 mm / sec 183-188 33 success probability column represents the best performance achieved in the corresponding power range. The 100% success rate indicates that in the power range described, the laser had operating parameters that were substantially 100% successful over the glass sheet over time.

Example 2 The same method, apparatus and laser as described in Example 1 were used and the laser power distribution was varied. As a different optical form, higher order modes were generated in the resonator. These modes were co-axially superposed with the 00 mode used in Example 1 and had a specific size compared to the 00 mode. A beam composed of such a plurality of sub-beams, each having a unique intensity shape, is called a multimode beam. Since these beams are independent, their net distribution is the algebraic sum of the individual shapes, weighted by the power rate of each mode. Therefore, the amount of TEM ₀₀ mode can be reduced by changing the curvature of the optical coupler or increasing the diameter of the opening. In Example 2, the power distribution of the laser was changed to a mixing ratio of TEM _{01 *} and TEM ₀₀ modes of about 60:40. This was achieved by replacing the 20 meter radius of curvature concave optical coupler with a "planar" optical coupler, resulting in a larger aperture. The laser power and speed varied as described in Table 2.

Table 2 Laser velocity Peak power (W) Success probability (%) 300 mm / sec 90-145W 100 500 mm / sec 155-195W 100 600 mm / sec 200W 100 650 mm / sec 200-220W 100 700 mm / sec 250W 50 Example 1 As can be seen by comparing the results of Example 2 and Example 2, the Gaussian laser has a cutting speed of up to 475 mm / sec.
A cut of 0% (successful in chopping almost all samples) could be achieved. Above these speeds, it was difficult to obtain consistently satisfactory results. For example, 500 mm /
In sec, cutting was successful only with a very small range of laser power, and cutting was successful within the power range of 33% or less in all samples.

Exactly the same laser with TEM _{01 *} mode and TE
Converting to M ₀₀ mode mixing, higher cutting speeds could be achieved even with low laser power. In addition, a wider range of laser powers appears to be acceptable to achieve a satisfactory kerf edge.

[Brief description of the drawings]

FIG. 1 is a perspective view of a glass cutting method step according to the present invention.

2 is a graph showing a desired intensity shape of the laser shown in FIG.

FIG. 3 is a graph showing a power distribution of a standard Gaussian laser.

[Explanation of reference numerals] 10 glass sheet 11 main surface of glass sheet 16 laser beam 18 laser spot 19 crack start point 20 crack 22 water jet

 ─────────────────────────────────────────────────── ─── Continued Front Page (72) Inventor Harry Jay Stevens New York, USA 14830 Corning Martin Hill Road 1512

Claims (8)

[Claims] 1. A method of making a flat glass sheet comprising the step of moving a laser beam across the glass sheet to form cracks across the glass sheet, the laser comprising a mixed component of TEM _{01 *} mode and TEM ₀₀ mode. A method for manufacturing a flat glass sheet having a power distribution. 2. The production of a flat glass sheet according to claim 1, wherein the laser beam in the moving step has a TEM _{01 *} mode component of at least 50%, and a residual component is a TEM ₀₀ mode component. Method. 3. The flat glass sheet manufacturing method according to claim 1, wherein the laser beam in the moving step has a TEM _{01 *} mode component of at least 70%, and a residual component is a TEM ₀₀ mode component. Method. 4. The production of a flat glass sheet according to claim 2, wherein the laser moving step consists of forming a crack that partially extends in the depth direction of the glass sheet and crosses the glass sheet. Method. 5. The method of manufacturing a flat glass sheet according to claim 4, further comprising the step of bending the sheet along the crack to divide the sheet into two smaller sheets. 6. The method of manufacturing a flat glass sheet according to claim 1, wherein the cross-sectional power distribution of the laser beam in the moving step has a central region of the power distribution smaller than an outer peripheral region of the power distribution. 7. A flat glass sheet manufacturing method comprising a step of moving a laser beam across a glass sheet to form a crack across the glass sheet, wherein the laser power distribution is at least one of outer peripheral regions of the power distribution. A flat glass sheet manufacturing method, characterized in that the central region of the power distribution is smaller than the central part. 8. The method of manufacturing a flat glass sheet according to claim 7, wherein the moving step comprises moving a laser beam having a power intensity of 0 in a central region of the power distribution.