RU2677519C1 - Method of cutting glass - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to the field of precision micro-processing of materials, in particular, to a method for cutting glasses using a comb of femtosecond laser pulses, and can be used for precision glass cutting in factories and research centers. Method of cutting glass includes the formation of a comb of femtosecond laser pulses, characterized by an interpulse interval, the creation of a line with data from the defects of the glass structure in the bulk of the glass and the fracture of the glass. Comb of femtosecond laser pulses is formed using an interferometer, and the interpulse interval, determined by the thickness of the interferometer, is 10–70 ps.EFFECT: invention allows to speed up the process of cutting glass by reducing the number of stages.1 cl, 4 ex, 1 dwg

Description

The invention relates to the field of precision microprocessing of materials, in particular, to a method for cutting glasses using a comb of laser pulses of femtosecond duration and can be used for precision cutting of glass at enterprises and in a research center.

The most common glass cutting method in production is diamond cutting. In this method, a scratch of a given geometry is created on the glass surface with diamond. Further, due to the application of bending stress to the glass, a crack located under the scratch propagates deep into the sample and the glass breaks. At the same time, the edges of the cleavage are of low quality, the presence of microcracks, and a large width of cut. This method is almost impossible to cut thin samples.

A common laser cutting method is thermal cracking. In this method, the surface and the surface glass are first heated by a focused laser beam. In this case, the glass expands and tensile stresses arise, which are amplified by the further action of the defocused beam. As a result, cracking occurs in the entire thickness of the glass.

Another rapidly developing method is laser ablation cutting. The basis of this method is the evaporation of the processed material due to the linear absorption of laser energy and subsequent heating of the surface. As a rule, excimer lasers operating in the UV range and CO ₂ lasers operating in the infrared range are used. This method also has a number of disadvantages: low processing speed, cracking, fusion of glass sections adjacent to the cutting area, smaller than diamond, but still a sufficiently large cut width, the need for linear absorption of the material at the laser wavelength. To reduce the width of the cut in the case of laser treatment, combined methods are used, including laser heating and parallel cooling with a water jet [US 5609284, US 6787732].

Improving cutting parameters is obtained through the use of pulsed lasers. Due to the high peak intensity, nonlinear absorption processes occur in the focusing region. Such a mechanism removes restrictions on the wavelength of the laser used, which makes it possible to focus radiation into a spot of micron and submicron scale, hence the increased precision of cutting. At the same time, as a result of using this method, microcracks still form and the surface becomes clogged with the ablated surface material.

The closest in technical essence and the achieved result is the method of processing the material with a laser beam, presented in [K. Mishik, Ultrashort pulse laser cutting of glass by controlled fracture propagation, 2016], which consists in modifying glass with a comb of femtosecond laser pulses with a pulse repetition rate within the comb of 25 ns.

The specified prototype has several advantages: when modifying glass in this mode, a heat accumulation mechanism is implemented in which the heat that occurs at the focal point when the laser acts on the glass does not have time to dissipate until the next pulse in the comb. Thus, a continuous increase in temperature occurs during irradiation. This allows you to get rid of the stresses that inevitably accompany the modification of the glass structure.

The flip side of the effect of heat storage is the melting of the boundaries of the modification, which leads to the melting of microcracks that underlie the fragility of the glass, thus preventing the subsequent breaking of the glass sample. In this prototype, the cutting process consists of three stages: first, at a speed of 1 mm / s, a line is “burned” on the glass surface, then a line is created at the same speed in the volume of glass. Next, bending stress is applied to the sample and glass breaks. Such multi-stage significantly slows down the process. The optimum cutting speed identified by the authors is 2 mm / s.

The use of combs of femtosecond pulses with an inter-pulse interval of the order of ps can significantly increase the efficiency of the glass cutting process. It is known that when a laser pulse interacts with a glass, a shock wave arises [A. Mermillod-Blondin, Dynamics of femtosecond laser induced void-like structures in fused silica], which creates a rarefaction in the modifiable region, which grows on a subnanosecond scale. In this case, if the laser pulse interacts with the modified region at the time of the occurrence of vacuum, there is an increase in the number of stable structural defects, leading to the formation of microcracks necessary for successful cutting.

The objective of the present invention is to accelerate the process of cutting glass by reducing the number of stages.

The problem is solved by a method of cutting glass, including the formation of a comb of femtosecond laser pulses, characterized by an interpulse interval, the creation by these combs of a line of glass structure defects in the volume of glass and a glass break, while the comb of femtosecond laser pulses is formed using an interferometer, and the interpulse interval, determined by the thickness interferometer is 10-70 ps.

For glass cutting, an installation (Fig. 1) based on a femtosecond laser (1) with an operating wavelength of 1030 nm was used. Laser pulses with a duration of 180 fs and an energy of 4 μJ were passed through an interferometer (2), which is a glass plate with reflective coatings on both surfaces (reflection coefficient 0.75), to create a comb of pulses. Depending on the thickness of the used interferometer (1 mm, 2 mm, 4 mm, 7 mm), the distance between the pulses inside the comb changed (10 ps, 20 ps, 40 ps, 70 ps). Next, the radiation was focused into the bulk of the glass (sample) (4) with a lens (3) with a numerical aperture of 0.15 to a depth of 10 μm. The lines formed as a result of the action of pulse combs on glass were recorded by moving a sample mounted on a three-coordinate table (5) relative to a stationary laser beam at a speed of 1 to 2 mm / s.

The achievement of the claimed technical result is confirmed by the following examples. The optimum speed for recording the line was taken to be such a speed at which the fracture of the sample passed strictly along the recorded line.

Example 1

A 1 mm thick interferometer was used to form a comb of femtosecond laser pulses with an inter-pulse interval of 10 ps, the duration of a femtosecond pulse was 180 fs, and the pulse comb energy was 1 μJ. Then, using a lens with a numerical aperture of 0.15, the pulse comb was focused into the volume of a glass sample mounted on a three-coordinate table. By moving the sample relative to a stationary laser beam in the volume of the glass, a line was formed at a speed of 1.7 mm / s. After that, the glass was broken.

Example 2

A 2 mm thick interferometer was used to form a comb of femtosecond laser pulses with an inter-pulse interval of 20 ps, the duration of a femtosecond pulse was 180 fs, and the pulse comb energy was 1 μJ. Then, using a lens with a numerical aperture of 0.15, the pulse comb was focused into the volume of a glass sample mounted on a three-coordinate table. By moving the sample relative to a stationary laser beam in the volume of the glass, a line was formed at a speed of 1.5 mm / s. After that, the glass was broken.

Example 3

A 4 mm thick interferometer was used to form a comb of femtosecond laser pulses with an inter-pulse interval of 40 ps, the duration of a femtosecond pulse was 180 fs, and the pulse comb energy was 1 μJ. Then, using a lens with a numerical aperture of 0.15, the pulse comb was focused into the volume of a glass sample mounted on a three-coordinate table. By moving the sample relative to a stationary laser beam in the volume of the glass, a line was formed at a speed of 1.5 mm / s. After that, the glass was broken.

Example 4

Using a 7 mm thick interferometer, a comb of femtosecond laser pulses was formed with an inter-pulse interval of 70 ps, the duration of the femtosecond pulse was 180 fs, and the energy of the pulse comb was 1 μJ. Then, using a lens with a numerical aperture of 0.15, the pulse comb was focused into the volume of a glass sample mounted on a three-coordinate table. By moving the sample relative to a stationary laser beam in the volume of the glass, a line was formed at a speed of 1 mm / s. After that, the glass was broken.

findings

As can be seen from the above examples, the use of femtosecond comb combs with an inter-pulse distance of 10 to 70 ps makes it possible to reduce the number of glass cutting stages to two: 1) drawing a fault line on the surface of the sample in one pass, 2) breaking the sample. The use of pulse combs in glass cutting made it possible to increase the process speed by 15-50%.

Claims (1)

A method of cutting glass, including the formation of a comb of femtosecond laser pulses characterized by an interpulse interval, the creation by these combs of a line of glass structure defects in the volume of glass and a glass break, characterized in that the comb of femtosecond laser pulses is formed using an interferometer, and the interpulse interval, determined by the thickness of the interferometer is 10-70 ps.

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