WO2011083205A1

WO2011083205A1 - Method for machining material by a laser device

Info

Publication number: WO2011083205A1
Application number: PCT/FI2011/050004
Authority: WO
Inventors: Antti Salminen; Heidi Piili; Tuomas Purtonen
Original assignee: Lappeenrannan Teknillinen Yliopisto
Current assignee: Lappeenrannan Teknillinen Yliopisto
Priority date: 2010-01-08
Filing date: 2011-01-05
Publication date: 2011-07-14
Anticipated expiration: 2012-07-08
Also published as: FI20105011A0

Abstract

The invention relates to a method for machining material by a laser device. According to the invention the employed material to be machined is a substantially transparent material, the material is machined by a laser device that uses optical fiber having a laser beam wavelength of between 300nm and 5000nm and a sufficient quality of the laser beam in order to focus the beam as a small point and to provide sufficient depth of field and absorption, a base material is provided under the material to be machined, a non-metallic material is used as the base material, the laser beam is directed and focused to the surface of the base material through the material to be machined, wherein the base material absorbs the employed wavelength and the surface of the base material is heated by the effect of the beam so that the temperature on the lower surface of the material to be machined, locally rises to the extent that micro-cracks are formed on the lower surface of the material to be machined, generating a mark on the surface of the material to be machined.

Description

METHOD FOR MACHINING MATERIAL BY A LASER DEVICE

FIELD OF THE INVENTION

The invention relates to the method defined in the preamble of claim 1 for treating and machining transparent material by a laser device.

BACKGROUND OF THE INVENTION

Known from the prior art are methods and ap- paratuses for machining glass. Known from the prior art are also methods for marking glass by a laser. It is known to form a permanent mark by a focused laser beam on the surface of a material to be marked by laser marking. The most employed laser device has been the C0₂ laser device due to its better absorption in glass compared with laser devices provided with shorter wavelengths. A problem in the laser marking of glass at short wavelengths, e.g. 400 to 3000 nra, has been that the beam penetrates the glass, whereby the formation of a pattern has been difficult. In addition, a problem in using C0₂ laser devices has been their short depth of field and the absorption of C0₂ wavelength in the surface of glass and the inability to mark tempered glass.

Publication US 6130401 discloses a method wherein a laser beam is focused to a metallic material that absorbs the beam and is placed under a glass, and when the beam is moved a mark is formed on the surface of the piece.

OBJECTIVE OF THE INVENTION

An objective of the invention is to disclose a new method for providing easy machining of a transparent material and to eliminate the preceding prob- lems. SUMMARY OF THE INVENTION

The method according to the invention is characterized by what has been presented in the claims .

The invention is based on a method for machining material by a laser device. According to the invention the employed material to be machined is a substantially transparent material, the material is machined by a laser device that uses optical fiber having a laser beam wavelength of between 300nm and 5000nm and a sufficient quality of the laser beam in order to focus the beam as a small point and to provide sufficient depth of field and absorption, a base material is provided under the material to be machined, a non-metallic material is used as the base material, the laser beam is directed and focused to the surface of the base material through the material to be machined, wherein the base material absorbs the employed wavelength and the surface of the base material is heated by the effect of the beam so that the temperature on the lower surface of the material to be machined locally rises to the extent that micro-cracks are formed on the lower surface of the material to be machined, generating a mark on the surface of the material to be machined.

In one embodiment of the invention the material is machined by a laser device having a sufficient quality of the laser beam in order to provide non- linear absorption behavior.

In one embodiment of the invention a threshold intensity of the laser beam produced by the .laser device is determined, wherein the threshold intensity is to be determined according to application of use and has to be sufficient in order to provide sufficient absorption of the laser beam and depends on the material to be machined and the base material and the employed wavelength of the laser beam.

In one embodiment the material is machined by a laser device having a sufficient quality of the laser beam in order to reduce the size of the focal point. In one embodiment the employed size of the focal point of the laser beam in the laser device which depends on the material to be machined and its dimensions and the base material is adapted to be suitable for the employed ma- chining method in order to provide sufficient quality for the machining, e.g. depth of field.

In one embodiment of the invention transparent material is machined by directing the laser beam of the laser device to the base material through the transpar- ent material at an intensity exceeding a threshold intensity that is ^'required for absorption, and the material is machined in the intensity area of non-linear absorption behavior where a sufficient absorption of the laser beam in the base material is obtained.

In this connection a transparent material signifies any material that is substantially penetrated by the wavelength of the employed laser device, e.g. transparent plastic, glass material, glass and their combinations or equivalent material. The transparent material can be colorless, colored, patterned or their combination material. In one embodiment the material to be machined is selected from the group of glass material, transparent plastic, other transparent material and their different combinations. In one embodiment the em- ployed material to be machined is tempered glass. In one embodiment the employed material to be machined is a material that is substantially transparent to the employed wavelength.

As the base material, any non-metallic base material that is suitable for the purpose of use can be used. Non-metallic materials have a cheap purchase price and are easily available. In one embodiment the base material is a natural fiber based material, e.g. a fiber material, paper, paperboard or cardboard. In this connection a natural fiber based material signifies any material that is at least mainly manufactured from natural fibers, fibers that come from the nature or recycled fibers, e.g. a paper material, intermediate product, end product or other reprocessed product manufactured from fibers or pulp. In one embodiment the base material is a plastic based material.

In one embodiment of the invention the employed base material is a paper material . In this connection a paper material signifies any material that is manufactured from fiber based pulp. The fiber based pulp can be formed from soft- or hardwood or a parallel wdody plant or other botanical material and/or recycled fibers. The fiber based pulp can be mechanical, chemical or chemi-mechanical pulp or parallel pulp or recycled pulp. Alternatively the fiber based pulp can be formed by any method. A paper material signifies in this connection any paper material, e.g. paper, cardboard, paperboard, tissue paper, dried chemical pulp, dried mechanical pulp or a parallel material. The paper material can contain plastic or pigment or be plastic coated or pigment coated.

In one embodiment of the invention the employed laser device is any laser device that uses optical fiber and produces a laser beam having a wavelength of 300 to 5000 nm that can be conveyed in optical fi- ber. In one embodiment a continuous laser device is used, e.g. a continuous beam laser device, e.g. a CW laser device. In one embodiment a fiber laser device is used. In one embodiment a disk laser device is used. Also other laser devices that are suitable for the purpose of use can be used. Preferably the laser device can be selected from laser devices having a pulse length of Ins up to continuous beam laser devices. In one embodiment a laser device is used having a continuous beam that is pulsed in pulses of one nanosecond or longer. In one embodiment a laser device is used having a pulse duration of more than 900 picoseconds, preferably more than Ins. The beam of the laser device must have a sufficiently good beam quality in order to be able to focus the beam as a small point and to have a sufficiently small size of the focal point, whereby the appearance of non-linear absorption behavior and sufficiently good quality of machining are provided. In one embodiment a non-ablative laser device is used. Preferably a pulsed laser device having the beam pulsed in pulses of a very short duration, especially less than 900 picoseconds, is not used.

Preferably a laser device that is suitable for the purpose of use and produces a laser beam wherein the power may vary is used. In one preferred embodiment the good beam quality of the laser device provides for high intensity, whereby the material to be processed can be the machined at a very low laser power .

In one embodiment of the invention the machining method for the material is selected from the group of: laser cutting, laser marking, laser engraving and their combinations or an equivalent machining method.

In one embodiment of the invention the laser beam is moved in order to form a marked pattern.

In one embodiment of the invention a mark is made on at least one surface of the material to be machined. In one embodiment a mark is made on one surface of the material to be machined. In one embodiment a mark is made on more than one surface of the material to be machined.

In one embodiment of the invention the method is used in machining a two-dimensional piece. In one embodiment the method is used in machining a three- dimensional piece.

In one embodiment the laser beam of the laser device is split in at least two parts. In one embodi- ment the laser beam is split in e.g. 2 to 5 parts and the split beam can be used in machining the material. In one embodiment the laser beam of the laser device is split so as simultaneously to acquire at least 2, e.g. 2 to 10, beams by beam splitting optics and optical fibers. The length of the optical fiber may vary and machining points can be located at different areas of the material to be machined.

In one embodiment of the invention the parameters for the laser machining are determined, wherein the parameters are selected from the group of selecting a laser device, selecting a material to be machined, selecting a base material, wavelength of the laser beam, depth of field of the laser beam, size of the point to be focused and their combinations; a parameter library is generated; the desired parameters are selected from the parameter library in order to machine the material; the machining is controlled in order to provide sufficient absorption of the laser beam to the base material through the material to be machined by utilizing the selected parameters; and the laser beam is focused to the surface of the base material in order to heat the surface so that the temperature on the lower surface of the material to be machined locally rises to the extent that micro-cracks are formed on the lower surface of the material to be machined, generating a mark on the surface of the material to be machined.

In one embodiment of the invention the parameters for the laser machining are determined, wherein the parameters are selected from the group of select- ing a laser device, selecting a material to be machined, selecting a base material, wavelength of the laser beam, depth of field of the laser beam, threshold intensity of the laser beam, size of the point to be focused, size of the focal point and their combinations; a parameter library is generated; the desired parameters are selected from the parameter library in order to machine the material to be machined; the material to be machined is machined in the area of nonlinear absorption behavior by directing the laser beam of the laser device to the base material through the material to be machined at an intensity exceeding the threshold intensity; the machining is controlled in order to provide sufficient absorption of the laser beam in the base material through the material to be machined by utilizing the selected parameters; and the laser beam is focused to the surface of the base material in order to heat the surface so that the temperature on the lower surface of the material to be machined locally rises to the extent that . micro-cracks are formed on the lower surface of the material to be machined, generating a mark on the surface of the material to be machined.

In one embodiment the method is used for laser marking of a transparent material . Laser marking signifies herein any decorative or informative mark produced on the surface of a material. In one embodiment the method is used for laser engraving of a transparent material by removing material from the surface of the transparent material and forming a groove of a particular geometry.

The method according to the invention provides considerable advantages as compared with the prior art .

The invention provides a method that does not impose restrictions of the transparent material to be marked and its shape. Thanks to the invention, a meth- od is provided for marking transparent materials with an accurate, sharp, clean and permanent mark.

By the method according to the invention a massive thermal shock is not caused on the surface of the transparent material to be marked, so that a clean mark is provided and the method can also be utilized in marking applications of tempered glass.

Thanks to the invention a flexible, good, quick, efficient laser machining method is provided that is applicable industrially or on a smaller scale to several applications and saves time and energy and is maintenance-free. In addition, high marking speeds are achieved in machining transparent material, thanks to the invention. Furthermore, the apparatus used in the method according to the invention has only a few wearing parts which reduces the service operations.

The method according to the invention can be used for example in the manufacture of decorative and informative elements, in the manufacture of fagade glazings and architectural glasses, in the manufacture of ornaments and works of art and in equivalent applications of use.

DETAILED DESCRIPTION OF THE INVENTION

In the following, the invention will be described by a detailed example of an embodiment .

Example 1

In these experiments laser marking of differ- ent transparent glass materials including tempered glass by a fiber laser device was examined.

In the experiments the laser marking of two- and three-dimensional glass pieces was examined.

As the thin flat base material, a paper mate- rial was used such as polyethylene fiber containing paper and paperboard, pulp board manufactured from unbleached chemical pulp and plastic.

As the laser device a CW fiber laser, was used having a laser beam wavelength of between 300nm and 5000nm and sufficient quality of the laser beam in order to focus the beam as a small point and to provide sufficient depth of field and absorption. The employed values of the laser power were approximately 20W and the employed marking speeds varied between 150 and 300 mm/s .

The base material was provided under the glass material to be machined. The glass material was machined using the base material in the area of nonlinear absorption behavior by directing the laser beam of the laser device to the base material through the glass material at an intensity exceeding a threshold intensity. The threshold intensity of the laser beam produced by the laser device was determined in order to provide sufficient absorption for each material combination. The laser beam was focused to the surface of the base material in order to heat the surface so that the temperature on the lower surface of the glass material locally rose to the extent that micro-cracks were formed on the lower surface of the glass materi- al , generating a mark on the surface.

In the experiments it was discovered that glass materials could be easily marked by the fiber laser device by using said base materials. The mark was clean.

In addition, it was discovered that the marking result of the material could be influenced by adjusting the intensity of the laser beam. Each combination of glass material and base material was- found to have a threshold intensity that was to be exceeded in order to provide very successful marking of the material . In connection with the studies it was discovered that transparent materials can be machined by laser devices that use optical fiber and produce a laser beam having a wavelength of between 300 and 5000 nm with the aid of a suitable base material . In the prior art methods the absorption of the laser beam in the base material has typically been improved as the wavelength has been extended. However, it has not been possible to focus the long wavelengths as a small point. In addition, the surface absorption has pronouncedly raised the temperature. A short wavelength of less than 5000nm has not absorbed in the base material, except at very high intensity and very short pulses. Conventionally the absorption coefficient of a particular wave- length in the interaction between base material and laser beam remains constant and the absorption in the material increases proportionally to the increase of the wavelength of the introduced laser beam and/or to the increase of the intensity. In this connection it was discovered that in acting in the area of non-linear absorption behavior and the intensity of a particular laser beam exceeding a particular threshold intensity the absorption of the laser beam in the base material quickly rises. In this case the ability of the material to absorb the wavelength of the laser beam therein rises to be substantially greater than expected as the cross-sectional area of laser power per laser beam exceeds a particular limit. The phenomenon and the threshold intensity were found to depend on the materi- al to be machined and the base material and the wavelength of the laser beam. It was discovered that the threshold intensity can be exceeded when the laser beam has particular properties, i.e. a sufficiently good beam quality in order to have a sufficiently small size of the focal point, whereby the appearance of nonlinear absorption behavior is provided. It was discov- ered that the machinability is improved as the absorption of the laser beam in the base material improves. Surprisingly it was discovered that very good laser machining with a transparent piece is provided by the combination of a laser beam of a good quality having a wavelength of 300 to 5000 nm that can be conveyed in optical fiber, use of a paper based base material, exceeding of the threshold intensity and non-linear absorption behavior.

The method according to the invention lends itself as different embodiments to be used in different machining applications of the most different transparent materials.

The invention is not limited merely to the examples referred to above; instead, many variations are possible within the scope of the inventive idea defined by the claims.

Claims

1. A method for machining material by a laser device, charac t e r i zed in that the employed material to be machined is a substantially transparent material, the material is machined by a laser device that uses optical fiber having a laser beam wavelength of between 300nm and 5000nm and a sufficient quality of the laser beam in order to focus the beam as a small point and to provide sufficient depth of field and absorption, a base material is provided under the material to be machined, a non-metallic material is used as the base material, the laser beam is directed and focused to the surface of the base material through the material to be machined, wherein the base material absorbs the employed wavelength and the surface of the base material is heated by the effect of the beam so that the temperature on the lower surface of the material to be machined locally rises to the extent that micro-cracks are formed on the lower surface of the ma- ' terial to be machined, generating a mark on the surface of the material to be machined.

2. The method according to claim 1, char ac t eri zed in that the material to be machined is selected from the group of glass material, transparent plastic, other transparent material and their combinations.

3. The method according to claim 1 or 2, charac t eri z ed in that the employed material to be machined is tempered glass.

4. The method according to any one of claims 1 to 3, charac t er i zed in that the employed base material is a natural fiber based material.

5. The method according to any one of claims 1 to 4, charact eri zed in that the mark is made on at least one surface of the material to be machined.

6. The method according to any one of claims 1 to 5, charac t e ri z ed in that transparent material is machined by a laser device having a sufficient quality of the laser beam in order to provide non-linear absorption behavior.

7. The method according to any one of claims 1 to 6, charac t e ri z ed in that a threshold intensity of the laser beam produced by the laser device is determined in order to provide sufficient absorp- tion.

8. The method according to any one of claims 1 to 7, charac t e ri zed in that transparent material is machined by directing the laser beam of the laser device to the base material through the transpar- ent material at an intensity exceeding the threshold intensity and the material is machined in the intensity area of non-linear absorption behavior in order to provide sufficient absorption of the laser beam.

9. The method according to any one of claims 1 to 8, charac t e ri zed in that the laser device is selected from the group of fiber laser device, disk laser device and their combinations.

10. The method according to any one of claims 1 to 9, charac t e ri z ed in that the laser device is a continuous laser device.

11. The method according to any one of claims 1 to 10, charac t e ri zed in that the laser beam is moved in order to form a marked pattern.

12. The method according to any one of claims 1 to 11, charact eri z ed in that the machining method for the material is selected from the group of: laser cutting, laser marking, laser engraving and their combinations.

13. The method according to any one of claims 1 to 12, charact e r i zed in that the method is used in machining a two-dimensional piece.

14. The method according to any one of claims 1 to 13, charact e ri z ed in that the method is used in machining a three-dimensional piece.

15. The method according to any one of claims 1 to 14, charac t er i zed in that the parameters for the laser machining are determined, wherein the parameters are selected from the group of selecting a laser device, selecting a material to be machined, selecting a base material, wavelength of the laser beam, depth of field of the laser beam, size of the point to be focused and their combinations; a parameter library is generated; the desired parameters are selected from the parameter library in order to machine the material; the machining is controlled in order to provide sufficient absorption of the laser beam to the base material through the material to be machined by utilizing the selected parameters; and the laser beam is focused to the surface of the base material in order to heat the surface so that the temperature on the low- er surface of the material to be machined locally rises to the extent that micro-cracks are formed on the lower surface of the material to be machined, generating a mark on the surface of the material to be machined.

16. The method according to any one of claims 1 to 15, charact e ri z ed in that the parameters for the laser machining are determined, wherein the parameters are selected from the group of selecting a laser device, selecting a material to be machined, selecting a base material, wavelength of the laser beam, depth of field of the laser beam, threshold intensity of the laser beam, size of the point to be focused, size of the focal point and their combinations; a parameter library is generated; the desired parameters are selected from the parameter library in order to ma- chine the material to be machined; the material to be machined is machined in the area of non-linear absorp- tion behavior by directing the laser beam of the laser device to the base material through the material to be machined at an intensity exceeding the threshold intensity; the machining is controlled in order to provide sufficient absorption of the laser beam to the base material through the material to be machined by utilizing the selected parameters; and the laser beam is focused to the surface of the base material in order to heat the surface so that the temperature on the lower sur- face of the material to be machined locally rises to the extent that micro-cracks are formed on the lower surface of the material to be machined, generating a mark on the surface of the material to be machined.