WO2009097987A1

WO2009097987A1 - Method for laser cutting of a nonmetal workpiece

Info

Publication number: WO2009097987A1
Application number: PCT/EP2009/000489
Authority: WO
Inventors: Vitalij Lissotschenko
Original assignee: Limo Patentverwaltung Gmbh & Co. Kg
Priority date: 2008-02-04
Filing date: 2009-01-27
Publication date: 2009-08-13
Also published as: DE102008007632A1

Abstract

The present invention relates to a method for laser cutting a nonmetal workpiece (1) along at least one cut line (SL) for generating at least two workpiece parts (1a, 1b), wherein the workpiece (1) has laser light (2) applied thereto, locally heating a three-dimensional heat application zone (100) having a lateral width E in an area of the workpiece (1) adjacent to the cut line (SL) to be generated, such that thermally induced tensile stresses are generated in two opposing side surfaces (12, 13) of the workpiece, said stresses being great enough to generate a crack propagating along the cut line (SL), so that the workpiece (1) is separated into at least two workpiece parts (1a, 1b) each having a cut surface (16a, 16b).

Description

"Method of laser cutting a non-metallic

Workpiece "

The present invention relates to a method of laser cutting a non-metallic workpiece along at least one cutting line for producing at least two workpiece parts.

Methods for laser cutting non-metallic workpieces are already known from the prior art in different process variants.

International Patent Application WO 93/20015 A1 discloses a method for cutting non-metallic workpieces, which may in particular consist of glass, under the action of thermoelastic stresses. In this method, a single laser light source is provided, which is movable relative to the workpiece. The laser light emitted by the laser light source strikes the surface of the workpiece and locally heats it to a temperature that is below the softening point of the material that makes up the workpiece. In this way, a crack is generated along the intended cutting line in near-surface areas of the workpiece. After local heating of the surface of the workpiece with laser light, it is supplied with a cooling fluid, so that finally a blind crack in a certain depth of the workpiece is generated and the workpiece can be divided into two parts. A disadvantage of the known from the above-mentioned document method is that directly in the region of the forming cut surfaces, a high heat input takes place and that by the following Cooling unwanted material eruptions in the area of the cut surfaces can arise. The cutting of a workpiece with this method known from the prior art thus often provides only insufficient cutting results. US Pat. No. 6,259,068 B1 discloses a device for cutting non-metallic workpieces, in which a laser beam serving as a writing beam is provided, by means of which first microcracks are produced in the surface of the workpiece along the desired cutting line. The surface area of the workpiece which is acted upon by the writing beam with laser light is then quenched by application of a gas and / or fluid, so that the microcracks can propagate further along the desired cutting line. With the help of two other laser beams, which hit the surface after quenching, tensile forces are induced to split the workpiece into two parts along the desired cutting line. The intermediate cooling after the previous heating of the workpiece with the writing beam can also lead to unwanted material chipping in the area of the cut surfaces.

International Patent Application WO 2006/045130 A1 discloses a method of laser cutting a glass substrate using a collimated laser beam to create a slit and two laser beams to the left and right of the slit to divide the glass substrate into two parts.

European Patent Application EP 1 803 538 A1 discloses a method of cutting a workpiece from a brittle material, such as glass, with laser beams. Along the desired cutting line, two areas on the surface of the workpiece are irradiated with laser light. Between these two areas there is an area with a certain width, the in turn is not acted upon with laser light, wherein the cutting line itself is not acted upon by the laser light. Further, a cooling device is provided which can generate a cooling spot in the region of the cutting line. In the areas acted upon by the laser beams, a compressive stress is first generated. By the subsequent cooling, a tensile stress is generated in the vicinity of the cooling spot, so that the workpiece can be divided into two parts along the desired cutting line. Even with such a method, the problem may arise that it can come in the area of the cut surfaces to unwanted material chipping.

This is where the present invention begins.

The present invention has for its object to provide a method for laser cutting a non-metallic workpiece, which is easy to handle and in which the problem of material eruptions in the region of the cutting surfaces of the workpiece can be effectively prevented.

This object is achieved by a method of the type mentioned above with the features of the characterizing part of claim 1. The subclaims relate to advantageous developments of the invention.

An inventive method for laser cutting a non-metallic workpiece along at least one cutting line for generating at least two workpiece parts is characterized according to claim 1 characterized in that the workpiece is exposed to laser light in ai adjacent to the cutting line to be generated region of the workpiece, a three-dimensional heat input zone with a lateral width E locally heated such that thermally induced tensile stresses are generated in two opposite side surfaces of the workpiece, which are so large that they generate a crack, which propagates along the cutting line, so that the workpiece is divided into at least two workpiece parts, each having a cut surface. An advantage of the solution according to the invention is that only at the opposite side surfaces very high tensile stresses are generated, which induce cracking and a workpiece inwardly directed crack propagation. It has been found that this can effectively prevent the problem of material eruptions which frequently occurs in the prior art in the area of the cut surfaces of the workpiece parts. It should be noted in this context that in this application the term "cut line" is to be understood to mean straight as well as at least partially curved cut line courses.The cut line courses may be curved one or more times, but linear cut line courses can be generated particularly easily and are therefore For carrying out the method described here, different laser light sources, in particular semiconductor laser diode bars, and suitable ones can be used

Beam shaping devices are used to produce the desired beam shape in the region of the heat input zone on the surface of the workpiece. Non-metallic workpieces which can be cut into at least two parts by means of the method according to the invention may consist, for example, of silicon, glass or ceramic.

In a particularly advantageous embodiment, it is proposed that the workpiece is acted upon by the laser light over its entire length L at the same time. It may be provided in a particularly preferred embodiment that thermally induced elevations are generated at the two opposite side surfaces of the workpiece, which extend away from the side surfaces. These bumps may be generated due to uneven heating of the workpiece in these areas of the heat input zone. The local heat input of the laser light into the heat input zone, there due to thermal expansions to heat-induced changes in the material structure, leading to the formation of the surveys. The tensile stress-induced cracking and crack propagation thus takes place from the outside - that is, starting from the elevations of the two side surfaces - inwardly towards the center of the workpiece.

In a particularly advantageous embodiment it is provided that thermally induced tensile stresses are generated in the region of the elevations, which are higher than the elastic limit of the workpiece. In particular, thermally induced tensile stresses can be generated in the region of the elevations, which are higher than the breaking stress of the workpiece. This can effectively improve cracking and crack propagation in these areas. The maximum tensile stresses σ _x in the region of the elevations may advantageously be on the order of about 300 to about 400 N / mm ² .

In a preferred embodiment, it is proposed that the heat input zone of the workpiece acted upon by the laser light have a total lateral width E of between approximately 0.25 mm and approximately 0.35 mm. In particular, the heat input zone may have a total lateral width of about 0.3 mm. This ensures that the heat input over the entire length of the workpiece only takes place in a comparatively narrow, spatially limited area.

It is particularly advantageous if the thermal energy introduced by the laser light into the heat input zone is at least as great as the energy required to form the cut surfaces of the workpiece parts. It can thereby be achieved that a macrocrack once created in the region of the side surfaces can spread almost instantaneously along the desired cutting line over the entire length L from the outside inwards to the middle of the workpiece. Thus, if a total of two identical cut surfaces (ie, a cut surface on each of the two workpiece parts) are produced when the workpiece is divided into two workpiece parts, the energy introduced by the laser light into the heat input zone must therefore be at least twice the energy required to produce a cut surface , The total introduced into the heat input zone heat energy can also be slightly larger than the necessary energy to form the cut surfaces of the workpiece parts.

In an advantageous embodiment it can be provided that the wavelength λ of the laser light is <1 μm. It has been shown that at these wavelengths the cracking in the workpiece is not adversely affected.

In a preferred embodiment, it is proposed that the heat input zone is generated by the laser light of a single laser light source. In an alternative embodiment, it is also possible for the heat input zone to be generated by the laser light from at least two laser light sources arranged at a distance from one another. The beam shapes and beam parameters are chosen so that, depending on the material, an optimized entry of the Laser light in the heat input zone of the workpiece to effect. For example, when two laser light sources are used, there is a possibility that the laser beams emitted from the laser light sources have substantially identical beam profiles. In order to be able to generate linear sectional line courses in a simple manner, it is proposed in an advantageous embodiment that the workpiece is heated with laser beams which generate substantially linear intensity distributions on the surface. It has also been found that the intensity profiles of the laser light, which may for example be substantially rectangular, triangular or even substantially Gaussian, do not adversely affect the cracking and crack propagation along the desired cutting line of the workpiece.

In order to further reduce the risk of material eruptions in the area of the cut surfaces and to keep them as low as possible, a particularly advantageous embodiment provides that the laser cutting of the workpiece takes place without coolant.

In order to be able to cut, for example, also workpieces of comparatively hard materials by means of the method presented here particularly easily, it can be provided in an advantageous development that the workpiece is mechanically pre-cut along the cutting line before the workpiece is exposed to the laser light. For this purpose, for example, a mechanical cutting device can be guided over the surface of the workpiece in order to cut it at least in sections along the desired cutting line. The desired cutting line course can be scratched in particular mechanically into the surface of the workpiece. According to the principle presented here, several cutting lines can be produced in the workpiece in order to cut out more than two parts from a workpiece.

Further features and advantages of the present invention will become apparent from the following description of a preferred embodiment with reference to the accompanying drawings. Show in it

1 a to 1 c schematically greatly simplifies the basic principle of a method for laser cutting a non-metallic workpiece according to a preferred embodiment of the present invention;

Fig. 2 shows the course of the tension in the y-direction within the workpiece relative to the distance from the origin of the coordinate system.

With reference to FIGS. 1 a to 1 c, the basic principle of a method for laser cutting a non-metallic workpiece 1 according to a preferred exemplary embodiment of the present invention will first be explained in more detail below. In Fig. 1 a, a non-metallic, in this embodiment, substantially cuboid workpiece 1 is shown prior to the laser cutting process. To simplify the further illustration, a Cartesian coordinate system, whose origin lies exactly in the center of the workpiece 1, is shown here as well as in FIG. The workpiece 1 consists of a non-metallic material, in particular of silicon, glass or ceramic, and has a width B in the x-direction, a length L in the y-direction and a thickness D in the z-direction. It can be seen that the thickness D of the workpiece 1 is substantially smaller than its length L and its width B, so that it is formed overall substantially plate-shaped. The workpiece 1 has at a distance + D / 2 from the coordinate system origin a first surface 10 and at a distance -D / 2 from the coordinate system origin a second surface 1 1, which is oriented substantially parallel to the first surface 10. In the y-direction (= longitudinal direction of the workpiece 1), the workpiece 1 at a distance + L / 2 from

Coordinate system originates a first side surface 12 and at a distance -L / 2 from the coordinate system origin a second side surface 13. In the x direction (= transverse direction of the workpiece 1), the workpiece 1 has a third side surface 14 at a distance + B / 2 from the coordinate system origin and a fourth side surface 15 at a distance -B / 2 from the coordinate system origin.

Referring to FIG. 1 b, laser light 2 generated by at least one laser light source is directed onto the first surface 10 of the workpiece 1 to cut the workpiece 1 along a desired cut line SL shown here in phantom under the influence of thermally induced tensile stresses , It should be noted at this point that the term "cut line" is to be understood to mean straight as well as at least partially curved cut line courses.The cut line courses may be curved one or more times, a substantially linear course of the cut line SL, as illustrated here , however, can be produced particularly easily and is therefore particularly advantageous.

During the laser cutting process, the surface 10 is not completely, but only partially exposed to the laser light 2. The workpiece 1 is doing in the longitudinal direction (y direction) over its entire length L simultaneously with the laser light 2, on the surface 10 of the workpiece 1 a certain preset or presettable width, applied. Due to the absorption of the laser light 2, the workpiece 1 is locally heated, so that over the entire length L a three-dimensional heat input zone 100 is produced which has a lateral width E and a thickness D. The thickness of the heat input zone 100 in the z direction thus corresponds to the thickness D of the workpiece 1. It is clear that the length L of the heat input zone 100 is substantially greater than the width E thereof. Preferably, the applied with the laser light 2 heat input zone 100 of the workpiece 1 has a lateral width E between about 0.25 mm and about 0.35 mm. In particular, the total lateral width E of the heat input zone 100 applied to the laser light 2 can be about 0.3 mm. This ensures that the heat input takes place only in a comparatively narrow region of the workpiece 1.

According to a first advantageous variant of the method, the laser light 2 can be generated by a single laser light source not explicitly illustrated in FIG. 1 b. According to a second advantageous variant of the method, the laser light 2 can also be generated by two separate, spaced-apart laser light sources, each of which generates a substantially line-shaped laser beam. Thereby, the effectiveness of the thermally induced laser cutting process can be increased, as long as it leads to an increase of the stored elastic energy, by means of which the crack growth can be supported. The same can be achieved with the broadening of a single laser beam of a single laser light source. For carrying out the method presented here, various types of laser light sources, in particular semiconductor laser diode bars, and suitable beam shaping devices can be used to generate the desired beam shape in the region of the heat input zone 100 on the first surface 10 of the workpiece 1, so that the Workpiece 1 can be cut along the desired cutting line SL and then divided into two parts 1 a, 1 b. In particular, at least one highly efficient, low-aberration-generating, refractive micro-optics adapted to the laser light source or to the laser light sources can produce homogeneous line profiles with very high intensity and high beam quality on the surface 10 of the workpiece.

The wavelength of the laser light 2 used in the laser cutting method presented here is preferably λ <1 μm. It has been shown that at these wavelengths the cracking in the workpiece 1 is not adversely affected. It has also been shown that the intensity distribution of the laser light 2, which may for example be substantially rectangular, triangular or even substantially Gaussian, also does not adversely affect the cracking and crack propagation along the desired cutting line SL of the workpiece 1.

Due to the local heat input of the laser light 2 into the heat input zone 100, heat-induced changes in the material structure occur there due to thermal expansions. It can be seen in FIG. 1 b that, on the first side face 12 and on the second side face 13 of the workpiece 1, which lie opposite one another and each extend transversely to the desired cutting line SL, thermally induced, away from the two opposite side faces 12, 13 extending surveys 101, 102 are generated. These elevations 101, 102 forming through the local heat input into the heat input zone 100 generate high thermally induced tensile stresses σ _x in these regions of the heat input zone 100 in the x direction (ie in the transverse direction of the workpiece 1). Due to these high tensile stresses σ _x , which are generated in the heat input zone 100 in the region of the side surfaces 12, 13, cracking occurs along the desired cutting line SL in the y direction (longitudinal direction of the workpiece 1). Finally, the workpiece 1 breaks along the cutting line SL and is thereby divided into two workpiece parts 1 a, 1 b (see FIG. 1 c). The crack propagation thus takes place from the outside (that is, starting from the elevations 101, 102 of the two side surfaces 12, 13) inwardly toward the center of the workpiece. The maximum value of the tensile stresses σ _x , which are generated in the elevations 101, 102 of the side surfaces 12, 13, should preferably exceed the breaking stress of the material of which the workpiece 1 is made. With reference to FIG. 1 c, it becomes clear that each of the two workpiece parts 1 a, 1 b obtained by the laser cutting process presented here has a cut surface 16 a, 16 b.

When the workpiece 1 is heated up to 1000 K, thermally induced tensile stresses σ _x in the order of magnitude of approximately 300 N / mm ² can arise, which can exceed the breaking stress of the workpiece 1. The reason for the formation of cracks along the desired cutting line SL in the method presented here are thus the tensile stresses caused by the loading of the workpiece 1 with the laser light 2 in the comparatively narrow elevations 101, 102 in the region of the first and second side surfaces 12, 13 of the workpiece 1 are generated selectively and exceed the elastic limit. In other words, the relatively high tensile stresses arise from the formation of the elevations 101, 102 in the side surfaces 12, 13 due to uneven heating of the workpiece 1 in these regions of the heat input zone 100. Under the conditions described here, such high tensile stresses thus form directly on the side surfaces 12, 13 of the workpiece 1, specifically only in the near-surface elevations 101, 102 of the heat input zone 100. A macroscopic crack forming in the region of the side surfaces 12, 13 propagates further along the desired cutting line SL, as long as the elastic energy released during its propagation exceeds the energy losses during the formation of the newly forming free surfaces (cut surfaces 16a, 16b) of the two workpiece parts 1a, 1b. Therefore, the laser light 2 impinging on the first surface 10 of the workpiece 1 must have a sufficient width so that the energy stored in the heat input zone 100 of the workpiece 1, which is consumed in the crack propagation in the workpiece 1 along the desired cutting line SL, the losses of the System absorbed energy that is consumed for the formation of new free surfaces (cut surfaces 16a, 16b) always exceeds. Then, a macro-crack once formed in the area of the side surfaces 1 1, 12 develops almost instantaneously along the desired cutting line SL over the entire length L from outside to inside, so that the workpiece 1 is divided into two parts 1 a, 1 b.

The maximum achievable tensile stresses σ _x , which can be generated in the region of the elevations 101, 102, amount to about 400 N / mm ² , which corresponds to a temperature of about 1073 K. Assuming that the workpiece 1 has a breaking stress of 270 N / mm ² , the thickness D of the workpiece 1 divided into two workpiece parts 1 a, 1 b may be about 0.05 to 0.3 mm. For example, if the workpiece 1 has a breaking stress of 215 N / mm ² , the range of the maximum allowable thickness D of the workpiece 1 may be extended to about 0.5 mm. FIG. 2 shows the course of the tensile stress σ _x as a function of the distance to the center of the workpiece 1 (= origin of the coordinate system with x = 0) in the y-direction over the entire length L of the workpiece 1. It is clear that the tensile stress σ _x at the opposite side surfaces 12, 13 of the workpiece 1 in the region of the elevations 101, 102 is greatest. Thus, it is once more understandable that the cracking and crack propagation at the edge of the workpiece 1 at the two opposite side surfaces 12, 13 have their origin. The tensile stress σ _x thus exceeds the fracture stress of the workpiece 1 only in relatively narrow regions on the opposite side surfaces 12, 13 of the workpiece 1, where the elevations 101, 102 have formed due to the heat input into the heat input zone 100.

With the aid of the laser cutting method presented here, a workpiece 1 can be easily divided into (at least) two workpiece parts 1 a, 1 b. One advantage of the solution presented here is that material chippings in the region of the cut surfaces 16a, 16b, which can arise in the methods known from the prior art due to the high heat input and the subsequent cooling in the region of the cutting zone, can be effectively avoided.

It can be provided according to a further advantageous development of the laser cutting method described here, that the workpiece 1 along the desired cutting line SL mechanically pre-cut (in particular scribed) before the workpiece 1 is acted upon by the laser light 2 to the workpiece 1 along the section line SL finally in the two workpiece parts 1 a, 1 b to share.

Claims

claims:

1 . Method for laser cutting a non-metallic workpiece (1) along at least one cutting line (SL) for producing at least two workpiece parts (1 a, 1 b), characterized in that the workpiece (1) is acted upon by laser light (2) in one the cutting line (SL) adjacent to the region of the workpiece (1) thermally heats a three-dimensional heat input zone (100) with a lateral width E such that thermally induced tensile stresses are generated in two opposite side surfaces (12, 13) of the workpiece are large that they generate a crack that propagates along the cutting line (SL), so that the workpiece (1) in at least two workpiece parts (1 a, 1 b), each having a cut surface (16 a, 16 b) is divided.

2. The method according to claim 1, characterized in that the workpiece (1) over its entire length L simultaneously with the laser light (2) is acted upon.

3. The method according to claim 1 or 2, characterized in that on the two opposite side surfaces (12, 13) of the workpiece (1) thermally induced elevations (101, 102) are generated, extending from the side surfaces (12, 13) extend away.

4. The method according to claim 3, characterized in that in the region of the elevations (101, 102) thermally induced tensile stresses are generated which are higher than the elastic limit of the workpiece (1).

5. The method according to claim 3 or 4, characterized in that in the region of the elevations (101, 102) thermally induced tensile stresses are generated which are higher than the breaking stress of the workpiece (1).

6. The method according to any one of claims 3 to 5, characterized in that the maximum tensile stresses σ _x in the region of the elevations (101, 102) in the order of about 300 to about 400 N / mm ² .

7. The method according to any one of claims 1 to 6, characterized in that the laser light (2) acted upon heat input zone (100) of the workpiece (1) has a total lateral width E between about 0.25 mm and about 0.35 mm.

8. The method according to any one of claims 1 to 7, characterized in that the laser light (2) in the heat input zone (100) total introduced heat energy is at least as large as the formation of the cut surfaces (16a, 16b) necessary energy.

9. The method according to any one of claims 1 to 8, characterized in that the wavelength λ of the laser light (2) <1 micron.

10. The method according to any one of claims 1 to 9, characterized in that the heat input zone (100) from the laser light (2) of a single laser light source is generated.

1 1. Method according to one of claims 1 to 9, characterized in that the heat input zone (100) of Laser light (2) is generated by at least two spaced-apart laser light sources.

12. The method according to any one of claims 1 to 1 1, characterized in that the laser cutting of the workpiece (1) is carried out without coolant.

13. The method according to any one of claims 1 to 12, characterized in that the workpiece (1) is mechanically pre-cut along the cutting line (SL) before the workpiece (1) with the laser light (2) is acted upon.

14. The method according to claim 13, characterized in that the cutting line (SL) is mechanically scored.