Method and device for laser-assisted separation of a portion from a sheet glass element

Abstract

A method for separating a portion from a sheet glass element having a thickness of at least 2 millimeters along an intended separation line that divides the sheet glass element into the portion and a remaining main part is provided. The method includes producing filamentary damages comprising sub-micrometer hollow channels in a volume of the glass sheet element adjacently aligned along the separation line; and heating and/or cooling the glass sheet element to cause expansion and/or contraction so that the portion detaches from the main part along the separation line. The portion and the remaining main part each remain intact as a whole. The step of producing the filamentary damages includes generating a plasma within the volume with laser pulses of an ultrashort pulse laser; and displacing points of incidence of the laser pulses over a surface of the glass sheet element along the separation line.

Claims

1. A method for separating a portion from a sheet glass element having a thickness of at least 2 millimeters along a non-rectilinear separation line that divides the sheet glass element into the portion and a remaining main part, the method comprising: producing filamentary damages comprising sub-micrometer hollow channels in a volume of the glass sheet element adjacently aligned along the non-rectilinear separation line; heating and/or cooling the glass sheet element to cause expansion and/or contraction so that the portion and the remaining main part change size differently from each other to produce local tensile stresses in the glass sheet element, wherein, due to the local tensile stresses, the portion detaches splinter-free from the main part along the non-rectilinear separation line, wherein the portion and the remaining main part each remain intact as a whole; and coordinating an adjustment of L, ΔT, and α such that a minimal gap width (S) between the portion and the remaining main part is greater than a mean roughness (R), wherein L is a minimum extension of the portion in a plane of the glass sheet element, ΔT is a temperature difference in Kelvin between an average temperature of the remaining main part and an average temperature of the portion during the heating and/or cooling step, α is a coefficient of thermal expansion of the material of the glass sheet element, and R is an average roughness of an edge surface of the portion along which the portion separates from the remaining main part, wherein the step of producing the filamentary damages comprises: generating a plasma within the volume with laser pulses of an ultrashort pulse laser, wherein the sheet glass element comprises a material that is transparent to the laser pulses, and displacing points of incidence of the laser pulses over a surface of the glass sheet element along the non-rectilinear separation line.

2. The method as in claim 1, wherein the heating step comprises heating a region of the remaining main part.

3. The method as in claim 2, further comprising thermally toughening the remaining main part exploiting heat from the heating step.

4. The method as in claim 1, wherein the cooling step comprises cooling a region of the portion.

5. The method as in claim 1, further comprising, after producing the filamentary damages, causing crack formation between adjacent filamentary damages by displacing laser radiation on the glass sheet element along the non-rectilinear separation line so as to cause the local tensile stresses in the glass along the non-rectilinear separation line.

6. The method as in claim 1, wherein the step of heating and/or cooling comprises producing a temperature difference between an average temperature of the remaining main part and an average temperature of the portion that is at least 150 degrees Celsius.

7. The method as in claim 1, wherein the material of the glass sheet element has a coefficient of thermal expansion that is greater than 3×10.sup.−6K.sup.−1.

8. The method as in claim 1, wherein the glass sheet element has a thickness of at least 3 millimeters.

9. The method as in claim 1, wherein the portion has a first minimum extension of at least 5 millimeters along a first lateral dimension and a second minimum extension of at least 5 millimeters along a second lateral dimension that is orthogonal to the first lateral dimension.

10. The method as in claim 1, further comprising satisfying an inequation L.Math.ΔT.Math.α>R.

11. The method as in claim 1, wherein the non-rectilinear separation line is configured so that the remaining main part has a two-dimensional shape that is not star-shaped in a sense of mathematical topology in a plane of the glass sheet element.

12. The method as in claim 1, wherein the non-rectilinear separation line is configured so that the remaining main part completely encloses the portion in a plane of the glass sheet element.

13. The method as in claim 1, further comprising producing secondary filamentary damages in the volume of the glass sheet element adjacently aligned along an offset line which is spaced from the non-rectilinear separation line by at least 5 and at most 50 micrometers.

14. The method as in claim 13, further comprising a projection of the secondary filamentary damages onto a longitudinal extension of the filamentary damages exhibit an overlap of less than 200 micrometers.

15. The method as in claim 1, wherein the step of generating the plasma within the volume with the laser pulses comprises directing the laser pulses obliquely on the surface so that the laser pulses have a light propagation direction that extends obliquely relative to the surface and so that the filamentary damages resulting from the laser pulses have the longitudinal extension that extends obliquely relative to the surface, wherein the non-rectilinear separation line extends obliquely to a light incidence plane of the laser pulses.

16. A method for removing a portion from a glass sheet element having a thickness of at least 2 millimeters along a non-rectilinear separation line that divides the glass sheet element into the portion and a remaining main part, the method comprising: producing filamentary damages comprising sub-micrometer hollow channels in a volume of the glass sheet element adjacently aligned along the non-rectilinear separation line; toughening the glass sheet element having the filamentary damages; changing sizes of the remaining main part and the portion differently from each other by heating and/or cooling to produce local tensile stresses in the glass sheet element and cause cracks and propagation of the cracks in a region of the portion delimited by the filamentary damages so that the portion can be removed splinter-free from the remaining main part along the non-rectilinear separation line with the remaining main part remaining intact as a whole; and coordinating an adjustment of L, ΔT, and α such that a minimal gap width (S) between the portion and the remaining main part is greater than a mean roughness (R), wherein L is a minimum extension of the portion in a plane of the glass sheet element, ΔT is a temperature difference in Kelvin between an average temperature of the remaining main part and an average temperature of the portion during the heating and/or cooling step, α is a coefficient of thermal expansion of the material of the glass sheet element, and R is an average roughness of an edge surface of the portion along which the portion separates from the remaining main part, wherein the step of producing the filamentary damages comprises: generating a plasma within the volume with laser pulses of an ultrashort pulse laser, wherein the glass sheet element comprises a material that is transparent to the laser pulses, and displacing points of incidence of the laser pulses over a surface of the glass sheet element along the non-rectilinear separation line.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The invention will now be explained in more detail with reference to the accompanying figures, wherein the same reference numerals designate the same or equivalent elements, and wherein:

(2) FIGS. 1a through 1d are schematic perspective views of a laser processing device for producing filamentary damages in the volume of a glass element along different separation lines;

(3) FIG. 2 is a schematic perspective view of a heating device for heating the glass element in the region of the main part;

(4) FIG. 3 is a schematic diagram of graphs of temperature as a function of the location with respect to the lateral dimensions of a sheet glass element;

(5) FIGS. 4a through 4h shows plan views schematically illustrating tensile stresses in a sheet glass element as produced by heating/cooling;

(6) FIG. 5 is a schematic perspective view of a filamented glass element which has been heated in the region of the main part so that the portion can be removed;

(7) FIGS. 6a through 6f shows plan views schematically illustrating various forms of a separation line and of the corresponding main part and portion;

(8) FIGS. 7a and 7b are schematic perspective views of an alternative laser processing device for producing oblique filamentary damages;

(9) FIGS. 8a through 8h show schematic side views of glass elements after repeated laser processing;

(10) FIGS. 9a and 9b are perspective views of glass elements after repeated laser processing along a separation line and along additional offset lines;

(11) FIGS. 10a and 10b are schematic perspective views of sets of two respective sheet glass elements;

(12) FIGS. 11a and 11b are schematic perspective views of sheet glass elements with offset(s) in the edge surface.

DETAILED DESCRIPTION

(13) FIGS. 1a through 1d schematically shows a laser processing device 1, which can be used for microperforating a glass element 2 by introducing filamentary damages 20 along a defined separation line 21 and thus preparing it for subsequent separation.

(14) Laser processing device 1 comprises an ultrashort pulse laser 10 for directing laser pulses 12 onto the glass element 2. For this purpose, the laser pulses 12 are focused onto the glass element 2 using focusing means 11. The wavelength of the ultrashort pulse laser 10 is selected so that the laser pulses 12 can penetrate into the glass element 2.

(15) The laser pulses 12 generate a plasma in the volume of the glass element 2 causing the filamentary damages 20. The incidence points 13 of the laser pulses 12 on the glass element 2 are successively displaced over the surface 22 along the defined separation line 21.

(16) Separation line 21 is defined so that it completely divides the glass element 2 into a portion 4 to be separated and a remaining main part 3.

(17) FIGS. 1a through 1d illustrate different exemplary separation lines 21. FIG. 1a shows a curved non-rectilinear separation line which does not form a closed loop. FIGS. 1b-d show closed-loop separation lines 21 of different shapes. FIG. 1b shows an oval separation line 21, FIG. 1c shows a separation line 21 in the form of a regular pentagon, and FIG. 1d shows a separation line 21 in the form of a regular pentagon with rounded corners.

(18) FIG. 2 schematically illustrates an exemplary heating device 5 for heating the glass element 2 in the region of main part 3. For the sake of better illustration, glass element 2 is considerably spaced from heating device 5 in FIG. 2. In reality, by contrast, the glass element 2 may contact the heating device 5. Accordingly, the lower surface of sheet glass element 2 may rest on heating device 5.

(19) In FIG. 2, sheet glass element 2 has its longest extensions along the x and y dimensions shown. The two dimensions extending along the longest extensions of glass element 2 will also be referred to as first lateral dimension 6 and second lateral dimension 7. Along the dimension which is orthogonal to lateral dimensions 6 and 7, the glass has a thickness 23.

(20) The heating device 5 which is shown in FIG. 2 by way of example has a planar design and may accordingly also be referred to as a heating plate. Here, the surface of this heating plate is in parallel to the two lateral dimensions 6 and 7 of glass element 2, i.e. to the x and y dimensions shown in FIG. 2.

(21) The heating plate heats the glass element 2 in the region of main part 3. More generally, without being limited to the exemplary heating device, the heating plate may have a heating zone 50 that is adapted to the shape of the main part 3. In the case shown, the heating zone extends along the first lateral dimension 6 from value x=0 to value x=x.sub.3 and along the second lateral dimension 7 from value y=0 to value y=y.sub.2, and has a central recess matching portion 4, extending from x=x.sub.1 to x=x.sub.2 for the value y=y.sub.1, for example. Accordingly, glass element 2 will be subjected to different temperatures on a surface extending in the plane of the two lateral dimensions (x and y dimensions), as a function of the location on this surface (x and y values).

(22) FIG. 3 shows different schematic temperature profiles in glass element 2, which are suitable for the separation of portion 4 from main part 3 according to the invention. The temperature profiles are shown as functions of the location x of a first lateral dimension 6 at a predefined value y=y.sub.1 of the second lateral dimension 7. Predefined value y=y.sub.1 of the second lateral dimension is chosen so that the profile of value x along the first lateral dimension includes locations in the region of main part 3 as well as locations in the region of portion 4. In FIG. 3, profile (a) shows an idealized temperature profile for the case in which main part 3 has a consistent temperature which is higher than the temperature of portion 4. In FIG. 3, profile (c) shows a similar temperature profile for the case of a temperature gradient extending across the predetermined breaking point defined by the separation line 21. In FIG. 3, profiles (b) and (d) also show temperature profiles for the case of existing temperature gradients, here with temperature gradients extending completely within portion 4 or within main part 3. All temperature profiles (a) through (d) illustrated in FIG. 3 have in common that the average temperature in main part 3 is higher than the average temperature in portion 4. It is not important here, whether the glass element 2 was heated in the region of main part 3 or cooled in the region of portion 4, or whether both was performed simultaneously or with a time delay. What is important for the method of the invention is only that as a result of the generated temperature profile, glass element 2 expands in the region of main part 3 and/or contracts in the region of portion 4.

(23) FIGS. 4a through 4h shows plan views of glass element 2 illustrating tensile stresses generated in glass element 2 by the heating and/or cooling according to the invention, that means for the case that no cleaving step has been performed. The tensile stresses are schematically illustrated by arrows. Assuming, that glass element 2 includes a series of filamentary damages aligned along separation line 21, which already have been introduced previously. FIG. 4a shows tensile stresses as a result of heating the glass element 2 in the region of main part 3 in accordance with a temperature profile (d) as illustrated in FIG. 3. FIG. 4b shows tensile stresses as a result of heating in the region of main part 3 in accordance with a temperature profile (c) as illustrated in FIG. 3. FIG. 4c shows tensile stresses as a result of cooling in the region of portion 4 in accordance with a temperature profile (b) as illustrated in FIG. 3. FIG. 4d shows tensile stresses as a result of cooling in the region of portion 4 in accordance with a temperature profile (c) as illustrated in FIG. 3. FIG. 4e shows tensile stresses as a result of heating in the region of main part 3 in accordance with a temperature profile (d) as illustrated in FIG. 3 with simultaneous or time-delayed cooling in the region of portion 4 in accordance with a temperature profile (b) as illustrated in FIG. 3. FIG. 4f shows tensile stresses as a result of heating in the region of main part 3 in accordance with a temperature profile (c) as illustrated in FIG. 3 with simultaneous or time-delayed cooling in the region of portion 4 in accordance with a temperature profile (b) as illustrated in FIG. 3. FIG. 4g shows tensile stresses as a result of heating in the region of main part 3 in accordance with a temperature profile (d) as illustrated in FIG. 3 with simultaneous or time-delayed cooling in the region of portion 4 in accordance with a temperature profile (c) as illustrated in FIG. 3. FIG. 4h shows tensile stresses as a result of heating in the region of main part 3 in accordance with a temperature profile (c) as illustrated in FIG. 3 with simultaneous or time-delayed cooling in the region of portion 4 in accordance with a temperature profile (c) as illustrated in FIG. 3.

(24) All variants illustrated in FIGS. 4a-h for creating tensile stresses in glass element 2 by heating and/or cooling can cause the portion 4 to separate from the main part 3 along the separation line 21 at the adjacent filamentary damages.

(25) FIG. 5 shows a schematic perspective view of a glass element 2 which was heated and caused to expand in the region of main part 3. Portion 4 of glass element 2 has detached from the main part 3 along the separation line at the adjacent filamentary damages. Therefore, portion 4 can be removed from main part 3.

(26) As long as the main part 3 is still in a heated state, the removal of portion 4 is easily possible, i.e. in particular without jamming with the main part 3, and without deterioration or permanent deformation of portion 4. This is due to the fact that with the relative expansion of main part 3 relative to portion 4 not only separation along the separation line was cause but moreover a gap 24 has been formed between main part 3 and portion 4 along the course of the separation line. This gap provides a certain clearance which allows to remove the portion 4 from the main part 3 without jamming due to tilting.

(27) While in separation processes employing the application of bending moments or local heating by laser radiation, for example by CO.sub.2 lasers, growing difficulties are encountered with increasing thickness of the glass element 2, the inventive method allows to particularly easily remove the portion 4 even in the case of glass elements 2 that have a thickness 23 of at least 2 millimeters, preferably at least 3 millimeters, more preferably at least 4 millimeters, yet more preferably at least 5 millimeters.

(28) The width of the gap formed by the heating in the region of main part 3 and/or the cooling in the region of portion 4 depends, inter alia, on the difference between the average temperatures that were generated between main part 3 and portion 4. However, the gap width also depends on the size of the surface area of the portion 4 along the two lateral dimensions 6 and 7. It is advantageous for the method of the invention that the portion 4 has certain minimum extensions along these two dimensions, in particular that the minimum extension of portion 4 in a first lateral dimension 6 and the minimum extension of portion 4 in a second lateral dimension 7 each have a minimum length. In one embodiment of the invention, this minimum length is 5 millimeters, preferably 10 millimeters, more preferably 20 millimeters.

(29) Alternatively, however, it is also possible that the smallest rectangle enclosing portion 4 in the plane spanned by lateral dimensions 6 and 7 has side lengths 41 and 42 each having a certain minimum length. Then, both the maximum extension of portion 4 in a first lateral dimension 6 and the maximum extension of portion 4 in a second lateral dimension 7 each have a minimum length.

(30) FIGS. 6a through 6f illustrates plan views of glass element 2 with different forms of a separation line 21 and corresponding main parts 3 and portions 4. A damage-free separation of portion 4 from main part 3, that means separation in such a way that both the main part 3 and the portion 4 experience no further damage except for the microperforation at the separation edge, is easily possible if the separation line 21 is rectilinear, as shown in FIG. 6a. In such a case, damage-free separation is possible using the inventive method, but it is also possible using conventional separation methods such as the application of a sufficient bending moment. This is similarly true for slightly curved or slightly angled separation lines 21 such as those shown in FIG. 6b and FIG. 6c, respectively.

(31) With common separation methods, difficulties will in particular be encountered if the separation line 21 is strongly curved or has strongly angled sections, i.e. if in the plane of glass element 2 the portion 4 can be referred to as a predominantly inner or completely inner portion, as is illustrated in FIG. 6d or FIG. 6e by way of example. By contrast, the method of the invention is very well suited for such cases.

(32) FIG. 6d shows a case in which portion 4 is predominantly located in the interior of glass element 2. A criterion that can be applied for this case is that the two-dimensional shape of the main part 3 in the plane of glass element 2 is not star-shaped in the sense of mathematical topology. That is, within the two-dimensional area corresponding to main part 3 there is not a single point 31 which has the property of a star point. The indicated point 31 lacks the property of a star point, since it is not possible when starting from point 31 to draw straight lines to all other points within the two-dimensional area corresponding to main part 3, which lie entirely within this two-dimensional area. Therefore, when starting from point 31, the hatched areas of the surface area of main part 3 cannot be reached in the described manner. The area of main part 3 is therefore not star-shaped. The same applies to the area of main part 3 shown in FIG. 6e, which is neither star-shaped nor simply contiguous. Portion 4 is even completely located inside here, that is, it is completely enclosed in the plane of glass element 2. Such an inner portion 4 is sometimes also referred to as an inner contour or inner geometry.

(33) For the method of the invention it is generally advantageous if the two-dimensional shape of portion 4 in the plane of glass element 2 is star-shaped, that means, if at least one star point 43 exists in the two-dimensional area corresponding to the portion 4. This is the case in the situations shown in FIG. 6d and FIG. 6e. Even any point of the area of portion 4 is a star point in the examples shown in FIG. 6d and FIG. 6e. In other words, the areas of portions 4 are even convex areas in these examples. For the separation it is advantageous when portions 4 represent convex areas in the plane of the sheet glass element 2. According to one embodiment of the invention it is therefore generally contemplated, without being limited to the illustrated examples, that portions are detached which have a two-dimensional shape of a convex area in the plane of the sheet glass element.

(34) However, it is not absolutely necessary for the functioning of the method according to the invention that the shape of the portion is star-shaped or even convex in the plane of the glass. This is because the separation along the predetermined breaking point which extends along the separation line 21 tends to proceed once it has started in certain areas. In addition, uneven cooling and/or heating of the main part 3 and/or of the portion 4 may also promote the separation of non-star-shaped portions 4.

(35) Another exemplary case in which neither the main part nor the portion 4 is star-shaped or convex in the plane of the glass is shown in FIG. 6f. Here, the two-dimensional area corresponding to the glass element 2 is neither star-shaped nor convex nor simply continuous. Such a glass element 2 which has a hole may for example be the result of a separation of an inner portion according to the invention, as shown in FIG. 6e. In this case, the separation line 21 has the shape of a closed loop. Mathematically, the portion 4 defined by separation line 21 is not an inner portion 4 anymore. However, it is not uncommon in practice, depending on the size of the hole, to speak of an inner geometry. The non-star-shaped and not simply contiguous portion 4 can be separated from the non-star-shaped and not simply contiguous main part 3 using the method of the invention without causing damage and without jamming.

(36) As can be seen from FIG. 7a, it is also possible according to one embodiment of the invention, to obliquely direct the laser pulses 12 onto the surface 22 of glass element 2, so that an angle exists between the surface normal 14 and the direction of laser pulses 12. Therefore, the longitudinal extension of the filamentary damages 20 will also extend obliquely to the surface 22. Moreover, the influence of refraction of the laser light on the surface 22 of glass element 2 has to be considered.

(37) In order to facilitate the separation of the portion, the angle between the light incident direction and the surface normal 14 may be in a range from a few degrees to well over 10°. Preferably, an angle in a range from 3° to 30°, more preferably 3° to 15°, most preferably at least 5° is set between the light incident direction of the laser pulses 12 and the surface normal 14 of the surface 22 of glass element 2.

(38) As can be seen from FIG. 7a, the laser pulses 12 are furthermore directed obliquely onto the surface 22 in such a way that the plane 15 of light incidence is transverse, preferably perpendicular to the separation line 21. Accordingly, the direction of advancement along which the point of incidence 13 is displaced over the surface 22 is also transverse, preferably perpendicular, to the light incidence plane 15. Light incidence plane 15 is spanned by the light incident direction and surface normal 14. If the separation line 21 is curved, for example circular, as in the example shown, the orientation of the separation line 21 transverse to the light incident plane 15 is to be understood as meaning that the tangent to the separation line 21 is transverse, preferably perpendicular, to the light incident plane 15.

(39) FIG. 7b shows a sectional view of glass element 2 corresponding to FIG. 7a. Due to the angle between the longitudinal extension of filamentary damages 20 and the surface normal 22, a preferred direction is resulting along which the portion 4 can be separated from the main part 3, as indicated by the arrow.

(40) FIGS. 8a through 8h show sectional views illustrating glass elements in a view similar to FIG. 7b after a plurality of laser processing steps in different focal depths. That means, after a processing step in which damages 20 are produced in the volume of glass element 2 by laser pulses 12 of an ultrashort pulse laser by moving the points of incidence 13 of the laser pulses 12 on the glass element 2 over the surface 22 thereof along separation line 21, further processing steps are performed in which damages 20′, 20″, etc. are generated in similar manner, but with different focal depths of the laser pulses 12, in other depths in the volume of glass element 2.

(41) Such multiple laser processing is particularly suitable for thicker glass elements 2, where it is often no longer possible or at least unfavorable to perform the microperforation over the entire thickness 23 in a single processing step or by displacing the point of incidence 13 of the laser beam 12 along the separation line 21 in only one pass.

(42) A problem that may arise when repeatedly passing the laser beam in different focal depths is that the damages in different depths of the volume of glass element 2 will not be aligned ideally.

(43) FIG. 8a schematically illustrates, by way of example, a glass element 2 after two laser processing steps over the surface 22 thereof. Damages 20 were produced in a first processing step, while damages 20′ were produced in a second step at a greater depth. Damages 20 and 20′ have a certain offset from each other, which typically exhibits statistical variations due to finite positioning accuracy. This offset makes it difficult to separate portion 4 from main part 3 using the method according to the invention. Due to the offset, a roughness R′ of the cut edge will result that is increased as compared to the roughness R caused by the filamentation.

(44) According to a refinement of the invention it is contemplated to cause the offset between damages 20 and 20′ in such a manner that only the roughness R caused by filamentation is relevant for a separation of portion 4 from main part 3, but not the roughness R′ of the edge surface when taking into account the offset.

(45) As illustrated in FIG. 8b, the damages 20′ which are located deeper in the volume of glass element 2 with respect to surface 22, are produced in such a manner that the portion 4 is slightly larger on the face opposite to surface 22 than on the face of surface 22. Thereby, a preferred direction is resulting along which the portion 4 can be separated from the main part 3, as indicated by the arrow. Along this preferred direction, only the roughness R caused by the filamentation is decisive for the separation, while in the direction opposite to the preferred direction, the roughness R′ additionally resulting from the offset between damages 20 and 20′ is decisive for the separation. Portion 4 does not need to be a completely inner portion, rather, all forms mentioned above are eligible. In case the portion 4 is a circular inner portion, it will have a cake shape, figuratively speaking, due to the offset between damages 20 and 20′.

(46) While the damages 20 according to FIGS. 1a through 1d are generated by displacing the points of incidence 13 of the laser pulses 12 on the glass element 2 over the surface 22 thereof along separation line 21, the damages 20′ according to FIG. 9a are generated by displacing the points of incidence 13 of the laser pulses 12 on the glass element 2 over the surface 22 thereof along an offset line 21′ that is slightly spaced from separation line 21. The offset line advantageously extends completely on one side of the separation line 21, however it is not necessary, albeit advantageous, that the spacing between offset line 21′ and separation line 21 is consistent along the lines.

(47) The described embodiment of the invention is not limited to two laser processing steps. It is also possible to perform three or even more passes with the laser. FIG. 8c schematically shows, by way of example, a sectional view through a glass element 2 after three laser processing steps which caused damages 20, 20′, and 20″. FIG. 8d in turn illustrates how the offsets between damages 20 and 20′ and between damages 20′ and 20″ can be produced according to this embodiment of the invention in such a manner that a preferred direction is resulting for separating portion 4 from main part 3, as indicated by the arrow.

(48) In this case, the damages 20′ according to FIG. 9b have been produced by moving the points of incidence 13 of the laser pulses 12 on the glass element 2 over the surface 22 thereof along a first offset line 21′ that is slightly spaced from separation line 21. Furthermore, damages 20″ have been produced by moving the points of incidence 13 of the laser pulses 12 on the glass element 2 over the surface 22 thereof along a second offset line 21″ that is spaced slightly further from separation line 21 than the first offset line 21′. Advantageously, the second offset line 21″ extends completely on one side of the first offset line 21′, however it is not necessary, albeit advantageous, that the spacing between the second offset line 21″ and the first offset line 21′ is consistent along the lines.

(49) It is also possible to perform more than two laser processing steps. For this purpose, further offset lines can be defined which are again spaced slightly further from the separation line 21 and along which the points of incidence 13 of the laser pulses 12 are displaced over the surface 22 of glass element 2.

(50) The selective controlling of one or more offset(s) between damages that are produced by multiple laser processing steps with different focal depths can be combined with the laser processing illustrated in FIGS. 7a and 7b according to which the laser pulses 12 are directed obliquely onto the surface 22 of glass element 2. In practice, it is usually not possible for the angle between the direction of light incidence and the surface normal 14 to be exactly set to zero degrees. Thus, strictly speaking, there will always be a (very) small angle, so that the longitudinal extensions of the damage channels will always be at a certain angle relative to the surface normal 14 of the glass element 2. Similarly to the positioning, a statistical deviation smaller than the alignment accuracy has to be assumed here.

(51) FIG. 8e shows oblique damages 20 and 20′ caused by two laser processing steps on a glass element 2. Again, damages 20 and 20′ are not exactly aligned (not exactly in one plane) but have a certain offset from each other. Again, this makes it difficult to separate the portion 4 from the main part 3 using the method according to the invention.

(52) However, as shown in FIG. 8f, the offset can advantageously be adjusted such that the preferred direction for separation is resulting as indicated by the arrow. Along the preferred direction, portion 4 can be separated from main part 3 without any interfering effect by the edges that are caused by the offset.

(53) The described embodiment of the invention is not limited to two laser processing steps with laser pulses 12 obliquely impinging on the surface 22. It is also possible to perform three or more laser processing steps in different focal depths. FIG. 8g schematically illustrates, by way of example, a sectional view through a glass element 2 after three laser processing steps with laser pulses 12 that are obliquely directed onto the surface, resulting in damages 20, 20′, and 20″. FIG. 8d shows how the offsets between damages 20 and 20′ and between damages 20′ and 20″ can again be arranged in this embodiment of the invention such that a preferred direction is resulting for separating portion 4 from main part 3, as indicated by the arrow. The offsets do not need to be equal in practice.

(54) FIGS. 10a and 10b shows two sets each one consisting of two sheet glass elements which can be produced by the method of the invention. While the set of two sheet glass elements shown in FIG. 10b is formed so that the two-dimensional shape that one of the sheet glass elements 2 has in its plane completely encloses the two-dimensional shape the other one of the sheet glass elements 2′ has in its plane, this is not the case for the set of two sheet glass elements shown in FIG. 10a. For the set shown in FIG. 10b this means that the glass element 2′ is an inner portion fitting to glass element 2. For the set shown in FIG. 10a this means that the glass element 2′ is a portion which fits to glass element 2 and which may be referred to herein as predominantly inner portion.

(55) What applies to both illustrated sets (FIG. 10a and FIG. 10b) is that the one sheet glass element 2 could be combined with the other sheet glass element 2′ with a perfect fit, at least theoretically.

(56) Each sheet glass element 2 (or 2′) of a set has an edge surface 25 (or 25′) which has adjacently aligned filamentary damages 26 (or 26′) forming indentations in this edge surface 25 (or 25′). These filamentary damages can be caused by a microperforating laser processing process according to the method of the invention.

(57) The longitudinal extension of the filamentary damages 26 (or 26′) in an edge surface 25 (or 25′) of a sheet glass element of a set of two glass sheet elements extends in the direction from one edge to the other edge which define the transition between the edge surface 25 (or 25′) and the faces 29 (or 29′) and 30 (or 30′) of the glass element. When a glass element 2 (or 2′) of a set of two glass elements is produced by the method according to the invention, this longitudinal extension of the filamentary damages 26 (or 26′) corresponds to the direction of light propagation of the laser pulses.

(58) If the two sheet glass elements 2 and 2′ of a set would be combined in perfect fitting manner, the edge surfaces 25 and 25′ of glass elements 2 and 2′ would touch one another or would come very close to each other. Also, the edges 27 and 27′ would touch one another or would come very close to each other, and edges 28 and 28′ would also touch one another or would come very close to each other. The two-dimensional surfaces in the planes of sheet glass elements 2 and 2′ would fit together like two puzzle pieces when the two glass elements 2 and 2′ are joined.

(59) The two sheet glass elements of a set are preferably originating from the same separation process. That means, by applying the method of the invention, an original sheet glass element was divided into a main part and a portion, which when taken together form a set of sheet glass elements according to the invention. If the two sheet glass elements of a set originate from the same process, a highest possible accuracy of fit is guaranteed, which is even higher than if a series of portions equivalent to each other were produced by a number of equivalent separation processes and a series of main parts equivalent to each other were produced by a number of equivalent separation processes and a set of sheet glass elements according to the invention would be chosen to consist of any portion of the series of portions and any main part of the series of main parts.

(60) According to one further embodiment of the invention it is contemplated that each sheet glass element 2 (or 2′) of a set of two sheet glass elements has an edge surface 25 (or 25′) which exhibits at least one offset 32 (or 32′), i.e. a step, that extends transversely, preferably substantially perpendicular to the longitudinal extension of the adjacently aligned filamentary damages 26 (or 26′). FIGS. 11a and 11b show illustrations of such sheet glass elements 2.

(61) The at least one offset 32 (or 32′) may result in a roughness R′ of the edge surface 25 (or 25′) which is increased compared to the roughness R as caused by the filamentary damages 26 (or 26′).

(62) The at least one offset is a step that is imperceptible to the naked eye, so that it is still possible to speak of a single edge surface 25 (or 25′). Preferably, the at least one offset is a step of at least 5 micrometers and at most 50 micrometers.

(63) FIG. 11a shows a sheet glass element 2 according to the invention, which is distinguished by an edge surface 25 having adjacently aligned filamentary damages 26 forming indentations in the edge surface 25, wherein a longitudinal extension of the filamentary damages 26 extends in the direction from one edge 27 to the other edge 28, which edges define the transition between the edge surface 25 and the faces 30 of sheet glass element 2, and wherein the edge surface 25 has an offset 32 extending along the entire edge surface 25 and extending substantially perpendicular to the longitudinal extension of the filamentary damages 26. The offset preferably extends in the middle of the edge surface, with a deviation of 20 percent, that is in the middle between edges 27 and 28 with a deviation of 20 percent.

(64) FIG. 11b shows another sheet glass element 2 according to the invention, which is distinguished by an edge surface 25 that has two offsets 32 extending along the entire edge surface 25 and extending substantially perpendicular to the longitudinal extension of the filamentary damages 26. The two offsets preferably extend with a spacing from the surface 30 of glass element 2 of one third and two thirds, respectively, of the width 23 of edge surface 25, with a deviation of 20 percent.

LIST OF REFERENCE NUMERALS

(65) TABLE-US-00001  1 Laser processing device 10 Ultrashort pulse laser 11 Focusing means 12 Laser pulse 13 Points of incidence of the laser pulses on the glass element 14 Surface normal of glass element 15 Light incidence plane of the laser pulses  2 Sheet glass element  2′ Sheet glass element 20, 20′, 20″ Filamentary damages 21, 21′, 21″ Separation line 22 Surface of glass element 23 Thickness of glass element 24 Gap between the portion and the main part 25 Edge surface with adjacently aligned filamentary damages  25′ Edge surface with adjacently aligned filamentary damages 26 Filamentary damages in an edge surface  26′ Filamentary damages in an edge surface 27, 28 Edges of a sheet glass element defining the transition between the faces and an edge surface connecting these faces 27′, 28′ Edges of a sheet glass element defining the transition between the faces and an edge surface connecting these faces 29, 30 Faces of a sheet glass element 29′, 30′ Faces of a sheet glass element 32 Offset in an edge surface  3 Main part 31 Point within the two-dimensional area corresponding to the main part  4 Portion to be separated 41 Maximum extension of the portion along the first lateral dimension 42 Maximum extension of the portion along the second lateral dimension 43 Point within the two-dimensional area corresponding to the portion  5 Heating device 50 Heating zone  6 First lateral dimension of glass element  7 Second lateral dimension of glass element