Controllable separation of brittle materials by laser processing

Abstract

A method for cutting and separating articles (102) from a workpiece (12) made of a brittle material is disclosed. The method uses straight and circular demolding features (112A, 112B) arranged to induce controlled cracking in scrap (104) near each internal curve in the contour of the article (102). A first pulsed laser beam (14) weakens the material along the contour of the article (102) and along the demolding features (112A, 112B). A second laser beam (40) selectively heats the demolding features (112A, 112B) for a sufficient time to cause melting and deformation, thereby inducing controlled cracking.

Description

[0001] This application is a divisional application of the invention patent with application number 2018800185019, application date March 12, 2018, and invention name “Controllable separation of brittle materials processed by laser”.

[0002] Claim priority

[0003] This application claims priority to U.S. Provisional Application Serial No. 62 / 470,587, filed March 13, 2017, the disclosure of which is incorporated herein in its entirety. Technical Field

[0004] The present invention generally relates to cutting brittle materials using a beam of laser radiation. In particular, the present invention relates to cutting brittle materials using a focused beam of pulsed laser radiation and controlling the separation of the cut material using the laser radiation beam. Background Art

[0005] Laser material processing is increasingly used to cut, drill, mark, and scribing a wide variety of materials, including brittle materials such as glass, ceramics, silicon, and sapphire. Conventional mechanical machining produces unwanted defects, such as microcracks that can propagate when the machined brittle material is stressed, thereby degrading and weakening the machined brittle material. Laser machining of brittle materials using a focused beam of laser radiation can produce precise cuts and holes with high-quality edges and walls while minimizing the formation of such unwanted defects. Advances in scientific research and manufacturing are leading to the laser processing of an increasing number of brittle materials, coupled with demands for increased processing speed and accuracy.

[0006] A transparent, brittle material interacts with a focused beam of pulsed laser radiation through nonlinear absorption of the laser radiation. The pulsed laser radiation may include a series of individual pulses or a rapid burst of pulses. Each individual pulse or burst of pulses creates a defect in the transparent, brittle material workpiece at the beam's focal point. The article is cut from the workpiece by translating the focused beam to create a line of defects along the cut line in the workpiece.

[0007] Defect lines often weaken the material along the cut line. To completely separate the article from the rest of the workpiece, an additional step of applying stress along the cut line is required. Applying mechanical stress is sometimes sufficient to induce separation along the cut line. Thermal stress is applied in applications that require a high-quality edge without unwanted defects such as chips and microcracks. Precise and controlled separation has been demonstrated using laser beams with wavelengths absorbed by the material and relatively high average power. The absorbed laser power creates a thermal gradient along the cut line, which causes cracks to propagate between the discrete defects created by the pulsed laser radiation, forming a continuous fracture along the cut line.

[0008] For example, a highly focused beam of ultrashort laser pulses creates a self-guided "filament" in a glass workpiece. The propagation of this filament through the workpiece creates a long defect in the form of a void. A line of voids is created by translating the focused ultrashort pulsed laser beam along the cutting line. A carbon dioxide (CO2) laser with a wavelength of approximately 10 microns (μm) is then used to separate the glass by translating the CO2 laser beam along the cutting line. This laser cutting process, "SmartCleave," was developed by Rofin-Sinar Technologies Inc. and is described in U.S. Patent No. 9,102,007 and U.S. Patent No. 9,296,066, each of which is owned by the assignee of the present invention, and the entire disclosure of each is incorporated herein by reference.

[0009] In traditional "score and break" cutting and laser cutting, a "relief line" may be required to separate rounded items. A relief line is an additional line that radiates from the curved portion of the cutting line into the portion of the workpiece to be scrapped. This curved portion can be concave or convex. The relief line can be scored or cut in the same manner as the cutting line. Sacrificially breaking the scrapped part into multiple sections defined by the relief line results in a more controlled and reliable separation along the cutting line.

[0010] Although the additional separation step of applying stress breaks any residual bond between the article and the rest of the workpiece, in some applications the article is still physically prohibited from being separated from the rest of the workpiece. This is a particular problem for articles with concave curved portions and for cutting processes that remove relatively little material and produce rough edges. For example, focused ultrashort laser pulse beams can precisely cut glass. Typical Rz surface roughness for filament cutting processes using laser pulses with a duration of about 10 picoseconds (ps) is about 10 μm. Even this modest surface roughness on the cut edge generates sufficient static friction to prevent separation of the curved portion.

[0011] There is a need for a method of laser cutting an article having a circular shape made of a brittle material that provides a reliable and clean separation of the article from the remainder of the workpiece. Preferably, the method requires minimal additional aperture and minimal additional processing time. SUMMARY OF THE INVENTION

[0012] In one aspect, a method for cutting and separating an article from a workpiece made of a brittle material using a first beam of pulsed laser radiation and a second beam of laser radiation is disclosed. The method includes creating a cut line and a plurality of release features by focusing the first beam onto the workpiece while simultaneously translating the focused first beam along the contour of the article and along the path of the release features. The release features are located within the workpiece and on the exterior of the article. At least one release feature is located within the cut line near an internal curve. The focused first beam weakens the workpiece along the cut line and along the release features. The second beam is directed onto the cut line and translated along the cut line. The directed second beam further weakens the workpiece along the cut line. The second beam is directed to a location on the at least one release feature and heats the workpiece at that location for a period of time. The heating time is sufficient to cause the workpiece to deform and crack. The at least one release feature is arranged to cause a crack to propagate between the at least one release feature and the internal curve during heating. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate preferred embodiments of the invention and, together with the general description given above and the detailed description of the preferred embodiments given below, serve to explain the principles of the invention.

[0014] Figure 1A and 1B A preferred embodiment of a laser cutting aperture for implementing the laser cutting and separation method of the present invention is schematically described, the aperture comprising two laser sources, each delivering a beam of laser radiation which is directed to the workpieces to be cut and separated.

[0015] Figure 2A A prior art solution for laser cutting and separating items from a workpiece made of brittle material is schematically described.

[0016] Figure 2B -2E schematically depicts a preferred embodiment of the laser cutting and separating method according to the invention for cutting objects from a workpiece made of brittle material and for controlled separation of waste material from the cut objects.

[0017] Figure 3A - 3C schematically depicts an exemplary inventive demolding feature for cutting and separating articles according to the present invention.

[0018] Figure 4A - 10B schematically depicts an exemplary inventive demolding feature for separating waste material from cut articles having internal curves. Detailed Description of the Invention

[0019] Referring now to the drawings, wherein like parts are designated by like numerals, Figure 1A and 1B An aperture 10 is schematically depicted as used in the laser cutting method of the prior art, and is also used in the laser cutting method of the present invention. In the prior art and prior art method, a workpiece 12 made of a brittle material is exposed to a focused beam of pulsed laser radiation 14. The focusing of the pulsed laser radiation 14 is represented by converging rays 16A and 16B, representing the boundary rays of the focused beam of laser radiation. The beam of pulsed laser radiation 14 is generated by a pulsed laser radiation source 18 and has a wavelength at which the brittle material is transparent. The beam of pulsed laser radiation 14 is a beam of repeated single laser pulses (only three are shown here) or repeated bursts of laser pulses. Each pulse or each burst of pulses produces a defect 20 in the workpiece. As shown by the arrows, a linear array 22 of defects 20 is produced by translating the workpiece 12 laterally relative to the beam of pulsed laser radiation 14. The focused beam traces a cutting line 24, which follows the contour of the item to be cut from the workpiece.

[0020] The aperture 10 also includes optional beam steering optics 26 , optional beam conditioning optics 28 , and a focusing lens 30 . Figure 1A The beam steering optics 26 are shown as a plane mirror arranged to intercept the beam of pulsed laser radiation 14 from the laser source 18 and direct it toward the workpiece 12. The beam conditioning optics 28 are depicted as an afocal beam expander arranged to intercept the directed beam of pulsed laser radiation 14 and expand it to primarily fill the clear aperture CA of the focusing lens 30. The focusing lens 30 is depicted as a plano-convex lens arranged to intercept the expanded beam of pulsed laser radiation 14 and focus it into the workpiece 12. Beam steering optics and beam conditioning optics are well known in the art of optical design, and a description thereof is not necessary to understand the principles of the present invention.

[0021] The focusing lens 30 may be a single element lens or a multi-element lens assembly as shown. The workpiece 12 is depicted as being translated relative to the stationary focused beam of pulsed laser radiation 14. Alternatively, a galvanometer-driven mirror may be included in the beam conditioning optics 28 and the flat-field objective for the focusing lens 30, thereby enabling the focused beam of pulsed laser radiation 14 to be translated relative to the stationary workpiece 12.

[0022] The focused beam of pulsed laser radiation 14 converges to an elongated focus 32. Rays emerging from near the center of focusing lens 28 converge further than boundary rays 16A and 16B. Workpiece 12 is positioned such that elongated focus 32 overlaps, or at least partially overlaps, workpiece 12. The elongated focus is advantageous in laser cutting processes, particularly in creating filaments to form voids, because the focused laser radiation is distributed to facilitate the creation of long voids extending through the thickness of the workpiece. For example, the elongated focus can be created by filling the clear aperture of a focusing lens having spherical aberration.

[0023] Both the prior art method and the method of the present invention include exposing the workpiece 12 to a beam of laser radiation 40 generated by a laser radiation source 42. Figure 1B depicted in and different from the laser source 18, Figure 1A The beam of laser radiation 40 has a wavelength that is absorbed by the brittle material. The workpiece 12 is laterally translated relative to the beam of laser radiation 40 so that the beam traces along the linear array 22 of defects 20 previously created by the beam of pulsed laser radiation 14. The beam of laser radiation 40 heats the brittle material weakened by the defects 20, causing it to completely fracture and produce cut edges 44, as shown by the hatching in the figure.

[0024] The aperture 10 also includes a laser source 42, an optional beam steering optics 46, an optional beam forming optics 48, and an optional focusing lens 50. In some applications, the beam forming optics 48 converts the beam of laser radiation 40 from a Gaussian mode to a top-hat transverse mode. In some applications, an unfocused beam of laser radiation 40 may be sufficient to completely cut the workpiece 12. Otherwise, a focused beam of laser radiation 40 may be required to illuminate a smaller area on the surface of the workpiece 12. As shown, the workpiece 12 can be translated relative to the fixed beam of laser radiation 40. Similarly, the laser beam can be scanned across a fixed workpiece.

[0025] Figure 2A A prior art solution 100 is schematically described for using Figure 1A and 1B Aperture 10 laser cutting and separation of workpieces made of brittle materials. Figure 2A The workpiece 12 is depicted being cut from an exemplary article 102 (shaded). The remaining portion of the workpiece 12, which will become waste material 104 (unshaded), is separated from the article 102. The cut line 24 follows the contour of the article 102 and includes an inner curve 106A and an outer curve 106B. A prior art relief line 108 (represented by a long dashed line) extends from the curved portion of the cut line 24 into the waste material 104. The cut line 24 and the relief line 108 are formed by Figure 1AThe workpiece 12 is formed by focusing a focused beam of pulsed laser radiation 14 onto the workpiece 12 and translating the focused beam along the path of the cut line 24 and the relief line 108. Exposure to the focused beam of pulsed laser radiation 14 produces defects that weaken the workpiece 12 along the cut line and the relief line. The figure depicts the workpiece 12 after exposure to the beam of pulsed laser radiation 14.

[0026] Figure 2B -2E schematically illustrates a preferred embodiment 110 of the laser cutting and separation method according to the present invention, using Figure 1A and 1B of aperture. Figure 2B A workpiece 12 is depicted from which the same exemplary article 102 is to be cut. In addition to the cut lines 24 and the prior art relief lines 108, release features 112A and 112B (both represented by dashed lines) of the present invention are fabricated in the scrap material 104 by translating the focused beam of pulsed laser radiation 14 along the paths of the release features 112A and 112B. Release feature 112A has a straight form, while release feature 112B has a circular form. Relief lines 108 and release features 112A and 112B together help separate the scrap material 104 from the article 102.

[0027] Figure 2C Depicts a first separation of waste material 104 from article 102. Method 110 also includes Figure 1B A beam of laser radiation 40 is directed onto the workpiece 12 and translated along the cut line 24 and the relief line 108. During this translation step, the release lines 112A and 112B are not exposed to the laser radiation 40. The workpiece 12 is cleaved along the cut line and exposed to the relief line of the laser radiation beam (indicated by a solid line in the figure).

[0028] In the next heating step, a beam of laser radiation 40 is directed to heat each shaded circular release feature 112B for a sufficient time to melt and shrink the brittle material within each heated circular release feature. The stresses induced by melting and shrinking, in turn, lead to controlled cracking of scrap 104. Cracks propagate out along straight release feature 112A, which connects to the heated circular release features. Additional controlled crack propagation is guided by straight release feature 112A, which aligns with the intended direction of additional cracks 114. The arrows in the figure indicate the initial separation of crack fragments 104 from article 102.

[0029] Figure 2DThe second separation of the remaining fragment material 104 from the article 102 is depicted. Within the remaining circular release features 112B, shaded in the figure, a beam of laser radiation 40 is directed and heats the brittle material for a period of time. As previously described, cracks propagate outward along the remaining straight release features 112A, and additional cracks 114 are guided by some of the straight release features 112A. The arrows in the figure indicate the second separation of the cracked fragments 104 from the article 102.

[0030] Figure 2E Depicts Figure 2C 1 . The prolonged heating of circular release features 112B causes melting and may also crack the brittle material within each heated circular release feature. In addition to causing cracks in waste material 104, the prolonged heating causes it to deform, which further facilitates separation of waste material 104 from article 102. Typically, thinner workpieces exhibit more deformation. For example, workpieces made of glass less than approximately 1 millimeter (mm) thick deform easily. Glass approximately 2 mm thick still deforms sufficiently to facilitate separation.

[0031] Each additional crack 114 is guided to some extent by a complementary straight release feature 112A located on the opposite side of the heated circular release feature. "Somewhat guided" means that the additional cracks propagate radially and randomly from the heated circular release feature, but within a predictable region 116 depicted in the figure, bounded by two dashed lines. The heated circular features have a minimum radius for predictable, slightly directed crack propagation. For example, for a workpiece made of glass having a thickness of approximately 2 mm, the minimum radius ranges from approximately 0.2 mm to approximately 1.0 mm, depending on the specific pattern of release features selected and the type of glass.

[0032] Figure 3A -3C schematically depicts exemplary inventive release features for cutting and separating articles 102 having different exemplary interior curves 106A. Figure 3A Describing and Figure 2A and 2D The arrows in the figure depict the orientation of the critical straight draft feature 112A for reliable separation of the exemplary inner curve 106A. The critical straight draft feature is tangent to the inner curve and intercepts the cut line 24 at the inflection point between the straight portion and its curved portion. The crack will propagate in the direction of the arrow, continuing along the critical straight feature to the inner curve. Figure 3B Depicting another exemplary inner curve 106A, the critical straight draft feature 112A and crack propagation meets the straight portion of the cut line 24 at a shallow angle. Figure 3CDepicting another exemplary inner curve 106A, a critical straight draft feature 112A and crack propagation forms a sharp edge with the straight portion of the cut line 24. Again, the critical straight draft feature is tangent to the inner curve.

[0033] Figure 4A - 10A schematically depicts an exemplary inventive demolding feature for separating waste material from a cut article 102 having an inner curve 106A. Figure 4B -10B schematically depicts controlled crack initiation and propagation after a corresponding exemplary demolding feature is selectively heated for a period of time. Figure 4A The mold release features 112A and 112B are straight and have a perfect circular shape. These mold release features are close to the inner curve. Figure 4B One additional crack 114 is depicted, produced by heating the circular demolding feature 112B.

[0034] In addition to the circular demolding feature 112B having a semicircular shape, Figure 5A The demoulding characteristics are similar to Figure 4A Demolding characteristics. Figure 5B There is also an additional crack 114 created by heating within the circular demolding feature 112B. Figure 4B and 5B In the example of , crack propagation is guided by straight demolding features 112A in the manner described above. Moreover, in both examples, the rupture along cut line 24 is sufficient to stop additional cracks 114 before they propagate into article 102.

[0035] Figure 6A Omit Figure 4A Circular demoulding features. Typically, as Figure 6B As shown, an additional crack 114 is created by applying heat to the straight demolding feature 112A for a period of time. However, the inventors have found that the straight demolding feature alone, without any circular demolding features, provides less controlled and less predictable cracks. Figure 4A and 5A As in the embodiment of the present invention, it is preferred to include a rounded demolding feature for reliable cracking and separation. Among other advantages, the rounded demolding feature also contains high internal stress caused by prolonged heating by the laser radiation beam.

[0036] Figure 7A The demoulding characteristics are similar to Figure 4A The mold release feature of FIG. 112 is shown in FIG. 112B , but a straight mold release feature 112A is added between the circular mold release feature 112B and the cut line 24. In some cases, the additional straight mold release feature provides a more controlled crack between the circular mold release feature and the cut line, such as Figure 7B shown.

[0037] exist Figure 8A In the case of circular demolding features, Figure 5A The semicircular form of the mold is shown, but there are two straight mold release features 112A instead of one direct crack propagation. The heating in the circular mold release feature creates additional cracks 114, such as Figure 8B As shown, cracks along the two straight demolding features destroyed the scrap. Figure 8B and Figure 4A , two straight knockout features separate additional wedges from the waste, which can improve separation in some cases. Figure 9A and 9B The demolding features 112A and 112B depicted in FIG. 1 are implemented identically, but the circular demolding feature 112B has the form of a complete circle.

[0038] Figure 10A Demolding characteristics and Figure 9A The demoulding characteristics are the same. However, Figure 10A The demolding feature in is displaced to produce a crack that propagates to the cut line 24 at a shallow angle and near (but not inside) the curve 106A, as shown in FIG. Figure 10B Here, "shallow angle" refers to an angle less than 45°, preferably less than 30°. In some cases, cracks that propagate directly to the cutting line 24 at a high angle of incidence may produce undesirable chipping.

[0039] In a practical example of the present invention for cutting and separating soda-lime glass using aperture 10 and method 110, laser source 18 is a "StarPico" ultrashort pulse laser, and laser source 42 is an "SR 25i" CO2 laser, both supplied by Coherent-Rofin GmbH of Hamburg, Germany. The exemplary glass has a thickness of approximately 2 mm. Laser source 18 generates pulses having a duration of approximately 10 ps and a wavelength of 1064 nanometers (nm). When a burst repetition rate of approximately 5 kilohertz (kHz) is selected, the burst energy of the four individual pulses has a burst energy of approximately 650 microjoules (μJ). These processing parameters produce filaments, thereby forming defects in the form of voids. During exposure of the workpiece to the beam of pulsed laser radiation 14, a preferred translation speed is approximately 20 mm / s.

[0040] Laser source 42 generates pulses with a duration of approximately 10 μs and a wavelength of approximately 10,600 nm. The pulse repetition rate is approximately 14 kHz. The beam of laser radiation 40 illuminates an area on workpiece 12 having a diameter in the range of 2 mm to 12 mm, preferably approximately 5 mm. During exposure of cut lines 24 and relief lines 108, the preferred translation speed is in the range of 100 mm / s to 250 mm / s. The dwell time for heating demolding features 112A and 112B is in the range of 0.5 to 1.0 seconds, which is sufficient to cause localized melting and fracture of scrap material 104.

[0041] Although the embodiments and figures presented herein cut and separate articles having waste material located along only a portion of the article's contour, the present invention can be used to cut and separate articles that are completely enclosed by waste material. The optimal number and arrangement of release features depends on the geometry of the workpiece and the article to be separated therefrom, as well as the type of brittle material and the thickness of the workpiece. In most cases, straight release features are preferred for guiding crack formation. However, curved release features are also generally suitable for separating articles and may be preferred for articles with complex contours. Similarly, circular release features can have different circular shapes, including circular, semi-circular, elliptical, and oval.

[0042] The present invention has been described above with reference to preferred embodiments and other embodiments. However, the present invention is not limited to the embodiments described and illustrated herein. Instead, the present invention is limited only by the appended claims.

Claims

1. A method for cutting and separating an article from a workpiece made of a brittle material using a first beam of pulsed laser radiation and a second beam of laser radiation, the method comprising: focusing the first pulsed laser radiation onto the workpiece; making a cut line by translating a focused first pulsed laser radiation along a contour of the article, the contour of the article including an internal curve; separating a plurality of release features from a cut line by translating a focused first pulsed laser radiation along a path of the release features, the release features being located within the workpiece and external to the article, at least one release feature having a circular form, the at least one circular release feature being adjacent an interior curve within the cut line, the focused first pulsed laser radiation weakening the workpiece along the cut line and along the release features; directing the second beam of laser radiation onto the cutting line; a second beam of laser radiation directed translationally along the cut line, the directed second beam of laser radiation further weakening the workpiece along the cut line; directing the second beam of laser radiation to a location on the at least one circular demolding feature; and heating the workpiece by directing the second laser radiation at the location for a dwell time sufficient to deform and crack the workpiece; wherein a crack propagates between the at least one circular demolding feature and the inner curve during the heating step, the propagation of the crack being guided in part by at least one complementary straight demolding feature located on a side of the at least one circular demolding feature opposite the crack; wherein the first beam of pulsed laser radiation is generated by an ultrashort pulse laser; The second beam of laser radiation is generated by a CO2 laser.

2. A method of cutting and separating articles as claimed in claim 1, wherein said focusing produces an elongated focal spot of said first beam of pulsed laser radiation that at least partially overlaps said workpiece.

3. A method of cutting and separating articles as claimed in claim 2, wherein the elongated focus is produced by filling the clear aperture of a focusing lens having spherical aberration.

4. The method of cutting and separating articles of claim 1, wherein said focused first pulsed laser radiation generates filaments to produce defects in said workpiece.

5. A method of cutting and separating articles as claimed in claim 4, wherein the defects are in the form of voids.

6. The method of cutting and separating articles as claimed in claim 1, wherein the dwell time is in the range of 0.5 seconds to 1.0 seconds.

7. The method of cutting and separating articles of claim 1, wherein the at least one circular demolding feature has one of the group consisting of a circle and a semicircle.

8. The method of cutting and separating articles of claim 1, wherein the at least one circular demolding feature has a radius in the range of 0.2 mm to 1.0 mm.

9. The method of cutting and separating articles as claimed in claim 1, wherein the brittle material is glass.

10. A method of cutting and separating an article from a workpiece made of a brittle material using a first beam of pulsed laser radiation and a second beam of laser radiation, the method comprising: focusing the first pulsed laser radiation onto the workpiece; making a cut line by translating a focused first pulsed laser radiation along a contour of the article, the contour of the article including an internal curve; a plurality of release features separated from the cut line by translating a focused first pulsed laser radiation along a path of the release features, the release features being located within the workpiece and external to the article, at least one release feature having a circular form, the at least one circular release feature being located proximate an inner curve within the cut line, the focused first pulsed laser radiation weakening the workpiece along the cut line and along the release features; directing the second beam of laser radiation onto the cutting line; a second beam of laser radiation directed translationally along the cut line, the directed second beam of laser radiation further weakening the workpiece along the cut line; directing the second beam of laser radiation to a location within the at least one circular demolding feature; and heating the workpiece for a dwell time by directing the second laser radiation at the location, the heating time causing the workpiece to crack; wherein the at least one circular demolding feature is adjacent to at least one other demolding feature having a straight form, the at least one straight demolding feature being located between the at least one circular feature and the inner curve, and during the heating step, a crack propagates between the at least one circular demolding feature and the inner curve, the propagation of the crack being guided by the at least one straight demolding feature.

11. A method of cutting and separating articles as claimed in claim 10, wherein said focusing produces an elongated focal spot of said first beam of pulsed laser radiation that at least partially overlaps said workpiece.

12. A method of cutting and separating articles as claimed in claim 11, wherein the elongated focus is produced by filling the clear aperture of a focusing lens having spherical aberration.

13. The method of cutting and separating articles of claim 10, wherein said focused first pulsed laser radiation generates filaments to create defects in said workpiece.

14. A method of cutting and separating articles as claimed in claim 13, wherein the defects are in the form of voids.

15. The method of cutting and separating articles according to claim 10, wherein the first beam of pulsed laser radiation is generated by an ultrashort pulse laser.

16. The method of cutting and separating articles of claim 10, wherein the second beam of laser radiation is generated by a CO2 laser.

17. The method of cutting and separating articles according to claim 10, wherein the heating time is in the range of 0.5 seconds to 1.0 seconds.

18. The method of cutting and separating articles of claim 10, wherein the at least one straight draft feature is tangent to the interior curve.

19. The method of cutting and separating articles of claim 10, wherein the at least one circular demolding feature has one of a group consisting of a circle and a semicircle.

20. The method of cutting and separating articles of claim 10, wherein the at least one circular demolding feature has a radius in the range of 0.2 mm to 1.0 mm.

21. The method of cutting and separating articles of claim 10, wherein the at least one straight demolding feature is arranged to propagate the crack into the cut line at a shallow angle.

22. The method of cutting and separating articles of claim 10, wherein the brittle material is glass.

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