WO2025053963A1

WO2025053963A1 - Complexly curved glass articles and methods of forming the same

Info

Publication number: WO2025053963A1
Application number: PCT/US2024/042000
Authority: WO
Inventors: Yveric CUVREAU; Thierry Luc Alain Dannoux; Cyril Rémy André Dedieu; Kevin Robert Claude MICHEL; Jean-Marc PLESSIER; Chao YU
Original assignee: Corning Inc
Current assignee: Corning Inc
Priority date: 2023-09-06
Filing date: 2024-08-13
Publication date: 2025-03-13
Anticipated expiration: 2026-03-06
Also published as: TW202513488A

Abstract

Reformed glass articles with non-developable shapes and associated molds and reforming techniques are described. The glass articles can be formed using a vacuum mold including a mold with a mold surface defining a mold cavity. The mold can also include a frame comprising a body that is disposed on the mold, the body comprising a top surface including one or more vacuum openings formed in the top surface. The top surface includes, an outer edge an inner edge, and a width, W, measured between the inner edge and the outer edge. The width W does not vary by more than 10% from an average value around an entire circumference of the vacuum mold. The vacuum mold comprises a length, L, depth, D, that is from 10% to 30% of L. W is from 0.06*L to 0.10*L. Reformed glass articles can be reformed from glass sheets to conform to the mold.

Description

COMPLEXLY CURVED GLASS ARTICLES AND METHODS OF FORMING THE SAME

Cross-reference to Related Applications

[0001] This application claims the benefit of priority under 35 U.S.C. § 119 of U.S. Provisional Application Serial No. 63/536,763, filed on September 06, 2023, the content of which is relied upon and incorporated herein by reference in its entirety.

FIELD

[0002] The present disclosure relates to vacuum forming of articles for use in various industries, for example, consumer electronics, automotive, appliances, transportation, architecture, defense, and medicine. In particular, the present disclosure relates to vacuum forming of glass articles having a non-developable shape and the resulting vacuum-formed glass articles having a non-developable shape.

BACKGROUND

[0003] Many products include a three-dimensional (3D) glass article. Some examples of articles include a 3D glass article include curved LCD or LED TV screens, smart phones, and windows. Innovations in the shape of products brings new challenges to the manufacturing processes for 3D parts, an in particular 3D parts that are made of glass, which should have excellent optical properties, along with desirable scratch-resistant and impact-resistant properties.

[0004] Therefore, a continuing need exists for methods of manufacturing 3D articles, and in particular 3D glass articles, having complex shapes and desirable optical and mechanical properties.

BRIEF SUMMARY

[0005] The present disclosure is directed to vacuum forming apparatuses, methods for re-forming glass sheets into curved glass articles having shapes (e.g., exhibiting a non- developable shape and a depth of bend of at least 200 mm) that are relatively difficult to obtain using certain existing reforming techniques. Using the apparatuses and methods described herein, glass articles with such shapes can be obtained while also exhibiting thickness uniformity and relatively low optical distortion as compared to such existing methods. Particularly, the glass articles formed via the methods and apparatuses described herein exhibit relatively low amounts of buckling due to careful configuration of a frame that supports a periphery of the glass sheet during the forming process.

[0006] An aspect (1) of the present disclosure pertains to a curved glass article in an as-formed condition, the curved glass article comprising: a first major surface; a second major surface disposed opposite the first major surface; a minor surface extending between the first major surface and the second major surface; a peripheral region extending inward from the minor surface to a boundary region, wherein a majority of the peripheral portion is substantially flat; a central curved region disposed inward of the boundary region; and a length L, representing a maximum linear distance between separate points on the minor surface measured in a first direction parallel to the first major surface in the peripheral region, wherein: within the central curved region, the first major surface comprises a concave shape and the second major surface comprises a convex shape and the first and second major surfaces exhibit non-zero Gaussian curvature, the curved glass article exhibits a depth of bend, DOB, represented by a maximum distance between portions the first major surface in the peripheral region and in the central curved region measured in a second direction perpendicular to the first direction, that is from 10% of the length to 30% of the length, the peripheral region comprises a width measured parallel to the first major surface that varies by no more than 10% of an average value around the peripheral region, and the peripheral region exhibits one or fewer buckles around an entire circumference thereof.

[0007] An aspect (2) of the present disclosure pertains to a curved glass article according to the aspect (1), wherein: 400 mm < L < 4000 mm, and 50 mm < DOB < 700 mm. [0008] An aspect (3) of the present disclosure pertains to a curved glass article according to any of the aspects (l)-(2), wherein the glass article comprises a width W, representing a maximum linear distance between separate points on the minor surface measured in a third direction parallel to the first major surface in the peripheral region and perpendicular to the first direction, wherein 200 mm < W < 2500 mm.

[0009] An aspect (4) of the present disclosure pertains to a curved glass article according to any of the aspects (l)-(3), wherein: the first major surface in a portion of the central curved region comprises a surface area of 60,000 mm² or more, and within the portion, the thickness has a uniformity of +/- 75 microns per 1000 mm² of surface area on the first major surface.

[0010] An aspect (5) of the present disclosure pertains to a curved glass article according to the aspect (4), wherein, the portion comprises a non-developable curved shape comprising a maximum compressive strain shape parameter, as measured between an imaginary central surface disposed between the first major surface and the second major surface and an imaginary surface, of greater than or equal to 3.0% and less than or equal to 10%.

[0011] An aspect (6) of the present disclosure pertains to a curved glass article according to any of the aspects (4)-(5), wherein, within the portion, wherein an average value of the thickness, measured over an entirety of the first major surface, is greater than or equal to 0.5 mm and less than or equal to 2.5 mm.

[0012] An aspect (7) of the present disclosure pertains to a vacuum mold, the vacuum mold comprising: a mold comprising a mold surface with a complex non-deve lopable shape and defining a mold cavity; and a frame comprising a body that is disposed on the mold, the body comprising a top surface that circumferentially surrounds the mold surface and comprises one or more vacuum openings formed in the top surface, wherein the top surface comprises: an outer edge; an inner edge where the body forms an interface with the mold; and a width, W, measured in a first direction parallel to the top surface between the inner edge and the outer edge, wherein: the width W does not vary by more than 10% from an average value around an entire circumference of the vacuum mold, the vacuum mold comprises a length, L, representing a maximum linear distance between separate points on the outer edge parallel to the top surface, the vacuum mold comprises a depth, D, measured as a maximum vertical distance between the top surface and the mold surface in a direction perpendicular to the top surface, that is from 10% to 30% of L, and W is from 0.06*L to 0.10*L.

[0013] An aspect (8) of the present disclosure pertains to a curved glass article according to the aspect (7), wherein the inner edge comprises a circumferential shape without linear segments having a length that is more than L/4.

[0014] An aspect (9) of the present disclosure pertains to a curved glass article according to the aspect (8), wherein a second derivative of the circumferential shape is continuous over an entirety thereof.

[0015] An aspect (10) of the present disclosure pertains to a curved glass article according to the aspect (8), wherein the width W does not vary by more than 5% from an average value around an entire circumference of the vacuum mold.

[0016] An aspect (11) of the present disclosure pertains to a curved glass article according to any of the aspects (7)-( 10), wherein: 300 mm < L < 4000 mm, and 50 mm < D < 700 mm. [0017] An aspect (12) of the present disclosure pertains to a curved glass article according to any of the aspects (7)-( 11), wherein the body is formed of graphite, wherein the vacuum mold further comprises a metallic frame disposed on the top surface and around the outer edge.

[0018] An aspect (13) of the present disclosure pertains to a curved glass article according to the aspect (12), wherein an inner edge of the metallic frame is disposed outward of the one or more vacuum openings.

[0019] An aspect (14) of the present disclosure pertains to a curved glass article according to the aspect (13), wherein further comprising stainless steel cloth welded around the inner edge and disposed around the outer edge.

[0020] An aspect (15) of the present disclosure pertains to a method of forming a curved glass article, the method comprising: placing a glass sheet over a vacuum mold comprising a mold surface at least partially defining a vacuum cavity, wherein the glass sheet is placed on the vacuum mold such that the glass sheet contacts a top surface of a body of a frame circumferentially surrounding the mold surface, wherein the top surface comprises: one or more vacuum openings formed therein; an outer edge; an inner edge where the body forms an interface with the mold; and a width, W, measured parallel to the top surface between the inner edge and the outer edge, wherein the width W does not vary by more than 10% from an average value around an entire circumference of the vacuum mold, wherein the vacuum mold comprises a length, L, representing a maximum linear distance between separate points on the outer edge measured parallel to the sop surface, wherein the vacuum mold comprises a depth, D, measured as a maximum vertical distance between the top surface and the mold surface in a second direction perpendicular to top surface, that is from 10% to 30% of L, wherein W is from 0.06*L to 0.10*L; heating the glass sheet to a reforming temperature; applying vacuum pressure to the one or more vacuum openings such that one or more first portions of the glass sheet are pulled into the one or more of vacuum openings; and applying vacuum pressure to the vacuum cavity such that a second portion of the first glass sheet is pulled into the vacuum cavity such that the glass sheet contacts a portion of the mold surface disposed at the depth D relative to the top surface.

[0021] An aspect (16) of the present disclosure pertains to a method according to the aspect (15), wherein, prior to the heating, a static coefficient of friction between the top surface and the glass sheet is greater than 0. 1 and less than or equal to 1.6. [0022] An aspect (17) of the present disclosure pertains to a method according to any of the aspects ( 15)-( 16), wherein, when the glass sheet is placed on the top surface, an entire peripheral edge of the glass sheet is aligned with the outer edge.

[0023] An aspect (18) of the present disclosure pertains to a method according to the aspect (14), wherein, during the heating, the first portions are heated to a first temperature and the second portion is heated to a second temperature that is less than the first temperature.

[0024] An aspect (19) of the present disclosure pertains to a method according to the aspect (18), wherein the second temperature is from 20°C to 120°C less than the first temperature.

[0025] An aspect (20) of the present disclosure pertains to a method according to any of the aspects (15)-(19), wherein the second portion of the glass sheet comprises an initial thickness (tl) before reforming the glass sheet and a final thickness (t2) after reforming the tl glass sheet, and wherein — ranges from 1. 1 to 2.

[0026] An aspect (21) of the present disclosure pertains to a method according to any of the aspects (15)-(20), wherein the inner edge comprises a circumferential shape without linear segments having a length that is more than L/4.

[0027] An aspect (22) of the present disclosure pertains to a method according to the aspect (21), wherein a second derivative of the circumferential shape is continuous over an entirety thereof.

[0028] An aspect (23) of the present disclosure pertains to a method according to any of the aspects (15)-(22), wherein: 300 mm < L < 4000 mm, and 50 mm < D < 700 mm.

[0029] An aspect (24) of the present disclosure pertains to a method according to any of the aspects (15)-(23), wherein the body is formed of graphite, wherein the vacuum mold further comprises a metallic frame disposed on the top surface and around the outer edge, wherein the metallic frame comprises athickness from 0.7 to 1.5 mm.

[0030] An aspect (25) of the present disclosure pertains to a method according to the aspect (24), wherein an inner edge of the metallic frame is disposed outward of the one or more vacuum openings.

[0031] An aspect (26) of the present disclosure pertains to a method according to the aspect (25), wherein the vacuum mold further comprises stainless steel cloth welded around the inner edge and disposed around the outer edge. BRIEF DESCRIPTION OF THE DRA WINGS

[0032] The accompanying figures, which are incorporated herein, form part of the specification and illustrate embodiments of the present disclosure. Together with the description, the figures further serve to explain the principles of and to enable a person skilled in the relevant art(s) to make and use the disclosed embodiments. These figures are intended to be illustrative, not limiting. Although the disclosure is generally described in the context of these embodiments, it should be understood that it is not intended to limit the scope of the disclosure to these particular embodiments. In the drawings, like reference numbers indicate identical or functionally similar elements.

[0033] FIGS. 1 A and IB show an apparatus for reforming a sheet of material, according to one or more embodiments of the present disclosure;

[0034] FIG. 2 depicts a perspective view of a mold and frame of the apparatus shown in FIGS. 1A and IB, according to one or more embodiments of the present disclosure;

[0035] FIG. 3A depicts a cross-sectional view of an upper wall of the frame through the line III -III in FIG. 2, according to one or more embodiments of the present disclosure;

[0036] FIG. 3B depicts a perspective view of a retention frame of the upper wall shown in FIG. 3A, according to one or more embodiments of the present disclosure;

[0037] FIG. 4 is a flow diagram of a method forming a curved glass article with a non- developable shape, according to one or more embodiments of the present disclosure;

[0038] FIG. 5 is a cross-sectional view of a reformed glass article formed via performance of a portion of the method shown in FIG. 4, according to one or more embodiments of the present disclosure;

[0039] FIG. 6 schematically depicts a side-view of a curved glass article formed via the method shown in FIG. 4, according to one or more embodiments of the present disclosure;

[0040] FIGS. 7A and 7B schematically depict mold constructions used in simulations of reforming processes for first and second example glass articles, according to one or more embodiments of the present disclosure;

[0041] FIGS. 8A and 8B depict simulated shapes resulting from reforming processes conducted on the mold constructions depicted in FIGS. 7A and 7B, according to one or more embodiments of the present disclosure; and

[0042] FIGS. 9A and 9B depict simulated shapes resulting from reforming processes conducted on the mold constructions depicted in FIGS. 7A and 7B, after being modified to have upper frame surfaces of increased width, according to one or more embodiments of the present disclosure.

DETAILED DESCRIPTION

[0043] The following examples are illustrative, but not limiting, of the present disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the art, are within the spirit and scope of the disclosure.

[0044] Glass articles having a non-developable curvature can be used in a variety of applications in which a transparent surface having a non-developable curvature is desired. Glass articles having a non-developable curvature can provide desirable optical and mechanical properties while also providing the desired curvature. As used herein, the terms “non- developable curvature” or “non-zero Gaussian curvature” means a curvature with crossed radii that cannot be formed with a sheet of paper by bending without also stretching, tearing, or wrinkling the paper. Exemplary non-developable curvatures include, but are not limited to, spherical curvatures, spheroid curvatures, partially spheroid curvatures, and three-dimensional saddle curvatures. A “developable curvature” or a “zero Gaussian curvature” means a curvature that can be formed with a sheet of paper by bending alone. Exemplary developable curvatures include, but are not limited to, cylindrical and conical curvatures.

[0045] Reforming processes described herein facilitate the formation of glass articles having non-developable curvatures, suitable optical properties, and suitable mechanical properties. The reforming processes utilize vacuum forming techniques to make reformed glass articles having a non-developable curved shape. The non-developable curved shape can be created while maintaining thickness uniformity in the curved shape and avoiding wrinkling in the glass. By facilitating thickness uniformity and avoiding wrinkling, a non-developable curved shape with desirable optical and mechanical properties can be formed. Moreover, by facilitating thickness uniformity and avoiding wrinkling, a non-developable curved shape having a large convex surface area (e.g., a surface area greater than or equal to 10,000 mm², greater than or equal to 20,000 mm², greater than or equal to 30,000 mm², or greater than or equal to 60,000 mm², greater than 1,000,000 mm², and less than 2,000,000 mm²) can be created without introducing optical or mechanical defects.

[0046] Vacuum-forming techniques described herein can create glass articles having complex curvatures, as quantified by the maximum compressive strain shape parameter described herein, without generating glass wrinkling or breakage. Vacuum-forming techniques described herein can include vacuum reforming a glass sheet using a vacuum mold with one or more side retention mechanisms that prevent glass wrinkling during deep Gaussian deformation of the glass for creating a non-deve lopable curved shape. As used herein, the term “deep” Gaussian deformation refers to processes where a glass sheet having an initial length L is reformed to have a depth of bend (measured as by a maximum distance between portions on a major surface of the reformed glass article in a direction perpendicular to that which the length is measured), that at least 10% of the length. The one or more side retention mechanisms can include a vacuum opening designed to hold the glass sheet in place during vacuum forming while also facilitating free movement of the glass sheet, thus preventing the formation of wrinkles during deformation. The one or more side retention mechanisms can be a self-release retaining mechanism that helps prevent breakage of a reformed glass sheet during cooling and demolding.

[0047] Vacuuming forming techniques described herein offer one or more of the following advantageous features. In one or more embodiments, the vacuum pressure forming allows the progressive local expansion of a glass sheet up to a final highly non-developable three-dimensional (3D) shape without wrinkling. In one or more embodiments, the vacuum pressure forming allows the progressive local expansion of the glass sheet up to a final highly non-developable 3D shape without significant localized thickness reduction. In one or more embodiments, one side of the glass article can remain untouched during vacuum forming, thus reducing the possibility of defects. In one or more embodiments, the side retention mechanisms can prevent glass bucking, which can lead to vacuum leakage and incomplete reformation of the glass sheet. In one or more embodiments, the side retention mechanisms can prevent glasssliding motion during reforming, which can result in scuffinarks affecting the aesthetical and optical properties of the reformed glass. In one or more embodiments, multiple glass sheets can be reformed simultaneously.

[0048] In some embodiments, the vacuum-forming techniques described herein can be used to reform multi-layer glass sheets. The multi-layer glass sheets can include a first layer (e.g., top layer) formed of a first glass composition and a second layer (e.g., bottom layer) formed of a second glass composition. In some embodiments, one of the glass layers can be sacrificial layer that is removed after reforming the glass sheet. For example, the bottom layer of a multi-layer glass sheet that was in contact a mold surface during reforming can be removed after the reforming process is complete. In such embodiments, removal of the bottom glass layer can improve the surface quality of the reformed glass article because any defects on the mold surface transferred to the bottom glass layer are removed. In some cases, removal of a layer of a multi-layer glass sheet can reduce or eliminate costly surface finishing process, such as polishing processes. In some embodiments, an etching process can be used to remove a layer of a multi-layer glass sheet.

[0049] FIGS. 1A and IB show an apparatus 100 for reforming a glass sheet 200 according to some embodiments. FIG. 1A shows glass sheet 200 before reforming. FIG. IB shows glass sheet 200 after reforming according to some embodiments. Glass sheet 200 has a top surface 202, a bottom surface 204 opposite top surface 202, and an initial thickness 206 (i.e., the thickness of the glass sheet 200 before reforming) measured between top surface 202 and bottom surface 204. Glass sheet 200 also includes a perimeter edge 208 defining a perimeter shape of glass sheet 200.

[0050] Dimensions of the apparatus 100 can be described with reference to the coordinate axes depicted in FIGS. 1A, IB, and 2. Unless otherwise noted, the apparatus 100 is configured to reform the glass sheet in a direction parallel to the gravitational direction, which is the Z-direction in FIGS. 1A, IB, and 2. That is, a maximum amount of deformation of the glass article occurs in the Z-direction to exhibit a depth of bend at a particular location. An X-Y plane is depicted as being perpendicular to the Z-direction. The apparatus 100 includes a frame 130 with an upper wall 132 having a top surface 134 that is planar and disposed in the X-Y plain (the top surface 134 can also be approximated as being planar with average height relative to an arbitrary reference plane in the X-Y directions). Accordingly, various dimensions of the glass sheet 200 and apparatus 100, unless otherwise noted, are expressed as being measured in the gravitational direction or in a plane perpendicular thereto, when the apparatus 100 is set up for reforming operations.

[0051] In some embodiments, initial thickness 206 of glass sheet 200 can range from 0.5 millimeters (mm) to 10 millimeters, including subranges. In embodiments, the initial thickness 206 can range from 0.1 millimeters to 10 millimeters, from 0.2 millimeters to 10 millimeters, from 0.3 millimeters to 10 millimeters, from 0.4 millimeters to 10 millimeters, from 0.5 millimeters to 10 millimeters, from 0.5 millimeters to 7 millimeters, from 0.5 millimeters to 4 millimeters, or within a range having any two of these values as endpoints.

[0052] Apparatus 100 includes a vacuum mold 110 having a vacuum cavity 112 in which glass sheet 200 can be reformed. In embodiments, the glass sheet 200 can at least partially define the vacuum cavity 112 after being placed on the apparatus 100. In some embodiments, apparatus 100 can include one or more vacuum sources 170. Vacuum source(s) 170 can be, for example, a vacuum pump. Vacuum mold 110 can include a frame 130 disposed around vacuum cavity 112. Frame 130 includes a top wall 132 having a top surface 134 and one or more vacuum openings 140. Each vacuum opening 140 includes a through hole 142 formed in top wall 132. Through hole(s) 142 can be formed in top surface 134 of frame 130 and extend through the thickness of top wall 132. Top surface 134 of frame 130 has an exterior perimeter edge 136 defining a perimeter shape of top surface 134. In some embodiments, the one or more vacuum openings 140 disposed around vacuum cavity 112 can include at least a single vacuum opening, which can include a through hole 142 having a full or partial ringshape disposed around all or a portion of vacuum cavity 112. For example, FIG. 2 depicts an embodiment where the top surface 134 includes a plurality of vacuum openings 140 circumferentially surrounding the vacuum cavity 112. In some embodiments, adjacent ones of the plurality of vacuum openings 140 are spaced apart from each other by a spacing distance 148, representing a minimum linear edge-to-edge separation distance between adjacent ones of the plurality of vacuum openings 140 (e.g., measured in a direction parallel to the top surface 134). Spacing distance 148 can be greater than or equal to the effective diameter 146 of the through holes 142 and less than or equal to three times the effective diameter 146 of the through holes 142. A spacing distance 148 within this range can facilitate reforming glass sheet 200 into a non-developable shape without wrinkling.

[0053] While in the example depicted in FIGS. 1A-2, the top surface 134 is flat, it should be understood that embodiments are envisioned where the top surface 134 is curved and/or has non-linear transitions in surface height. In such embodiments, distances expressed as being measured in a direction parallel or perpendicular to the top surface 134 can be calculated by treating such non-flat surfaces as a flat surface at the average height of the top surface 134.

[0054] Referring back to FIGS. 1A-1B, the one or more vacuum sources 170 are in fluid communication with vacuum cavity 112 and the one or more vacuum openings 140 such that the one or more vacuum sources 170 can apply vacuum pressure to vacuum cavity 112, the one or more vacuum openings 140, or both. In some embodiments, apparatus 100 can include one vacuum source 170a. In such embodiments, the vacuum source 170a can apply vacuum pressure to both vacuum cavity 112 and the one or more vacuum openings 140. Vacuum source 170a can apply vacuum pressure to vacuum cavity 112 and the one or more vacuum openings 140 simultaneously. In some embodiments, vacuum source 170a can apply vacuum pressure to vacuum cavity 112 and the one or more vacuum openings 140 sequentially. For example, vacuum source 170a can first apply vacuum pressure to the one or more vacuum openings 140, and while still applying vacuum pressure to the one or more vacuum openings 140, then apply vacuum pressure to vacuum cavity 112. A vacuum pipe 172a can connect vacuum source 170a to vacuum cavity 112 and the one or more vacuum openings 140.

[0055] In some embodiments, apparatus 100 can include a first vacuum source 170a in fluid communication with vacuum cavity 112 and a second vacuum source 170b in fluid communication with the one or more vacuum openings 140. In such embodiments, first vacuum source 170a can apply vacuum pressure to vacuum cavity 112 independent from second vacuum source 170b applying vacuum pressure to the one or more vacuum openings 140. First vacuum source 170a and second vacuum source 170b can simultaneously apply vacuum pressure to vacuum cavity 112 and the one more vacuum openings 140, respectively. In some embodiments, first vacuum source 170a can apply vacuum pressure to vacuum cavity

112 and second vacuum source 170b can apply vacuum pressure to the one or more vacuum openings 140 sequentially. For example, second vacuum source 170b can first apply vacuum pressure to the one or more vacuum openings 140, and while second vacuum source 170b is still applying vacuum pressure to the one or more vacuum openings 140, first vacuum source 170a can apply vacuum pressure to vacuum cavity 112.

[0056] In embodiments including first vacuum source 170a and second vacuum source 170b, a first vacuum pipe 172a can connect first vacuum source 170a to vacuum cavity 112 and a second vacuum pipe 172b can connect second vacuum source 170b to the one or more vacuum openings 140. In some embodiments, second vacuum pipe 172b can be connected to a vacuum distributor 174 configured to supply vacuum pressure to the one or more vacuum openings 140.

[0057] In some embodiments, apparatus 100 can include a vacuum box 160 defining a vacuum chamber 162. In such embodiments, frame 130 can be coupled to vacuum box 160. Frame 130 coupled to vacuum box 160 may be integrally formed with vacuum box 160 or mechanically coupled to vacuum box 160 via one or more mechanical fasteners (e.g., bolts or screws). In some embodiments, frame 130 may be integrally formed with vacuum box 160. In some embodiments, frame 130 may be a component of a mold 114 mechanically coupled to vacuum box 160. In some embodiments, frame 130 can be vertically adjustable to relative to vacuum cavity 112 to facilitate accurate adjustment of top surface 134 and a top surface 113 of vacuum cavity 112. It should be understood that, while FIGS. 1A-1B depict the top surface

113 as being vertically aligned with the top surface 134, it should be understood that embodiments are also contemplated where the top wall 132 extends over the top surface 113 and comprises a terminal edge (inner edge) that transitions to the mold surface 116. In such embodiments, the top wall 132 interfaces with the mold surface 116 at the inner edge. [0058] In some embodiments, vacuum cavity 112 can be defined by a mold 114 disposed in vacuum chamber 162. Mold 114 includes a mold surface 116 and can include one or more vacuum holes 118 formed in mold surface 116. Vacuum holes 118 can be through holes extending from mold surface 116 through mold 114 to a bottom surface 120 of mold 114. Vacuum holes 118 can be in fluid communication one or more vacuum sources 170 such that vacuum sources 170 can apply vacuum pressure to vacuum cavity 112 via vacuum holes 118. [0059] Vacuum holes 118 can have a small diameter to minimize impact on bottom surface 204 of glass sheet 200 during reforming. In some embodiments, vacuum holes 118 can have a diameter ranging from 0.5 millimeters to 2 millimeters. In some embodiments, the one or more vacuum openings 140 can be in fluid communication with vacuum chamber 162 of vacuum box 160. In embodiments including mold 114, a second portion 230 of glass sheet 200 can be pulled against mold surface 116 during reforming. For example, as shown in FIG. IB, second portion 230 of glass sheet 200 can be pulled against mold surface 116, thereby causing second portion 230 to take on the curvature of mold surface 116.

[0060] Mold surface 116 can comprise a material that resists adhesion to glass sheet 200 during reformation. Exemplary materials for mold surface 116 include, but are not limited to graphite, boron nitride, silica soot, calcium carbonate, carbon soot, a refractory metallic alloy, molybdenum disulfide, or tungsten disulfide. In some embodiments, mold 114 may be formed of any of these materials. In some embodiments, any of these materials can be coated on mold 114 to define mold surface 116. For example, in some embodiments, mold 114 can be a made of a refractory metallic alloy coated with molybdenum disulfide or tungsten disulfide to define mold surface 116.

[0061] In some embodiments, bottom surface 204 of glass sheet 200 can be coated with one or more protecting layers to help prevent adhesion of glass sheet 200 to mold surface 116 and help prevent the introduction of mold-induced defects on bottom surface 204. Exemplary protecting layers are described in U.S. Pat. No. 10,364,175, which is hereby incorporated by reference in its entirety.

[0062] In some embodiments, the coefficients of thermal expansion (CTE) for the materials of mold surface 116, glass sheet 200, and top surface 134 of frame 130 can be tailored to help prevent glass adhesion, prevent glass sliding during reformation, and prevent glass breakage under differential shrinkage rates during cooling. In addition, the CTE for the materials of mold surface 116, glass sheet 200, and top surface 134 of frame 130 can be tailored to facilitate self-re lease of glass sheet 200 from both mold surface 116 and top surface 134. [0063] As used herein, the term coefficient of thermal expansion or “CTE” refers to the coefficient of thermal expansion of the glass composition averaged over a temperature range from 20 °C to 300 °C. Unless specified otherwise, a CTE for a layer is expressed in terms of 10'⁷/°C and is determined using a push-rod dilatometer in accordance with ASTM E228- 11. [0064] In some embodiments, mold surface 116 can comprise a first material comprising a first CTE, glass sheet 200 can comprise a second material comprising a second CTE, and at least a portion of top surface 134 of frame 130 can comprise a third material comprising a third CTE. The third CTE can be greater than the second CTE and the second CTE can be greater than the first CTE. In such embodiments, the differential shrinkage rates of the materials can facilitate self-release of glass sheet 200 from vacuum mold 110 without breakage. In some embodiments, the CTE of the material of mold surface 116 can range from 35 x 10 ⁷/°C to 45 x 10 ⁷/°C. In some embodiments, the CTE of the material of glass sheet 200 can range from 70 x 10 ⁷/°C to 85 x 10 ⁷/°C. In some embodiments, the CTE of the material of top surface 134 of frame 130 can range from 1 10/ 10 ⁷/°C to 130/ 10 ⁷/°C. In some embodiments, the material of top surface 134 of frame 130 can be a metallic material having a CTE ranging from I l ()/ I ⁷/°C to 130/ 10 ⁷/°C. In some embodiments, the CTE of the material of top surface 134 of frame 130 can range from 170x 1 ⁷/°C to 180x 1 ⁷/°C. In some embodiments, the material of top surface 134 of frame 130 can be an austenitic stainless steel having a CTE ranging from 170x 10 ⁷/°C to 180x 10 ⁷/°C.

[0065] In some embodiments, a through hole 142 can have an effective diameter and a top surface of a stop wall (not depicted) is vertically spaced from the top surface 134 of the top wall 132 by a depth. In such embodiments, the depth can be less than or equal to one half (Vz) of the effective diameter. By positioning the stop wall at a depth less than or equal to one half (Vz) of the effective diameter, the one or more vacuum openings 140 can prevent a first portion 220 of glass sheet 200 from being pulled too far into the through hole 142. If a first portion 220 is pulled too far into the through hole 142, this can cause glass breakage during cooling and/or demolding. In particular, a depth less than or equal to one half (Vz) of the effective diameter can prevent a first portion 220 from being pulled into a shape having an effective dimeter larger than the effective diameter of a through hole 142. If a first portion 220 is pulled into a shape having an effective dimeter larger than the effective diameter of through hole 142, a reformed glass sheet will become stuck in the through hole 142, and will thus be not be allowed to freely move during cooling and/or demolding, which can result in glass breakage.

[0066] As used herein, the term “effective diameter” is utilized to describe the size of a hole or opening, but this term should not be interpreted as requiring a hole or opening to have a circular diameter or shape. Instead, holes or openings may have non-circular shapes, and in such embodiments the term “effective diameter” is intended to refer to the maximum cross- sectional dimension of the shape. For example, the “effective diameter” of a hole or opening having an elliptical cross-sectional shape would be the length of the major axis of the elliptical shape. For a hole or opening having an effective diameter that varies along the depth of the hole or opening, the effective diameter is the largest effective diameter. In some embodiments, the size of the through holes 142 can be selected based on the initial thickness 206 of the glass sheet 200. In some embodiments, the glass sheet 200 can have an initial thickness 206 and the through holes 142 can have an effective diameter ten to fifteen times greater than the initial thickness 206. An effective diameter that is ten to fifteen times greater than the initial thickness can allow a first portion 220 of glass sheet 200 to be pulled into a through hole without the application of excessively high vacuum pressure. Accordingly, in embodiments, the effective diameter of the through holes 142 can range from 5 millimeters to 120 millimeters, including subranges. For example, in some embodiments, the effective diameter of the through holes 142 can range from 5 millimeters to 10 millimeters, 10 millimeters to 30 millimeters, 10 millimeters to 50 millimeters, 10 millimeters to 100 millimeters, 10 millimeters to 120 millimeters, or within a range having any two of these values as endpoints.

[0067] As shown in FIGS. 1A-1B, the apparatus 100 may be constructed such that, over the course of reforming the glass sheet 200, a total contact area between the bottom surface 204 and the combined structure of the mold 114 and frame 130 has a length L. The length L may represent a maximum linear dimension of the total contact area between the glass sheet 200 and the combination of the mold 114 and top surface 134, measured in a direction extending parallel to the top surface 134. As such, when the glass sheet 200 (in an as-cut condition prior to reforming) is placed on the top surface 134, an area of overlap between the glass sheet 200 and the top surface 134 and the mold 114 can determine the length L. In embodiments, when the glass sheet 200 is placed on the top surface 134, central axes of the glass sheet 200 and the combined structure of the frame 130 and mold 114 are aligned. As such, the area of overlap between the glass sheet 200 and top surface 134 can depend on the peripheral shapes of both the top surface 134 and the glass sheet 200 prior to reforming being initiated. For example, when peripheries of the top surface 134 and the bottom surface 204 are in alignment and completely overlap, the total contact area may represent a surface area of the bottom surface 204 prior to reforming (in the configuration shown in FIG. 1A). Preferred arrangements between the glass sheet 200 and the top surface 134 to aid in minimizing wrinkling during reforming are described in greater detail herein. [0068] When the glass sheet 200 is heated to a reforming temperature after being placed on the top surface 134 (as shown in FIG. 1A), the glass sheet 200 tends to sag in its center under the load of gravity as the viscosity of the glass reduces. As shown in FIG. 1A, for example, at the start of heating, the glass sheet 200 comprises a supported portion 240 that is in contact with at least one of the mold 114 and the top surface 134 and a loaded portion 245 that is not supported by the frame 130 or mold 114. In embodiments, the loaded portion 245 has a length that is at least 50% (e.g., at least 60%, at least 70%, at least 80%, or even at least 85% and less than or equal to 95%) of the length L. During reforming, the loaded portion 245 tends to sag downward under gravity, causing the supported portion 240 to lift from the top surface 134. The edge of the flat upper surface (the outer transition or comer of the curved mold surface 116) serves as a pivot point of the glass when this initial sagging of the glass occurs. Such lifting of the supported portion 240 can eliminate the ability to form a quality vacuum seal between the top surface 134 and the supported portion 240, reducing the efficacy of the one or more vacuum openings 140. This can lead to buckling of the glass sheet 200 during reforming and to various optical defects (e.g., thickness non-uniformity) in the resultant part. Particularly, a critical buckling load, defining a lowest load that leads to buckling of the glass sheet, can be defined as follows:

where o_cr is a critical buckling stress, D is a bending stiffness of the glass sheet 200, b is a length of the loaded portion 245, h is the thickness of the glass sheet 200, E is the elastic modulus of the glass sheet 200, v is the Poisson’s ratio of the glass sheet, and k_cis a Buckling coefficient, which is related to an aspect ratio of unloaded and loaded lengths. Equations 1 and 2 reveal that the critical buckling load is proportional to the thickness of the glass and inversely proportional to the length of the loaded portion 245 squared. As the length of the loaded portion increases, the critical bending load decreases substantially, rendering the glass sheet 200 more sensitive to buckling. Buckling can therefore become problem for particularly large parts.

[0069] As shown in FIG. IB, the apparatus 100 may generally be configured such that, after reforming via the methods described herein to provide a reformed glass article 250, the bottom surface 204 substantially conforms with the mold surface 116. As a result, the reformed glass article exhibits a depth of bend 246 representing a maximum vertical distance between different points on the top surface 202 in the gravitational direction. In embodiments, the depth of bend 246 can range from 200 mm to 600 mm (e.g., from 300 mm to 500 mm). In embodiments, the depth of bend 246 is at least 10% of the length L of the contact area between the glass sheet 200 and the combined structure of the upper surface 134 and mold 114. For example, the depth of bend 246 can range from 0. 10*L to 0.30*L, while the mold surface 116 exhibits a non-zero Gaussian curvature. In such embodiments, L can range from 1000 mm to 5000 mm (e.g., from 1000 mm to 3000 mm).

[0070] Certain structural features of the frame 130 have been found to aid in reforming the glass sheet 200 to have such a depth of bend 246 without introducing buckling that prohibitively degrades optical performance of the reformed glass article 250. These features of the frame 130 have been found to be particularly beneficial when the glass sheet 200 is cut to have the same peripheral shape as the top surface 134 of the frame 130. This contrasts with certain other reforming methods. For example, certain existing methods, such as some of those described in International Patent Application No. PCT/US2022/025696, published as WIPO Publication No. WO 2022/231933 Al, hereby incorporated by reference in its entirety, include an oversized glass sheet, such that a perimeter portion of the glass sheet extends outward from the frame 130. After heating of the glass sheet, such a perimeter portion can bend around the outside of the frame 130 to increase stiffness and prevent severe buckling. It has been found, however, that relatively large overhangs (of more than 150 mm) are needed to achieve desired sealing conditions. Such large overhangs lead to decreased material utilization. The frame 130 in accordance with the present disclosure is designed to eliminate severe buckling without the need for such costly overhangs.

[0071] The shape of the upper surface 134 of the frame 130 has been found to be a factor that impacts the buckling performance of the apparatus 100. In the embodiment depicted in FIG. 2, for example, the upper surface 134 is shown to include an external (or “outer”) edge 262 and an internal (or “inner”) edge 264. In the depicted embodiment, the internal edge 264 represents a point of transition between the upper surface 134 and the mold surface 116 having a non-zero Gaussian curvature. As such, the internal edge 264 can be a location where a contact area between the glass sheet 200 (see FIGS. 1A-1B) and the combined structure of the upper surface 134 and the mold 114 transitions from a flat area (e.g., on the upper surface 134) to a curved area (e.g., on the mold surface 116). The external edge 262 circumferentially surrounds the internal edge 264 so that the upper surface 134 has a width 268, which, at a particular point around the circumference of the frame 130 is measured in a direction perpendicular to the internal edge 264 and perpendicular to the gravitational direction.

[0072] In some embodiments, frame 130 can include a channel 156 formed in the top surface 134 and fluidly connecting the plurality of vacuum openings 140. In such embodiments, channel 156 can include a plurality of channel portions 158 connecting two adjacent ones of the one or more vacuum openings 140. In embodiments including channel 156, channel 156 can extend through each of the plurality of vacuum openings 140 to facilitate application of vacuum pressure to each vacuum opening 140.

[0073] In embodiments, the frame 130 can be used when the perimeter edge 208 (see FIG. 1A) of the glass sheet 200 is coincident with the external edge 262 of the upper surface 134 (i.e., the glass sheet 200 can be cut to have the same external shape as the upper surface 134). As such, the length L (see FIG. IB) of contact area between the glass sheet 200 and the combined structure of the upper surface 134 and the mold 114 can equal a maximum length 266 of the external edge 262 (a maximum linear distance between two points on the external edge 262, measured in a direction parallel to the upper surface 134). A maximum width 270 can also be defined as a maximum linear distance between two points on the external edge 262, measured in a direction perpendicular to the maximum length 266. In embodiments, the maximum width 270 is greater than or equal to 500 mm and less than or equal to 2000 mm. The maximum length 266 and maximum width 270 are sized in the depicted embodiment for forming windows for automotive applications. It should be understood that different sizes can be used for alternative applications for various curved glass articles formed via the techniques described herein.

[0074] Referring to the upper surface 134, structuring the external and internal edges 262 and 264 so that the width 268 is relatively consistent around the circumference of the frame 130 has been found to aid in reducing buckling by providing uniform support at the periphery of the glass sheet 200. In embodiments, for example, the width 268 varies by no more than 10% of an average value thereof (the average value can be computed by measuring the width at 268 at 100 equally spaced locations around the internal edge 264). Differences between maximum and minimum values of the width and an average value of the width can be less than 10% of the average value in magnitude. In embodiments, the width 268 varies by no more than 5% of the average value, or even by no more than 2% of the average value.

[0075] It has also been found that the average value of the width 268 should be greater than or equal to 6% of the maximum length 266 in order to effectively reduce the loaded length of the glass sheet and reduce buckling sensitivity. Maintaining the average value of the width 268 at less than or equal to 10% of the maximum length 266 also aids in providing a relatively high amount of material utilization. Less than or equal to 8% of the maximum length 266 has also been found to provide an adequate amount of support to prevent buckling while providing an even greater amount of material utilization. Accordingly, the average value of the width 268 can range from 6% to 10% of the maximum length 266, or even more preferably from 6% to 8% of the maximum length.

[0076] The 6% floor for the average value of the width 268 is to provide adequate contact area between the glass sheet 200 and the upper surface 134. The contact area provides friction between the glass sheet 200 and the upper surface 134 to limit tangential displacement of the glass as the glass sheet 200 is heated to a reforming temperature. Constraining movement of the glass in a direction tangential to the top surface 134 (e.g., towards a geometric center of the mold 114) beneficially prevents the glass sheet 200 from sagging as the glass is heated. Preventing central sagging of the glass aids in maintaining a vacuum seal at the one or more vacuum openings 140, which facilitates strain management within the glass throughout the reforming process and improved buckling performance. Such constraining via the size of the upper surface 134 described herein can be achieved without contacting (e.g., without clamping or without placing any weight) on the top surface 202 of the glass sheet 200. Limiting contact with the top surface 202 beneficially eliminates potential optical defects.

[0077] Irrespective of peripheral shape the final glass article that is ultimately used (e.g., a portion of the reformed glass article 250 can be cut out and put to a desired end use), it has been found that the shape of the internal edge 264 is an important factor for reducing buckling. Particularly, it has been found that the internal edge 264 should have limited abrupt changes in curvature (or a continuous second derivative around an entire circumference defined by the internal edge 264). Moreover, any linear segments of the internal edge 264 should be limited in length. A “linear segment” can be characterized as a segment in which a straight line connecting points at both ends of the segment does not deviate from the segment by more than 1 mm in a direction perpendicular to the straight line. Particularly, it has been found that the internal edge 264 should have no linear segments that are greater than 25% of the maximum length 266 to facilitate improved buckling performance in the reformed glass article 250. Providing a smooth internal edge 264 that is devoid of long linear segments beneficially avoids strains in the glass during reforming and greater control during sagging.

[0078] Another parameter that can be used to reduce buckling during the reforming process is a temperature distribution with which the glass sheet 200 is heated after placement on the frame 130. It has been found that heating a central portion of the glass sheet 200 (e.g., a portion of the loaded portion 245 depicted in FIG. 1A) to a lesser temperature than a peripheral portion of the glass sheet 200 (e.g., including the supported portion 240 in FIG. 1A) during heating can prevent center sagging prior to formation of a vacuum seal and aid in preventing buckling. Such temperature differentials can be achieved via any suitable mechanism. For example, in some embodiments, vacuum mold 110 can include a cooling block 192 (see FIG. 1A) in contact with bottom surface 120 of vacuum mold 110 opposite mold surface 116. In some embodiments, cooling block 192 can include a circuit for circulating a coolant. In such embodiments, cooling block 192 can include a coolant inlet 194 and a coolant outlet 196. Exemplary coolants for cooling block 192 include, but are not limited to, air and water. In some embodiments, cooling block 192 can additionally or alternatively include a heat sink or cooling ribs. In some embodiments, cooling block 192 can be in contact with bottom surface 120 of vacuum mold 110 opposite central surface region 122 of mold surface 116. Cooling block 192 can locally reduce the temperature of mold surface 116 during reforming. In embodiments, the central surface region 122 can be heated to a temperature that is from 20°C to 120°C less than the supported portion 240 to facilitate forming a vacuum seal. [0079] In the embodiment shown in FIG. 2, the mold surface 116 includes a central surface region 122 and a perimeter surface region 124. In such embodiments, a surface temperature of central surface region 122 can be controlled to have a first maximum temperature during reforming and a surface temperature of perimeter surface region 124 can be controlled to have a second maximum temperature during reforming. In some embodiments, one or more cooling blocks 192 (see FIGS. 1A-1B) can be utilized to control the maximum surface temperature of central surface region 122 and/or perimeter surface region 124. In some embodiments, the first maximum temperature can be 20 °C to 50 °C less than the second maximum temperature. In some embodiments, the first maximum temperature can be 20 °C to 120 °C less than the second maximum temperature. In some embodiments, the first maximum temperature can be 50 °C to 120 °C less than the second maximum temperature.

[0080] In embodiments, the central surface region 122 can have a first maximum radius of curvature and the perimeter surface region 124 adjacent central surface region 122 can have a second maximum radius of curvature less than the first maximum radius of curvature. In some embodiments, the second maximum radius of curvature can be at least 5% less than the first maximum radius of curvature. In embodiments, central surface region 122 can be a region of mold surface 116 comprising a desired shape of a final glass article (e.g., cut from the reformed glass article). That is, the central surface region 122 can have a concave surface curvature matching the convex surface bottom surface 204 of reformed glass article 250. In such embodiments, a central portion of glass sheet 200 can be pulled against central surface region 122 of mold surface 116, thereby causing second portion 230 to take on the curvature of central surface region 122. [0081] In embodiments, one or more vacuum holes 118 of vacuum mold 110 can be formed in perimeter surface region 124 of mold surface 116. In embodiments, mold vacuum 110 can have no vacuum holes 118 formed in central surface region 122. By locating no vacuum holes 118 in central surface region 122, any potential defects introduced by vacuum holes 118 during reforming of a glass sheet on central surface region 122 can be avoided. In embodiments, central surface region 122 can have a surface area of 10,000 mm² or even 60,000 mm² or more. In some embodiments, central surface region 122 can have a surface area ranging from 00,000 mm² to 8 m². In some embodiments, central surface region 122 can have a surface area ranging from 60,000 mm² to 6 m². In some embodiments, central surface region 122 can have a surface area ranging from 60,000 mm² to 3 m².

[0082] In some embodiments, vacuum mold 110 can include a slot 126 formed in mold surface 116 and demarcating central surface region 122 from perimeter surface region 124. Slot 126 can be sized such that a portion of reformed glass article 250 is not pulled into slot 126 during reforming. In some embodiments, one or more vacuum holes 118 can be formed in slot 126. In embodiments, slot 126 can have a width in a range of 1 mm to 4 mm. In embodiments, the width of slot 126 can be tailored to the initial thickness 206 of glass sheet 200 reformed using vacuum mold 110. In some embodiments, the width of slot 126 can be in a range of 100% to 300% of initial thickness 206. In embodiments, slot 126 can have a depth of 1 mm or less. In embodiments, slot 126 can have a depth in a range of 30% to 50% of the slot’s width. In such embodiments, slot 126 can have a depth ranging from 20 microns to 1 mm. In embodiments, slot 126 extends through the mold 110 to provide apath for laser cutting the central surface region 122 out of the reformed glass article 250.

[0083] In embodiments, mold surface 116 can include a contact indicator 128. Contact indicator 128 can be, for example, a raised dimple or a contact sensor. In embodiments including contact indicator 128, contact indicator 128 can provide a signal that a reformed glass sheet 201 is in contact with mold surface 116. In some embodiments, contact indicator 128 can be located on mold surface 116 on perimeter surface region 124.

[0084] Referring now to FIG. 3A, additional features of the top wall 132 of the frame 130 are described, according to an example embodiment. FIG. 3 A shows a cross-sectional view of the top wall 132 through the line III-III shown in FIG. 2. As shown, the top wall 132 includes a body 300 and a retention frame 310 disposed on the body 300. The body 300 includes an internal surface 302 and an external surface 304. In embodiments, the body 300 is attached to the mold 114 (e.g., via regularly spaced screws in an upper surface 306 of the body 300) such that the internal surface 302 transitions into the mold surface 116 (e.g., the internal edge 264 of the upper surface 134 can be formed in the body 300 either at or outward of the internal surface 302). In embodiments, the internal surface 302 is shaped to be an extension of the mold surface 116 (see FIGS. 1A-1B) so as to form a smooth interface with the mold 114. In embodiments, the retention frame 310 extends around the external surface 304 of the body 300 (e.g., wraps around the external surface 304 to an underside surface of the body 300) so that the external edge 262 of the upper surface 134 is formed by the retention frame 310. In embodiments, the body 300 is formed of the same material as that of the mold 114 (e.g., both can be constructed of graphite) and also comprises the same thickness as the mold 114 to provide consistent thermal mass throughout the combined structure of the frame 130 and mold 114. Uniform distribution of thermal mass has been found to control stresses in the glass and aid in reducing wrinkling.

[0085] In the depicted embodiment, an inner portion of the upper surface 134 (proximate the internal edge 264) is made up by the body 300, while an outer portion of the upper surface 134 is made up of the retention frame 310. The retention frame 310 can be formed of a metallic material or alloy (e.g., stainless steel) and serves to prevent oxidation of the body 300 during heating and cooling. The retention frame 310 can have a thickness that is much less than that of the body 300 so as to not effectively change the thermal mass of the body 300. In embodiments, the thickness of the retention frame 310 ranges from 0.7 mm to 1.5 mm. The combination of the retention frame 310 and body 300 therefore facilitates providing a uniform thermal mass distribution to control wrinkling while also protecting the body 300 from oxidation. The retention frame 310 can include an inner edge 312 that is disposed on the upper surface 306 of the body 300. The inner edge 312 can be disposed outward of the channel portions 158 (and thus outward of the one or more vacuum openings 140) so that the retention frame 310 does not disrupt the formation of a vacuum seal.

[0086] In embodiments, the retention frame 310 can be used to attach a friction enhancing structure to the body 300. In embodiments, a coefficient of static friction between the glass sheet 200 and this friction enhancing structure can be greater than 0.1 when the glass sheet 200 is initially placed in contact with the frame 130 (prior to heating). FIG. 3B, for example, depicts a view of the retention frame 310 removed from the body 300. As shown, the retention frame 310 includes a first portion 314 and a second portion 316. When disposed on the body 300 (see FIG. 3 A), the first portion 314 can be disposed adjacent to (or in contact with) the upper surface 306 and the second portion 316 can be disposed adjacent to (or in contact with) an underside surface of the body 300. As shown, the first portion 314 forms the inner edge 312 disposed on the upper surface 306 when installed on the body 300. [0087] As shown in FIG. 3A, a stainless steel cloth 320 can be spot welded to the retention frame 310 and positioned such that, when the glass sheet 200 is initially disposed on the frame 130, the glass sheet 200 contacts the stainless steel cloth 320. Stainless steel cloth is beneficial because it provides a high coefficient of friction with the glass (greater than 0. 1 and less than or equal to 1.6) to prevent tangential movement of the glass that causes center sagging. Moreover, the low modulus of the steel cloth allows the cloth to follow local dimensional changes of the glass during heating and cooling. The stainless steel cloth 320 provides a temporary point of attachment with the glass that follows the glass during the reforming process to prevent the glass from lifting off of the frame 130 and facilitate forming a vacuum seal. In embodiments, the stainless steel cloth 320 is wrapped around the inner edge 312 of the retention frame 310 and molded to an underside of the first portion 314. Such a structure maximizes contact area between the stainless steel cloth 320 and the glass sheet 200 to maximize friction. Moreover, the stainless steel cloth may be wrapped around the external surface 304 of the body 300 (see FIG. 3 A) and also spot molded to an underside surface of the second portion 316. This way, the entirety of the retention frame 310 contacting the glass sheet 200 is covered with the stainless steel cloth 320 to maximize contact area.

[0088] FIG. 4 illustrates a method 400 of reforming a glass sheet 200 according to some embodiments. Unless stated otherwise, the steps of method 400 need not be performed in the order set forth herein. In embodiments, the method 400 can be performed using the apparatus 100 described herein with respect to FIGS. 1A-3B. Accordingly, reference will be made to various components depicted in FIGS. 1A-3B to aid in description of the method, with the understanding that the method 400.

[0089] In step 402, glass sheet 200 is placed over vacuum mold 110. When glass sheet 200 is placed over vacuum mold 110, glass sheet can be positioned such that glass sheet 200 covers vacuum cavity 112 and bottom surface 204 of glass sheet 200 is in direct contact with top surface 134 of frame 130. In some embodiments, glass sheet 200 can have a perimeter shape defined by perimeter edge 208 and having a first perimeter, and exterior perimeter edge 136 of frame 130 can have a shape that matches that of the first perimeter. In some embodiments, step 402 can include placing multiple glass sheets 200 over vacuum mold 110. The plurality of glass sheets 200 can be placed over vacuum mold 110 in a stacked configuration. In such embodiments, method 400 can simultaneously reform the plurality of glass sheets 200.

[0090] In step 404, glass sheet 200 is heated to a reforming temperature. One or more heat sources 190 of apparatus 100 can heat glass sheet 200 to the reforming temperature. In some embodiments, the reforming temperature can range from 600 °C to 900 °C. Exemplary heat sources 190 include convention heating devices and infrared (IR) heating devices. In some embodiments, a heat shield 180 can be placed on top surface 202 of glass sheet 200 during reforming to help control the temperature of glass sheet 200.

[0091] In step 406, vacuum pressure can be applied to one or more vacuum openings 140. The vacuum pressure applied to the one or more vacuum openings 140 in step 406 can be sufficient to pull one or more first portions 220 of the glass sheet 200 into the one or more of vacuum openings 140. In embodiments including a plurality of vacuum openings 140, applying vacuum pressure to the plurality of vacuum openings 140 can pull a plurality of first portions 220 of glass sheet 200 into the plurality of vacuum openings 140. In some embodiments, the vacuum pressure applied to vacuum openings 140 in step 406 can pull a third portion of glass sheet 200 into channel 156 of vacuum mold 110. In some embodiments, the vacuum pressure applied to the one or more vacuum openings 140 can range from 0. 1 bars to 0.3 bars. In some embodiments, vacuum pressure can be applied to the one or more vacuum openings 140 in step 406 for a time ranging from 30 seconds to 120 seconds. In some embodiments, vacuum pressure can be applied to the one or more vacuum openings 140 at a rate of 5 liters per minute to 20 liters per minute.

[0092] The vacuum pressure applied in step 406 can seal glass sheet 200 to top surface 134 of frame 130, thus creating a vacuum tight seal around the perimeter of second portion 230 of glass sheet 200. Additionally, the vacuum pressure applied in step 406 can help hold glass sheet 200 and prevent any lateral glass motion during the application of vacuum pressure in the reforming process. This facilitates controlled local deformation and elongation of second portion 230 of glass sheet 200 to create a reformed glass article without wrinkling.

[0093] By utilizing vacuum pressure to hold glass sheet 200 in place during reforming, the reforming process can be performed without mechanically clamping glass sheet 200 to top surface 134 of frame 130 during reforming of glass sheet 200. By eliminating mechanical clamping, stresses imparted on glass sheet 200 during heating and cooling can be minimized. Excessive stress, for example mechanical stresses and/or thermal stresses created at the interface of the glass and clamping mechanisms can cause undesirable glass deformation and/or glass failure during heating and cooling. Additionally, the use of vacuum pressure to hold glass sheet 200 during reforming can eliminate the need for any mechanical release mechanisms, which can damage the glass when removing glass sheet 200 from vacuum mold 110. The one or more vacuum openings 140 described herein allow self-release of glass sheet 200 during cooling and demolding, thus minimizing stresses imparted on the glass. [0094] In step 408, vacuum pressure can be applied to vacuum cavity 112. The vacuum pressure applied to vacuum cavity 112 can be sufficient to pull second portion 230 of glass sheet 200 into vacuum cavity 112. In some embodiments, the vacuum pressure applied to vacuum cavity 112 in step 408 can range from 0.1 bars to 0.3 bars. In some embodiments, vacuum pressure can be applied to vacuum cavity 112 for a time ranging from 30 seconds to 120 seconds. In some embodiments, vacuum pressure applied to vacuum cavity 112 at a rate of 10 liters per minute to 100 liters per minute. In some embodiments, vacuum pressure is applied to the one or more vacuum openings 140 in step 406 before vacuum pressure is applied to vacuum cavity 112 in step 408. In some embodiments, steps 406 and 408 can be performed simultaneously such that vacuum pressure is applied to the one or more vacuum openings 140 at the same time vacuum pressure is applied to vacuum cavity 112. In some embodiments, applying vacuum pressure to vacuum cavity 112 in step 408 can pull second portion 230 of glass sheet 200 against mold surface 116 of mold 114 defining vacuum cavity 112. In some embodiments, applying vacuum pressure to vacuum cavity 112 in step 408 can pull second portion 230 of glass sheet 200 into vacuum cavity 112 and the second portion 230 can be free- formed within vacuum cavity 112. In such embodiments, second portion 230 can be reformed within vacuum cavity 112 without being pulled against a mold surface of a mold by controlling the vacuum pressure, time, and temperature within vacuum cavity 112.

[0095] In some embodiments, vacuum pressure can be applied to vacuum cavity 112 and/or the one or more vacuum openings 140 without the use of a vacuum source. In such embodiments, vacuum pressure can be applied by suddenly stopping the application of heat after reaching the reforming temperature. This can lead to rapid cooling of the air in vacuum cavity 112 and/or vacuum chamber 162, thus creating significant gas volume contraction within vacuum cavity 112 and/or vacuum chamber 162. This significant gas volume contraction can pull the one or more first portions 220 of glass sheet 200 into the one or more vacuum openings 140 and/or pull second portion 230 of glass sheet into vacuum cavity 112.

[0096] In some embodiments, second portion 230 of glass sheet 200 can have an initial thickness 206 (tl) before reforming glass sheet 200 and a final thickness 207 (t2) after reforming the glass sheet. This different in thickness can be a result of glass sheet deformation during reformation. In some embodiments, the ratio of initial thickness 206 to final thickness tl tl

207 (— ) can ranges from 1.1 to 2. A ratio of initial thickness to final thickness (— ) indicates that glass sheet 200 was deformed and stretched into its final shape. This deformation and stretching of the glass is akin to how glass is formed during glass blowing. By allowing the glass to freely deform and stretch into its final shape, stresses imparted on the glass can be minimized, which in turn helps prevent glass breakage and wrinkling.

[0097] After reforming glass sheet 200 in step 408, the vacuum pressure applied to vacuum cavity 112 and the one or more vacuum openings 140 can be released and the reformed glass sheet can be allowed to cool to an annealing temperature in step 412. In step 412, the reformed glass sheet can be held at the annealing temperature to relieve internal residual stresses created during the reforming. After annealing, the reformed glass sheet can be cooled to room temperature in step 414 and removed from vacuum mold 110 in step 416. The steps 410-414 can utilize any suitable heating profile, such as those described in International Patent Application No. PCT/US2022/025696, published as WIPO Publication No. WO 2022/231933 Al.

[0098] FIG. 5 schematically depicts the reformed glass article 250 formed via steps 402-416 of the method 400, according to an example embodiment. As shown, the reformed glass article comprises a first major surface 502 (corresponding to the top surface 202), a second major surface 504 (corresponding to the bottom surface 204) opposite the first major surface 502, and a minor surface 506 extending between the first major surface 502 and the second major surface 504. The minor surface 506 can correspond to the perimeter edge 208 of the glass sheet 200 prior to reforming, which, as described herein, may be cut to have the same peripheral shape as the upper surface 134. The method 400 can result in the second major surface 504 conforming to a shape ofthe combined structure ofthe upper surface 134 and mold surface 116 contacting the glass sheet 200 during reforming. Accordingly, the structure ofthe reformed glass article 250 is substantially dictated by the structure of the mold 114 and the frame 130.

[0099] As shown in FIG. 5, the reformed glass article 250 includes a peripheral region 510 extending inward from the minor surface 506 to a boundary region 520. A majority of the peripheral region 510 can be substantially flat. As used herein, the term “substantially flat” means that the article appears to have a planar shape when viewed unmagnified from a distance of 1 m. The peripheral region 510 can correspond to the supported portion 240 described herein with respect to FIGS. 1A-1B, with the exception that first portions 220 of the glass sheet 200 have been shaped via interaction with the one or more vacuum openings 140. In embodiments, the peripheral region 510 comprises a width corresponding to the width 268 of the upper surface 134 described herein with respect to FIG. 2. The boundary region 520 represents a portion of the glass sheet 200 that is bent around the internal edge 264 of the upper surface 134 during reforming, and/or where a shape of the reformed glass article 250 transitions from a flat shape to a non-developable shape. The reformed glass article 250 further includes a central curved region 530 disposed inward of the boundary region 520. The central curved region 530 can correspond to the second portion 230 pulled against the mold surface 116 during performance of the method 400. Within the central curved region 530, the first major surface 502 comprises a concave shape and the second major surface 504 comprises a convex shape. [0100] The dimensions of the reformed glass article 250 may correspond to the dimensions of the combined structure of the frame 130 and mold 114 that contact the glass sheet 200 during reforming. As such, the reformed glass article 250 can comprises a maximum length, representing a maximum linear distance between separate points on the minor surface 506 measured in a first direction parallel to the first major surface 502 in the peripheral region 510. The maximum length can correspond to the values provided herein for the maximum length 266 depicted in FIG. 2. The reformed glass article 250 exhibits a depth of bend, DOB, represented by a maximum distance between portions the first major surface 502 in the peripheral region 510 and in the central curved region 530 measured in a second direction perpendicular to the first direction, that is from 10% of the length to 30% of the maximum length. Due to conformance with the upper surface 134, the peripheral region 510 comprises a width 540 measured in the first direction that varies by no more than 10% of an average value around the peripheral region 510.

[0101] As a result of the design of the frame 130 described herein with respect to FIGS.

2-3B, the reformed glass article 250 can be characterized as exhibiting minimal buckling directly after reforming. Providing the width 268 of the upper surface 134 described herein with respect to FIG. 2 (e.g., from 6% to 10% of the length), for example, has been found to reduce the number of buckles in the reformed glass article compared with those having smaller frame widths. As used herein, the term “buckle” refers to a localized convexity in a surface of a reformed glass article facing upward during reforming. Glass articles formed in the present disclosure have been found to exhibit 1 or fewer buckles in the peripheral region 510 (in some cases zero buckles were observed when the internal edge 264 exhibited the shape characteristics described herein and/or when the stainless steel cloth was used). Glass articles reformed to similar shapes with other processes, in contrast, were found to exhibit more than two buckles. These buckles can form in the peripheral portion prior to vacuum pressure being applied, thereby causing the central curved region to significantly deviate from a desired shape and have poor optical distortion performance. In some embodiments, the reformed glass article can exhibit a maximum buckling amplitude (height of a buckle above a surrounding portion of the first major surface 502) of less than 20 mm in the peripheral region 510. [0102] Referring again to FIG. 4, after removing reformed glass article 250 from vacuum mold 110, excess glass sheet material can be removed therefrom in step 418 to create curved glass article. For example, removing excess glass sheet material can include removing all portions of reformed glass sheet 201 that were formed outside of central surface region 122. With reference to FIG. 5, a portion 550 of the central curved region 530 can be cut out of the reformed glass article 250 to form a curved glass article. In some embodiments, excess glass sheet material can be removed using a cutting process, for example a laser cutting process or a waterjet cutting process. In some embodiments, excess glass sheet material can be removed using mechanical scoring and breakage of the glass along the score line. In step 420, one or more post-reforming processes can be performed on reformed glass sheet 201 or reformed glass article 250. Post-reforming processes include, but are not limited to, a polishing process, an ion-exchange process, an etching process, a lamination process. Post-reforming processes can be performed before or after step 418.

[0103] FIG. 6 depicts a curved glass article 1400 formed via the method 400. For example, the curved glass article 1400 can be formed by cutting out the portion 550 of the reformed glass article 250 depicted in FIG. 5. An imaginary surface 1402 is shown and can be used to determine a maximum compressive strain shape parameter indicative of the complexity of the curved shape of the curved glass article 1400. In embodiments, the imaginary surface 1402 represents an imaginary plane that points contained in an imaginary central surface 1412 defined by the glass article 1400 may be displaced into, as signified by the arrows 1414, during a simulation to determine a complexity of the curved shape of the glass article 1400. The reforming techniques described herein are capable of producing glass articles having higher complexity than certain pre-existing hot-forming techniques, with the glass article 1400 beneficially exhibiting high thickness uniformity and relatively low levels of optical distortion. [0104] As shown, the glass article 1400 comprises a first curved surface 1404, a second curved surface 1406, and a thickness 1408 extending between the first curved surface 1404 and the second curved surface 1406. In embodiments, the first curved surface 1404 and the second curved surface 1406 define a non-developable curved shape of the glass article 1400. In embodiments, the thickness 1408 represents a distance between the first curved surface 1404 and the second curved surface 1406 along a direction 1410 extending perpendicular to the first curved surface 1404. As will be appreciated, the direction 1410 in which the thickness 1408 is measured may vary as a function of position on the first curved surface 1404 given the non- developable curved shape. In embodiments, the thickness 1408 may correspond to a minimum distance from the first curved surface 1404 to the second curved surface 1406, as measured from a particular point on the first curved surface 1404. In embodiments, the thickness 1408 can range from 0.25 millimeters to 10 millimeters, 0.5 millimeters to 5 millimeters, 0.5 millimeters to 2.5 millimeters, 2.5 millimeters to 5 millimeters, 2.5 millimeters to 10 millimeters, or within a range having any two of these values as endpoints. In embodiments, the thickness 1408 can range from 0.1 millimeters to 10 millimeters, from 0.2 millimeters to 10 millimeters, from 0.3 millimeters to 10 millimeters, from 0.4 millimeters to 10 millimeters, from 0.5 millimeters to 10 millimeters, from 0.6 millimeters to 10 millimeters, from 0.7 millimeters to 10 millimeters, from 0.8 millimeters to 10 millimeters, from 0.9 millimeters to 10 millimeters, from 1 millimeter to 10 millimeters, from 1.1 millimeters to 10 millimeters, from 1.2 millimeters to 10 millimeters, from 1.4 millimeters to 10 millimeters, from 1.5 millimeters to 10 millimeters, from 1.6 millimeters to 10 millimeters, from 1.8 millimeters to 10 millimeters, from 2 millimeters to 10 millimeters, from 2.1 millimeters to 10 millimeters, from 2.5 millimeters to 10 millimeters, from 3 millimeters to 10 millimeters, from 4 millimeters to 10 millimeters, from 5 millimeters to 10 millimeters, from 0. 1 millimeters to 9 millimeters, from 0.1 millimeters to 8 millimeters, from 0.1 millimeters to 7 millimeters, from 0.1 millimeters to 6.5 millimeters, from 0.1 millimeters to 6 millimeters, from 0.1 millimeters to 5.5 millimeters, from 0.1 millimeters to 5 millimeters, from 0.5 millimeters to 4 millimeters, from 0.7 millimeters to 3.6 millimeters, from 0.7 millimeters to 3.3 millimeters, from 0.7 millimeters to 2.1 millimeters, from 0.7 millimeters to 1.6 millimeters, or from 0.7 millimeters to 1. 1 millimeters, or within a range having any two of these values as endpoints.

[0105] The value obtained when measuring the thickness 1408 may vary depending on the location on the first curved surface 1404. As described herein, the deep vacuum forming methods described herein facilitate the thickness 1408 being substantially uniform over the entire first curved surface 1404. For example, if a plurality of measurements of the thickness 1408 (e.g., 10 measurements) are taken over a particular 1000 mm² portion of the surface area of the first curved surface 1404, the measurements may all be within 150 pm of one another (e.g., such that a difference between a maximum value of the values obtained and a minimum value is less than or equal to 150 pm). That is, the thickness uniformity of the glass article 1400 may be +/- 75 microns per 1000 mm² of surface area on the first curved surface 1404. In embodiments, the thickness uniformity of the glass article 1400 may be +/- 75 microns per 10000 mm² of surface area on the first curved surface 1404. In embodiments, the thickness uniformity is +/- 50 microns per 1000 mm² of surface area on the first curved surface 1404. In embodiments, the thickness uniformity is +/- 25 microns per 1000 mm² of surface area on the first curved surface 1404. [0106] In embodiments, at least one of the first curved surface 1404 and the second curved surface 1406 comprises a surface area in the range of 10,000 mm² to 6 m² and a thickness uniformity of +/- 75 microns per 1000 mm². In embodiments, at least one of the first curved surface 1404 and the second curved surface 1406 comprises a surface area in the range of 10,000 mm² to 6 m² and a thickness uniformity of +/- 75 microns per 10000 mm². In embodiments, at least one of the first curved surface 1404 and the second curved surface 1406 comprises a surface area in the range of 60,000 mm² to 6 m² and a thickness uniformity of +/- 50 microns per 10000 mm². In embodiments, at least one of the first curved surface 1404 and the second curved surface 1406 comprises a surface area in the range of 60,000 mm² to 6 m² and a thickness uniformity of +/- 25 microns per 10000 mm².

[0107] In embodiments, the non-developable curved shape defined by the first curved surface 1404 and the second curved surface 1406 comprises a maximum compressive strain shape parameter, defined by the imaginary central surface 1412 of the glass article 1400 and the imaginary surface 1402. The maximum compressive strain shape parameter represents a complexity of the shape into which the processes described herein are capable of reforming flat glass sheets without introducing wrinkling or other significant thickness deviations. The maximum compressive strain shape parameter is primarily a function of the Gaussian curvature associated with the imaginary central surface 1412 and the dimensions thereof (e.g., a length and a width in an assigned coordinate system). The thickness of the glass has a minor effect on the maximum compressive strain shape parameter, but the effect is negligible.

[0108] The maximum compressive strain shape parameter may be computed by simulating the imaginary central surface 1412 as an imaginary glass sheet. The properties of the imaginary glass sheet may be independent of the properties of the actual glass article 1400 (physically produced via the methods described herein). Unless otherwise specified, the imaginary glass sheet has a thickness of 0.7 mm, a Young’s modulus of 71.7 GPa, and a Poisson’s ratio of 0.21, and a density of 2440 kg/m³. The imaginary glass sheet is discretized into trilateral or quadrilateral shell elements (or a combination thereof) associated with a commercially available finite element analyzer. In embodiments, Ansys® Mechanical™ is used to compute the maximum compressive strain shape parameter, with the imaginary central surface 1412 being discretized using SHELL181 elements (avoiding use of the degenerate triangular option, except when used as a filler in mesh generation). Particularly, a simulation is conducted of the strains that would be present in the imaginary glass sheet when the imaginary glass sheet (initially having the shape of the imaginary central surface 1412) is flattened to have the planar shape of the imaginary surface 1402. A command script is used to assign boundary conditions associated with the nodal displacements of the simulation (e.g., to define the imaginary surface 1402 for flattening the imaginary glass sheet). The boundary conditions may also prevent rigid body motion of the imaginary glass sheet (e.g., by assigning the imaginary surface 1402 to be tangent to a portion of the imaginary central surface 1412). Nodes associated with each shell element are displaced along the arrows 1414 until the nodes are each located on the imaginary surface 1402 (e.g., the z-coordinates of each of the nodes are zeroed out in the coordinate system established by the boundary conditions, without the x or y coordinates of each node changing, such that the length and width of the simulated flattened glass sheet is the same as that of the initial glass article 1400 being simulated). The finite element analysis is carried out using the implicit method, including nonlinear analysis. The maximum value of the major principal strain is the maximum compressive strain shape parameter described herein. The mesh size associated with the shell elements is less than or equal to 0.5 mm to ensure a convergent solution.

[0109] The imaginary central surface 1412 is a surface representing a central plane of the glass article 1400. Each point on the imaginary central surface 1412 is equidistant from the first curved surface 1404 and the second curved surface 1406 along a direction extending perpendicular to the imaginary central surface 1412 at that point.

[0110] Certain existing vacuum forming methods may not be capable of producing glass articles having non-developable shapes with a maximum compressive strain parameter of greater than 1% or 2% without substantial defects or thickness variations. The deep vacuum forming methods described herein, in contrast, are able to reform flat glass sheets to curved glass articles with curved surfaces defining a non-developable shape with a maximum compressive strain shape parameter of greater than or equal to 3.0% (e.g., greater than or equal to 3.5%, greater than or equal to 4.0%, greater than or equal to 4.5%, greater than or equal to 5.0%). In one or more embodiments, the curved glass articles have curved surfaces defining a non-developable shape with such maximum compressive strain shape parameter ranges while still exhibiting a thickness uniformity of +/- 75 pm (e.g., +/- 50 pm, +/- 25 pm) per at least 1000 mm² of surface area of the part.

[0111] In embodiments, the maximum compressive strain shape parameter associated with the glass article 1400 may be approximated using the following equation when the glass article has a periphery that is substantially parallelepiped shaped (or in cases where a majority of the periphery of the glass article has a radius of curvature of greater than 10 m):

MCSSP = 0.0725 * K * (1.0667 - 10.9477 * e“^{3 3572}*T ) * I² (1) where K is an average Gaussian curvature of the imaginary central surface 1412, 1 is a length of a flat glass sheet that the imaginary glass sheet is simulated to be flattened into, and w is a width of the flat glass sheet (units of each constant are such that the result is in units of mm/m, which can be converted to a percent by dividing the numerical mm/m result by 10). When the glass article comprises a substantially circular (or where a majority of the periphery of the glass article has a radius of curvature of less than 10 m), the maximum compressive strain shape parameter may be approximated mathematically based on the following relationship:

MCSSP = 0.0354 * K * D² (2) where D is the diameter of the circular glass plate that the imaginary glass sheet is flattened into. Units associated with the constants in equations (1) and (2) are set such that the output of equations ( 1 ) and (2) are in the units of mm/m (which may be converted to a percent by dividing the output by 10).

[0112] In embodiments, the curved shape of reformed glass article 1400 can have an optical power distortion measured through the thickness 1408 below 300 millidiopters in absolute value. In some embodiments, the curved shape of reformed glass article 1400 can have an optical power distortion measured through the thickness 1408 ranging from 20 millidiopters to 300 millidiopters (in absolute value). In some embodiments, the curved shape of reformed glass article 1400 can have an optical power distortion measured through the thickness 1408 ranging from 50 millidiopters to 300 millidiopters (in absolute value). In some embodiments, the curved shape of reformed glass article 1400 can have an optical power distortion measured through the thickness 1408 ranging from 100 millidiopters to 300 millidiopters (in absolute value). The optical power distortion of the curved shape can be measured in accordance with DIN 52305: 1995 (“Determining the optical distortion and refractive power of safety glazing material for road vehicles”).

[0113] In some embodiments, the first curved surface 1404 of reformed glass article 1400 can have a measurable dimple density of less than 10 dimples per 100 mm² convex surface area. As used herein, a measurable dimple is a raised or recessed dimple formed on the first curved surface 1404 and comprising an effective diameter of greater than 1 mm. Measurable dimples can be identified by measuring optical distortion of light transmitted through the first curved surface 1404 of glass article 1400. An optical distortion of 50 or more millidiopters (mdpt) after a noise filter is applied to the measurement data can indicate the presence of a measurable dimple, or an optical distortion of 100 or more millidiopters (mdpt) before a noise filter is applied to the measurement data can indicate the presence of a measurable dimple. Optical distortion can be measured using a device that measures transmitted optical distortions on glass. For example, optical distortion can be measured using a LABSCAN-SCREEN system available from ISRA Vision. For purposes of evaluating a measurable dimple density, at least one 50,000 mm² surface area on the first curved surface 1404 is analyzed and the number of measurable dimples per 100 mm² is calculated based on the total number of measurable dimples present. To confirm the accuracy of the number of dimples per 100 mm² for the 50,000 mm² surface area, a 5,000 mm² surface area inside the 50,000 mm² surface area can be re-analyzed and the number of measurable dimples per 100 mm² is calculated based on the total number of measurable dimples present in the 5,000 mm² surface area.

[0114] As will be appreciated, the glass article 1400 may have a variety of shapes and the particular form of the glass article 1400 is not particularly limiting. For example, in embodiments, an outer peripheral shape of the glass article 1400 can comprise a length (L) extending in a first direction extending parallel to the imaginary surface 1402 and a width (W) extending in a second direction parallel to the imaginary surface 1402 and perpendicular to the first direction. The length (L) and width (W) may represent the maximum dimensions of the glass article 1400 in the first and second directions, respectively. In embodiments, an outer peripheral edge of the glass article 1400 may be substantially parallelepiped (e.g., rectangular) shaped. In embodiments, the outer peripheral edge of the glass article 1400 may be substantially circular-shaped (e.g., such that a majority of the peripheral edge possesses radius of curvature of less than 10 m) and comprise a diameter (D) representing a maximum distance between two points on the outer peripheral edge.

Examples

[0115] Embodiments of the present disclosure can be further understood in view of the following examples.

[0116] Modelling was conducted for reforming a 2.3 mm thick piece of soda lime glass being reformed when heated using isothermal heating to a reforming temperature above 570°C. Modelling was conducted for the molds depicted in FIGS. 7A-7B. The glass sheet was cut to have a peripheral shape matching the peripheral shape of the upper frame surfaces. As shown in FIG. 7A, the mold 1500 according to a first example included an upper frame surface 1502 with a width of 120 mm. As shown, the width was thus less than 6% of the overall length of the mold 1500. The upper frame surface 1502 also comprised an inner edge 1504 not having a shape prescribed herein, with a discontinuous second derivative and relatively long linear segments. As shown in FIG. 7B, the mold 1506 according to a second example included an upper frame surface 1508 with a width of 120 mm. The width was thus less than 6% of the overall length of the mold 1506. In contrast to the mold 1500, the upper frame surface 1508 of the mold 1506 included an inner edge 1510 with a continuous second derivative and no linear segments longer than 25% of the overall length.

[0117] Results of the reforming simulation for the molds depicted in FIGS. 7A and 7B are depicted in FIGS. 8A-8B. As shown, both of the molds resulted in three buckles in the peripheral portions of the articles. However, as shown in FIG. 8 A, the buckles caused by the mold 1500 extended further inward towards the center of the glass article than those shown in FIG. 8B, potentially effecting the shape to a greater extent. As shown, the redesigned shape of the inner edge 1510 exhibited superior edge quality (uniformity) and the buckles were less pronounced, demonstrating the efficacy of the molds described herein. Another simulation conducted for molds having designs similar to those depicted in FIGS. 7A and 7B, but with the widths of the upper surfaces increased to 150 mm, to be above 6% of the overall lengths of the molds. The results for the redesigned version of the mold depicted in FIG. 7A are shown in FIG. 9A. The results for the redesigned version of the mold depicted in FIG. 7B are shown in FIG. 9B. As shown in FIG. 9A, increasing the width of the upper frame surface 1502 eliminated two of the three wrinkles. As shown in FIG. 9B, increasing the width of the upper frame surface 1508 eliminated all of the wrinkles present. These results demonstrate the efficacy of the molds described herein in eliminating wrinkles at the periphery of glass articles reformed to complex gaussian shapes.

[0118] The examples are illustrative, but not limiting, of the present disclosure. Other suitable modifications and adaptations of the variety of conditions and parameters normally encountered in the field, and which would be apparent to those skilled in the art, are within the spirit and scope of the disclosure.

[0119] The indefinite articles “a” and “an” to describe an element or component means that one or more than one of these elements or components is present. Although these articles are conventionally employed to signify that the modified noun is a singular noun, as used herein the articles “a” and “an” also include the plural, unless otherwise stated in specific instances. Similarly, the definite article “the,” as used herein, also signifies that the modified noun may be singular or plural, again unless otherwise stated in specific instances.

[0120] Directional terms as used herein - for example up, down, right, left, front, back, top, bottom, inward, outward — are made only with reference to the figures as drawn and are not intended to imply absolute orientation.

[0121] As used in the claims, “comprising” is an open-ended transitional phrase. A list of elements following the transitional phrase “comprising” is a non-exclusive list, such that elements in addition to those specifically recited in the list may also be present. As used in the claims, “consisting essentially of’ or “composed essentially of’ limits the composition of a material to the specified materials and those that do not materially affect the basic and novel characteristic(s) of the material. As used in the claims, “consisting of’ or “composed entirely of’ limits the composition of a material to the specified materials and excludes any material not specified.

[0122] Where a range of numerical values is recited herein, comprising upper and lower values, unless otherwise stated in specific circumstances, the range is intended to include the endpoints thereof, and all integers and fractions within the range. It is not intended that the scope of the claims be limited to the specific values recited when defining a range. Further, when an amount, concentration, or other value or parameter is given as a range, one or more preferred ranges or a list of upper preferable values and lower preferable values, this is to be understood as specifically disclosing all ranges formed from any pair of any upper range limit or preferred value and any lower range limit or preferred value, regardless of whether such pairs are separately disclosed. Finally, when the term “about” is used in describing a value or an end-point of a range, the disclosure should be understood to include the specific value or end-point referred to. Whether or not a numerical value or end-point of a range recites “about,” the numerical value or end-point of a range is intended to include two embodiments: one modified by “about,” and one not modified by “about.”

[0123] As used herein, the term “about” refers to a value that is within ± 5% of the value stated. For example, about 3 MPa can include any number between 2.85 MPa and 3.15 MPa.

[0124] The present embodiment(s) have been described above with the aid of functional building blocks illustrating the implementation of specified functions and relationships thereof. The boundaries of these functional building blocks have been arbitrarily defined herein for the convenience of the description. Alternate boundaries can be defined so long as the specified functions and relationships thereof are appropriately performed.

[0125] It is to be understood that the phraseology or terminology used herein is for the purpose of description and not of limitation. The breadth and scope of the present disclosure should not be limited by any of the above-described exemplary embodiments, but should be defined in accordance with the following claims and their equivalents.

Claims

WHAT IS CLAIMED IS:

1 . A curved glass article in an as-formed condition, the curved glass article comprising: a first major surface; a second major surface disposed opposite the first major surface; a minor surface extending between the first major surface and the second major surface; a peripheral region extending inward from the minor surface to a boundary region, wherein a majority of the peripheral region is substantially flat; a central curved region disposed inward of the boundary region; and a length L, representing a maximum linear distance between separate points on the minor surface measured in a first direction parallel to the first major surface in the peripheral region, wherein: within the central curved region, the first major surface comprises a concave shape and the second major surface comprises a convex shape and the first and second major surfaces exhibit non-zero Gaussian curvature, the curved glass article exhibits a depth of bend, DOB, represented by a maximum distance between portions the first major surface in the peripheral region and in the central curved region measured in a second direction perpendicular to the first direction, that is from 10% of the length to 30% of the length, the peripheral region comprises a width measured parallel to the first major surface that varies by no more than 10% of an average value around the peripheral region, and the peripheral region exhibits one or fewer buckles around an entire circumference thereof.

2. The curved glass article according to claim 1, wherein:

300 mm < L < 4000 mm, and

50 mm < DOB < 700 mm.

3. The curved glass article according to any one of claims 1 -2, wherein the glass article comprises a width W, representing a maximum linear distance between separate points on the minor surface measured in a third direction parallel to the first major surface in the peripheral region and perpendicular to the first direction, wherein

200 mm < W < 2500 mm.

4. The curved glass article according to any one of claims 1-3, wherein: the first major surface in a portion of the central curved region comprises a surface area of 60,000 mm² or more, and within the portion, a thickness measured between the first major surface and the second major surface has a uniformity of +/- 75 microns per 1000 mm² of surface area on the first major surface.

5. The curved glass article according to claim 4, wherein, the portion comprises a non-developable curved shape comprising a maximum compressive strain shape parameter, as measured between an imaginary central surface disposed between the first major surface and the second major surface and an imaginary surface, of greater than or equal to 3.0% and less than or equal to 10%.

6. The curved glass article according to any one of claims 4-5, wherein, within the portion, wherein an average value of the thickness, measured over an entirety of the first major surface, is greater than or equal to 0.5 mm and less than or equal to 2.5 mm.

7. A vacuum mold, the vacuum mold comprising: a mold comprising a mold surface with a complex non-developable shape and defining a mold cavity; and a frame comprising a body that is disposed on the mold, the body comprising a top surface that circumferentially surrounds the mold surface and comprises one or more vacuum openings formed in the top surface, wherein the top surface comprises: an outer edge; an inner edge where the body forms an interface with the mold; and a width, W, measured in a first direction parallel to the top surface between the inner edge and the outer edge, wherein: the width W does not vary by more than 10% from an average value around an entire circumference of the vacuum mold, the vacuum mold comprises a length, L, representing a maximum linear distance between separate points on the outer edge parallel to the top surface, the vacuum mold comprises a depth, D, measured as a maximum vertical distance between the top surface and the mold surface in a direction perpendicular to the top surface, that is from 10% to 30% of L, and

W is from 0.06*L to 0.10*L.

8. The vacuum mold of claim 7, wherein the inner edge comprises a circumferential shape without linear segments having a length that is more than L/4.

9. The vacuum mold of claim 8, wherein a second derivative of the circumferential shape is continuous over an entirety thereof.

10. The vacuum mold of claim 8, wherein the width W does not vary by more than 5% from an average value around an entire circumference of the vacuum mold.

11. The vacuum mold of any one of claims 7-10, wherein: 300 mm < L < 4000 mm, and

50 mm < D < 700 mm.

12. The vacuum mold of any one of claims 7-11, wherein the body is formed of graphite, wherein the vacuum mold further comprises a metallic frame disposed on the top surface and around the outer edge.

13. The vacuum mold of claim 12, wherein an inner edge of the metallic frame is disposed outward of the one or more vacuum openings.

14. The vacuum mold of claim 13, wherein further comprising stainless steel cloth welded around the inner edge and disposed around the outer edge.

15. A method of forming a curved glass article, the method comprising: placing a glass sheet over a vacuum mold comprising a mold surface at least partially defining a vacuum cavity, wherein the glass sheet is placed on the vacuum mold such that the glass sheet contacts a top surface of a body of a frame circumferentially surrounding the mold surface, wherein the top surface comprises: one or more vacuum openings formed therein; an outer edge; an inner edge where the body forms an interface with the mold; and a width, W, measured parallel to the top surface between the inner edge and the outer edge, wherein the width W does not vary by more than 10% from an average value around an entire circumference of the vacuum mold, wherein the vacuum mold comprises a length, L, representing a maximum linear distance between separate points on the outer edge measured parallel to the top surface, wherein the vacuum mold comprises a depth, D, measured as a maximum vertical distance between the top surface and the mold surface in a second direction perpendicular to top surface, that is from 10% to 30% of L, wherein W is from 0.06*L to 0. 10*L; heating the glass sheet to a reforming temperature; applying vacuum pressure to the one or more vacuum openings such that one or more first portions of the glass sheet are pulled into the one or more of vacuum openings; and applying vacuum pressure to the vacuum cavity such that a second portion of the first glass sheet is pulled into the vacuum cavity such that the glass sheet contacts a portion of the mold surface disposed at the depth D relative to the top surface.

16. The method of claim 15, wherein, prior to the heating, a static coefficient of friction between the top surface and the glass sheet is greater than 0. 1 and less than or equal to 1.6.

17. The method of any of claims 15-16, wherein, when the glass sheet is placed on the top surface, an entire peripheral edge of the glass sheet is aligned with the outer edge.

18. The method of claim 15, wherein, during the heating, the first portions are heated to a first temperature and the second portion is heated to a second temperature that is less than the first temperature.

19. The method of claim 18, wherein the second temperature is from 20°C to

120°C less than the first temperature.

20. The method of any one of claims 15-19, wherein the second portion of the glass sheet comprises an initial thickness (tl) before reforming the glass sheet and a final tl thickness (t2) after reforming the glass sheet, and wherein — ranges from 1.1 to 2.

21. The method of any one of claims 15-20, wherein the inner edge comprises a circumferential shape without linear segments having a length that is more than L/4.

22. The method of claim 21, wherein a second derivative of the circumferential shape is continuous over an entirety thereof.

23. The method of any one of claims 15-22, wherein:

300 mm < L < 4000 mm, and

50 mm < D < 700 mm.

24. The method of any one of claims 15-23, wherein the body is formed of graphite, wherein the vacuum mold further comprises a metallic frame disposed on the top surface and around the outer edge, wherein the metallic frame comprises a thickness from 0.7 to 1.5 mm.

25. The method of claim 24, wherein an inner edge of the metallic frame is disposed outward of the one or more vacuum openings.

26. The method of claim 25, wherein the vacuum mold further comprises stainless steel cloth welded around the inner edge and disposed around the outer edge.