COMPLEX GLAZING AND METHOD OF FORMING

Abstract

Automotive glazing has long been a factor which has frustrated and limited the freedom of automotive designers to embody their vision. The idealized initial design often must be changed and sometimes even radically altered due to the limitations on the shapes of glazing that can be produced due to the methods used to form the glazing. While sheet metal can be formed to just about any conceivable shape, glass is limited to relatively simple large radii cylindrical/spherical shapes. By means of a multi-stage forming method, it is possible to produce glazing with complex curvature, comprising small compound radii with excellent optical quality, that exceed the forming limits and dimensional accuracy of what has previously been possible.

Claims

1. A method for forming an automotive glazing with high complexity geometry, comprising the following steps: heating at least one glass layer to its forming temperature; bending the glass layer to the high complex geometry shape by not exceeding the maximum stress during pressing at which defects occur; and repeating the previous steps at least two times until the final shape of the high complexity geometry is achieved. repeating the previous steps n times until the final shape of the high complexity geometry is achieved, wherein n is at least two.

2. The method of claim 1, wherein the bending step is selected from any of the following group of technologies: gravity bending, full surface male or female press bending, vacuum assisted male or female press bending and the combination thereof.

3. The method of claim 1, wherein the maximum stress during pressing is 100 MPa.

4. The method of claim 1, wherein the bending step is carried out using different surface molds in each press bending stage.

5. The method of claim 1, wherein the automotive glazing forming steps are optimized by means of computer simulations such as FEA or CAD.

6. The method of claim 1, wherein the number of repetitions of the automotive glazing forming steps are calculated using computer simulations such as FEA or CAD.

7. The method of claim 1, wherein a ring type support is used to convey the glass through at least one stage of the method.

8. The method of claim 1, wherein the forming steps of the automotive glazing are assembled such that the glass exits each stage and enters the next stage without allowing the glass to cool to a temperature that is substantially below the glass transition range.

9. The method of claim 1, wherein the number of forming stages is n wherein n is an integer number greater than one and corresponds to the number of increments required to bend the glass to the design shape without exceeding 100 MPa during pressing.

10. The method of claim 8, wherein the number of forming stages n is at least three, more preferably at least four, more preferably at least five, more preferably at least six, more preferably at least seven.

11. The method of claim 1, wherein the automotive glazing is subjected to an annealed, heat strengthened or fully heat tempered process after carrying out all the heating and bending steps.

12. The method of claim 1, wherein the maximum stress at each bending step can be incremental but not exceeding 100 MPa.

13. The method of claim 1, wherein after repeating the stages n times, the formed glazing comprises the following features: at least one surface area of at least 1.5 square meters; a depth of bend of at least 100 mm; a minimum radius of less than 500 mm; and an additional portion with a radius in the direction perpendicular to the first portion with a minimum radius of curvature of less than 2,000 mm.

14. A method for forming an automotive glazing with high complexity geometry, comprising the following steps: a. heating at least one glass layer to its forming temperature; b. bending the glass layer to the high complex geometry shape by not exceeding the maximum stress during pressing at which defects occur; and repeating the bending step n times until the final shape of the high complexity geometry is achieved, wherein n is at least two.

15. The method of claim 12, wherein the repeating step further comprises reheating the glass layer prior to bending.

16. A vehicle glazing, comprising: 1. at least one glass layer having a high complexity geometry shape; wherein the at least one glass layer has at least one surface area of at least 1.5 square meters; wherein at least one glass layer has a depth of bend of at least 100 mm; wherein at least one glass layer has a minimum radius of less than 500 mm; and wherein at least one glass layer has an additional portion with a radius in the direction perpendicular to the first portion with a minimum radius of curvature of less than 2,000 mm.

17. The vehicle of claim 16, wherein the automotive glazing comprises a surface area in excess of 1.5 square meters, a depth of bend of at least 100 mm, and a radius of curvature less than 500 mm in one direction and less than 2,000 mm in the direction perpendicular to the smaller first minimum radius.

18. The vehicle glazing of claim 16, wherein the glazing is a laminated glazing comprising at least one glass layer and at least one plastic interlayer.

19. The vehicle glazing of claim 16, wherein the glazing is a laminated glazing comprising at least two glass layers and at least one plastic interlayer; said at least two glass layers having different thicknesses.

20. The vehicle glazing of claim 16, wherein the at least one glass layer is selected from the group of: soda-lime, aluminosilicate, lithium aluminosilicate, borosilicate, glass ceramics, and the combination thereof.

21. A vehicle glazing manufactured according to the method of claim 1.

Description

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

[0066] FIG. 1A shows a cross section of a typical laminated automotive glazing

[0067] FIG. 1B shows a cross section of a typical laminated automotive glazing with performance film and coating

[0068] FIG. 1C shows a cross section of a typical tempered monolithic automotive glazing

[0069] FIG. 2 is a flow chart illustrating the steps of the method.

[0070] FIG. 3 is a four-stage forming process.

[0071] FIG. 4A is an isometric view of a glazing produced by the method.

[0072] FIG. 4B is a front view of a glazing produced by the method.

[0073] FIG. 5A is a top view of a glazing produced by the method.

[0074] FIG. 5B is a side view of a glazing produced by the method.

[0075] FIG. 6A is a horizontal Section AA, running from the bottom A pillar tips, at 0, 20,30, 40, 50, 60, 70, 80, 90 and 100% of bend.

[0076] FIG. 6B shows the vertical centerline sections (Y=0) at 0, 20,30, 40, 50, 60, 70, 80, 90 and 100% of bend. The rear edge of the glazing is to the left looking at the figure.

[0077] FIG. 7A shows the horizontal Section B, in the transition from the windshield to the roof, at 0, 20,30, 40, 50, 60, 70, 80, 90 and 100% of bend.

[0078] FIG. 7B shows the vertical sections (Y=600) at 0, 20,30, 40, 50, 60, 70, 80, 90 and 100% of bend. The rear edge of the glazing is to the left looking at the figure.

[0079] FIG. 8 is an isometric view of the full surface at 40, 60, 80 and 100% of bend.

[0080] FIG. 9 is a side view of the full surface at 40, 60, 80 and 100% of bend.

[0081] FIG. 10 is a front view of the full surface at 40, 60, 80 and 100% of bend.

REFERENCE NUMERALS OF DRAWINGS

[0082] 2 Glass [0083] 4 Bonding/Adhesive layer (plastic Interlayer) [0084] 6 Obscuration/Black Paint [0085] 12 Infrared reflecting film [0086] 20 Infrared reflecting coating [0087] 24 Region of minimum compound curvature [0088] 26 Bounding Box/Depth of bend [0089] 28 Centerline cross bend [0090] 31 Constant X [0091] 32 Constant Y [0092] 33 Constant Z [0093] 40 Flat glass [0094] 41 10% of bend [0095] 42 20% of bend [0096] 43 30% of bend [0097] 44 40% of bend [0098] 45 50% of bend [0099] 46 60% of bend [0100] 47 70% of bend [0101] 48 80% of bend [0102] 49 90% of bend [0103] 50 100% of bend [0104] 51 Forming section 1 [0105] 52 Forming section 2 [0106] 53 Forming section 3 [0107] 54 Forming section 4 [0108] 61 Heating section 1 [0109] 62 Heating section 2 [0110] 63 Heating section 3 [0111] 64 Heating section 4 [0112] 71 Annealing zone [0113] 101 Exterior side of glass layer 1 (201), number one surface. [0114] 102 Interior side of glass layer 1 (201), number two surface. [0115] 103 Exterior side of glass layer 2 (202), number 3 surface. [0116] 104 Interior side of glass layer 2 (202), number 4 surface. [0117] 201 Outer glass layer [0118] 202 Inner glass layer

DETAILED DESCRIPTION OF THE INVENTION

[0119] The following terminology is used to describe the laminated glazing of the invention.

[0120] A glazing is an article comprised of at least one layer of a transparent material which serves to provide for the transmission of light and/or to provide for viewing of the side opposite the viewer and which is mounted in an opening in a building, vehicle, wall or roof or other framing member or enclosure.

[0121] Laminates, in general, are articles comprised of multiple layers of thin, relative to their length and width, material, with each thin layer having two oppositely disposed major faces, typically of relatively uniform thickness, which are permanently bonded to one and other across at least one major face of each layer. The layers of a laminate may alternately be described as sheets or plies. In addition, the glass layers may also be referred to as panes.

[0122] Laminated safety glass is made by bonding two layers, an exterior layer 201 and an interior layer 202 of annealed glass 2 together using a plastic bonding layer comprised of a thin sheet of transparent thermoplastic 4 (interlayer) as shown in FIG. 1A and 1B.

[0123] Annealed glass is glass that has been slowly cooled from the bending temperature down through the glass transition range. This process relieves any stress left in the glass from the bending process. Annealed glass breaks into large shards with sharp edges. When laminated glass breaks, the shards of broken glass are held together, much like the pieces of a jigsaw puzzle, by the plastic layer helping to maintain the structural integrity of the glass. A vehicle with a broken windshield can still be operated. The plastic layer 4 also helps to prevent penetration by objects striking the laminate from the exterior and in the event of a crash occupant retention is improved.

[0124] Typical automotive laminated glazing cross sections are illustrated in FIGS. 1A and 1B. In a laminate, the glass surface that is on the exterior of the vehicle is referred to as surface one 101 or the number one surface. The opposite face of the exterior glass layer 201 is surface two 102 or the number two surface. The glass 2 surface that is on the interior of the vehicle is referred to as surface four 104 or the number four surface. The opposite face of the interior layer of glass 202 is surface three 103 or the number three surface. Surfaces two 102 and three 103 are bonded together by the plastic layer 4. An obscuration 6 may be also applied to the glass. Obscurations are commonly comprised of black enamel frit printed on either the number two 102 or number four surface 104 or on both. The laminate may have a coating 20 on one or more of the surfaces. The laminate may also comprise a functional film 12 such as solar control film laminated between at least two plastic layers 4.

[0125] The types of glass that may be used include but are not limited to: the common soda-lime variety typical of automotive glazing as well as aluminosilicate, lithium aluminosilicate, borosilicate, glass ceramics, and the various other inorganic solid amorphous compositions which undergo a glass transition and are classified as glass included those that are not transparent. The glass layers may be comprised of heat absorbing glass compositions as well as infrared reflecting and other types of coatings.

[0126] For the purpose of this document, a stage corresponds to the set of steps required to complete a single heating and bending cycle. Rather than bending the glass to its final shape in a single stage, multiple heating/bending stages are used. During each stage the glass is at least partially formed. The stages are repeated until the final desired shape is achieved. The present disclosure can use different bending technologies combined in order to achieve the complex shapes by any bending process, for instance, may use a combination of gravity bending, full or partial surface male or female press bending and full or partial surface pressing with both a male and a female press.

[0127] FIG. 1C shows a typical tempered automotive glazing cross section. Tempered glazing is typically comprised of a single layer of glass 201 which has been heat strengthened. The number two surface 102 of a tempered glazing is on the interior of the vehicle. An obscuration 6 may be also applied to the glass. Obscurations are commonly comprised of black enamel frit printed on the number two 102 surface. The glazing may have a coating 20 on the number one 101 and/or number two 102 surfaces as shown in FIG. 1B.

[0128] The glass layers of a laminate glazing may be annealed or strengthened. There are two processes that can be used to increase the strength of glass. They are thermal strengthening, in which the hot glass is rapidly cooled (quenched) and chemical tempering which achieves the same effect through an ion exchange chemical treatment.

[0129] Heat strengthened, full temper soda-lime float glass, with a compressive strength in the range of at least 70 MPa, can be used in all vehicle positions other than the windshield. Heat strengthened (tempered) glass has a layer of high compression on the outside surfaces of the glass, balanced by tension on the inside of the glass which is produced by the rapid cooling of the hot softened glass. When tempered glass breaks, the tension and compression are no longer in balance and the glass breaks into small beads with dull edges. Tempered glass is much stronger than annealed laminated glass. The thickness limits of the typical automotive heat strengthening process are in the 3.2 mm to 3.6 mm range. This is due to the rapid heat transfer that is required. It is not possible to achieve the high surface compression needed with thinner glass using the typical blower type low pressure air quenching systems.

[0130] FIG. 2 shows a flow chart illustrating the steps employed by the method of the present disclosure. A first stage comprises a first step of heating the glass to the bending temperature and a second step of press bending the glass.

[0131] Rather than attempting to bend the glass to its final shape in a single stage as proposed by the prior art, the present disclosure partially forms the glass in at least two stages, each stage comprised by a heating and press bending steps. The process repeats the stage of two steps until the final shape is achieved. The number of heating and bending stages required is variable and denoted as n. A minimum number of stages n=two stages are required.

[0132] The number of stages required is determined through an iterative analysis of the stress generated by the bending. Assisted FEA/CAD code can be generated to calculate several surfaces, defining intermediate levels of bend between the flat and design shape. Using a FEA code, the stress is analyzed at each increment to find a surface that allows to partially bend the glass without exceeding 100 MPa at each forming stage which is the maximum level of stress a glass can withstand when pressed that would result in defects for breakage. This process is then repeated to find the next incremental surface until the final design shape is reached.

[0133] The stages are assembled such that the glass exiting each stage feeds into the next stage. In this manner, the hot glass exits each forming stage and is immediately conveyed into the heating section of the next stage. Advantageously, the heating pattern can be altered for each stage so as to optimize the viscosity of the glass for forming. In the second forming stage, the glass is again partially formed. The process repeats until the final design shape is achieved. The method requires at least two heating and bending stages. The heating and bending stages can be performed in inline sequential heating sections, such as those illustrated in FIG. 3, or can also be performed in a single chamber, so that the glass remains in the chamber, where the bending technique is adapted to incrementally change the shape of the glass.

[0134] In the flow chart, the number of stages is designated by the variable “n.” By repeating the heating and bending steps, the final otherwise infeasible shape may be achieved by approaching the final shape in increments where the material and process limits are not exceeded at any one stage.

[0135] The method of the invention may be practiced with any type of heating or bending means. The glass may be heated by convective, conductive, radiant, electromagnetic or any combination of heating means. Single or multiple glass layers may be simultaneously formed at each forming stage. The forming method may use the various methods known in the art of gravity bending, full surface and partial surface bending as well as combinations thereof. The bending method may further utilize vacuum and or pressure in conjunction with the other mentioned methods. The glass may be annealed, heat strengthened or fully heat tempered after the last forming stage.

[0136] In this manner, complex glazings such as one with a surface area in excess of 1.5 square meters and/or a depth of bend of at least 100 mm, and a radius of curvature less than 500 mm in one direction and less than 2,000 mm in the direction perpendicular to the smaller first minimum radius may be produced. Glazings which are substantially symmetrical, such as windshields, backlites and roofs may be produced by the method of the invention which have a centerline of symmetry cross bend of at least 100 mm.

DESCRIPTION OF EMBODIMENTS

Embodiment 1

[0137] A conceptual drawing of an embodiment with four stages is shown in FIG. 3. For the sake of simplicity, the pressing equipment is not shown, but should be noted that a male or female press bend may be used. Note that the Figure is not to scale and is only intended to illustrate the concept. A bending process for automotive glass is equipped with four inline sequential heating sections, 61, 62, 63 and 64, and four inline sequential bending sections, 51, 52, 53 and 54, as illustrated in FIG. 3. Each heating section is equipped with roof mounted resistive radiant heating elements divided into zones. The heating elements of each zone are further subdivided into multiple separately controlled circuits to allow for fine control of the temperature profile across the glass.

[0138] The glass is conveyed through the process on an articulated ring type mold enclosed in a movable insulated box. The boxes are sized to span one heating zone each. During operation, the boxes move through the heating portion. The boxes remain stationary for a period of time in each zone before being advanced to the next. In this manner the glass is heated to the bending or softening temperature and then moved to the next stage. In order to ensure the correct distribution of temperature to the glass, the bending temperature has been increased by 20° C. and then slightly cool down to press the glass. In this embodiment, the bending temperature was 600° C. where press was applied in each forming stage. The bending temperature is determined by the composition of the glass.

[0139] In this embodiment, each forming stage comprises at least a heating section and a full surface male press forming section. A variation of the present embodiment may comprise different surface molds for press bending the glass in each press bending stage. The hot glass is at least partially formed by each stage. The press surface mold is designed to form the glass without exceeding the physical limits of the glass which could result in defects, breakage, distortion or marking. The press surface mold is covered with a pliable material so as to not mark the glass. The face is also provided with holes connecting to a plenum in the back of the press which is used to apply vacuum during the bending process. The vacuum pulls the hot glass tightly to the press surface mold, eliminating the need for an opposite side female press.

[0140] The press mold shape and temperature profile for each stage is critical to the method. Computer simulation, FEA and CAD, is used to determine optimal parameters.

[0141] FIGS. 4 to 10 show various aspects of a glazing produced by the method of the invention. The glazing illustrated is a large complex symmetrical panoramic windshield where the top of the windshield has been extended to include a substantial portion of the roof.

[0142] With the four corners of the formed glazing in a plane, the depth of bend of the part is 260 mm. The area of the formed shape is 2.5 m.sup.2. The area denoted by the oval 24 in FIGS. 4A, 4B, 5A, is where the maximum stress and minimum radii occur. The minimum radius of the part is 400 mm. The direction of the minimum radius is horizontal or left to right from the drivers' viewpoint. In the direction perpendicular to the minimum radius (vertical or front to rear), the minimum radius is 1,000 mm.

[0143] Adding to the complexity, this part has a vertical centerline 28 (centerline of symmetry) cross bend of 150 mm. This part would be difficult if not impossible to economically produce by any other means.

[0144] To evaluate the feasibility of this part a set of 10 subsequent surfaces were simulated using FEA and CAD. Starting with the flat glass and ending with the final shape, surfaces representing increments of 10% in bending were produced. Section curves are shown in FIGS. 6A, 6B, 7A and 7B. Each of these sections are shown at 0, 20, 30, 40, 50, 60, 70, 80, 90 and 100% of bend (numerals 40, 42, 43, 44, 45, 46, 47, 48, 49 and 50). Starting with the flat surface, the stress required to achieve each percentage of bend was calculated but maintaining the stress levels in the glass at each stage below 100 MPa.

[0145] Based upon this result, 40% of the bend 44 was selected for the first bending increment. Using the 40% bending 44 as the next starting point and assuming zero strain resulting from the reheating, the analysis was repeated. 60% of the bending 46 was selected for the second bending increment. The calculations were then repeated a third and fourth time arriving at 80% of the bending 48 for the third increment. At each of the four bending increments, the compression is minimized and kept well below 100 MPa which is the critical level at which defects would be likely. The simulated surfaces can be seen in FIGS. 8, 9 and 10.

[0146] As the glass progresses through the bending process it approaches the final design shape, 100% of bend 50, each of which is obtainable without exceeding the limits of the process.

[0147] The maximum stress at each bending stage was incremental as of 50, 66, 70 and 70 MPa, well under the 100 MPa rule of thumb. It should be noted that each bending stage does not necessarily need to have an incremental value but can differ depending on the complexity of the shape required in each stage. Bending the flat glass to the final design shape in a single stage would generate maximum stress in excess of 300 MPa and not be successful, generating wrinkles resulting in the distortion of the glass and glass breakage.

[0148] Upon exiting the final stage, the glass enters a cooling section 71 where the glass may be annealed to release internal stresses.

Embodiment 2

[0149] A second embodiment not illustrated consists of seven stages. The bending process is equipped with seven sequential heating sections. Each section equipped with roof mounted resistive radiant heating elements divided into zones. The depth of bend is 290 mm, the area of the formed shape is 2.8 m.sup.2. The minimum radius of the part is 380 mm. The direction perpendicular to the minimum radius (vertical or front to rear), the minimum radius is 1,100 mm. The vertical centerline 28 (centerline of symmetry) cross bend of 190 mm.

[0150] The FEA and CAD simulations provided the following increment in shapes: first increment of 20% of the bending, the second increment of 40%, the third increment of 60%, the fourth increment of 65%, the fifth increment of 78%, the sixth increment of 91% and the seventh increment of 100%. The maximum stress at each bending stage was as of 40, 70, 55, 90, 40, 85 and 90 MPa. Upon exiting the final stage, the glass enters a cooling section 71 where the glass may be annealed to release internal stresses. In this embodiment, a single heating chamber may be used, allowing the use of different surface molds in each press bending stage.

[0151] It must be understood that the present disclosure is not limited to the embodiments described and illustrated, as it will be obvious for an expert on the art, there are different variations and possible modifications that do not strive away from the disclosure's essence, which is only defined by the following claims.