Laser-assisted glass bending process

Description

[0001] The invention relates to a method for bending glass sheets using a laser.

[0002] Vehicle glazing typically exhibits a bend. To create such a bend, the initially flat glass pane is heated to at least its softening temperature, typically using radiant heaters. The glass pane is then deformed in a one- or multi-stage process. Various bending methods are commonly used, such as gravity bending (also known as...). gravity bending or sag bending ), press bending or suction bending.

[0003] To ensure high optical quality of the glass pane, allowing for largely distortion-free viewing, so-called bending frames (also known as frame-like bending dies) are frequently used. Such a bending die does not contact the entire pane surface during bending, but only a peripheral edge area. However, there are limits to the degree of bending that can be achieved. In particular, pane shapes with local areas of strong curvature (small radii of curvature) and / or strong changes in curvature (high curvature gradient) that are relatively far from the edge of the pane are difficult or even impossible to produce.

[0004] To achieve such complex pane shapes, it is helpful to locally heat the affected areas to ensure greater formability of the pane. This is relatively easy to achieve with discontinuous bending processes. In such bending processes, known, for example, from EP 1 358 131 A1 and EP 2 463 247 A1, the glass pane is typically supported on a transport form and remains in one position, including in the heating oven, for a relatively long time, one or more times during the bending process. There, a desired temperature profile can be generated on the glass pane by precisely designing the heating elements. These elaborate discontinuous bending processes are particularly common for high-quality laminated glass such as windshields.

[0005] However, continuous bending processes also exist, which are carried out at a significantly higher rate, particularly for single-pane safety glass such as side or rear windows. In these processes, the glass pane is continuously moved through the bending device, especially on a roller conveyor system, without pausing at any point. These processes offer the glass manufacturer considerably fewer opportunities to influence the heating of the glass pane and to create a specific temperature profile. For example, WO 2017 / 178733 A1 discloses such a bending process.

[0006] German patent DE102007012146A1 discloses a bending process for glass articles in which the areas of the glass to be bent are heated by a laser and then deform under the influence of gravity. A bending die is not used; instead, the desired shape is achieved by selective heating of the glass article. Such a process requires long cycle times and is therefore unsuitable for industrial mass production.

[0007] US2018297886A1 discloses a device in which a glass pane is heated over its entire surface by means of laser radiation between a heating oven and a bending oven in order to prevent the glass pane from cooling down before bending.

[0008] DE102006035555A1 and WO2019179842A1 disclose methods in which a glass pane is preheated by means of a heating medium to a temperature below the softening temperature and subsequently a partial area of ​​the glass pane is heated by means of laser radiation above the softening temperature in order to be able to bend this partial area locally.

[0009] US2016031737A1 and DE102007012146A1 disclose methods in which a glass pane is heated to softening temperature exclusively by means of laser radiation, in order to subsequently be shaped without the influence of an external pressure by a contact medium, but purely due to the effect of gravity.

[0010] Therefore, there is a need for improved bending processes that allow the glass pane to be heated according to a specific temperature profile before bending, in order to achieve complex pane geometries. The present invention aims to provide such a bending process. The bending process should be suitable for industrial mass production and, in particular, capable of continuous operation.

[0011] The object of the invention is achieved according to the invention by a method for bending a glass sheet according to the independent claim. Preferred embodiments and configurations are described in the dependent claims.

[0012] The device for bending a glass pane comprises at least one, and in particular several, heating elements for heating the glass pane to be bent and a contact element for shaping (in particular bending) the glass pane. The heating elements are suitable for heating the glass pane substantially uniformly, as is common with conventional bending devices. Uniform heating is understood to mean heating in such a way that the entire main surface of the glass pane is exposed to essentially the same temperature, without creating a pronounced temperature profile. The contact element is suitable for influencing the shape of the heated glass pane by direct contact in order to bend it into the desired geometry. The device according to the invention also comprises at least one laser.The laser is suitable and intended to further increase the temperature of at least one area of ​​the glass pane after the glass pane has been heated with the heating medium and before the glass pane is bent, i.e., before the shape of the glass pane is influenced by the contact medium.

[0013] In the inventive method for bending a glass sheet, the glass sheet is first heated substantially uniformly by a heating medium. The glass sheet is thereby heated to at least its softening temperature, at which point the glass enters a malleable state. Subsequently, the temperature of at least one area of ​​the glass sheet is further increased by means of a laser. The glass sheet is then bent into the desired shape by means of a contact medium; that is, the shape of the glass sheet is influenced by the contact medium.

[0014] The apparatus and the method are presented together below, with explanations and preferred embodiments applying equally to both. If preferred features are described in connection with the method, it follows that the apparatus is also preferably designed and suitable accordingly. Conversely, if preferred features are described in connection with the apparatus, it follows that the method is also preferably carried out accordingly.

[0015] The invention is based on selectively heating areas of the glass pane with a laser beyond the temperature achieved with the heating medium, thereby increasing their malleability. In principle, the entire pane can be heated with a single laser or multiple lasers, which can be advantageous for certain applications. However, according to the invention, only a specific area or areas of the glass pane are heated locally with the laser to raise their temperature above that of the rest of the pane. These areas are particularly those where the glass pane is intended to have a pronounced curvature, i.e., particularly small radii of curvature, and / or where significant changes in curvature, i.e., a high curvature gradient, are desired. The additional local heating provides these areas with increased malleability, making it easier to create the desired curvatures.This is a major advantage of the present invention. For certain applications, the invention also allows for a reduction in the bending temperature (provided by the heating element), which is selected to be just high enough to achieve maximum curvature across most of the disk, while more highly curved areas are achieved through local additional heating by the laser. Since a lower bending temperature results in better optical quality of the disk, the quality of most of the transparent area can be improved by the invention. If a thermal prestressing process follows the bending process, a higher prestress can also be achieved locally by the additional heating from the laser, if desired. During thermal prestressing, the heated disk is rapidly cooled by means of an airflow, with the degree of prestress depending significantly on the initial temperature.These are further advantages of the present invention.

[0016] The contact element acts on the heated glass pane through direct contact, thereby bending the glass pane. In particular, the glass pane is adapted to the shape of the contact element. In one embodiment of the invention, the contact element is designed as at least one bending element. However, the contact element can also be designed as a roller conveyor, i.e., as an arrangement of opposing rollers that describe a curved path and between which the glass pane is conveyed. During its passage through the roller conveyor, the glass pane is adapted to the shape of the curved path.

[0017] In particular, contact elements are used that exert pressure on the glass pane to deform it. The contact element is preferably a press bending die, a suction bending die, or a roller conveyor.

[0018] The glass pane to be bent is typically flat in its initial state. It is heated by means of the heating elements and the laser and then bent using the contact medium. According to the invention, the fact that the laser irradiation is carried out after heating with the heating elements does not mean that the heating elements must cease functioning when the laser irradiation begins. The pane is first heated with the heating elements and then (locally) brought to an even higher temperature by the laser radiation. This can be achieved in various ways. For example, the heating elements and the laser can act on the glass pane simultaneously throughout the entire process; the laser radiation can begin with a delay compared to the heating elements, while the heating elements continue to function; or the effect of the heating elements can already be complete when the laser radiation begins.

[0019] The glass pane has two opposing main surfaces designed for transparency and a circumferential edge extending between these main surfaces. The heating elements act essentially uniformly and across the entire surface of at least the two main surfaces of the glass pane, in particular by means of thermal radiation or convection. The heating elements are, in particular, those also used in conventional bending devices. For example, the heating elements can be designed like a convection oven, in which heated air is supplied to a heating chamber, thereby heating the glass pane within the chamber. Typically, however, the heating elements are designed as radiant heaters.Preferably, at least one, and in particular several, radiant heaters are assigned to and directed towards one main surface of the glass pane, and likewise at least one, and in particular several, radiant heaters are assigned to and directed towards the other main surface. The main surfaces are exposed to heat radiation by the radiant heaters assigned to and directed towards them, thereby heating the glass pane. Advantageously, the glass pane is transported horizontally on a transport device into a heating chamber, where the radiant heaters are arranged above and below the transport device to act on both main surfaces.

[0020] The glass pane is heated by the heating medium(s) to at least its softening temperature. Preferably, the glass pane is heated above its softening temperature by the heating medium(s). The softening temperature is the glass transition temperature at which the glass transitions from the brittle, energy-elastic region to the soft, entropy-elastic region. Upon reaching the softening temperature, the glass pane becomes plastically deformable. The entire glass pane is thus heated, making it plastically deformable. This can also be described as a volumetric heating of the glass pane.

[0021] In one embodiment, at least one bending die is used as a contact element for bending the glass pane. All types of bending dies commonly used in conventional bending devices can be employed. A bending die has an effective surface that comes into contact with the glass pane and acts to shape it, adapting it to the shape of the effective surface and thereby bending it. The effective surface is suitable for influencing the shape of the glass pane. The effective surface can also be referred to as a bearing surface or contact surface. The effective surface determines the shape of the bent glass pane. The effective surface can be in direct contact with the glass pane. However, the effective surface can also be, for example, covered with a fabric that is positioned between the actual effective surface and the glass pane.

[0022] The working surface can be solid or frame-like. A solid bending form or working surface can also be described as solid and is in contact with a large portion of the glass pane at the end of the bending step. The solid working surface can be equipped with holes or openings through which a suction effect can be exerted on the surface of the glass pane facing the working surface. In this case, the device also includes means for generating a suction effect that are connected to the working surface, for example, Venturi nozzles, fans, or pumps. A frame-like bending form or working surface can also be described as a ring (bending ring) or frame (frame shape). The working surface is designed in the form of a complete or interrupted frame.Only a small portion of the glass pane's surface is in contact with the frame-like working surface during bending, while the majority of the pane has no direct contact with the tool. This allows for the production of panes with exceptionally high optical quality. The area of ​​the glass pane in contact with the working surface is typically its circumferential edge, but the glass pane can also extend beyond the working surface.

[0023] In a particularly advantageous embodiment, at least one frame-like bending die (bend die with a frame-like working surface) is used. Complex bends away from the peripheral edge region are difficult to produce with such dies because the shaping possibilities are limited without direct contact with the working surface. Therefore, the advantages of the invention become particularly apparent with the additional heating by the laser in conjunction with frame-like bending dies. The frame-like bending die is, in particular, a frame-like press bending die.

[0024] The working surface of a bending die can be convex, concave, or a combination of both. A concave shape is defined as one in which the corners and edges of the glass pane, when in contact with the working surface, are bent away from the bending die. Conversely, a convex shape is defined as one in which the corners and edges of the glass pane, when in contact with the working surface, are bent towards the bending die. A predominantly concave working surface may also have convex areas, and vice versa.

[0025] The glass pane is typically transported horizontally through the bending device. The at least one bending die can then be an upper or a lower bending die. For the purposes of the invention, a lower bending die is understood to be a die that touches or is associated with and acts upon the lower surface of the glass pane, the surface facing the ground. Typically, at the beginning of the bending step, only a portion of the effective surface is in contact with the glass pane, and the glass pane conforms to the effective surface during the bending step. This can occur under the influence of gravity, pressure, or suction.

[0026] An upper bending die is a form that is assigned to and acts upon the upper surface of the glass pane, the surface facing away from the ground. The glass pane is blown and / or suctioned against the effective surface of the upper bending die by the transport device, or pressed against the upper bending die by a tool, such as a lower bending die. The upper bending die can be stationary or lower itself to receive or press the glass pane.

[0027] In principle, all common bending dies can be used. The bending die (or one of the bending dies, if several are used) can, for example, be a gravity bending die. A gravity bending die is a lower bending die onto which the glass pane is placed, whereupon it bends against the working surface under the influence of gravity. The working surface is typically and preferably frame-like, but can also be a solid surface.

[0028] In a preferred embodiment, the bending die (or one of the bending dies, if several are used) is an upper bending die, at whose effective surface the glass pane is blown and / or drawn by the transport device. Particularly short cycle times can be achieved with such bending dies. The effective surface is preferably a solid surface, but can also be frame-like.

[0029] In a particularly preferred embodiment, the device comprises an upper bending die and a lower bending die, between which the glass sheet is pressed for bending (press bending). The upper bending die preferably has a solid working surface, but can also have a frame-like working surface. The lower bending die preferably has a frame-like working surface, enabling the bending of glass sheets with high optical quality. In an advantageous embodiment, the glass sheet is blown and / or suctioned onto the working surface of the upper bending die by the transport device. The device then also includes means for moving the lower and upper bending dies relative to each other, for example, cylinders, actuators, a chain hoist system, or a robot arm, with which the upper bending die can be lowered and / or the lower bending die raised.

[0030] The device is preferably equipped with transport means for moving the glass pane. These transport means serve to move the glass pane to be bent to the heating elements, the laser, and the bending die. In a preferred embodiment, the transport means are designed as a roller conveyor system or belt conveyor system, on which the glass pane rests directly and is moved horizontally. This allows for particularly short cycle times. Alternatively, the glass pane can also be supported on a transport form, in particular a form with a frame-like support surface, which in turn is moved, for example, by means of a roller, belt, or rail conveyor system.

[0031] In a preferred embodiment, the transport means are designed as a continuous conveying system, particularly preferably a continuous roller conveyor system. In such a conveying system, the glass sheet is continuously moved through the device towards the bending die without remaining in one position for any extended period. The glass sheet is fed to the heating elements and the bending die in a continuous motion by means of the continuous conveying system. The glass sheet is heated by the heating elements during this continuous movement. The heating elements, in particular radiant heaters, are preferably arranged above and below the rollers of the roller conveyor system and directed towards the roller conveyor system so that they act simultaneously on both main surfaces of the glass sheet, thereby achieving efficient heating of the glass sheet.In such a continuous process, the advantages of the invention are particularly evident because the continuous movement offers limited possibilities for generating a desired temperature profile on the glass pane through the design and / or operation of the heating elements. This can then be achieved through the heating process according to the invention using the laser. Continuous roller conveyor systems are particularly common in the bending of relatively inexpensive tempered safety glass, for example, for side, roof, or rear windows of vehicles. The conveying speed of the continuous conveyor system is preferably from 100 mm / s to 600 mm / s. However, the invention can also be used in principle for non-continuous bending devices in which the movement of the glass pane is interrupted and the glass pane remains in one position for an extended period of time, particularly for heating with the heating elements, or is moved back and forth.Instead of a continuous roller conveyor system, a continuous belt conveyor system can also be used. The conveyor system can also be designed entirely or partially as an air cushion conveyor system.

[0032] The time between heating the glass pane with the laser and bending it with the contact medium should be kept to a minimum to minimize the time the glass pane has to equalize temperature, which would otherwise cause the laser-heated areas to cool down again. The time between the end of the laser irradiation and the start of the bending process by the at least one bending device is preferably at most 10 s (for example, from 1 s to 10 s), and particularly preferably at most 5 s (for example, from 1 s to 5 s).

[0033] The glass pane is preferably heated by the heating medium to a temperature of 500 °C to 700 °C, particularly preferably from 550 °C to 670 °C, for example, approximately 650 °C. This corresponds to typical bending temperatures for glass panes, especially those made of soda-lime glass. The laser preferably increases the temperature of the irradiated areas by at least 5 °C, particularly preferably by at least 10 °C, most preferably by at least 15 °C, and particularly preferably by at least 20 °C. Smaller temperature increases can already offer advantages with regard to prestressing if the pane is thermally prestressed after bending. Larger temperature increases are particularly advantageous with regard to improved formability, which allows for the realization of more complex bent shapes.

[0034] In one embodiment of the invention, the heating elements are arranged in a heating chamber, and the contact element for forming the glass sheet (in particular, a bending die or several bending dies) is located in a bending chamber. The heating chamber and bending chamber are separated from each other and (largely) sealed off from the surroundings by a chamber wall. The transport elements pass through the heating chamber and lead into or through the bending chamber. The glass sheet is transported into and out of the heating chamber by the transport elements. Preferably, the inlet and outlet of the heating chamber are located on opposite sides, so that the glass sheet is transported through the heating chamber by the transport elements. Subsequently, the glass sheet is transported into the bending chamber and transferred to the contact element.After bending, the glass pane can be placed back onto the transport vehicles for removal from the bending chamber, or transported from the bending chamber by other means. Both the heating and bending chambers have openings for transporting the glass pane. At least in the heating chamber, the openings are preferably slot-shaped with the smallest possible height to prevent excessive cooling of the chamber. The openings can optionally be closed with a sliding door or curtain system when no glass pane is being transported through them.

[0035] In this embodiment, the at least one laser is preferably arranged outside the heating chamber and outside the bending chamber. The laser can be directed into the heating chamber, into the bending chamber, or between the heating chamber and the bending chamber, and irradiate the glass pane there once it has been moved to the appropriate position by the conveying system. If the laser is directed into a chamber, the chamber wall must, of course, have an opening for the laser radiation, i.e., an area that is largely transparent to the laser radiation. Optionally, the opening can be closed, for example, with a glass pane that exhibits the lowest possible absorption of the laser radiation. Alternatively, the opening can simply be formed by a break in the chamber wall, which can optionally be closed, for example, by a sliding door when no laser irradiation is taking place.

[0036] In a further embodiment of the invention, the heating element and the contact element (in particular a bending die or several bending dies) are arranged in a common chamber, which is referred to as a combined heating and bending chamber. The combined heating and bending chamber is (largely) sealed off from the surroundings by a chamber wall. The transport elements lead into or pass through the heating and bending chamber. The glass sheet is transported into the heating and bending chamber by the transport elements. There, the glass sheet is first exposed to the heating element and then transferred to the contact element. After bending, the glass sheet can be placed back onto the transport elements to transport it out of the heating and bending chamber, or it can be transported out of the heating and bending chamber by other means. The heating and bending chamber has openings for transporting the glass sheet.The openings can optionally be closed with a sliding door or curtain system when no glass pane is being transported through the opening.

[0037] In this embodiment, the at least one laser is preferably arranged outside the combined heating and bending chamber and directed into it, irradiating the glass pane once it has been moved to a suitable location by the conveying system, preferably a location between the heating elements and the at least one bending die. Here, too, the chamber wall must naturally have an opening for the laser radiation, which can optionally be closed, for example, with a glass pane exhibiting minimal absorption of the laser radiation. Alternatively, the opening can simply be formed by a break in the chamber wall, which can optionally be closed, for example, by a sliding door when no laser irradiation is taking place.

[0038] If the laser is directed into the bending chamber or the combined heating and bending chamber, in an advantageous embodiment it can be directed at the contact medium in such a way that it heats the glass pane when it is already in contact with the contact medium. This minimizes the time between laser heating and bending.

[0039] In principle, any laser suitable for heating the glass pane can be used for the invention. Lasers with a radiation wavelength for which the glass pane has a high absorption coefficient are particularly suitable. If the glass pane is not highly tinted or colored, as is common for window glazing, wavelengths in the mid-infrared range are especially suitable. The laser radiation preferably has a wavelength of 500 nm to 20 µm, more preferably 1000 nm to 15 µm, and particularly preferably 5 µm to 15 µm. A CO₂ laser, typically with a wavelength of 9.4 µm or 10.6 µm, is particularly suitable. However, a diode laser or a solid-state laser (for example, an Nd:YAG laser) can also be used.

[0040] The laser is preferably used in continuous wave (CW) mode. continuous wave) operated. It has been shown that this achieves good heating of the glass pane. Furthermore, continuous operation is technically easier to implement than pulsed operation. Alternatively, pulsed operation of the laser is also possible.

[0041] The laser is preferably operated with an output power of at least 1 kW to ensure effective heating of the glass pane. The output power is preferably between 1 kW and 10 kW.

[0042] The extent of the laser radiation ("area of ​​the laser spot") on the glass pane is advantageously at least 1 mm², preferably from 1 mm² to 10,000 mm², particularly preferably from 100 mm² to 2,500 mm², and most preferably from 400 mm² to 1,000 mm². Within this range, the laser radiation is sufficiently concentrated to effectively heat the glass pane and sufficiently extensive to heat a suitable area simultaneously. The desired laser spot can be adjusted in the laser beam path using suitable optics, in particular lenses or objectives, for example, f-theta lenses or f-theta objectives, or polygon scanners. Other elements can also be arranged in the beam path, such as optical waveguides (like fiber optics), collimators, apertures, or optical filters.

[0043] In a preferred embodiment, the laser is equipped with a laser scanning system to move the radiation across the glass pane. If the area of ​​the glass pane to be heated is larger than the laser spot, the laser radiation can be moved across the entire area to heat it. Furthermore, different types of glass panes can be bent using the same device without complex modifications to the laser system – the laser radiation is simply positioned at the required location using the laser scanning system. The laser scanning system can be designed for one-dimensional (along one spatial direction) or two-dimensional (along two mutually orthogonal spatial directions) movement of the laser radiation. A one-dimensional laser scanning system typically includes a mirror that can be tilted in one direction to move the radiation.A two-dimensional laser scanning system comprises a mirror that can be tilted in two directions (preferably orthogonal to each other), or (preferably) two mirrors, each of which can be tilted in one direction, wherein these two directions are different (preferably orthogonal to each other). The speed at which the laser radiation is moved across the glass pane is preferably at least 10 m / s in order to effectively heat the glass pane.

[0044] The device can be equipped with means that allow the working distance between the laser scanning system and the glass pane to be adjusted. This can be achieved, for example, by mounting the laser scanning system on a movable axis or by using a three-dimensional scanner.

[0045] If the device is designed for a continuous bending process, in which the glass sheets are continuously moved under the laser radiation, a one-dimensional laser scanning system is sufficient, the scanning direction of which is preferably transverse, and in particular orthogonal, to the direction of movement of the glass sheet. The laser radiation can then be moved orthogonally to the direction of movement of the glass sheet (direction of travel of the transport means) in order to cover and irradiate the entire width of the area to be heated. The entire area to be heated is exposed to the laser radiation by the advancement of the transport system of the glass sheet.

[0046] The device can include more than one laser. If the glass pane has several separate areas that are to be heated by laser radiation, each area is preferably assigned its own laser. The desired heating can thus be achieved more quickly than if a single laser had to be moved across the multiple areas.

[0047] It is sufficient to irradiate the glass pane with laser radiation from one side. However, two opposing lasers can also be used, irradiating both main surfaces of the glass pane simultaneously.

[0048] In an advantageous embodiment, only a single glass pane is heated and bent by the laser at any one time. However, the device can also be used for processes in which two (or more) superimposed glass panes are bent simultaneously, as is sometimes the case in the production of laminated glass. However, several superimposed glass panes are less effectively heated by the laser than a single pane. It is readily possible, however, to move several glass panes directly or staggered side by side on a continuous conveyor system, whereby the multiple glass panes are heated simultaneously by the heating medium and then further heated by laser radiation, either simultaneously by their own separate lasers or sequentially by the same laser.

[0049] In a preferred embodiment, the glass pane is thermally tempered after bending, as is common practice in the production of tempered safety glass. For this purpose, the glass pane is placed on a support form with a frame-like bearing surface (tempering frame). Preferably, the pane is placed directly from a bending die, particularly an upper bending die. The device is therefore preferably equipped with means for moving a tempering frame beneath the upper bending die. On the tempering frame, the glass pane is removed from the bending chamber and fed into a tempering device. Alternatively, the glass pane can also be transferred to the tempering frame after leaving the bending device. However, the additional time required for this would result in the glass pane cooling down in the interim, which reduces the tempering effect.For thermal tempering, the surfaces of the still-heated glass pane are exposed to a gas stream and thus cooled rapidly (quenched). This creates a characteristic stress profile in the glass pane (compressive stresses on the surfaces, tensile stresses in the core), which improves the glass's fracture resistance. Furthermore, in the event of breakage or penetration of the central tensile stress zone by a sharp object, the glass pane shatters into very small fragments, posing only a minimal risk of injury.

[0050] In a particularly preferred embodiment, the transport means are designed as a continuous roller conveyor system. The heating elements are designed as radiant heaters arranged above and below the rollers in a heating chamber or a combined heating and bending chamber. The glass sheet is continuously moved between the radiant heaters by the roller conveyor system and fed to an upper bending die, preferably with a full-surface working area, which is arranged either in a separate bending chamber or in the combined heating and bending chamber above the rollers. If the glass sheet is positioned below the upper bending die, it is blown (by an airflow from below) and / or drawn against the upper bending die.A lower bending die with a frame-like working surface is then moved beneath the upper bending die holding the glass pane. The glass pane is pressed between the upper and lower bending dies to bend it into the desired shape. The lower bending die is then removed, while the glass pane remains fixed to the upper bending die by blowing and / or suction. A tempering frame is then moved beneath the upper bending die holding the glass pane, and the glass pane is transferred to the tempering frame by switching off the blowing or suction action. The glass pane is then removed from the bending chamber or the combined heating and bending chamber on the tempering frame and fed into a tempering device, where it is cooled and thermally tempered by an airflow.

[0051] In a preferred embodiment, the glass panes to be bent are made of soda-lime glass, as is common for window panes. However, the glass panes to be bent can also be made of other types of glass, such as borosilicate glass or quartz glass. The thickness of the glass pane is typically from 0.2 mm to 10 mm, preferably from 0.5 mm to 5 mm. In an advantageous embodiment, the glass pane has a thickness of at least 2 mm, for example, from 2 mm to 5 mm. In a preferred embodiment, the bent glass pane is intended as a window pane of a vehicle, in particular as a side window or rear window of a motor vehicle.

[0052] The invention is particularly suitable for bending glass panes with complex curvatures that are difficult to produce using conventional methods. Such complex curvatures can be characterized, for example, by areas with small radii of curvature or with significant changes in curvature, especially when frame-like bending dies are used and these areas are located far from the side edges of the glass pane. In an advantageous embodiment, the bent glass pane therefore has at least one area with radii of curvature less than 800 mm. These radii of curvature preferably occur at a distance of at least 100 mm from the side edges of the glass pane. That is, the areas with strong curvature are at least partially located in a region of the glass pane that is at least 100 mm away from the side edges of the glass pane.The area can be a transparent section of the glass pane or made opaque, for example, by a printed overlay. The areas with high curvature are those that are additionally heated by the laser. The size of the laser-irradiated area and the temperature change required to achieve the desired bend can be determined by a specialist through simulations.

[0053] The invention comprises the use of a laser for the local heating of glass panes in glass bending processes. In this process, an area of ​​a glass pane that has been preheated substantially uniformly by means of a heating medium is further heated by the laser radiation before the glass pane is bent using at least one bending die.

[0054] The invention is explained in more detail below with reference to a drawing and exemplary embodiments. The drawing is a schematic representation and not to scale. The drawing does not limit the invention in any way.

[0055] They show: Fig. 1 shows a cross-section through an embodiment of the device during a first part of the method according to the invention, Fig. 2 shows a cross-section through the device made of Fig. 1 during a subsequent second part of the method according to the invention, Fig. 3 shows a cross-section through a further embodiment of the device, Fig. 4 shows a cross-section through a glass pane bent according to the invention, and Fig. 5 shows a top view of the glass pane made of Fig. 4 .

[0056] Figure 1 shows a device during a first part of a method according to the invention for bending a glass pane I.

[0057] The device comprises a heating chamber 1 in which heating elements 4, designed as radiant heaters, are arranged. The device also comprises a bending chamber 2 in which an upper bending die 5 is installed. The bending die 5 has a fully convex working surface. The device also comprises a roller conveyor system 8 that extends through the heating chamber 1 and into the bending chamber 2. The device also comprises a laser 10 (CO₂ laser, 10.6 µm, continuous wave operation) that is directed between the heating chamber 1 and the bending chamber 2 onto the roller conveyor system 8.

[0058] The initially flat glass pane I is positioned directly on the roller conveyor system 8 and moved in a continuous motion (coming from the left in the illustration) into the heating chamber 1, through it, and then into the bending chamber 2. In the heating chamber 1, the glass pane I is heated essentially uniformly by the heating medium 4, for example to a temperature of approximately 650 °C ( Fig. 1a The heating elements 4 are arranged in the heating chamber 1 above and below the roller conveyor system 8 in order to irradiate both surfaces of the glass pane I simultaneously.

[0059] Between heating chamber 1 and bending chamber 2, an area of ​​the glass pane I is irradiated by the laser 10 ( Fig. 1bThe area of ​​the glass pane I is thereby further heated, for example by 20 °C. This gives it a special flexibility. The radiation S of the laser 10 can be moved orthogonally to the conveying direction of the roller conveyor system 8, for example by a laser scanning system (not shown), thus covering the entire width of the area. The feed of the roller conveyor system 8 ensures that the area enters the effective range of the laser 10 along its entire length. This ensures that the entire area of ​​the glass pane I to be heated is exposed to laser radiation S. The conveying speed of the roller conveyor system is, for example, 450 mm / s, and the scanning speed of the laser radiation S is, for example, 10 mm / s. The output power of the laser 10 is, for example, 5 kW, and the extent of the laser radiation S on the glass pane I is, for example, 625 mm².

[0060] After irradiation by the laser 10, the glass pane I is transported by the roller conveyor system 8 into the bending chamber 2 until it reaches below the bending die 5 ( Fig. 1c ).

[0061] The device is designed for a continuous bending process. It can transport the next glass sheet to be bent into the heating chamber as soon as the previous glass sheet I has arrived in the bending chamber 2, although this is not shown for the sake of simplicity. The distance between successive glass sheets I depends in particular on the cycle time of bending into the bending chamber 2.

[0062] As an alternative to the configuration shown, the laser can also be directed into heating chamber 1 or bending chamber 2. Heating chamber 1 and bending chamber 2 must each have a window or opening that is transparent to the laser radiation.

[0063] Figure 2 The device shows Fig. 1during a second part of the proceedings, continuing the Fig. 1 The glass pane I is blown onto the upper bending die 5 by an airflow passing from below through the rollers of the roller conveyor system 8, which is supported by a suction effect through openings in the effective surface of the bending die 5 ( Fig. 2a ). Now, by means of a chain pull system or movable cylinders, a lower bending die 6 is moved under the upper bending die 5 and the glass pane I is pressed between the upper bending die 5 and the lower bending die 6 ( Fig. 2bFor this purpose, the upper bending die 5 is lowered onto the lower bending die 6 with the glass pane I. The lower bending die 6 has a frame-like concave working surface that is complementary to the convex working surface of the upper bending die 5. By pressing between the bending dies 5 and 6, the glass pane I is bent into the desired shape. Subsequently, the lower bending die 6 is removed, and a tempering frame 7 with a frame-like support surface is moved under the glass pane I. By interrupting the blowing and suction action, the glass pane I is released from the upper bending die 5 and placed on the tempering frame 7. Fig. 2c The glass pane I is subsequently removed from the bending chamber with the prestressing frame 7 and fed to a prestressing device, where it is thermally prestressed by rapid cooling using a strong gas flow, in particular an air flow.

[0064] Figure 3shows a further embodiment of the device. In contrast to the embodiment of the Figure 1 and 2 The device has heating chamber 1 and bending chamber 2, which are separate from each other. Instead, the heating element 4 and the bending die 5 are arranged in a combined heating and bending chamber 3. The heating element 4 is positioned upstream of the bending die 5 in the conveying direction of the roller conveyor system 8, so that the glass pane I first passes through the heating element 4 before reaching the bending die 5. The laser 10 is located outside the combined heating and bending chamber 3 and directed into it. The radiation S of the laser 10 enters the heating and bending chamber 3 through a transparent window or opening, where it strikes the glass pane I. The heating element 4, bending die 5, and laser 10 are arranged as shown in Fig. 1 designed.

[0065] Figure 4 and Figure 5Figure 1 shows a glass pane I with a complex curvature that can be realized using the method according to the invention. The glass pane I has two sections B that are strongly curved and also characterized by a significant change in curvature. The minimum radius of curvature is 150 mm. Outside of section B, the glass pane I is less strongly curved with radii of curvature typical for vehicle glazing. Since section B extends over the viewing area of ​​the glass pane I and is therefore not contacted by the frame-like lower bending form 6, the complex shape is difficult to produce using conventional methods. While the shape could be achieved with a full-surface lower bending form 6, this would significantly reduce the optical quality of the glass pane I.

[0066] According to the present invention, the sub-areas B are additionally heated by the laser 10, thereby increasing their malleability. The complex shape can now also be achieved with the frame-like lower bending form 6. Example

[0067] A glass pane I (soda-lime glass, 4 mm thick) as in the Figures 4 and 5 The bending process was shown and described using a device as shown in the Figure 1 and 2 The process was illustrated and described. Subsequently, the maximum absolute deviation Δx of the actual disc shape from the desired geometry was determined. For the comparison example, the same device was used, but without the laser 10. Otherwise, the same bending dies 5, 6 and the same settings were used. Table 1 Δx Example 3.3 mm Comparative example 6.5 mm

[0068] Table 1 shows that the inventive method with local laser irradiation led to a significantly improved bending: the deviations from the desired geometry were significantly smaller than in the comparison example. This result was unexpected and surprising for the person skilled in the art. Reference symbol list:

[0069] (1) Heating chamber (2) Bending chamber (3) Combined heating and bending chamber (4) Heating medium (5) Bending die / upper bending die (6) Lower bending die (7) Pre-tensioning frame (8) Roller conveyor system (10) Laser (I) Glass pane (S) Laser radiation 10 (B) Partial area of ​​the glass pane I

Claims

1. Method for bending a glass pane (I), comprising the following steps: (a) Heating a glass pane (I) substantially uniformly by means of heating means (4) to at least its softening temperature, (b) Further locally increasing the temperature only in one or more partial areas (B) of the glass pane (I) by means of a laser (10), (c) Bending the glass pane (I) by means of a contact means for shaping the glass pane (I).

2. Method according to claim 1, wherein the time span between process steps (b) and (c) is at most 10 seconds, preferably at most 5 seconds.

3. Method according to claim 1 or 2, wherein the temperature of the one or more partial areas (B) is increased by at least 5 °C in process step (b), preferably by at least 15 °C.

4. Method according to one of claims 1 to 3, wherein the glass pane (I) is fed to the heating means (4) and the contact means in a continuous movement by means of a roller conveyor system (8) or belt conveyor system.

5. Method according to claim 4, wherein the radiation of the laser (4) is moved with a laser scanning system transversely, preferably orthogonally, to the conveying direction of the roller conveyor system (8) or belt conveyor system in order to irradiate the entire width of the partial area (B).

6. Method according to one of claims 1 to 5, wherein the one or more partial areas (B) of the glass pane (I) are provided with a radius of curvature of less than 800 mm in process step (c).

7. Method according to claim 6, wherein at least one bending mould (5, 6) with a frame-like effective surface is used and wherein the said radius of curvature occurs at a distance of at least 100 mm from the side edges of the glass pane (I).

8. Method according to one of claims 1 to 7, wherein the heating means (4) are arranged in a heating chamber (1) and the contact means for forming the glass pane (I) are arranged in a bending chamber (2); and wherein the laser (10) is arranged outside the heating chamber (1) and outside the bending chamber (2) and is directed into the heating chamber (1), into the bending chamber (2) or between the heating chamber (1) and the bending chamber (2).

9. Method according to one of claims 1 to 7, wherein the heating means (4) and the contact means for forming the glass pane (I) are arranged in a combined heating and bending chamber (3); and wherein the laser (10) is arranged outside the heating and bending chamber (3) and is directed into the heating and bending chamber (3).

10. Method according to one of claims 1 to 9, wherein the laser (10) has an emission wavelength of 500 nm to 20 µm, preferably from 5 µm to 15 µm.