WO2012028630A1

WO2012028630A1 - Process for producing glazing shapes

Info

Publication number: WO2012028630A1
Application number: PCT/EP2011/064944
Authority: WO
Inventors: Quentin Gillard; Benoît LECOMTE; Florence Scheyvaerts
Original assignee: Agc Glass Europe
Priority date: 2010-09-03
Filing date: 2011-08-31
Publication date: 2012-03-08
Also published as: EP2611746A1; BE1019471A3

Abstract

The invention relates to a process for producing curved glazing shapes using an expert system comprising a computerized database including the determination of the shapes as a function of the spatial distribution of the temperatures required for the conversion from flat glass sheets, for a set of tools that can be used, in which process the starting geometric data relating to the initially proposed glazing are introduced, the treatment leading to the spatial distribution of temperature and to a first resulting shape, from which the differences with the geometric initial data are determined in order to establish new data that is used as a basis for reiteration of the process until the shape closest to the initial data is obtained according to the tolerances chosen previously.

Description

Process for producing glazing shapes

The present invention relates to the manufacture of automotive glazing. More specifically, it relates to obtaining glazing whose shape meets the demands of manufacturers both in their appearance and in their functionalities, in particular their aptitude for satisfactory scanning by windscreen wipers, with optical qualities characterized by the absence deformations of images in transmission, and simultaneously that are achievable by the glass forming techniques available.

These forming techniques systematically comprise from flat glass sheets previously cut, raising the temperature of the sheets to a softening temperature, and forming under these conditions by gravity, the sheets supported at their periphery by a frame , deforming under their own weight, and / or by pressing on all or part of the surface. The shape being obtained is frozen by controlled cooling.

The sheets are formed either one by one or in pairs, the latter being the most usual mode when it comes to obtaining sheets used in the constitution of laminated glazings in which the two sheets are assembled by means of a thermoplastic interlayer.

The development of the forms of automotive glazing traditionally passes through different stages involving long and expensive iterations made of exchanges between the wishes of the manufacturers and the technical training means that the glass manufacturers have. In addition to the frames which determine the contours of the windows, and the pressing means, the sheet heating means are inseparable from these techniques. Various types of furnaces are likely to be used for these operations. Industrial furnaces are of the "tunnel" type. The flat glass sheets are introduced at one end of the furnace and progress in it, either continuously or stepwise, their temperature being gradually raised to reach the forming temperature.

In practice the car manufacturers define a glazing model corresponding to the overall appearance they want to give to the vehicle. This model comprises a certain number of elements determined in the form of dimensions and curvatures, to which are added the requirements relating to specific elements which must comprise the completed glazing, functional thin layers, enamelled zones ... The model provided by the constructor is presented in digitized form. For their part, glass manufacturers confront this model with the means they have to form the glazing requested, forming mode: by gravity, by total or localized pressing; type of tools: ovens, molds etc, and communicate the result of their investigation on the feasibility of the form requested, and on the elements of the project which raise difficulties or even impossibilities

The builders collect this information and propose modifications of the initial project which they consider acceptable. The process is renewed until an agreement is reached. These exchanges significantly lengthen the outcome. It may take several months before obtaining such an agreement on a given model.

An object of the invention is to simplify, accelerate and improve the process of shaping glazing shapes, this by offering not only information on the feasibility of the requested model from the beginning, but also by elaborating from this one, an actually feasible model as close as possible.

To achieve this objective the inventors propose the process forming the subject of claim 1. The inventors have developed an expert system simulating the temperature conditions necessary to obtain the shapes of glazing, and this for different types of tools used.

The computerized database of the system implements, first, the relationship between the temperature of the glass and its viscosity, which determines the deformation capacity necessary to achieve the desired shape. Starting from the geometrical parameters concerning the sheets of glass and tools implemented, the system determines by finite elements computation, a field of temperature which makes it possible to approach the chosen form. This result is not dependent on the structure of a certain oven. It is what the glassmaker should get from an ideal oven to achieve the proper form. The result determines the deviations from the shape in question and compares it with the previously specified tolerances, and elaborates an alternating temperature field which serves as a basis for iteration of the operations until a shape which satisfies the tolerances is obtained. imposed.

The advantage in this process is to lead to obtaining a model, certainly different from the one requested by the manufacturer, but which differs as little as possible and is actually achievable by the glassmaker. The approach can be resumed if the manufacturer wishes. In taking into account factors influencing the spatial distribution of temperatures, it is obvious that these temperatures are not reached instantaneously. Even if for practical reasons related to the furnaces used or the fact that the leaves should not undergo a violent thermal shock, obtaining temperatures requires a rise time that generally extends over several minutes. Cycle time is an element that comes into play in creating particular temperature gradients. The invention therefore involves the determination of a spatio-temporal temperature field. But the time factor is often very simply analyzed to the extent that the operations envisaged are largely conditioned by existing furnaces, for which, with some exceptions, Operating conditions differ little from each other. Nevertheless, the time factor is likely, in a limited way, to open additional perspectives on the feasibility of spatial temperature distributions. To obtain a satisfactory result, it is advantageous to enter the data concerning the geometry of the glazing in a mesh which takes into account the relative difficulties of the desired shape. In the forming of the glass sheets to make the feasible shape coincide and the desired shape is more or less difficult depending on the parts of the glazing concerned. As an indication, the curvatures of small radius, especially if they are located at the corners of the leaves, are likely to lead to impossibilities on the basis of the required temperatures and especially their gradient on limited spaces.

Regardless of these particular forms the major concern, when the forming operation takes place essentially by gravity, is to completely control the shape away from the frame supporting the glass sheets. The mesh in the center may nevertheless be relatively loose in that the shape is not very complex in this part of the glazing, and in particular where the curvatures are usually not very accentuated.

Tightening the mesh in the only zones that are more sensitive to deviations, makes it possible to lighten the machine treatment leading to the result, without losing overall quality. Of course a very tight mesh is nevertheless possible in every respect.

In practice, the operator also has the choice of imposing a forming mode, for example by gravity alone, or by gravity and localized or general pressing. These choices imposed on the system also make it possible to reduce the range of possible significant and consequently the necessary treatment time.

Similarly, the operator can choose a support frame with articulations to give this frame a form that changes during the process. This type of joint is used in particular to accompany the support of the sheets when a strong curvature is required. The most common type corresponds to windshields whose side parts are strongly curved, referred to as the "panoramic" windshield. In cases such as these, the frame moves from an "open" position in which the side portions are lowered to receive the flat sheets, to a "closed" position, the side portions of the frame being more or less raised. Not only can the operator plan to impose the presence of moving parts, but he can still fix the position of the joints on the frame. Still on the possible choice of the frame, it is known from the patent

EP 885 851, for glazing having curvatures in two directions, in particular windshields, to use frames whose side parts are doubled. One element of these sides is substantially rectilinear and supports the flat glass sheet while in the other direction the glass can follow the curved shape of the frame. After forming this first curvature, a second constituent element of the lateral part of the frame which is curved is substituted and leads to the formation of the second curvature. This dissociation promotes double curvature and prevents the appearance of "counter-bending". The operator can also impose on the system the implementation of these double lateral supports, thus contributing to a limitation of the processing operations.

The choices imposed by the operator are based on his personal experience. They remain, anyway, optional.

The system as indicated above may further include additional parameters that may affect the temperature conditions, and hence the shape.

Among these parameters it is important to underline a frequent case, that of the double sheets intended to enter a laminated glazing. In practice, the two sheets are preferably treated simultaneously for guarantee a good pairing. It is possible, however, to successively bend each sheet.

When the two sheets are formed simultaneously, the temperatures reached by each are never strictly identical even if the differences are relatively small. It is possible to consider the two sheets as constituting only one presenting the thickness corresponding to the sum of the thicknesses. But during the practical realization the sheet of the outermost glazing remains the one that controls the quality in terms of shape. It is therefore the one to which preferably according to the invention it is sought to impose the spatio-temporal distribution of temperatures. The shape of the inner sheet which is the one above during the shaping, will be controlled by the sheet constituting the outer face and which is located below.

Another important optional parameter concerns the thermal behavior of the glass sheet linked to the possible presence of layers having infrared reflection properties. The presence of such layers may require a correction with respect to the "temperature" data of the base used.

The general method according to the invention described above can be completed with additional modules intended to extend the operations relating to the determination of the capacity of the glassmaker to produce the glazing requested, or to respond to additional requests from the manufacturer concerning properties that are also related to the shape of the glazing.

The glass manufacturers have furnaces whose general characteristics are those indicated above, but which differ in their construction and the means with which they are equipped. This is particularly true of heating arrangements. These are distributed in the oven so that they are generally able to ensure a controllable temperature rise at all points treated sheets.

The basic distribution of the heating means must allow a substantially uniform temperature rise. However, all the furnaces still include means that also make it possible to modulate the temperature rise in a differentiated manner according to the area of the glazing concerned.

Whatever the sophistication of industrial furnaces, their ability to generate temperatures in principle to access the forms determined as "feasible", there are practical limits to their flexibility. The capacity of the furnaces available to the glassmaker, to produce spatial temperature distributions, are advantageously coupled with the determination of temperatures to achieve the required shapes. The data processing then directly makes it possible to know to what extent the glazings in question are actually achievable in practice with the available tools. This measure applies not only to the heating means themselves, namely mainly the radiating elements arranged in the furnace, their provision their power, but also to the possibilities of controlling heat flows for example by the local arrangement of absorbing masses, or means providing forced convection. It also applies to additional means that can correct what the thermal does not fully satisfy, and in particular all the pressing means they are localized or apply to the entire surface.

The shape of the glazing is primarily a function of the model requested by the manufacturer, who sets his choice for aesthetic and aerodynamic issues. To be perfectly satisfactory, the glazing must also offer very precise optical qualities. The light transmission in practice is conditioned by the nature of the glass and its thickness. Beyond the manufacturers also demand that the windows offer a sufficient optical quality. The vision through the glazing must not be altered by deformations embarrassing. Deformations of this type are related in particular to variations in the radii of curvature generating, for example, double images. As perfection is not possible, it must be ensured that the sheets composing the glazing, after their shaping, comply with the limits set as acceptable.

Since the forming of the sheets modifies the optical geometry, it is advantageous to subject the proposed forms coming from the previous treatments to a verification of the conformity of these forms with the optical quality requirements. This can be further processed. Other properties of the glazing still condition the usable forms. Especially when it comes to windshields, they must be able to be properly swept by the wiper or wipers. Various factors intervene for this "wiping". Of these, form is a significant element. The shape and position of the windscreen wipers also occur but are defined by the manufacturer with limited possibilities of modification. The glazing whose shape is the result of the treatment can still be the subject of a wiping simulation, ensuring that this form is not incompatible with the desired quality. The difficulties are mainly related to accentuated curvatures in the swept areas, but irregularities in the definition of the surface over a limited area may also oppose proper wiping.

The invention is described in detail in the following example with reference to the appended figures schematically the process steps for the development of glazing forms. In the example chosen, in the case of symmetrical glazing, it is possible to limit the treatment to a half-surface thereby reducing the necessary treatment. The appended figures are therefore representations of half-windshield. The first step of the operation consists of starting from the manufacturer's data, most often in the form of a computer-aided design file, transforming the file into data corresponding to the spatial distribution as used by the expert system. The transformation is performed for a set of points covering the entire surface.

FIG. 1 graphically illustrates the geometrical data corresponding to the half-windshield in the position requested by the manufacturer. Each point represented corresponds to a point of the surface defined by the manufacturer. The windshield is symmetrical with respect to the plane P.

In the example chosen the half-windshield is curved in two directions which are indicated on the lower part (Cl), and on the side (C2).

The model thus defined is related to a sheet of flat glass corresponding to the blank which will be cut in practice.

In the choice of the frame used, by default the system proposes a simple frame whose curvatures are defined according to the curvatures of the model proposed by the manufacturer.

Figure 2 illustrates the shape of the frame C supporting the flat glass sheet represented by the mesh laid flat (in the form of a grid).

Apart from the definition of the frame for supporting the glass sheet at its periphery, additional means may also be imposed on the system to present the best possible approach to the requested shape. In the tools it is possible to provide the articulation of the frame so that the lateral ends can rotate during the bending operation. This construction facilitates the formation of accentuated curvatures without requiring too different local temperature conditions difficult to master in practice.

FIG. 3 illustrates this particular mode with the point of articulation A whose position along the frame C is also chosen by the operator to correspond as closely as possible to the imposed shape.

In the same figure the local "pressure" parameter is also applied. In the case envisaged the pressure is exerted so as to apply the glass sheet against the frame in the lateral part, so that the curvature is exactly that of the corresponding part of the frame. In this case the formation by pressure is substituted for that resulting from the gravity in the definition of the form, without, of course, the gravity being absent in the actual forming process.

In FIG. 3 the pressure is illustrated by the zone facing the arrow F. It goes without saying that the pressure and the articulation can be applied independently of one another according to the models concerned and their specific complexity.

Another example of a "tool" that can be used in the simulation as well as in practice is illustrated in FIG. 4. In this example, the curvature along one side of the frame is dissociated in time from the bend on the other side. As in the figure, the curvature along Cl is retained at the beginning of the treatment by resting the glass sheet on a substantially less curved or even rectilinear support, represented by the line B_; B. After the curvature along C2 conducts the glass in contact with the frame _A, the support B is lowered, releasing the glass sheet which, by gravity, then applies to the part C1 of the frame.

The arrangement of the type B support is combinable with the other tools presented previously. Starting from the flat glass sheets, the shape of the glazing sought does not impose in every point of this sheet changes of the same magnitude. The parts having areas of small radius of curvature in particular are more restrictive to obtain. It is therefore advantageous to model with particular care the result of the modifications imposed in these parts of the glass sheets. To follow these changes the shape of the glazing is followed point by point following a mesh all the more tight as obtaining the desired shape is more restrictive.

Figure 5 illustrates a mesh choice for areas whose curvatures are difficult to obtain. In the illustrated case, these areas are located along the frame. The meshes M are accordingly narrower in the model subject of the treatment according to the invention.

The data introduced and the possible choices of tools being also made, the treatment using the system leads to a mapping of the temperatures necessary to obtain the desired shape, or an approximate shape.

In a way of accelerating the processing, the operator can sketch a rudimentary distribution as represented in FIG. 6 as a starting point. This is not absolutely necessary but reduces the iterative operations accordingly. The chosen representation matches the darkest areas with the highest temperatures.

The treatment pursued, the spatial distribution of temperature leads to an af finement of this distribution. Figure 7 is an illustration of what may be the end result of this treatment under the chosen conditions. As in the previous figure, the darkest areas are those requiring the highest temperatures. In the example, these temperatures range from about 590 to 650 ° C. Dimensions scales are given in mm. FIG. 8 illustrates for a windshield slightly different from that of FIG. 7 a temperature distribution (the gray scale of the temperatures is reversed compared to that of the preceding figure) in the figure on the right, and on the part left its translation in terms of deviation in the bending direction (substantially orthogonal to the initial plane of the glass sheet) relative to the required shape ,. In the case represented, the largest differences observed do not exceed 0.5 mm. Note that the deviations not to exceed are in most applications, less than ± 1mm.

In Figure 8 is still seen in the case of a bending obtained by gravity areas for which the differences are greatest, while remaining limited. This is a part of the central area of the windshield for positive deviations. It is also the edges for negative deviations, which in this case have the most delicate curvatures to obtain.

FIG. 9 illustrates the simulation mode for determining the capacity of a defined windshield, to lend itself to good wiping by the brushes.

Different criteria are proposed by the manufacturers for this wiping ability. A conventional criterion is, for example, the variation in the radius of curvature of the glazing in the scanned zones. The determination of the form resulting from the previous treatment is directly usable for the evaluation of this aptitude.

In Figure 9 the variations of radius of curvature are indicated for the scanned area. The darker parts are the smaller ones, the more difficult ones. Since the curvature limits determined for the efficiency of the wipers are known, the fitness of the shape for this wiping immediately follows.

Claims

A method for producing curved glazing shapes by means of an expert system comprising a computerized base including the determination of shapes according to the spatial and temporal distribution of the temperatures required for processing from flat glass sheets, for a set of tools usable method in which the initial geometric data relating to the initially projected glazing are introduced, the processing leading to the spatial distribution of temperature and to a first resultant form, from which the deviations with the initial geometric data are determined to establish new data serving as a basis for repetition of the process until the closest shape of the initial data is obtained according to the previously chosen tolerances.

2. Method according to claim 1 wherein the geometric data initially introduced are established according to a spatial mesh of the form, taking into account the local specificities of the glazing according to their position thereon.

3. Method according to one of the preceding claims wherein out of those relating to the desired form of the additional parameters are treated including at least the thickness of the glass.

4. Method according to one of the preceding claims applied to a set of two superimposed glass sheets for subsequent laminated assembly, the spatio-temporal distribution of temperatures being established substantially based on the sheet disposed in the lower position during the formatting.

The method according to claim 3 or claim 4 wherein the presence of athermic layers is one of the additional parameters to account for their impact on temperature setting.

6. Method according to one of the preceding claims wherein the set of forming tools taken into account comprises at least one frame corresponding to the peripheral shape of the glazing.

7. The method of claim 6 wherein the frame is provided with movable joints for the formation of curvatures accentuated during the forming process, the movable parts being optionally provided with mobilisable supports.

8. Method according to one of the preceding claims wherein the set of tools comprises a press applied to a part or the entire surface of the glass.

9. Process according to any one of the preceding claims, in which the spatial temperature distribution is subjected to an analysis comparing this distribution with the capacities for obtaining these temperatures by means of one or more ovens typical of these techniques and for periods of time. also typical treatment.

10. Method according to one of the preceding claims wherein the result of the determination of the form is further subjected to an optical quality analysis simulating the deformations of the glazing in the final operating conditions of this glazing.

11. Method according to one of the preceding claims wherein the result of the determination of the form is still subjected to a wiping analysis which involves various indicators relating to the wiping means.