WO2018178881A1

WO2018178881A1 - Low cost glass bending mold

Info

Publication number: WO2018178881A1
Application number: PCT/IB2018/052105
Authority: WO
Inventors: Mario Arturo MANNHEIM ASTETE; Juan Carlos Casas; Edwin Gonzales; Eliecer MONCADA; Tiago RAMIRES; Jairton POZZEBON; Charles Stephen Voeltzel
Original assignee: Agp America S.A.
Priority date: 2017-03-28
Filing date: 2018-03-27
Publication date: 2018-10-04

Abstract

A large percentage of the bent glass laminates manufactured worldwide each year is produced using the gravity bending process. Inherent drawbacks to the process include the expense of the molds required, marking of the glass by the mold and the lack of precise surface control. By using an inexpensive ceramic mold to bend a sheet of glass having a higher bending temperature than the glass to be used in the fabricated product, a glass female is produced which is then provides the means to produce a full surface gravity bending mold which produces parts having superior quality, optics and dimensional control.

Description

LOW COST GLASS BENDING MOLD

Field of the invention

This invention relates to the field of bent laminated glass glazing.

Background of the invention

A large percentage of bent glass laminates manufactured worldwide each year is produced using the gravity bending process in which the glass, supported near the edges, is heated and allowed to sag to shape under the force of gravity acting on the mass of the glass. The process has been in use for many years and is well known in the art. Gravity bending is the typical method used to manufacture automotive windshields and other automotive laminated glazing.

The gravity bending process allows bending two or more flat sheets of glass at the same time. The tool used is known as a bending mold (Figures 1, 2 and 3).

A typical bending mold comprises a support structure connected to a female metal ring that supports the glass around the entire periphery. The ring is offset inboard from the edge of glass, typically in a range of 6 mm to 12 mm. The ring is typically constructed of 3 mm - 6.3 5mm x 25 - 100 mm 304 stainless steel flat stock or sheet or equivalent. Likewise, other steels with good behavior at high temperatures (low geometrical variations) can be used, such as cold/hot rolling steels.

Figure IB shows an example of a bending mold 7 in which the orientation of the bent glass is such that the bottom and top corner points of the bent glass are level and horizontal. The flat unbent cold glass 10 is loaded onto the mold 7 and supported at four contact points 9. The bending mold 7 and flat glass 10 are heated. At the glass transition temperature range, the glass is allowed to sag under its own weight (gravity bending) until the desired shape is obtained. The periphery support ring 8 provides the glass with the desired shape to fit in a vehicle opening. As contact is made with the surface of the glass only around the periphery, the shape in all other areas of the glass is controlled by means of temperature, heat sinks and heat shields. As can be expected, dimensional accuracy of the portions of the glass in direct contact with the periphery support ring 8, are much better than in other areas. Frequently, the inboard portions of the glass tend to remain relatively flat. This shape is known as a "bathtub" shape and is typical of many gravity bent windshields. If the glass gets too hot in the inboard portion, the glass may sag too far and fall off of the ring. This is one of the drawbacks of gravity bending.

Another drawback results from the contact points. While the cold glass will sometimes partially sag under its own weight to the contour of the periphery support ring 8 prior to heating, the contact and support is essentially point contact (rather than line or surface). The entire weight of the glass is initially supported only at the four contact points 9. As the glass softens, the contact points 9 can leave marks on the glass surface. Also, as the glass sags and conforms to the shape of the ring, the glass surface moves relative to the periphery support ring 8 which can also leave marks on the glass. This results in a defect known as mold mark. In the past, mold mark was hidden by decorative trim and molding applied to the installed glass. More recent design trends have eliminated this, favoring a flush glazed look with an exposed edge of glass. This has required modifications to the bending mold such as applying a soft heat resistance material, such as fiberglass or alumina based ceramic cloth to the ring and contact points, all of which are high maintenance items and add cost.

On some glass designs, when leveled at the corner points, the vertical centerline of the windshield may be too far from level to bend. If the bent centerline part does not also sit close to level on the bending mold, the glass will tend to move on the mold as the bending mold travels through the bending furnace. In these cases, the ring must be modified, including articulated movable sections. To do so, the bending mold is cut into three sections, as shown in Figure 2A, the center section 8', along the top and bottom edges and the two wings sections 18 in the pillar areas. The points where the cuts are made along the ring are selected such that the flat glass 10 will rest in the horizontal plane at the cut points. This allows the vertical centerline of the part to rest in horizontal position. The articulated outboard wing sections are connected to the inboard stationary center sections of the ring by means of a hinge mechanism designed to rotate the wing sections to an open position, such that the corner points of the glass lie in the plane formed by the inboard cut points with the mold in the open position. In the open position, as shown in Figure 2B, the flat glass 10 is supported at eight points 9' which improves support.

Figures 2 and 3 show an articulated bending mold in the full open (Figures 2 A and 2B) and full close positions (Figures 3A and 3B). The flat glass 10 is loaded onto the open bending mold, with the mold supporting the glass at eight points 9' and then heated. As the glass softens and sags, the hinged portions of the bending mold move to the closed position, forming a bent glass 12. Other drawbacks include the high initial cost of bending mold tooling and high cost of maintenance. The fabrication of a bending mold is labor intensive, requiring many hours of skilled craftsmanship to convert the flat sheet metal to the three dimensional shape of the glass. While a single mold can be used for extremely low volume production, fifty or more molds may be required to fill a bending furnace used to run a large volume operation.

Constant maintenance is required during production. The welded steel construction tends to be unstable over time due to repeated heating and cooling. This involves another unwanted source of variation in the final glass product where dimensional tolerances are challenging. The molds must be checked for accuracy on a regular basis and adjusted as needed.

For many automotive designs, gravity bending does not have the capability of producing acceptable parts, due to lack of precision. While the glass may fit in the opening, the "bathtub" shape can lead to problems keeping the window clear of water, snow and ice, due to the inability of wiper blades to follow the contour of the surface and the abrupt rate of change in curvature. The shape is especially a problem when the glazing is to be used in conjunction with camera systems, heads up displays, and other devices which require a high level of optical clarity. To meet these needs, laminates must be produced using a full or partial surface press bending process. This type of bending has superior dimensional control but higher cost, lower throughput and is not suitable for very thin glass as the glass is heated on rollers in some implementations. Summary of the invention

The limitations of the prior art are overcome through a novel method used to bend a sheet of high bending temperature glass (HBT) to the desired shape. A HBT mold (bent HBT glass) replaces the metal periphery support ring of a conventional bending mold. This substantially lowers the initial cost of the bending mold, as the forming of the ring is labor intense. Routine maintenance is also substantially reduced, as the HBT mold is dimensionally stable and does not need to be periodically checked for accuracy and adjusted. If the HBT mold needs to be replaced, the mold can be quickly refurbished with a new HBT mold and returned to service.

The HBT mold is formed by constructing a female sand mold to a male model of the surface to be bent. The sand mold is loaded with a sheet of flat HBT and placed in a furnace, which is then bent to the desired shape. The HBT then is checked, the bent HBT is mounted to a support structure and used to bend lower temperate glass. If needed, the HBT can be cut to make an articulated mold. This novel method allows obtaining bent glass without mold marks at reduced costs and wherein the tools used, including the molds, require low maintenance, being functional in manufacturing operations for long periods. Additionally, this method provides bent glass with precise full surface control and superior dimensional control. Brief description of the drawings

These features and advantages of the present invention will become apparent from the detailed description of the following embodiments in conjunction with the accompanying drawings, wherein: Figure 1A shows an isometric view of ring style bending mold with flat glass loaded according to prior art.

Figure IB shows a corner section A- A' of Figure 1A. Figure 2A shows a front view of ring style bending mold with articulated wing sections and with flat glass loaded according to prior art.

Figure 2B shows an isometric view of the ring style bending mold of Figure 2A. Figure 3A shows the front view of ring style bending mold of Figure 2A with bent glass.

Figure 3B shows the isometric view of ring style bending mold with bent glass of Figure 3A. Figure 4 shows an isometric view of male surface master tool.

Figure 5 shows an isometric view of male surface master with sand mold box in place.

Figure 6 shows an isometric view of filled mold box. Figure 7 shows an isometric view of cast female ceramic mold. Figure 8 shows an isometric view of cast female ceramic mold loaded with flat glass. Figure 9A shows an isometric view of bent high bending temperature glass.

Figure 9B shows an isometric view of cast female ceramic mold loaded with bent high bending temperature glass.

Figure 10A shows a high bending temperature glass full surface female bending mold loaded with flat low temperature glass: corner detail of Figure 10B.

Figure 10B shows a high bending temperature glass full surface female bending mold having a support ring loaded with flat low temperature glass. Figure 11A shows a high bending temperature glass full surface female bending mold loaded with bent low temperature glass: corner detail of Figure 1 IB.

Figure 11B shows a high bending temperature glass full surface female bending mold loaded with bent low temperature glass.

Figure 12A shows a high bending temperature glass full surface female bending mold: cross section B-B' of Figure 12B.

Figure 12B shows a high bending temperature glass full surface female bending mold loaded with flat low temperature glass.

Figure 13A shows an isometric view of a high bending temperature glass articulated full surface female bending mold in closed position. Figure 13B shows a front view of a high bending temperature glass articulated full surface female bending mold in closed position.

Figure 14A shows an isometric view of a high bending temperature glass articulated full surface female bending mold in open position. Figure 14B shows a front view of a high bending temperature glass articulated full surface female bending mold in open position.

REFERENCE NUMERALS

1 male surface model

2 box

3 sand mix

4 female mold

5 flat HBT glass

6 bent HBT glass

7 bending mold

8, 8' periphery support rin

9, 9' contact points

10 flat glass

12 bent glass

18 wings sections

Detailed description of the invention

The instant invention provides a method for manufacturing a full surface female bending mold to produce bent glass, by using a sand mold or ceramic molds made from either castable or grinded ceramic boards.

There are many materials that are classified as glass. Glass, as used in this document, includes but are not limited to: the common soda-lime variety typical of automotive glazing, as well as aluminosilicate, lithium aluminosilicate, borosilicate, glass ceramics, and other inorganic solid amorphous or crystalline compositions which undergo glass transition and are classified as glass, included those that are not transparent. The term glass also includes glass like ceramic materials.

The basic principle upon which the invention is based, is that different types of glass have different glass transition temperature ranges. In the first place, a HBT glass having a transition temperature range that is sufficiently higher than the transition temperature range of the glass that will be bent in the final product, is selected. At the lower transition temperature of the glass that will be bent, the HBT glass must retain its shape and strength. For example, in the case of bending operations of ordinary soda-lime glass or borosilicate glass, certain formulations of lithium aluminosilicate glass meet the criteria of a HBT glass. To provide the precisely desired shape to the HBT glass, a sand mold is firstly made. Sand molds have been used for well over 100 years in the foundry industry and are well known in the art. Numerous methods and materials for producing sand molds exist, any of which may be used. As the operating temperature required to bend the glass is substantially lower than the typical mold used for metal castings, some methods and materials are more economical than others.

A male surface model 1 (Figure 4) is cut from tooling board or any other suitable tooling material. The mold is enclosed in a box 2 (Figure 5) having an open top and metal or wood sides of sufficient strength, in order to contain the sand that will be used to fill the box. The box is then filled with the sand mix 3 (Figure 6), tamped firmly into place to eliminate voids and then cured. The sand mold is inverted (Figure 7). The box and the male model are removed, leaving a female sand mold 4.

Other materials and processes can be used, including but not limited to castable ceramics and ceramic grinded boards, all of which can be used to produce equivalent bent HBT shapes.

A sheet of flat HBT glass 5 is loaded onto the mold 4 (Figure 8). The mold is then heated to the transition temperature of the HBT glass, which is allowed to sag for a period of time sufficient to allow the flat HBT glass 5 to bend and adopt the shape of the sand mold 4. The glass is allowed to slowly cool and anneal.

The bent HBT glass 6 is removed (Figures 9A and 9B) and then used as a full surface bending mold, attached to a support structure (Figures 10A and 10B). The structure may be made of a ring 8, similar to the bending mold of the prior art, as shown in Figures 10B and 11B, or any other suitable structure, as shown in Figure 12B. Figures 13A, 13B, 14A and 14 show an articulated ring type support with the HBT glass. Example 1 -manufacturing of a 3D male surface model

A 3D male surface model is cut from wood, resin, tooling board or any other suitable tooling material, preferably though the use of a 5 axis mill. The surface of the model must have a very good smooth finish as a female sand mold will be directly cast from it. The 3D model has the desired male glass surface shape that will be transferred to the sand. Example 2 -manufacturing of a female sand mold

A box is built around the male 3D surface model to hold the sand. The box can be made of metal or wood as a low temperature process is used to cure the ceramic. The box should have the same high/thickness that is wanted for the sand mold.

A mixture comprising 85-95% silica sand and 5-15% of a 50/50 solution of water and sodium silicate is used to produce the female sand mold. In addition, other oxides, carbonates, fibers or nano-powders could be added to improve performance and hardness of the mixture. Sodium silicate is a high strength binder used with silica molding sand. To cure the sodium silicate binder, carbon dioxide gas is used, which creates the following reaction: Na₂SiC>3 +C(¾ = Na₂C0₃ + 2Si0₂ +Heat

The sand used should have an adequate particle size for achieving a smooth surface but at the same time allowing the C(¾ gas to infiltrate in the sand and harden them.

After mixing the components, the sand mixture is poured over the 3D resin/wood/metal model filling the frame box. After homogeneously compacting the sand, the excess of sand is removed from the box by drawing a straight edge across the box.

CO2 gas is applied to harden and cure the pre-mixed and compacted sand. The female sand mold is ready to use, after it is inverted and the box removed.

Example 3 -manufacturing of bent HBT

A flat HBT glass sheet is loaded over the female sand mold. The mold and HBT glass are placed in the bending furnace. In the case of lithium aluminosilicate glass, a temperature between 640°C and 670°C, is used. The bending time needs to be sufficient for the glass to adopt the shape of the sand mold surface.

The bent HBT glass is then attached to a support frame to form the low cost bending mold of the invention, which is then used in the bending process for standard lower transition temperature glass. The support structure can comprise a ring type support or the HBT glass can be bonded to any other suitable structure. The HBT glass may need to be covered with a thin metallic or ceramic fabric to prevent sticking of the low temperature glass to the HBT glass during bending.

Example 4 -manufacturing of bent low transition temperature glass

A set of cut soda lime glass layers are loaded onto the female mold. The mold travels through a bending furnace where the glass and the mold are heated into the glass transition temperature range of soda lime glass. The soda lime glass sags to the shape of the HBT surface. The temperature profile and time is precisely controlled so as to achieve the optimum shape and optics. The glass is then slowly cooled to below the glass transition range so as to stress relieve and anneal the glass. The bent glass is removed from the HBT glass bending mold and the process is repeated with new flat soda lime glass.

It must be understood that this invention is not limited to the embodiments described and illustrated above. A person skilled in the art will understand that numerous variations and modifications can be carried out that do not depart from the spirit of the invention, which is only defined by the following claims.

Claims

1. A method for manufacturing a full surface bending mold comprising;

selecting a sheet of glass having a higher transition temperature range than the transition temperature range of the glass for the final product;

producing a male surface model;

producing a female mold from the male surface model;

bending the sheet of glass having a higher transition temperature range to the shape of said female mold.

2. The method of Claim 1, wherein a glass having a lower transition temperature range is bent over the bent sheet of glass having a higher transition temperature range.

3. The method of Claim 1, wherein the glass having a higher transition temperature range is made of lithium aluminosilicate glass.

4. A surface bending mold produced through the method of Claim 1.

5. The surface bending mold of Claim 4, mounted on a support comprising hinged articulated wing sections.

6. The surface bending mold of Claim 4, mounted on a support comprising a ring structure.

7. A laminate comprising at least one glass layer produced through the use of said bending mold of claim 4.

8. The laminate of claim 7, wherein at least one of said at least one glass layer is a borosilicate glass layer.

9. The laminate of claim 7, wherein at least one of said at least one glass layer is an aluminosilicate glass layer.

10. The laminate of claim 7, wherein at least one of said at least one glass layer has a thickness in the range of about 0.4 mm to 1.0 mm.

11. A vehicle comprising the laminate of claim 6.