1. Field
The present invention relates to methods and apparatus for forming three-dimensional (3D) glass articles. The present invention relates to methods and apparatus for bending glass without using molds. The present invention relates to glass covers for electronic devices.
2. Background
Simple and complex 3D glass articles can be formed by conforming glass sheets to mold surfaces with the desired 3D profiles. The conforming is done while the glass is at a relatively low viscosity, typically 108 to 1010 Poise. At this low viscosity, any contact between the glass and mold surface can result in imprinting of mold surface defects on the glass. In addition, depending on the mold material, the glass may stick to the mold surface, which would degrade the glass surface. For applications where glass aesthetics and strength are important, such as in glass covers for electronic devices, the mold surface would need to be free of defects and made of a material that would not stick to the glass at high temperatures to avoid the problems mentioned above. The cost of such a mold is high and increases as the article size increases. Also, because the glass is conformed to the mold surface, each new glass article shape will require a new mold design, even if the new shape is just a prototype. A new mold for each new shape will increase production costs and prototyping costs per article and hamper the ability of the manufacturer to respond to requests for new shapes quickly.
U.S. Provisional Application No. 61/546687 (“Thermo-mechanical reforming method and system and mechanical reforming tool”) describes a method of forming 3D glass articles that does not involve use of molds. The method involves placing a glass sheet on a flat support and heating the glass sheet to a first temperature corresponding to a relatively high viscosity at which the glass cannot be permanently deformed. The glass sheet is then locally heated to a second temperature corresponding to a relatively low viscosity at which the glass can be permanently deformed. In the region affected by the local heating, temperature will rise from the first temperature to the second temperature. In the region unaffected by the local heating, temperature will be somewhat constant at or near the first temperature.
An actuated force is applied to the glass sheet. When the affected region is at the second temperature or relatively low viscosity, the actuated force will produce a bend in the affected region. A bend will not be produced in the unaffected region that is at a relatively high viscosity. The level of deformation in the affected region is controlled by the linear amplitude of the actuated force, and the radius of curvature in the affected region is controlled by the angular amplitude of the actuated force. However, these two controls do not allow easy fine-tuning of the bending profile in the affected region, which in reality depends on the local equilibrium between the bending momentum induced by the actuation force and the local glass viscosity. With this method, the bend profiles that can be achieved are somewhat limited to “natural profiles,” which are composed from two straight regions and a nearly constant radius of curvature in between. More complex designs that can be mathematically expressed as a varying curvature radius depending on the curvilinear length of the glass may enable more interesting and useful shaped glass articles.