Abstract:
An apparatus for forming a shaped article having a first surface with a first surface profile and a second surface with a second surface profile is provided. The apparatus includes a first end mold having a cavity formed therein, where the cavity is defined by a surface having at least a portion of the first surface profile. The apparatus includes an intermediate mold having a hole formed therein. The intermediate mold is distinct from the first end mold and is configured for stacking against the first end mold such that the hole is aligned with the cavity. The apparatus includes a second end mold having a protuberance formed on a surface thereof. The protuberance is defined by a surface having at least a portion of the second surface profile and is sized for insertion into the hole and cavity.

Description:
FIELD 
       [0001]    The invention relates generally to methods and apparatus for forming shaped articles. More specifically, the invention relates to a method and an apparatus for reforming a thin sheet of material into a shaped article. 
       BACKGROUND 
       [0002]    Molding is a common technique used to make shaped objects. Precision molding is suitable for forming shaped glass articles, particularly when the final glass article is required to have a high dimensional accuracy and a high-quality surface finish. In precision molding, a glass preform having an overall geometry similar to that of the final glass article is pressed between a pair of mold surfaces to form the final glass article. The process requires high accuracy in delivery of the glass preform to the molds as well as precision ground and polished mold surfaces and is therefore expensive. 
         [0003]    Press molding based on pressing a gob of molten glass into a desired shape with a plunger can be used to produce shaped glass articles at a relatively low cost, but generally not to the high tolerance and optical quality achievable with precision molding. Where the molten glass has to be spread thinly to make a thin-walled glass article having complex curvatures, the molten glass may become cold, or form a cold skin, before reaching the final desired shape. Shaped glass articles formed from press molding a gob of molten glass may exhibit one or more of shear marking, warping, optical distortion due to low surface quality, and overall low dimensional precision. 
       SUMMARY 
       [0004]    In one aspect, the invention relates to an apparatus for forming a shaped article having a first surface with a first surface profile and a second surface with a second surface profile. The apparatus comprises a first end mold having a cavity formed therein. The cavity is defined by a surface having at least a portion of the first surface profile. The apparatus further includes an intermediate mold having a hole formed therein. The intermediate mold is distinct from the first end mold and is configured for stacking against the first end mold such that the hole is aligned with the cavity. The apparatus includes a second end mold having a protuberance formed on a surface thereof. The protuberance is defined by a surface having at least a portion of the second surface profile and is sized for insertion into the hole and cavity. 
         [0005]    In another aspect, the invention relates to an apparatus for forming a plurality of shaped articles, wherein each shaped article has a first surface with a surface profile and a second surface with a second surface profile. The apparatus comprises a first end mold having a plurality of cavities formed therein. Each of the cavities is defined by a surface having at least a portion of the first surface profile. The apparatus includes an intermediate mold having a plurality of holes formed therein. The intermediate mold is distinct from the first end mold and is configured for stacking against the first end mold such that each of the holes is aligned with one of the cavities. The apparatus includes a second end mold having a plurality of protuberances formed on a surface thereof. Each of the protuberances is defined by a surface having at least a portion of the second surface profile and is sized for insertion into one of the holes and one of the cavities. 
         [0006]    In yet another aspect, the invention relates to a method of making a shaped article having a first surface with a first surface profile and a second surface with a second surface profile. The method comprises aligning a cavity in a first end mold with a protuberance in a second end mold. The cavity is defined by a surface having at least a portion of the first surface profile. The protuberance is defined by a surface having at least a portion of the second surface profile. The method includes placing a sheet of glass-based material at a bottom of the cavity. The method further includes compressing the sheet between the surface having at least a portion of the first surface profile and the surface having at least a portion of the second surface profile to impress at least a portion of the first surface profile and at least a portion of the second surface profile on a first surface and a second surface, respectively, of the sheet, thereby forming a shaped article. 
         [0007]    Other features and advantages of the invention will be apparent from the following description and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0008]    The accompanying drawings, described below, illustrate typical embodiments of the invention and are not to be considered limiting of the scope of the invention, for the invention may admit to other equally effective embodiments. The figures are not necessarily to scale, and certain features and certain views of the figures may be shown exaggerated in scale or in schematic in the interest of clarity and conciseness. 
           [0009]      FIG. 1  is a cross-sectional view of an apparatus for making a shaped article. 
           [0010]      FIG. 2  is a cross-sectional view of an apparatus for making a plurality of shaped articles. 
           [0011]      FIG. 3  shows a sheet of material disposed in a bottom of a cavity in a mold. 
           [0012]      FIG. 4  shows a protuberance inserted into a cavity of a mold containing a sheet of material. 
           [0013]      FIG. 5  shows a sheet of material compressed between a protuberance and a cavity of a mold. 
           [0014]      FIG. 6  shows apparatus stacked for making multiple shaped articles. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The invention will now be described in detail with reference to a few embodiments, as illustrated in the accompanying drawings. In describing the embodiments, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to one skilled in the art that the invention may be practiced without some or all of these specific details. In other instances, well-known features and/or process steps have not been described in detail so as not to unnecessarily obscure the invention. In addition, like or identical reference numerals are used to identify common or similar elements. 
         [0016]      FIG. 1  is a cross-sectional view of an apparatus  100  for making a shaped article. In general, a shaped article will be considered herein as having a top surface with a top surface profile and a bottom surface with a bottom surface profile. The terms “top surface” and “bottom surface” are arbitrary. Each of the top surface and bottom surface may be the inner or outer surface (front or back surface) of the shaped article. The apparatus  100  includes a bottom mold  102 . In one example, the bottom mold  102  is in plate form. A cavity  104  is formed in the bottom mold  102 . The cavity  104  is defined by a surface  106  having a surface profile which matches at least a portion of the bottom surface profile of the shaped article. The surface  106  is generally concave, as illustrated in  FIG. 1 . The surface profile of the surface  106  may be smooth or may be more complex, e.g., including convex and/or textured portions (e.g., bumps and/or depressions). 
         [0017]    The apparatus  100  further includes an intermediate mold  108 . In one example, the intermediate mold  108  may be in a plate form. In one example, the intermediate mold  108  is distinct from the bottom mold  102  and is selectively (or temporarily) stacked on the bottom mold  102  as shown in  FIG. 1 . The intermediate mold  108  includes a hole  110  defined by a surface  112 . The hole  110  is aligned with the cavity  104  in the bottom mold  102  when the intermediate mold  108  is stacked on the bottom mold  102 . Surface  112  is generally vertical, and may be straight or slightly slanted inwardly or outwardly to align with the cavity  104 . While the intermediate mold  108  is stacked on the bottom mold  102 , any suitable mechanism for aligning the hole  110  in the intermediate mold  108  with the cavity  104  in the bottom mold  102  may be used. In one example, the hole  110  in the intermediate mold  108  and the cavity  104  in the bottom mold  102  are aligned by alignment features in the intermediate mold  108  and the cavity  104 . In one non-limiting example, the alignment features may be complementary holes  114 ,  116  in the intermediate mold  108  and cavity  104 , respectively, which can receive an alignment pin  118 . A plurality of such alignment features  114 ,  116 ,  118  may be provided in the intermediate mold  108  and cavity  104 . 
         [0018]    The hole  110  in the intermediate mold  108  and the cavity  104  in the bottom mold  102 , when stacked and aligned as illustrated in  FIG. 1 , define a continuous mold cavity, generally indicated at  120 , for molding the bottom surface of the shaped article. As such, the bottom surface profile of the shaped article may be provided completely by the surface  106  defining the cavity  104  or partially by the surface  106  defining the cavity  104  and partially by the surface  112  defining the hole  110 . The latter forms a basis for the previous statement that the surface  106  defining the cavity  104  is defined by a surface profile matching at least a portion of the bottom surface profile of the shaped article. 
         [0019]    The apparatus  100  further includes a top mold  124  having a base  122 , which may be in the form of a plate, and a protuberance  126  formed on a surface  125  of the base  122 . In the illustrated example, the protuberance  126  has a top protuberance portion  128  and a bottom protuberance portion  130 . The bottom protuberance portion  130  is defined by a surface  132  having a surface profile matching the top surface profile of the shaped article. The protuberance  126  is sized for insertion into the hole  110  and cavity  104  in the intermediate mold  108  and bottom mold  102 , respectively. The top protuberance portion  128  is sized to plug the hole  110  by insertion in the hole  110 . In general, the top protuberance portion  128  is larger in size, or diameter, than the bottom protuberance  130  to allow the bottom protuberance portion  130  to pass through the hole  110  in the intermediate mold  108 . 
         [0020]    For an apparatus  100  for making a plurality of shaped articles, as illustrated in  FIG. 2 , the bottom mold  102  includes a plurality of cavities  104  (as described above) spaced apart from each other. The intermediate mold  108  likewise includes a plurality of holes  110  (as described above) spaced apart from each other. The holes  110  and cavities  104  are arranged in the intermediate and bottom molds  108 ,  102 , respectively, such that when the intermediate mold  108  is stacked on the bottom mold  102 , each hole  110  in the intermediate mold  108  is aligned with one of the cavities  104  in the bottom mold  102 . Alignment features, such as described above, may assist in aligning the holes  110  and cavities  104 . The top mold  124  also includes a plurality of protuberances  126  (as described above) for insertion into each aligned hole  110  and cavity  104 . Each corresponding set of hole  110 , cavity  104 , and protuberance  126  may be custom-shaped to form a particular shaped article. 
         [0021]    The bottom, intermediate, and top molds  112 ,  108 ,  124  may be made of a suitable heat resistant material, i.e., one that would not interact with the material to be used in forming the shaped article(s). Typically, the mold material is selected such that there isn&#39;t a large mismatch in coefficient of thermal expansion (CTE) between the mold material and the material of the shaped article(s). In one non-limiting example, the mold material is selected such that the absolute CTE mismatch between the mold material and the material of the shaped article(s) is less than about 1×10 −6 /°C. In one non-limiting example, the shaped article is made of a glass-based material, such as a glass or glass-ceramic. For glass-based materials, examples of suitable material for the molds include, but are not limited to, stainless steel and graphite. The surface of the molds including the shaping profiles may be coated with a non-stick material, such as, but not limited to, boron nitride, calcium hydroxide, and carbon soot to facilitate separation of the shaped article from the molds. 
         [0022]      FIGS. 3-5  illustrate a method of making a shaped article. In  FIG. 3 , the intermediate mold  108  is stacked on the bottom mold  102  such that the hole  110  in the intermediate mold  108  and the cavity  104  in the bottom mold  102  are aligned. Next, a sheet of glass-based material  134  is disposed at the bottom of the cavity  104 . At this point, the sheet  134  is a flat piece of glass-based material (as opposed to a preform having a shape that approximates the shape of the shaped article to be formed). The sheet of glass-based material  134  is heated to a temperature above the softening temperature of the glass-based material while being disposed at the bottom of the cavity  104 . Typically, heating of the sheet  134  also includes heating of the intermediate and bottom molds  108 ,  102 . The top mold  124  may also be heated. In one example, the sheet  134  is heated to a temperature of about 20° C. higher than the softening point of the glass-based material. In another example, the sheet  134  is heated to a temperature of about 50° C. higher than the softening point of the glass-based material. 
         [0023]      FIG. 3  shows the top mold  124  suspended over the intermediate and bottom molds  108 ,  102  with the protuberance  126  aligned with the hole  110  and cavity  104  in the intermediate and bottom molds  108 ,  102 , respectively. In  FIG. 4 , the protuberance  126  is inserted into the aligned hole  110  and cavity  104  and brought into contact with the sheet  134 . In  FIG. 5 , a load F is applied to the sheet  134  through the protuberance  126 . The applied load compresses the sheet  134  between the surface  132  of the protuberance  126  and the surface  106  of the cavity  104  so that the sheet  134  deforms and fills the space between the protuberance  126  and the cavity  104 . The surface of the sheet  134  in contact with the protuberance  126  takes on the top surface profile carried by the protuberance  126 , while the surface of the sheet  134  in contact with the cavity  104  takes on the bottom surface profile carried by the cavity  134 . Where the sheet  134  is also squeezed into the hole  110 , the sheet  134  also takes on the bottom surface profile carried by the hole  110 . The protuberance  126  plugs the hole  110  by insertion, thereby preventing the sheet  134  from being squeezed out of the hole  110 . 
         [0024]    The amount of force applied to the sheet  134  through the protuberance  126  in  FIG. 5  should be sufficient to compress the sheet  134  between the protuberance  126  and cavity  104  and may be based on the desired thinness of the final shaped article. In general, shaped articles having walls with thickness below about 2 mm can be formed by this method. Shaped articles with thicker walls may also be formed by this method. In one non-limiting example, a force of  100  to  500  N may be applied to the sheet  134  for a few seconds to a few minutes to achieve the desired compression of the sheet  134 . It should be noted that the force applied to the sheet  134  may come from the sheer weight of the top mold  124 . Additional load may be applied to the top mold  124  as necessary to achieve the desired force to compress the sheet  134 . In  FIG. 5 , a gap  136  is present between the opposing surfaces of the top mold  124  and the intermediate mold  110  at the completion of pressing of the sheet  134  (i.e., when the space between the protuberance  126 , the hole  110  and cavity  104  is filled by the sheet  134 ). The gap  136  facilitates subsequent separation of the top mold  124  from the intermediate and bottom molds  110 , 102 . 
         [0025]    The pressed sheet  134  in  FIG. 5  is the desired shaped article  138 . The shaped article  138  is allowed to cool between the molds  124 ,  110 ,  102 . The shaped article  138  may be allowed to cool to a temperature below the strain point of the glass-based material from which the shaped article is formed. For example, the shaped article may be cooled to a temperature of about 50° C. below the glass strain point. Then, the top mold  124  is separated from the intermediate and bottom molds  110 ,  102 . Next, the intermediate mold  110  is separated from the bottom mold  102 , for example, by removing the alignment pins  118 , to liberate the shaped article  138 . Additional processing of the shaped article  138  may include annealing the shaped article  138  and chemically strengthening the shaped article  138 . The shaped article may also be finished, e.g., by fire polishing, to improve its surface quality. The method described herein can be used to form a plurality of discrete shaped articles  138 . Further, a stack of apparatus  100  as explained above can be used to make several discrete shaped articles  138  in a single operation or step (see  FIG. 6 ). 
         [0026]    In one example, the sheet  134  used in making the shaped article is made of a glass-based material that can be chemically strengthened by ion-exchange. Typically, the presence of small alkali metal ions such as Li +  and Na +  in the glass structure that can be exchanged for larger alkali metal ions such as K +  render the glass composition suitable for chemical strengthening by ion-exchange. The base glass composition can be variable. For example, U.S. patent application Ser. No. 11/888,213, assigned to the instant assignee, discloses alkali-aluminosilicate glasses that are capable of being strengthened by ion-exchange and down-drawn into sheets. The glasses have a melting temperature of less than about 1650° C. and a liquidus viscosity of at least about 1.3×10 5  Poise and, in one embodiment, greater than about 2.5×10 5  Poise. The glasses can be ion-exchanged at relatively low temperatures and to a depth of at least 30 μm. Compositionally the glass comprises: 64 mol %≦SiO 2 ≦68 mol %; 12 mol %≦Na 2 O≦16 mol %; 8 mol %≦Al 2 O 3 ≦12 mol %; 0 mol %≦B 2 O 3 ≦3 mol %; 2 mol %≦K 2 O≦5 mol %; 4 mol %≦MgO≦6 mol %; and 0 mol %≦CaO≦5 mol %, wherein: 66 mol %≦SiO 2 +B 2 O 3 +CaO≦69 mol %; Na 2 O+K 2 O+B 2 O 3 +MgO+CaO+SrO&gt;10 mol %; 5 mol %≦MgO+CaO+SrO≦8 mol %; (Na 2 O+B 2 O 3 )—Al 2 O 3 ≦2 mol %; 2 mol %≦Na 2 O—Al 2 O 3 ≦6 mol %; and 4 mol %≦(Na 2 O+K 2 O)—Al 2 O 3 ≦10 mol %. 
         [0027]    The ion-exchange process typically occurs at an elevated temperature range that does not exceed the transition temperature of the glass. The glass is dipped into a molten bath comprising a salt of an alkali metal, the alkali metal having an ionic radius that is larger than that of the alkali metal ions contained in the glass. The smaller alkali metal ions in the glass are exchanged for the larger alkali metal ions. For example, a glass sheet containing sodium ions may be immersed in a bath of molten potassium nitrate (KNO 3 ). The larger potassium ions present in the molten bath will replace smaller sodium ions in the glass. The presence of the large potassium ions at sites formerly occupied by sodium ions creates a compressive stress at or near the surface of the glass. The glass is then cooled following ion exchange. The depth of the ion-exchange in the glass is controlled by the glass composition. For potassium/sodium ion-exchange process, for example, the elevated temperature at which the ion-exchange occurs can be in a range from about 390° C. to about 430° C., and the time period for which the sodium-based glass is dipped in a molten bath comprising a salt of potassium can range from about 7 up to about 12 hours (with less time being required at higher temperatures, and more time being required at lower temperatures). In general, the deeper the ion-exchange, the higher the surface compression and the stronger the glass can be. 
         [0028]    While the invention has been described with respect to a limited number of embodiments, those skilled in the art, having benefit of this disclosure, will appreciate that other embodiments can be devised which do not depart from the scope of the invention as disclosed herein. Accordingly, the scope of the invention should be limited only by the attached claims.