Patent Publication Number: US-8535505-B2

Title: Method for making metallic cover

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application is a divisional application of U.S. patent application Ser. No. 11/954,228, filed on Dec. 12, 2007, now U.S. Pat. No. 8,277,008, which claims all benefits accruing under 35 U.S.C. §119 from CN 200710200819.2, filed on Jun. 14, 2007, the contents of which are hereby incorporated by reference. 
    
    
     BACKGROUND 
     1. Field of the Invention 
     The present disclosure generally relates to a method for making a metallic cover used for electronic device. 
     2. Description of the Related Art 
     Generally, a metallic cover has a more appealing appearance and a better surface feeling than a plastic cover, thus metallic covers are popularly used for electronic devices such as flat-panel display devices. 
     Referring to  FIG. 7 , a typical metallic cover  10  is shown. The metallic cover  10  includes a rectangular bottom base  11 , a first side wall  12 , a second side wall  13 , a third side wall  14 , and a fourth side wall  15 . The side walls  12 ,  13 ,  14 ,  15  perpendicularly extend from a periphery of the rectangular bottom base  11 . Each of the side walls  12 ,  13 ,  14 ,  15  and the bottom base  11  are connected by an edge structure  16 . The edge structure  16  is generally designed to be a curve-cornered edge so that the metallic cover  10  is easy to be made by metal drawing method. Each of the side walls  12 ,  13 ,  14 ,  15  connects to its adjacent side walls, thus the side walls  12 ,  13 ,  14 ,  15  cooperatively define a cavity (not labeled) for receiving electronic components (not shown). 
     In order to obtain a different appearance, an edge structure of another typical cover for connecting the side walls and the bottom base may be a sharp-cornered edge instead of the curve-cornered edge. Generally, the sharp-cornered edge is impossible to be made by metal drawing method. A typical method for making a metallic cover with a sharp-cornered edge is made by the two following steps: drawing a metal sheet into a preformed cover; pressing the preformed cover into a metallic cover with a sharp-cornered edge by a forming die. However, the above described method is prone to cause cracks in the edge structure of the metallic cover, thus decreasing quality of the metallic covers. 
     In addition, the metallic covers made by the above described method need to be processed by an anodizing process. After the anodizing process, color of surface of the edge structure of the metallic cover is quite different from that of other parts of the metallic cover, thereby decreasing the quality of the appearance of the cover. 
     Therefore, a new metallic cover is desired in order to overcome the above described shortcomings. A method for making the metallic cover is also needed. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The components in the drawings are not necessarily drawn to scale, the emphasis instead being placed upon clearly illustrating principles of the present metallic cover and method for making the same. Moreover, in the drawings, like reference numerals designate corresponding parts throughout several views, and all the views are schematic. 
         FIG. 1  is an isometric view of a metallic cover in accordance with one embodiment of the present disclosure. 
         FIG. 2  is an isometric of an aluminum alloy sheet used for making the metallic cover shown in  FIG. 1 . 
         FIG. 3  is an enlarged view of an encircled portion III shown in  FIG. 2 . 
         FIG. 4  is a cross-sectional view of a forming die used for pressing a preformed metallic cover to form the present metallic cover. 
         FIG. 5  is similar to  FIG. 4 , but showing another state. 
         FIG. 6  is partial, cross-sectional view of an edge structure of the preformed metallic cover pressed by the forming die of  FIG. 4 . 
         FIG. 7  is an isometric view of a conventional metallic cover. 
     
    
    
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     Reference will now be made to the drawings to describe preferred embodiments of the present metallic cover and method in detail. 
     Referring to  FIG. 1 , a metallic cover  20  according to one embodiment is shown. In the illustrated embodiment, the metallic cover  20  is used as a cover for a flat-panel display device. The metallic cover  20  includes a rectangular bottom base  21 , a first side wall  22 , a second side wall  23 , a third side wall  24 , and a fourth side wall  25 . The side walls  22 ,  23 ,  24 ,  25  perpendicularly extend from a periphery of the rectangular bottom base  21 . The side walls  22 ,  23 ,  24 ,  25  cooperatively define a cavity (not labeled). The bottom base  21  and each of the side walls  22 ,  23 ,  24 ,  25  are correspondingly connected by an edge structure  26 . The edge structure  26  is a sharp-cornered edge. The angle formed between an outer surface  261  (see  FIG. 6 ) of the bottom base  21  and the outer surface  261  of each of the sidewalls  22 ,  23 ,  24 ,  25  at the edge structure  26  is in the range from 90 degrees to 135 degrees. 
     Empirical data shows that the cause of the cracks and the discolorations in the conventional metallic cover is due to the material of the conventional metallic cover. The conventional metallic cover is made of a material that has a relatively large yield strength (about 197 megapascals (Mpa)) and a relatively low elongation ratio (about 12%). The material at and around the edge structure of the metallic cover deforms badly, thereby causing cracks and discolorations on the conventional cover. In order to avoid or decrease cracks and discolorations in the metallic cover  20 , the metallic cover  20  should be made of a material that has a relatively low yield strength and a relatively large elongation ratio. In a preferred embodiment, the metallic cover  20  is made of a metallic material that has a yield strength in the range from 80 MPa to 150 MPa, an elongation ratio in the range from 15% to 28%, and a hardness in the range from 45 Vickers Hardness 0.2, (HV0.2) to 70 HV0.2. The metallic material is preferred to be aluminum alloys such as 5052-O aluminum alloy and 6061-T4 aluminum alloy. A zinc concentration in the above described aluminum alloys is less than 0.1%. 
     A yield strength of the 5052-O aluminum alloy is about 110 MPa, an elongation ratio of the 5052-O aluminum alloy is about 26%, a hardness of the 5052-O aluminum alloy is about 65 HV0.2, and a zinc concentration is about 0.07%. A yield strength of the 6061-T4 aluminum alloy is about 90 MPa, an elongation ratio of the 6061-T4 aluminum alloy is about 26%, a hardness of the 6061-T4 aluminum alloy is about 60 HV0.2, and a zinc concentration is about 0.06%. 
     Aluminum alloys used in making the metallic cover  20  have a relatively low yield strength and a relatively large elongation ratio, thus the aluminum alloys generally have good malleability, good corrosion resistance, and easy to anodize. The material of the edge structure of the metallic cover allows edge structures to be easily formed and limits deformation, thus, effectively reducing cracks in the edge structure  26 . In addition, the material of the edge structure  26  is deformed slightly, and has a good corrosion resistance, thus effectively reducing discolorations of the metallic cover  20  that is processed by an anodizing process. Therefore, the metallic cover  20  has a good appearance. 
     Referring to  FIGS. 2 and 3 , a cross-sectional view of an aluminum alloy sheet  100  used for making the metallic cover  20  is shown, and t the cross-sectional view is taken along a direction for measuring a thickness of the aluminum alloy sheet  100 . Viewed from the thickness direction, an inner structure the aluminum alloy sheet includes two regular portions  101  and a sensitive portion  103  sandwiched between the two regular portions  101 . The color of the sensitive portion  103  is darker than that of the regular portion  101 . In order to further increase the quality of the surface of the edge structure  26 , a width-thickness ratio of the sensitive portion  103  is preferably to be 0&lt;W/t&lt;0.33, wherein W represents a width of the sensitive portion  103 , and t represents a thickness of the aluminum alloy sheet. For example, the aluminum alloy sheet is made of 5052-O aluminum alloy, and W/t=0.23. 
     Referring to  FIGS. 4 and 5 , an exemplary method for making the metallic cover  20  will now be described. In the illustrated embodiment, the metallic cover  20  is made of the aluminum alloy sheet  100 . The method for making the metallic cover includes the following steps: a drawing process; a pressing process; a polishing process; and an anodizing process. 
     In the drawing process, the aluminum alloy sheet  100  that has a yield strength in the range from 80 MPa to 150 Mpa, an elongation ratio in the range from 15% to 28%, and a hardness in the range from 45 HV0.2 to 70 HV0.2 is drawn to form a preformed cover  30 . The aluminum alloy sheet is preferred to be made of 5052-O aluminum alloy or 6061-T4 aluminum alloy. The preformed cover  30  includes a bottom base  31  and a plurality of side walls  32 . The side walls  32  cooperatively define a cavity (not shown) for receiving electronic components (not shown). After drawn, the bottom base  31  and each of the sidewalls  32  is connected by a curved-cornered edge  33 . 
     In the pressing process, the curved-cornered edge  33  of the preformed cover  30  is pressed into a sharp-cornered edge structure  26  (see  FIG. 6 ) by a forming die  200 . The forming die  200  includes an upper die  210  and a lower die  230 . The upper die  210  is movable relative to the lower die  230 . The upper die  210  defines mold groove  212  and the mold groove  212  faces a forming surface  2311  of the lower die  230 . In use, the preformed cover  30  is mounted on the forming surface  2311  of the lower die  230 , and the mold groove  212  of the upper mold  210  and the forming surface  2311  of the lower die  230  cooperatively press the curved-cornered edge  33  of the preformed cover  30  into the sharp-cornered edge structure  26  (see  FIG. 6 ). 
     After the pressing process, the preformed cover  30  is polished. 
     After the polishing process, the preformed cover  30  is anodized, and then the preformed cover  30  is made into the metallic cover  20 . 
     In alternative embodiments, after the pressing process, the preformed cover  30  is milled by a milling process so that the preformed cover  30  can have a relative better appearance. 
     It is believed that the present embodiments and their advantages will be understood from the foregoing description, and it will be apparent that various changes may be made thereto without departing from the spirit and scope of the disclosure or sacrificing all of its material advantages, the examples hereinbefore described merely being preferred or exemplary embodiments of the disclosure.