Abstract:
A method for manufacturing plastic product includes the steps of: forming a work piece ( 30 ) in an injection molding apparatus, the work piece ( 30 ) including at least an original product ( 34 ), a butt end ( 36 ), and gate ( 32 ), the gate ( 32 ) connecting a corresponding original product ( 34 ) with the butt end ( 36 ); precutting the gate ( 32 ) in a mold before the work piece ( 30 ) has completely cooled; removing the work piece ( 30 ) from the injection molding apparatus; separating each original product ( 34 ).

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention generally relates to methods for manufacturing plastic products, and more particularly, to a method for manufacturing small plastic products by means of an injection molding apparatus. 
     2. Description of Related Art 
     Nowadays, electronic devices such as mobile phones and digital cameras are widely used and bring convenience to our lives. In order to attract customer, producers of these products are increasingly concentrating on the appearance of the electronic devices. Since some small parts, e.g., covers for protecting camera lenses, infrared windows, keys, are generally mounted on an outside surface of an electronic device, these small parts might effect the appearance of the electronic device. These small parts are generally formed in an injection molding apparatus, and gate is formed at the same time. In order to achieve final product, gate must be removed. However, after the gate is removed defects will appear in the final product. Therefore, removal of gate has become an important factor affecting the quality of the product. 
     One conventional method of removing gate is cutting off the gate inside the mold. However, the product may be adhered to the mold in this method. In addition, the workers directly contact with the products during surface treatment so that the surfaces of the products may easily become scratched and polluted. 
     Another conventional method for removing gate is cutting off the gate outside the mold. The gate may be removed by means of hot cutting or cold cutting. If the products are thin and the gate is relatively thick compared to the product the product easily become damaged in hot cutting, and may easily form burrs during cold cutting. 
     What is needed, therefore, is a method for manufacturing plastic products which can overcome the above-described shortcomings. 
     SUMMARY OF THE INVENTION 
     In a preferred embodiment, a method for manufacturing plastic product includes the steps of: forming a work piece in an injection molding apparatus, the work piece including at least one original product, a butt end, and at least one gate, each gate connecting a corresponding original product with the butt end; precutting each gate in mold before the work piece is completely cooled; removing the work piece from the injection molding apparatus; separating each original product from the butt end. 
     Other advantages and novel features of preferred embodiments of the present method and its applications will become more apparent from the following detailed description when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic, cross-sectional view of a mold in accordance with a preferred method according to the present invention, showing a work piece formed in an injection molding apparatus; 
         FIG. 2  is an isometric, top plan view of the work piece of  FIG. 1 , the work piece including four products, and a butt end; and 
         FIG. 3  is a cross-sectional view of the work piece in  FIG. 2  along a line III-III. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     In a first preferred embodiment, a method for manufacturing protective covers applied to electronic devices is disclosed according to the present invention. The protective covers are used to protect lenses mounted on electronic devices. The protective covers are generally square and roughly 0.75 mm thick. Each protective cover has a circular transparent portion at a central area thereof and an opaque portion around the transparent portion. 
     Referring to  FIG. 1 , a work piece  30  is formed in an injection molding apparatus (not labeled). 
     The material of the work piece  30  is polymethylmethacrylate (PMMA). The injection molding apparatus includes an upper mold  10 , a lower mold  20 , and a precutting mechanism (not labeled). The upper mold  10  has a main runner  11 , and four divaricate runners  12  extending from the main runner  11 . The lower mold  20  has four mold cavities  22  defined therein. The shape of each mold cavity  22  corresponds to the protective cover in design. Each divaricate runner  12  communicates with a corresponding mold cavity  22 . A plurality of ejector pins  24  are moveably positioned in the lower mold  20 . The ejector pins  24  are used to push products out from the lower mold  20 . The precutting mechanism includes four precutting pins  26 . The precutting pins  26  are moveably disposed in the lower mold  20 , and are positioned under the joining points of the corresponding cavities  22  and the divaricate runners  12 . 
     The molten material is injected into the mold cavities  22  via the main runner  11  and the divaricate runners  12 , a gate  32  is thus formed between a corresponding mold cavity  22  and a corresponding divaricate runner  12 . The precutting pins  26  move upward and press the gate  32  before the material in mold is not completely cooled, and the material of the gate  32  is thus partly move away and the gate  32  becomes thinner. When the material in mold is completely cooled, a work piece  30  is formed. The work piece  30  includes four original lenses  34 , four precut gates  32 , and a butt end  36 . The original lens  34  connects with the butt end  36  by means of the precut gates  32 . 
     The thickness of the precut gates  32  can be controlled by the precutting mechanism. The thickness of the precut gates  32  depends on the moving distance of the precutting pins  26 . In this preferred embodiment, the optimal leaving thickness of the gate  32  is 0.1 mm. In this case, on one hand, the gates  32  connect the original lens  34  with the butt end  36  so that the original lens  34  can be picked up by means of the butt end  36  thus avoiding the original lens  34  being scratched and polluted. On the other hand, the gate  32  becomes thinner is weakened as a result. Therefore the gate  32  can easily be broken without forming burr or gaps. 
     The work piece  30  is pushed out from the lower mold  20  by the ejector pins  24 . A manipulator picks up the work piece  30  and lays it down on a reused carrier. The carrier has lots of cavities for receiving the original lens  34 . The carrier is made of flexible material. 
     The carrier receiving the work piece  30  is transported to the printing room. The work piece  30  is picked up by hand or manipulator via the butt end  36 , and laid down on a holder. One surface of each original lens  34  is printed using transfer printing, forming a circular transparent portion in a central area of the original lens  34  and an opaque portion around the transparent portion. The work piece  30  is dried by ultraviolet radiation in a drying apparatus. The work piece  30  is put on the carrier again. Touching of the lens  34  during operation is avoided, and of pollution and damage to the lens  34  is reduced as a result. Accordingly, the quality rate of the product is increased. 
     The work pieces  30  received in the carriers are transported to the assembly room. The gate  32  can be broken off by hand, in this way each lens  34  is separated from the butt end  36 . The protective lens  34  can then be assembled with other parts and used in optical devices. 
     During the transportation of the work piece  30 , the carriers protect the lens  34  instead of plastic bags used in the conventional method. In this case, the process of packing the work piece  30  with plastic bags is omitted. Accordingly, the production efficiency is increased, and the cost of manufacturing is reduced. 
     In a second preferred embodiment according to the present invention, the method is used for manufacturing keys. The material of the keys is made of acrylonitrile-butadiene-styrene (ABS). The surface treatment on the keys may involve many different methods such as crazing, spray painting, plating, and physical vapor deposition (PVD). 
     In a third preferred embodiment according to the present invention, the method is used for manufacturing infrared windows. The infrared windows can be made of polycarbonate (PC). In this case, the surface treatment is omitted, in which the work pieces formed in the mold are directly transported to the assembly room. 
     It is to be further understood that even though numerous characteristics and advantages of the present embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.