Patent Publication Number: US-2007098831-A1

Title: Mold for injection molding

Description:
The present application claims priority under 35 U.S.C. 119 and 35 U.S.C. 365 to Korean Patent Application No. 2005-84136 (filed on Sep. 9, 2005), which is hereby incorporated by reference in its entirety.  
     BACKGROUND OF THE INVENTION  
      1. Field of Invention  
      The present invention relates to a mold for injection molding, and more particularly, to a mold for injection molding capable of manufacturing a hemispherical molded product with protrusions of a predetermined shape formed on an inner surface thereof.  
      2. Description of the Prior Art  
      Generally, a mold for injection molding, which is provided therein with a molding space corresponding to an external shape of a product to be molded, is configured by incorporating a plurality of unit molds that can be disassembled from each other so as to remove a molded product formed in the molding space to the outside.  
      Meanwhile, in a case of a molded product with a complex external shape, there is also a method in which the molded product or a part of the unit molds is enabled to rotate during a process of separating the incorporated unit molds in order to easily remove the molded product.  
      However, while easily used to manufacture a molded product such as a helical gear, the aforementioned method cannot be applied to the molded product which has a concavo-convex portion of various shapes on an internal or external surface thereof.  
     SUMMARY OF THE INVENTION  
      Accordingly, the present invention is conceived to solve the aforementioned problems in the prior art. An object of the present invention is to provide a mold for injection molding which makes it possible to easily remove a hemispherical molded product from the mold when injection molding of the hemispherical product with protrusions of a predetermined shape formed on an inner surface thereof.  
      According to an aspect of the present invention for achieving the object, there is provided a mold for injection molding comprising a first mold having a concave molding surface, and a second mold arranged to be spaced from the first mold at a predetermined distance in order for a cavity to be formed between the molding surface and the second mold. The second mold includes a plurality of unit molds which can be coupled with and disassembled from each other. The molding surface is formed thereon with protrusions having a predetermined shape. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
      The above and other objects, features and advantages of the present invention will become apparent from the following description of a preferred embodiment given in conjunction with the accompanying drawings, in which:  
       FIG. 1  is a perspective view showing a mold for injection molding according to the present invention;  
       FIG. 2  is a perspective view showing a state where a second mold of the mold for injection molding of  FIG. 1  is disassembled; and  
      FIGS.  3  to  5  are views showing a process of removing the second mold from a molded product when manufacturing the molded product using the mold for injection molding according to the present invention.  
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
      Hereinafter, a preferred embodiment according to the present invention will be described in detail with reference to the accompanying drawings.  
       FIG. 1  is a perspective view showing a mold for injection molding according to the present invention, and  FIG. 2  is a perspective view showing a state where a second mold of the mold for injection molding of  FIG. 1  is disassembled.  
      As shown in the drawings, the mold for injection molding according to the present invention comprises a first mold  100  and a second mold  200 .  
      The first mold  100  is provided with a gate  110  for feeding a molten material, and a first molding surface  120  communicating with the gate  110  is concavely formed on the top surface of the first mold  100 . In addition, a second molding surface  220  is formed on an outer wall surface of the second mold  200 . The first and second molds  100  and  200  are arranged to be spaced by a certain distance from each other so that a predetermined cavity  210  is formed between the first and second molding surfaces  120  and  220 . The second molding surface  220  is provided with a plurality of protrusions  230  formed in a lattice shape.  
      The second mold  200  includes a plurality of unit molds  240 ,  250  and  260  that can be coupled with and disassembled from each other. This is to remove the second mold  200  without damaging the molded product.  
      In more detail on the second mold, the second mold  200  is configured so that nine unit molds which are classified into three kinds of shapes are coupled to each other to be formed into a cylindrical shape with a hemispheric lower part.  
      The first unit mold  240 , which is a single component, is positioned in the center of the second mold  200 . The first unit mold  240  has a top surface  242  formed in a regular octagonal shape and a bottom surface  244  convexly formed to partially define the second molding surface  220 . The bottom surface  244  is formed with a part of the protrusions  230 . It is described in the present embodiment that the shape of the top surface of the first unit mold  240  is described as the regular octagon, but the shape is not limited thereto. For example, the top surface may have a polygonal shape including an octagon, a hexagon or a regular hexagon.  
      The second unit molds  250 , the number of which is four, are arranged radially from the first unit mold  240  and coupled thereto to be equi-angularly spaced from each other. In other words, an angle between the adjacent second unit molds  250   a  and  250   b  is 90 degrees and an angle between the opposite second unit molds  250   b  and  250   c  is 180 degrees. The top surface  252  of the second unit mold  250  is formed in a rectangular shape. An inside surface  254  of a shorter side of the rectangle is formed to be brought into contact with a surface  246  of the first unit mold  24 . An outside surface  256  positioned opposite to the surface  254  of the shorter side is convexly formed to partially define the second molding surface  220 , wherein the convex surface  256  is formed with a part of the protrusions  230 .  
      The third unit molds  260  are coupled between the adjacent second unit molds and are arranged radially from the first unit mold  240 . An inside surface  262  of the third unit mold  260  is formed to be brought into contact with a surface  248  of the first unit mold  240 . An outside surface  264  positioned opposite to the surface  262  is convexly formed to partially define the second molding surface  220  of the second mold  200 , wherein the surface  264  is formed with a part of the protrusions  230 . Also, both side surfaces  266  are formed to be brought into contact with adjacent longer side surfaces  258  of the second unit molds  250 .  
      The respective unit molds  240 ,  250 ,  260  constructed as above are coupled with each other to be formed into the hemispherical second mold  200 , the protrusions  230  are connected with each other to be formed in a lattice shape on the second molding surface  220 .  
      In the meantime, the first unit mold  240  is formed to taper downward such that the second mold  200  is easily coupled and disassembled. It is preferred that the top surface  252  of the second unit mold  250  is formed in an outwardly tapered shape.  
      FIGS.  3  to  5  are views showing a process of removing the second mold from a molded product when manufacturing the molded product using the mold for injection molding according to the present invention.  
      The aforementioned process, which is to remove the second mold without damaging the protrusions formed on the surface of the molded product, will be described with reference to the drawings.  
      In order to remove the second mold  200  from an initial state where the molded product  300  is attached to the molding surface  220  of the second mold  200 , the first unit mold  240  is removed upwardly as shown in  FIG. 3 . Since the protrusions formed on the bottom surface of the first unit mold  240  are formed in the vertical or nearly vertical direction, the protrusions of the molded product cannot be damaged although the first unit mold  240  is removed upwardly.  
      Then, each of the second unit molds  250  is removed in the direction of the arrow in  FIG. 4 . At this time, the removal direction of the second unit mold  250  should be an oblique direction so that the protrusions  310  of the molded product  300  cannot be damaged.  
      Finally, each of the third unit molds  260  should be removed in the direction of the arrow in  FIG. 5 . At this time, the third unit mold  260  should be removed in an oblique direction similar with the removing direction of the second unit mold  250  so that the protrusions  310  of the molded product  300  cannot be damaged.  
      If the second mold  200  is removed according to the aforementioned process, the second mold  200  can be removed without damaging the protrusions  310  of the molded product  300 . Thus, it is possible to obtain the molded product of a good quality. Further, the mold can be applied to a plastic injection molding process, or a powder injection molding process that is used to manufacture a metal or ceramics product by mixing a metal or ceramics powder with a binder of an organic material, molding the mixture using the injection molding process, removing the binder, and then sintering the same. Particularly, it is possible to obtain more advantageous effects when the mold is applied to a tungsten powder injection molding process.  
      According to the mold for injection molding of the present invention, there is an advantageous effect in that the mold can be easily removed without damaging protrusions formed on the inner surface of the molded product by using a plurality of unit molds which can be coupled with and disassembled from each other.  
      While the construction and operation of the mold for injection molding according to the preferred embodiment of the present invention has been described with reference to the accompanying drawings, it will be apparent that those skilled in the art can make various modifications and changes thereto within the scope of the invention defined by the claims.