Patent Publication Number: US-2009224135-A1

Title: Mold unit with replaceable mold core holder

Description:
BACKGROUND 
     1. Field of the Invention 
     The present invention relates to an injection molding apparatus, and particularly to a mold unit applicable in an injection molding apparatus that has individual replaceable mold core holders. 
     2. Description of Related Art 
     Many kinds of workpieces need to be made via molds. Mold cores are widely used in many mold units to configure workpieces. Referring to  FIG. 4 , a related molding apparatus  10  including a lower mold unit  11  and an upper mold unit  12  facing the lower mold unit  11  is shown. The lower mold unit  11  has a lower mold base  111 , a plurality of lower mold cores  112  disposed within the lower mold base  111 , and a lower fixing base  113  to be fixed to a bottom portion of the lower mold base  111  to retain the lower mold cores  112  in the lower mold base  111 . The lower mold base  111  is formed with a plurality of lower mold core holes  114 , each of which has a narrow upper portion and a wide lower portion. Each of the lower mold cores  112  has a shape corresponding to that of a respective one of the lower mold core holes  114 , and forms a lower molding surface  115  at an end facing the upper mold base  121 . After the lower mold cores  112  are inserted respectively into the lower mold core holes  114 , the lower fixing base  113  is secured to the bottom portion of the lower mold base  111  so that the lower mold cores  112  are retained in the lower mold core holes  114 . 
     The upper mold unit  12  has an upper mold base  121 , a plurality of upper mold cores  122  disposed within the upper mold base  121 , and an upper fixing base  123  to be fixed to a top portion of the upper mold base  121  to retain the upper mold cores  122  in the upper mold base  121 . The upper mold base  121  is formed with a plurality of upper mold core holes  124 , each of which has a narrow lower portion and a wide upper portion. Each of the upper mold cores  122  has a shape corresponding to that of a respective one of the upper mold core holes  124 , and forms an upper molding surface  125  at an end facing the lower mold base  111 . After the upper mold cores  122  are inserted respectively into the upper mold core holes  124 , the upper fixing base  123  is secured to the top portion of the upper mold base  121  so that the upper mold cores  122  are retained in the upper mold core holes  124 . When the molding apparatus  10  is in use, the upper mold unit  12  abuts against the lower mold unit  11 , and thus a chamber is defined by each upper molding surface  125  of the upper mold cores  122 , an inner surface face  116  of the upper mold base  121 , an inner surface face  126  of the lower mold base  111  and the corresponding lower molding surface  115  of the lower mold core  112  for configuring the workpieces. 
     When the lower molding surface  115  or the upper molding surfaces  125  is damaged, the defective lower or upper mold core  112 ,  122  can be removed and replaced. However, if the inner surface  116  of the lower mold base  111  or the inner surfaces  126  of the upper mold base  121  is damaged, the lower mold base  111  or the upper mold base  121  is needed to be replaced. Removal and replacement operations of the lower mold base  111  or the upper mold base  121  are not only time consuming, but also heavily increase the maintenance cost of the molding apparatus  10 . 
     What is needed, therefore, is an improved molding apparatus which can overcome the problems described. 
     SUMMARY 
     A mold unit includes a fixing plate, a mold core retaining plate mounted on the fixing plate, a plurality of mold core holders and a plurality of mold cores. The molding core retaining plate includes a first surface, an opposing second surface facing toward the fixing plate, and a plurality of receiving holes defined therein. The mold core holders are detachably engaged in the respective receiving holes. Each of the mold core holders includes a receiving cavity defined therein. The mold cores are respectively received in the receiving cavities of the mold core holders and are fixable to the fixing plate via the mold core holders. Each of the mold cores includes a molding surface adjacent to the first surface of the mold core retaining plate. 
     Other advantages and novel features will become more apparent from the following detailed description of embodiments when taken in conjunction with the accompanying drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is an isometric, assembled view of an exemplary embodiment of a mold unit. 
         FIG. 2  is an isometric, exploded view of the mold unit in  FIG. 1 . 
         FIG. 3  is a schematic, cross-sectional view of the mold unit in  FIG. 1 , taken along line III-III. 
         FIG. 4  is a partly sectional exploded schematic view of a related molding apparatus. 
     
    
    
     DETAILED DESCRIPTION 
       FIGS. 1-2  show an exemplary embodiment of a mold unit  20  that includes a mold core retaining plate  21 , a fixing plate  22 , a plurality of mold core holders  23  and a plurality of mold cores  24 . 
     Referring also to  FIG. 3 , the mold core retaining plate  21  includes a parting surface  211  (i.e., first surface) and an opposing fixing surface  213  (i.e., second surface) facing toward the fixing plate  22 . Four cylindrical shaped receiving holes  212  are defined in the mold core retaining plate  21  for receiving the corresponding mold core holders  23  therein. The four receiving holes  212  are arranged in a rectangular array. Each of the four receiving holes  212  extends through the mold core retaining plate  21  from the fixing surface  213  to the parting surface  211 . 
     The mold core holder  23  is cylindrical corresponding to the receiving hole  212 . An outer diameter of the mold core holder  23  is slightly greater than that of the receiving hole  212  of the mold core retaining plate  21 . The mold core holder  23  includes a first end surface  234  and an opposing second end surface  235 . When the mold core holder  23  is mounted into the receiving hole  212  of the mold core retaining plate  21 , the first end surface  234  of the mold core holder  23  is flush with the parting surface  211  and the second end surface  235  of the mold core holder  23  is flush with the fixing surface  213  of the mold core retaining plate  21 . A receiving cavity  231  is defined axially in each mold core holder  23  and extends downwardly from the first end surface  234  to the second end surface  235  of the mold core holder  23 . The receiving cavity  231  includes a first cavity portion  232  adjacent to the first end surface  234  of the mold core holder  23 , and a second cavity portion  233  adjacent to the second end surface  235 . The first cavity portion  232  and the second cavity portion  233  are cylindrical and coaxial. A diameter of the first cavity portion  232  is less than that of the second cavity portion  233 . An inner surface  236  of the base  21  surrounds the receiving cavity  231 , and includes an upper portion and a lower portion with a diameter greater than that of the upper portion. A step is thus formed between the upper portion and the lower portion of the inner surface  236  of the mold core holder  23 . 
     The mold core  24  includes a main body  242  and a raised portion  241  extending upwardly from a top surface of the main body  242 . The main body  242  and the raised portion  241  are coaxial cylinders, and the raised portion  241  is coaxially with the main body  242 . A diameter of the raised portion  241  is substantially equal to that of the first cavity portion  232 , and a diameter of the main body  242  is substantially equal to that of the second cavity portion  233 , thereby facilitating respective precision slide fits of the first cavity portion  232  and the second cavity portion  233 . Furthermore, a height of the main body  242  is approximately the same as a depth of the second cavity portion  233 , whilst a height of the raised portion  241  is less than a depth of the first cavity portion  232 , i.e., a height of each mold core  24  is less than a depth of the receiving cavity  231 . A molding surface  243  is formed at a free end of the raised portion  241 . The molding surface  243  of each mold core  24  is lower than the parting surface  211  of the mold core retaining plate  21 . The molding surface  243  can be formed as a concave surface, convex surface, or a planar surface according to the desired shape of the workpieces to be formed. 
     In assembly, the mold core holders  23  are detachably engaged in the respective receiving holes  212 . The mold core holders  23  can be mounted to the mold core retaining plate  21  in a press-fit manner. In this embodiment, the mold core holders  23  are mounted to the mold core retaining plate  21  by temperature difference assembly method, i.e., the mold core holders  23  are mounted into the receiving holes  212  of the mold core retaining plate  21  by heating the mold core retaining plate  21  to expand dimensions of the receiving holes  212 , or by cooling the mold core holders  23  to shrink dimensions of the mold core holders  23 . The raised portion  241  and the main body  242  of the mold core  24  are received in the first cavity portion  232  and the second cavity portion  233 , respectively. The fixing plate  22  is then mounted to the mold core retaining plate  21  and abuts against the fixing surface  213  of the mold core retaining plate  21 . The fixing plate  22  can prevent the mold cores  24  from falling off. Each of the mold cores  24  received in the receiving holes  212  of the mold core retaining plate  21  has a bottom end abutting the fixing plate  22 . Since the height of the raised portion  241  is less than the depth of the first cavity portion  232  of the mold core holder  23 , the molding surface  243  of each mold core  24  is lower than the first end surface  234  of the mold core holder  23 . The molding surface  243  of each mold core  24  and the inner surface  236  in the receiving hole  212  of a corresponding mold core holder  23  cooperatively define a mold cavity  25  for molding a workpiece. In use, a pair of mold units  20  are arranged facing each other with the parting surfaces  211  thereof abutting against each other. A chamber according to a size of the workpiece is defined between each two corresponding molding surfaces of the two mold units  20 . When one of the inner surfaces  236  of the mold core holders  23  of the mold unit  20  is damaged, the damaged or defective mold core holder  23  can be detached easily from the mold core retaining plate  21  by temperature difference, i.e., by cooling the damaged or defective mold core holder  23  to shrink dimensions of the mold core holder  23 . 
     Because the mold cavity  25  of the present embodiment is formed by the inner surface  236  of the mold core holder  23  and the molding surfaces  243  of the mold cores  24 , when the inner surface  236  of mold core holder  23  is damaged or defective, only mold core holder  23  need to be replaced. The replacement time and the maintenance cost of the mold unit  20  are reduced. 
     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.