Patent Publication Number: US-9840033-B2

Title: Mold for resin injection molding

Description:
TECHNICAL FIELD 
     The present invention relates to a mold for resin injection molding to be manufactured by three-dimensional laser sintering. 
     BACKGROUND OF THE INVENTION 
     Background Art 
     In the above-described molds for resin injection molding, a constitution having a shaping region divided by a low-density shaped portion having a sintered density that allows a gas blown or sucked by the above-described three-dimensional laser sintering to pass therethrough and a high-density shaped portion having a sintered density that does not allow the gas to pass therethrough has recently been adopted. 
     In the case of such a divisional constitution, as described in Patent Document 1, a gas venting function via the low-density shaped portion can be fulfilled during resin injection molding. 
     However, in Patent Document 1, it has not been particularly studied how to effectively achieve heating and cooling by a blown or sucked gas with efficiency during resin injection molding and to cause gas to smoothly flow when filling resin. 
     On the other hand, in Patent Document 2 and Patent Document 3, it is intended to achieve the heating and cooling as described above with efficiency by adopting a constitution in which all of the ventilation channels through which a gas blown or sucked by a primary vent passes and a secondary vent which are in contact with a resin molding portion are formed by a low-density shaped portion. 
     However, when all of the primary vents and the secondary vents are formed by a low-density shaped portion, a pressure necessary for blowing or suction may not avoid a state of extremely high due to the cause of communication resistance in the low-density shaped portion interposed between the primary vents and the secondary vents. 
     Furthermore, because the pressure at the secondary vent is not uniform but depends on the degree of the density within the low-density shaped portion and the mold shape, the ventilation volume per unit area of a gas that flows in or out in a section with the resin molding portion is not always uniform, resulting in the case where uniform heating and cooling arise. 
     PRIOR ART DOCUMENTS 
     Patent Documents 
     [Patent Document 1] Japanese Published Unexamined Patent Application No. 2007-160580 
     [Patent Document 2] Japanese Patent No. 5575374 
     [Patent Document 3] Japanese Published Unexamined Patent Application No. H08-300363 
     SUMMARY OF THE INVENTION 
     Disclosure of the Invention 
     Problem to be Solved by the Invention 
     It is an object of the present invention to provide a constitution of a mold for resin injection molding that brings the pressure at the secondary vent into a uniform state while achieving efficient blowing or suction of gas. 
     Means for Solving the Problem 
     In order to achieve the above-described object, a basic construction of the present invention is as follows: 
     A mold for resin injection molding has a shaping region with an inner wall and an outer wall formed by a low-density shaped portion provided between the inner wall and the outer wall having a sintered density that allows gas discharged and sucking in with heating or cooling, and gas passing with resin blown, and a high-density shaped portion having a sintered density that does not allow the gas to pass therethrough and surrounding the low-density shaped portion. 
     There is at least one ventilation channel for gas, with each ventilation channel being formed between at least one primary vent connecting communicatively with an exterior and at least one secondary vent connecting communicatively with a resin molding portion at an inside and with each ventilation channel communicating with both of at least one primary vent and at least one secondary vent, and each ventilation channel forms a hollow state surrounded by a peripheral wall having any one or both of the high-density shaped portion and the low-density shaped portion, and that each secondary vent is formed only by the low-density shaped portion in a state of having a wall with thickness thinner than all thicknesses of the shaping region. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  shows a state of Example 1 characterized in that plural ventilation channels are provided in a cavity shape mold for resin injection molding. 
         FIG. 2  shows a state of Example 2 characterized in that the degree of the sintered density gradually changes in a boundary region between a high-density shaped portion and a low-density shaped portion. 
         FIG. 3  shows a typical embodiment of the present invention. 
         FIG. 4  shows another embodiment in a core shape mold having a projection region inside of a peripheral wall. 
         FIG. 5  shows an embodiment in a state in which the thickness of the secondary vent is reduced at the inside as compared with a surrounding region. 
     
    
    
     DESCRIPTION OF THE SYMBOLS 
     
         
           1 : Mold for resin injection molding 
           11 : Core shape mold 
           12 : Cavity shape mold 
           21 : High-density shaped portion 
           22 : Low-density shaped portion 
           31 : Primary vent 
           32 : Ventilation channel 
           33 : Secondary vent 
           4 : Base plate 
           5 : Resin providing portion 
           6 : Resin molding portion 
           7 : Forming enclosed region portion 
       
    
     DETAILED DESCRIPTION 
     Best Mode for Carrying Out the Invention 
     As shown in a typical embodiment of  FIG. 3 , in a basic constitution of the present invention, each ventilation channel  32  exists between one primary vent or plural primary vents  31  and one secondary vent or plural secondary vents  33 , and forms a hollow state surrounded by a peripheral wall having any one or both of the high-density shaped portion  21  and the low-density shaped portion  22 . 
     In such a hollow ventilation channel  32 , a pressure loss is smaller compared with a state that gas passes through the low-density shaped portion  22  as in the case of Patent Document 2, so efficient ventilation can be achieved. 
     Furthermore, because the pressure in the case of an ordinary ventilation channel  32  is equal, the pressure at the respective secondary vent  33  in the identical ventilation channel  32  is equal regardless of the mold shape, and when plural secondary vents  33  are made equal in average wall thickness, the ventilation volume per unit area can be brought into an equal state. 
     Additionally, most of the molds  1  for resin injection molding are, as shown in  FIG. 3 , composed of both of a core shape mold  11  with projected region and a cavity shape mold  12  without projected region, and when blowing is performed in the primary vent  31  of one of the core shape mold  11  and the cavity shape mold  12 , discharge of gas is performed in the primary vent  31  of the other of the core shape mold  11  and the cavity shape mold  12  and when suction is performed in one of the core shape mold  11  and the cavity shape mold  12 , entry of gas is performed in the primary vent  31  of the other of the core shape mold  11  and the cavity shape mold  12 . 
     However, of course, it is also possible to adopt such an embodiment that blowing is performed in the primary vent  31  of one of the core shape mold  11  and the cavity shape mold  12  and suction is performed in the primary vent  31  of the other of the core shape mold  11  and the cavity shape mold  12 . 
     In  FIG. 3 , the entire peripheral wall is formed for the ventilation channel  32  by the high-density shaped portion  21  in both of the core shape mold  11  and the cavity shape mold  12 , and the peripheral wall can also be formed partially or entirely by the low-density shaped portion  22 . 
     Because, even if the peripheral wall is formed partially or entirely by the low-density shaped portion  22 , gas inevitably passes through the secondary vent  33  due to the cause that the secondary vent  33  has a wall with thickness thinner than that of the shaping region, and a state of causing a pressure loss as is the case of the conventional technology does not arise in which gas passes through a shaping region formed by the low-density shaped portion  22 , and so the resin molding portion  6  and the primary vent  31  are connected communicatively. 
     However, in the case of a peripheral wall by the low-density shaped portion  22 , because of entry of gas into a partial region of the low-density shaped portion  22 , the ventilation volume at the secondary vent  33  decreases, and considering such a decreasing of the ventilation volume, it is preferable that the peripheral wall is entirely formed by the high-density shaped portion  21  as is shown in  FIG. 3 . 
     In a region of forming a wall portion that contacts the resin molding portion  6 , persons skilled in the art can arbitrarily select which of the high-density shaped portion  21  as shown in  FIG. 3  or the low-density shaped portion  22  as shown in  FIG. 4  should be adopted. 
     However, taking into consideration the lifetime of the mold, the high-density shaped portion  21  is preferably adopted for the region of forming the wall. 
     In the core shape mold  11 , an embodiment is often adopted which is characterized, as shown in  FIG. 3 , in that the secondary vent  33  is provided in any one or both of a gap between an inner wall portion and the projection region and a gap between projection regions. 
     However, as shown in  FIG. 4 , one secondary vent or plural secondary vents  33  can also be provided for the core shape mold  11  in the peripheral wall of the projection region. 
     In the cavity shape mold  12 , as shown in  FIG. 3 , one secondary vent is or plural secondary vents  33  are often provided in a bottom portion surrounded by a peripheral wall. 
     Gas can flow into the resin molding portion  6  or flow out from the resin molding portion  6  almost equivalently through plural secondary vents  33 . 
     However, in the case that a distance between peripheral walls is shorter than their height, an embodiment in which the secondary vent  33  is provided inside of the peripheral wall may be adopted. 
     The secondary vent  33  is required to satisfy both items that can stand a pressure associated with resin molding and that gas outflows or inflows efficiently between the secondary vent  33  and the resin molding portion  6 . 
     The wall thickness of the secondary vent  33  is dependent on a sintered density of the low-density shaped portion  22 , and in most cases both requirements are satisfied by adopting the wall of thickness from 2 mm to 5 mm. 
       FIG. 5  shows an embodiment of the secondary vent  33  characterized in that a region at the inside thereof is formed with a gradually thin state compared with a surrounding region. 
     In the case of above embodiment, a pressure associated with resin molding is supported by the surrounding region of the secondary vent  33  or a vicinity thereof, while gas can blow out or blow in efficiently thorough a thin-walled region in the center or a vicinity thereof. 
     Additionally, also in the embodiment shown in  FIG. 5 , by setting an average value of the wall thicknesses of the secondary vent  33  to be in a range from 2 mm to 5 mm, both requirements of the wall standing the pressure associated with resin molding and sufficient gas outflowing or inflowing can be satisfied. 
     EXAMPLES 
     Hereinafter, the following examples are described. 
     Example 1 
     Example 1 is characterized in that, as shown in  FIG. 1 , plural ventilation channels  32  are set up for communicating with each primary vent  31  and each secondary vent  33 . 
     In Example 1 with such a characteristic, when the degree of necessary heating or cooling is different arisen by a difference of the shape of a resin molding region, ventilation volume can be controlled separately according to respective ventilation channels  32 , and so proper heating or cooling of a corresponding resin molding region can be achieved. 
     Example 2 
     Example 2 is characterized in that, as shown in  FIG. 2 , the degree of the sintered density gradually changes in a boundary region between a high-density shaped portion  21  and a low-density shaped portion  22 . 
     Example 2 with such a characteristic may be achieved by the process that in respectively molding the high-density shaped portion  21  and the low-density shaped portion  22 , gradually reducing the pressure of air to be injected into the low-density shaped portion  22  in the vicinity of a boundary of the high-density shaped portion  21  allows gradual change to molding of the high-density shaped portion  21 . 
     As in  FIG. 3 ,  FIG. 4 , and  FIG. 5 , the high-density shaped portion  21  and the low-density shaped portion  22  must be separately molded when both shaped portions are clearly divided at a boundary, whereas continuous molding can be achieved in the case of Example 2. 
     Effect of the Invention 
     In the basic construction of this invention, the ventilation channel is a hollow state surrounded by the peripheral wall formed by any one or both of the high-density shaped portion and the low-density shaped portion, and the primary vent and the secondary vent are connected communicatively with each other, a gas blown or sucked by the primary vent can flow in or flow out through the secondary vent having a wall with thickness thinner than that of the shaping region and flow efficiently between the resin molding portion. 
     So that in heating and cooling in the mold and ventilation with filling of resin, a pressure loss in conventional technology can be prevented. 
     Further, as a pressure is equal in an identical ventilation channel, so the pressure at the secondary vent is equal regardless of the mold shape, and the ventilation volume per unit area can be brought into an equal state by setting an equal wall thickness for the secondary vent. 
     Therefore, this invention can achieve heating and cooling with efficient and uniform ventilation, and can be widely applied to molds for resin injection molding.