Abstract:
An object of the present invention is to improve operability. Stoppers ( 74 ) are detachably mounted in a lower mold ( 70 ) of a mold. Nuts ( 30 ) are screwed down onto the stoppers ( 74 ) while being held upside down. After the mold is closed in this state and molten resin is filled into a cavity ( 77 ) and solidified therein, the mold is opened. The stoppers ( 74 ) are separated from the lower mold ( 70 ) as the mold is opened. When the stoppers ( 74 ) are separated from the nuts ( 30 ) thereafter, a casing  10  having no pin withdrawal hole can be obtained. Accordingly, it is not necessary to apply potting or the like to close the pin withdrawal hole.

Description:
BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The invention relates to a method for producing an insert-molded article and a mold assembly therefor. 
   2. Description of the Related Art 
   An electronic control unit has a casing made of a synthetic resin and a printed circuit board is mounted in the casing. Various electronic components and an electronic control circuit are disposed on the printed circuit board and in the casing. Japanese Unexamined Patent Publication No. 2004-40945 discloses a grounding path for such an electronic control unit. 
   The electronic control unit has a metal nut and a metal collar that are held in contact with an intermediate busbar. The casing is formed by insert molding using the metal nut and the metal collar as inserts. Thus, the metal nut, the intermediate busbar and the metal collar are embedded and are connected successively. The casing can be fixed to a body while a grounding wire from the electronic control circuit is connected with the metal nut. Thus, the grounding wire, the metal nut, the intermediate busbar and the metal collar are connected electrically with the body and are grounded. 
   The metal nut is set in the mold by supporting a bottom part of the metal nut on a resting pin that projects from the mold. However, a pin withdrawal hole is left below the bottom part of the nut when the pressing pin is withdrawn. Thus, a potting material is used to close the pin withdrawal hole and to provide airtightness after insert molding. The potting material adds to the cost for raw material and an additional operation load is required for potting. 
   The present invention is developed in view of the above problem, and an object thereof is to improve operability. 
   SUMMARY OF THE INVENTION 
   The invention relates to a method for producing an insert-molded article. The method includes mounting at least one stopper in or on a mold. The stopper is capable of locking an insert member. The method then includes engaging the insert member with the stopper to hold the insert member in position and to prevent loose movements of the insert member. The mold then is closed, and molten resin is filled at least partly into a cavity and solidified. The stopper then is separated from the insert member. Thus, no pin withdrawal hole is left in the molded article, and there is not need for potting or the like to close the pin withdrawal hole. 
   The at least one stopper preferably is capable of locking the insert member by the engagement of projections and recesses, and preferably by threaded engagement. 
   The stopper preferably is mounted detachably in or on the mold. 
   The mold preferably is opened until the insert member is separated from the stopper after the molten resin is filled at least partly into the cavity and solidified. The stopper preferably is separated from the mold as the mold is opened, thereby improving operational efficiency. 
   According to a preferred embodiment of the invention, the insert member is a nut spirally or threadingly engageable with the stopper. 
   The insert member preferably is a nut that is engageable with the stopper. The nut can be held easily and securely in position merely by being threadedly engaged with the stopper. 
   The invention also relates to a mold assembly for producing an insert-molded article. The assembly comprises a mold and at least one stopper capable of locking an insert member. The stopper is mounted in or on the mold and the insert member is engageable with the stopper to hold the insert member in position while preventing loose movements of the insert member. The mold is configured to be closeable in this state, and the stopper is separable from the insert member after molten resin is filled at least partly into a cavity and solidified therein. 
   The at least one stopper preferably is capable of locking the insert member by the engagement of projections and recesses or by threads. 
   The stopper preferably is detachably mountable in or on the mold. 
   The insert member preferably comprises a nut threadedly engageable with the stopper. 
   These and other objects, features and advantages of the present invention will become more apparent upon reading of the following detailed description of preferred embodiments and accompanying drawings. It should be understood that even though embodiments are separately described, single features thereof may be combined to additional embodiments. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
       FIG. 1  is a plan view of a casing according to one embodiment of the present invention. 
       FIG. 2  is a front view showing an essential portion. 
       FIG. 3  is a section showing a state before nuts are engaged with stoppers. 
       FIG. 4  is a section showing a state where the nuts are engaged with the stoppers. 
       FIG. 5  is a section showing a state where a mold is closed. 
       FIG. 6  is a section showing a state where a resin is filled in a cavity. 
       FIG. 7  is a section showing a state where an upper and a lower molds are separated. 
       FIG. 8  is a section showing a state where a molded article can be taken out by means of ejector pins. 
       FIG. 9  is a section showing an essential portion. 
       FIG. 10  is a section of an essential portion showing a state where terminal fittings and rubber plugs are mounted on wires. 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   The method and molding assembly of the subject invention are described herein with respect to the manufacture of a casing for an electronic control unit. The casing is made e.g. of a synthetic resin and is identified by the numeral  10  in  FIG. 1 . The casing  10  is in the form of a box with an open top. At least one printed circuit board  11  and/or bus system is accommodated in the casing  10  and at least one circuit board connector, capacitor, fuse and/or other electrical or electronic component  12  is connected with the printed circuit board  11 . An unillustrated cover is mounted on the casing  10  and the covered casing  10  is mounted on an unillustrated body. 
   A function portion  20  bulges out sideways from one sidewall of the casing  10 . Long narrow metallic cap nuts  30  are at least partly embedded in the function portion  20 , as shown in  FIGS. 9 and 10 , and can be connected respectively with two conductors. One of the conductors is a terminal fitting  40  connected with an end of a wire W that extends outside the casing  10 . The other conductor is a busbar  80  that extends inside the casing  10 . 
   The nuts  30  are arranged substantially side by side and stand vertically in the function portion  20 . As shown in  FIGS. 2 and 9 , the function portion  20  has first tubes  21  that correspond with the respective nuts  30 . Each first tube  21  covers substantially all of the respective nut  30  except opening thereof. The function portion  20  also has second tubes  22  that are unitarily continuous with the first tubes  21 . The second tubes  22  have introducing holes  23  that communicate from above with the openings of the nuts  30  and that are configured for receiving male screws. The function portion  20  also has third tubes  24  that are unitarily continuous with the first and second tubes  21 ,  22  and that extend transversely therefrom. The third tubes  24  have insertion holes  25  that communicate with the openings of the nuts  30  (see e.g.  FIG. 9 ) and that are configured for receiving terminal fittings. The terminal fittings  40  are inserted into the insertion holes  25  of the third tubes  24  so that leading ends of the terminal fittings  40  face the openings of the nuts  30  from above. 
   The second tubes  22  are arranged vertically and open up. However, the third tubes  24  are arranged substantially normal to the second tubes  22  and open sideways. The introducing holes  23  extend substantially vertically along a first direction  1 D in the second tubes  22  and the introducing holes  25  extend substantially horizontally along a second direction  2 D in the third tubes  24 . Thus, the first and second introducing holes  23  and  25  communicate with each other at substantially right angles above the openings of the nuts  30 . The second tubes  22  are adjacent to each other and their ends are joined unitarily. Circumferentially spaced ribs  26  extend from the outer circumferential surface of each third tube  24 . One rib  26 A spans between and unitarily connects the adjacent third tubes  24 . 
   A substantially cylindrical rubber plug  60  is fit into the introducing hole  23  of each second tube  22  after the male screw  50  is introduced. A plurality of circumferential lips  61  are provided on the outer circumferential surface of the rubber plug  60  and closely contact the inner wall of the introducing hole  23  to seal the introducing hole  23 . A step  23 A is provided at an intermediate position of the inner wall of each introducing hole  23  along the first direction  1 D, and the rubber plug  60  is placed to abut the step  23 A. 
   The terminal fitting  40  is formed by bending a metal plate to define a barrel  41  and a main portion  42  continuous with and in front of the barrel  41 . The barrel  41  is configured to be crimped, bent or folded into connection with an exposed end section of the wire W. The main portion  42  is substantially flat and is arranged substantially normal to the first direction  1 D. The leading end of the main portion  42  is substantially ring-shaped. Thus, a shaft  51  of the male screw  50  can be inserted through the ring-shaped main portion  42  and into the nut  30  when the main portion  42  is above the opening of the nut  30  (see e.g.  FIG. 10 ). The busbar  80  has a ring-shaped first end disposed above the opening of the nut  30  and dimensioned to receive the shaft  51  of the male screw  50 . The busbar  80  also has a second end arranged in the casing  10  for connection with a conductor path of the printed circuit board  11  or another electric/electronic device. An intermediate portion of the busbar  80  is embedded in the casing  10 . The first end of the busbar  80  and the leading end of the main portion  42  are placed one over the other above the opening of the nut  30 . As a result that the shaft  51  of the male screw  50  can be introduced through communicating holes to engage the nut  30 . 
   A hollow cylindrical seal  90  is mounted on the insulation coating of the wire W behind a rear portion of the terminal fitting  40 . Two annular lips  91  are formed on the outer circumferential surface of the seal  90 . The lips  91  closely contact and seal with the inner wall of the insertion hole  25 . 
   A mold assembly for insert molding is shown in  FIG. 5 . The mold assembly has a first mold  70 , a second mold  71  and a slidable mold  72 . The second mold  71  is movable along a first moving direction  1 MD towards and away from the first mold  70 . The slidable mold  72  is movable sideways along a second moving direction  2 MD substantially normal to the first moving direction  1 MD. The slidable mold  72  is used to form the insertion holes  25  of the third tubes  24  and is shaped in conformity with shapes of the insertion holes  25 . As shown in  FIG. 3 , the lower mold  70  has support columns  73  for forming the introducing holes  23  of the second tubes  22 . 
   A stepped cylindrical stopper  74  penetrates each support column  73  and has a plurality of diameters along the moving direction MD 1 . Each stopper  74  has a fixing portion  75  at least partly embedded in the support column  73 . A screw  76  is continuous with the upper end of the fixing portion  75  and has a diameter smaller than the fixing portion  75 . An external thread is formed on the screw  75  and is spirally engageable with the nut  30 . The stopper  74  is slidable along the moving direction MD 1  and relative to the support column  73 . Thus, the fixing portion  75  can project from and retract into the upper surface of the support column  73 . The nut  30  is screwed down onto the screw  76  of the stopper  74  to prevent loose movements of the nut  30  in response to pressure from the resin during insert molding. A projecting distance of the screw  76  is shorter than the shaft  51  of the male screw  50  and the screw  76  is engaged only with a part of an internally threaded area of the nut  30 . 
   The first end of each busbar  80  is fit on the screw  76  of the corresponding stopper  74 . Each nut  30  then is turned upside down and screwed down until the leading end surface of the nut  30  contacts the upper surface of the busbar  80 , as shown in  FIG. 4 . As a result, the nut  30  is held in position and loose movements are prevented. The slidable mold  72  then is moved and the upper mold  71  is lowered to close the mold, as shown in  FIGS. 5 and 6 . Molten resin then is injected and filled into a cavity  77  of the mold to form the function portion  20 . 
   The mold is opened after the synthetic resin has cooled and solidified. Ejector pins  78  then push the stoppers  74  up, as shown in  FIG. 8 , and the second tubes  22  are removed from the support columns  73 . The entire casing  10 , including the function portion  20 , then can be taken out of the mold. The molded article then is turned upside down and the stoppers  74  are turned and separated from the nuts  30  to complete the casing  10 . 
   The seals  90  are mounted on the wires W and the terminal fittings  40  are crimped into connection with the ends of the wires W and the seals  90 . The terminal fittings  40  then are inserted into the insertion hole  25  of the corresponding second tube  22  so that the main portion  42  of the terminal fitting  40  is placed on the first end of the busbar  80 . The screw  50  then is inserted in the opening of the introducing hole  23 . The shaft  51  of the screw  50  passes through the leading end of the terminal fitting  40 , through the first end of the busbar  80  and into the nut  30 . The screw  50  then is tightened so that the terminal fitting  40  and the busbar  80  are squeezed between the head  52  of the screw  50  and the nut  30  along the first direction  1 D. In this way, the terminal fitting  40  and the busbar  80  are connected electrically. The rubber plug  60  is fit into the introducing hole  23  of the second tube  22  in the first direction  1 D after this screw-fastening is completed to seal the introducing hole  23  hermetically. Further, the insertion hole  25  of the third tube  24  is sealed hermetically by the seal  90  mounted on the terminal fitting  40 . 
   As described above, the nuts  30  are screwed at least partly onto the stoppers  74  mounted in the first mold  70  and are held in position while having loose movements thereof prevented. The mold then is closed and the molten resin is filled into the cavity  77 . The stoppers  74  are separated from the nuts  30  after the resin is solidified. Thus, no pin withdrawal hole is left, and there is no need for potting or the like to close the pin withdrawal holes. 
   The molten resin is filled into the cavity and solidified therein. The mold then is opened and the stoppers  74  are separated from the lower mold  70  as the mold is opened. Thus, the lower mold  70  does not accompany the stoppers  74  upon separating the stoppers  74  from the nuts  30 , and operability is even better. 
   The invention is not limited to the above described and illustrated embodiment. For example, the following embodiments are also embraced by the technical scope of the present invention as defined by the claims. Beside the following embodiments, various changes can be made without departing from the scope and spirit of the present invention as defined by the claims. 
   The stoppers are mounted in the mold and the nuts are inserts assembled with the stoppers in the foregoing embodiment. However, the nuts may be mounted in the mold and the stoppers may be the inserts assembled with the nuts according to the invention. 
   The fastening nuts for connecting the terminal fittings and the busbars are used as inserts in the foregoing embodiment. However, other nuts or the like may be used as inserts instead of the inserts having the above-described function. 
   The stoppers are mounted detachably in the mold in the foregoing embodiment. However, the stoppers may be fixed to the mold according to the present invention.