Abstract:
A simplified lost-core molding system that combines otherwise redundant features such as platens and hydraulic cylinders ordinarily found in separate core molding stations and product molding stations. The preferred system locates the core mold and the product mold between the platens of an injection molding machine and applies a common clamping force to the core mold and to the product mold.

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates generally to a meltable core molding system for forming hollow plastic products by molding plastic over a meltable core and, more particularly, to an improved system wherein the core molding process and overmolding process are combined in one injection molding machine to share a common clamping force and eliminate redundant machinery. 
     2. Description of the Related Art 
     Meltable core technology has long been used to make hollow plastic products. A conventional “lost-core” system resides in a large production “cell” consisting of a core molding station, a core cooling station, a product molding station, and a core melting station. The cores and plastic products are typically moved from station to station with one or more robotic carriers or arms. 
     In general, cores of desired geometry are formed in the core molding station by injecting a molten metal alloy into a suitable core mold. The core is then ejected from the core mold and moved to the core cooling station. After cooling, the core is transferred to the product molding station where it is placed in a product mold block located between the platens of an injection-molding machine. After closing and clamping the product mold under suitable clamp tonnage, molten plastic is injected into the product mold and around the core to form an overmolded assembly. The product mold is opened after a sufficient time has passed for the plastic to cool and become suitably rigid for removal from the mold. The overmolded assembly is then ejected from the product mold and moved to the core melting station where it is placed in a hot oil tank that is at a temperature above the melting point of the core but below the melting point of the plastic. The core material melts out of the overmolded assembly to leave only the hollow plastic product. The molten core material sinks to the bottom of the hot oil tank where it is gathered and returned to the core molding station to make more cores. 
     Lost-core production cells are capable of producing hollow-core parts such as bicycle and wheelchair wheels, T-fittings, water meter housings, impellers, and so on. Lost-core molding is often not used for such products, however, because its considered too “complicated,” too slow, and too expensive in terms of machinery costs, energy usage, maintenance, and so on. As a result, lost-core molding is often used only as a last resort where other molding techniques are unavailable (due typically to intricate part geometries). As one example, a T-fitting is likely to be produced in a conventional injection molding machine that cycles a complicated mold with multiple core-pulls (three) that must remain in position until the part solidifies. As another example, an impeller is likely to be produced in a conventional injection molding machine that runs a mold for producing two sub-components that do not have a hollow core and must be ultrasonically welded together to complete the impeller. 
     The present invention makes it possible to produce complicated parts (e.g. automotive manifolds and hollow bicycle wheels), that are already being made with lost-core techniques, at less cost. The invention, moreover, makes it cost effective to produce less complicated parts such as T-fittings and impellers with lost-core techniques because, for the first time, the lost-core equipment can be cost effectively acquired, operated and maintained, and can be operated at higher production rates owing to the features of this invention and advantages associated with lost-core techniques in general (e.g. the elimination of dwell-time for parts to solidify before pulling cores in a conventional injection molding process). 
     The prior art lost-core cells known to these inventors have made less than optimal use of the clamp tonnage available in the injection molding machine used to form the overmold assembly. The core and product molding stations are usually separated because it is generally the companies that make core molding machines who assemble the entire cell. From their point of view, the injection molding machine, the robots, the cooling and so on, orbit around their core molding machine. 
     Moreover, because the molten metal is usually injected into the core mold at relatively low pressure (e.g. 500 PSI) to provide a flow-like introduction, rather than a spray-like introduction, the core molding machines are often made with correspondingly low clamp tonnage, the result being less than ideal mold closure and “flashing” where some of the injected metal is squeezed out of the mold cavity at the interface between two mold halves. Cores that suffer from flashing must be manually “de-flashed” before being loaded into the injection molding machine. 
     The use of separate core and product molding stations may impose a longer than otherwise reach requirement on the robot from the core molding station or even worse, require additional robots. For example, two robots may be needed, one to move a hot core to the cooling station and one to move a cool core from the cooling station to the product molding station, to remove an overmolded assembly from the product mold, to replace it with a new core from the cooling station, and to move the overmolded assembly to the core melting station. 
     In summary, the prior art core molding stations suffer from having the core molding station separate from the product molding station. As a result, the conventional lost-core cell is unnecessarily expensive to purchase, requires excessive floor space, consumes more energy than needed, and is relatively difficult to maintain because it requires redundant molding machines that are separately acquired, located, operated and maintained. 
     There remains a need, therefore, for a lost-core molding cell of simplified construction and operation. 
     SUMMARY OF THE INVENTION 
     The invention is a simplified lost-core molding system that combines otherwise redundant features such as platens and hydraulic cylinders ordinarily found in separate core molding stations and product molding stations. The preferred system locates the core mold and the product mold between the platens of an injection molding machine and applies a common clamping force to the core mold and to the product mold. 
     In a first aspect, the invention may be regarded as a method of producing a hollow plastic product comprising the steps of: providing molten metal; providing molten plastic; providing an injection molding machine with first and second platens; locating a core mold between the first and second platens; locating a product mold between the first and second platens; loading a core into the product mold; closing the core mold and the product mold by bringing together the first and second platens; clamping the core mold and product mold between the first and second platens with a common clamping force; injecting molten metal into the core mold to form a new core; injecting molten plastic into the product mold and around the core to form an overmolded assembly comprising a hollow plastic product that covers the core; removing the common clamping force; opening the core mold and the product mold by separating the first and second platens; removing the new core from the core mold; removing the overmolded assembly from the product mold; and loading the new core into the product mold. 
     In a second aspect, the invention may be regarded as molding apparatus adapted for simultaneously forming a core and an overmold assembly comprising: first and second platens that are moveable relative to one another; a core mold located between the first and second platens; a product mold located between the first and second platens; and a source of clamp tonnage for applying a common clamp tonnage to the first and second platens and, thereby, to the core mold and the product mold. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The just summarized invention may be best understood with reference to the following drawings of which: 
     FIG. 1 is a perspective view of a dual purpose molding apparatus  10  according to this invention, the apparatus being shown in the open position at the beginning of a molding cycle where a core and an overmolded assembly are formed with the same clamp tonnage; 
     FIG. 2 shows the apparatus  10  with the platens closed and subject to clamp tonnage during which time a new core and a new overmolded assembly are produced; 
     FIG. 3 shows the apparatus  10  with the platens open, a new core  100  being visible; 
     FIG. 4 shows a robot having moved downward into the core molding region to grip the new core  100 ; 
     FIG. 5 shows the robot  90  having moved upward from the core molding region with the new core  100 ; 
     FIG. 6 shows the robot  90  moving the new core  100  over the product molding region; 
     FIG. 7 shows the robot  90  diving downward with the new core  100  into the product molding region, the robot  90  placing the new core  100  on one of the product mold blocks; 
     FIG. 8 shows the robot  90  moving from one product mold block to the other product mold block where the robot grips the overmolded assembly  200  that was produced when the apparatus  10  was as shown in FIG. 2; 
     FIG. 9 shows the robot  90  moving upward with the overmolded assembly  200 ; 
     FIG. 10 shows the robot  90  taking the overmolded assembly  200  away from the apparatus  10  for downstream proceeding and a melt-out station; 
     FIG. 11 is a perspective view of a second dual purpose molding apparatus  310  according to this invention, the apparatus being shown in the open position at the beginning of a molding cycle where a core and an overmolded assembly are formed with the same clamp tonnage in an injection molding machine having only two platens, an A-side platen  340  and a B-side platen  350 ; 
     FIG. 12 shows the apparatus  310  with the B-side platen  350  being moved toward the A-side platen  340  at the start of a molding cycle; 
     FIG. 13 shows the apparatus  310  with the B-side platen  350  fully clamped against the A-side platen  340  followed by the simultaneous injection of molten plastic into the overmold cavity and the injection of molten metal into the core cavity; 
     FIG. 14 shows the apparatus  310  with the platens open, a new core and a new overmolded assembly being visible; 
     FIG. 15 shows the apparatus  310  with the robot having dived into the space between the platens such that its gripping mechanism is, in this case, simultaneously adjacent to both the new core and the new overmolded assembly; 
     FIG. 16 shows the robot&#39;s gripping mechanism grabbing the new core and new overmolded assembly; 
     FIG. 17 shows the apparatus  310  with the robot  390  moving upward such that the new core is brought adjacent to the now empty overmold cavity; 
     FIG. 18 shows the apparatus  310  with the robot  390  depositing the new core into the overmold cavity; 
     FIG. 19 shows the apparatus  310  with the robot  390  continuing upward with the new overmold assembly in hand; 
     FIG. 20 shows the apparatus  310  with the robot moving away from the apparatus with the overmold assembly; and 
     FIG. 21 shows the apparatus  310  with the robot “dropping” the overmold assembly so that it may proceed forward to the core melting station. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     FIG. 1 shows a first embodiment of a dual-purpose molding apparatus  10  according to this invention. The apparatus  10  shown is a planned modification to an existing injection molding machine used to make hollow-core bicycle wheels by overmolding cores that were formed in a separate core molding station. In the apparatus  10  of FIG. 1, however, a core and an overmolded assembly are formed at the same time and under the same clamp tonnage. 
     In more detail, the molding apparatus  10  of FIG. 1 comprises a base  20  which supports a first plate  40  and a second plate  50 . The first plate  40  is stationary and fixedly secured to the base. The second plate  50 , however, is movable along main support rails  21 ,  22  of the base  20 . The second platen, therefore, is movable back and forth relative to the first platen  40 . Also shown is an injection assembly  30  located next to the first stationary platen  40 . The injection assembly  30  includes a source  31  of plastic pellets, a feed mechanism  32  and a heated injection barrel  33  that forces molten plastic through a “sprue” in the first platen  40 . 
     As further shown in FIG. 1, the apparatus  10  comprises a product molding region  70  containing a first product mold block  71  and a second product mold block  72  that collectively define the cavity inside of which the injection molded product is formed. Ordinarily, the first and second product mold blocks  71 ,  72  are secured to the first and second platens  40 ,  50  so that the mold blocks  71 ,  72  may be operatively opened and closed to form and inject new products. In the new dual-purpose molding apparatus  10  of FIG. 1, however, the injection molding machine has been modified to include an additional intermediate platen  60  that divides the space between the first and second platens  40 ,  50  to include a product molding region  70  and a core molding region  80 . The core molding region  80  is fed by a source of molten metal  83  as figuratively shown. The core mold, like the product mold, comprises a first core mold block  81  and a second core mold block  82 . In the embodiment shown, the first core mold block  81  is secured to the second platen  50  and the second core mold block  82  is secured to the intermediate platen  60 . The product mold block  71 , remains secured to the first platen  40 , but the second product mold block  72  is secured to the intermediate platen  60  opposite to the second core mold block  82 . In the preferred embodiment, suitable ejection mechanism for both the product mold and core mold are carried by intermediate platen  60  such that the new core  100  is picked up by one side of the gripping mechanism  92  and the new overmolded assembly  200  is picked up by the opposite side of the gripping mechanism  92 . The intermediate platen  60  is supported on a pair of support members  44  extending from the first platen  40 . Each of those support members  44  includes an intermediate support rail  45  along which the intermediate platen  60  may be moved relative to the first platen  40 . 
     For use in transporting cores and for unloading overmolded assemblies, a robot  90  having a moveable arm  91  with a suitable gripping mechanism  92  is provided adjacent to the molding apparatus  10 . The cyclical operation of the apparatus  10  will now be described with reference to FIGS. 2-10. 
     In FIG. 2, the robot  90  is held out of the way to allow the molding apparatus  10  to close and begin the molding operation. The closing proceeds in two steps as suggested by arrows “A 1 ” and “A 2 .” At step “A 1 ”, the intermediate platen  60  is moved toward the stationary platen  40  along the intermediate support rails  45  of the support members  44 . Next, as suggested by arrow “A 2 ,” the movable platen  50  is moved toward the stationary and intermediate platens  40 ,  60  to provide full clamp tonnage to simultaneously apply full clamp tonnage to both the product molding region  70  and the core molding region  80 . With this clamp tonnage applied, the molten plastic is introduced into the product molding region by way of the heated injection barrel  33  and the molten metal is introduced into the core molding region  80  from the source of molten metal  83 . 
     In FIG. 3, after allowing the core and overmolded assembly to solidify somewhat, the molding apparatus  10  is opened as shown. In particular, the movable plate  50  is moved away from the intermediate and stationary platens  40 ,  60  as suggested by “arrow B 1 ” and then, the intermediate platen  60  is moved away from the stationary platen  40  as suggested by arrow “B 2 ”. At this point, the core molding region  80  and the product molding region  70  are opened and accessible. 
     FIG. 4 shows the robot  90  diving into the core molding region  80 . In particular, a gripping mechanism  92  carried at the robot&#39;s arm  91  far end is brought adjacent to a new core  100 . The gripping mechanism  92  contains suitable structure for gripping the new core  100  and lifting it out of and away from the second core mold block  82 . 
     FIG. 5 shows the robot  90  moving upward as suggested by arrow “D”. As a result, the robot&#39;s gripping mechanism  92  brings the new core  100  up and out of the core molding station  80 . 
     FIG. 6 shows the robot  90  moving over the product molding region  70  and suggested by arrow “E”. At this point, the robot  90  is now ready to move downward into the product molding region  70 . 
     FIG. 7 shows the robot  90  diving downward into the product molding region  70  as suggested by arrow “F”. When the robot  90  has moved sufficiently downward that the new core  100  carried by its gripping mechanism  92  is located adjacent to the first product mold block  71 , then the robot  90  hangs the new core on suitable structure within the mold block  71 . 
     FIG. 8 shows the robot  90  moving sideways, as suggested by arrow “G” such that an opposite side of the gripping mechanism  92  is brought adjacent to the freshly made overmolded assembly  200 . At this position, suitable structure on the gripping mechanism  92  grabs the overmolded assembly  200  in order to transport it out of and away from the molding apparatus  10 . 
     FIG. 9 shows the robot  90 , as just suggested, moving upward in the direction of arrow “H” with the new overmolded assembly carried by the gripping mechanism  92 . Recall that the new core  100  is left behind within the product molding region  70  back in FIG.  7 . 
     FIG. 10 shows the robot moving in a direction generally indicated by arrow “I” in order to take the new overmolded assembly  200  to an appropriate melt-out station (not shown). After delivering the overmolded assembly  200  to the melt-out station, the system  10  is in the state originally shown in FIG.  1  and the cycle may repeat. 
     FIGS. 11-21 show a second preferred, dual molding apparatus  310  that uses only two platens  340 ,  350  as found in a conventional injection molding machine. As shown in FIG. 11, the molding apparatus  310  comprises a base  320  which fixedly supports an A-side platen  340  and movably supports a B-side platen  350 . The two platens  340 ,  350  each support the two halves of a core mold and a product mold as best shown in FIG. 15, discussed below. The core mold and product mold may be embodied in a single pair of mold blocks as shown, or may be arranged as separate mold blocks if desired. In addition, there would be one or more core mold cavities and one or more product mold cavities if desired. As with the embodiment of FIG. 1, the apparatus  310  includes an injection assembly  330  that includes a source  331  of plastic pellets, a feed mechanism  332 , and a heated injection barrel  333  that forces molten plastic through a “sprue” in the A-side platen  340 . Also present is a source of molten metal  383  and a suitable conduit (not separately numbered) for introducing molten metal into the core molding cavity (located at the bottom side of the platens  340 ,  350  in this particular case). The particular conduit used may be any suitable arrangement such as a flexible conduit that moves with the B-side platen  350  or a conduit that is fixed in location and engages a suitable entry orifice when the B-side platen  350  is moved to the closed position. 
     As further shown in FIG. 12, a robot  390  is located adjacent to the apparatus  310 . The robot  390 , like the robot  90  of the first embodiment, includes and arm  391  which supports a gripping mechanism  392  at its distal end. In this case, however, the gripping mechanism  392  is a tandem mechanism that is capable of simultaneously grabbing a new core and a new overmolded assembly as will become clear below. 
     In FIG. 12, the robot  390  is held out of the way to allow the molding apparatus  310  to close and begin the molding operation. As suggested by Arrow “A” the B-side platen  350  is moved toward the A-side platen  340 . 
     In FIG. 13, as suggested by the Arrow “B 1 ” the B-side platen completes its closure and the full clamp tonnage is applied. Subsequently, the injection barrel  333  of the injection assembly  330  is pressed against the entry orifice or “sprue” of the A-side platen as suggested by Arrow “B 2 .” At this point, therefore, with the full clamp tonnage applied, molten plastic is injected into the product mold and molten metal is simultaneously injected into the core mold. 
     In FIG. 14, as suggested by Arrow “C 1 ” the B-side platen is moved leftward to open the core and product molds and the robot  390 , as suggested by Arrow “C 2 ,” dives into the space between the two platens  340 ,  350 . 
     In FIG. 15, the robot&#39;s arm  391  is positioned such that the gripping mechanism  392  is adjacent to a new core  100 ′ and a new overmolded assembly  200 ′ that was formed during the molding operation of FIG.  13 . 
     In FIG. 16, as suggested by Arrows “D 1 ” and “D 2 ,” the new core  100 ′ and the new overmolded assembly  200 ′ are ejected toward the tandem gripping mechanism  392  which suitably grabs the core and overmolded assembly for transport upward (in the case of the core  100 ′) and outward (in the case of the overmolded assembly  200 ′). 
     In FIG. 17, as suggested by Arrow “E,” the robot  390  is indexed upward such that the new core  100 ′ at the bottom of the tandem gripping mechanism  392  is brought adjacent to the now empty product cavity  373 . 
     In FIG. 18, as suggested by Arrow “F,” the core  100 ′ is placed into the product cavity  373 . 
     In FIG. 19, as suggested by Arrow “G,” the robot  390  now continues upwards such that its arm  391  and tandem gripping mechanism  392  carry the overmolded assembly upward and out of the space between the platens  340 ,  350 . Note, as a result of the action taken in FIG. 18, the core  100 ′ is left behind in the product mold  373  while the core mold  383  is empty. At this point, therefore, the product mold  373  and the core mold  383  are ready for a subsequent cycle. 
     In FIG. 20, as suggested by Arrow “H,” the robot moves away from the apparatus  310  with the new overmolded assembly  200 ′ in hand. At this point, the platens  340 ,  350  could be brought together again to begin another cycle as shown beginning with FIG. 11 above. 
     In FIG. 21, as suggested by Arrow “I,” the robot  390  “drops” the new overmolded assembly so that it may proceed to a suitable core melting station which melts out the core material from inside of the product. FIG. 21 shows the overmolded assembly  200 ′ being dropped, however it is more likely that the overmolded assembly  200 ′ would be hung on a suitable mechanism for carrying the overmolded assembly  200 ′ into and through a hot oil bath or other such suitable arrangement. 
     Two presently preferred embodiments of the invention have just been described, but it should be understood that numerous other modifications are possible without departing from the claimed invention. The first embodiment shows an apparatus  10  where the product and core molding regions are in a stacked arrangement between first and second platens on either side of an intermediate platen. The second embodiment shows an apparatus  310  where the core and product molding regions are arranged in a common plane between only first and second platens. In both cases, however, a new core  100 ,  100 ′ and a new overmolded assembly  200 ,  200 ′ are uniquely formed with the same clamp tonnage, thereby eliminating the need for separate core and product molding stations as required in the past. In the common plane arrangement of the second embodiment, the core and product molds are shown in an integrated and vertical arrangement but they could, of course, be separate, arranged horizontally relative to one another in that same common plane, or both. It is also possible in both embodiments to use core and product molds with multiple cavities to increase overall throughput.