Patent Publication Number: US-2023140739-A1

Title: Molding Apparatus with Combined Core Plunger/Ejector and Methods Therefor

Description:
FIELD OF THE INVENTION 
     The present invention relates to the molding processes. 
     BACKGROUND 
     It can be problematic to fabricate plastic parts having varying cross-sections, geometries, and fine/thin features via conventional molding processes such as injection molding and compression molding. Among other issues, once such a part is formed, extreme care must be taken when ejecting the part from the mold to prevent damaging the part. To make such parts, molding apparatuses typically include relatively complex, integrated ejection systems, which may include ejector pins, ejector blades, and/or stripper plates. These systems, which are arranged in a part-specific layout, support a part at various locations when the time comes to eject the part from a mold. 
       FIGS.  1 A and  1 B  depict, via cross sectional views, portions of a conventional injection-molding system  100 , including integrated ejection system  102 . The ejection system depicted uses ejector pins for the removal of a finished part.  FIG.  1 A  depicts system  100  during molding operations to form a part, and  FIG.  1 B  shows the system after the part has been molded, and removed from the mold via the ejection system. 
     Injection molding system  100  includes top clamping plate  104 , sprue  106 , cavity plate  108 , cavity  110 A, core plate  112 , core  114 A/B, core support plate  116 , ejector retaining plate  118 , ejector plate  120 , bottom clamping plate  122 , ejector bar  124 , spring  126 , three ejector pins  128 A (fully visible in  FIGS.  1 A /B), three ejector pins  128 B (partially obscured in  FIGS.  1 A /B), and return pin  130 . Ejection system  102  includes ejector retaining plate  118 , ejector plate  120 , ejector bar  124 , spring  126 , ejector pins  128 A, ejector pins  128 B, and return pin  130 . 
       FIG.  1 A  depicts liquified molding material  132  (resin, or resin and fiber) in cavity  110 A (see,  FIG.  1 B ). It is injected under pressure through sprue  106 . Core (or plunger)  114 A protrudes into cavity  110 A, and these two elements are responsible for one of the resulting (hollow) domed portions of finished part  134  (see  FIG.  1 B ). Molding system  100  also includes a second core  114 B/cavity pairing, which is responsible for forming the second domed portion of finished part  134 . (The cavity that pairs with second core  114 B is obscured in  FIGS.  1 A and  1 B .) 
     In  FIG.  1 A , ejection system  102  is in an unactuated state, wherein ejector pins  128 A and  128 B are positioned “below” the bottom surface of nascent part  134 . The ends of (the three) pins  128 A and (the three) pins  128 B, which will support various regions of the finished part, are flush with the top surface of core plate  112 . In this unactuated state, ejector retaining plate  118  and catch plate  116  are separated by gap G 1 , and spring  126  is in an uncompressed state. 
     In  FIG.  1 B , part  134  has been formed, and the upper portion of molding system  100 , including cavity plate  108 , top clamping plate  104 , and sprue  106 , has been separated from the lower portion of the molding system to facilitate the part&#39;s removal. Ejection system  102  has been actuated to remove part  134 . When actuated, ejector bar  124  is advanced by a distance G 2 , and spring  124  is compressed. The ejector bar drives ejector plate  120  and ejector retaining plate  118  forward, advancing ejector pins  128 A and  128 B. Ultimately, gap G 1  between ejector retaining plate  118  and catch plate  116  fully collapses. As the ejector pins move proud of core plate  112 , they contact the base of part  134 , thereby forcing the part away from core plate  112  and ejecting the part. 
     Ejector pins  128 A and  128 B must be situated to provide sufficient support to part  134  by appropriately distributing the load applied thereto. Doing so ameliorates deformation of the part, thereby preventing damage to part  134  during the ejection process. 
     A number of drawbacks are associated with the presence of prior-art ejection system  102 . Among any other drawbacks, the ejection system:
         increases the parts count of the molding system, resulting in increased capital cost;   complicates assembly/disassembly of the molding system, increasing overall molding time and labor cost;   increases the presence of flash near a part&#39;s ejection surface as the ejector pins wear, resulting in substantial post processing of a finished part, and increasing overall molding time and labor cost;   only suitable for supporting a non-cosmetic surface of a part (due to marring caused by the pins);   creates a large number of failure modes;   requires frequent parts replacement as the ejector pins buckle, such as when the force required to eject the part from the core exceeds the strength of the pin; and from galling (metal-on-metal wear as an off-center ejector pin moves through holes in various plates during actuation of the ejection system); and   decreases the interchangeability of mold components and parts.       

     Many of the same drawbacks are associated with ejection systems using ejector blades, and stripper plates/rings. Although the ejection system discussed above was used in conjunction with an injection-molding system, ejection systems for use in conjunction with other types of molding apparatus, such as a compression molding system, are similar in design and operation, and have all the same drawbacks. 
     SUMMARY 
     Some embodiments of the invention provide a means and a method for ejecting parts from a molding apparatus that avoid many of the costs and disadvantages of the prior art. 
     In accordance with an illustrative embodiment, a one-piece mold component—a core plunger/ejector—replaces the multi-piece ejection systems of the prior art. In addition to providing part-ejection functionality, the core plunger/ejector of the present invention also participates in molding operations. For example, in some embodiments, the core plunger/ejector is used to consolidate the feed material in the mold cavity, compacting it to its final form. This is unlike the ejection systems of the prior art, wherein the pins, etc., do not in any way participate in the actual molding (consolidation) of the resin or resin/fiber feed into the final form of a part. 
     In some embodiments, the core plunger/ejector is integrated into compression-molding systems to provide improved variants of such processes. Thus, a molding apparatus for injection molding or compression molding in accordance with the present teachings nominally include three main elements: an “A” portion of a mold, a “B” portion of the mold, and the core plunger/ejector. 
     It is notable that a conventional compression mold has two main elements: a top, typically male-mold half (sometimes called the “A” portion of the mold) and a bottom, typically female-mold half (sometimes called the “B” portion of the mold). In such a conventional compression mold, the A portion functions as a “plunger” to press down and consolidate feed material (i.e., resin and fiber) that resides in a cavity in the B portion. To provide part-ejection functionality, a conventional mold includes a plurality of minor elements, such as pins and an accompanying actuation system, as previously discussed (see, e.g.,  FIGS.  1 A,  1 B  for an injection molding system). 
     In accordance with some embodiments, and in contrast to conventional compression molding, the A and B portions of the mold function collaboratively to create a cavity, wherein it is the core plunger/ejector compacts the feed material and seals the cavity. In some embodiments, more than one core plunger/ejector is used in conjunction with a single mold cavity. 
     Embodiments of the invention provide substantial benefits compared to the prior art. These include, among any others, a substantial reduction in: (i) molding apparatus complexity, (ii) mold part count, (iii) maintenance and repair, (iv) failure modes, and (v) flash, and a substantial improvement in interchangeability. 
     In some embodiments, the invention provides a molding apparatus having an A-portion; a B-portion, and a core plunger/ejector. At least one of the A-portion or the B-portion is movable to open and close the molding apparatus, and the core plunger/ejector is movable to (a) consolidate a charge into a geometry of the part; and (b) eject a molded part from the molding apparatus. 
     In some other embodiments, the invention provides a method for molding comprising: advancing a core plunger/ejector of a molding apparatus to consolidate a charge in a cavity to a shape of the part; cooling the molding apparatus to form the part; opening the molding apparatus; moving the core plunger/ejector to break a bond between the part and the core plunger/ejector; and moving the core plunger/ejector to break a bond between the part and an A-portion or a B-portion of the molding apparatus. 
     Summarizing, a molding apparatus, as depicted and described, comprises: (i) an A-portion of a mold, (ii) a B-portion of a mold, and a core plunger/ejector. Embodiments of the molding apparatus may further comprise at least one of the following features, in any (non-conflicting) combination, among other features disclosed herein:
         the core plunger/ejector is movable to form a sealed cavity, in conjunction with the A-portion and the B-portion, in which a charge is received.   the core plunger/ejector is movable to consolidate the charge in the cavity to a shape of the part.   the core plunger/ejector is movable to break a bond formed between the finished part and the core plunger/ejector.   the core plunger/ejector is movable to break a bond formed between the part and at least one of the A-portion or the B-portion of the mold.   the core plunger/ejector advances to form the sealed cavity.   the core plunger/ejector advances to consolidate the charge.   the core plunger/ejector retracts to break the bond between the part and the core plunger/ejector.   the core plunger/ejector advances to break the bond between the part and at least one of the A-portion or the B-portion of the molding apparatus.   the molding apparatus is a compression molding apparatus.   the molding apparatus in an injection molding apparatus.   the molding apparatus includes more than one core plunger/ejector.   the core plunger/ejector is symmetric about a vertical center line.   the core plunger/ejector is asymmetric about a vertical center line.   the core plunger/ejector actuates in the z direction.   other than the core plunger/ejector, the molding apparatus does not include ejector pins or any other structure that is used to separate/eject a finished part from any surface (e.g., a surface of the A-portion, a surface of the B-portion, etc.) of the molding apparatus.       

    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG.  1 A  depicts a conventional injection-molding system, including an ejection system, wherein the ejection system is in an unactuated state. 
         FIG.  1 B  depicts the conventional injection-molding system of  FIG.  1 A , wherein the ejection system is fully actuated thereby removing a finished part from the mold. 
         FIGS.  2 A- 2 C  depict a part that is to be made using a compression molding apparatus that includes a core plunger/ejector in accordance with an illustrative embodiment of the present invention. 
         FIGS.  3 A- 3 F  depict, via a sectional view of, a sequence of operations for making the part of  FIGS.  2 A- 2 C  using a compression molding apparatus including a core plunger/ejector. 
         FIG.  4    depicts a perspective view of a portion of the compression molding apparatus depicted in  FIGS.  3 A- 3 F . 
     
    
    
     DETAILED DESCRIPTION 
       FIGS.  2 A- 2 C  depict a part—a frame for ski goggles—that is made by an improved compression-molding apparatus that includes a core plunger/ejector, in accordance with an illustrative embodiment of the invention. 
       FIG.  2 A  depicts a perspective view of frame  240  for the ski googles.  FIG.  2 B  depicts a front view of frame  240 , and  FIG.  2 C  depicts a sectional view of frame  240  through the line A-A in  FIG.  2 B  and in the direction shown. 
       FIGS.  3 A through  3 F  depict a molding sequence for forming frame  240  of  FIGS.  2 A through  2 C , as illustrated by the relative positions of the three major portions of compression-molding apparatus  300 . The portions of apparatus  300  are shown via sectional views for clarity.  FIG.  4    depicts a perspective view of compression-molding apparatus  300  (to supplement the sectional views depicted in  FIGS.  3 A- 3 F ), wherein the configuration of apparatus  300  depicted in  FIG.  4    (as a function of depicted progress of the molding sequence) corresponds to  FIG.  3 C . 
       FIG.  3 A  depicts a sectional view of compression-molding apparatus  300 . Apparatus  300  includes “A” portion  350  (identified within dashed lines), “B” portion  356 , and core plunger/ejector  360  (identified within dashed lines). Other elements of apparatus  300 , such as an actuator to move core plunger/ejector  360  “upwards” or “downwards,” are not depicted in the figures to maintain a focus on elements that are most germane to an understanding of the invention. These three portions—A portion  350 , B portion  356 , and core plunger/ejector  360 —are depicted in perspective in  FIG.  4   . The various unidentified channels and openings that appear in  FIG.  4   , which for the most part do not appear in  FIGS.  3 A- 3 F , are for purposes of tool machinability or mold operability. As to the latter, such channels and openings are used for thermocouple placement, as a heater-cartridge housing, for mold assembly, for mold fixation to a press, etc. These channels and openings are not germane to an understanding of the invention and, consequently, will not be described in further detail. 
     In  FIG.  3 A , compression-molding apparatus  300  is “open,” such that A-portion  350  and B-portion  356  are separated from one another. In this state, core plunger/ejector  360  is in a retracted state. Charge  370  of resin or resin/fiber has been placed on surface  364  of core plunger/ejector  360 . 
       FIG.  3 B  depicts molding apparatus  300  with the cavity in a sealed state (although the mold itself is not necessarily closed), wherein surface  352  of A-portion  350  and surface  358  of B-portion  356  abut one another, forming parting line  382 . Moreover, sealed cavity  384  is formed the abutment of various surfaces of A-portion  350 , B-portion  356 , and core plunger/ejector  360  with one another. Charge  370  is within sealed cavity  384 . After the mold is closed, A-portion  350 , B-portion  356 , and core plunger/ejector  360  are heated to the processing temperature, which causes the resin in charge  370  to melt. 
     In  FIG.  3 C , core plunger/ejector  360  is advanced (i.e., moved upwards in the figure), consolidating the charge into the final shape of frame  240 . Movement of core plunger/ejector  360  to its final position creates additional tooling interfaces; namely, interface  386  between B-portion  356  and core plunger/ejector  360 , and interface  388  between A-portion  350  and core plunger/ejector  360 . After a dwell (e.g., typically a few minutes) at the processing temperature, mold apparatus  300  starts cooling, and cools until an ejection temperature is reached. 
     In  FIG.  3 D , mold apparatus  300  is opened. With the upward movement of A-portion  350  to open the mold, the bond between the A-portion and the finished part—frame  240  (shown in section, as in  FIG.  2 C )— is broken. 
     In  FIG.  3 E , core plunger/ejector  360  is retracted (i.e., moves downward in the figure), breaking the bond between the molding surface of the core plunger/ejector and the finished part (frame  240 ). In  FIG.  3 F , core plunger/ejector  360  is once again advanced, breaking the bond between the bottom surface of frame  240  and the upper surface of A-portion  356 , ejecting the part. 
     It is notable that the aforementioned sequence of operations is permutable. For example, the operation depicted in  FIG.  3 E  can be performed before the operation depicted in  FIG.  3 D . 
     In the embodiment of molding apparatus  300  depicted in the figures, A-portion  350 , B-portion  356 , and core plunger/ejector  360  are symmetric about a vertical center line. However, the overall mold is not necessarily symmetric about all axes, nor is symmetry a requirement of embodiments of the invention. Furthermore, although the illustrations in  FIGS.  3 A- 3 F  depict a specific cross section for frame  240 , embodiments of the invention can be used to make parts having any cross-sectional geometry, which, in fact, can even vary along the part being fabricated. 
     In the illustrative embodiment depicted in  FIGS.  3 A- 3 F , core plunger/ejector  360  actuates in the Z direction (the vertical direction in the figure). As the sequence shows, the core plunger/ejector operates by first consolidating the resin or resin/fiber charge to finalize part geometry, and then ejects the part after the charge is solidified to a finished part. 
     It will be appreciated that the continuous surface of the core plunger/ejector  360  supports a finished part for ejection in a way that ejector pins cannot. In fact, since the surface of the core plunger/ejector provides much of the surface that serves as a molding cavity, it necessarily perfectly conforms to much of the shape of the finished part. Thus, virtually all of the concerns related to ejection pins are avoided by the use of the core plunger/ejector in accordance with the present teachings. 
     It is to be understood that the disclosure describes a few embodiments and that many variations of the invention can easily be devised by those skilled in the art after reading this disclosure and that the scope of the present invention is to be determined by the following claims.