Abstract:
A wedge-lock system for injection molds, using a protrusion on one side of the mold and a mating opening and sets of wedges which act together upon mold closing to provide and maintain accurate centering of the core and cavity halves in reference to each other, to prevent core shifts and compensate for uneven thermal expansion of mold components.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates to plastic injection molds, and in particular to a centering wedge system to maintain concentricity between core and cavity halves and achieve consistent wall thickness of the molded parts. 
       BACKGROUND OF THE INVENTION 
       [0002]    A common challenge of injection molds is the difficulty to achieve and maintain a uniform wall thickness of the molded part while overcoming and compensating for various injection molding processing conditions. Prior art injection molds typically have a core versus cavity locking system, with wedges having various clamp angles such as 7° to 20° angles. While the clamping force of the injection press holds the mold closed during injection, injection forces sometimes overcome the clamping force, causing the mold to breathe at the parting line. As an example, a breathing gap of 0.001″-0.007″ at the parting line, combined with angles of 7°-20° on wedges, produces gaps of 0.0009″-0.0024″ between core and cavity wedges, resulting in loss of concentricity where one side of the mold half shifts out of center to the opposing side and causes inconsistent wall thickness of the molded part. A typical procedure to restore concentricity is to shim the wedges; this method however is time consuming and offers only temporary results since the processing conditions that caused the core verses cavity shifting is continuously present. A solution to counter this problem is to use smaller angles on wedges (3° or 1° or less), but such small angle makes for difficult control of thermal expansions and tends to cause the wedges to gall and/or seize. Furthermore the tolerances required to build a mold and maintain the same mold increases which results in more cost. 
         [0003]    Therefore, existing locking systems pose an ongoing challenge to remove the floating effect caused by high injection pressures. A solution is desired, which allows the locking system to constantly self-adjust in order to maintain concentricity, while allowing control of thermal expansions and preventing galling of the wedges ans. 
       SUMMARY OF THE INVENTION 
       [0004]    The present invention is directed towards a wedge-lock system for injection molds, using sets of wedges which act together upon mold closing to provide and maintain accurate centering of the core and cavity halves in reference to each other, to prevent core shifts and compensate for uneven thermal expansion of mold components, whilst using the clamping force of the injection press to aid the centering of mold halves. 
         [0005]    In accordance with an aspect of the invention there is provided, a wedge lock system for injection molds comprising a mating core block and cavity block which move between an open position and closed position, and in said closed position molten plastic may be injected between the faces of said core and cavity blocks to form a plastic injection mold product, said wedge lock system comprising: a forward protrusion in the core block which mates with a corresponding opening in the cavity block, said protrusion having a first lateral side and an opposite angled lateral side; a first cavity wedge, secured to the cavity block within the cavity block opening; a core wedge assembly including a core wedge piece positioned adjacent the first side of the protrusion and being connected by compressible attachment means which extends laterally through said protrusion to at least one floating puck, said at least one puck extending laterally outwardly from said angled side of the protrusion; a second cavity wedge secured to the cavity block having a mating angled surface to the angled side of the protrusion, which in said closed position, engages the angled side of said protrusion and urges said laterally outwardly extending at least one floating puck inwardly to compress said compressible attachment means and thereby urge said core wedge piece into firm contact with said first cavity wedge. 
         [0006]    In accordance with a further aspect of the invention, there is provided a wedge lock system for injection molds comprising a mating core block and cavity block which move between an open position and closed position, and in said closed position molten plastic may be injected between the faces of said core and cavity blocks to form a plastic injection mold product, said wedge lock system comprising: a wedge compressibly mounted to the face of said core block or cavity block, biased in a floating position away from said block, said wedge having an angled surface to the direction of movement of the mold machine, said wedge being compressed against said block as the angled surface of the wedge comes into engagement with a mating angled surface of a wedge secured to the opposite side of the mold (or with a mating angled surface of the opposite side of the mold directly), as the mold approaches the closed position thereby providing enhanced clamping force in the closed position during plastic injection. 
         [0007]    In accordance with a further aspect of the invention, there is provided, a wedge lock system for injection molds comprising a mating core block and cavity block which move between an open position and closed position, and in said closed position molten plastic may be injected between the faces of said core and cavity blocks to form a plastic injection mold product, said wedge lock system comprising: a forward protrusion in the core block (or cavity block) which mates with a corresponding opening in the opposite block, said protrusion having a first angled lateral side and an opposite angled lateral side; a first opposite block portion, situated opposite said first angled lateral side of the protrusion having a mating surface to the first angled side of the protrusion; a second opposite block portion, situated opposite said second angled lateral side, wherein, in said closed position, said first and second opposite block portions engage the respective first and second angled sides of the protrusions, thereby creating increased clamping force in the closed position. Wedges may be secured to one or both sides of the protrusion and/or one or more of the opposite block portions. 
         [0008]    Other advantages, features and characteristics of the present invention, as well as methods of operation and functions of the related elements of the structure, and the combination of parts and economies of manufacture, will become apparent upon consideration of the following detailed description and the appended claims with reference to the accompanying drawings, the latter being briefly described hereinafter. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0009]      FIG. 1  is an exemplary vertical sectional view of an injection mold of prior art, having a locking system comprising core and cavity wedges with a taper between 7° and 20°; 
           [0010]      FIG. 2  is an exemplary plan view of the core half of an injection mold having a locking system in accordance with an example embodiment of the present invention; 
           [0011]      FIG. 3  is an exemplary plan view of the cavity half of the injection mold of  FIG. 2 ; 
           [0012]      FIG. 4  is an exemplary vertical sectional view taken along line A-A of  FIG. 2 ; 
           [0013]      FIG. 4A  is an exemplary vertical sectional view corresponding to that of  FIG. 4 , showing the mold in a partially open position; 
           [0014]      FIG. 4B  is an exemplary vertical section view similar to that of  FIG. 4 , showing an alternate embodiment of the invention; 
           [0015]      FIG. 5  is a detail showing a comparison between various angles of locking wedges in accordance with various embodiments of the invention; 
           [0016]      FIG. 6  is a spatial view of the mold core half of  FIG. 2 ; 
           [0017]      FIG. 7  is a spatial view of the mold cavity half of  FIG. 3 ; 
           [0018]      FIG. 8A  is an enlarged detail of a cross-section taken along line B-B of  FIG. 7 , showing a gap-free design between core block and cavity wedge, having floating core wedges, spring-activated transversally; 
           [0019]      FIG. 8B  is an enlarged detail of a cross-section taken along line B-B of  FIG. 7 , showing a design with gap between core block and cavity wedge, having floating core wedges, spring-activated transversally; 
           [0020]      FIG. 9  is an enlarged detail of a cross-section similar with that of  FIG. 8A , but of a first alternate embodiment using floating core wedges, spring-activated transversally and providing roller bearing contact between core and cavity wedges. 
           [0021]      FIG. 10  is an enlarged detail of a cross-section similar with that of  FIG. 8A , but of a second alternate embodiment using floating core wedges, spring-activated axially. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0022]    An example embodiment of the invention is described with reference to  FIGS. 1 to 7 , and in particular the sectional views of  FIG. 4  and  FIG. 4A . A typical injection mold comprises a bottom plate  10 , a core block  12 , a cavity block  14 , and a top plate  16 . Bottom plate  10  and top plate  16  are securely attached to the injection machine platens (not shown), and the mold opening and closing motion is guided by a leader pin system  18 . 
         [0023]    In accordance with an aspect of the invention, core wedges (also referred to as core wedge pieces)  20 , together with cavity wedges  22 , form the main locking system  24  of the mold. In the embodiment shown, cavity wedges  22  are firmly secured to the cavity block  14  with socket head cap screws  26  or other suitable means. Core wedges  20  are attached to but not secured firmly to core block  12 , being allowed to float as will be explained in more detail below. In the embodiment shown, core wedges  20  and cavity wedges  22  have a small taper (0°-3°). 
         [0024]    As shown in  FIGS. 4 and 4A , core block  12  has protrusions  28  extending forwardly towards the cavity block  14 . Protrusions  28  have a straight face (90°) oriented parallel to the direction of movement of the mold, backing each core wedge  20 , and an angled surface with a taper of 3° to 20° on the opposite angled lateral side (For example the embodiment of  FIG. 4  shows a 7° taper on this surface). Opposite this taper of protrusions  28  is another set of cavity wedges (second cavity wedge)  30 , which are firmly secured to the cavity block  14  with socket head cap screws  32  or other suitable means. It should be understood that although a preferred range of angle is 3° to 20° an angled surface with a taper of less than 3° and more than 20° is contemplated by the invention. 
         [0025]    As can be seen in  FIGS. 2 and 4 ,  4 A, each core block protrusion  28  is provided with a pair of compressible spring-loaded pucks  34  which are connected, through the protrusion to core wedges  20  by way of shoulder bolts  36 . The system formed by core wedges  20 , spring washers  38  (such as for example Belleville type), pucks  34  and shoulder bolts  36 , has some degree of floating freedom in core block protrusions  28  when the mold is open, along axes of shoulder bolts  36 . 
         [0026]    When the mold is in open position (such as shown in  FIG. 4A ), compression means such as spring washers  38  release until the counter bores of pucks  34  come to rest against the heads of shoulder bolts  36 . This causes core wedges  20  to be pulled against protrusions  28  as the pucks  34  extend slightly over the angled surfaces of protrusions  28 . As the mold closes for a new injection cycle, cavity wedges  30  come in contact with pucks  34 , causing the pucks to compress spring washers  38  and forcing the core wedges  20  into firm contact with cavity wedges  22 . The combined effect of the large angle (3° to 20°) of cavity wedges  30 /pucks  34  and the floating allowance of pucks  34  allows core wedges  20  and cavity wedges  22  to engage into firm contact only at the final moment of mold closing, thus preventing wear at this interface. Thus, the clamp force of the injection press is applied to the core and cavity wedge interface only in the final moments of mold closing, and is used to achieve and maintain firm contact between the wedges at all times during injection, even if the mold should breathe slightly at the parting line. Furthermore, the small angle between wedges  20  and  22  (3° or less) provides for improved concentricity. 
         [0027]    As can be seen in  FIG. 5 , a 0.007″ gap at the parting line amounts to only a 0.0004″ gap between wedges having a 3° taper. Therefore, the combined effect of the main locking system having a small angle, and the spring loaded core wedges transferring the clamp force of the machine to achieve concentricity, provide a considerable improvement over prior art designs, as mold breathing ceases to have an effect on the centering of mold halves or the wall thickness of the molded part. Furthermore, as soon as the mold starts to open, the spring-loaded pucks  34  release and pull core wedges  20  away from cavity wedges  22 , thus preventing galling of these items. The larger angle of protrusions  28  and pucks  34  against cavity wedges  30  allows for quick release of the effect of clamping forces on wedges  20  and  22 . 
         [0028]    As can be seen in  FIG. 2 , the example embodiment of the invention shows a pair of pucks  34  for each core wedge  20 , but it should be understood that a larger number of pucks could be employed if desired, space permitting. Similarly, a single puck  34  could be used for each core wedge  20 . While a pair of pucks  34  on each core wedge has some functionality advantages, a design with a single puck per core wedge could be utilized as a more economical alternative or for other situations, such as when space is restricted. 
         [0029]    Further variations of the main embodiment of the invention are described below. 
         [0030]    An alternate design as shown in  FIG. 7  provides a network of grease grooves  40  on the active surfaces of cavity wedges  22 . A supply system  42 , attached to the outer surface of the mold, delivers the correct amount of grease via internal channels, through holes  44  of cavity wedges  22  to the network of grooves, to improve contact between cavity wedges  22  and core wedges  20  and further prevent wear on the 0°-3° taper. 
         [0031]    A detail of the wedge lock system of  FIG. 4  is shown in  FIGS. 8A and 8B .  FIG. 8A  presents a gap-free design, where both core protrusions  28  and spring-loaded pucks  34  are in contact with cavity wedges  30  when mold is closed.  FIG. 8B  presents a design with gap, where only the spring-loaded pucks  34  are in contact with cavity wedges  30  when mold is closed, the tapered surfaces of core protrusions  28  being below the front surfaces of spring-loaded pucks  34 . 
         [0032]    A version of an alternate embodiment is shown in part  FIG. 4B  and described herein, in which a forward protrusion ( 130 ) in the core block as shown (or alternately the cavity block) mates with a corresponding opening in the opposite block, said protrusion having a first angled lateral side and an opposite angled lateral side. The first opposite block portion, situated opposite said first angled lateral side of the protrusion has a mating surface to the first angled side of the protrusion. The second opposite block portion is situated opposite said second angled lateral side and in said closed position, said first and second opposite block portions engage the respective first and second angled sides of the protrusions, thereby creating increased clamping force in the closed position. As shown in  FIG. 4B , the opposite block is the cavity block and cavity wedges are secured to the first and second cavity block portions. If cavity wedges are present, they have mating surfaces to the angled sides of the protrusion (or if desired, such as shown, a protrusion wedge shown on one side as item  120  or protrusion wedges on both sides of the protrusion may be utilized). If protrusion wedges are utilized, the sides of the protrusion itself may or may not be angled and said cavity wedges engage the angled sides of the protrusion wedges. The angled sides of the protrusion or if present protrusion wedges attached to the protrusion are typically angled each angled at a range of 0° to 30° to said direction of mold movement, but may be even greater an angle. 
         [0033]    An alternate embodiment is presented in  FIG. 9 . The design is similar to that of  FIG. 8A , in that the core wedge  20 ′ is activated transversally by spring-loaded pucks  34 ′, but this embodiment has no taper on the active surfaces of the core and cavity wedges, the relative motion between them being allowed by a set of roller bearings  46  inserted in the active face of the core wedge  20 ′ (and prevented from accidental removal by a slotted cover plate  48 ). When the mold opens, the spring-loaded pucks  34 ′ move the core wedges  20 ′ (complete with roller bearings  46  and cover plate  48 ) away from the center of the mold (away from cavity wedges  22 ′ and out of contact with these). As the mold closes, cavity wedges  30 ′ urge pucks  34 ′ into their pockets in core protrusions  28 ′, and the compressed spring washers  38 ′ urge the core wedges  20 ′ with roller bearings  46  into contact with cavity wedges  22 ′, the roller bearings  46  guiding the relative travel between wedges until the mold is completely closed. 
         [0034]    The embodiment of the invention (as presented in  FIGS. 8A and 8B ) and the alternate embodiment of  FIG. 9  both present a core wedge design activated by springs to float in a transversal direction (along the axis of the spring-loaded pucks  34 ,  34 ′). 
         [0035]    An alternate embodiment in accordance with the invention, as shown in  FIG. 10 , presents a core wedge  20 ″ floating axially (i.e. parallel to the centerline of the injection mold), as will be explained in more detail below. As shown in  FIG. 10 , core wedge  20 ″, attached to core block  12 ″ with shoulder bolts  50 , is activated axially by springs  52 . This design also allows for larger tapers on the active faces of core wedges  20 ″ and cavity wedges  22 ″, with the advantage that it achieves immediate release of contact when mold opens. The presence of cavity wedges  30 ″ is not mandatory in this design, as the pair of core wedges  20 ″ and cavity wedges  22 ″ achieves the desired degree of centering accuracy. When the mold opens, springs  52  extend core wedges  20 ″ axially away from core block  12 ″, until they bottom out against heads of shoulder bolts  50 . To prevent friction wear or seizing of the core wedges  20 ″ against the core block  12 ″, protrusions  28 ″ of core block  12 ″ are provided with wear plates  54 , made of a material with low coefficient of friction, which allow axial travel of core wedges  20 ″ with minimal surface wear. 
         [0036]    Another alternate embodiment is presented in  FIG. 10 . The design is similar to that of  FIG. 8A , in that the core wedge  20 ″ is activated transversally by spring-loaded pucks  34 ″, but this embodiment has no taper on the active faces of the core and cavity wedges, the relative motion between them being allowed by a set of roller bearings  52  inserted in the active face of the core wedge  20 ″ (and prevented from accidental removal by a slotted cover plate  54 ). When the mold opens, the spring-loaded pucks  34 ″ move the core wedge  20 ″ (complete with roller bearings  52  and cover plate  54 ) towards the center of the mold (towards the cavity wedge  22 ″). As the mold closes, a lead-in taper  56  of the cavity wedge  22 ″ will start pushing the extended core wedge  20 ″ back into place, and the roller bearings  52  take over right after, guiding the relative travel until the mold is completely closed. 
         [0037]    While spring washers (Belleville type) are illustrated as means of compression to activate the pucks to provide continuous contact between the sets of wedges, it should be understood that any type of technology that achieves compression could be used, such as compressible bumpers (urethane or other non-metallic compounds), as well as other means such as gas springs. 
         [0038]    As well, it should be understood that the floating assembly (pucks, springs, shoulder bolts and wedges), which was presented as part of the core half of the mold, could alternately be reversed and designed as part of the cavity half of the mold. In such case, the positioning of all of the components of the system would be reversed between the core and cavity side. 
         [0039]    Furthermore, with regards to the plan views of the mold halves, in accordance with an aspect of the invention, wedges may be located at 45°, 135°, 225° and 315° (as shown in  FIG. 2 ,  3 , and spatially in  FIGS. 6 and 7 ), but they could alternately be placed at quadrants (i.e., at 0°, 90°, 180°, and 270°) without any changes to mold behaviour. It is also contemplated that more or less than 4 wedge sets, spaced around the central axis of the mold could be utilized in accordance with an aspect of the invention. 
         [0040]    It should be further understood that the mold may include bottom  10  and top  16  plates or alternately may have solid core and cavity blocks without backing plates, such as bottom  10  and top  16  plates). The function of the wedge lock system of the invention herein would not impacted by the presence or absence of such backing plates in the mold. In fact, some of the figures show an embodiment with backing plates (such as bottom plate  10  and top plates  16  shown in  FIG. 4 ) and some show solid core and cavity blocks (such as in  FIG. 4A ). It should be understood that many changes, modifications, variations and other uses and applications will become apparent to those skilled in the art after considering the specification and the accompanying drawings. For example, each said core wedge assembly and cavity wedge may be made of high hardened low friction steel material or non ferrous low friction material, or other suitable material, not specifically described. 
         [0041]    Therefore, any and all such changes, modifications, variations and other uses and applications which do not depart from the spirit and the scope of the invention are deemed to be covered by the invention. Accordingly, the invention should be understood to be limited only by the claims appended hereto, purposively construed.