Abstract:
An improved golf ball injection process and mold uses electrically driven part ejection mechanisms as actuators to control retractable core pins that support a preformed core in a spherical mold cavity. The electrically driven, actuator controlled pins can be precisely and independently controlled in both the upper and lower mold segments to achieve the desired positioning and velocities in the vertical axis, with varying degrees of pinch to hold the spherical core inserts. The forward and retract position of the core pins, as well as the ability to profile pin velocities, can be easily adjusted by the molding machine&#39;s computer process controller without changing mechanical stops internal to the mold. The sequence timing can be set so that the core insert can be suspended and encapsulated by plastic with varying timing, allowing for the core insert to be shifted during the molding process.

Description:
CROSS-REFERENCE TO RELATED APPLICATION  
       [0001]    This application claims the benefit of U.S. Provisional Application No. 60/179,661, filed Feb. 2, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates generally to the molding of a cover layer over a preformed core to manufacture a golf ball and, more particularly to an improved method for controlling the molding process as it relates to centering the core insert within the mold cavity.  
           [0004]    2. Description of the Related Art  
           [0005]    In the golf ball manufacturing process, it is a common practice to form the cover of the ball using injection molding. A mold comprising a pair of parallel plates containing opposed hemispherical cavities is used to form a spherical cavity within which a previously formed golf ball core is suspended by retractable pins within the mold construction. The retractable pins must be accurately set at a forward position to suspend the ball core properly, while often using a pinching effect to prevent movement of the core while the thermoplastic material for the cover is injected and flows around the insert. Current methods use piston/cylinder devices (hydraulic or pneumatic) to position the pins and incorporate mechanical stops to limit the extension and retraction of the pins. Adjustment of the mechanical stops for the pins is critical to producing a ball with a properly centered core and often requires removal and/or disassembly of the mold.  
           [0006]    The runner that conveys the plastic material for the cover to the mold cavity is typically provided around the parting line defined where the hemispherical cavities terminate at the surface of the molding plates. Gates connect the runner with the cavities. While the thermoplastic material is supplied to the cavity via a runner and a plurality of gates within the mold, the retractable pins are retracted to their full reverse position. The variation of the timing and speed of this process determines the consistency and accuracy of centering the core in the golf ball. After the thermoplastic material sets, the plates are separated and the golf ball is removed from the cavity.  
           [0007]    Injection molds for forming golf balls are well known in patented prior art. Prior related U.S. patents include U.S. Pat. Nos. 5,147,657; 5,122,046; and 4,959,000 covering different aspects of the mold design, including retractable pins. While the prior devices operate satisfactorily, they still possess inherent drawbacks related to setting the positions and speeds of the retractable pins.  
         SUMMARY OF THE INVENTION  
         [0008]    The present invention was developed in order to overcome the drawbacks of prior golf ball molds and associated manufacturing processes, while improving the quality of the golf ball and enhancing automation capabilities. Accordingly, an objective of the present invention is to provide an improved method for controlling the molding process for a golf ball as it relates to centering the preformed core insert. Another objective of the invention is to reduce the change-out time required for presetting positions of the retractable pins which center the core within the mold cavity. Still another objective of the invention is to achieve accurate, independent speed control of both the upper and lower retractable pins in the mold for a golf ball.  
           [0009]    This invention accomplishes these objectives by providing a process of molding golf balls that improves on the amount of time required to make adjustment to the position and pinch of the various sizes of spherical core inserts in a golf ball mold, while providing additional flexibility of precision control for the retract speeds of the retractable pins. More specifically, the improved golf ball injection process of the present invention incorporates electrically driven mechanical actuators for the retractable pins in the upper and lower mold plates that together define a spherical cavity for the finished golf ball. The electric motors for the actuators and/or the actuators themselves can be mounted on the injection molding machine or directly on the mold, to control the positioning of a plurality of retractable core pins that extend into each hemispherical segment of the mold cavity to support a preformed core for a golf ball. Preferably, the electrically driven eject mechanisms typically provided on an all-electric injection molding machine function as the electrically driven actuators of the invention, thereby minimizing system cost by using the molding machine&#39;s eject motor control to actuate the pins.  
           [0010]    The mechanical stops of a conventional golf ball mold must either be modified or removed so that the necessary modifications to the lower and upper ejector plates of the mold can be made to incorporate the retractable core support pins of the present invention. In addition, the ejector plate of the lower mold segment is modified to incorporate the ejector pins for removal of the runner. In particular, the ejector pin mounting in the ejector plate is designed so that there is no movement of the ejector pins while the retractable pins that hold the core insert are moved to their forward position. The forward limit of the stroke of the retractable pins, as accomplished by the associated upper and lower ejector plates, is readily adjusted by the microprocessor based machine control set point parameters. The upper and lower ejector plate positions are achieved and maintained by the electrically controlled actuator connected to each ejector plate, where the actuators are either included as part of the mold assembly or mounted on the injection molding machine.  
           [0011]    Independent set points for position of both the upper and lower ejector plates connected to the upper and lower retractable pins are used to shift the core insert along a vertical axis, to allow for proper positioning during the injection process. Additionally, the position set points are also used to create a pre-load (pinch) to the core insert as to prevent premature movement during the injection process. Independent speed settings (velocity) and timers are provided for both the upper and lower electrically controlled actuators. The speed and timing set points provide the flexibility to prevent the core insert from shifting too fast, thereby maintaining proper orientation of the core insert.  
           [0012]    There are several advantages in using electrically driven actuators to control the support plates for the retractable pins, as taught by the present invention. First, the actuators can precisely and independently control both position and velocity of the upper and lower retractable core pins. This enables the desired pin movement in the vertical axis, including, for example, pin positioning to accommodate different sizes of core inserts, profiling of pin velocities, and providing varying degrees of pinch to the spherical core insert. In addition, the forward and retract positions of the retractable core pins can be easily adjusted via a computer process controller without disassembly of the mold to change internal mechanical stop settings. Furthermore, the sequence timing of the machine molding process can be set so that the insert can be suspended and encapsulated by plastic with varying timing allowing for the core insert to be shifted during the molding process, if desired. Finally, the pins in the upper and lower mold segments can be set to another position during the finished part extraction phase of the machine cycle, allowing for better separation of the runner and finished parts. This capability facilitates automation for part and runner removal.  
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0013]    [0013]FIG. 1 is a partial front sectional view of a vertical injection molding machine incorporating upper and lower electrically controlled actuators mechanically connected to the retractable pins of a golf ball mold in accordance with the present invention.  
         [0014]    [0014]FIG. 2 is a side view of the vertical injection molding machine showing the relative orientation of the injection unit that supplies the thermoplastic material for the golf ball cover into the mold cavity.  
         [0015]    [0015]FIG. 3 is a diagrammatic, cross-sectional view showing how the upper and lower retractable pins suspend the core insert within the mold cavity.  
         [0016]    [0016]FIG. 4 is a cross-sectional view of a golf ball mold construction in accordance with the present invention, showing the upper and lower mold halves and the relationship of the ejector plate mounted with the ejector and retractable pins.  
         [0017]    [0017]FIG. 5 is a plan view taken along line  5 - 5  of FIG. 1, showing the ejector mechanism of the injection molding machine in greater detail, with certain unrelated parts removed for clarity.  
         [0018]    [0018]FIG. 6 shows a typical parameter setting screen used by the operator to enter the information required by the machine control to operate the electrically driven actuators for the retractable pins.  
         [0019]    [0019]FIG. 7 shows a typical timing sequence for controlling an injection molding machine that includes upper and lower actuators for retractable pins in accordance with the present invention. 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0020]    Referring now to the drawings, and particularly to FIGS. 1 and 2, there is shown an injection molding machine  1 , the structure of which will be described in some detail to clarify the interaction of the components of the present invention. Specifically, the injection molding machine  1  includes a base  14  that supports an injection unit  13  for plasticating a thermoplastic material into a flowable, viscous state and injecting the plasticated material into a golf ball mold consisting of upper and lower segments  2 ,  4 . The point of injection into the mold is optimized for each molding application and is not restricted to occurring at the parting line of the mold segments  2 ,  4 . In addition, although the injection molding machine shown in the drawings has a vertically oriented, toggle-type clamping mechanism  24 , the concepts of the present invention are equally applicable to other injection molding machine constructions and clamp configurations, as known in the plastics processing industry.  
         [0021]    The mold segments  2 , 4  are mounted in the clamping mechanism  24  of the injection molding machine  1  and movable relative to each other to open and close selectively a spherical mold cavity  8  (see FIG. 4). The clamping device  24  can be either electrically or fluid power driven to provide vertical clamp motion. Electrically driven actuators  26 ,  28  are preferably provided as independent upper and/or lower ejector assemblies in conjunction with the clamping device  24  of the injection molding machine  1 , as shown. Alternatively, the actuators can be included as independent assemblies in the upper and lower mold segments  2 ,  4 .  
         [0022]    The mold traversing and clamping mechanism  24  includes a stationary platen  42  connected to vertical frame  44  to support securely the mold segment  4 . The mold segment  2  is secured to a moving platen  46  that is attached to tie rods  48  that extend between the moving platen  46  and a toggle support platen  50 . The mold traversing and clamping mechanism  24 , as shown, is a toggle-type system that acts in conjunction with the tie rods  48  and moving platen  46  to move the mold segment  2  toward and away from the mold segment  4 , and securely hold together the mold segments  2 ,  4  when the plasticated material is injected into and contained within the mold cavity  8  under high pressure. The mold traversing and clamping mechanism  24  is mounted on the vertical frame  44 , which is generally rectangular in form and of a construction that is generally known to those skilled in the art. The stationary platen  42 , which is a generally rectangular structure, is rigidly secured to the frame  44  and includes a planar face  36  to which the mold segment  4  is securely mounted.  
         [0023]    Positioned on the base  14  and adjacent the mold segments  2 ,  4  is the injection unit  13 , which plasticates solid or powder thermoplastic material for the golf ball cover to provide a molten, flowable mass suitable for injection into the mold cavity  8 . The injection unit  13  includes a tubular barrel that carries a rotatable screw (not shown) to aid in plasticating the material, to convey material toward the mold cavity  8 , and to inject the material into the mold cavity  8  under high pressure. Since the structure and operation of the plastication and injection unit  13  are well known to those skilled in the art and not critical to the understanding of the present invention, no further description of that unit will be provided herein.  
         [0024]    The four parallel tie rods  48  of the clamping mechanism  24  have their respective longitudinal axes disposed in a generally vertical, rectangular array. The tie rods  48  connect to the moving platen  46  by means of nuts  52  (see FIG. 1) and are slidable through appropriately sized bores (see FIG. 5) in the stationary platen  42 . The opposite ends of the tie rods  48  connect to the toggle support platen  50 , which moves with the moving platen  46  during the molding cycle.  
         [0025]    The moving platen  46  is carried on the tie rods  48  for movement by the toggle support platen  50 , all of which are movable with respect to the stationary platen  42 . The moving platen  46  includes a mold mounting surface  32  that is opposite the face  36  of stationary platen  42 , and carries the mold segment  2 . The mold segment  2  engages the mold segment  4  to define one or more spherical mold cavities  8  into which the molten thermoplastic material is injected to form the desired parts. The rear face  54  of the stationary platen  42  includes appropriately sized bores to carry rotatable pivot pins  56  that are joined to a toggle linkage  58  connected to the toggle support platen  50 . When the toggle linkage  58  is actuated by a motor  60 , it acts on the toggle support platen  50  to raise or lower the moving platen  46  with respect to the stationary platen  42 .  
         [0026]    In FIG. 1, the moving platen  46  is shown in its fully lowered (closed) position relative to the stationary platen  42 . The toggle linkage  58  has been operated by the motor  60  to the fully extended position shown. When the moving platen  46  is in the position shown in FIG. 1, the mold segments  2 ,  4  are in contact and define the mold cavity  8 , into which the molten thermoplastic material is injected under high pressure to surround the core with the cover material. The toggle linkage  58  serves to maintain the position of the moving platen  46  relative to the stationary platen  42 , so there is no separation of the mold segments  2 ,  4  due to the force imposed on the surfaces of the mold cavity  8  by the injected material.  
         [0027]    After the injection phase of the molding cycle is finished, the toggle linkage  58  is operated in reverse by the motor  60 , thereby drawing upward the toggle support platen  50  and tie rods  48 . This movement of the tie rods  48  causes the moving platen  46  to likewise move upward, away from the stationary platen  42 , to separate the mold segments  2 ,  4  and permit the molded part to be removed from the mold cavity  8 . As shown in FIG. 2, the moving platen  46  is completely raised (open) and is in its furthest position relative to the stationary platen  42 .  
         [0028]    The upper and lower electric actuators  26 ,  28  provide multiple functions in connection with the present invention. The configuration of the electric actuators  26 ,  28  is essentially the same as that generally provided in an all-electric machine to actuate conventional ejector pins. For example, as illustrated, parallel screw and nut assemblies  62  are provided in both of the actuators  26 ,  28  to convert the rotary output of an electric motor  68  (see FIG. 5) to a linear movement that is transmitted to the ejector plate  22  of the mold assembly (see FIG. 5). The movement of the ejector plate  22  causes the associated ejector pins  60  to extend into or to retract from the mold cavity  8 . This drive arrangement for the actuators  26 ,  28  involves rotating the motor  68  in a first direction to cause the ejector pins  60  to move at a predetermined speed into the mold cavity  8 , stopping movement after the preset ejection stroke is complete, and rotating the motor in a reverse direction to cause the ejector pins  60  to retract to their starting position. As will be more fully explained below, the actuators  26 ,  28  of such an electric ejector mechanism can be used in conjunction with a specially constructed golf ball mold having retractable core pins  16 ,  18  to center and hold a preformed core insert  12 .  
         [0029]    [0029]FIG. 3 shows portions of the upper mold segment  2  and the lower mold segment  4  with their respective hemispherical cavity sections  10 ,  6 , which together form the spherical cavity  8  when the mold segments  2 ,  4  are closed. A spherical core insert  12  is suspended in the cavity  8  by the upper retractable pins  16  and lower retractable pins  18 . Both sets of upper and lower pins  16 ,  18  are connected to respective upper and lower ejector plates  20 ,  22 . The strokes L 1  and L 2  of the individual ejector plates  22 ,  20  connected to the retractable pins  16 ,  18  can be independently set and selected via the injection molding machine&#39;s microprocessor based control.  
         [0030]    [0030]FIG. 4 shows the details of the preferred mold construction that cooperates with the electrically controlled actuators  26 ,  28  connected to the ejector plates  20 ,  22 . While a single cavity golf ball mold is shown for purposes of illustration, the concepts of the present invention are equally applicable to multi-cavity mold constructions. As noted previously, the mold upper segment  2  and lower segment  4  together form the spherical mold cavity  8 . Those knowledgeable in the art will understand that the mold segments  2 ,  4  are substantially similar in overall construction, except that the lower mold segment  4  further includes the ejector pins  60  for a runner  70  of material that feeds into the cavity  8 . The retractable pins  16  and  18  are fitted in the respective mold segments  2 ,  4  and connected to the corresponding ejector plates  20 ,  22 . Referring specifically to the elements of the lower mold segment  4  shown in FIG. 4, the intermediate forward position of the ejector plate  22  is identified by reference no.  64 , while the retracted position is identified by reference no.  66 . A similar range of movement would also be applicable to upper ejector plate  20   
         [0031]    When the electrically controlled actuators  26 ,  28  are machine mounted, as shown, the connection bars  30  are attached between the ejector plates  20 ,  22  and the actuators  26 ,  28 . If the electrically controlled actuators are part of the mold construction (not shown), then the actuators are connected between the ejector plate  22  and the mold base plate  34  or the mold mounting surface  36  of the stationary platen  42  in the injection molding machine  1 . The ejector plate  22  in the lower mold segment  4  is provided with recesses  40  to accept shouldered ejector pins  60 , which are configured so that they are not moved when the retractable pins  18  are moved their forward position (ejector plate  22  at  64 ). When the ejector plate  22  is retracted (at  66 ), the retractable pins  18  are also retracted but the recesses  40  still prevent the ejector pins  60  from being moved. However, when the molding process is complete and the mold segments  2 ,  4  have separated during the clamp opening phase, the ejector plate  22  is moved past the pre-set retractable pin forward position set point, so that the shoulder of the ejector pin  60  in the recess  40  is engaged by the plate  22  to allow for ejection of the finished golf ball from the mold cavity section  6  and the runner  70  from the lower mold segment  4 .  
         [0032]    [0032]FIG. 6 shows an example of a parameter setting screen used by the operator to enter the information required by the machine control to operate the electrically driven actuators for the retractable pins. In particular, the relevant parameters shown in this representative screen include:  
         [0033]    Lower Pin ON/OFF  
         [0034]    ON: Lower Pin (Ejector pin) moves to lower pin “Forward Position” when the clamp reaches lock-up position.  
         [0035]    Lower Pin Trigger  
         [0036]    Injection Pressure: When the actual injection pressure exceeds the setting pressure during the injection process, lower pin starts to move to the lower pin “Retract Position”.  
         [0037]    Injection Time: When the injection time exceeds the setting time, lower pin starts to move to the lower pin “Retract Position.” 
         [0038]    Screw Position: When the actual screw position reaches the setting position, lower pin starts to move to the lower pin “Retract Position.” 
         [0039]    The injection process starts when the lower pin reaches the lower pin “Forward Position”.  
         [0040]    If trigger requirement is not made in injection or packing process, trigger is forcedly switched “ON” at starting of extruder sequence.  
         [0041]    Lower Pin Forward and Retract Position  
         [0042]    Setting range: 0.000 inch through specified maximum stroke limit of the machine.  
         [0043]    Upper Pin ON/OFF  
         [0044]    ON: Upper pin sequence is available. Clamp closing sequence in automatic/semi-automatic cycle is allowed only when Upper Pin is in forward position. Manual upper pin operation is available.  
         [0045]    OFF: Upper pin sequence is not available. Clamp closing sequence in automatic/semi-automatic cycle is allowed only when Upper Pin is in Retract Position. Manual upper pin operation is not available.  
         [0046]    Upper Pin Trigger  
         [0047]    Injection Pressure: When the actual injection pressure exceeds the setting pressure during injection process upper pin starts to move to the upper pin “Retract Position”.  
         [0048]    Injection Time: When the injection time exceeds the setting time, upper pin starts to move to the upper pin “Retract Position”.  
         [0049]    Screw Position: When the actual screw position reaches the setting position, upper pin starts to move to the upper pin “Retract Position”.  
         [0050]    If trigger requirement is not made in injection or packing process, trigger is forcedly switched “ON” at starting of extruder sequence.  
         [0051]    Upper Pin Start Position  
         [0052]    When the actual clamp position reaches this position, upper pin starts to move forward. Current cycle is not finished until upper pin reaches “Forward Position”.  
         [0053]    Upper Pin Forward and Retract Position  
         [0054]    Setting range: 0.000 inch through specified maximum stroke limit of the machine.  
         [0055]    The sequence and timing for a typical molding cycle is shown by the chart in FIG. 7. The operator has previously set the machine operating parameters, including those associated with the pins  16 ,  18  driven by the actuators  26 ,  28 , as reflected by the control set-up screen shown in FIG. 6. Generally speaking, the cycle begins by placing the preformed core insert  12  in the cavity section  6  in the lower mold segment  4 . The upper core pins  16  are in their pre-set forward support position and the clamp mechanism  24  of the injection molding machine  1  is operated to closed the mold, as previously described, so that the core insert  12  is confined within the spherical cavity  8 . The ejector plate  22  in the lower mold segment  4  is then moved by the associated electric actuator  28  to move the lower pins  18  to their pre-set forward support position, so that the upper pins  16  and lower pins  18  together hold the core  12  in the desired central position with the cavity  8 .  
         [0056]    As soon as the core  12  is properly supported, the thermoplastic material for the cover layer is injected into the mold cavity  8  to surround the core  12 . The motors for the actuators  26 ,  28  are operated so that the upper pins  16  and lower pins  18  are retracted to their rearward preset position, after injection has progressed to the point where it is no longer necessary for the pins  16 ,  18  to support the core  12 . Additional cover material is packed into the cavity  8  to fill the voids momentary left by the retraction of the pins  16 ,  18 .  
         [0057]    When the molded part has sufficiently cooled, the clamp mechanism  24  is operated to open the mold, separating the mold segments  2 ,  4 . If desired, the upper ejector plate  20  can be set to move forward during the opening phase so that the upper pins  16  extend into the upper cavity section  10  of mold segment  2 , thereby ensuring that the molded parts remain in the lower mold segment  4 . The lower ejector plate  22  is then moved by the associated actuator  28  to the preset extreme forward position so that the core pins  18  eject the finished part from the lower cavity section  6  and the ejector pins  60  are moved to eject the runner  70  from the lower mold segment  4 . After the part is removed, the lower core pins  18  (and ejector pins  60 ) retract to their reward position, while the upper core pins  16  move to their preset forward position. A new core  12  is then placed in the lower cavity section  6 , just prior to the mold closing as a new cycle begins.  
         [0058]    Although particular embodiments of the present invention have been illustrated and described, it will be apparent to those skilled in the art that various changes and modification can be made without departing from the concepts of the present invention. It is therefore intended to encompass within the appended claims all such changes and modification that fall within the scope of the present invention.