Abstract:
A plastic injection mold assembly is disclosed in which an electric servo motor very precisely controls rotational speeds and amounts of torque applied to cores which extend into the mold cavities as the cores are withdrawn from plastic components being molded and simultaneously directs the linear distances which the cores travel during such withdrawal. A method of accomplishing the molding of plastic components in this manner is also disclosed.

Description:
[0001]     This application is a continuation of application Ser. No. 10/375,745 filed Feb. 28, 2003, the entire contents of which is incorporated herein by reference. 
     
    
       [0002]     This invention relates to plastic injection molds for producing internally and externally threaded components. More particularly, it relates to a mold assembly in which an electric motor very precisely controls the various rotational speeds and amounts of torque applied to cores which extend into the mold cavities as they are withdrawn from the plastic components being molded and simultaneously directs the linear distances which the cores travel during such withdrawal. A method of accomplishing the molding of plastic components in this manner is also disclosed.  
       BACKGROUND OF THE INVENTION  
       [0003]     Heretofore, a variety of limitations have affected the molding of threaded plastic components. When a hydraulically powered rack was employed for extracting a metal core from a mold cavity, the number of threads which could be made on the inside or the outside of a component was limited because the number of threads was restricted by the number of rotations required for unscrewing the metal core from the component. The number of rotations which a core could make was dependent upon the space required around the mold to accommodate the length of the rack. Moreover, hydraulically powered equipment had problems of fluid spills and fluid leakage. Keeping an adequate supply of hydraulic fluid on hand was a limitation as well. In addition, halting a hydraulically driven rack&#39;s travel precisely was difficult to achieve, and the result was that substantial tolerances in the finished components were required. Also, because substantial mechanical movement was required for the rack, the speed of ejecting finished components was restricted.  
         [0004]     Electric motors have been used in molding machine applications also. For example, U.S. Pat. No. 3,737,268, FIG. 12, illustrates the use of an electric motor for driving a shaft connected to a metal core with a threaded end inside a molded plastic component in order to turn and loosen the core and free it. In that patent, the core is moved rotationally by a belt-driven motor. A pair of ejector rods, powered by a second motor timed to cooperate with the first, are linearly moved to push the loosened component off the core.  
         [0005]     Another patent illustrating the use of a pair of electric motors is U.S. Pat. No. 5,110,522. This patent relates particularly to an injection molding machine in which two motors are required for handling certain rectilinear and rotative drive requirements. Similarly, two motors are required for the rectilinear and rotative drives identified in U.S. Pat. Nos. 5,792,483 and 5,911,924.  
         [0006]     U.S. Pat. No. 6,051,896 is an example of a patent which discloses the use of servo controlled electric motors in a molding machine. In that patent, one of the motors controls linear motion, and a second motor controls rotary motion. U.S. Pat. No. 6,142,760 is generally similar, as is U.S. Pat. No. 6,267,580.  
       SUMMARY OF THE INVENTION  
       [0007]     The present invention incorporates a servo motor to drive one or more cores in an injection mold. In the new mold, the motor&#39;s engagement to one or more threaded end cores turns the cores at programmed speeds and at programmed torque to withdraw the cores from the components which have been molded around or into them. The motor continues to drive the cores in a programmed manner rectilinearly backwards and away from the mold cavities and from the components. Thereafter, as the mold is opened, the components are ejected, usually by pushing them out of the mold. To repeat the operation, the motor is reversed, and the threaded ends of the cores are moved back into their original positions in the cavities to be immersed again in or filled with plasticized molding material, depending upon whether the components being molded are internally or externally threaded.  
         [0008]     Accordingly, in its first embodiment described below, this invention is incorporated in a mold assembly for forming a continuous internal thread inside a molded plastic element. A recess in a plastic injection mold, defined by internal walls inside the mold, forms the shape of the plastic article which one desires to make in the molding process. An end cap for a pipe is an example. A core is utilized which has a body portion with an externally threaded segment extending into the recess defined by the internal walls of the mold. The core also has a drive segment on the body portion spaced apart from the threaded segment. A drive member which has a drive portion complementary to and engaged upon the drive segment on the core is connected to a programmable electric motor. The motor is arranged to move the drive member programmed distances at programmed speeds. When the motor is activated, the drive portion on the drive member and the drive segment on the core cooperatively move the core through sufficient revolutions with any desired variations in speed to disengage the threaded segment from the plastic article within the recess by the end of the molding interval.  
         [0009]     In an alternative embodiment, largely duplicative of the first embodiment just described, the body portion of a core has a segment having an aperture or pocket which is internally threaded extending into the cavity defined by the internal walls of the mold. A molded plastic component formed on such a segment of a core has external threads arranged on the outside of the component.  
         [0010]     From the foregoing, and from what follows, it will be apparent that the present invention achieves numerous advantages over the molding processes and equipment which preceded it.  
         [0011]     It is an object of the present invention to provide a mold assembly for producing internally or externally threaded plastic components which have very exact tolerances with rapidly repeatable precision.  
         [0012]     It is also an object of the present invention to provide a mold assembly for producing internally or externally threaded components with threaded segments substantially longer than those which were obtainable with rack-driven cores.  
         [0013]     It is also an object of the present invention to provide a mold assembly for producing an internally or externally threaded component which controls the rotary distance traveled by a core used in the molding process, the various speeds to be accomplished by the core, and the linear distances to be traveled by the core.  
         [0014]     It is also an object of the present invention to provide a mold assembly for producing an internally or externally threaded component in which only one servo controlled electric motor is needed for both rotational and linear movement of a core.  
         [0015]     It is also an object of the present invention to provide a mold assembly for simultaneously producing numerous internally or externally threaded components during the same molding interval utilizing several cores connected to the same servo controlled electric motor.  
         [0016]     It is also an object of the present invention to provide a mold assembly for producing internally or externally threaded components having very exact tolerances in substantial quantities in a compact portion of the production space which is available.  
         [0017]     It is also an object of the present invention to provide a mold assembly for producing internally or externally threaded components which does not utilize hydraulic fluids.  
         [0018]     Other objects and advantages of the invention will be apparent to those skilled in the art of designing and using molds for threaded plastic parts from an examination of the following detailed description of preferred embodiments of the invention and of the accompanying drawings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0019]      FIG. 1  is a perspective view of part of a mold assembly embodying the present invention showing an electrical control component with its front cover panel partially open and cable connections arranged to extend from the component to the mold, and also showing a motor-carrying half of the mold with its inner face exposed and turned upwardly;  
         [0020]      FIG. 2  is a perspective view of an enlarged portion of the mold assembly shown in  FIG. 1  showing the control box door fully open;  
         [0021]      FIG. 3  is a perspective view of the motor-carrying mold half shown in  FIG. 1  and also including a perspective view of a second mold half complementary to and aligned for mating engagement with the motor-carrying half of the mold;  
         [0022]      FIG. 4  is a perspective view of the motor-carrying half of the mold shown in  FIG. 1  rotated approximately 180 degrees in the direction of arrow  4  in  FIG. 1 ;  
         [0023]      FIG. 5  is an elevational sectional view of the mold halves shown in  FIG. 3  in assembled, mating engagement taken in the direction of and also along the line of arrows  5 - 5  shown in  FIGS. 1 and 4 ;  
         [0024]      FIG. 6  is an enlarged perspective view isolating some of the elements of the motor-carrying mold half shown in  FIG. 1 ;  
         [0025]      FIG. 7  is a perspective view isolating some of the elements of the motor-carrying mold half shown in  FIG. 6 ;  
         [0026]      FIG. 8  is a perspective view, partly broken away, of an enlarged portion of some of the elements shown in  FIG. 7  in assembled relation with elements of the mold half shown in  FIG. 1 ;  
         [0027]      FIG. 9  is a perspective view, partly broken away, of an enlarged portion of some of the elements of the motor-carrying mold half shown in  FIG. 7  taken in the direction of arrow  9  in  FIG. 7 ;  
         [0028]      FIG. 10  is a diagrammatic layout of the electrical control component of the mold assembly shown in  FIG. 1 ;  
         [0029]      FIG. 10A  is an enlarged portion of the electrical layout shown in  FIG. 10  taken along the line  10 A- 10 A in  FIG. 10 ;  
         [0030]      FIG. 11  is an enlarged perspective view of an internally threaded plastic component molded on the assembly shown in  FIGS. 1 through 10 ;  
         [0031]      FIG. 12  is an enlarged perspective view, partly broken away, of the component shown in  FIG. 11 , taken along line  12 - 12  in  FIG. 11 ;  
         [0032]      FIG. 13  is a perspective view, partly broken away, of an alternative form of the partially broken away element shown in  FIG. 8 ; and  
         [0033]      FIG. 14  is an enlarged perspective view of an externally threaded component molded on the element shown in  FIG. 13 . 
     
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0034]     The preferred embodiments of this invention shown in the accompanying drawings will now be described, it being understood that the preferred forms are illustrative and that the invention described herein is embodied in the claims which are appended hereto.  
         [0035]     One embodiment of this invention is the mold assembly  10  which is particularly depicted in  FIGS. 1 and 3 . The assembly includes a controls component  12  and a mold, one half of which is the motor-carrying mold half  14 , and the other half of which is the complementary mold half  16  (See  FIG. 3 ). The latter is configured to sealingly engage the motor-carrying mold half  14  (See  FIG. 5 ) in order to form one or more cavities  18  and  18   a  inside the mold in which plastic articles such as the fitting  20  (See  FIGS. 11 and 12 ) may be formed. In the embodiment of the mold assembly shown in  FIGS. 1 and 3 , the outer configuration of a molded fitting, such as the fitting  20  in  FIGS. 11 and 12 , depends upon the shape of the cavity  18 . The inner configuration, namely, the internally threaded portion  22  of the fitting  20 , depends upon the outwardly facing threaded surface  46  of the end segment  24  (or  24   a  shown in  FIG. 5 ) of a cylindrically shaped metal core  26  around which the molten plastic from which the fitting  20  is made is formed.  
         [0036]     Alignment of the mold halves  14  and  16  as they are engaged upon each other, in order to form the cavities  18  and  18   a,  is achieved by lodging engagement rods  16 A (on the mold half  16 ) in sockets  14 A in the motor-carrying mold half  14 , as shown by arrows  17  in  FIG. 3 . Such alignment is assured further by engaging male wedge member  15 A in female wedge members  15 B on the mold halves  14  and  16 , respectively, accompanied by engagement of pins  16 B on the mold half  16  in sockets  14 B in the motor-carrying mold half  14 .  
         [0037]     As shown in  FIG. 1 , the motor-carrying mold half  14  has two motors,  28  and  30 . Each motor is similarly arranged so that each one is connected to and operates a set of four cores, as will shortly be explained in detail. The motors  28  and  30  are connected to their sets of cores in gear boxes  32  and  34 , respectively. The gear boxes  32  and  34  are mounted in mold frame members such as  36  and  38 . The frame members are, in turn, mounted on support rails such as are shown at  40  in  FIG. 1 , and those rails are attached to a clamp plate such as is shown at  42  in  FIG. 1 . The clamp plate is normally attached to a platen in a molding machine, neither one of which is shown here since such molding machine configurations, and how to operate them, are well known.  
         [0038]     Injection molding machines are designed to hold various molds, and also to open and close the mold halves. When the halves are closed, molten plastic materials are injected into cavities inside the molds so that the shape of the walls of the cavities, as well as any other formative shapes inside the cavities, can be transferred to the plastic material while it is in its liquid state. After the molten plastic material has been cooled and has frozen into the shape of the cavity walls and of the other shaping forms inside the cavities, the molding machines open and separate the mold halves so that the elements formed by the molten plastic can be removed or ejected from the mold. Usually the mold halves are arranged so that the separation plane between the halves is substantially vertical. Then, when the halves are separated, the plastic elements can easily drop into a bin below the mold when they are ejected from the mold cavities.  
         [0039]     Accordingly, with respect to  FIG. 1 , it will be understood that a molding machine (not shown) operates a platen holding mold half  14  and another platen holding mold half  16 . The halves are moved apart when a cycle of the molding process for creating fittings  20  has been completed, and the fittings gathered from a bin or other receptacle into which they have been ejected. Thereafter, as further fittings are needed, the halves of the mold are moved together, closing the cavities so that molten plastic may be injected into them.  
         [0040]     The cores  26  and  26 a are identical. Each core has an end segment  46  which extends into a molding cavity such as  18  or  18   a  (See  FIGS. 3, 4 , and  5 ). Inside each core a water-cooling tube  44  extends axially to carry cooling water into the end segments  46  of the cores at appropriate intervals during the molding interval when it is desired to cool the molten plastic which has flowed around the segments  46 . The tubes  44  are connected to unions  48  which carry cooling water from hoses  50 . Notably, the unions  48 , while stationary themselves, permit the tubes  44  connected to them in junctions such as  51  adjacent motor  28  to rotate around their longitudinal axes inside the cores so that the cores  26  which contain them can be rotated too. Tubes  44   a,  unions  48   a  and junctions  5  la adjacent motor  30  (See  FIGS. 4 and 5 ) are identically constructed and perform the same way as tubes  44 , unions  48  and junctions  51 , respectively.  
         [0041]     Each of the motors  28  and  30  may be connected to a set of four cores, such as illustrated in  FIGS. 6, 7 , and  8 , or to more or less than that number, depending upon a variety of considerations such as the size of the motor, the type of molding material which is being used, and other molding parameters. As shown particularly in  FIG. 6 , the motor  28  is connected to the four cores  26  inside a gear box  32 .  
         [0042]      FIG. 7  shows the internal arrangement of gear box  32  and how the cores  26  are connected to the motor  28 . The drive shaft  52  of the motor is connected to a worm gear shaft  54  that carries a worm gear  56  for each core  26 . On each core there is a worm wheel  58  forming part of a drive segment of core  26  which the worm gear  54  is engaged upon and drives. As detailed in  FIG. 7 , for example, each worm wheel  58  is connected to the core  26  which it is engaged upon by splines  60  arranged about the outside surfaces of the core  26 . The splines are cooperatively engaged between and against the walls  62  of an aperture  64  formed in the center of worm wheel  58 . The walls  62  forming the aperture  64  have land portions  66  and groove portions  68  which correspond to and matingly engage the outer configuration of the splines  60  and adjacent surfaces of core  26 . When the worm gear is activated and driven by motor  28 , worm wheel  58  is rotated by the worm gear, thus moving the walls  62  of the worm wheel and causing the core  26  to rotate. When there are a number of worm gears and corresponding cores, the cores are rotated in unison in response to the rotation of the worm gears by the motor.  
         [0043]     The splines  60  may be machined on one end of the generally cylindrical steel body of a core  26  to form, along with the worm wheel, a drive segment of the core body. Alternatively, the splines  60  may be made separately and fastened in place on the core body by appropriately sized bolts or screws (not shown).  
         [0044]     The radially outwardly facing surfaces  70  of the splines  60  are provided with threads  72  which are cooperatively engaged in threads  74  disposed in a wall of the gear box in which the core  26  is mounted. In the embodiment illustrated (See  FIGS. 8 and 9 ) the threads  74  are arranged inside a ring  76  that is fastened with cap screws  78  and a locking ring  80  into a socket  82  formed in a wall of gear box  32 . The ring  76  is situated adjacent the drive segment of core  26  carrying the worm wheel  58 . Splines  60  and the adjacent surfaces of core  26  move slidably past the land portions  66  and groove portions  68  of aperture  64  in the center of worm wheel  58  when the core  26  is rotated, driven by motor  28  and directed by the cooperative engagement of threads  72  and  74 . Accordingly, as the core  26  is moved in a rotating manner by motor  28 , and the segment  46  of the core  26  is moved for any rotational distance, core  26  is simultaneously moved along the threads  72  and  74  by motor  28  in a linear direction.  
         [0045]     Motor  28  may be programmed to change from one rate of speed to another during the linear and rotational movement of core  26 , and from one rate of torque to another, with corresponding changes to the linear and rotational responses in core  26 . Thus, when it is desired to turn the core  26  with high torque and low speed, or intermittently, as when loosening and unscrewing the core from inside a hardened plastic article being molded (such as fitting  20 ), the motor may be directed by a program to operate in that manner. After the core has been loosened from the inside of the article, and it is desired to move the core  26  out of and away from the plastic article more rapidly in a linear direction, the motor  28  can be programmed to adopt a new speed and torque. The change may be made, if desired, without interrupting the continuous rotation of the core. In this assembly, the movements of the core are very precisely controlled, both linearly and rotationally, so that core movements can be limited to specified thousandths of an inch.  
         [0046]     It will be apparent immediately to those skilled in the art of designing mold assemblies of this general type that the distance which a rack would have to travel, in a straight line pathway away from the mold, in order to equal the rotational distance traveled by a given point on the threads  72  and accomplish a specified number of rotations of core  26  would require a lengthy open space or vacant runway in a molder&#39;s plant. Such movement of a rack is not practical, even if it were possible, when a substantial number of threads are desired inside a molded plastic component which would require a large number of core rotations in order to back out of the component. In the present invention, using the motor-driven threaded splines the core can be rotated many times without taking up plant space, and consequently a longer threaded segment at the end of the core can be employed, resulting in more threads and longer threaded portions in the plastic articles being molded.  
         [0047]     The over-all assembly  10  of the present invention is substantially illustrated in  FIGS. 1 and 2 . The motor-carrying half  14  of the mold has also been described with particularity above. In the embodiment referred to, the cores  26  include an externally threaded end portion  24  for forming an internally threaded component such as the component  20  shown in  FIGS. 11 and 12 . The present invention is also adapted to produce an externally threaded component such as the component  150  shown in  FIG. 14 .  
         [0048]     A core  160  is illustrated in  FIG. 13  for forming component  150 . The core  160  is rotated and linearly moved in a manner and by a physical arrangement identical to the manner and physical arrangement for simultaneously moving core  26  rotationally and linearly. However, the end portion of core  160  which extends into a mold cavity such as cavities  18  and  18   a  is provided with a central aperture  164  arranged longitudinally along axis  166  and extending into the end portion  162  of core  160 . The walls  168  of the aperture  164  are provided with a thread-forming helical groove  170  for forming an external arrangement  172  of threads on the outside of component  150 . If an area without threads is desired, such as segment  174  on the end of component  150  which might be used as a cap on the finished component, a portion of the walls  168  (such as the end portion  176 ) is not formed with a helical groove  170 .  
         [0049]     Turning now to a particular description of the assembly controls which may be used with cores formed like core  26  or like core  160 , it may be noted that the motors  28  and  30  (See  FIG. 1 ) are connected by cables  84  to the controls component  12 . Component  12  is powered from any convenient source (See  FIG. 6 , for example) through cable  86 . In the component  12  which is illustrated, a box  88  contains the electrical controls for the mold. A door  90  hinged to the box  88  carries a variety of switches for the component  12 . The illustrated arrangement of the contents of box  88  may be rearranged in any order or container. For example, control component  12  could be integrated into the molding machine. However it is collected and assembled, preferably it includes the following elements.  
         [0050]     There is a motor selector switch  92  which singles out which motor on the mold is to be activated, or it may also be used to designate which combination of motors to activate. The mold illustrated here only includes the two motors  28  and  30 , but it will be recognized that further motors and the cores associated with them in the manner described above may be used without departing from the scope of this invention. Switch  94  is the on/off switch to the motors.  
         [0051]     Motors  28  and  30  are reversible motors. When one or the other or both of them are driven in one direction to a maximum “in” position, they position the threaded segment ends of the cores which they respectively control, through the drive shaft, worm and worm wheel rotation, in a maximum “in” position within the cores&#39; respective mold cavities. Similarly, when the selected motors are driven in the opposite direction to a maximum “out” position, they put the ends of the cores adjacent the splines  60 , through drive shaft, worm gear and worm wheel rotation in the opposite direction, in a maximum withdrawal position from the cores&#39; respective mold cavities. A positioning switch  96  directs the selected motors to locate their respective cores at any desired position between maximum “in” and maximum “out.” Switch  98  may be set to always return the cores to a “home” position (usually maximum “in”) so that they begin each molding cycle at a preselected starting point and produce a series of products, such as fitting  20 , having very uniform specifications.  
         [0052]     A fourth switch, numbered  100  and located on door  90 , is provided to turn the selected motors on or off, and an indicator light  102  is provided to let an operator know that the core controls have or have not been activated. The master on/off switch to the control component  12  is shown at  104 . Cabinet door  90  is usually latched or locked in a closed position by a lock or handle  106 .  
         [0053]      FIG. 2  illustrates the inside of the controls component  12 . Housed in the cabinet side of control box  88  are amplifiers  108  and  108   a  which contain program modules controlling the movements of the cores. In particular, amplifier  108  controls motor  28 , and amplifier  108   a  controls motor  30 . The program modules  109  (for amplifier  108 ) and  109  (for amplifier  108   a ) hold and transmit the programs for the motors, i.e., starting, stopping, changing speeds at specified times and intervals, and similar motor movements pursuant to programmed commands. These, in turn, control the movements of the cores, including their disposition on or adjacent to the components which are being molded. A terminal strip  110  distributes the electrical commands of the programs from the program modules  109  and  109   a  and amplifiers  108  and  108   a  to signal delay timers  114 . The timers  114  are also connected to the molding machine servicing the mold halves  14  and  16 , and they regulate signals from the amplifiers for the motors to stop, start or otherwise move the cores according to programmed commands. Electrical signals to the motors  28  and  30  are carried from the control component  12  through motor cables  116  and  116   a.    
         [0054]     A diagrammatic layout of the contents of the control component  12  is shown in  FIGS. 10 and 10 A. The motors  28  and  30  are supplied from a  240  volt three phase line brought to the site and into the box  88  through cable  86 . In  FIG. 10 , the main power input, which is fused, is shown at  118 . From the main input  118 , power is supplied to the control functions  108  and  109 , and their counterparts, for motors  28  and  30 , respectively, through fused interconnects  120  (to motor  30 ) and  122  (to motor  28 ), through a  24  volt power supply  124 , and through terminal strip  110 . The connections for motor  28  duplicate those for motor  30  and are not shown in  FIG. 10  simply for the purpose of avoiding visual confusion. The terminal strip  110  is primarily an organizing element to keep order among and to follow the conductors inside control component  12 . Such a strip may be as long as the unit shown in  FIGS. 10 and 10 A, or longer or shorter, depending mainly upon the number of motors utilized in the mold. The several inputs on the terminal strip  110  to motor  28  are shown as switches in  FIG. 10A  numbered  1 , 2 , 3 , 4 , 5  and  6 , and the inputs on the terminal strip  110  to motor  30  are shown as switches numbered  11 ,  12 ,  13 ,  14 ,  15  and  16 . The power-on light for motor  28  is shown as L 1  in  FIG. 10A , and the power-on light for motor  30  is shown in that Figure as L 2 . A drive selector is shown as switch  45 , and the switches connecting the internal power supply to the molding machine are designated +24. Power for the various control functions is supplied through switches numbered  0  at the right end of terminal strip  110  in  FIG. 10A . The motors  28  and  30  may be selectively operated to stop, start, move to a “home” position and may be operated to withdraw the threaded molding segments of the core members at various speeds partially or completely from their respective molding chambers utilizing the channels of power connections established through the terminal strip.  
         [0055]     It is evident from the foregoing disclosure that even though particular forms of the invention have been illustrated and described, still, various modifications can be made without departing from the true spirit and scope of the invention. Accordingly, no limitations on the invention are intended by the foregoing description of its preferred embodiments, and its scope is covered by the following claims.