Abstract:
A system is described for precise injection molding and creation of fiber optic plastic ferrules or other molded parts. In a described application, a molded plastic part is formed that yields four ferrules. The plastic part has a central hub from which four arms extend, each having a ferrule-carrying portion. The mold has a pair of interengageable halves that mate to form a series of channels and gates for formation of the plastic part. Molten plastic flows from a central chamber through the channels. From each channel, the molten plastic then flows into a fan-shaped gate, a ring-shaped gate and an annular parabolic-shaped gate and finally into a molding chamber for molding the tubular ferrule. The molten plastic is temporarily accumulated by the gating system and then flows into the molding chamber in an evenly distributed manner.

Description:
BACKGROUND 
     The present invention is directed to systems for the injection molding of plastic parts. In particular aspects, the invention is directed to a gating system useful in the molding process for creating optical fiber ferrules. 
     A fiber optic ferrule is a tubular member that receives the end of an optical fiber or fibers and is then abutted against an opposing ferrule in order to precisely align the fibers so that an optical signal can be transmitted between them. FIGS. 1 and 1A of the drawings depict an exemplary ferrule  10  of a type that is known in the art. As shown there, the ferrule  10  has a generally cylindrical body  12  having ends  14  and  16 . The first end  14  has a reduced diameter portion  18  that is adapted to retain a sleeve (not shown) to form an abutting connection with a like ferrule. 
     The cylindrical body  12  also defines a pair of concentric bores  20  and  22  therewithin. The first bore  20  has a large diameter with an opening  24  at one end of the body  12 . The first bore  20  may be slightly tapered along its length. The second bore  22  has a reduced diameter with an opening  26  at the other end of the body  12 . The diameter of the second bore  22  is very small—on the order of 0.02 mm. 
     Ferrules are typically formed of a polymer or other plastic and are created by injection molding. In order to operate properly, ferrules must be fashioned with great precision. The allowable tolerances for these components are typically only a few microns. Therefore, the details of the molding process must be carefully controlled. Conventional injection molding processes, however, often result in uneven plastic flow patterns and high failure rates. Improved molding processes and systems are desired. Also, even with ferrules that meet specifications, the amount of discarded polymer to usable polymer is high. 
     SUMMARY OF THE INVENTION 
     The present invention describes devices and methods for the precise molding and creation of ferrules or other plastic parts. In the exemplary embodiment described herein, a molded plastic part is formed that yields four ferrules. The plastic part has a central hub from which four arms extend, each having a ferrule-carrying portion. 
     A mold is described for molding the plastic part. The mold has a pair of interengageable halves that mate to form a novel series of runners and gates for formation of the plastic part. When molten plastic is injected into the mold, the runners and gates provide for improved plastic flow to form the ferrule-carrying portions of the part. In the described embodiment, molten plastic is flowed from a central chamber through four substantially cylindrical channels. From each channel, the molten plastic then flows into a fan-shaped gate, a ring gate and a parabolic gate. The molten plastic is temporarily accumulated by the gating system and then flowed into a ferrule molding chamber in an evenly distributed manner. 
     It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention as claimed. 
    
    
     The following drawings, which are incorporated in and constitute a part of this specification, illustrate several embodiments of the invention and, together with the description, serve to explain the principles of the invention. 
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a cross-sectional side view of an exemplary polymer ferrule used in fiber optic connections. 
     FIG. 1A is an isometric view of the ferrule shown in FIG.  1 . 
     FIG. 2 is an isometric view of an exemplary molded part containing four molded ferrules. 
     FIG. 2A is an enlarged isometric view of a portion of the molded part depicted in FIG.  2 . 
     FIG. 3 is a partial cross-sectional view of an exemplary mold for injection molding of the plastic part shown in FIGS. 2 and 2A. 
     FIG. 3A is an enlarged partial cross-sectional view of some of the components shown in FIG.  3 . 
     FIG. 3B is a simplified bottom view of an exemplary A-side mold plate. 
     FIG. 4 is an isometric view of an exemplary A-side mold insert. 
     FIG. 5 is an isometric view of an exemplary B-side mold insert with a core pin assembly disposed within it. 
     FIG. 5A is a partial cutaway view of the B-side mold insert and core pin assembly shown in FIG.  5 . 
     FIG. 6 depicts an exemplary core pin assembly used in the mold of FIG.  3 . 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring to FIGS. 2 and 2A, there is shown an exemplary polymer part  50  that is formed using the injection molding devices and processes that will be described shortly. The polymer part  50  is a single molded piece that yields four ferrules  10  of the type depicted in FIGS. 1 and 1A. The remaining portion of part  50  is discarded. 
     The part  50  is unitarily molded and includes a central hub  52  with an upstanding conical spire  54  arising therefrom. Four arms  56  radiate outwardly from the hub  52  at approximate 90° angles from one another. Each of the arms  56  carries a single ferrule  10 . Each arm  56  includes a cylindrical runner  58  that is affixed to the central hub  52  and terminates in a fan portion  60 , which can be seen more clearly in FIG.  2 B. The fan portion  60  has a reduced height, as compared to the runner  58 , and, in the horizontal dimension, expands radially in the manner of a fan. The fan portion  60  is affixed to an annular ring portion  62 . A base portion  64  having an outer surface substantially in the shape of a conic parabola or a hollow dome is affixed atop the ring portion  62  and tapers to a reduced diameter support platform  66  that carries the ferrule  10 . FIG. 2A shows the ferrule-carrying portion of a single arm  56  in greater detail. As can be seen, the ring and parabola portions  62 ,  64  are hollow, forming a space or chamber  70  beneath. 
     After the part  50  is formed and cooled, the ferrules  10  may be snapped or cut off of the support platforms  66 . It is pointed out that the part  50  also includes a number of knock-out tabs  68  that are useful in the molding process for ejecting the part  50  from its mold. 
     Referring now to FIGS. 3,  3 A and  3 B, an exemplary mold  100  is shown that is used to form the part  50 . The mold  100  is designed to be used within an injection molding assembly of a type known in the art. The mold  100  is basically formed by a pair of interengageable halves that are often referred to as “A-side” and “B-side” halves,  102 ,  104 , respectively. Each of the mold halves  102 ,  104  includes a substantially rectangular plate and a number of inserts that fit within apertures in the plate. FIG. 3B provides a simplified bottom view of an A-side plate  106  in order to illustrate the general layout of some of the exemplary mold components. 
     It will be understood that injection molding plates include a number of features such as thermal couplings, heat tube fittings, side lock vents and oil channels that are well understood and, thus, will not be described in any detail here. The plate  106  for the A-side half  102  includes four guide post bushings  108  that extend through the thickness of the plate  106  and are sized and shaped to receive guide posts  110 . The central portion of the upper plate  106  contains a hardened sleeve  112  that is disposed through the thickness of the plate  106  and defines an upwardly-facing receptacle  114  into which a nozzle  116  is disposed for the injection of molten plastic. The receptacle  114  contains a fitting  118  upon which the nozzle  116  is received. The fitting  118  defines a plastic flow passage  120  into which molten plastic is injected under pressure from the nozzle  116 . The preferred molten plastic material is a fiberglass-filled thermoset plastic material named Radel B available from RTP located in Winona, Minn. 
     The lower, or B-side, mold half  104  also includes a plate  122  that is shaped and sized to be generally complimentary to the upper plate  106 . The lower plate  122  retains four guide post bases  124  from which the guide posts  110  extend upwardly into the guide post bushings  108  of the upper plate  106 . A pin  123  is retained within the central portion of the plate  122 . The upper portion of the pin  123  presents a horizontal surface  125  from which four semicylindrical channels  127  extend toward the lower plate&#39;s insert apertures  152 . 
     The mold halves  102 ,  104  can be moved toward each other for engagement (as shown in FIG. 3) or apart from one another for removal of a molded piece, and the disposal of the guide posts  110  within the guide post bushings  108  ensures that the mold halves  102 ,  104  remain properly aligned with one another as this occurs. 
     The upper and lower mold halves  102 ,  104  also each include mold inserts that are retained within the plates  106 ,  122 . Upper, or A-side, mold inserts  126  are disposed within apertures  128  in the upper plate  106 . As FIG. 3B shows, the insert apertures  128  are interconnected with the central flow passage  120  via semicylindrical channels  129 . 
     The four upper mold inserts  126  (only two shown) are substantially cylindrical in shape and define a vertical bore  130  therethrough. FIG. 4 provides an isometric view of one such insert  126  as viewed substantially from its lower end. As can be seen, the lower end of the vertical bore  130  adjoins a chamber surface  132  that is shaped substantially as a conic parabola. Surface  132  tapers and converges in an upward direction. An engagement lip  134  surrounds the chamber surface  132 . As best shown in FIG. 4, a flattened fan-shaped recess  136  extends radially outwardly from the chamber surface  132 . A rounded semicylindrical channel  138  adjoins the fan-shaped recess  136  and extends radially outward. The fan-shaped recess  136  converges in a radial outward direction from the axis of mold insert  126 . 
     It is noted that the circumferential exterior of the upper end of the A-side insert  126  provides a radially outward-extending annular flange  140  that is used to engage a matching groove ( 141  in FIG. 3) in the upper mold plate  106 . One side of the flange  140  is flattened at  142  and fits within a complimentary flattened portion (not shown) of the groove  141  so as to provide a keying arrangement with the mold plate  106 . The keying arrangement  130  ensures that the insert  126  is properly oriented when inserted into the plate  106 . 
     The lower, or B-side, mold inserts  150  are disposed in insert apertures  152  in the B-side plate  122  (FIG.  3 ). An exemplary B-side insert  150 , as viewed substantially from its upper end and side, is shown in an isometric view in FIG.  5 . The B-side insert  150  includes a generally cylindrical body  154  having a radially extending annular flange  156  at its lower end. The flange  156  includes a flattened portion  158 . The flange  156  fits within a complimentary groove  160  in the lower plate  122 , and the flattened portion  158  fits within a complimentary flattened portion (not shown) of the groove  160  to provide a keying arrangement that ensures correct orientation of the insert  150  within the aperture  152 . 
     Extending upwardly from the body  154  of the B-side insert  150  is a platform  162  that has a conical sidewall and a substantially flat upper surface  164 . A central bore  166  extends longitudinally through the platform  162  and the body  154 . The bore  166  has a radially enlarged portion  168  at its lower end. 
     A ring groove  170  is disposed within the flat surface  164  of the platform  162  and surrounds the bore  166 . One or more knock-out tab molding chambers  172  may be formed along the circumferential exterior of the ring groove  170 . A flattened fan-shaped recess  174 , having the same configuration as the fan-shaped recess  136  on the A-side insert  126 , adjoins the ring groove  170 . Recess  174  converges in a radially outward direction. A rounded semicylindrical channel  176 , having the same configuration as the channel  138  of the A-side insert  126 , adjoins the recess  174  and extends radially to the edge of the upper surface  164 . 
     A core pin assembly  180  is disposed within the bore  166  and enlarged bore portion  168  of each lower mold insert  150 , as best shown in FIG.  5 . An exemplary core pin assembly  180  is also shown apart from the lower mold insert  150  in FIG.  6 . One or more assembly pins (not shown) may be inserted into pin holes  182  in the lower mold insert  150  in order to retain the core pin assembly  180  in place. 
     The core pin assembly  180  features a narrow solid cylindrical body  184  with an enlarged cylindrical base  186 . The upper end of the body  184  presents a tapered conical portion  188  that supports an upstanding narrowed core pin  190 . The upper end of the core pin  190  retains a gage wire  192  in a vertical orientation. Gage wire  192  is very small in diameter for forming bore  26  (FIG.  1 ). Uneven flow distribution of the molten plastic can cause lateral deflection of the gage wire  192 , resulting in a misaligned bore  26 . 
     When the mold halves  102 ,  104  are mated, as shown in FIGS. 3 and 3A, a number of molding passages and cavities are formed that permit molding of the plastic part  50 . Four cylindrically shaped channels  200  (two shown in FIG. 3) extend outwardly from the flow passage  120  at about 90 degree angles from one another. It is noted that each channel  200  is formed by the mating semicylindrical halves  129 ,  127  of the A-side and B-side plates  102 ,  104  and the semicylindrical halves  138 ,  176  of the A-side and B-side inserts  106 ,  122 . 
     Each of the channels  200  terminates at a flattened, or reduced height, fan gate  202  that is best shown in FIG.  3 A. The fan gate  202  is defined by mating of the fan-shaped recesses  136  (FIG. 4) and  174  (FIG. 5) of the A-side and B-side inserts  106 ,  122 . As will be appreciated by reference to FIGS. 4 and 5, the fan gate  202  diverges angularly in the horizontal dimension, in the manner of a fan, widening out as it approaches conical portion  188  of core pin assembly  180 . Fan gate  202  slows the velocity of injected plastic and evenly distributes the plastic. 
     Referring again to FIG. 3A, a ring gate  204  adjoins the fan gate  202  and annularly surrounds the lower end of the tapered portion  188  of the core pin assembly  180 . The ring gate  204  is essentially an annular trough that is defined by the ring groove  168  and the tapered portion  188  of the core pin assembly  180 . The wider end of the fan gate  202  joins ring gate  204 . Ring gate  204  causes the molten plastic to flow around the tapered portion  188  of the core pin assembly  180  before flowing upward. 
     Parabolic gate  206  is a chamber that extends upwardly from the ring gate  204 , being formed between the parabolically-shaped chamber surface  132  of the A-side insert  126  above, and the tapered surface  188  of the core pin assembly  180  below. It is noted, with reference to FIG. 3A, that the parabolic gate  206  narrows and becomes more restrictive toward its upper end. Fan gate  202  is much shorter in height that parabolic gate  206 . The radial dimension or thickness between the core pin tapered section  188  and the parabolic surface  132  decreases toward the upper end of the parabolic gate  206 . Parabolic gate  206  serves to cause the molten plastic flowing upward from ring gate  204  to flow evenly. 
     A ferrule molding cavity  210  is formed between the core pin  190  and the bore  130  of the A-side insert  126 . The molding cavity  210  opens at its lower end into the reduced diameter portion  208  of the parabolic gate  206 . A ceramic plug  212  is fitted within the bore  130  and has an axial passage for receiving the gage wire  192  therein. The plug  212  provides an upper limit to the molding cavity  210 . 
     It will be understood that the ferrule molding cavity  210  is the portion of the mold  100  that forms a ferrule  10  of the type shown in FIGS. 1 and 1A. The first bore  20  of the ferrule  10  is formed about the core pin  190  while the second bore  26  of the ferrule  10  is formed around the gage wire  192  below the plug  212 . 
     During a molding operation, heated polymeric material (not shown) is flowed through the nozzle  116  into the mold  100  under pressure. The polymer flows down through the central passage or chamber  120 , and from there it spreads radially outwardly through each of the channels  200 . 
     Upon leaving each of the channels  200 , the polymer enters the fan gate  202 , which distributes or spreads the molten material horizontally into the ring gate  204 . The reduced height of the fan gate  202  promotes controlled laminar flow of the molten material into the ring gate  204 . 
     The ring gate  204  receives molten plastic from the fan gate  202  and distributes it annularly about the tapered portion  188  of the core pin assembly  180 . The ring gate  204  thus fills and accumulates the molten plastic in an annular configuration. The molten plastic then rises into the lower end of the parabolic gate  206  so that it will flow around core pin tapered section  188 , as will be understood from reference to FIG.  3 A. 
     Flow of the plastic material becomes more restricted by the narrowing width and thickness of parabolic gate  206  at its upper end. The flow restriction of the parabolic gate  206  causes the molten material to enter the molding cavity  210  under increased pressure. It is noted that the ring gate  204  and parabolic gate  206  also serve to accumulate the molten material momentarily before permitting it to flow into the molding cavity  210 . The annular configuration of the ring gate  204  and the parabolic gate  206 , along with the accumulation function, ensure that the molten material will be substantially evenly distributed about the circumference of the tapered surface  188  prior to entry of the molten material into the cylindrical molding cavity  210 . This helps ensure that the molten material is injected in a relatively even annular distribution about the core pin  210  upon entry into the molding cavity  210 . This reduces the chance for the very thin gage wire  192  to become laterally displaced due to uneven plastic flow. After curing, the mold halves  102 ,  104  separate and molded part  50  is ejected. 
     In practice, the molding system of the present invention has resulted in greatly improved plastic flow patterns and a much lower failure rate for molding operations. The combination of the particular gates described herein results in optimum flow conditions for molten molding materials such as plastics and polymers, particularly where small precision parts such as ferrules are to be molded. The unused portion of the molded part is less in weight than prior art molded parts. The molding cycle time is also faster than prior art cycling times. 
     While the invention has been shown or described in only some of its forms, it should be apparent to those skilled in the art that it is not so limited, but is susceptible to various changes within departing from the scope of the invention.