Method of forming ferrule for optical fiber connector and mold thereof

Abstract: A method of molding ferrule of plastic resin and provided with at least one hole (42A) having a small diameter and positioned at a predetermined position by a mold having a pair of associated molding ferrule halves (1A, 1B), including the steps of arranging a molding core (34, 35) having at least one pin (36) for defining the hole in a cavity (20) defined by the pair of molding ferrule halves holding the molding ferrule halves by the clamping force (CP), the molding ferrule halves having inner members (4a, 4b) for positioning the pin and being free from the clamping force, supplying plastic resin into said cavity, and pressing the inner members of the molding ferrule halves by a force free from the mold clamping force.

Description: The present invention relates to a method of molding a ferrule as defined in the preamble of claim 1, and, more particularly, to a method of molding a ferrule for an optical fiber connector, an optical fiber switch or the like, using plastic resin, and a mold. Optical fibers of glass comprise a core having a diameter of 10 µm, a cladding formed on an outer surface of the core and having a diameter of 125 µm, and a protective cover of resin surrounding the cladding. Ferrules for optical fiber connectors which connect both ends of optical fibers must be manufactured precisely to that the ends of the optical fibers meet. The ferrules are injection-molded using a fluid plastic resin at a temperature of approximately 180°C and a high injection pressure. More specifically, as shown in Fig. 1, a ferrule 45A of a half of an optical fiber connector comprises a plurality of fiber holes 42A into which a plurality of optical fiber 41A are inserted. The ferrule 45B of the other half of the optical fiber connector has a structure as ferrule 45A. Two fitting pins 43 are inserted into pin holes 44A and 44B to integrate the halves and for assembly of the optical fiber connector. The optical connector is assembled by inserting the optical fibers 41A and 41B into the fiber holes 42A and 42B and fixing the halves by an adhesive. The ferrule 45A and 45B of the optical fiber connector are produced by injection-molding or transfer-molding using plastic material. The mold for producing the ferrules 45A and 45B has a pair of molding ferrule halves which can be opened and closed. The molding cores have pins for forming the fiber holes 42A and 42B and other pins for the pin holes 44A and 44B. The molding cores are arranged in a cavity, defined between abutting end faces of the molding ferrule halves, and held and fixed with the clamping force applied to the pair of molding ferrule halves. In this state, plastic resin is supplied into a cavity to mold the desired ferrules 45A and 45B. When holding and fixing the molding cores in place, it is necessary to firmly fix the molding cores from both top and bottom sides without any clearance so as to precisely hold the molding cores at a fixed position without play. However, when forming the ferrule 45A and 45B, plastic resin is supplied to the cavity at a high pressure of several hundred kg/cm 2 , for example, to reduce the shrinkage and deformation of the molding resin and to maintain a size. Therefore, to overcome the pressure due to the plastic resin, it is necessary to clamp the molding ferrule halves with a large molding clamping force of, for example, several tens of tons but, when this large mold clamping force is applied directly to the molding cores, the pins of the molding cores may become damaged (Japanese unexamined publication No. 55-36809 published on March 14, 1980). An object of the present invention is to provide a method of forming a ferrule and a mold therefor by which the ferrule can be produced with high quality. Another object of the present invention is to provide a method of forming a ferrule and a mold by means of which the ferrule can be manufactured at a high yield. According to the present invention, there is provided a method of molding ferrule of plastic resin, wherein the ferrule is provided with at least one hole having a small diameter and positioned at a predetermined position, by a mold comprising a pair of mold halves, inner members, at least one of said inner members being a positioning member, and at least one core member; characterised by the following combination of steps:- arranging said inner members in a first cavity, defined by said pair of mold halves, to thereby define a second cavity wherein is arranged at least one molding member forming at least one hole having a small diameter after completion of molding; holding said mold halves and said inner members by a clamping force CP such that at least one of said inner members is free from the clamping force and can be used as a positioning member; applying a force to said positioning member, which force is smaller than and separate of said clamping force, for positioning said molding member; and supplying a plastic resin in said second cavity to form a ferrule, Preferably, the force applied to said positioning member is generated by a member that generates the force in response to electric power, an elastic member, a pressurized fluid, a compressed gas, or an electromagnet. According to the present invention, there is provided a mold for forming a ferrule provided with at least one hole having a small diameter and being positioned at a predetermined position comprising a pair of mold halves defining a first cavity wherein inner members, of which at least one is a positioning member, are arranged to define a common cavity; at least one molding member which is disposed in said common cavity, characterised in that said pair of mold halves and the inner members being configurated such they may be held by a common clamping force exempt at least one inner member which is free of the clamping force and forms a positioning member for positioning said molding member; and a force means for applying separately from said clamping force a force to said positioning member for positioning of said molding member. Preferably, the pressing means comprises a member that generates the force in response to electric power, an elastic member, a pressurized fluid, a compressed gas, or an electromagnet. Preferably, the pin holders are positioned by a groove having at least one inclined surface, such as a V-shaped surface, or a trapezoid. The groove is connected with the pressing means for applying the holding force of the pin independent from the mold clamping force. Specifically, the ferrule is used for an optical fiber connector, an optical fiber switch or the like, and the hole of small diameter is formed to fit an optical fiber. The above-mentioned object and other objects and the above-mentioned feature and other features of the present invention will be described in detail with reference to the accompanying drawings, in which; Fig. 1 is a perspective view of a pair of ferrules for an optical fiber connector; Fig. 2 is a sectional view of a first embodiment of a mold according to the present invention; Fig. 3 is a sectional view of the mold shown in Fig. 2 taken along the line Z1-Z1'; Fig. 4 is a top view of a molding ferrule half of the mold shown in Fig. 2; Fig. 5 is a bottom view of another molding ferrule half of the mold shown in Fig. 2; Fig. 6 is a disassembled perspective view showing major components of the mold; Fig. 7 is a sectional view of a second embodiment of a mold according to the present invention; Fig. 8 is a sectional view of a third embodiment of a mold according to the present invention; Fig. 9 is a partial sectional view of a fourth embodiment of mold according to the present invention; Fig. 10a to 10c are sectional views of modifications of a positioning groove in Fig. 3; Fig. 11 is a perspective view of a pair of ferrules for an optical fibers switch, and Fig. 12a and 12b are plan views explaining modes of switching of the optical fiber switch shown in Fig. 11. An embodiment of a mold for forming a ferrule which can be used for an optical fiber connector, will be described with reference to Figs. 2 to 6. In Figs. 2 and 3, a mold comprises a molding ferrule half 1A and another molding ferrule half 1B which are accommodated in a movable mold 21 and a stationary mold 22. A push plate 23 is mounted on the stationary mold 22. Portions 20a and 20b are defined between the molding ferrule halves 1A and 1B. Portions 20a and 20b are connected to each other to define a common second cavity 20. Molding cores 34 and 35 are placed in the common second cavity 20. As shown in Figs. 1 and 6, a first molding core 34 consists of a plurality of thin pins 36 for defining the optical fiber holes 42a in the ferrule 45A, and a fixing block 37 for fixing the pins 36. Second molding cores 35 are pins used for defining the holes 44A of the ferrule 45A. The molding ferrule half 1A comprises a combination of a plurality of mold components (inner molding members) 2a, 3a, 4a, 5a, 6a, 7a, and 8a, while the other molding ferrule half 1B comprises a combination of a plurality of mold components (inner molding members) 2b, 3b, 4b, 5b, 6b, 7b, and 8b. These mold components 2a to 8a and the mold components 2b to 8b consist of the same materials which may be selected from metals and ceramics. In a specific example, the mold components 4a and 4b, which position the pins 36 and pins 35 in place, are free from the clamping force and are of cemented carbide. The mold components other than the mold components 4a and 4b can be of hardened steel (die steel). Figure 3 is a view of the mold taken along the line Z1 and Z1' in Fig. 2. In Figs. 2 and 3, the molding ferrule half 1A includes the stationary mold component 4a, and the molding ferrule half 1B includes the movable mold component 4b. The stationary mold component 4a and the movable mold component 4b cooperate to position the pins 36 of the first molding core 34 and the pins 35 of the second molding core. It should be noted that the mold component 4a is fixed or stationary. The mold component 4b is movable by the piezoelectric element 32. When the mold component 4b is pressed by the piezoelectric element 32, a space 50 is formed between the mold component 4b and the plate 3b. The mold components 7a and 7b, as shown along the line Z2-Z2' in Fig. 2, are similar to the mold components 4a and 4b. Note that the clamping force CP is applied to the molding ferrule halves 1A and 1B. The mold component 4b and the mold component 7b, however, are not affected by the clamping force CP. They receive only forces from the piezoelectric elements 32 and 33, respectively. In the molding ferrule half 1A, the mold component 2a is formed as a base plate, the mold component 3a is formed as a closing plate, and the remaining mold components 4a to 8a are formed as blocks. In the same way, in the molding ferrule half 1B, the mold component 2b is formed as a base plate, the mold component 3b is formed as a closing plate, and the remaining mold components 4b to 8b are formed as blocks. On the surface of the mold component 2a, an opening 9a serving as a pocket is formed. The bottom of the opening 9a is closed by the mold component 3a. The mold components 4a, 5a, 6a, 7a, and 8a are accommodated in the opening 9a in line. At the center of the top surface of the mold component 4a and at the two sides of the top surface, V-shaped molding core holding portions 10a and 11a are formed. The top surface of the mold component 5a is formed as a flat surface which is lower than the top end face of the mold component 4a. The top end face of the mold component 6a is also formed as a flat surface which is slightly lower than the top end face of the mold component 5a. At the center of the top surface of the mold component 7a and at the two sides of the top surface, concave core grooves 13a and 14a are formed. Further, at the center of the top surface of the mold component 8a and at the two sides of the top surface, concave core holding portions 15a and 16a are formed. On the surface of the mold component 2b, an opening 9b serving as a pocket is formed, and the mold components 4b, 5b, 6b, 7b, and 8b are accommodated in the opening 9b in line. At the center of the bottom surface of the mold component 4b and at the two sides of the bottom surface, the core holding portions 10b and 11b are formed, respectively. The bottom surface of the mold component 5b is formed as a flat surface which is positioned higher than the bottom surface of the mold component 4b. Further, the bottom surface of the mold component 6b is also formed as a flat surface, which is positioned slightly above the bottom surface of the mold component 5b. The bottom surface of the mold component 7b lies at the same level as the bottom surface of the mold component 4b. At the center of the bottom surface of the mold component 7b and at the two sides of the bottom surface, concave core grooves 13b and 14b are formed, respectively. At the center of the bottom surface of the mold component 8b and at the two sides of the bottom surface, concave core holding portions 15b and 16b are formed, respectively. The mold component 3b is placed to abut against the top surface of the mold component 2b. Insertion holes 17 and 18 are formed in the mold component 3b at a position facing the mold components 4b and 7b. When the molding ferrule half 1A is assembled from the above-mentioned mold components 2a to 8a, the mold component 3a is placed so as to abut against the bottom surface of the mold component 2a, the mold components 2a and 3a are clamped with each other by a screw fastening means, and the mold components 4a to 8a are inserted into the opening 9a of the mold component 2a in a predetermined arrangement, to construct the molding ferrule half 1A. The resulting molding half 1A has a recess position 20a defining the second cavity 20. When assembling the molding ferrule half 1B by means of the above-mentioned mold components 2b to 8b, the mold component 3b is placed so as to abut against the bottom surface of the mold component 2b, the mold components 2b and 3b are clamped to each other by a screw fastening means, and the mold components 4b to 8b are inserted into the opening 9b of the mold component 2b in a predetermined arrangement, to construct the molding ferrule half 1B. The resultant molding ferrule half 1B has another recess 20b defining the cavity 20. In the assembled molding ferrule halves 1A and 1B, the mold components 4a and 4b, the mold components 5a and 5b, the mold components 6a and 6b, the mold components 7a and 7b, and the mold components 8a and 8b are correspondingly positioned vertically to each other, and the mold components 4a and 4b and the mold components 7a and 7b function as pin holders of the molding cores. The molding ferrule half 1A is mounted on the movable mold 21, while the molding ferrule half 1B is mounted on the stationary mold 22. At the top of the stationary mold 22, the push plate 23 is fixed. The stationary mold 22 further has through holes 24 and 25 formed at positions corresponding to the insertion holes 17 and 18 and has concave holes 26 and 27 formed at the bottom of the push plate 23 facing the through holes 24 and 25. The pressing pin 28 is inserted in the insertion hole 17 and the through hole 24. The top surface of the mold component 4b is placed so as to abut against the bottom surface of the pressing pin 28. A piezoelectric element 32 is placed between the top end of the pressing pin 28 and the bottom surface 30 of the concave hole 26. The piezoelectric element 32 and the pressing pin 28 constitute a pressing means for pressing the mold component 4b downward. Similarly, a pressing pin 29 is inserted into the insertion hold 18 and the through hole 25. The bottom surface of the pressing pin 29 is placed to abut against the top end of the mold component 7b. A piezoelectric element 33 is placed between the top end of the pressing pin 29 and the bottom surface 31 of the concave hole 27. The piezoelectric element 33 and the pressing pin 29 constitute a pressing means for pressing the mold component 7b downward. Note that a voltage applying means, not shown, is connected to the piezoelectric elements 32 and 33. The molding core 34, as will be clear with reference to Fig. 6 comprises a plurality of thin pins 36, each having a small diameter and both arranged in parallel at equal distances and a connecting member 37 which connects the base portions of the thin pin 36 to integrate them. The tips of the thin pins 36 are extremely small in diameter corresponding to the outer diameter of the optical fibers. The connecting member 37 is formed of die steel or the like while the thin pins 36 are formed of a metal material or the like which can be precisely worked. The molding core 35, as shown in Fig. 6, is molded as a pin. The molding core 35 has an outer diameter corresponding to the fitting pins 43 shown in Fig. 1. The molding core 35 is also formed of a metal material or the like which can be precisely worked. However, the movable mold 21 and the stationary mold 22 shown in Fig. 2 can, as is well known, be moved relative to each other in the mold opening and closing direction. The molding ferrule half 1A is mounted on the movable mold 21, and the molding ferrule half 1B is mounted on the stationary mold 22. In this state, the thin pins 36 and the connecting member 37 of the molding core 34 are fitted in the core holding portions 10a, 13a and 15a, and the two ends of the molding core 35 are fitted in the core holding portions 11a, 14a and 16a. When the molding ferrule halves 1A and 1B are clamped to each other, the thin pins 36 and the connecting member 37 of the molding core 34 are forcibly stopped by the core holding portions 10b and 13b and the two ends of the molding core 35 are forcibly stopped by the core holding members 11b and 14b. In this case, the tips of the pins of the molding cores 34 and 35 are gripped between the mold components 4a and 4b. When voltage is applied to the piezoelectric element 32 to expand the piezoelectric element 32, the resultant force is transmitted to the mold component 4b through the pressing pin 28, so that the tips of the pins of the molding cores 34 and 35 are held by optimum force which does not allow looseness or a damage of the pins. Similarly, the ends of the bases of the pins of the molding cores 34 and 35 are gripped by the mold components 7a and 7b. When voltage is applied to the piezoelectric element 33 to expand the piezoelectric element 33, the resultant force is transmitted to the mold component 7b through the pressing pin 29, so that the ends of the bases of the pins of the molding cores 34 and 35 are held between the mold components 7a and 7b by optimum force which does not allow looseness or a damage of the pins. By varying the magnitudes of the voltages applied to the piezoelectric elements 32 and 33, the holding force of the pins of the molding cores 34 and 35 are adjusted, and the amount of deformation due to expansion and contraction of the piezoelectric elements 32 and 33 is changed, and thus, the holding force of the pins of the molding cores 34 and 35 can be controlled. As a result, the two molding cores 34 and 35 are held between the clamping surfaces of the two clamped molding ferrule halves 1A and 1B, and correctly disposed at fixed positions in the cavity 20 defined by recesses 20a and 20b. Note that known gates and runners (not shown) are formed at the clamping surfaces of the two molding ferrule halves 1A and 1B. The runners and known runners (not shown) provided in the movable mold 21 and the stationary mold 22 or the like, are connected with each other. Further, the movable mold 21 can be provided with ejector pins for ejecting the two molding cores 34 and 35, the molded article or the like. The through holes (not shown) for the ejector pins are then formed in predetermined mold components in the molding ferrule half 1A. According to the first embodiment, the molding ferrule halves 1A and 1B which are heated to a predetermined molding temperature, are clamped to each other. Thereafter, a fluid and high temperature plastic material (heat curing resin or thermoplastic resin) is injected into the cavity 20 to form a predetermined mold article, that is, the optical fiber connector ferrule 45 shown in Fig. 1. During the molding process, the pins of the molding cores 34 and 35 are held by the holding force generated by the pressing means independent from the mold clamping force, that is, by the piezoelectric elements 32 and 33, so that an excessive force is not applied to the pins and to evade the problem that the pins are damaged by an excessive force. A second embodiment of a mold according to the present invention will be described with reference to Fig. 7. Figure 7 is a sectional view of the mold corresponding to that of Fig. 2. In this mold shown in Fig. 7, the insertion hole 18, the through hole 25, the pressing pin 29 and the piezoelectric element 33, which are shown in Fig. 2, are removed, and, consequently, the injection of the plastic resin in carried out through resin injection holes (not shown), and the pressing is carried out by the piezoelectric element 32 and the pressing pin 28. The mold shown in Fig. 7 acts in the same manner as the mold shown in Fig. 2 and produces a ferrule. A third embodiment of a mold according to the present invention will be described with reference to Fig. 8. Figure 8 is a sectional view of the mold corresponding to that of Fig. 2. In this mold, the pressing pins 28 and 29 shown in Fig. 2 are removed, and springs 51 and 52 are inserted into the holes 26 and 27 instead of the piezoelectric elements 32 and 33 as shown in Fig. 2. The springs 51 and 52 press directly the molding components 4b and 7b. Alternatively, other elastic members for generating the force for pressing the molding components 4b and 7b, such as rubber sheets, can be applied instead of the springs 51 and 52. As seen from the second embodiment of a mold according to the present invention will be described with reference to Fig. 9. Figure 9 is a partial sectional view of the mold corresponding to that of Figs. 2 and 7. In this mold, a pressurized fluid such as fluid oil or a compressed gas such as compressed air, which presses the molding component 4b through the pressing pin 28A, functions as a pressing means. O-rings 52 and 53 are attached to the wall of the hole in order to hermetically seal off the pressurized fluid or the compressed gas. Other pressing means such as electromagnets and/or permanent magnets can also be applied. An excessive molding clamping force does not act on the above pressing means. As a result, a short time deterioration is prevented. As seen from the above described embodiments, the holding force for holding the pins of the molding cores, disposed in the cavity of the mold, is provided by a pressing means independent from the molding clamping force. As a result, it becomes possible for the pins of the molding cores to be held by the optimum force, and it is possible to hold the pins of the molding cores precisely at a fixed position without play. Thus, the molding precision of the molded ferrule can be improved sufficiently. Further, since the pins of the molding cores are not subjected to an excessive force such as the molding clamping force, the pins are not damaged, and therefore, the molding cores can be used for a long period of time, and the present invention is extremely advantageous in economical terms. Figures 10a to 10c are sectional view of modification of the V-shaped grooves 11b shown in Figs. 2 to 5. Figure 10a shows a semi V-shaped groove 53, Fig. 10b shows a trapezoid groove 54, and Fig. 10c shows a U-shaped groove 55. Other grooves similar to those can be used. Another ferrule of the present invention will be described with reference to Fig. 11 and Figs. 12a and 12b. These ferrules are used for an optical fiber switch, which comprises a first ferrule 45c and a second ferrule 45B. The second ferrule 45B has a structure identical to that shown in Fig. 1. The first ferrule 45c has a structure similar to the ferrule 45A except that a pair of elongated through holes 44C are formed instead of the round through holes 44A. The formation of the first and second ferrules 45C and 45B can be carried out by using the mold as discussed above. When assembling the optical fiber switch, the optical fibers 41A are inserted into the fiber holes 42A, while the optical fibers 41B are inserted into the fiber holes 43B, and then the fitting pins 43 are inserted into the pin holes 44C and the pin holes 44B, to integrate the ferrules 45C and 45B. Normally, when both ferrules 44C and 44B face each other at a correct position, as shown in Fig. 12a, ends of the optical fibers 41A and 41B face each other to establish five optical paths. When the first ferrule 45C is moved by one pitch defining a distance between adjacent optical fibers, in a direction A, the fitting pins 43 are moved to the left side edges of the elongated holes 44C, to thereby change the above optical paths, as shown in Fig. 12b.

Claims: A method of molding a ferrule of plastic resin, wherein the ferrule (45A, 45B) is provided with at least one hole (42A, 42B) having a small diameter and positioned at a predetermined position, by a mold comprising:- a pair of mold halves (21, 22); inner members (4a-8a, 4b-8b), at least one of said inner members being a positioning member; and at least one molding member (35, 36); characterised by the following steps:- arranging said inner members (4a-8a, 4b-8b) in a first cavity (20), defined by said pair of mold halves (21, 22), to thereby define a second cavity (20) wherein is arranged at least one molding member (36, 35) forming at least one hole (42A, 42B) having a small diameter after completion of molding; holding said mold halves (21, 22) and said inner members (4a-8a, 4b-8b) by a clamping force (CP) such that at least one of said inner members (4a-8a, 4b-8b) is free from the clamping force and can be used as a positioning member (4b, 7b); applying a force to said positioning member, which force is smaller than and separate of said clamping force, for positioning said molding member (36, 35); and supplying a plastic resin in said second cavity (20) to form a ferrule, A method of molding a ferrule according to claim 1, wherein the force to said positioning member is generated by a member which generates the force in response to electric power. A method of molding a ferrule according to claim 1, wherein the force to said positioning member is generated by an elastic member. A method of molding a ferrule according to claim 1, wherein the force to said positioning member is generated by a pressurized fluid. A method of molding a ferrule according to claim 1, wherein the force to said positioning member is generated by a compressed gas. A method of molding a ferrule according to claim 1, wherein the force to said positioning member is generated by a magnet. A mold for forming a ferrule provided with at least one hole having a small diameter and positioned at a predetermined position, comprising:- a pair of mold halves (21, 22) defining a first cavity (50) wherein inner members (4a-8a, 4b-8b), of which at least one is a positioning member (4b, 7b), are arranged to define a common cavity (20); at least one molding member (36, 35) which is disposed in said common cavity (20), characterised in that said pair of mold halves and the inner members (4a-8a, 4b-8b) being configurated such they may be held by a common clamping force exempt at least one inner member (4b, 7b) which is free of the clamping force and forms a positioning member (4b, 7b) for positioning said molding member (36, 35); and a force means (28) for applying separately from said clamping force a force to said positioning member for positioning of said molding member (36, 35). A mold for forming a ferrule according to claim 7, wherein said force means comprises a member (32, 33) which generates the force in response to electric power. A mold for forming a ferrule according to claim 7, wherein said pressing means (51, 52) comprises an elastic member. A mold for forming a ferrule according to claim 7, wherein said pressing means comprises a pressurized fluid. A mold for forming a ferrule according to claim 7, wherein said pressing means comprises a compressed gas. A mold for forming a ferrule according to claim 7, wherein said pressing means comprises a magnet means. A mold for forming a ferrule according to claim 7, wherein said inner member comprises a groove having at least one inclined surface, such as a V-shaped surface, a trapezoid. A mold for forming a ferrule according to claim 7, wherein said ferrule is used for an optical fiber connector, an optical fiber switch or the like, and said hole having a small diameter is formed to fit an optical fiber (41A). A mold for forming a ferrule according to claim 7, wherein said molding ferrule cores further comprises at least one additional pin member (35) for forming a hole (44A) through which a connecting pin (43) is inserted.

Inventors: IMAMIZO SEIICHI, KIMURA TAKAHIDE, SHIGEMATSU TAKASHI, TAKAGI KOICHI, IMAMIZO, SEIICHI, KIMURA, TAKAHIDE, SHIGEMATSU, TAKASHI, TAKAGI, KOICHI, Imamizo, Seiichi, c/o The Furukawa Elec. Co.Ltd, Kimura, Takahide, c/o The Furukawa Elec. Co.Ltd, Shigematsu, Takashi, c/o The Furukawa Elec. Co.Ltd, Takagi, Koichi, c/o The Furukawa Electric Co., Ltd
Applicants: FURUKAWA ELECTRIC CO LTD, THE FURUKAWA ELECTRIC CO., LTD.
Application year: 1992
Main classification: B29D11
IPC codes: B29C33, B29C45, B29D11, G02B6, B29L22, B29L31