Process of producing slit-formed sleeve connector

Abstract

A process of producing a slit-formed cylindrical sleeve connector for press-fitting and joining thin wires or thin rods, rigid or elastic, together in close or contacting relationship using an electroforming process that includes providing a thin conductive electroforming mandrel having an external surface finished to a specified grade of surface finish, forming a given pattern of nonconductive layer so as to define at least one cylindrical but circumferentially discontinuous electrodeposition cell on the electroforming mandrel electrodepositing an electroformed metal layer in the electrodeposition cell on the electroforming mandrel by an electroforming process, and removing the electroformed metal layer from the electroforming mandrel, thereby providing a cylindrical metal tube formed with a longitudinal slit as a slit-formed cylindrical sleeve connector having an internal wall with the same grade of surface finish as the external surface of the mandrel.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates to a process of producing a precise cylindrical sleeve connector, in particular a slit-formed cylindrical sleeve connector, for interconnecting round filamentary members using an electroforming process.

[0003] 2. Description of Related Art

[0004] There have been used various processes of producing cylindrical sleeve connectors for joining thin wires or thin rods, rigid or elastic, including optical fibers, electric wires, etc. (which are generally named as thin round filamentary members in this specification), together in close or contacting relationship. The most popular processes of producing such a cylindrical sleeve connector include drawing out a thin cylindrical hollow tube through a die or pressing a round sleeve with a longitudinal slit. For cylindrical sleeve connectors that are demanded to have high fitting accuracy, it is essential to satisfy completely such requirements as, for example, a specified grade of inner surface finish, a specified degree of dimensional precision necessary for ensured suitable interference for press-fit, inwardly chamfered or rounded configuration of end walls that guide press-fit of thin round filamentary members into the sleeve connector through entry openings against the interference, etc.

[0005] The process of drawing out a thin cylindrical hollow tube through a die includes providing a comparatively thin cylindrical metal tube, drawing the thin cylindrical metal tube repeatedly using dies that have different sizes of longitudinal taper bores and applying thermal treatment to the drawn metal tube after every drawing. Each die has different internal diameters at opposite ends, i.e. a larger internal diameter at an entrance end and a smaller diameter at a drawing end. The drawn metal tube is gradually made thinner and thinner in external diameter whenever it is passed through the dies one after another and thermally treated. Accordingly, there occurs a reduction in internal diameter of the drawn metal tube merely as a result of plastic deformation that is caused through each drawing step. Because any additional finishing is not applied to the drawn metal tube in order to provide the drawn metal tube with the specified grade of surface finish and the degree of dimensional accuracy, the drawn metal tube is hardly available as a sleeve connector into which thin round filamentary members are press-fitted for close or contacting interconnection.

[0006] Therefore, in order to complete the drawn metal tube as a sleeve connector so that the drawn metal tube satisfies the requirements, the drawn metal tube must be subjected to additional or secondary works. The additional works include, for example, finishing the inner surface of the drawn metal tube to the specified grade of surface finish, forming a longitudinal slit along the full length of the drawn metal tube, expanding the range of elasticity for a complement to the dimensional accuracy that is suited for press-fit of thin round filamentary members, and machining the drawn metal tube so as to provide the opposite end walls with inwardly chamfered or tapered configurations, respectively. However, there is no available way of finishing inner surfaces of thin metal tubes having small diameters of longitudinal bores. Slitting and chamfering such a thin metal tube is inevitably accompanied by burrs. This makes insertion of thin round filamentary members into the metal tube very hard and troublesome. Further, the additional work of slitting the thin metal tube is one of causes of unbalanced distribution of internal stress contained in the thin cylindrical metal tube which leads to deformation in shape.

[0007] While on one hand the process of pressing and rolling a thin metal sheet and shaping the rolled member to a slit-formed cylindrical sleeve connector is suitable to provide the cylindrical sleeve connector with an expand range of elasticity, the process is awfully unreliable in light of surly providing the internal cylindrical bore of the rolled member with accurate roundness and, in consequence, is hard to eliminate the additional work of chamfering the opposite end walls with an intention to provide the cylindrical sleeve connector with suitable interference for press-fit as unnecessary.

[0008] In the prior art process of producing a slit-formed cylindrical sleeve connector for joining thin round filamentary members together with high precision, as-primary worked metal tube is hardly available as a high precision sleeve connector and, as a result, the metal tube is subjected to required secondary works in order to fulfill the required functions. While these secondary works are time consumable as compared with the primary works, they still include technical problems that should be overcome.

[0009] Many electro-mechanical processes that are different in principle from general mechanical processes have been attempted to produce precision slit-formed cylindrical sleeve connectors. Some of the electro-mechanical processes are technically successful but are practically unavailable from the standpoint of productivity.

[0010] As apparent from the above discussion, it is essential for the precision slit-formed cylindrical sleeve connector for joining thin round filamentary members together in, in particular, close or contacting relationship to satisfy the following requirements. A primary requirement is that while the slit-formed cylindrical sleeve connector provides easy press-fit of thin round filamentary members, it provides reliable retention of the thin round filamentary members therein such as to prevent the thin round filamentary members from being pulled out with pull-out force less than a specified force. In order to satisfy the primary requirement, the slit-formed cylindrical sleeve connector is required to have an internal surface finished to desired surface quality, desired elasticity, accurate roundness of the cylindrical bore, desired configurations of the end walls and ensured suitable interference for press-fit. There has been no way to accomplish these requirements all at once.

SUMMARY OF THE INVENTION

[0011] It is an object of the present invention to provide a process of producing a precise slit-formed cylindrical sleeve connector using an electroforming process in which a surface quality of an electroforming mandrel is exactly copied to an internal surface of the slit-formed cylindrical sleeve connector.

[0012] It is another object of the present invention to provide a process of producing a precise slit-formed cylindrical sleeve connector using an electroforming process in which the slit-formed cylindrical sleeve connector is provided with a longitudinal slit along the full length thereof and chamfered end walls at the opposite ends thereof during progress of the electroforming process.

[0013] The foregoing objects of the present invention are achieved by a process of producing a slit-formed cylindrical sleeve connector for press-fitting thin round member therein using an electroforming process. The process comprises the steps of forming a given pattern of nonconductive layer by, for example, a printing process using non-conductive inks or a photoengraving process using non-conductive photo-resists, so as to define at least a cylindrical but circumferentially discontinuous electrodeposition cell on a cylindrical mandrel made of a conductive metal string having an external surface finished to a specified grade of surface finish, electrodepositing an electroformed metal layer in the electrodeposition cell on the cylindrical mandrel by an electroforming process, and removing the electroformed metal layer from the cylindrical mandrel, thereby providing a cylindrical metal tube formed with a longitudinal slit as a slit-formed cylindrical sleeve connector that has an internal wall with the same grade of surface finish as the external surface of the mandrel. The electroforming process is controlled so as to provide the electroformed metal layer with a uniform thickness and a specified internal stress that is desirably zero or compressive.

[0014] The patterned non-conductive layer may comprise two circumferential annular segments separated at a distance, desirably slightly less than an intended longitudinal length of the cylindrical metal tube, in the longitudinal direction and a longitudinal segment extending straight between the two circumferential annular segments. Each of the circumferential annular segments has outwardly chamfered or rounded side walls at opposite circumferential side edges.

[0015] In the electroforming process, an electrolytic fluid desirably comprises a solution of nickel sulfamic acid desirably containing naphthlin sodium trisulfoacid or saccharin as an additive.

[0016] The slit-formed cylindrical metal tube of as-electroformed product is directly available as a precise slit-formed cylindrical sleeve connector or a precise slit-formed sleeve-like a ferrule without being additionally machined or processed. This is because the surface quality and the external dimension and configuration of the mandrel with a patterned layer are precisely copied to the electroformed metal layer, and hence the cylindrical metal tube formed with a longitudinal slit. The electroformed metal layer on the mandrel that is provided with a compressive stress is easily removed from the mandrel. The slit-formed cylindrical metal tube can provides ensured press-fitting characteristics suitable for various applications such as a connector and a ferrule by choices of combination of electrolytic fluids and additives in addition to electroforming conditions. In addition, the slit-formed cylindrical metal tube has the end walls provided with desired configurations during electroforming so as to provide smooth introduction of thin round filamentary members and suitable interference for press-fit of the thin round filamentary members.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and other objects and features of the present invention will be understood from the following description in accordance with preferred embodiments thereof when reading in connection with the accompanying drawings in which parts and elements denoted by the same reference numbers are same or similar in structure and operation throughout the drawings, and wherein:

[0018] FIG. 1A is a side view of a slit-formed cylindrical sleeve connector partly cut-away that is produced by a process of the present invention;

[0019] FIG. 1B is a front view of the lit-formed sleeve connector;

[0020] FIG. 1C is an oblique perspective view of the slit-formed cylindrical sleeve connector;

[0021] FIG. 2 is an oblique perspective view of an electroforming mandrel with a plurality of electrodeposition cells on which electroformed metal layers are electrodeposited and built up;

[0022] FIG. 3 is a front view showing a mandrel holder for holding the electroforming mandrel forming a part of electroforming apparatus implementing the process of producing a slit-formed cylindrical sleeve connector of the present invention;

[0023] FIG. 4 is a schematic view showing the electroforming apparatus;

[0024] FIGS. 5A and 5B are graphical diagrams illustrating changes in internal stress of an electroformed nickel layer according to electroforming conditions;

[0025] FIG. 6 is an enlarged cross-sectional view of an circumferential annular segment forming part of a given pattern of non-conductive layer taken along line VI-VI of FIG. 2; and

[0026] FIG. 7 is an explanatory view showing the slit-formed cylindrical sleeve connector that is used to join thin round filamentary members together in close or contacting relationship.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Referring to the drawings in detail and, in particular, to FIGS. 1A to 1C showing a slit-formed cylindrical sleeve connector 10 produced using an electroforming process, the slit-formed cylindrical sleeve connector 10 that is used to join end portions of thin round filamentary members, rigid or elastic and/or naked or ferrule protected, together in close or contacting relationship, is made from a slit-formed cylindrical metal tube 1 that is produced by the electroforming process. The slit-formed cylindrical metal tube 1 has a longitudinal cylindrical bore 1e defined by an inner wall 1f in which end portions of thin round filamentary members or ferrules are received in close or contacting relationship. The longitudinal bore 1e forms inwardly chamfered or rounded end walls 1a and 1b at opposite ends of the slit-formed cylindrical metal tube 1. The slit-formed cylindrical metal tube 1 further has a longitudinal slit 1d extending end to end or along the full length L thereof. The longitudinal bore 1e also forms inwardly chamfered side walls 1c at opposite sides of the longitudinal slit 1d. In the case where the slit-formed cylindrical sleeve connector 10 is used as a connector for thin round filamentary members, the inner surface of the thin slit-formed cylindrical metal tube 1 is finished to such a grade of surface finish as required for needles for use with needle bearings, i.e. a grade of surface finish specified by a finish mark of four triangles, or higher.

[0028] The process of producing the slit-formed cylindrical sleeve connector 10 using the electroforming process includes a step of providing an electroforming mandrel 20 as shown in FIG. 2.

[0029] Referring to FIG. 2 showing the electroforming mandrel 20 that is used to form the high precision thin slit-formed cylindrical sleeve connector 10. The electroforming mandrel 20 comprises a thin conductive rod 2 having a cylindrical configuration and a given pattern of non-conductive layer 3 formed on the conductive rod 2. The conductive rod 2 has an outer surface finished to the same grade of surface finish as required for needles for use with needle bearings, i.e. the grade of surface finish specified by a finish mark of four triangles, or higher. The patterned non-conductive layer 3 defines a plurality of electrodeposition cells 3c on the conductive rod 2. That is, the patterned non-conductive layer 3 comprises a plurality of circumferential annular segments 3b having specified regular widths and arranged at regular distances D in a lengthwise direction of the conductive rod 2 and a longitudinal straight segment 3a extending between opposite extreme circumferential annular segments 3b. The regular distance D by which each adjacent circumferential annular segments 3b are separated is equal to the total of the width of the circumferential annular segment 3b and the length L of the sleeve connector 10. The surface area of the conductive rod 2 that is defined by each adjacent circumferential annular segments 3b and a segment of the longitudinal straight segment 3a forms an electrodeposition cell 3c.

[0030] The patterned of non-conductive layer 3 may be formed by any manner such as printing and photo-resist coating. In such a manner, the given pattern of non-conductive layer 2 is formed so that each of the longitudinal segment 3a and the circumferential annular segments 3b has slightly convexly rounded or tapered side edges.

[0031] As shown in FIG. 3, before forming a slit-formed cylindrical metal tube 1 with the electroforming mandrel 20 by means of the electroforming process, the mandrel 20 is attached to a mandrel holder 5. The mandrel holder 5 comprises a generally U-shaped holding body 4, upper and lower holding fixtures 7 detachably screwed into upper and lower arms of the holding body 4 and a coupling joint 8. At least the upper holding fixture 7 and the coupling joint 8 are made of conductive members. After fixing the mandrel 20 at a lower end to the lower holding fixture 7, the upper holding fixture 7 is adjusted so as to fix the mandrel 20 at the upper end. Masking tapes 6 such as self adhesive tapes are put on the mandrel 20 so as to hide opposite extreme end portions of the mandrel 20 except the portion between the opposite extreme circumferential annular segments 3b of the patterned non-conductive layer 3 for isolation from an electroforming solution during electroforming. The mandrel holder 5 with the mandrel 20 attached is subsequently put in an electroforming apparatus 30 shown by way of example in FIG. 4.

[0032] Referring to FIG. 4, the electroforming apparatus 30 comprises an electrolytic fluid vessel 14 in which an electrolyte fluid 13 is contained, a plurality of nickel electrodes 11 which are the anode under electrodeposition conditions, a power supply 9 and a drive motor 15 with a shaft having a coupling joint 8' that is disposed outside the electrolytic fluid vessel 14 so as to be stationary with respect to the electrolytic fluid vessel 14. The mandrel holder 5 holding the mandrel 20 is coupled to the drive motor 15 through coupling between the coupling joints 8 and 8' and driven by the drive motor 15 to rotate together with the mandrel 20 in the electrolyte fluid 13. The power supply 9 supplies a commercial direct current between the anode and cathode, i.e. the nickel electrodes 11 and the mandrel 20 held by the mandrel holder 5. The power supply 9 also supplies a commercial direct current to the mandrel 10.

[0033] A conventional electroforming process is implemented to deposit a metal layers 12 on the electrodeposition cells 3c of the mandrel 20, respectively, while the mandrel 20 is rotated by the motor 15. The electroformed metal layer 12 is circumferentially discontinuous along the longitudinal segment 3a. The electroforming is implemented under controls so as to provide the electroformed metal layer 12 with a given thickness and a given internal stress. The resultant products that are obtained by removing the electroformed metal layers 12 from the mandrel 20 are metal tubes 1 each of which is cylindrical in shape and provided with a longitudinal slit extending along the full length and, in addition, inwardly chamfered or rounded end walls at opposite ends, respectively. The patterned non-conductive layer 3 is broken by the electroformed metal layers 12 and peeled of from the mandrel 20 as the electroformed metal layers 12 are removed from the mandrel 20. The electroforming process is controlled so as to provide the electroformed metal layer 12 with a given internal stress preferably circumferential compressive stress.

[0034] Generally, because a nickel layer deposited on a mandrel or mother die by an electroforming process that has a comparatively large thickness is given a comparatively large internal stress during electroforming, it is essential to control the internal stress. If the internal stress is too large, the electroformed nickel layer is apt to peel off from the mandrel or mother die. This makes it hard to obtain an intended product. In the case where a nickel product is cylindrical in shape, the electroformed nickel layer is easily removed from the mandrel or mother die if it is given a circumferential compressive stress or hardly removable from the mandrel or mother die if it is given a circumferential tensile stress. Further, in the case where the cylindrical nickel product is circumferentially discontinuous such as a nickel tube formed with a longitudinal slit, the electroformed nickel layer is easily removed and provides the slit-formed cylindrical nickel tube having a tendency to shrink in a radial direction. The magnitude of internal stress of an electroformed nickel layer deposited on the mandrel or mother die is significantly different according to kinds of electrolyte fluids such as a solution of borofluoride, a solution of watt and a solution of sulfamic acid. In light of the internal stress, the solution of sulfamic acid is most suitable. The magnitude of internal stress of the electroformed nickel layer is variable according to density and hydrogen exponent (pH) of the solution of sulfamic acid, density of an electroforming current and additives.

[0035] FIGS. 5A and 5B show, by way of example, changes in internal stress of an electroformed nickel layer 12 electrodeposited on the mandrel 20 according to additives and temperature of the electrolytic fluid. FIG. 5(A) shows a change in internal stress of an electroformed nickel layer 12 according to temperature of an electrolytic fluid with a hydrogen exponent of 4.0 that comprises a solution of nickel sulfamic acid containing a 5 g/l of naphthlin sodium trisulfoacid as an additive. FIG. 5(B) shows changes in internal stress of an electroformed nickel layer 12 according to additive contents in weight ratio of an electrolytic fluid with a hydrogen exponent of 4.0 that comprises a solution of nickel sulfamic acid containing saccharin as an additive for different electroforming currents and temperatures of the electrolytic fluid. In the figures measurements taking positive internal stress is tensile and measurements taking negative is compressive.

[0036] As apparently described in FIGS. 5A and 5B, the internal stress can be controlled according to electroforming conditions, i.e. combinations of various control factors including hydrogen exponent (pH), electroforming current (A) and temperature of the electrolytic solution in centigrade. In particular, in order to develop high compressive stress that provides the electroformed nickel layer 12 with suitable separation performance, it is desirable to employ a comparatively higher temperature of the electrolytic fluid and a comparatively higher current. Further, it is desirable to use saccharin as an additive that has a high stress control effect.

[0037] FIG. 6 shows a cross-section of the circumferential annular segment 3b of the patterned non-conductive layer 3 formed on the conductive rod 2 by printing or photo-resist processing. As shown, the patterned non-conductive layer 3 is such that the each circumferential annular segment 3b has opposite side edges convexly chamfered or rounded in the lengthwise direction of the conductive rod 2 and each segment of the longitudinal straight segment 3a has opposite side edges convexly chamfered or convexly rounded in the circumferential direction of the conductive rod 2. The convexly rounded side edge of the circumferential annular segment 3b desirably has a length approximately equal to the given thickness of the slit-formed cylindrical metal tube 1.

[0038] In the electroforming process, while metal layers 12 are gradually built up on the electrodeposition cells 3c surrounded by the segments 3a and 3b of the patterned non-conductive layer 3, respectively, and peripheries of each of the metal layers 12 have chamfered or rounded configurations copied from the convexly chamfered or rounded edges of the segments 3a and 3b of the patterned non-conductive layer 3, respectively, in a manner like die-casting. In the case where the patterned non-conductive layer 3 has a thickness less than the given thickness of an intended slit-formed cylindrical metal tube 1, the electroformed metal layer 12 is built up partly overlapping margins of the segments 3a and 3b.

[0039] FIG. 7 shows, by way of example, a slit-formed cylindrical metal tube 1 produced by the process of the present invention that is used as a precise thin slit-formed sleeve connector 10 to join thin round filamentary members such as optical fibers together in contacting relationship. In this instance, the slit-formed cylindrical sleeve connector 10 is provided in order to join thin rounded members such as, for example, thin round filamentary members 15 and 16 having a same external diameter of approximately 1.2 mm together in close or contacting relationship. The slit-formed cylindrical metal tube 1 is such as to have an internal diameter smaller by 3 microns than the thin round filamentary members 15 and 16. The difference between the external diameter of the thin round filamentary members 15 and 16 and the internal diameter of the slit-formed cylindrical metal tube 1 works as interference for press-fit for the thin round filamentary members 15 and 16 in the slit-formed cylindrical sleeve connector 10.

[0040] In operation of joining the thin round filamentary members 15 and 16 together in close or contacting relationship, at the beginning of insertion of the thin round filamentary member 15 into the slit-formed cylindrical sleeve connector 10 through one of the opposite ends, the thin round filamentary member 15 at the end is guided by the inwardly chamfered or inwardly rounded edges 1a of the slit-formed cylindrical sleeve connector 10 and then expands the slit-formed cylindrical sleeve connector 10 as it is further forced into the slit-formed cylindrical sleeve connector 10. As a result, the thin round filamentary member 15 is tightly press-fitted in the slit-formed cylindrical sleeve connector 10. Another thin round filamentary member 16 is inserted into the slit-formed cylindrical sleeve connector 10 through another end until it abuts against the thin round filamentary member 15 previously press-fitted in the slit-formed cylindrical sleeve connector 10. In this manner the thin round filamentary members 15 and 16 are tightly press-fitted and joined together in close or contacting relationship in the slit-formed cylindrical sleeve connector 10.

[0041] As described above, the slit-formed cylindrical sleeve connector 10 has an internal surface exactly copied from the electroforming mandrel 20 with the external surface finished with high dimensional precision and high surface quality. This provides the slit-formed cylindrical sleeve connector 10 with significantly reduced frictional resistance to insertion of the thin round filamentary members 15 and 16 and ensured stable interference for press-fit for thin round filamentary members and ensured stable retention force for the thin round filamentary members in the slit-formed cylindrical sleeve connector 10. The slit-formed cylindrical sleeve connector 1 at the opposite end walls is inwardly chamfered or rounded following the chamfered or inwardly rounded side edges of the segments 3a and 3b of the patterned non-conductive layer 3 as the electroformed metal layer 12 is built up. This eliminates the necessity of applying secondary works, such as inwardly chamfering or rounding to the end walls 1a and 1b of the cylindrical metal tube 1 and forming a longitudinal slit in the cylindrical metal tube 1 which are often accompanied by burrs that must be removed by further machining. The burr-free slit-formed cylindrical metal tube 1 as a connector makes introduction of thin round filamentary members quite easy and smooth.

[0042] The electroforming mandrel 20 can be long such as to form deposition cells 3c as many as possible thereon. Even in the quantity production, the electroformed metal layers 12 are easily removed maintaining a cylindrical shape from the electroforming mandrel 20 since they are electrodeposited separately from one another by the non-conductive segments. This makes quantity production of slit-formed cylindrical metal tubes easy and efficient.

[0043] Although the slit-formed cylindrical metal tube 1 has been described as a connector used to join thin round filamentary members, naked or ferrule protected, together in close or contacting relationship, it can be available as a ferrule for protecting an end portion of a thin round filamentary member.

[0044] It is to be understood that although the present invention has been described with regard to a preferred embodiment thereof, various other embodiments and variants may occur to those skilled in the art, which are within the scope and spirit of the invention, and such other embodiments and variants are intended to be covered by the following claims.

Claims

What is claimed is:

1. A process of producing a slit-formed cylindrical sleeve connector in which a thin round string member is press-fitted using an electroforming process, sand process comprising the steps of: providing a cylindrical mandrel made up from a conductive metal string member having an external surface finished to a specified grade of surface finish; forming a given pattern of nonconductive layer which defines at least an electrodeposition cell on said cylindrical mandrel, said electrodeposition cell being cylindrical but circumferentially discontinuous; electrodepositing a specified thickness of electroformed metal layer in said electrodeposition cell on said cylindrical mandrel by an electroforming process; and removing said electroformed metal layer from said cylindrical mandrel, thereby providing a cylindrical metal tube slit in a longitudinal direction as a slit-formed cylindrical sleeve connector having an internal wall with the same specified grade of surface finish as said cylindrical mandrel.

2. A process of producing a slit-formed cylindrical metal sleeve connector as defined in claim 1, wherein said electroforming process is controlled so as to provide said electroformed metal layer with a specified internal stress that is zero or compressive.

3. A process of producing a slit-formed cylindrical metal sleeve connector as defined in claim 1, wherein said given pattern of non-conductive layer comprises circumferential annular segments separated at a specified distance in said longitudinal direction and a longitudinal segment extending between said circumferential annular segments.

4. A process of producing a slit-formed cylindrical metal sleeve connector as defined in claim 3, wherein each said circumferential annular segment having outwardly chamfered or rounded side walls at opposite side edges.

5. A process of producing a slit-formned cylindrical metal sleeve connector as defined in claim 1, wherein said uniform thickness of electroformed metal layer is electrodeposited on said cylindrical mandrel in an electrolytic fluid comprising a solution of nickel sulfamic acid.

6. A process of producing a slit-formned cylindrical metal sleeve connector as defined in claim 5, wherein said electrolytic fluid contains naphthlin sodium trisulfoacid as an additive.

7. A process of producing a slit-formed cylindrical metal sleeve connector as defined in claim 4, wherein said electrolytic fluid contains saccharin as an additive.