METHOD OF MANUFACTURING PLUG-IN ELECTRICAL FUSES AND A FUSE PRODUCED BY THE METHOD

Abstract: A plug-in electrical fuse comprises a fusible wire (9) disposed within an insulating housing (1) and connected between the ends of two blade-like terminals (4) secured within and projecting from the housing. Fuses of this type are manufactured by forming a strip of terminal members from strip metal, each member comprising two spaced substantially-coplanar blade-like terminal portions interconnected at their leading ends (5) by an integral cross-bar portion, and each terminal member being integrally connected with each adjacent terminal member in the strip by an interconnecting bar of the metal strip. Fusible wire is secured to the terminal portions adjacent their rear ends to form a strip of terminal and wire assemblies, and this strip of assemblies is mounted in a strip of insulating housings with the fusible wires disposed within the housings and the leading ends of the terminal portions projecting therefrom. The interconnecting and crossbar portions between adjacent assemblies and between the terminal portions of each assembly are then severed so as to separate the strip into individual fuses. The housings may be retained connected together in strip form and be separated only when the fuses are required for use.

Description: METHOD OF MANUFACTURING PLUG-IN ELECTRICAL FUSES AND A FUSE PRODUCED BY THE METHOD The present invention relates to plug-in electrical fuses of the type designed to be plugged directly into socket openings which extend transversely to the length of the fuse body. Such fuses are especially suitable for use in protecting automobile electrical circuits. A typical plug-in fuse of the above type is des¬ cribed in British Patent Speci ication No. 1500183. This fuse includes a fuse element in the form of a one-piece, plate-like body of fuse metal, the body comprising a P a ir of laterally spaced generally parallel terminals, each of which comprises a blade portion adapted, in use, to be inserted into a socket, such as a pressure clip terminal, in a mounting panel, and a fusible link portion, of smaller cross-sectional area than the blade terminals, integral with the tenninals at positions remote from their leading ends. The fuse element is mounted in an insulat¬ ing housing so that the fusible link portion is enclosed in the housing and the leading ends of the blade terminals project therefrom for plugging into cooperating sockets. Such fuse elements may readily be mass-produced by stamp¬ ing them from the end of a strip o£ fuse metal, preferably, after selected areas have been milled and/or compressed to reduce the cross-sectional areas of the portions of the strip which are to constitute the fusible link portions of the fuse elements. Λn object of the present invention is to provide an improved method of manufacturing plug-in fuses of the type referred to which facilitates mass production of such fuses. The improved method also results in a novel construction of plug-in fuse which is interchangeable with other known fuses of this type. From one aspect, the present invention consists in a method of making a plug-in electrical fuse of the type referred to, comprising the steps of forming a terminal member from sheet metal material, which member comprises two spaced, substantially coplanar, blade-like terminal portions interconnected at or adjacent leading ends by an integral cross-bar portion, securing a fusible element to the terminal portions at or adjacent rear ends there¬ of, mounting the resulting assembly in an insulating housing with the fusible element disposed within the housing and the leading ends of the terminal portions projecting therefrom, and severing the cross bar from the terminal portions. The terminal member may be formed as a simple stamp¬ ing from sheet metal material. Alternatively, it may be formed by stamping a generally H-shaped blank from the sheet material, folding the blank about an axis substan- tially parallel to the cross bar of the Iϊ-shape so as to dispose upper and lower portions of the uprights of the "II" in mutually opposed relation to form two blade-like terminal portions of double laminar construction. The laminar forming each of the terminal portions are inte- grally joined at the leading ends of the terminals, and the terminal portions remain joined together by the cross¬ bar of the original H-shape until this cross-bar is severed at a later stage in the production of the fuse. The fusible element, which may comprise a length of fusible wire, may be soldered or welded to the terminal portions adjacent the rear ends thereof. To permit the length of the fusible link provided by the fuse element to be maximized, the terminal portions may be formed, at their rear ends, with mutually opposed rebates, and the fuse element may be connected between the remaining, rear- wardly projecting lugs of the terminals. These rearward- ly projecting lugs may be engaged in openings extending through the adjacent wall of the insulating housing so as to be accessible through the wall of the housing. Such a construction affords the terminals increased stability and permits testing of a circuit in which the fuse is connected without removal of the fuse. When the terminal member is formed from a folded, H-shaped blank so that the blade-like terminal portions have a double laminar construction, the fuse element may be held or clamped between the opposed laminar portions of each terminal, which are folded and flattened with the element disposed therebetween, whereafter the element may be soldered or welded in position. For this purpose, the sheet material from which the terminal blank is formed may be tinned or solder coated and the fusible element may have blobs of solder- attached thereto at appropriate positions. Soldering of the fusible element between the laminar portions is then accomplished -by the application of heat and pressure. Alternatively, when the fusible element is not provided with solder blobs, the terminal and fusible elemen assembly may be dip soldered to secure the wire in position. For higher current ratings, which would require a fuse wire of relatively large diameter, it may be desir- able to use a rolled, flattened fusible wire, thereby to reduce the bulk of the fuse wire disposed between the laminar portions of the terminals and permit the laminar portions to be satisfactorily flattened together into abutting relation. Alternatively, to permit the laminar portions to be completely flattened together with a fusible clement therebetween, one or both of the laminar portions may be formed with an inwardly facing transverse groove at the position where the fusible element is to be secured. By solder dipping, the groove may be filled with solder before positioning of the fusible element, which would not require solder blobs at its fixing positions. The application of heat and pressure closes the laminar portions together and secures the element in the groove(s). This method of securing the fusible element may also be used where the terminal member comprises a single lamina¬ tion and is formed as a simple stamping from sheet material. -h- In this case, transverse grooves are formed respectively in corresponding faces of the blade-like terminal por¬ tions, at the positions where the fusible element is to be fixed, and these grooves are filled with solder by dip soldering and the fusible element is secured in the groove by the application of heat and pressure. The insulating housing may have a slot-like cavity extending thereinto from one edge of the housing for receiving the rear ends of the blade terminals and the fusible element. The terminal and element assembly may be secured in the housing by means of dimples or detents form ed in the terminal portions which snap into engagement wit cooperating detents or dimples formed in the cavity walls when the assembly is inserted into the housing cavity. In one embodiment, the transverse grooves formed in the ter¬ minal portion for the purposes of locating and fixing the fusible element may form transverse ribs on the outsides of the terminals which serve as detents and snap into cooperating dimples in the cavity walls to secure the terminals in position. The present invention is particularly adapted to enable the manufacture of plug-in fuses by mass production techniques. Hence, from another aspect, the invention consists in a method of manufacturing a multiplicity of plug-in electrical fuses of the type referred to, com¬ prising the stops of forming a strip of terminal members from sheet metal material, each member comprising two spaced, substantially coplanar, blade-like terminal por¬ tions interconnected at or adjacent leading ends by an integral cross-bar portion, and each member being inte¬ grally connected with the or each adjacent terminal member in the strip by an interconnecting bar of the sheet mater¬ ial, securing a fusible element or elements to the terminal portions at or adjacent rear ends thereof to form a strip of terminal and element assemblies, mounting the assem¬ blies in insulating housings with the fusible elements disposed within the housings and the leading ends of the terminal portions projecting therefrom, and severing the interconnecting and cross-bar portions of sheet material from between adjacent assemblies and from between the terminal portions of each assembly so as to separate the strip into individual fuses. The strip of terminal members may be a simple stamp¬ ing from strip metal material or may be stamped as a strip of H-shaped terminal blanks, each of which is integral with the or each adjacent blank in the strip via an intercon¬ necting bar of the sheet material extending substantially parallel to the cross-bars of the H-shaped blanks. In the latter event, the strip of H-shaped blanks is folded about an axis substantially parallel to the cross-bars of the H-shapes so as to dispose upper and lower laminar por¬ tions of the uprights of each H-shape in mutually opposed relation for forming the two blade-like terminal portions of double laminar construction for each fuse. Conveniently, adjacent terminal blanks in the strip are spaced from one another, by the interconnecting bars, by the same distance as the spacing between the terminal portions of each blank, and these interconnecting bars are disposed coaxially wi h the cross-bar portions of the terminal blanks. The fusible clement may be formed from a- fuse wire which is of sufficient length to be secured to the terminal portions of all the blanks in the strip. If this fuse wire is welded or soldered with the aid of blobs of solder previously attached to the wire, in the manner described above, the solder blobs are attached to the wire at intervals corresponding to the spacing between adjacent terminal portions. From a further aspect, the present invention consists in a plug-in electrical fuse of the type referred to, com¬ prising an insulating housing, a pair of substantially co- planar, blade-like terminals projecting from the housing substantially parallel to one another, and a fusible element OMPI secured between the blade terminals within the housing. In one embodiment, each blade-like terminal comprises two laminar portions disposed in mutually opposed abutting relation and integrally joined at the projecting or lead- ing end of the terminal. In order that the present invention may be more readily understood, reference ^^ill now be made to the accompanying drawings, in which:- Fig. 1 is a side elevation of a plug-in electrical fuse constructed in accordance with the invention, Fig. 2 is a section on the line II-II of Fig. 1 , Fig. 3 is a plan view of a strip of terminal blanks used in the manufacture of plug-in fuses of the type illus¬ trated in Figs. 1 and 2, Figs, h , 5 and 6 illustrate steps in the method of manufacturing such fuses, Figs. 7, 8 and 9 illustrate the method of manufac¬ turing another embodiment of the invention, and Figs. 10 and 11 illustrate the method of manufactur- ing a urther embodiment. Referring to Figs. 1 and 2, the plug-in electrical fuse comprises a generally rectangular housing 1 made from insulating material, such as a plastics material, and having a slot-like cavity 2 extending into the housing from the bottom edge thereof. The housing has small shoulders 3 moulded at opposite ends thereof for facilitat¬ ing plugging-in and removal of the fuse. A pair of sub¬ stantially coplanar, blade-like terminals h are mounted within the slot-like cavity 2 of the housing in substan- tially parallel relation and have leading ends project¬ ing from the housing. The rear ends of the terminals are formed with mutually opposed rebates 6 and the remaining, rearwardly-pro ecting lugs 7 are engaged in openings 8 extending through the adjacent, top wall of the housing 1 so that electrical contact can be made witli the terminals, if desired, for example, for the purposes of circuit test- OMPI ing without necessitating removal of the fuse. Each terminal h is composed of two laminar portions 10a, 10b disposed in mutually opposed, abutting relation and inte¬ grally joined together at the leading end 5 of the terminal, about which these laminar portions are folded to produce the terminal, as will hereinafter be more fully described. During the manu acturing process, the laminar portions 10a,10b of each ' terminal are flattened together and a fusible wire 9 » which extends between the lugs 7 adjacent the rear wall of the . slot 3 is secured to each terminal by being clamped and soldered between the flattened laminar portions 10a, 10b. The terminals are retained in position in the housing by detents 11 on the outside surfaces of the laminar portions 10a,10b which snap into engagement with cooperating dimples 12 on the opposing inside sur¬ faces of the slot-like cavity 2. Fuses of the construction described with reference to Figs. 1 and 2 may be mass-produced as follows. Re¬ ferring to Fig. 3 , a continuous strip of terminal blanks 13 is stamped from sheet metal strip. Each blank 13 is of generally H—shape in plan and comprises upright laminar portions 1^, which have mutually opposed rebates 1 at opposite ends, and a central cross-bar 16. Adjacent blanks in the strip are joined together by interconnecting bars 17 of the strip material which arc coaxial with and iden¬ tical to the cross-bars 16. To facilitate folding of the strip about the central longitudinal axis Λ-Λ of the bars 16,1 » elongated openings 18 are formed centrally of the bars during the stamping process. Also, during the stamp- ing process, the small detents 11, such as tags, are formed in the upper and lower portions 10a,10b of the uprights 1^ so as to project from one side of the strip. Following stamping, the strip of terminal blanks 13 is folded longitudinally about the axis Λ-A so as to dis- pose the upper and lower laminar portions 10^,10} of the uprights Λ k in mutually opposed relation for forming the blade-like terminals h of the fuses. The detents 11 are disposed on the outsides of the folded strip. As shown in Fig. h , the strip is initially folded only to a partial¬ ly closed position, whereupon a continuous length of fusibl wire 19 having blobs 20 of solder attached thereto at intervals corresponding to the spacing between adjacent terminals is located between the partially folded laminar portions 10a,10b adjacent their ends remote from the fold, that is, between the projecting lug portions 21 formed by the rebates 15 and which constitute the lugs 7 in the fin¬ ished fuses. The opposing laminar portions 10a,10b are then flattened together into abutting relationship, as shown in Figs. 5 and 6, in order to produce terminal mem¬ bers having blade-like terminals and clamp and hold the fuse wire 19 > and the wire is soldered in position by the application of heat and pressure. The terminal blanks 13 are tinned or solder coated prior to the folding process in order to permit this soldering operation. Having severed the continuous fuse wire 19 at loca- tions between adjacent terminal members or pairs of termin¬ als so as to leave the pairs of terminals electrically connected by the fuse wire links 9 » the resulting strip of terminal and fuse wire assemblies are attached to insulat¬ ing housings 1. The latter are moulded in "chocolate block" form and are fitted to the terminal and fuse wire assemblies as a strip of housings interconnected by thin webs of the plastics insulating material. These webs space the housings at intervals corresponding to the spacing between the terminal and wire assemblies of the terminal strip. The rear ends (sec Figs. 1 and 2) of the pair of terminals h of each assembly are inserted into the slot- like cavity 2 of an associated housing and the lugs 7 engage in the openings 8 in the rear wall of the housing whilst the detents 11 on the outside faces of the terminals snap into engagement with the cooperating dimples 12 mould¬ ed on the inside surfaces of the slot-like cavity so as to O PI mount and retain the terminals, together with the associat¬ ed fuse wire link 9 » in the housing. After assembling the terminals to the housings, the interconnecting bars 17 of strip material (see Fig. 5) between adjacent assemblies, and the cross-bars 16 between the terminals of each assem¬ bly are cropped out in order to separate the terminal strip into individual fuses. However, the fuses may be retained connected together in strip form by the plastics webs interconnecting the housings and these may be broken to separate the fuses only when they are required for use. Figs. 7, 8 and 9 illustrate a modified method of fixing the fusible wire, whereby the wire fixing arrange¬ ment also serves as detents for securing the terminals within the insulating housing. Hence, the projecting lugs 21 at opposite ends of the uprights 1 are formed with transverse grooves 22 which, when the upper and lower lam¬ inar portions 10a,10b of the uprights are folded into opposing relation, are themselves disposed in opposing relation on the insides of the portions -and in alignment with the grooves in the associated laminar portions. Prior to folding, the grooves are filled with solder by a solder dipping process and, after the strip is folded to its partially closed position shown in J r ig. 7 > continuous fusible wire 23, without solder blobs, is located between the partially folded portions in register with the grooves, and then the laminar portions 10_a,10t> are flattened to¬ gether with the application of pressure and heat so that the wire is soldered in position within the grooves 22 and the laminar portions are fully flattened together (Figs. 8 and 9). The grooves 22 form ribs 2 on the outsides of the laminar portions and are so shaped that these ribs are generally barb-like in cross section, with the barbs facing towards the formed, leading ends 5 of the laminar portions. These barb-like ribs 2k serve as detents to secure the ter- minals within the slot-like cavity 2 in the housing 1 and, when a terminal assembly is inserted into the slot-like cavity in its associated housing, the ribs 2k snap into cooperating grooves 25.in the inside surfaces of the cavity when the assembly is fully inserted (Fig. 9) ^ Figs. 10 and 11 illustrate the manufacture of plug- in electrical fuses in which, the blade-like terminals consist of a single thickness 'of sheet metal. A continuou strip of terminal members 26 is blanked or stamped from sheet metal strip. Each member or blank 26 comprises two, spaced, blade-like terminal portions 27 interconnect- ed by an integral cross-bar portion 28 adjacent the lead¬ ing ends 29 of the terminals. Adjacent members in the strip are joined together by interconnecting bars 30 of the strip material which are coaxial with and identical to the cross-bar portions 28. At their rear ends, each pair of terminal portions 27 is formed with mutually opposed rebates 31 so as to leave rearwardly projecting lugs 2. During the stamping process, these lugs are formed in corresponding faces with aligned grooves 33 which define a projecting rib 3k on the opposite face of barb-like configuration. The lugs 32 are solder-dipped to fill the grooves 33 with solder and, thereafter, a continuoiis length of fusible wire 35 s located along the grooves and is soldered in position in the grooves by the application of pressure and heat. The wire 35 is then severed, the strip of terminal and fuse wire assemblies is mounted in a strip of insulating housings (not shown) similar to those of the previous embodiments and the intercoiuecting bars 30 of strip mo. erial between adjacent assemblies and the cross-bar portions 20 between the terminal portions 27 of each assembly are severed in order to separate the strip into individual fuses. The termin¬ als are retained in the insulating housings by the ribs 3^ which snap into engagement with cooperating grooves moulded on the inside surfaces of the slot-like cavities i the housings. Whilst particular embodiments have been described, O / , I it will be vmderstood that various modifications can be made without departing from the scope of the invention. For example, where a short fusible link is acceptable, rebates 6 need not be formed at the rear ends of the blade-like terminals in the region where the fusible wire is to be secured and the wire may simply be secured between the main bodies of tho tenninals.

Claims: CLΛIMS 1. A method of making a plug-in electrical fuse of the type in which a fusible element (9) is disposed within an insulating housing (1 ) and is connected between the adja¬ cent ends of two spaced substantially-coplanar blade-like terminals (k) secured within and projecting from the housing, characterized by the steps of forming a terminal member from sheet metal material, which member comprises two spaced substantially-coplanar blade-like terminal por¬ tions (4,27) interconnected at or adjacent leading ends (5*29) t>y an integral cross-bar portion (l6,28), securing a fusible element (9*19,23,35) "fco "tlle terminal portions at or adjacent rear ends thereof, mounting the resulting assembly in an insulating housing (1 ) with the fusible element disposed within the housing and the leading ends of the terminal portions projecting therefrom, and sever¬ ing the cross—bar (l6,28) from between the terminal portio 2. A method as claimed in claim 1 , characterized by the steps of stamping a generally H-shaped blank (13) from sheet metal material, folding the blank about an axis (A-A substantially parallel to the cross-bar (1 ) of the H- shape so as to dispose upper and lower portions (l0a,10b) of the uprights (l ) of the H-shape in mutually opposed relation to form two blade-like terminal portions ( k) of double laminar construction integrally joined at the lead- i ends (5) of the terminals. • 3. A method of manufacturing plug-in electrical fuses of the type in whic a fusible element (9) is disposed within an insulating housing (1 ) and is connected between the adjacent ends of two spaced substantially-coplanar blade-like terminals {k) secured within and projecting from the housing, characterized by the steps of forming a strip of terminal members from sheet metal material, each member comprising two spaced substantially-coplanar blade¬ like terminal portions (4,27) interconnected at or adja- Oϊ F cent leading ends (5*29) by an integral cross-bar por¬ tion (16,28), and each member being integrally connected with the or each adjacent terminal member in the strip by an interconnecting bar (17*30) of the sheet material, securing a fusible element or elements (9 » *23, 5) to the terminal portions at or adjacent rear ends thereof to form a strip of terminal and element assemblies, mounting the assemblies in insulating housings (1 ) with the fusible elements disposed within the housings and the leading ends of the terminal portions projecting therefrom, and sever¬ ing the interconnecting and cross-bar portions of sheet material from between adjacent assemblies and from between the terminal portions of each assembly so as to separate the strip into individual fuses. 4. A method as claimed in claim 3 > characterized by the steps of stamping a strip of H-shaped terminal blanks (13) from sheet metal material, each of said terminal blanks being integral with the or each adjacent blank in the strip via an interconnecting bar (17) of the sheet material extending substantially parallel to the cross-bars (16) of the H-shaped blanks, folding the strip of blanks about an axis (A-A) substantially parallel to the cross¬ bars of the H—shapes so as to dispose upper and lower laminar portions (l0a,10b) of the uprights (14) of each H-shape in mutually opposed relation for forming the two blade-like terminal portions ( k) of double laminar con¬ struction for each terminal member. 5. A method as claimed in claim 3 or k , characterized in that adjacent terminal blanks (13,26) in the strip are spaced from one another, by the interconnecting bars (17 > 3θ), by the same distance as the spacing between the ter¬ minal portions (4,27) of each blank, and said intercon¬ necting bars are disposed coaxially with the cross-bar portions (16,28) of the terminal blanks. 6. A method as claimed in any one of the preceding - OREAT OMPI claims, characterized in that the fusible element (9,1 , 23 > 35) comprises a fusible wire soldered or welded to the terminal portions (4,27) adjacent the rear ends thereof. . A method as claimed in any one of the preceding claims, characterized in that the terminal portions of the or each terminal member are formed, at their rear ends, with mutually opposed rebates (15,31) > and the fuse ele¬ ment is connected between the rearwardly projecting lugs - (7*32) defined by said rebates. " 8. A method as claimed in claim 7* characterized in that the rearwardly projecting lugs are engaged in openings (8) extending through the adjacent wall of the associated insulating housing (1 ) so as to be accessible through the wall of the housing. 9« A method as claimed in claim 2 or 4, characterized by locating the fuse element (9 * 19 * 23) between the opposed laminar portions (10a,10b) of the or each terminal member, which portions are folded and flattened with the element disposed therebetween. 0 * A method as claimed in claim 9* characterized in that the sheet material from which the or each terminal member is formed is tinned or solder coated and the fusible element (19) has blobs. (20) of solder attached thereto at positions corresponding to the terminal portions (4) , and the fuse element is soldered in position between the lamin¬ ar portions (l0a,10b) of the terminal member by applying heat and pressure thereto. 11. A method as claimed in claim 9* characterized in that the or each terminal and fusible element assembly is dip soldered to secure the wire in position. 12. A method as claimed in any one of the preceding claims, characterized by forming one or both of the laminar portions (l0a,10b,27) with an inwardly facing transverse groove (22,33) at the position where the fusible element to be secured. OM - IP 13» A method as claimed in any one of the preceding claims, characterized in ' that the or each insulating housing (l) has a slot-like cavity (2) extending there¬ into from one edge of the housing for receiving the rear ends of the associated terminals (4,27) and the fusible element (9*23,35)* and Further characterized in that the or each terminal and element assembly is secured in the associated housing by means of dimples or detents (11, 24,34) formed in the terminal portions which snap into engagement with cooperating detents or dimples (12,25) formed in the cavity walls when the assembly is inserted into the housing cavity. 14. A method as claimed in claims 12 and 13, character¬ ized in that the transverse grooves (22,33) formed in the terminal portions for the purposes of locating and fixing the fusible element produce transverse ribs (24,34) on the outsides of the terminals which serve as detents and snap into cooperating dimples in the cavity walls to secure the terminals in position. 15« plug-in electrical fuse in which a fusible element (9) is disposed within an insulating housing (1 ) and is connected between the adjacent ends of two blade—like terminals (4) secured within and projecting from the hous¬ ing, characterized in that the insulating housing has a slot-like cavity (2) extending thereinto from one edge of the housing and receives the rear ends of the blade ter¬ minals and the fuse element, and in that the terminals and element are retained in the housing by means of dimples or detents (11,24,34) formed in the terminals which snap into engagement with cooperating detents or dimples (12, 25) formed in the cavity walls. 16. A fuse as claimed in claim 15, characterized in that each blade-like terminal comprises two laminar portions (l0a,10b) disposed in mutually opposed abutting relation and integrally joined at the projecting or leading end (5) of the terminal.

Inventors: BESWICK D
Applicants: BESWICK D, BESWICK KENNETH E LTD, KENNETH E BESWICK LTD
Application year: 1980
Main classification: H01H69
IPC codes: H01H37, H01H69, H01H85