Method of making a push rod for a switch

Abstract: A push rod (5) for a push switch is formed integrally with a contact plate (10) by introducing a strip (35) of contact plate material between upper and lower mold parts (21,22) for forming the push rod, stamping out the contact plate by closing the mold, and then injecting resin into the mold to form the push rod integrally with the contact plate.

Description: The present invention relates to a method of making a push rod to be used in a push switch or the like. A push switch is known in which, by pressing the end of a push rod, a movable contact provided at the other end of the push rod is brought into contact with a fixed contact provided inside the switch body, to effect switching ON. A known way of making such a push rod is by cutting a strip of contact plate material to a suitable length and forming it into a contact part by a punching operation, then placing the so formed contact place in a forming mold, closing the mold, and then injecting a resin into the mold to form a push rod integral with the contact plate. This method requires an independent pressing process for cutting the material for the contact plate and punching out the contact part, involving extra labor and a press mold. According to the present invention there is provided a method of making a push rod for use in a switch, comprising a first step of introducing a strip of contact plate material into a forming mold, a second step of cutting the contact plate material to a desired length and shaping the contact plate simultaneously with closing of the forming mold, and a third step of forming a push rod integrally with the contact plate by injecting a resin into the forming mold. Thus, by closure of the forming mold for forming the push rod, the contact plate is cut to a desired length from strip material and is formed by the closing pressure. Accordingly, as compared with a conventional process, it is unnecessary to press form the contact plate by means of a press mold separately from the forming mold, and it thus becomes possible to reduce the number of manufacturing steps and the number of metal molds used. In a preferred form of the invention, in the said second step, a press pin is provided along the central axis of the push rod, the press pin being formed to cause an end face of the push rod, and a part of the contact plate with which it is in direct contact, to be formed in a concave or convex shape. Such an arrangement serves to strengthen the engagement between the push rod and the contact plate. An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings, in which:- Fig. 1 illustrates diagrammatically a method of making a push rod according to the present invention; Fig. 2 is a sectional view to illustrate a process of finishing the push rod after molding; Fig. 3 is a top view of what is shown in Fig. 2; and Fig. 4 is a sectional view of a push switch incorporating the push rod. First the structure of a push switch will be explained with reference to Fig. 4. This push switch comprises a substantially cylindrical cup-like resin case 1, a metal lid 2 covering the case opening and fixed around the rim of the case by caulking, a cylindrical mounting part 3, formed with a screw thread on its outer circumference, extending from the central part of the lid 2, and a push rod 5 having a guide part 4 which is received in freely slidable manner in the mounting part 3. The push rod 5 is a substantially bar-shaped resin member with a tip part 6 of larger diameter than the guide part 4 extending into the case 1. An internal axial passage 7 in the tip part 6 receives a return spring 9 which acts against a retainer 8 of resin seated at the bottom of the case 1. A contact plate 10 extends on opposite sides of the push rod tip part 6, in an approximately V-shaped configuration. The contact plate 10 is typically a strip of relatively soft metal such as phosphor bronze or brass. The opposite ends 10a of the contact plate are free and are bent inwards so as not to interfere with operation of the switch. In the vicinity of the ends 10a of the contact plate are contact parts 11 thereof, which project outwards. When the contact plate 10 is moved downward together with the push rod tip part 6, by pushing the push rod against the return spring 9, the contact parts 11 are brought into engagement with fixed contacts 13 which extend vertically downwards from an insulating part 12 located at the upper part of the inner wall surface of the case 1, so as to switch the switch ON. The ends of the fixed contacts 13 project from the bottom of the case 1 to form coupling terminals 14, extending into a coupling part 15 integral with the resin case 1. Guide members 16 extend from the tip part 6 of the push rod 5 in directions at right angles to the contact plate 10 (see Fig. 3). The guide members 16 are received in axial grooves 17 formed in the insulating part 12 and are movable in such grooves as the push rod moves. Referring now to Fig. 1, a forming mold 20 for forming the push rod comprises an upper mold 21 and a lower mold 22. The parting lines 23,27 for the upper and lower molds are arranged to receive the contact plate 10 therebetween before it is integrated with the tip part 6. The forming mold 20 has a cavity 24 for forming a part of the tip part 6 and the guide part 4. The upper mold 21 is formed with recesses 25 for forming contact parts 11, and is also formed with a cutting edge 26. The lower mold 22 has a cavity 28 for forming the foremost part of the tip part 6. At the central part of the lower mold a press pin 29 is formed, terminating at the same level as the parting line 27, the pin having a concave recess 30 at its tip. The lower mold also has convex parts 31 for forming the contact parts 11, and a cutting edge 32 for cooperating with the edge 26. A strip of raw material 35 for forming the contact plate 10 is supplied between the upper mold 21 and the lower mold 22, from a roll 36. Then, when the upper and lower molds are closed together, the material 35 is cut to form a contact plate 10 of the desired length. The process for forming the push rod 5 comprises a first step in which the strip of raw material 35 is supplied, a second step of forming the contact plate 10 from the raw material, a third step of injecting the forming resin to form the push rod in a predetermined shape, and a final finishing step. In the said second step, the upper mold 21 and the lower mold 22 are closed together so as to cut the strip of raw material 35 by means of the edge parts 26,32. At the same time the convex parts 31 and the concave parts 25 form the contact parts 11 by pressing out parts of the strip of raw material 35. At this time, the tip of the press pin 29 is in direct contact with the central part of the strip of raw material 35, to act as a presser for the raw material. In the third step, a suitable resin for forming is injected in the cavities 24 and 28 to form a push rod 5 integrated with the contact plate 10, which projects from the push rod in opposite directions approximately in the form of a cross. However, as the contact plate 10 is not yet bent to the desired V-shape, it is necessary to process it further in a finishing step, which is illustrated in Figs. 2 and 3. As shown in Fig. 2, a jig 40 for finishing the forming process is provided with a central slot 41 corresponding to the guide part 4 of the push rod 5, and a larger diameter recess 42 which is wider than the tip part 6. Fig. 3 is a top view of Fig. 2 showing the parts in the condition prior to pushing the tip part 6 into the recess 42, which is formed with wall parts 43 for shaping the contact plate 10 and guide grooves 44 for the guide members 16. Accordingly, when the guide part 4 is inserted in the slot 41 of the jig 40 and then the whole push rod 5 is pushed further.in, the tip part 6 is pushed into the recess 42 so that, as shown in imaginary lines, the contact plate 10 is bent into its desired shape. It will thus be understood that, by using the forming mold 20 to form a push rod, the contact plate 10 is also cut from the strip of raw material 35 and the contact parts 11 are also formed, in the same operation. Accordingly, as compared with known procedures, it is unnecessary to form the contact plate in a press mold separate from the push rod forming mold, and it thus becomes possible to reduce both the number of the manufacturing steps and the number of metal molds. Moreover, the concave recess 30 at the tip of the press pin 29 causes a central part of the contact plate 10 to be corresponding deformed by the molding pressure of the resin, thereby strengthening the engagement between the tip part 6 and the contact plate 10. The concave recess 30 may instead be a convex part. In addition, because the finishing of the contact plate 10 is carried out using the jig 40, it becomes possible to achieve automatic assembly, and it is easy to control the contact pressure. The structure of the push switch may be of various kinds other than that illustrated, without leaving the scope of the appended claims.

Claims: A method of making a push rod (4) for use in a switch, comprising a first step of introducing a strip of contact plate material (35) into a forming mold (20), a second step of cutting the contact plate material to a desired length and shaping the contact plate (10) simultaneously with closing of the forming mold, and a third step of forming a push rod integrally with the contact plate by injecting a resin into the forming mold. A method according to claim 1, wherein, in the said second step, a press pin (29) is provided along the central axis of the push rod (4), the press pin being formed (30), to cause an end face of the push rod, and a part of the contact plate (10) with which it is in direct contact, to be formed in a concave or convex shape.

Inventors: IWATA KEIJI, IWATA, KEIJI, Iwata, Keiji, c/o Toyodenso Kabushiki Kaisha
Applicants: TOYO DENSO KK, TOYODENSO KABUSHIKI KAISHA
Application year: 1998
Main classification: H01H11
IPC codes: H01H11, B29L31, B29C39, H01H13