US2625737A - Method of making electrical contacts - Google Patents

Description

Jan. 20, 1953 H. E. SPOONER 2,625,737

METHOD OF MAKING ELECTRICAL CONTACTS Filed Aug. 25, 1950 III" E INVENTOR. HOWARD E SPOONER 19 ATTORNEY Patented Jan. 20, 1953 METHOD OF MAKING ELECTRICAL CONTACTS Howard E. Spooner, Attleboro, Mass., assignor to D. E.- Makepeace Company, Attleboro, Mass., a corporation of Massachusetts Application August 25, 1950, Serial No. 181,449

- 3 Claims.

This invention relates to electrical contact elements suitable for use in the making and breaking of electric circuits and to methods for manufacturing such elements.

Heretofore electric make-and-break contacts for applications such as voltage regulators, relays and the like have been formed from base metal strips with precious metal inserts or inlays or rivets which serve as the contact points. The precious metals have excellent current carrying capacities due to their low electrical resistance and they are highly resistant to tarnish and electrical erosion whereby electrical contacts formed from these metals have low contact surface resistance even with small contact pressures and they are capable of maintaining a low electrical resistance in service for long periods of operation.

The present invention provides for improvements in the methods of making contacts, and an object of this invention is to produce improved electrical contacts and to save precious metals in the manufacture thereof. Further objects and various advantages of this invention will become apparent from the following description of preferred forms, reference being made to the accompanying drawings, in which, unless otherwise indicated, corresponding elements are similarly numbered throughout the Various figures. The essential characteristics are summarized in the claims.

In the drawing:

Fig. 1 is a face view of a base metal strip used in fabricating contacts embodying the invention;

Fig. 2 is a side elevation of an individual plug greatly enlarged;

Fig. 3 shows the operation of punching the plug from a laminated metal strip greatly enlarged;

Fig. 4 is a face view of the die shown in Fig. 3;

Fig. 5 is an enlarged section of a contact element drawn and cut from the strip of Fig. 1.

Referring to the drawing, there is shown in Fig. 1 a wide fiat strip I0 formed of any suitable electrically conductive base metal, e. g. copper, nickel, and so forth, or alloys thereof, such for example as brass, bronze, nickel-silver, etc. The strip I0 is run through a punch press which punches out a series of bores H, the location and number of the bores being dependent upon the shape and construction of the electrical contact element that is to be manufactured. The contact element which was chosen for illustration purposes has three precious metal contact points and accordingly there are three bores H punched in the strip Ill for each contact element to be manufactured.

A series of locating or centering holes I2 is also punched in the strip in in a line parallel to an edge of the metal strip, the centering holes being spaced apart by a distance equal to the length of strip needed to form one contact element.

In Fig. 2, there is shown a flat laminated metal plug IS, the shape and size of which is such that it will press fit into a bore H. The thickness of the plug i3 preferably approximates that of the metal strip H3. The plug I3 is punched out from a metal strip l4 (Fig. 3) having a film or layer a of solder on the bottom surface thereof. The strip It is preferably formed from a compound metal stock having a relatively thick base or foundation b of an inexpensive metal, such as, for example, that from which the metal strip H1 is formed, and a thin layer 0 of a precious metal such as gold, silver, platinum, palladium and alloys of these metals. The layer 0 may be electroplated on the surface of the foundation I), or the layers of metal may be integrally bonded together by direct weld with the application of heat and pressure, or by brazing or soldering, all as is well known to those skilled in the art. Obviously, of course, the strip 14 may consist entirely of precious metal with a film a of solder on one of its surfaces.

The plug l3, herein shown as a disc, is punched out from the metal strip 14 by passing the strip between a die It and punch H, with the solder face a of the strip towards the dieand its precious metal face towards the punch. The die I6 is provided with serrations l8 around the rim of the die hole l9 (see Fig. 4). These serrations cause the solder layer a to be drawn up around the sides of the disc [3 as the disc is being punched out from the strip l4, thereby forming the scalloped edge 23 of the solder layer as is shown in Fig. 2.

With the strip l0 prepared as illustrated in Fig. 1, the next step in the manufacture of the electric contacts of this invention comprises fixing the discs l3 into the bores II. This may be accomplished by supporting the die I6 upon a base 2| and passing the flat strip I0 between the base and the die so that the discs l3 when punched from the strip M will pass through the die hole 19 and become seated in the bores II in the strip 10. In order to maintain the strip in proper relative position so that the bores H are aligned with the die hole I9, the die I6 is provided in its bottom surface with a recess 2| The assembly of the strip l containing. the discs I 3 is: then heated as by passing'the stripi through a furnace at the liquidus temperature of the solder. will flow between the sides of the discs and the Walls of the base metal bore ll so that the discs I become firmly bonded into the strip.

The finished contacts 25- (Fig; 5) are-formed v from the assembled strip byJa series of-stamping, drawing and cutting operations, the particulan sequence of these operations being immaterial. for the purposes of this inventions'o longas'pro jections 26 which serve as the contact pointsrare drawn out with their precious metal layers on the outer surface of the projection.

It is thus apparent that .this invention provides a method for manufacturing an improved electricalcontact having longer wearing properties and greater corrosion resistance exactly where needed and permits of the. most.economi-- cal use-of costly noble or precious metals or alloys of these metals, since only the very point of contact is made from these metals.

It is understood that this invention is not limited to the-specific embodiments shown and 'described-and that various deviations may be made,

therefrom without departing fromthe spirit and scope of the appended claims.

What I claim is:

1. The method of making an electrical contact from a base metal strip including at. least one disc-like plug formed from a laminated stock having a precious metal top layer and a bottom layer of solder, said method comprising the steps ofinserting said plug with its bottom layer facing said strip into a hole in said strip while simultaneously causing solder to be drawn up around the sides of said disc, bonding said plug at its peripheral surfaces in said hole in the strip by heating said plug and strip assembly to a ternperature sufficient to cause said solder to bond the peripheral ides of said plug to the walls of said hole to form a completed base strip capable of being further worked, and thereafter forming a projectionin the bonded assembly including at least said plug with its precious metal layer being projected forward to serve as the contact point.

2. The method of making an electrical contact comprising sequentially punching at least onedisc from a laminated stock having a precious metal bonded to one side of a base metal foundation layer. and a film of solder on the other side thereof with the solder film facing downwardly,

Upon being heated, melted solder? said punching step being performed by means of a die having serrations around the rim of the die opening whereby the solder is caused to be drawn up around the sides of the disc, and inserting said disc into a perforation in a second .base metal strip, heating said disc while being carried. in said perforation. to the. liquidus temperature of said solder'so thatthe disc becomes joined to said strip at its peripheral edges, and thereafter forming a projection in said bonded assembly, the apex of said projection comprising said'disc with'said precious metal layer forming theouter surface of said projection whereby an electriccontact is. formed having the precious metal, contact material only at the point where needed.-

3. The method of making electrical contacts comprisingbondinga precious metal layer to one surface of a first strip of an electrically conductive base metal, depositing a layer of solder on the other surface of. said first strip whereby. a laminated metal strip is. formed, punching a series of holes in a second strip. of. electrically conductive base metal, positioning said firststrip above said. second strip with the solderlayer facing towards said second strip, sequentially punching a disc from said first laminated strip by means of a die having serrationsaround the rim of the die opening and inserting said disc into a hole in said second stripwhereby the solderis caused to be drawn up around the sides of said disc, heating said disc and second strip assembly to a temperature sufficient tocause said solder to bond the peripheral sides of said disc to the second base strip to form a completed base strip capable of being further worked, stamping a series of blank electrical contact forms from said completed base strip each of said forms including at least one of said discs, and thereafter forming projections to serve as contact points in said electrical contact forms including at least one disc with the precious metal layer of said disc on the outer surface thereof.

HOWARD E. SPOONER.

REFERENCES CITED The following references are of record in the fileof this patent:

UNITED STATES PATENTS

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