US3191275A - Method of making electrical contacts - Google Patents

Description

June 29, 1965 c. B. GwYN, JR 3,191,275

METHOD 0F MAKING ELECTRICAL CONTACTS P19/0R ART Filed Sept. 26. 1961 45 llll 4g IN V EN TOR. cf/M yffff @wy/v, m.

United States Patent O 3 191 275 Martien or MArnNi; nincrnrcar coNrAcrs Childress E. Gwyn, Jr., Export, Pa., assigner, by mesne assignments, to Talon, Inc., a corporation of Pennsyl- Vania Filed Sept. 26, 1961, Ser. No. 149,835 1 Claim. (Cl. Ztl-155.55)

This invention relates to electrical contacts and more particularly to a method of making contacts for projection welding in electrical assemblies.

In my prior patents, Nos. 2,049,771 and 2,199,240, there are shown methods of making electrical contacts having certain cost advantages wherein the method used is known as puddling In this method a base metal subhead, of disc shape, is used on which a segment of precious metal, for example, silver or the 4like is placed and subjected t-o heat. Thus, the precious metal melts and flows to form a contact facing for the subhead. The subhead may be of low carbon steel or the like, and can be produced by cold heading. Suitable fluxes or platings can, of course, be applied to the subhead so that upon melting of the silver segment the resulting molten silver coating adheres to the subhead. The method is fairly economical as compared with methods known in the art prior to my patents, which methods required fabrication of laminated strips and subsequent punching or coining with attendant waste due to scrap loss and/or costly reclamation of precious metal therefrom.

However, the puddling methods disclosed in my prior patents have certain drawbacks due to the fact that the melted silver hardens into a convex meniscus of semihemispherical shape, producing a product which is disproportionately high at the center of the contact face. Also, variations in coating height from contact to cont-act occur, due to variations in actual composition of the silver and variations in surface tension thereof when melted, as well as to variations in original dimensions of the silver segments. Thus, the height of the silver facing produced by the ordinary puddling process is many times greater at the center than at the outer edge of the subhead. Further, a thinning or ragged feathering of the facing occurs at such edge and sometimes the subhead surface adjacent the edge is not coated by the silver. Subsequent coining can not correct the condition insofar las the raggedness of or Scalloping of the coating at the periphery of the subhead is concerned.

It is, therefore, an object of the present invention to improve the puddling method and effect an electrical contact for projection welding which eliminates the above noted drawbacks and which produces a product that is completely uniform and electrically and mechanically sound.

Other objects and devices of the invention will be apparent from the appended drawing and from the description to follow:

Briefly my invention comprises the providing of a steel subhead disc-like, copper or otherwise plated, and having a raised concentric plateau on one side, or on both sides. A silver segment is placed on either plateau and heated to the melting point of the silver at which time it fuses as a coating on the face of the plateau and down the sides of the plateau and covers the surrounding marginal surface of the subhead to the edges thereof. Subsequent coining then flattens the silver coating at the center and across the edges of the subhead to produce a completely integrated contact element having uniformly coated edges. Thus, the coining process and the pressure applied flattens the plateau beneath the coating into intimate contact therewith, while at the same time a welding projection is formed.

Patented June 29, 1965 In the drawing:

FIGURES 1 through 5 show various steps in the prior art puddling process.

FIGURES 6 through 10 show the steps of the improved process; and

FIGURE l1 shows a modified type of subhead which may be used.

Referring now to the prior art process of FIGURES 1 through 5, FIGURES l and 2 show plan and side views, respectively, of a subhead disc 10 on which has been placed a precious metal cylindrical wire segment 13, such as silver or the like.

FIGURE 3 shows a cross-section of the composite article after the silver 13 has been melted to flow across the face of the disc 1d. It will be noted that there is a high spot in the center which is many times the thickness of the coating at the periphery or edges 14. At times the edge coating may be as low as .G03 inch to .O06 inch. Subsequent coining produces the effect shown in the cross-section of FIGURE 4, with the welding projection 16, wherein the center height of the silver coating 13 has been reduced to that which is desired, but wherein the coating thickness at the edges is not uniform nor even fully extending to the edges of the subhead in many instances. Thus, in the plan view of FIGURE 5, the ragged or scalloped and uneven effect is illustrated. This condition cannot be corrected by change of Shapes of coining tools, at least not to a satisfactory degree.

Referring now to FIGURES 6 through 10, the improved process and article is illustrated wherein it will be noted that a subhead disc 2) is provided with a concentric inner protuberance or plateau 23 leaving a marginal recessed area 26 from the base of the plateau to the edges 28 of the subhead. A silver segment 30 placed upon the plateau 23, when melted, will flow to assume the condition 3d as seen in FIGURE 8. It will be noted that the entire top surface of the subhead is covered and that the silver has ilowed down the sides of the plateau and across the marginal area 26 to the very edges of the subhead Z0. Thus, the slight rise in height afforded to the molten silver by the plateau effects a shaping of the molten mass to give a gravity or capillary assist which aids in dow down the sides of the plateau and out to the edges of the subhead, substantially filling the recess 26 between the plateau and the subhead edges. It will further be note-d that the thickness of the coating is considerably greater toward and at the subhead edges as compared with the prior art paddling process .at this step, for example, as seen by comparison with FIGURE 3.

The further step of coining achieves the effect of flattening the plateau beneath the coating and squaring olf the coating at the subhead edges, as illustrated in the crosssection of FIGURE 9 and the plan view of FIGURE 10. Thus, unevenness or scalloping, or lack of coating, are eliminated.

The modification shown in FIGURE l1 shows a subhead 49 having a plateau 43 on each side thereof. Such modification may be handled in mass production without regard to orientation for purposes of bringing a particular subhead face into upward position. In other words, the silver may be applied to either plateau in the manner illustrated and described hereinabove.

The welding projection (not shown) would be produced on the lower side of the subhead during coining.

Having thus described my invention, I am aware that various changes may be made without departing from the spirit thereof, and, therefore, do not seek to be limited to the precise illustration herein given, except as set forth in the appended claim.

I claim:

A method of making a contact element, which comprises providing a disc shaped subhead of base metal including, on at least one side thereof, a rst, substantially planar horizontal surface extending over the major portion thereof, a second, substantially planar horizontal surface disposed vertically below and annulsrly saisi. .first .Surface and extending ever a minor portion of said side, and a substantially vertial Wall member qtmrteting ,Said first and second surfaces; Y

@artistas a segment 0f Lpt teious metal Contact face material adjacent said first surface;

' heating the assembly t0. effect melting of the precious Vmetal segment and gravity ow of the molten metal acrossV said irst and second surfaces and sirnul-- taneously fusing the molten precious metal to form a contact -face of material Vthickness disposed 4in. juxtaposition of said subhead.

References Cited by the Examiner UNITED STATES PATENTS ll/39l 10/40l Imes et al. 200-166 Payette 29-:15555 Burns Y 29-l 55.55 ,Zollner 200-166 .Page ,--e-i--t--f 200-166 Holm et al. 200e-166 Jones et al. 20D-166 Tft-.V--i--r-'r l5 WHITMORE A. WrLTz, Primary Examiner,

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