US3015876A - Method of making resilient switch contacts - Google Patents

Description

Jan. 9, 1962 P. HUTT METHOD oF MAKING RESTLTENT swTTcH coNTAcTs Filed June 18, 1957 s ,IHM/m W. Cw M 2.5 wf/ MW a@ Ff ,WM .l /z f. u .M MH we United States Patent Oiitice 3,015,876 Patented Jan. 9, 1962 3,015,876 METHOD F MAKING RESILIENT SWITCH CONTACTS Philip Hutt, Milford, Conn., assignor to General Electric Company, a corporation of New York Filed .lune 18, 1957, Ser. No. 666,446 2 Claims. (Cl. 29-155.55)

The present invention relates to a method of producing spring contacts of thin strip material for use in electric switches of the type found in household appliances such as electric ranges.

In the past it has been common practice to provide the contacts for such switches with separate screw terminal means that are joined with the spring contacts by a welding, riveting, or staking operation. When screw terminals are used, it is necessary to strip the end of the insulation off of the wires that are to be connected to the switch, and wrap the bare conductor around the screw terminal so that the screw may be tightened to grip the wire. Some switches have as many as ten terminals so that a great deal of time and labor is then necessary in installing the switch in a particular appliance or circuit in which it is to be used. One solution has i been to substitute tab type terminals for screw terminals.

A tab type terminal has the shape of a thin blade for receiving a spring clip that is fastened to the end of a lead wire. The connection is made by merely pushing the clip over the tab type terminal.

For several years now, tab type terminals have been used in increasing numbers. Such terminals have been made separate from the spring contacts but joined to the contacts in the switch housing by suitable fastening means. This followed the custom used with relation to screw terminals. The industry standard for the thickness of tab type terminals is .031 inch, which is greater thanthe thickness of the material normally used for the spring contacts.

The principal object of this invention is to provide a method of producing spring contacts with integral terminals.

A further object of this invention is to provide a method of producing spring contacts of the class described where the contacts will have an intermediate portion o-f reduced thickness to enhance the exibility of the contacts.

A still further object of this invention is to provide a novel automatic method, using a progressive die, of making spring contacts having integral terminals by starting with thin strip material of uniform thickness and cutting away a longitudinally extending groove in the material, so that each spring contact that is stamped from the material will have an intermediate portion of reduced thickness to increase the springing action of the contact.

The present invention is practiced by starting with a supply of thin strip material such and performing a milling or cutting away operation on the material lengthwise thereof. This provides a region of reduced thickness uniformly along the length of the strip and parallel to the grain of the material. Such material is fed through a progressive die of a standard" punchv press which blanks out the spring contacts from the strip material in a direction across the grain. In a typical contact designthe terminal end or fixed end of the contact is folded at substantially a right angle so that the terminal end will extend out through the back of the switch housing. The intermediate portion of the Contact will have a reduced thickness which will enhance the flexibility of the cantilever spring action of the contact. This reduced thickness is necessary because of the relatively heavy gauge of the strip material from which the contact has been blanked. While-the preferred embodias phosphor bro-nze ment of this invention is illustrated and described with relation to spring contacts having tab type terminals, it should be appreciated that the invention is not limited to such terminals. It could be practiced with integral screw terminals also.

My invention will be better understood from the following description taken in connection with the accompanying drawing and its scope will be pointed out in the appended claims.

FIGURE l is atop plan view of a typical switch using the novel spring contacts of my invention, the cover plate of the switch housing and the cam being removed in order to illustrate the switch interior.

FIGURE 2 is a cross-sectional side View taken on the line 2-2 of FIGURE l showing the cam and cover plate.

FIGURE 3 is a perspective View of one of the four spring contacts shown in the switch housing of FIG- URE 1.

FIGURE 4 is a plan view of the thin strip material from which the contacts are blanked showing a longitudinal groove in the material, and the different operations which are performed on the material as it passes through a progressive die.

FIGURE 5 is a transverse cross-sectional view taken of the strip material of FIGURE 4.

Referring in detail to the drawing, and in particular to FIGURES l and 2, there is shown the main details of a rotary range switch lil. Such a switch is similar in operation to the switch shown in the Kimball Patent No. 2,203,224, which is assigned to the same assignee as is the present invention. The switch housingcomprises a recessed base 11 of suitable molded insulating material, and a metal cover plate 12. that closes the open face of the base. The bottom wall 13 of the base has a central cup formation 14 on its inner surface that serves asa bearing for the inner end of a shaft 15 that is manually actuated to change the positions of the switch. The outer end of the shaft 15 extends through an opening 16 in the cover plate 12 so that a switch handle or knob (not shown) may be fastened to the shaft.

A relatively large disc-shaped cam 17 is assembled onto the shaft 15 and turns therewith for controlling the movement of the spring contacts. Looking at FIG- URE 2, it should be understood that the right side or bottom side of the cam 17 includes four circular tracks (not shown), one for each spring contact. The four spring contacts are best seen in FIGURE l and identified as elements 20, 21, 22 and 23. The switch contacts 2li and 21 are arranged on one side of the shaft 15, and the remaining two contacts 22 and 23 are disposed on the opposite side. Actually, contacts 20 and 22 are identical in form, while contacts 21 and 23 are identical in order to reduce the tooling cost to a minimum.

The four spring contacts Ztl-23 are all fixed in the switch housing 11 at one side of the base, shown at the bottom of FIGURE l, as will be better understood hereinafter. This mounting arrangement provides each spring contact with la cantilever action,rwhile the for-ce or load applied to the cantilever is determined by the cam 17 engaging a cam follower 25 on Veach contact adjacent the center thereof. The fixed contacts are arranged a-t the side of the base opposite the fixed ends of the spring contacts as seen in FIGURE 1. There are three xed contacts in all, namely, contacts 26, 27 and 2S. Contacts Hence, the outermost spring contacts 20 and 23 are merely single throw contacts, while the innermost contacts 21 and 22 are double throw contacts. These xed contacts are made of heavy gauge brass or other suitable 3 electrical conducting material and they have integral tab type terminals 29 as seen in FIGURE 2.

Consideration will now be given Ito FGURE 3 which best illustrates the present invention. Spring contact Z3 is shown in perspective as comprising a spring blade 30, a fixed intermediate portion 31 and an integral tab type terminal 32. The free end, or end 33, opposite the xed portion .3l of the contact carries a silver rivet 34 which 1s adapted to make engagement with silver slugs 35 on the fixed contacts. Thus, the engagement between the movable and fixed contacts is silver to silver and the contacting surfaces will not become overheated because of oxide formation as would be the case with most nonprecious metals. The cam follower 25, mentioned previously, is merely a tab that extends from one side edge of the blade 3i) and is upwardly directed to engage with one of lthe cam tracks (not shown) of the cam 17. The end of the spring blade 36 that is remote from the silver rivet 34 is bent downwardly at a right angle as at 36, 'and the tab terminal 32 is an extension of one side edge "of the portion 36. Actually, the terminal 32 is connected to the portion 36 by a right angle bend 37 so tha-t the terminal 32. isv perpendicular to the plane of lthe spring blade 3ft, while being generally parallel with one side edge of the blade. The spring contacts are assembled in the base 1l by inserting the terminals through a suitable slot as at 3S in FlGURE 2, and the iixed portion 31 is staked therein by forming over the edges as at 39.

The tab lterminals 32 of the spring contacts are of relatively heavy material (.031 inch) as required by the industry standards. It will be understood that since the terminal is an integral part of the spring contact, the thickness throughout the contact would normally be the same. In the mass production of such switches, it is difficult to control dimensions within very close tolerances so that it is necessary to provide the spring blades with a large travel and overtravel. The travel of the blades is in spring parlance the deflection of the cantilever spring dueto the load being applied at a point between the 'fixed and free ends of the blade. If it were not necessary to limit the size and, hence, the length of the spring blade 30, the heavy thickness of the blade would not present a problem. The greater the length of the spring blades, the less will be the resultant stresses so that they may be held to an allowable limit within the capability of the spring material. In achieving greater flexibility of the spring blade, it has been found desirable to maintain the full cross-section of the blade at the fixed end where the stress-producing moment of the applied force is at a maximum. However greater flexibility can be obtained by reducing the cross-section at a point removed from the xed end of the contact blade. One precaution, however, must be taken to avoid reducing the cross-section to a point where it is not capable of carrying the required current without overheating.

The formula for deiiection of a cantilever spring of uniform rectangular cross-section is as follows:

F=deection P=applied load L=distance between fixed end and point of load application E=modulus of elasticity b=width h=thickness of the spring material The greatest increase in ilexibility with the least impairment of current carrying capacity is obtained by reducing the thickness of the material h, since it appears to the 3rd power in the formula above.

Having discovered the need for reducing the crosssection of the spring blade and of determining the best method by reducing the thickness of the blade as at 40 in FIGURE 3, mention will be made of the actual steps taken to manufacture the present invention. Attention is directed to FIGURE 4 of the drawing showing a section of thin strip material 45 of phosphor bronze with an approximate thickness of .i031 inch. The grain of this material runs longitudinally of the strip and the spring contacts are punched out of the strip in a transverse manner at approximately a 60 angle across the grain of the material. The reduced cross-section 40 of the spring blade is provided by cutting-away or milling a shallow groove 47 running with the grain of the material and adjacent the center thereof.

The strip material 45 is first processed by a preliminary milling operation which produces the longitudinal groove 47. This material is supplied to the punch press in this condition and the material is fed through a progressive die (not shown) which performs all of the necessary operations to complete the formation of the contact subassembly. First, all of the necessary holes 46 are punched into the material; then the silver rivet 34 is attached; next the contact is trimmed by cutting away most of the scrap around each cont-act but leaving a small portion 48 which joins the two adjacent contacts together. The next operation is -to fold the terminal 32 into the right angle bend 37. Then, the cam follower 25 is folded up and the terminal is folded again to establish the portion 36. Finally, the contact is freed by severing it from the small strip a8 connecting it with an adjacent contact. Thus, such a progressive die will perform the different operations of punching, blanking, forming, and cutting as will be well understood by those skilled in this art. Of primary importance is the fact that the reduced section 40 of each spring blade will be provided by a cutting operation rather than a planish operation which might work harden the material and create uncontrollable distortion in the material due to the tendency of the planished material to be displaced in all directions.

Having described above my invention of a novel method of producing spring contacts with integral tab type terminals, it will be readily apparent that I have produced the necessary flexibility in the spring blade by a preliminary cutting away or milling operation which permits the contacts to be made on an automatic punch press of standard construction. The novelty is not alone in the method but also in the finished product of a spring contact which represents an important part of a low cost, compact switch design.

Modifications of this invention will occur to those skilled in this art, and it is to be understood, therefore, that this invention is not limited to the particular embodiments disclosed, but that it is intended -to cover all modifications which are within the true spirit land scope of this invention.

What I claim as new and desire .to vsecure by Letters Patent of the United States is:

l. A method of producing resilient switch contacts with integral terminals comprising the steps of providing a thin strip of metal stock of uniform cross-section, eutting out a longitudinally extending groove adjacent the center of said strip to form a central section of reduced thickness, stamping the contacts with the integral terminals out of this metal strip with each of the contacts extending in a direction transverse to the longitudinal axis of the strip, and forming the stamped part into a finished switch subassembly with the central section of reduced thickness serving to increase the exibility of the contacts.

2. A method of producing switch contacts with a resilient blade and an integral tab type terminal comprising the steps `of providing a thin strip of metal stock, milling a longitudinally extending groove to form a central section of reduced thickness, stamping the contacts with the integral terminals out of this metal strip with the contacts extending transversely across the longitudinal axis of the strip, and forming the stamped part into a finished switch subassembly with the central vsection of reduced thickness serving to increase .the resilience of the contact blade.

References Cited in the le of this patent UNITED STATES PATENTS 128,184 Smith June 18, 1872 371,755 Hard Oct. 18, 1887 1,476,593 Coffey Oct. 30, 1920 1,697,872 Johnson Jan. 8, 1929 1,954,758 Reimer Apr. 10, 1934 10 2,096,054 Miller Oct. 19, 1937 2,513,147 Chorpening June 27, 1950 6 Deakin Apr. 8, 1952 Page May 20, 1952 Cochran July 29, 1952 Arms Ian. 18, 1955 Andrews June 7, 1955 Jonsson Feb. 14, 1956 Elliot May 22, 1956 FOREIGN PATENTS Germany June 13, 1918 Great Britain Nov. 17, 1954 Great Britain Dec. 21, 1955

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