GB2072057A - Method for manufacture of electric contact - Google Patents

Abstract

Electric contacts of a circular cross section are produced by feeding a strip sheet 2 of base plate material and an angular bar 1 of silver or the like destined to form contacts horizontally into a press device. The angular bar 1 has V notches formed in the opposite edges thereof in such a manner that cuts made across the angular bar along the planes including the bottoms of the opposed V notches produce a multiplicity of polygonal prisms or approximate cylinders. Within the press, holes 4 of a shape conforming to the cross section of the polygonal prisms or approximate cylinders are formed in the strip sheet 2, and the polygonal prisms or approximate cylinders cut from the angular bar are inserted one by one into the holes 4. The portions of the cut piece protruding from the opposite surfaces of the strip sheet are then molded with press dies to acquire a circular shape. <IMAGE>

Description

SPECIFICATION Method for manufacture of electric contact This invention relates to a method for producing an electric contact for use in a switch.

The typical methods heretofore adopted for the manufacture of electric contacts are the riveting method and the welding method. The former method comprises the steps of producing headed rivets of a prescribed shape from a contact metal such as silver and fastening the rivets, as contacts, in holes bored in base plates. The latter method comprises the steps of producing contact pieces each consisting of a head portion and a projection extended downwardly from the lower side of the head in much the same way as the shank of a rivet and resistance welding the projections of the contact pieces onto the surface of base plates having no holes.

These two methods are common in the procedure of preparatorily producing contact heads and fastening them to respective base plates. The inventor formerly developed a method for mass producing angular contacts by causing a strip sheet as the source of base plates and an angular bar of silver or the like as the source of contacts to be horizontally fed into a press, making angular holes serially in the strip sheet and cutting the aforementioned angular bar into pieces of a shape conforming to the shape of the angular holes, and fastening the cut pieces of silverto the angular holes by virtue of pressure (U.S.

Patent Application Serial No. 39,599).

The inventor's method for producing contacts by use of a press described above is free from the troublesome work of preparatorily producing contact heads, picking them up one by one and setting them in position on corresponding base plates as inevitably involved in the aforementioned riveting method and the welding method. The method is very efficient because contact pieces cut in a prescribed shape from an angular bar of silver or the like are inserted into holes formed in the corresponding base plates and fastened thereto with pressure as soon as they are cut from the angular bar.

This method suffers from the sole fault that it is applicable only to production of contacts of an angular cross section and not capable of producing contacts of a circular cross section.

One object of this invention is to provide a method for most efficiently producing electric contacts of a circular cross section by virtue of pressure without entailing even the least waste of the contact material.

Another object of this invention is to provide a method for the production of electric contacts of a circular cross section, which method comprises causing a strip sheet as the source of base plates for contacts and an angular bar of silver orthe like as the source of contacts to be simultaneously fed into one press device, allowing the perforating, cutting, pressing and separating works to be continuously performed on the incoming materials and enabling finished electric contacts of a circular cross section to be discharged from the press device.

Yet another object of this invention is to provide a method for producing compressed electric contacts of a circular cross section from a clad material having a contact material such as of silver as the cladding material.

Still another object of this invention is to provide a method which effects the production of electric contacts of a circular cross section solely by pressing and cutting work, so that the equipment and techno ques involved therein prove to be inexpensive and easy of operation.

A further object of this invention is to provide a method for producing electric contacts of a circular cross section having the contact pieces and the corresponding base plates joined with great compressive strength thereby enjoying extremly high electrical and thermal conductivity therebetween by subject the materials to high compressive force and great plastic molding force.

To accomplish the objects described above according to the present invention, there is provided a method which comprises the step of forming V notches symmetrically on the opposite edges of an angular bar of contact material at fixed intervals either during or after the production of the angular bar so that when the angular bar is consecutively cut along the lines connecting the bottoms of the opposed grooves, there are obtained separate pieces of the shape of an octagonal prism or an approximate cylinder; the step of feeding a strip sheet of material as the source of contact base plates into a press device and consecutively making holes conforming to the cross section of the aforementioned octagonal prisms or approximate cylinders in the strip sheet at the positions destined to seat the contacts; the step of feeding the angular bar of material for contacts containing the aforementioned notches in the direction of its leading end into the aforementioned press device thereby allowing the leading end of the bar to be superposed on the hole perforated in the aforementioned strip, cutting the leading end off the bar along the line connecting the bottoms of the opposed V notches and, at the same time, fitting the cut piece of the bar into the aforementioned perforated hole and fastening the cut piece to the perforated hole by temporary compression; the step of compressing the temporarily fastened cut piece in the opposed vertical directions thereby forming an upper and a lower swelled portion of the cut piece and causing the cut piece to be tightly joined to the strip sheet, and shaping one or both of the horizontally swelled ends of the cut piece by a press to the prescribed shape of a circular contact; and the step of punching the strip sheet into pieces each of the desired shape of a contact base plate thereby producing finished electric contacts.

The other and further objects and characteristics of this invention will become apparent from the further disclosure of the invention to be given hereinbelow with reference to the accompanying drawing.

Figure lisa plan view of an angular bar of a clad contact material having V notches formed therein according to the present invention.

Figure 2 is a side view of the contact material of Figure 1.

Figure 3 is a plan view of a strip sheet of material as the source of base plates and an angular bar of contact material which are intermittently advanced on a press device (not shown) to positions fixed for various steps of the method of this invention, with a separated finished contact shown in an enlarged scale on the righthand side.

Figure 4 is a perspective view illustrating the positional relationship between the angular bar of contact material and the perforated hole in the strip sheet of base plate material.

Figure 5 is a sectioned view of a typical mechanism for cutting the angular bar of contact material into individual contact pieces and, at the same time, fitting the cut contact pieces one by one to the matching holes perforated in the strip sheet.

Figure 6 is a sectioned view illustrating a hole formed in the strip sheet of base plate material.

Figure 7 is a sectioned view illustrating a chamfer formed along the lower edge of the hole.

Figure 8 is a sectioned view illustrating a cut piece of contact material fitted into the aforementioned hole and an upper and a lower press die ready for pressing the cut piece to fit tightly within the hole.

Figure 9 is a sectioned view illustrating the stage at which the cut piece is compressed and fitted tightly within the hole by the aforementioned press dies and, at the same time, its upper protruding end is molded to the shape of a circular contact.

Figure 10 is a sectioned view illustrating the upper surface of the contact of Figure 9 to be raised so as to acquire a sufficient height from the upper surface of the base plate.

Figures 11 and 12 are sectioned views of two typical contact portions finished by the method of this invention.

Figure 13 is a sectioned view of another typical angular bar of contact material symmetrically containing spaced grooves.

As already mentioned, the inventor formerly developed a method for producing angular contacts by causing a strip sheet of base plate material and an angular bar of contact material to be simultaneously fed into a press device and allowing cut pieces of the angular barto be compressed into the matching angular holes preformed in the strip sheet. This method not only gives high operational efficiency but also enjoys a salient feature that the expensive contact material is utilized with absolutely no waste.

Although this method is intended primarily for production of angular contacts, its application to the manufacture of contacts of a circular cross section can be attained, in accordance with common know ledge in the art, by making circular holes in the strip sheet of base plate material, punching cylinders of cross section conforming to the cross section of the perforated holes from the angular bar of contact material and fastening the cylinders into the holes with compressive force. This procedure, however, would entail a technical difficulty of punching cylin ders out of the angular bar and also encounter an economic problem in that the punching of cylinders would result in a great waste of the expensive con material.

The inventor, therefore, has not adopted the easily conceivable measure of fastening cylinders of contact material into matched circular holes of the base plates in the production of contacts of a circular cross section. The inventor has instead conceived the idea that since the upper and lower protruding portions of the contact pieces are converted into horizontally swelled circular portions when the contact pieces are fastened by compressive force into the holes in the base plates, it follows that so far as the compressive force so applied is great enough, the protruding portions are not required to be circularto produce contacts of a circular cross section.

Through experiments, the inventor has ascertained that this idea is fully practicable.

When an angular bar of contact material having plane surfaces is cut at intervals in perpendicularly intersecting lines, there are obtained only rectangular parallelapipeds. When V notches are formed at fixed intervals on the opposte edges of the angular bar as illustrated in Figure 1, the individual pieces which are cut off the bar in the lines connecting the bottoms of the opposed V notches assume the shape of octagonal prisms. The upper end of such an octagonal prism can be converted into a contact of circular cross section when the press die used to compress the prism is formed in a circular shape in advance.

The inventor has perfected this invention on the basis of this novel concept.

Now, the present invention will be described with reference to the accompanying drawing. The press device is universally known in the art and, therefore, is omitted from the drawing. It is of a type well known in the art and referred to popularly as a "continuous press". As is well implied by this name, the press possesses a plurality of positions for performing various types of work in a stated order, so that when the strip sheet of base plate material is intermittently advanced into the press, the press performs the work of punching holes, chamfering the edges of the punched holes, cutting individual contact pieces from the angular bar of contact material, compressing the contact pieces into the holes and cutting off the individual base plates, now containing the contact pieces, from the strip sheet.Figure 3 is a plan view of a strip sheet 2 of base plate material as mounted on a press device. The holes 4 represent the positions where the press performs the various operations. The position at which the leading piece 10 cut from the angular bar 1 of contact material is inserted into one of the holes 4 represents the position where the press cuts a contact piece from the angular bar (corresponding to Figure 5). Adjacent thereto is the position where the press is operated to perform the work of compressing the contact pieces and, therefore, is provided with upper and lower press dies 12, 13. Further two the right is the position where the press punches the base plates 2 to a prescribed shape. Still further to the right is the position where the press inserts cuts in the intervening portions of the base plates each containing a contact piece and gives rise to finished contacts as separate products. Those skilled in the art will require no illustration of the press to appreciate the sequence of operations to be performed by the press.

In the first step of the method of this invention, V notches 3 are symmetrically formed at fixed inter vals in the opposte edges of an angular bar 1 of contact material either during or after the production of the angular bar. The shape of these V notches 3 and the intervals separating the notches are selected so that when the angular bar 1 is consecutively cut along the lines connecting the bottoms of the opposed V notches 3, separate pieces 10 of the shape of polygonal prisms (octagonal prisms in the illustrated embodiment) are obtained one by one.

The angular bar 1 illustrated in Figures 1 and 2 is a clad material formed by covering a substrate of copper or copper alloy throughout the entire length thereof with a sheet of silver 1 a as the contact material, with a view to minimizing the consumption of silver.

Denoted by 1' and indicated by chain lines in Figure 1 is the angular bar in its state prior to formation of V notches 3. The formation of V notches in the angular bar is accomplished by a rolling operation during the manufacture of the angular bar or by a pressing operation after the manufacture. No cutting operation is performed on the angular bar.

When the angular bar 1 containing the V notches as described above is readied, a strip sheet 2 of contact base material is intermittently fed into the press device so that holes 4 of a shape conforming to the cross section of the aforementioned polygonal prisms or approximate cylinders are punched in the strip sheet 2 at positions destined to seat contact pieces.

In this illustrated embodiment, after the holes 4 have been formed as illustrated in Figure 6, the press produces a chamfered portion 6 at the lower edge of each hole as illustrated in Figure 7. The holes 5 illustrated in Figure 3 are used for determining the position of the press relative to the strip sheet. Eventually, these holes 5 will serve to facilitate attachment of the individual contacts at the time of actual use of the contacts.

The next step for insertion of contact pieces into the holes 4 involves feeding the angular bar 1 of contact material now containing the aforementioned V notches in the direction of its leading end into the aforementioned press thereby superposing the first polygonal prism in the angular bar on the perforated hole 4 of the strip sheet 2, then cutting the first polygonal prism offthe angular bar along the line connecting the bottoms of the first pair of opposed V notches and, at the same time, fitting the separated piece (polygonal prism) 10 in the perforated hole 4 and fjxing the separated piece in the hole by temporary compression.

Figure 4 represents an embodiment involving use of a two-face clad material instead of the one-face clad material of Figures 1 and 2. The diagram is intended to show more clearly the condition in which the leading end of the angular bar 1 is superposed on the perforated hole 4 as illustrated in Figure 3. Figure 5 illustrates one typical mechanism for fitting the separated piece into the hole 4 and fix the piece in the hole by temporary compression at the same time that the cutting of the piece from the bar is effected. This mechanism comprises a stopper 7 adapted to stop the leading polygonal prism in the angular bar directly above the hole 4 and an upper blade 8 and a lower blade 9 both serving to cut the first piece from the angular bar.The lower surfaces of the stopper 7 and the stationary lower blade 9 are separated from the upper surface of the lower die 11 by a space wide enough to permit passage of the base plate material 2. The lower die is provided with a recess 11 a directly below the position at which the hole 4 is stopped, so that the separated piece 10 is allowed to pass to the lower surface of the base plate material 2.

Figure 5 illustrates the condition in which the upper blade 8 has come down and collided with the leading piece in the angular bar 1 and is now ready to cut the leading piece in the plane S passing through the bottoms of the opposed V notches 3 to produce a cut piece 10 and insert the cut piece 10 into the hole 4. The upper blade 8, by virtue of its lower end, causes the cut piece 10 to be inserted into the hole 4 as illustrated in Figure 8 and, at the same time, applies temporary compression or slight pressure to the cut piece 10 and consequently causes the barrel portion of the cut piece 10 to swell out and come into tight pressed contact with the inner wall of the hole 4.

When the upper blade 8 is lifted from such position, the strip sheet 2 of base plate material is advanced by one position to the right and the cut piece 10 which has been temporarily fastened in position is moved to and stopped at the next position, namely in the space between the upper and lower press dies 12, 13 illustrated in Figure 8.

At this position, the press compresses the cut piece 10 in the opposed vertical directions to form horizontally swelled portions 1 0b, 1 0c at the upper and lower ends thereof and join the cut piece fast to the base plate material 2 and, at the same time, causes one or both of the horizontally swelled portions 10b, 10coo be molded in a circular or similar shape by a press die. In the illustrated embodiment, the upper end containing the cladding material 10a is molded to form a circular contact. This molding of the upper end of the cut piece 10 of the shape of an octagonal prism into a contact of circular cross section is accomplished with ease.All that is required for this purpose is to have formed in the lower surface of the upper die 12 a recess 12a conforming to the outer shape of the circular contact of a given size.

The upper end of the octagonal prism of the cut piece 10 converts itself into a contact of the same shape as the recess 1 2a when the upper end is crushed against the bottom of the recess, then swelled horizontally toward the peripheral wall of the recess 12a until the swelled portion fills up the entire inner volume of the recess.

In the embodiment of Figure 9, since the lower die 13 has a flat top, the horizontally swelled portion 1 0c ceases swelling after it has filled up the chamfered portion 6. Optionally, a two-face contact of the construction illustrated in Figure 11 may be obtained by using an angular bar 1 containing cladding materials 10a on the upper and lower ends as illustrated in Figure 4 and also using upper and lower press dies each containing a recess of a shape conforming to the cross section of the contact.

The embodiment of Figure 3 involves an operation comprising the steps of fastening the cut piece 10 fast in the perforated hole as illustrated in Figure 9, then raising the upper surface of the contact piece as illustrated in Figure 10 by pushing up the contact piece in the next position by a well-known device such as a punch or die, further cutting the strip sheet 2 of base plate material into individual contact base plates of a prescribed shape, and discharging the separated base plates each containing a contact piece as finished products into the product receptacle. All these steps are well known to the art and, therefore, are not specifically described.

Figure 12 illustrates an embodiment wherein the contacts are given a convex surface. This modification is accomplished simply by giving a corresponding concave surface to the recess 1 2a formed in the upper press die 12 of Figure 8 and forming the upper and lower swelled portions lOb, 1 Oc in correspondingly required shapes. Modifications of this sort can be made freely in this invention. When the cladding material 1 Oa is harder than the copper alloy used as the substrate and swells less in the horizontal direction than the substrate, it can be retained over the swelled portions of the substrate by having the surface thereof convexed as illustrated in Figure 12.In Figure 13 is illustrated an embodiment wherein notches 3 are formed by a roll press in the opposite edges of the angular bar 1 of contact material in such a manner that the angular bar will consist of a succession of approximate cylinders joined side by side with a common plane boundary.

As illustrated by the embodiments cited above, this invention is characterized by producing an electric contact having only the head portion thereof molded in a circular shape by preparing an angular bar of contact material having plastically formed therein V notches of a shape such that the angular bar will consist of a succession of polygonal prisms or approximate cylinders joined side by side, cutting the angular bar into individual polygonal prisms or approximate cylinders (cut pieces) and, at the same time, inserting the cut pieces into holes of a matched shape formed in advance in a strip sheet of base plate material and, during the subsequent application of pressure to the cut pieces, allowing only the head portions of the inserted cut pieces to be molded in a circular shape by means of a press die.

The individual steps of the procedure involved can be suitably modified without departing from the spirit of the invention. The selection of the equipment used for the production of contacts is left to the discretion of persons responsible for the work of press molding. From the practical point of view, the octagon involved in the illustrated embodiment proves to be the optimum shape for the polygonal prisms. Optionally, the polygonal prisms may be in a hexagonal shape. The ease with which such polygonal prisms are pressed into contacts of a cir cular cross section is enhanced in proportion as the number of angles contained in the polygon increases. In the case of the angular bar 1 having a succession of approximate cylinders joined side by side with a common plane boundary as illustrated in Figure 13, the cutting of the angular bar 1 in the common plane boundaries passing through the bottoms of the notches 3 gives rise to cut pieces of the shape of an approximate cylinder containing planes (cut faces) on the opposite sides. Although the ease with which the approximate cylinders cut from the angular bar are pressed into contacts of a circular cross section is enhanced in proportion as the area of the cut faces fs decreased, the depth of the notches formed in the angular bar must be selected by taking into full consideration the fact that a decrease in the width of the cut planes results from an increase in the size of notches formed in the angular bar.

Claims (5)

1. A method for manufacturing electric contacts, which comprises the steps of: forming V notches at prescribed intervals on the opposite edges of an angular bar of contact material, forming, in a strip sheet of contact base material, holes of a shape conforming to the cross section of polygonal prisms obtained by cutting said angular bar along the lines connecting the bottoms of the opposed V notches, at the positions selected for seating said polygonal prisms as contact pieces, feeding the angular bar of contact material containing said V notches in the direction of the leading end thereof thereby allowing the first polygonal prism in the angular bar to be superposed on a hole in the strip sheet, cutting the first polygonal prism off the angular bar in the plane including the bottoms of the opposed V notches and, at the same time, inserting the cut polygonal prism into said hole and fixing the cut polygonal prism in the hole by temporary compression, compressing the cut polygonal prism as held within the hole in the opposed vertical directions and causing at least one of the portions of the cut polygonal prism protruding from the opposite surfaces of the strip sheet to be molded buy a press die into a contact of a circular cross section, and cutting said strip sheet of base plate material containing compressed contact pieces in the holes therein into individual base plates each containing a contact, thereby producing electric contacts.

2. The method according to claim 1, wherein the angular bar of contact material is a clad material consisting of a substrate of copper or copper alloy and a cladding material fastened to the substrate throughout the entire length thereof.

3. The method according to claim 1, wherein the polygonal prisms formed in succession in the angular bar have an octagonal cross section.

4. The method according to claim 1, wherein the polygonal prism is cut from the angular bar of contact material above the perforated hole with an upper blade which is adapted to insert the cut polygonal prism downwardly into the hole and, at the same time, apply temporary compression to the cut polygonal prism inserted within the hole.

5. The method according to claim 1, wherein the steps of press operation are effected at a plurality of work positions in a single press device.