Method and apparatus for constructing an electrical contact

A method and apparatus for constructing an electrical contact including welding means for welding a base element to a blank comprised of contact facing material, separating means for separating finished electrodes from the balance of the contact facing material, examining means for examining an aperture formed within the contact material blank when the finished electrode is separated from the blank, and classifying means for classifying the finished electrode as acceptable or unacceptable depending upon the examination.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention is related to a method and apparatus for constructing 
an electrical contact or electrode, which may, for example, comprise a 
sparkplug. 
2. Disclosure Information 
Designers have long recognized the need for constructing electrical 
contacts or electrodes from composite materials. The need for such 
composites results from the motivation, on the one hand, to reduce the 
cost of the electrical contact or electrode by using a relatively cheaper 
conducting material for the bulk of the electrode, while maximizing, on 
the other hand, the durability of the electrode by introducing a more 
durable, but more costly, contact or tip material in the critical working 
area. Accordingly, U.S. Pat. No. 3,431,614 discloses a method for 
manufacturing an electrode having a metal core, a tubular metal sheath 
surrounding the core, and a welded metal cap enclosing the sheath. The 
metal cap is sheared from the material from which the cap is formed. It is 
possible, however, that electrodes may be produced according to this 
method which appear to be satisfactory but have caps which are not 
completely welded to the outer tubular sheath. This occurs because the 
shearing action will not seriously stress the bond between the metal cap 
and the tubular metal sheath. Separation of the tip from the balance of 
the electrode is a serious defect for any electrical component, but it is 
particularly serious with respect to automotive sparkplugs because a 
metallic object such as an electrode cap could cause destruction of an 
engine were the cap to become loose in the engine's combustion chamber. 
A second type of electrode formation is disclosed in U.S. Pat. No. 
3,976,240 in which an ultrasonic welding unit is employed for the purpose 
of welding a gold foil element onto a second metal member within the 
confines of a perforated metal plate. The balance of the gold foil element 
lying outside the welded portion is then stripped off through the shearing 
action of the perforated metal plate. This method suffers from a similar 
deficiency to that previously noted inasmuch as the shearing action 
employed for separating the balance of the non-welded contact material 
from the piece to which the contact is being applied may be conducted 
successfully, i.e., the shearing may occur successfully, even when the 
precious metal contact strip has not been properly applied to the 
electrode material. 
Examples of methods for welding strips and pins together are shown in U.S. 
Pat. Nos. 2,784,297 and 3,891,789. Neither of these patents, however, are 
directed to a solution of the previously described problem regarding 
integrity of welding or bonding used for electrodes and electronic 
contacts. 
U.S. Pat. No. 3,643,101 discloses a means for measuring the diameter of a 
small orifice based upon multiple detectors arranged to measure the 
intensity of radiation from a laser source emanating through the hole to 
be measured. This technique, as will be understood in view of this 
disclosure, may be employed with the method disclosed herein for assessing 
the quality of a welded electrode assembly. 
SUMMARY OF THE DISCLOSURE 
An electrode or electrical contact comprises a base element which may, for 
example, be of a generally cylindrical configuration, and having a free 
end, and a contact facing applied to the free end in the form of a blank 
of contact facing material having a larger area than the free end to which 
the contact facing material is applied. The final shape of the contact 
facing material is determined by tensile fracture of the contact facing 
material in a region circumscribing the outer periphery of the generally 
cylindrical element. The tensile fracture results from axial pulling of 
the electrode away from the contact facing material blank. A method for 
constructing an electrical contact or electrode as described above 
preferably comprises the steps of attaching a base element to one segment 
of a blank comprised of contact facing material and separating the 
attached segment from the remainder of the blank by subjecting the blank 
to tensile stress applied at least in part by the base element. The 
contact facing material is preferably attached to the base element by 
welding, brazing, soldering, chemical bonding or other known means. 
Following the attachment of the base element and contact facing, the 
aperture formed within the blank by the separation of the segment of 
contact facing material from the balance of the blank may be examined, so 
as to assess the quality of the attachment of the contact facing material 
to the base element. This gaging will also disclose the extent to which 
the base element is covered by the contact facing material. The gaging of 
the aperture may be by mechanical means or by optical gaging such as 
through the use of laser techniques as disclosed in U.S. Pat. No. 
3,643,101, which is hereby incorporated by reference into the 
specification of this application. 
An apparatus for constructing electrodes according to the invention 
preferably comprises welding means for welding a base element to a blank 
comprised of contact facing material, separating means for separating the 
electrode from the blank of contact facing material, and means for 
examining the aperture formed in the blank when the electrode is separated 
from the blank, so that proper operation of the welding means may be 
verified. The apparatus may further comprise classifying means for 
classifying electrodes produced by the apparatus as acceptable or 
unacceptable based upon the reading from the examining means. A method and 
apparatus according to the present invention may be used for constructing 
a variety of electrical contact devices, including a sparkplug. 
It is an object of the present invention to provide an electrode or 
electrical contact having a composite construction in which a contact 
facing applied to a base element has its final shape determined by tensile 
fracture of the contact facing material in a region circumscribing the 
outer periphery of the base element. 
It is another object of the present invention to provide a method for 
constructing an electrical contact or electrode in which proper attachment 
of a base element to a contact facing is assured by virtue of the fact 
that the segment of contact facing material attached to the base element 
is separated from a larger blank of contact facing material by pulling the 
base element and an attached piece of contact facing material from the 
contact facing material blank. The resulting aperture in the contact 
facing material is then examined to determine the quality of the 
attachment between the base element and the contact facing material. 
It is a further object of the present invention to provide a method and 
apparatus for inspecting the quality of the weld between the base element 
and the contact facing material. 
The method and apparatus of the present invention solve the problems of the 
prior art because attachment of the contact facing material to the base 
element may readily be assured through inspection of the blank from which 
the contact facing is removed by tensile force. Accordingly, if the 
aperture formed in the contact facing material is less than a full circle, 
the electrode should be rejected. Similarly, in the event that no aperture 
is formed within the contact facing blank, the electrode should clearly be 
rejected because little or no contact facing material has been deposited 
upon the electrode. It is thus an advantage of the present invention that 
electrodes produced with the disclosed method and apparatus will have 
greater integrity than those produced with prior art methods.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
As shown in FIG. 1, the method and apparatus of this invention may be used 
for producing sparkplugs of the type commonly employed in automotive 
engines. Such sparkplugs typically comprise a cylindrical center 
electrode, 1; an insulator, 2, surrounding electrode 1 for the balance of 
its length; a generally cylindrical shell, 3, which surrounds a portion of 
insulator 2, and an outer electrode, 4, which is attached to shell 3, and 
which is in juxtaposition with center electrode 1. The sparkplug shown in 
FIG. 1 further comprises contact facing 10 applied to center electrode 1 
according to the method of the present invention. The method and apparatus 
described and claimed herein may be used beneficially to produce a variety 
of electrical contacts, contactors, contact sets, sparkplugs, or other 
electrode containing devices in which a base element comprised of a 
material such as a nickel alloy, for example, or another type of alloy 
containing ferrous or nonferrous metals or non-metals is desired to be 
joined with a relatively more durable, or perhaps, more expensive material 
such as platinum, gold or other metals or nonmetallic substances. 
As shown in FIG. 2, a blank or ribbon of contact facing material 6 is moved 
through the apparatus shown therein by means of lead rollers 22a and 22b 
and tail rollers 24a and 24b. In the first step of the process, base 
element 4 is abutted to blank 6 by means of welding fixture 12. Welding 
fixture 12 comprises a chuck 13 which grips base element 4, a ram 42 for 
advancing base element 4 against blank 6, and a base 44 for mounting the 
welding fixture. Base element 4 is maintained in abutment with contact 
facing material 6 and welding tip 18 is advanced against the opposite side 
of contact facing material 6. Power source 20 provides a source of 
electrical current which is passed through contact facing material 6, 
thence through base element 4 and welding fixture 12. In this manner, a 
segment of contact facing material blank 6 is welded to base element 4. In 
view of this disclosure those skilled in the art will recognize that the 
method and apparatus employed for attaching a segment of contact facing 
material blank 6 to base element 4 may be selected from one of a variety 
of methods including not only resistance welding, but also other types of 
welding, brazing, soldering, impact welding, ultrasonic welding, chemical 
bonding, and other methods compatible with apparatus other than that 
illustrated in this document. 
FIG. 3 shows a welded composite of contact material blank 6 and base 
element 4. Fusion zone 8 is generally elliptical in shape and marks the 
area in which base element 4 and contact facing material 6 were melted and 
intermixed during the welding process. 
Once having been welded to contact facing material blank 6, base element 4 
is conveyed by rollers 22 and 24 to a separating station in which 
separating die 16 and separating fixture 14 are operated to remove the 
finished electrode from contact facing material blank 6. Those skilled in 
the art will appreciate in view of this disclosure that separating die 16 
could, depending upon the requirements posed by the composition of 
material blank 6, comprise a clamping type of die fixture, a slip die, or 
yet other types of holding fixtures. 
The general position of separating fixture 14 with respect to separating 
die 16 and further with respect to contact facing material blank 6 is 
generally shown in FIG. 2 and more particularly shown in FIGS. 4 and 5. 
Separating fixture 14 comprises chuck 15 which tightly grips base element 
4, ram 46 to which chuck 15 is fixed, and base 48. The separating fixture 
is capable of exerting considerable force to pull base element 4 and an 
attached segment of contact facing material 6 axially away from the 
balance of contact facing material 6, as described below. 
FIG. 4 shows separating fixture 15, and separating die 16, in their 
positions prior to separation of the finished electrode from contact 
material blank 6. Detailed construction of the separating die is shown in 
(FIG. 5. The die comprises shank 34 having a headstock 36 attached 
thereto. A slot 38 is provided for contact facing material blank 6 to 
slide through. Aperture 40 is circular in shape and allows access of base 
element 4 into the interior of the die. As shown in FIG. 5, axial 
separation of base element 4 and contact facing 10, comprising a segment 
of contact facing material blank 6, produces an aperture within contact 
facing material blank 6. The outline of the aperture will be approximately 
as shown in FIG. 6 provided the weld between base element 4 and contact 
facing material blank 6 was properly performed. As shown in FIG. 6, a 
circular aperture 50 is opened in contact facing material blank 6 when the 
attached segment 10 of contact facing material blank 6 was pulled from the 
balance of the contact facing material blank. If, on the other hand, an 
aperture 52, as shown in FIG. 7, is formed in contact material blank 6, 
the irregular shape of aperture 52 indicates that the weld between base 
element 4 and contact facing material blank 6 was not properly performed. 
The shape of the aperture 50 or 52 formed in contact facing material blank 
6 may be used to classify the resultant finished electrode as being 
acceptable or unacceptable. 
As can be seen from FIGS. 5-7, the outline of contact element 10 is 
determined by the tensile fracture of contact facing material 6, which 
occurs when the separating fixture pulls the finished electrode away from 
the remainder of contact facing material blank 6. Because considerable 
force is required to fracture blank 6, fusion zone 8 must be well 
developed to cause a circular aperture of the type shown in FIG. 6 to be 
opened in blank 6. In this connection it should be noted that this 
disclosure will suggest other arrangements for the apparatus illustrated 
in FIG. 2, which is merely intended to be exemplary of a class of 
apparatus suitable for practicing the present invention. 
Those skilled in the art will appreciate that several of the known 
techniques for examining the integrity of spot welds have, for years, 
included the separation or pulling of such welds to determine whether an 
aperture or torn area is opened into one of the two metals which have been 
spot welded. The apparatus of this invention, including an energy source 
26, receiver 28, processor 30 and classifier 32 allows such a technique to 
be used with the present invention. In this case, contact facing material 
blank 6 is advanced along each station sequentially so that following 
axial separation of the finished electrode by the separating die, the 
contact facing material blank is then positioned so that the aperture 
formed in the contact material blank may be optically gaged. Accordingly, 
as shown in FIG. 2, energy source 26 is arranged so as to impinge upon 
contact material blank 6 in the locus of an aperture. The energy emanating 
from energy source 26 and passing through the aperture within the contact 
material blank is received by receiver 28, which transmits a signal to 
processor 30. Depending upon the level of energy received by receiver 28, 
processor 30 transmits a signal to classifier 32 regarding the 
acceptability of a particular finished electrode. In the event that the 
finished electrode is unacceptable, it will be rejected by classifier 32. 
If the electrode is acceptable, classifier 32 will allow the electrode to 
continue for further processing. In view of this disclosure those skilled 
in the art will recognize that other means could be used for gaging the 
apertures 50, 52 within contact material blank 6. Accordingly, mechanical 
gaging means such as those employing tapered pins or the like which would 
be inserted into the aperture could be used. Other gaging means could be 
used as well including X-ray inspection, ultrasonic methods, laser 
techniques and others. 
Additional methods could be employed for assessing the quality of the weld 
or to the extent to which the base element is covered by the contact 
facing material. For example, the amount of force required to be imparted 
by separating fixture 14 in order to axially pull base element 4 and the 
welded segment of contact facing material blank 6 from the balance of the 
contact facing material blank could be measured. Another method could 
involve measurement of the current passing through welding electrode 18 
during the welding process. In any event, other methods will be suggested 
by this disclosure. 
The invention has thus been shown and described as reference to specific 
embodiments. However, it should be noted that the present invention is in 
no way limited to the details of the illustrated structure and methods, 
but changes and modifications may be made without departing from the scope 
of the appended claims.