Dual Tip Rotating Welding Electrode

1. Field of the Invention

The present invention relates to welding of electronic circuit components and, more particularly, concerns improved mounting of welding electrodes to enhance and facilitate such welding.

2. Description of Related Art

Resistance welding of electronic circuit components can be carried out by a pair of elongated parallel electrodes, sometimes known as "duo-tip" electrodes, which are closely spaced but mutually insulated from one another and have tips that are designed to be moved down upon an area to be welded. When welding current is applied to the electrodes, current flows between the electrode tips through the parts of the workpiece to be welded. Flow of current through the workpiece between the electrodes has a preferred orientation with respect to the orientation of the workpiece. However, the various components in the workpiece may be differently oriented with respect to one another, requiring variable orientation of the workpiece relative to the electrodes. The fixed orientation of welding electrodes in resistance welding weld heads requires that the workpiece, together with the components mounted thereon, be rotated relative to the weld head to obtain proper relative orientation. Such rotation is cumbersome, time consuming and often restricted by available throat depth of the weld head. The prior art arrangement does not lend itself to rapid, efficient operation nor to automation of the welding operation.

Slip rings have been employed in the past for passing current through rotating connections. Such arrangements have been employed for low current circuits, currents having a magnitude considerably less than required for welding, and thus have not been adapted to application for high current resistant welding applications. Slip rings or other prior rotating contact arrangements may introduce a relatively high resistance at such contacts, which is acceptable because of the continuous motion. However, if a high welding current were to be applied through such contacts while they were not moving, the relatively high resistance at the contact junction could tend to weld the contacts.

Accordingly, it is an object of the present invention to provide for resistance welding in a manner and with apparatus that avoids or eliminates above mentioned problems.

In carrying out the principles of the present invention in accordance with a preferred embodiment thereof, a pair of electrodes is mounted in a pair of aligned rotatably mounted bobbins with each electrode being pressed into electrical contact with one of the bobbins and electrically insulated from the other. Electrical contacts are firmly pressed into hard sliding contact with the respective bobbins which are electrically insulated from one another so that current can flow from the bobbins between the electrodes. The bobbins are mounted for rotation in a weld head so that a minimum of electrical resistance is provided between the contacts and the bobbins.

In the accompanying drawings:

FIG. 1 is a pictorial illustration of a welding head employing rotatable duo-tip electrodes in position to weld electronic components;

FIG. 2 is a sectional elevation taken along lines 2--2 of FIG. 1;

FIG. 3 is a vertical sectional view taken along lines 3--3 of FIG. 1;

FIG. 4 is a sectional view taken along lines 4--4 of FIG. 3;

FIG. 5 is a sectional view taken along lines 5--5 of FIG. 3; and

FIG. 6 is a sectional view taken along lines 6--6 of FIG. 4.

Referring now to FIG. 1, a work table 10 is movably mounted for motion in X and Y directions upon a support (not shown) and has secured thereto a workpiece 12 upon which are mounted electronic circuit components such as those indicated at 14 and 15, for example. Pairs of such components 14, 15 are interconnected by electrical wires such as wire 16, of which the ends are welded to the respective components 14, 15.

To achieve a weld at a point such as point 18, between one end of wire 16 and component 14, a dual tip (duo-tip) electrode assembly is employed. The electrode assembly comprises first and second elongated, mutually insulated and fixedly interconnected electrodes 20, 22 having decreased area tips generally indicated at 24. The electrode assembly is positioned so that a line from one of the electrode tips to the other has a predetermined orientation with respect to one end of the wire to be welded. For example, it is preferred that an imaginary line from one of the electrode tips to the other be perpendicular to the length of a wire to be welded when the electrode tips are positioned at the wire end where it contacts the component. Accordingly, for accomplishment of the welding, the electrode tips are pressed against the component and wire so as to span the end of the interconnecting wire. While the electrodes remain in contact with the wire, a high welding current is passed through the electrodes, from one electrode to the other, and thus through the wire and component which bridge the two electrodes to accomplish the desired resistance welding of the wire end to the component.

Because a workpiece must be specifically aligned with the dual electrodes, it has been the practice in the past to rotate the work table 10 about a Z axis, perpendicular to the X,Y axes of linear motion of the table. The present invention avoids rotating the entire work table to different positions of angular orientation with respect to the electrodes. To this end, the electrode pair 20, 22 is mounted for rotation about a vertical axis 26 in a welding head generally indicated at 28. The welding head is mounted on a support (not shown) which is fixedly connected with respect to the support upon which the table 10 is movably mounted. The electrode welding head includes an electrode support arm 30 having a curved end 32 which has a right circular cylindrical bore 34 (FIGS. 2, 3) extending vertically through the support arm 30 and having upper and lower end surfaces 36, 38.

Mounted within the bore 34 of the electrode support arm are a pair of mutually aligned, vertically stacked bobbins 40, 42 having circumferentially extending radially projecting flanges 44, 46, respectively, on oppositely disposed outer ends thereof. Flanges 44, 46 abut the respective bobbin end surfaces 36, 38. Each bobbin, at its inner end, is formed with a shallow recess 50, 52 of a circular configuration which cooperate with one another to receive a short cylinder or circular disk 54 of an insulative material. Insulating disc 54 is snugly captured in both of the recesses 50, 52 to hold the two bobbins 40, 42 slightly apart and electrically insulated from one another, and yet to hold them in mutual axial alignment.

The bobbins are formed of a suitable material of high electrical conductivity and strength. Their outer surfaces have greatly increased electrical conductivity, provided by means of a gold plating or gold coating formed on the circularly cylindrical outer surfaces thereof.

A thumb wheel 60 having a diameter substantially equal to the diameter of the bobbin flanges is mounted atop the stacked bobbins. The assembly of bobbins and thumb wheel, with interposed insulating disk 54, is rigidly secured together, and thereby rotatably secured in the bore of support arm 30, by a pair of screws 62, 64 (FIG. 2) extending through the thumb wheel and through the upper bobbin 40 into threaded engagement within apertures formed in lower bobbin 42.

The bobbins are formed with mutually aligned electrode receiving apertures extending axially therethrough. The apertures have a dual rectangular cross-section to receive the dual rectangular cross-section electrodes and the electrical insulating strip 68 that is interposed between the electrodes. Thus, in lower bobbin 42 (FIG. 5), one part of the axially extending aperture is configured and dimensioned to snugly receive one electrode 20 which, accordingly, is in firm electrical contact with the lower bobbin. Lower bobbin 42 also has a second rectangular aperture portion indicated at 70, which is configured and dimensioned to receive the second electrode 22. But aperture portion 70 is dimensioned to be greater than the external dimensions of the electrode 22 so that the latter can extend through aperture section 70 without contact therewith. Thus, electrode 22 is insulated from lower bobbin 42 by the space between the electrode and bobbin.

In a similar manner, upper bobbin 40 (see FIG. 4) has a first aperture portion 74 that is configured and dimensioned to snugly receive second electrode 22 which is thus in firm electrical contact therewith and has a second aperture portion 76 which has greater dimensions than the dimensions of the first electrode 20 so that the latter will extend through the aperture portion 76 without contact with any part of the upper bobbin 40. Thus, the electrode assembly extends axially through the pair of stacked bobbins. The two bobbins are identical to one another except for the relative opposite hand disposition of electrode receiving apertures.

Although it is convenient to make the electrode assembly with both electrodes 20 and 22 of the same length, it will be readily understood that electrode 20, which is connected to the lower bobbin, but not to the upper bobbin, may be shorter. This electrode may have a length, from its welding tip, only sufficient to extend through the lower bobbin 42.

Threaded in the bobbins 40, 42 are upper and lower set screws 80, 82 having ends bearing on the respective electrodes 22 and 20, respectively. Suitable apertures 86, 88 are provided in the end 32 of electrode support arm 30 to allow access by a tool to rotate the set screws 80, 82. The latter may be turned to firmly press the respective electrodes 22 and 20 against the walls of the apertures in the electrically conductive bobbins, thus ensuring good electrical contact between the bobbins and the respective electrodes.

As noted above, bolts 62, 64 hold the assembly of thumb wheel and upper and lower bobbins together with the interposed insulated disc 54, and firmly but rotatably mount the entire assembly of bobbins, electrodes and thumb wheel in bore 34 of electrode support arm 30 by holding bobbin flanges 44, 46 against upper and lower surfaces 36, 38 of the electrode support arm.

A metallic electrically conductive contact 89, formed of an elongated conductive rod, and having an enlarged head 92, extends through an insulated grommet 94 in the weld support arm and is threadedly received in an electrically conductive connector 96 to which is electrically and mechanically connected a first weld current conducting cable 98. A spring 100 is compressed between the contact head 92 and grommet 94 and strongly urges the contact head 92 against the gold plated surface of bobbin 40. Preferably, contact head 92 is plated with a highly electrically conductive silver alloy.

An identical contact assembly is provided for lower bobbin 42 and comprises a contact rod 104 having a silver alloy plated head 106 that is urged firmly into contact with lower bobbin 42 by a spring 108 that is compressed between the bobbin head and the non-conductive grommet 110 through which rod 104 extends. The distal end of contact rod 104 is threaded in a connector 112 in which is mechanically and electrically secured a second cable 114 for conducting weld current to the electrodes.

A set screw 120 is threaded in an upper portion 122 of the electrode support arm and carries at an inner end a spring pressed ball detent 124, pressed by a spring 126. The ball 124 is received in temporary latching engagement in one of a plurality of vertically extending slots 128 (see FIG. 1) that are mutually spaced circumferentially around the outer periphery of thumb wheel 60. Thus, the electrodes can be rotated by manual rotation of the thumb wheel and will be temporarily locked in place by the spring pressed ball detent 124.

In order to monitor welding voltage, the voltage at each of the bobbins is detected by electrical spring probes mounted in the electrode support arm. Thus a first spring probe 140 (FIG. 6) is mounted in a bore 142 within the support arm and includes a contact head 144 that is pressed upwardly into sliding contact with a lower surface of flange 44 of upper bobbin 40 by means of a compression spring 146. An electrical lead 148 connects this probe to suitable monitoring equipment (not shown). Similarly, for the bobbin 42, an electrical probe 150 is mounted in a bore 152 of the electrode support and includes a head 154 that is spring pressed by means of a spring 156 into sliding contact with the upper surface of flange 46 of bobbin 42. An electrical connecting lead 158 is connected from probe 150 to suitable monitoring equipment (not shown).

With the described arrangement, contact heads 92, 106 are strongly and firmly pressed against the highly conductive surfaces of the bobbins in any position of rotation of the bobbins. The electrode assembly is maintained in a fixed, stationary position while weld current is applied. Thus, because of the good electrical contact between the bobbins and contacts, the high welding current which is passed between these elements in a non-moving condition of the elements is not likely to cause any arcing or welding at such contact points. If deemed necessary or desirable, resistance at the junction of the contact heads 92, 106 and the respective bobbins 40, 42 can be further decreased by forming the contact heads with a concave configuration that matches the curvature of the bobbin exteriors, thereby increasing the contact area between the contact heads and the bobbins, and thus further ensuring that minimal resistance at this junction.

The spring loading of the contacts against the bobbins allows relatively free rotation of the bobbins by use of the thumb wheel and thus there is little restriction on the angular orientation of the electrodes. Such rotational mounting of the electrodes greatly simplifies use of the dual tip welding apparatus, eliminates accidental damage due to cumbersome workpiece rotation, and increases the efficiency and throughput of the welding apparatus. Preferably, the detent slots of the thumb wheel are positioned at 45.degree. intervals to facilitate tip orientation angles most often encountered.

With this intermittent angular motion capability of the electrodes, workpiece movement is required only in X and Y translations and no rotation of the workpiece is necessary. Such an arrangement will greatly facilitate automation of the welding operation.

In an exemplary embodiment, insulator 54 between the bobbins is made of fiberglass, and the indexing thumb wheel is made of acetal as are bolts 62, 64.

Access holes 86, 88 in the electrode holder arm are positioned to allow access to the set screws 80, 82 when the rotatable assembly is in a home or 0.degree. position. The arrangement allows welding to be done in any rotational position from 0.degree. to 360.degree..