Patent Description:
Spot welding assemblies are known in the art for welding first and second work pieces to one another. Spot welding assemblies typically include a base for supporting a base electrode and a welding gun for supporting a gun electrode. During a welding operation, the welding gun is moved toward the base in order to draw the first and second work pieces against one another. A current is then applied through the base and gun electrodes and the first and second work pieces in order to melt regions of at least one of the first work piece and/or the second work piece to form a weld therebetween. Further prior art are disclosed in <CIT> (describing the preamble of claims <NUM>, <NUM>, <NUM>, <NUM>, and <NUM> respectively), <CIT> and <CIT>.

An issue with such spot welding assemblies, especially when the welding process is automated, is that the electrodes are static, and thus do not compensate for variations in work piece placement and/or dimensional variations among the work pieces, especially when the work pieces are not arranged parallel to a welding surface defined between the first and second electrodes. As such, the first and/or second work piece may not make adequately contact the electrodes, thus leading to an insufficient weld. In these situations, it is known to manually adjust an orientation of the welding gun and/or base to provide improved contact against the work pieces, however, such manual adjustments can be time consuming and labor intensive.

According to the present invention, there are defined spot welding assemblies having the features of any of claims <NUM>, <NUM>, <NUM>, <NUM> and <NUM>. In view of the foregoing, there remains a need for improvements to such spot welding assemblies.

According to a first aspect of the present invention, a spot welding assembly for welding a first work piece to a second work piece is defined in claim <NUM>.

Because both of the base and the gun electrodes are pivotable, the electrodes are able to quickly be oriented flat against the work pieces even when the work pieces are not parallel to an original plane of the base and gun electrodes, such as when the work pieces are improperly located or irregularly dimensioned. Orienting the electrodes in this manner ensure sufficient electrical and thermal conductivity during welding in order to provide a sufficient weld. Such adjustments may be provided in both automated and manual welding operations.

The subject spot welding assembly may be employed in projection welding applications, wherein at least one of the work pieces has at least one projection that engages the other work piece for focusing a current from the base and gun electrodes.

Referring to the Figures, wherein like numerals indicate correspond parts throughout the several views, a spot welding assembly <NUM> is generally shown. With reference to <FIG>, the spot welding assembly <NUM> generally has a base <NUM> for supporting a base electrode <NUM>, and a welding gun <NUM> for supporting a gun electrode <NUM>. As shown in <FIG>, a first work piece <NUM> and a second work piece <NUM> are positioned between the base and gun electrodes <NUM>, <NUM>. The first work piece <NUM> is supported by tooling <NUM>. With reference back to <FIG>, the welding gun <NUM> is moveable toward and away from the base <NUM> in order to make the first and second work pieces <NUM>, <NUM> engage one another, after which which a current is applied through the base and gun electrodes <NUM>, <NUM> and the first and second work pieces <NUM>, <NUM> in order to melt at least one of the first and/or second work pieces <NUM>, <NUM> to form a weld therebetween. According to the example embodiment, the first work piece <NUM> is a flat plate and the second work piece <NUM> is a nut, but other types of work pieces may be utilized. As presented in the example embodiment, the subject spot welding assembly <NUM> may specifically be a projection welding assembly, wherein at least one of the work pieces <NUM>, <NUM> has one or more projections for concentrating the current from the base and gun electrodes <NUM>, <NUM> in order to target the weld to specific areas.

As shown in <FIG> and <FIG>, the base <NUM> has a bottom portion <NUM> that is configured to be located on a die. The bottom portion <NUM> may have various shapes, such as a cylindrical shape (e.g., <FIG>) or a cuboid shaped (e.g., <FIG>). As best shown in <FIG>, the base <NUM> further has a generally cylindrical-shaped projection portion <NUM> that extends upwardly from the bottom portion <NUM> along an axis A and terminates at a top surface <NUM>. The top surface <NUM> defines a first hemispherical portion <NUM> that concaves axially downwardly. The projection portion <NUM> defines a plurality of first threads <NUM> adjacent to the bottom portion <NUM>. A plurality of first wire channels <NUM> extend through the projection portion <NUM> to the top surface <NUM> for receiving one or more wires for transmitting a current to the base electrode <NUM>. The first wire channels <NUM> are spaced apart and positioned so that at least one of the first wire channels <NUM> contacts the convex second hemispherical portion <NUM> of the base electrode <NUM> with the base electrode <NUM> being in any position throughout its range of motion.

As illustrated in <FIG> and <FIG>, the base electrode <NUM> is positioned against the first hemispherical portion <NUM> of the base <NUM>. According to the example embodiment, the base electrode is made of a class <NUM> copper material, but other highly conductive materials could be utilized. The base electrode <NUM> has a convex second hemispherical portion <NUM> that nests with the first hemispherical portion <NUM> such that the second hemispherical portion <NUM> is rotatable <NUM> degrees and pivotable <NUM> degrees relative to the first hemispherical portion <NUM>. The base electrode <NUM> further has a cylindrical projection <NUM> that extends upwardly from the second hemispherical portion <NUM> to a flat surface for supporting the first work piece <NUM>. The base electrode <NUM> further defines a passage <NUM> that extends axially therethrough.

As illustrated in <FIG> and <FIG>, a weld pin <NUM> is received by the passage <NUM> of the base electrode <NUM>. According to the example embodiment, the weld pin <NUM> is made of a non-magnetic stainless steel; however, other non-magnetic materials could be utilized. The weld pin <NUM> extends axially from a bulging end <NUM> to a tip <NUM> that tapers to a point axially outside of the passage <NUM>. The bulging end <NUM> of the weld pin <NUM> engages and is pivotable along the first hemispherical portion <NUM> with the second hemispherical portion <NUM> of the base electrode <NUM>. The weld pin <NUM> is configured to assist in aligning the second work piece <NUM> relative to the first work piece <NUM> by being received by the second work piece <NUM> and a tubular segment <NUM> of the gun electrode <NUM> (discussed in further detail below). The pointed tip <NUM> of the weld pin <NUM> assists in guiding the weld pin <NUM> into the second work piece <NUM> and tubular segment <NUM>. Alternatively or additionally, the weld pin <NUM> may be configured to contact the first work piece <NUM>. For example, the weld pin <NUM> may be located into a channel of the first work piece <NUM> to assist in locating the first work piece <NUM>.

As illustrated in <FIG> and <FIG>, a retaining collar <NUM> that generally has a tube shape receives the projection portion <NUM> of the base <NUM>. According to the example embodiment, the retaining collar <NUM> is made of a non-magnetic stainless steel material; however, other materials could be utilized. The retaining collar <NUM> extends axially between a bottom end <NUM> and a top end <NUM>. A plurality of second threads <NUM> are defined adjacent to the bottom end <NUM>. The second threads <NUM> are arranged to be threaded with the first threads <NUM> of the base <NUM> for securing the retaining collar <NUM> to the base <NUM>. A first flange <NUM> extends radially inwardly from the top end <NUM>. The first flange <NUM> terminates radially adjacent to, and in axial alignment with the projection <NUM> of the base electrode <NUM>. The first flange <NUM> limits the pivoting movement of the base electrode <NUM> relative to the first hemispherical portion <NUM> of the base <NUM>. More particularly, as generally shown in <FIG>, pivoting is limited to approximately <NUM> degrees in every direction according to the example embodiment, however, the first flange <NUM> could be sized to limit the pivoting to other angles. In addition to limiting pivoting movement of the base electrode <NUM>, the retaining collar <NUM> prevents debris from entering the region of the first and second hemispherical portions <NUM>, <NUM> in order to provide prolonged use of the welding assembly <NUM>.

As best shown in <FIG>, an upper adapter <NUM> is coupled with the welding gun <NUM>. According to the example embodiment, the upper adapter <NUM> is made of a class <NUM> copper material, however, other highly conductive materials could be utilized. The upper adapter <NUM> extends axially between a proximal end <NUM> and a distal end <NUM>, with a plurality of third threads <NUM> defined adjacent to the proximal end <NUM> for threadedly fixing the upper adapter <NUM> to the welding gun <NUM>. The distal end <NUM> of the upper adapter <NUM> defines a third hemispherical portion <NUM> that concaves into the distal end <NUM>. The upper adapter <NUM> further defines fourth threads <NUM> adjacent to the distal end <NUM>. A plurality of second wire channels <NUM> extend generally axially through the upper adapter <NUM> and terminate at the distal end <NUM> for receiving wires for transmitting a current to the gun electrode <NUM>. The second wire channels <NUM> are spaced apart and positioned so that at least one of the second wire channels <NUM> contacts the convex fourth hemispherical portion <NUM> of the gun electrode <NUM> with the gun electrode <NUM> being in any position throughout its range of motion.

As best shown in <FIG> and <FIG>, the gun electrode <NUM> is located against the upper adapter <NUM>. According to the example embodiment, the gun electrode <NUM> is made of a class <NUM> copper material, however, other highly conductive materials may be utilized. The gun electrode <NUM> has a convex fourth hemispherical portion <NUM> that nests with the third hemispherical portion <NUM> such that the convex fourth hemispherical portion <NUM> is rotatable <NUM> degrees and pivotable <NUM> degrees relative to the third hemispherical portion <NUM>. The gun electrode <NUM> further includes a tubular segment <NUM> that extends axially from the fourth hemispherical portion <NUM> and terminates at a flat end for receiving and locating the second work piece <NUM> and the weld pin <NUM>.

As best shown in <FIG> and <FIG>, an upper collar <NUM> that generally has a cylindrical shape is coupled with the upper adapter <NUM>. According to the example embodiment, the upper collar <NUM> is made of a non-magnetic stainless steel; however, other non-magnetic materials may be utilized. The upper collar <NUM> extends axially between a fixed end and <NUM> a guiding end <NUM>. Fifth threads <NUM> are defined adjacent to the fixed end <NUM> for being threaded with the fourth threads <NUM> of the upper adapter <NUM>. The upper collar <NUM> further includes a second flange <NUM> that extends radially inwardly from the guiding end <NUM> for limiting the pivoting movement of the gun electrode <NUM> relative to the upper adapter <NUM>. More particularly, as generally shown in <FIG>, pivoting is limited to approximately <NUM> degrees in every direction in the example embodiment, however, the second flange <NUM> could be sized to limit the pivoting to other angles. In addition to limiting pivoting movement of the gun electrode <NUM>, the upper collar <NUM> prevents debris from entering the region of the third and fourth hemispherical portions <NUM>, <NUM> in order to provide prolonged use of the welding assembly <NUM>.

During use of the spot welding assembly <NUM>, the pivoting movement and rotation of the base and gun electrodes <NUM>, <NUM> allows the base and gun electrodes <NUM>, <NUM> to be oriented flat against the first and second work pieces <NUM>, <NUM> to provide a large contact area against the first and second work pieces <NUM>, <NUM>, even when the first and second work pieces <NUM>, <NUM> do not lie parallel to an original plane that is defined between the base and gun electrodes <NUM>, <NUM> when they are in an un-pivoted / centered position, such as when they are improperly placed or irregularly shaped. The large contact area provides adequate electrical and thermal conductivity during welding, thus ensuring a successful weld even in non-ideal conditions. For example, <FIG> shows the base and gun electrodes <NUM>, <NUM> in a centered position with the first work piece <NUM> positioned generally along the original plane, <FIG> shows the base and gun electrodes <NUM>, <NUM> in a tilted left position while maintaining flat contact against the first and second work pieces <NUM>, <NUM>, and <FIG> shows the base and gun electrodes <NUM>, <NUM> in a tilted right position while maintaining flat contact against the first and second work pieces <NUM>, <NUM>.

As illustrated in <FIG>, during operation, the welding gun <NUM> starts in a raised position, and the base and gun electrodes <NUM>, <NUM> are in their centered, un-pivoted state. The first work piece <NUM> (a plate in the example embodiment) is positioned on the base electrode <NUM> via either automatic or manual load. At this point, the base electrode <NUM> may be rotated and pivoted to compensate for any angular deflection caused by the first work piece <NUM> not being located along the original plane to ensure proper contact of the base electrode <NUM> against the first work piece <NUM>. Specifically, the base electrode <NUM> may be rotated and pivoted to match an angle of the first work piece <NUM>. Once the first work piece <NUM> is located, the second work piece <NUM> (which is a projection fastener in the case of the example embodiment), is placed over the weld pin <NUM>. The gun electrode <NUM> is then lowered toward the base electrode <NUM> with the welding gun <NUM>. Upon contact of the second work piece <NUM> against the first work piece <NUM>, the gun electrode <NUM> automatically rotates and pivots to match an angle of the base electrode <NUM> to provide full contact between the first and second work pieces <NUM>, <NUM> (illustrated in <FIG>). An electrical current is then supplied to the base and gun electrodes <NUM>, <NUM>, melting the second work piece <NUM> to the first work piece <NUM>, to create a weld therebetween. It should be appreciated that one of the first and second work pieces <NUM>, <NUM> may present one or more projections that engage the other work piece for concentrating the current and weld.

Unless otherwise defined, the term "hemispherical," as used in the present application, includes any surface extending along a portion of a sphere. The term "hemispherical" is not limited to exactly one-half of a sphere shape.

Claim 1:
A spot welding assembly (<NUM>) comprising: a base (<NUM>); a base electrode (<NUM>) coupled with the base (<NUM>) for supporting a first work piece (<NUM>); a welding gun (<NUM>) moveable toward and away from the base (<NUM>); a gun electrode (<NUM>) coupled with the welding gun (<NUM>) for supporting a second work piece (<NUM>) and for locating the second work piece (<NUM>) against the first work piece (<NUM>) upon movement of the welding gun (<NUM>) toward the base (<NUM>) to allow the first and second work pieces (<NUM>, <NUM>) to be welded to one another,
the spot welding assembly (<NUM>) being characterised in that:
the base electrode (<NUM>) is pivotable relative to the base (<NUM>) and the gun electrode (<NUM>) is pivotable relative to the welding gun (<NUM>).