Welding Apparatus and Transformer Therefor

The present invention pertains to an apparatus for spot welding or linear welding. More particularly, the present invention pertains to a lightweight spot welding and/or linear welding apparatus which protects against electric shock and features a transformer formed of a toroidal core, a primary winding wound axially about the core, and a single-turn secondary winding comprising two arm sections which are electrically connected by a wound element.

In conventional welding apparatus, emphasis has been placed in developing particular features to make such apparatus better suited for various applications. For example, U.S. Pat. No. 3,211,885 states that commercial applicability of a portable welding tool depends upon the ease with which the tool can be used, and goes on to disclose a welding system including a capacitor discharge circuit for accommodating different sizes or gauge of material or wire to be welded. U.S. Pat. No. 2,269,726 relates to manual welder which is described as light in weight. U.S. Pat. No. 4,496,821 states that, due to their mass, conventional spot welder transformers are not well suited for use with, for example, a robot arm and goes on to disclose a lightweight transformer adapted for use with a welding gun mounted at the end of a robot arm. U.S. Pat. No. 2,491,169 is directed to a relatively lightweight welding means which incorporates a transformer containing little or no iron but which permits a relatively large throat.

The present invention relates to a spot welding apparatus and a linear welding apparatus which offers excellent protection against electric shock. According to the present invention, the transformer core and the primary winding are coated with a synthetic resin and encased in an insulating material to electrically insulate them and to make them moisture resistant. The casing walls of the welding machine of the invention likewise comprise electrical insulation to protect the operator from electrical shock. In a preferred embodiment of a spot welding apparatus in accordance with the invention, a stationary conductive arm provides the mounting for one of the welding electrodes and further provides the frame structure for the apparatus. The welding transformer is supported upon such stationary arm. This preferred arrangement permits further reduction of the ultimate weight of the welding device.

According to the invention, a welding transformer is provided with a toroidal core formed of a silicon steel strip coiled or rolled with an insulating material a multi-turn primary winding, and a single-turn secondary winding. The rolled or coiled core avoids high magnetic resistances and high eddy current losses and reduces core losses to 0.8 watts/kg. The primary winding is wound axially or lengthwise about the toroidal core. The secondary winding comprises a movable arm section, the fixed arm section which also acts as the frame, and a wound element which electrically connects the arms. A portion of the stationary arm extends axially through the core, adjacent to internal primary winding sections therein, to support the core and to form a single-turn about the core.

Further aspects and features of the present invention will be even more apparent from the following detailed description and drawings, and the appended claims. In the drawings:

FIG. 1 is an elevated side view of a welding apparatus in accordance with the present invention;

FIG. 2 is a side sectional view of the welding apparatus of FIG. 1;

FIG. 3 is a perspective view of a transformer core together with a primary winding thereon which core and winding are suitable for use with the welding apparatus in accordance with the invention;

FIG. 4 is a perspective view of a silicon steel tape together with layers of electrical insulation which are rolled to form the core shown in FIG. 3;

FIG. 5 is a sectional view of an insulated primary winding;

FIGS. 6-9 are side elevational views of different embodiments of the welding apparatus in accordance with the invention; and

FIG. 10 is a perspective view of an arrangement for providing a linear welding apparatus in accordance with the present invention.

FIG. 1 is an elevated side view of a spot welding apparatus 10 in accordance with the present invention. Spot welding apparatus 10 features a body or case 12 which is constructed from a material that has good electrical insulating properties such as, for example, TEXTOLITE (registered trademark of General Electric Co.), to provide protection against electrical shock as a result of high currents generated by the apparatus. Protruding out of the case 12 are two copper arms 14 and 16. In the embodiment of FIG. 1, copper arm 14 is journaled to move within the plane of the paper as indicated by double headed arrow A to accommodate positioning of the work piece (not shown in the drawings) between the welding electrodes 18 and 20. Copper arm 16 is fixed. It is contemplated that a pneumatic system (not shown) operating under an internal pressure of about six atmospheres could be used to move arm 14 and thereby press the work piece between the welding electrodes. Also, it is understood that either arm could be journaled for movement, or that both arms may be made movable. It also is contemplated that other conductive materials may be used to form arms 14 and 16.

Preferably, point electrodes 18 and 20 are formed of copper. Electrodes 18 and 20 may be affixed on arms 14 and 16 in any conventional way such as by fasteners 22 and 24 to provide good electrical contact between each electrode and its respective arm. Preferably, the copper electrodes 18 and 20 are of the water-cooled type. Hoses for circulating coolant for the electrodes are not shown in the drawings. A power cable 26 extends from the rear of housing 12 for connection with an external power supply such as a 220 volt, 50 Hz supply.

FIG. 2 is a side view of the spot welding apparatus 10 with a side wall of the casing 12 removed to feature the electrical and magnetic circuits therein. In FIG. 2, there is shown a transformer generally identified by reference numeral 27. Transformer 27 comprises a core 28, a primary winding 29, and a secondary winding 30 which in turn comprises arms 14, 16 and a connecting wound means 32. The transformer 27 and the primary and secondary windings 29, 30 provide a potential difference between electrodes 18 and 20.

With reference also to FIGS. 3 and 4, preferred transformer core 28 is constructed from a highly grain-oriented silicon strip or tape 34. The strip or tape 34 is conventional and comprises a cold-rolled silicon steel material which is grain-oriented so that the magnetic induction in the direction that the strip is rolled or coiled, as indicated by arrow C in FIG. 4, is 1.7 tesla (17,000 gauss). The magnetic induction in the direction transverse to the rolling direction as indicated by arrow D is 1.0 tesla (10,000 gauss). Strip 34 is encased within insulating layers 36 and 38. Layer 36 comprises any conventional electrical insulation and layer 38 comprises a tape to secure the insulation layer 36 about the strip 34. It is contemplated that a cotton tape comprising both layers 36 and 38 conveniently could be used to envelope the strip material 34. As understood from FIG. 4, the insulated silicon strip 34 is coiled or rolled to form the toroidal transformer core 28. It is convenient that the insulated strip be rolled upon a pressboard tube 40 or the like for easily forming an axial passage 42 through the core 28. The silicon steel strip 34 may be adhered to the pressboard center by the tape 38.

As a result of the rolled or coiled configuration of strip material 34 and its insulating layers 36 and 38, the magnetic flux flows in the direction of maximum magnetic induction. Further, the rolled core 28 in accordance with the present invention avoids high magnetic resistances and high losses due to eddy currents which commonly arise in composite core structures. Core 28 is characterized by power losses of no more than 0.8 walLs/kg due Lo hysteresis and eddy currents.

The primary winding 29 of the transformer is wound axially about the core 28 as best shown in FIG. 3. As such, primary winding 29 s considered to have external winding sections 44 that are adjacent to the outer walls 46 of the core 28 and internal winding sections 48 adjacent the inner walls 50 of the core. In a preferred embodiment, toroidal core 28 has a cross-sectional area of 58.5 cm.sup.2. The number of turns of the primary winding 29 is given by ##EQU1## where u is the supply voltage in volts, S is the cross-sectional area of the core 28 in cm.sup.2, and f is the frequency of the supply voltage in hertz. By substituting the appropriate values we get ##EQU2## With reference to FIG. 5, primary winding 29 comprises a copper strip 52 enclosed by glass fiber insulation 54. The dimensions of the copper strip 52 forming preferred primary winding 29 are 1 mm .times.3 mm whereby the strip has a cross-sectional area of 3 mm.sup.2. It is contemplated that other electrically conductive windings may be used for the primary winding without departing from the invention. Once the primary winding 29 has been wound about the core 28, the core and the primary winding are coated with a spirit-based insulating lacquer. Thereafter, the core 28 and primary winding 29 are dried at 60.degree. C.

The transformer core 28 is encased in a polyvinylchloride (PVC) tube 56 which is closed at each of its ends by electrically insulating disks 58 which likewise could comprise TEXTOLITE. Further, a thin PVC tube 60 is received within the opening 42 through the toroidal transformer core 28 to cover the internal sections 48 of the primary winding 29. Any interstices between the tubes 56, 60, the coated core 28 and winding 29, and the disks 58 are filled with a conventional epoxy resin. The composite core and primary winding structure in accordance with the invention are made moisture resistant. This resulting structure is not only water resistant, but resists many other agents as well. Furthermore, the composite core according to the invention is electrically insulated to prevent electrical shock.

In a preferred embodiment of the invention, the external diameter of the outer PVC pipe 56 is about 160 mm and the inside diameter about 152 mm. This corresponds to a pipe wall thickness of 4 mm. The end disks 58 have a 152 mm outside diameter so that they fit within the PVC pipe 56. Each disk 58 has an opening at its center which is 35 mm in diameter to receive inner PVC tube 60. Inner tubular member 60 has a 35 mm outside diameter and a 29 mm inside diameter whereby its wall thickness is 3 mm.

With particular reference again to FIG. 2, the secondary winding 30 comprises copper arms 14 and 16 together with the conductive connecting cable 32. The primary winding 29 and the secondary winding 30 generally are coupled by the portion of stationary arm 16 which extends through core opening 42, adjacent the internal sections 48 of the primary winding. Preferably arms 14 and 16 each have a 20 mm .times.20 mm square cross-section. Indeed, due to the thickness of arms 14 and 16, stationary arm 16 provides the main supporting frame structure for the apparatus 10. Transformer core 28 and the primary winding 29 thus are supported on the stationary arm 16 which passes through the opening 42 in the core. Arm 14 moves about pivot point B. Conveniently, the arms can have a length of 550 mm. Conductive connecting cable 32 comprises 0.155 mm diameter copper wire wound to have a 200 mm.sup.2 cross-section This cable 32 is electrically connected to the copper arms 14 and 16, preferably by solder containing 90% tin and 10% lead to hold the copper arms about 100 mm apart.

The spot welding apparatus 10 constructed as described above in accordance with the present invention provides a potential difference of 2 volts between its electrodes 18 and 20 when 220 volt, 50 Hz input energy is applied through power cable 26. Spot welding apparatus 10 is contemplated to operate at power in the range of 0.5 kw to 10 kw. It is also contemplated that the apparatus is compatible for operation in a frequency range from about 50 Hz to about 400 Hz. When using the apparatus for spot welding, 1 kilowatt hour of electrical input energy at 220 V, 50 Hz has been found sufficient to weld approximately one thousand 2.times.3 mm spots. In the exemplary embodiment described above, a test for breakdown from the primary winding to the secondary winding gave satisfactory results at 6,000 volts. The spot welding apparatus 10 described in the foregoing can be implemented to have a total weight of about 22 kg.

In operation, metal work pieces to be welded together are placed between the two electrodes 18 and 20 and in contact with electrode 20. With the supply source on, the transformer creates a potential difference between electrodes 18 and 20. Electrode 18 is lowered into pressure contact with the work pieces in order to complete an electrical circuit producing current to weld the pieces together.

FIGS. 6 through 9 show other embodiments in accordance with the present invention. In the embodiments of FIGS. 6 through 9, the electrodes have been configured to accommodate different sizes and shapes of different work pieces. Otherwise, it is understood that a similar transformer structure, as disclosed in connection with the embodiment of FIGS. 1 and 2, is preferred for use in each of the embodiments of FIGS. 6 through 9.

In each of the embodiments of FIGS. 6 through 8, the movable and stationary arms protrude out of the body 12 for only a short distance and rather the electrodes are made longer. For instance, in the embodiment of FIG. 6, electrodes 118 and 120 comprise elongated, bent members 122 and 124. The embodiment of FIG. 6 also comprises a handle 120 provided with its case 12. Of course, such a handle 120 could be furnished with any of the embodiments disclosed herein.

In the embodiment of FIG. 7, the electrode 218 is provided with a vertical extending portion 222 to provide a larger throat 224. The widened throat 224 permits the electrodes 218 and 220 to receive a larger work piece. In the embodiment of FIG. 8, the welding throat 326 has been configured by electrodes 318 and 320 provided with parallel portions 322 and 324. It is thus understood that the welding throat and the location of the gap between the electrodes may be made to suit the particular requirements of different work pieces. In each of the embodiments, the electrodes may be bolted to the copper arms 14 and 16, or electrically connected thereto by other suitable means.

FIG. 9 shows a welding apparatus in accordance with the invention wherein the movable copper arm 44 and its associated electrode 48 are displaceable in the horizontal direction as represented by arrow E. Electrode 420 mounted on arm 416 is stationary. This electrode configuration accommodates insertion of the work piece in the vertical direction between the electrodes 418 and 420.

An arrangement 500 for providing a line welding apparatus in accordance with the present invention is depicted in FIG. 10 ;n the embodiment of FIG. 0, the transformer core 528 likewise is constructed in the manner described in connection with the embodiment of FIGS. 1 and 2 and as depicted in FIGS. 3 and 4. Arrangement 500 has a first rod member 502 which passes through the opening 504 in the toroidal core 528. Another rod 506 is electrically connected to rod 502 by means of elements 508 and 510 to form the single-turn secondary winding for the arrangement 500. Preferably, the rods 502 and 506 are made of copper, however, other conductor materials may be utilized.

Elements 508 and 510 are made of electrically conductive material and are maintained in contact with each other as the rods 502 and 506 are rotated. Elements 508 and 510 may be provided to have a toothed engagement. However, electrical contact between elements 508 and 510 could be maintained by any other conventional means.

Disk-like electrodes 512 and 514 are located at the free ends of rods 502 and 506. Electrodes 512 and 514 are spaced apart from each other by a gap 516 across which is created an electrical potential for effecting welding. Electrodes 512 and 514 are rotated by the rods 502 and 504 as illustrated by arrows F and G. As is understood, the work pieces to be linearly welded together are fed into the gap 516 between the electrodes 512 and 514. When contact is made between the work pieces and the electrodes 512 and 514, the work pieces move in the direction of rod rotation. As the work pieces advance between and in contact with the electrodes 512 and 514, the work pieces are linearly welded together.

While the invention has been described in conjunction with particular embodiments, various modifications may be made without departing from the scope of the invention as defined in the appended claims.