The invention relates to a heavy-current transformer (12), in particular for a power source (10) in order to provide a welding current of a resistance welding device (1), with at least one primary winding (13) and at least one secondary winding (14) with center tapping, and to a transformer element, a contact plate (29) and a secondary winding (14) for such a heavy-current transformer (12) as well as a method for the manufacturing thereof. For reduction of losses and improvement of efficiency, at least four contacts (20, 21, 22, 23) are provided to form a multi-point contacting, said contacts (20, 21, 22, 23) being formed by four contact faces within which the at least one primary winding (13) and the at least one secondary winding (14) are arranged in a series/parallel connection.

A resistance welding device includes a power source in order to provide a welding current for welding workpieces, a welding gun with two gun arms having one electrode each in order to impress the welding current into the workpieces. The power source includes a heavy-current transformer with at least one primary winding and at least one secondary winding with center tapping, a synchronous rectifier connected with the secondary winding and including circuit elements, and a circuit for actuating the circuit elements of the synchronous rectifier. For reduction of losses and improvement of efficiency, the power source is arranged at the welding gun and the power source includes at least four contacts forming a multi-point contacting, wherein two first contacts of one polarity are connected to one gun arm and two additional contacts of opposite polarity are connected to the other gun arm.

The present invention relates to a direct-contact type alternating current (AC) trapezoidal wave aluminum resistance welding process method. AC trapezoidal wave inverter controller capable of controlling a positive and negative half-wave current rising rate, and an AC transformer (no rectifier or silicon-controlled rectifier on a secondary coil of the transformer) with an output voltage of 10-30V, a peak current of 32-70 kiloampere and a frequency of 25-80 Hz are included. The inverter controller and the AC transformer are connected by means of a conductor, a welding electrode, a pressurization mechanism and a cooling system to form resistance welding equipment to enable the equipment to output positive and negative alternating trapezoidal wave current on two sides of the electrode when a workpiece is pressurized and welded and to perform welding according to a specified duty ratio, welding current, frequencies, welding cycle number and welding pressure. Practice proves that the method has the advantages that 50-150 welding spots can be welded while grinding the electrode once each time, service life of the electrode is prolonged by 2-5 times, production efficiency and welding quality are greatly improved, and production cost is reduced, thereby realizing a qualitative leap in aluminum and aluminum alloy resistance welding processes.

A spot welding method is a method of performing spot welding to obtain a spot welded joint, the method including a spot welding with two-stage welding, setting a ratio (I.sub.2/I.sub.1) of a current I.sub.2 of a second welding process to a current I.sub.1 of a first welding process to from 0.5 to 0.8, setting a time tc of a cooling process within a range of from 0.8tmin to 2.5tmin wherein tmin is calculated using the equation (0.2H.sup.2) according to a sheet thickness H of the steel sheets, setting an welding time t2 of a second welding process within a range of from 0.7tmin to 2.5tmin, and setting a pressure from the cooling process onward to greater than a pressure until the first welding process.

Methods and systems for resistance spot welding using direct current micro pulses are described. One described method comprises comprising forming a weld joint by applying a plurality of direct current micro pulses to at least two pieces of materials through a first electrode and a second electrode.

A joining device for connecting a metal member and a resign member with a metal fastener including a penetrating tip comprises: a cylindrical nosepiece; a high frequency electromagnetic induction coil around the nosepiece; an electrode punch for pressing the fastener into the resign member; a electronic chopper for producing a high frequency current; a high frequency power supply for supplying an induction current to the induction coil; a welding power supply for supplying a welding current between the electrode punch and the metal member; a contact detector for sensing when the fastener tip touches the metal member; and a switching unit for automatically switching from the induction current to the welding current when the contact detector senses that the tip has contacted the metal member.

When two high-strength steel sheets (1A, 1B) whose sheet thickness ratio={the sum of sheet thicknesses of the steel sheets}/{the sheet thickness of the thinner steel sheet (when they have the same thickness, the sheet thickness per one sheet)} is within a range of not less than 2 nor more than 5 and which both have tensile strength of not less than 780 MPa nor more than 1850 MPa are stacked to be subjected to resistance spot welding, a first welding step being pre-welding with a pressurizing force P1 kN and a welding current I1 kA and a second welding step being main welding with a pressurizing force P2 kN and a welding current I2 kA are performed, the pressurizing forces P1, P2 are set to a fixed pressurizing force P=P1=P2 all through the first welding step and the second welding step and are set within a range expressed by {0.5P3.0t.sup.(1/3)}, where t mm is an average sheet thickness of the steel sheets (1A, 1B), the welding current I1 is set within a range of not less than 30% nor more than 90% of the welding current I2, and the second welding step is started within 0.1 s after the first welding step is finished.

Device (1) for the provision of electric power, wherein the device (1) comprises: at least one integrated temperature sensor (3-1, 3-2) which detects an operating temperature progression of at least one component (2-1, 2-2) of the device (1) and a monitoring unit (5) which, on the basis of the at least one detected operating temperature progression and the adjusted power, monitors the operating state of a device cooling arrangement of the device (1).

To provide a method and apparatus for manufacturing a joined member that inhibit occurrence of cracks in a joined member even when the joined portion is quenched when members are welded together. The method includes placing the first member D and the second member E with a joint target portion Df and a joint target portion Ef being in contact with each other, welding the joint target portions by heating, subjecting the first member D after the welding to a process for inhibiting occurrence of cracks, and tempering a portion where the first and second members have been welded to each other by electromagnetic heating. The apparatus includes a first electrode 11 to contact with the first member D; a second electrode 12 to contact with the second member E; and an induction heating coil 23 for performing induction heating of a portion where a joint target portions Df and Ef have been contacted and joined to each other, and the induction heating coil 23 is placed between the two electrodes 11 and 12 when the induction heating is performed.

A resistance welder may include a power input. A resistance welder may include a welding lead. A resistance welder may include a plurality of waveform modulators connected to the power input and the welding lead, each of the plurality of waveform modulators configured to receive input power from the power input and convert the input power into a welding output at the welding lead.