Abstract: In a short circuiting arc welding apparatus and method wherein a continuously fed welding wire alternates between an arcing condition during which the wire is spaced from the molten pool of the workpiece and a short circuit condition during which the melted metal on the end of the welding wire is in contact with the molten metal pool and thereafter transfers to the workpiece by a necking action breaking the melted metal from the wire, there is provided an improvement including providing a first high inductance current control circuit for continuously directing a low level, arc sustaining, background current between the welding wire and the workpiece and providing a second current control circuit for controlling current flow during the arcing condition of the process.

Abstract: An improved electronic welding station is disclosed. The welding station provides for an improved arc striking capability by providing a higher arc striking voltage and a large arc striking current and, once the arc is struck, automatically switches over to preselected parameters for conducting the welding operation. Also disclosed are a method for preventing transistor failure due to loads which tend to cause a very large instantaneous current flow and an apparatus for protecting the driver circuit and the remaining output transistors in the event that one of the output transistors should suffer a collector-to-base short. The welding station also describes a method of operating the cooling fan at a speed commensurate with the cooling requirements and periodically reversing the voltage to the cooling fan so as to extend the operating lifetime of the fan brushes.

Abstract: A power supply system for consumable electrode arc welding alternately switches between the reverse polarity and the straight polarity. The formation of an arc is detected. A polarity change control signal is generated when the arc duration reaches a predetermined time or when the quantity of charge reaches a predetermined value. The predetermined value of the welding current or voltage is reduced either immediately before or after the change in polarity.

Abstract: A pulse type arc welder with improved arc starting characteristics. An output voltage level sensor (2017) monitors the output voltage to determine whether the arc has been struck. If the arc has not been struck, a first oscillator (2000) gates a second, higher frequency oscillator (2002) so that the input to the driver (2010) is a chopped, pulsed, high duty cycle waveform. Also, the bandwidth of the output current level sensor (2012) is reduced so that the high value, short lived arc starting transient current does not cause the output current level sensor (2012) to improperly shut down the driver (2010). Additional current limiting protection is provided during this period since the high chopping frequency causes the reactor (2010a) to have a high impedance. After the arc has been struck, the output voltage will drop to the arc sustaining voltage and the output voltage level sensor (2017) will de-energize relay (2003).

Abstract: Apparatus and method to reduce spatter and allow better semi-automatic welding in short circuiting arc welding of the type using a single D.C. power supply for causing a welding current to pass through a welding wire extending variable distances from a holder and between the welding wire and a workpiece at a molten metal pool on the workpiece. The welding current flows in response to an arc voltage while the welding wire is fed from the holder toward the workpiece whereby the welding wire is subjected to a succession of welding cycles each of which include an arcing condition during which the wire is spaced from the pool and a short circuit condition during which a molten metal ball formed on the end of the wire contacts the metal pool and then transfers from the wire to the workpiece by a necking action.

Abstract: A method and apparatus for TIG welding by passing an alternating current between a non-consumable electrode and a workpiece to form an arc, which apparatus comprises a single reactor, passing a direct current from a direct current power supply through a first portion of the reactor and in a negative direction from the workpiece to the electrode for creating a heating cycle, switchably disconnecting the direct current power supply from the circuit and immediately connecting the second portion of the reactor in a positive direction across the electrode and workpiece for creating a short cleaning cycle for cleaning the workpiece preparatory to the next heating cycle. These cycles are continued to create a TIG welding process.

Abstract: The weldability of a part formed from an alloy having low impurity concentrations is determined by initiating an arc between a stationary welding torch and the part using a predetermined set of welding parameters selected to produce a partially penetrating molten weld pool. The natural frequency of oscillation of the molten weld pool is measured a predetermined time following initiation of the arc, and the measured natural frequency of oscillation is compared to empirically determined data for the alloy to determine the weldability of the particular part. Variations in trace element concentrations between different heats of the same alloy affect the three-dimensional geometry of the molten weld pool, and in turn affect its resonant frequency. The invention may be used to adjust the welding parameters to accommodate differences in weldability between different heats of the same alloy.

Abstract: An electrical power supply used on a motor vehicle is interconnected with the vehicle battery, alternator and regulator. The power supply includes a voltage multiplier for multiplying the rectified output voltage from the alternator, and welding sockets for facilitating a welding operation. A multi-pole switch exclusively selects the operating mode of the power supply from among normal battery charging, power appliance operation and welding.

Abstract: A method and device for controlling a power supply for arc welding in a manner to reduce spatter when the power supply is employed for depositing metal from a welding wire or electrode onto a workpiece by the short circuiting transfer mode wherein a welding current causes the welding wire to alternate between a short circuit condition and an arc condition with metal transfer occurring during a short circuit condition. This method and device includes the concept of shifting the welding current to a background current value in response to a short circuit condition, holding the welding current generally at the background current level for a preselected time, then allowing the welding current to reach the normal unimpeded current level, and causing the holding step to be terminated before the selected time in response to a detected arc condition.

Abstract: The heat input and mass input in a Gas Metal Arc welding process are controlled by a method that comprises calculating appropriate values for weld speed, filler wire feed rate and an expected value for the welding current by algorithmic function means, applying such values for weld speed and filler wire feed rate to the welding process, measuring the welding current, comparing the measured current to the calculated current, using said comparison to calculate corrections for the weld speed and filler wire feed rate, and applying corrections.

Abstract: An automatic arc-welding method, which comprises when welding two objects to be welded together by means of a welding wire along a groove formed between the objects to be welded, continuously detemrining by calculation a target welding current, with which a depth of penetration agrees with a target value thereof, on the basis of the root gap, the material of the welding wire and the like; continuously determining by calculation a target feeding rate of the welding wire, at which an extension length of the welding wire agrees with a target value thereof, on the basis of the welding current, the material of the welding wire and the like; continuously determining by calculation a target welding voltage, with which a length of the arc agrees with a target value thereof, on the basis of the welding current, the feeding rate of the welding wire, the material of the welding wire and the like; and automatically controlling the welding current, the feeding rate of the welding wire and the welding voltage on the basis

Abstract: An automatic arc-welding method, which comprises, when welding two objects to be welded together by means of a welding wire along a first groove formed between the objects to be welded on a first side thereof, continuously determining by calculation a target welding current, with which a depth of penetration agrees with a target value thereof, on the basis of the root gap, the material of the welding wire and the like; continuously determining by calculation a target feeding rate of the welding wire, at which an extension length of the welding wire agrees with a target value thereof, on the basis of the welding current, the material of the welding wire and the like; continuously determining by calculation a target welding speed, at which a height of the weld bead agrees with a target value thereof, on the basis of the feeding rate of the welding wire, the material of the welding wire, the root gap and the like; and on the other hand, when welding the objects to be welded together by means of the welding wire

Abstract: An automatic arc-welding method, which comprises, when welding two objects to be welded together by means of a welding wire along a groove formed between the objects to be welded, continuously determining by calculation a target welding current, with which a depth of penetration agrees with a target value thereof, on the basis of the root gap, the material of the welding wire and the like; continuously determining by calculation a target feeding rate of the welding wire, at which an extension length of the welding wire agrees with a target value thereof, on the basis of the welding current, the material of the welding wire and the like; and continuously determining by calculation a target welding speed, at which a height of the weld bead agrees with a target value thereof, on the basis of the feeding rate of the welding wire, the material of the welding wire, the root gap and the like; thereby automatically controlling the welding current, the feeding rate of the welding wire and the welding speed on the basi

Abstract: The invention provides a gas-shielded arc welding system using two side-by-side electrodes each of which is provided with current pulses superimposed on a respective background current level to maintain the desired controlled spray transfer mode of the weld metal without overheating effects. The pulses are supplied to the two arcs out of phase with one another to minimize interaction of their magnetic fields, but this alone is not sufficient to assure stability of the two arcs. In the system of the invention, one arc is designated as the master arc and the other as the slave arc. The master arc is stabilized by means of a feedback loop controlling its master pulse frequency. Each master pulse triggers a respective slave pulse after a preset time delay, in this way keeping corresponding master and slave pulses in synchronism.

Abstract: A method and an apparatus for controlling the hot-wire welding process is disclosed in which the heating power for a hot-wire is automatically regulated to a proper value. The wire-heating power after fusing of a filler wire by being overheated is set to a level lower than the heating power immediately before wire fusing, and the wire-heating power is again increased gradually from the set value until the wire is fused by being overheated. By repeating this process, the molten state of the filler wire in the hot-wire TIG welding is automatically kept in optimum condition without requiring any operation of the welding operator or his intuition.

Abstract: An improved welding system is shown. A single high capacity power supply (10) provides operating power for several weld selector stations (16). Each weld selector station (16) operates independently, is adjustable, and allows a welder to obtain the voltage and current characteristics desired for his particular welding operation. Each weld selector station (16) operates over a wide range of input voltages so that long runs of low-voltage interconnecting cable (14,15) can be used without adversely affecting the quality of the weld. Furthermore, the weld selector station (16) is small, lightweight and easily transportable. The result is a more efficient, less expensive, versatile welding system.

Abstract: A high frequency arc stabilizing circuit includes a free running oscillator for generating a non-synchronized square wave. An output from the oscillator is buffered and inverted. The asserted and inverted outputs drive field effect transistors coupled to the primary of a high voltage step-up transformer. The circuit can also be gated so as to only operate during selected time intervals.

Abstract: A method and apparatus for real-time determination of weld quality. A collimated light source 10 directs a beam 16 of collimated light to a point on the weld pool surface 24. A position sensor 34 measures the direction of the light after it is specularly reflected from the weld pool surface 24. Electronic means 36,38,40 analyze this measurement for determining changes in angles of the weld pool surface 24 for real-time indication of the state of penetration of the weld pool 26.

Abstract: The present arrangement comprises a welding current generator for the generation of a d.c. portion of the desired welding current, as well as a pulse current source, the output circuits of which are connected in parallel with one another to the output terminals of the arrangement. The pulse current source is of the type having a high-frequency transformer in association with control means connected at the primary side thereof and delivers current pulses from a series of high-frequency pulses with a high no-load peak voltage. This enables pulsed welding currents to be generated in an extremely economical way by the employment of existing d.c. welding generators together with small, relatively low-cost additional equipment.

Abstract: Metal deposition rate is increased with reduced energy input in pulsed arc welding with a consumable electrode and a shielding gas mixture of argon, helium and carbon dioxide, the helium content being in the range from about 16% to about 25% and the carbon dioxide content being from about 1% to 4%. The component gases are stored in separate containers until the welding operation during which precisely metered flows of each are entrained by a metering valve and directed to the weld region. Consistently finished welds are produced, on stainless steel, low alloy steels and nickel based alloys as well as other weldable ferrous metals, including during out of position welding operations.

Abstract: A welding system with an electronic control includes four switching elements coupled together to form a bridge. An inductor with a center tap is located between two legs of the bridge. A load, including an output electrode and the metal parts being welded, is coupled between the center tap of the inductor and the other two branches of the bridge. Two of the switching elements are turned on and off at a relatively high rate to control the power to the load. The other two are turned on and off at a relatively low rate to control the duty cycle and polarity of the load voltage and current.

Abstract: In order to maintain the degree of filling of weld seams constant, especially those seams having a changing size of the cross section of the weld groove, in arc welding, the spacing of the welding gun from the workpiece is kept constant, the welding amperage and/or the welding voltage are measured, and the thus-measured value for the welding amperage or the welding voltage, respectively, is compared with a predetermined set value corresponding to the desired degree of filling. In case of a deviation of the measured value from the predetermined set value, the welding speed and/or the welding output are changed correspondingly.

Abstract: A method of controlling a welding operation during arc welding between a fusible electrode and a workpiece, wherein the welding operation alternates between arc periods and short-circuiting periods, includes the steps of sensing a first parameter of the welding operation, for example the arc voltage between the electrode and the workpiece, generating a first signal representative of the first parameter, sensing a second parameter of the welding operation, generating a second signal representative of the second parameter, filtering the second signal to provide a filtered signal, generating a desired value signal based upon the filtered signal and controlling the welding operation based upon the difference between the desired value signal and the first signal.

Abstract: A method and device for controlling a power supply for arc welding in a manner to reduce spatter when the power supply is employed for depositing metal from a welding wire or electrode onto a workpiece by the short circuiting transfer mode wherein a welding current causes the welding wire to alternate between a short circuit condition and an arc condition with metal transfer occurring during a short circuit condition. This method and device includes the concept of shifting the welding current to a background current value in response to a short circuit condition, holding the welding current generally at the background current level for a preselected time, then allowing the welding current to reach the normal unimpeded current level, and causing the holding step to be terminated before the selected time in response to a detected arc condition.

Abstract: An improved welding system is shown. A single high capacity power supply (10) provides operating power for several weld selector stations (16). Each weld selector station (16) operates independently, is adjustable, and allows a welder to obtain the voltage and current characteristics desired for his particular welding operation. Each weld selector station (16) operates over a wide range of input voltages so that long runs of low-voltage interconnecting cable (14,15) can be used without adversely affecting the quality of the weld. Furthermore, the weld selector station (16) is small, lightweight and easily transportable. The result is a more efficient, less expensive, versatile welding system.

Abstract: An arc welder designed to receive its principal source of power from a vehicle's alternator which is controlled by a special controlled battery charger. This welder has a 36 volt battery system that is used as a supplement power supply. The principal power source only can be used in welding or the supplement power supply can be used in welding or both principal power source and the supplement power supply can be combined at the work load in welding, and during the time when the arc is not generated the battery system is being re-charged. Inductors and a switching system are used to control the current flow from the battery system to the work load in welding. Also, the battery system can be used direct for heavy duty cutting and/or for extra-heavy duty welding thus giving the operator an extremely wide range of current to fit his needs.

Abstract: An apparatus for a-c welding with a consumable electrode has a welding transformer having a secondary winding connected to an electrode gap and two pulse generators. Each pulse generator has a power circuit connected in parallel with the electrode gap and consisting of a series circuit including a thyristor switch, a power supply winding and a switched capacitor, and a unit for controlling the thyristor switch. Each control unit has a zero detector and a control pulse former, the zero detector of the control unit of the first pulse generator being connected in parallel with the electrode gap, and the zero detector of the control unit of the second pulse generator being connected in parallel with the switched capacitor of the first pulse generator.

Abstract: A welding machine for pulsed arc welding provided with a constant voltage source and having at least one transistor included in the welding circuit, and a pluse generator providing adjustable pulse duration and sequence frequency to provide pulsed arc.

Abstract: An electrical apparatus for regulating voltage polarity including a support for slidably receiving one or more carriers therein, with each carrier including circuitry. A positive and negative source of power is associated with the apparatus and each of the carriers includes connector means for coupling each carrier to the positive source of power when the carrier is in a first position, and for coupling each carrier to the negative source of power when the carrier is in a second position. In a preferred embodiment of the invention means are provided for preventing either intentional or accidental movement of the carriers from one of the first and second positions to the other position during operation of the carriers. Preferably a bridging connector is provided for coupling the circuitry of adjacent carriers to each other when the carriers are in a first position coupled to the positive source of power.

Abstract: An improved non-contact type arc starter for a welding apparatus is disclosed. A diode (25) is reversed biased when a high output DC voltage is provided by a power supply (26). When the arc is struck, the diode becomes forward biased allowing arc current to flow. The striking of the arc is detected by the dropping out of a relay coil (60) which in turn closes a contact set activating a solenoid coil (65). The solenoid coil (65) is part of a contactor having contact set (32) which closes, shunting the diode. This prevents the diode from carrying full welding current for more than several hundred milliseconds maintaining the junction temperature of the diode at a low value and allowing immediate restart after the arc is extinguished.

Abstract: An arc welding power source utilizing welding current from a two-step voltage conversion comprising a first target value setting circuit means for setting a first current target value V.sub.1 corresponding to a desired value of welding current, a current control circuit for controlling the welding current in accordance with the first current target value V.sub.1, a second target value setting circuit means for setting a second current target value V.sub.2 higher than the first current target value for satisfying a predetermined current waveform in response to an abrupt load variation, and a rapid operation current control circuit for controlling the welding current in accordance with the second current target value V.sub.2. Thus, even if the welding load tends to abruptly vary and the welding current tends to largely exceed the first current target value V.sub.1, the welding current is clipped by the second current target value V.sub.

Abstract: A shut-down control for a welding carriage supporting an arc welding gun automatically shuts down the gun after the carriage has stopped moving along a weld plate for a timing interval but before the continuously welding gun injures the plate.

Abstract: A consumable electrode type pulse arc welding machine is provided with means for controlling a welding output of the welding machine and the control means comprises a short-circuiting detector circuit for detecting the number of times of short-circuiting n occurring between an electrode wire and a weld part of a base metal at predetermined time intervals during a welding operation, a processing unit for calculating n.sub.d =n.sub.s -n, where n.sub.s is a preset number of short-circuiting times, and a control means for controlling a welding output of the welding machine by decreasing the welding arc voltage in accordance with the magnitude of n.sub.d, when n.sub.d is larger than zero, and by increasing the welding arc voltage in accordance with the magnitude of .vertline.n.sub.d .vertline., when n.sub.d is smaller than zero.

Abstract: A hot wire TIG welding apparatus has a current detector for detecting the peak period and base period of the arc current. The welding apparatus further has a controller which controls, in response to the detection signal from the current detector, the operation of the wire heating power supply such that the wire heating power is supplied only during the base period of the arc current. According to this arrangement, a hot wire switching TIG welding apparatus can be produced using commercially available power supply systems for TIG arc welders, without requiring substantial change or modification of the control circuits in the TIG arc welders.

Abstract: A method and apparatus for arc welding particularly regarding a pulse arc welding machine comprising a welding power source having an output characteristic control circuit, an overload protection circuit, a driving circuit, and a main power circuit, and a wire feeding unit having a wire feeding control circuit, a motor driving circuit and a wire feed motor. The output characteristic control circuit comprises a welding arc autoregulating control system which provides the power source with a multi-segmental and moving output characteristic with varying slope, a circuit for connecting arbitrary number of output characteristic segments with arbitrary or varying slope, and a scanning circuit for obtaining the output characteristic segment with varying slope. A particular use of the control system is in an easy to operate autoregulating controlled GMA welding machine with one-knob control of wire feed rate without having to adjust the other welding parameters.

Abstract: A method of pulsed arc welding and an apparatus for carrying out the method, employ welding current pulses having an amplitude greater than the value of a background current. The arc voltage is sensed to provide a signal for controlling the frequency of the welding current pulses to counteract variations in electrode wire feed speed or spacing of the electrode from the workpiece.

Abstract: Shielded arc welding apparatus advances a consumable electrode towards a workpiece; applies a welding voltage between the electrode and the workpiece; and applies an auxiliary voltage between the electrode and the workpiece, whereby the auxiliary voltage initiates an arc between the electrode and the workpiece before the electrode engages the workpiece.

Abstract: A hot-wire TIG welding apparatus capable of performing a stable welding regardless of change in the welding conditions. The welding apparatus comprises a hot-wire feed speed control means for controlling the speed of feed of a hot wire, and a heating power control means adapted to control the electric power for heating the hot wire. The condition of the control in either one of the control sections is changed in accordance with a change in the control condition of the other.

Abstract: A robotic arc welding system has an integrated vision sensor to image and analyze the weld scene in real time. The most effective weld puddle geometry discriminants for use in an adaptive feedback control, to assure full penetration welds, are weld puddle area and maximum width. The adaptive control system determines a puddle geometry error and a correction to nominal welding current to change the heat input to the weld pool, regulating a combination of puddle area and width, or only puddle area under some welding conditions, to control weld quality during the welding process. Arc voltage is modulated to reflect changes in welding current and maintain constant arc length.

Abstract: An improved welding power supply control circuit is disclosed. The control circuit, which incorporates a microprocessor, simultaneously adjusts the power supplied to a welding electrode and the speed of the electrode, in accordance with a selected power/speed relationship table or curve. The power/speed relationship of a selected table can be further modified manually, as by a potentiometer, to optimize the weld. Feedback circuitry senses the frequency of the weld and the weld voltage, to regulate the power and to modify the slope of the voltage/current output curve, respectively.

Abstract: A process for maintaining weld quality during welding operation, marking the fault spots on the workpiece and certifying of quality, in the course of which instantaneous values of arc current and arc voltage characterizing manual or mechanized welding process are continuously measured and from the values thus obtained relative short-circuit time of the arc, drop frequency and arc outputs are continuously calculated.The measured and calculated values are compared with empirically determined optimal values, thus defining absolute values and signals representing the directions of deviations, as well as duration of deviations, are compared on a predetermined span of time and averages of absolute values and signals representing the directions are defined.

Abstract: Video data generated at a high rate by a camera observing a welding operation is selectively stored in a video-computer interface to permit later computer analysis of the data. Special multiple memory techniques can be employed when the rate of which the data is generated is too fast for storage in a single memory in the interface. The width of the weld pool is detected by finding local minima of light intensity associated with these edges. The mass of the weld pool and the weld penetration can be measured and controlled by causing oscillations in the weld pool and measuring the natural frequency of such oscillations. The weld line can be tracked either by bouncing a beam of light off the welding electrode so as to form an illuminated area and detecting the resulting irregularity where the illuminated area crosses the weld line, or by detecting the deformation in the surface of the weld pool as the pool flows into the gap between the metal portions being joined.

Abstract: A pulse arc welding machine in which the welding operations and welding current are controlled such that the molten portion of a wire electrode is not significantly splattered and the welding arc length and welding bead are uniform. The welding machine of the invention includes a wire electrode, a welding torch confronting a base material while being spaced therefrom, a shielding gas supplying unit for supplying a shielding gas to the welding area on the base material, and a wire feeding unit for feeding the wire electrode to the welding torch. A base current source supplies a base current between the wire electrode and base material with a pulse current from a pulse current source being imposed thereon. A pulse frequency varying circuit varies a number of pulses per unit time for the pulse current so that the number of pulses is proportional to the speed at which the wire electrode is fed thereby to set the average arc current.

Abstract: An arc welder, designed to receive its source of power from a vehicle's alternator through a special controlled battery charger. The first portion of energy used in welding comes from the vehicle's battery charger and the balance of energy used in welding comes from the welder's battery pack. Between spurts of actual welding, the welder's batteries are re-charged by the vehicle's special controlled battery charger. The batteries in said battery pack are so arranged as to give the operator a choice of voltage for welding and inductors are used to control the current. Also, the batteries can be used direct by by-passing said inductors for extra-heavy cutting and/or extra-heavy duty welding thus giving the operator an extremely wide range of current to fit his needs.

Abstract: A device for arc welding having one or more fusible electrodes (15) which are in each case supplied from an alternating-current source (14) having a falling characteristic. The feed rate of the electrode (15) is regulated for constant arc length as a function of the arc voltage. Via a further regulator (37), the deposition efficiency is regulated by supplying the regulator (37) with the feed rate as actual value and changing the welding-current intensity as a function of this value. The change in welding-current intensity leads to an increase or decrease in arc length which, in turn, is compensated via the first regulator by changing the feed rate.

Abstract: A plasma arc system for plasma arc welding and cutting including a plasma arc torch in circuit with a constant current power supply comprising a transformer having a primary winding and at least one secondary winding with the primary winding connected to a source of alternating current and a bridge rectifier circuit connected across the secondary winding to provide a DC current output. A bank of capacitors is connected across the secondary winding of the transformer with its capacitive reactance matched to the inductive reactance of the transformer to establish a condition of resonance.

Abstract: A transformer with a rectifier is disclosed, wherein a transformer main body, having therein a primary coil and a secondary coil, is provided at its front surface with a secondary electrode plate connected to the secondary coil, and to secondary electrode plate is connected at its front surface to a terminal plate through a rectifier, and the two plates are fastened together by means of bolts, or the like, characterized in that the rectifier is formed of a semiconductor element comprising a semiconductor layer of silicon, or the like, having front and rear holding plates of molybdenum, or the like, the semiconductor element is held between metallic plated layers of gold, silver or the like previously formed on mutually facing inner surfaces of the two plates, and a frame seal member made of silicon rubber or the like surrounding the element is held between the two plates.

Abstract: Power sources for welding applications and the like are provided in accordance with the teachings of the present invention. An inverter arrangement comprising a plurality of inverters, having inputs connected in series, receive portions of a d.c. load from a plurality of series connected smoothing capacitors. The smoothing capacitors are connected to form a voltage divider and apply the resulting portions of the d.c. load to the plurality of inverters. This enables the plurality of inverters to be dimensioned in a manner so as to withstand the smaller portions of the d.c. load resulting from the voltage division.

Abstract: A consumable electrode type arc welding apparatus in which arcing can be positively started under a variety of welding conditions. A start current detector selects a predetermined limited start current according to the welding conditions. A start current period setting unit sets a start current period, also in accordance with the welding conditions. A start current control circuit supplies the predetermined limited start current to the workpiece and the wire electrode for the predetermined period of time at the start of arcing.

Abstract: A short circuiting arc welding machine increases an arc current density by adding a pulsed current having upper and lower limits to a current flowing when an arc is produced, thereby increasing the depth of bead penetration into a workpiece, removing welding defects, and speeding up the welding operation. The welding machine is capable of alternately changing the direction of flow of a welding current at desired periods to produce arcs in straight, reverse and mixed polarities for achieving intermediate characteristics of arcs of straight and reverse polarities, with a resultant ability to adjust in a wide range a wire melting rate and the amount of heat applied to the workpiece.