Device and process for short circuit arc welding.

This invention relates to arc welding using a consumable electrode, and more particularly to an improved apparatus and method for short circuit arc welding using a single DC power source that produces a variable current welding current through a welding wire and a molten metal spot to a workpiece at a distance from the holder includes an arc phase, during which the energy applied to the wire melts the wire end into a molten weld metal ball, and a short-circuiting step during which this molten metal ball contacts the molten metal spot and then shrinks into a droplet and moves off, after which the arc ignites to start the next welding cycle.

The present invention relates to an improvement to a splash control system of the same general type as described in Applicant's earlier U.S. Patent No. 4,717,807 and U.S. Patent No. 4,020,320.

Recent years have seen considerable effort to improve short circuit arc welding by controlling the welding current and / or arc voltage during various portions of the welding cycle that include a short circuit state followed by an arc state. The molten metal ball formed at the end of the moving welding wire during the short-circuit condition contacts the molten metal pool of the workpiece, causing a large current to flow through the wear welding wire and the molten metal ball. This short-circuit condition is terminated by an electrical constriction function, which causes the metal forming the molten sphere of the wire to shrink electrically and then break away from the welding wire by an explosion type. by an event often referred to as melting. The control of the current flow during the short-circuit part of the welding cycle is implemented by the power supply control circuit. In addition, an advance warning circuit is usually arranged so that dv / dt is specified

An increase in C30 indicates an impending formation of melting. As a result, the welding current can be dropped to its basic level I_B or lower immediately before melting occurs. In this way, the melting energy during each welding cycle is substantially reduced. This reduces splashing at the end of the short circuit condition. To control the current flow during the short circuit portion or state of the welding cycle, various circuits are known in the art as splash control circuits because melting is considered to be the main cause of cracking in short circuit10 arc welding. The applicant's two co-pending applications, which are incorporated by this reference, identified other dynamic factors that produce bursts in the welding process and prevent or modify them with different control principles. One way developed by the applicant was to provide a mouth energy pulse followed by a short time delay after melting so that the arcing state following melting can be initiated by a high energy current pulse, sometimes referred to as a plasma acceleration pulse. By using a high-energy plasma acceleration current pulse immediately after the start of the arc space of the welding cycle, melting by anode heating towards the molten metal pool of the workpiece at the end of the fed welding wire increased rapidly. This rapid melting allowed a molten metal ball to form at the end of the wire in a uniform size, which then moved toward the pool of molten metal as the wire was fed toward the workpiece. After the plasma acceleration pulse of the current, the ground current I was fed through the arc_Bto maintain the molten state of the molten ball. By controlling the current and using a fixed plasma acceleration pulse, the energy of the plasma acceleration pulse was controlled. The end of the wire melted to form a molten metal ball of approximately uniform size based on the amount of energy introduced during the accelerated current pulse of power. The arc was then operated at base current to maintain the melt state until a short circuit occurred.

Utilizing these prior principles, which have indeed substantially reduced spatter, the constant voltage control circuit during the plasma acceleration pulse caused a large current to flow during the pulse. This tended to drive the pond away from the front of the inwardly moving molten metal ball. In the event that the pond is displaced by the energy of the arc, a small contact may occur at a point spaced from the center of the arc. This short circuit during the plasma acceleration pulse caused a relatively large burst. Thus, applying a constant voltage to the power acceleration current pulse produced a large current that drove the pond away from the front of the ball, which, due to fluid dynamics, sometimes tended to cause a ripple effect that results in momentary short circuits. To overcome this difficulty, it has been proposed to use a variable voltage power control circuit to maintain a constant current during the plasma acceleration current pulse. This principle increased the frequency of random short circuits during arc mode, but each short circuit had less energy to discharge. The principle of variable voltage to provide a constant current state allowed for lower-energy momentary short circuits. In summary, using constant current or constant voltage during the power acceleration period either increased the frequency of instantaneous short-circuits during arc mode or their severity.

Using plasma acceleration pulses with a fixed time, a different amount of energy was introduced into the molten metal ball as the protrusion of the wear electrode or welding wire varied. Thus, · prior systems using a fixed • · · · time in the plasma acceleration current pulse can be used in automatic welding; however, in semi-automatic welding, where manual operation changes the elongation, a difficulty arises: 30 s. The plasma acceleration current pulse sometimes does not generate enough • · · heating at the end of the wire to melt it. This ai ·, throws articles. In addition, the duration of the welding cycle was not constant for long periods of time due to significant variations in the onset of the short-circuit mode of the individual cycles.

U.S. Pat. No. 4,546,234 describes a method for adjusting electrode power. The reference describes the repetition of a welding cycle consisting of a first step of maintaining a relatively low welding current before generating a short circuit between the wear electrode and the workpiece; a second step of maintaining a relatively high welding current value after the first step; a third step of lowering the welding current to a low value upon detecting a constriction, thereby predicting the rupture of the short-circuiting molten metal between the electrode and the workpiece; a fourth step of generating an arc in the gap between the electrode and the workpiece, thereby maintaining the welding current at a relatively high level that exceeds the average welding current; and a fifth step of keeping the welding current at a relatively low value until the gap between the electrode and the workpiece is short-circuited using constant current characteristics to obtain a relatively constant current independent of variations in the length of the light arc. EP-324 960 describes short-circuit arc welding, in which arc conditions and short-circuit conditions are alternately applied to a continuously fed welding wire so that a molten metal ball at the end of the welding wire contacts the workpiece during the short-circuit phase and then moves to the workpiece due to constriction. GB-2 021 816 describes a current which increases up to the point where the molten spot differs from the wire, after which the current falls to a relatively fixed plane, which is referred to as between arcs. The publication describes me^; ; between the electrode and the metal workpiece • · ·^:.· ^: the current flowing is limited for a while, but only after the arc. None of the procedures described in these publications apply to arc control in such a way that; 3 0 differences caused by varying protrusion of the welding wire • · *_;"I". head heating and melting should be compensated and «

\ that the spatter during welding is clearly reduced compared to the previous one · · · ·; ··.

The present invention relates to an improvement in short-circuited arc welding, which results in a substantially constant time during the welding cycle, reduces spatter and automatic compensation of the variable elongation or machine during semi-automatic welding in the short-circuit mode.

The disadvantages described above are eliminated and the defined objectives are realized by a device according to the invention characterized by what is defined in the characterizing part of claim 1 and by a method according to the invention characterized by what is defined in the characterizing part of claim 15. In summary of the various features of the invention, the subject is a welding current followed by a contraction step in which the welding current has a controlled level and which is divided into an acceleration portion and a subsequent plasma portion. The two sections have different controlled levels, which is made possible in the arrangement of the invention by using a series of fast current pulses, whereby the desired profiles of the fixed acceleration section and the plasma section of varying duration can be closely monitored. Together, these two portions form a melt current pulse that applies a certain energy to the end of the protruding electrode to form a molten metal ball that is exactly the same size in each successive welding cycle. Furthermore, the invention provides a fixed constant energy supply during the arc phase in each welding cycle by supplying a preset energy to the welding wire which exceeds a predetermined amount thereof; : the energy value required to melt the end of the wire • »«^J, · · During the selected section of each arc phase, which compensates for the varying protrusion of the wire. This substantially reduces spatter, especially in semi-automatic welding ai; 3 0 chicken.

Thus, in the improved device according to the invention, • · · * ·· is used.^Σ a direct current power supply to cause different levels of welding currents to pass through the welding wire projecting alternately; 35 from the core of the electrode and the wire and the workpiece ·,; to the molten metal pond in the workpiece. The current flowing during the welding process is in response to the voltage between the holder and the workpiece. The apparatus has means for introducing a preselected energy into the welding wire during a selected portion of each arc space of the welding cycle, wherein the preselected energy exceeds a given energy value required to melt the wire end to prepare a molten metal ball of a desired size. The selected portion of each arc state at which the constant energy is applied is a fixed acceleration current pulse of time and, in addition, a plasma current pulse. This plasma pulse terminates at a set time (constant time) to generate energy in the wire during the plasma acceleration of the welding cycle and the subsequent plasma portion. Thus, during each welding cycle, a selected constant energy is applied to the wire to heat the wire during each cycle. Such heating of the wire is divided into resistance heating, which causes the current to flow through the wire from the holder to the end of the wire, and anode heating at the end of the wire under the influence of the arc current. Such anode heating provides most of the heating energy that is introduced into the wire during each welding cycle. As the elongation or protrusion increases, the greater part of the heating per cycle is the resistance heating caused by the current flowing through the welding wire. By using a fixed constant energy input during the arc mode for each welding cycle, the system automatically compensates for the different protrusions. As the protrusion increases, more heating occurs from the resistance heating of the wire. When ul. ·,_; the machine decreases, a smaller share of the heating is the wire heating • · · heating. In all situations, the amount of constant energy is entered so that an automatic layout I is created²R-heat · '/ its amount before reaching the end portion of the wire where it • · · * · *. * 30 melts into a ball. Since the welding cycle occurs 30 to 100 times per second, each increment of the advancing wire, defined as the amount of advancement during a given welding cycle, includes:: the accumulated thermal energy supplied to the increment during all cycles before the wire reaches the bottom of the wire. Any change in protrusion occurs at a substantially slower rate than the accumulation of thermal energy in a single increment of each passing wire of each welding cycle. Because the welding operation is substantially faster than any rate of change in elongation or protrusion from the holder, each addition has substantially the energy that, combined with the actual energy of anode heating during each cycle, results in a fixed energy input to the last wire addition that is actually melted. The changes in protrusion are gradual compared to the normal operation of the system so that a constant energy is evolved in the molten metal ball during each welding cycle. The ball is of a fixed size and the spatter is reduced by principles applicable to semi-automatic operation.

According to a more limited aspect of the invention, the energy controlled current pulse has a first event portion known as a plasma acceleration portion that provides a relatively high current level and a second event portion known as a plasma portion that provides a second lower current level that is substantially above the base current. The plasma acceleration portion of the arc cycle has a fixed time so that during this portion of the welding20 cycle, the selected energy is supplied. However, the plasma portion used to complete the melting of the sphere has a variable length that terminates during each cycle at a time that produces solid actual energy on the wire during each welding cycle. Using this principle, changes in the magnitude of the elongation, joi._; does not change to the extent observed during welding, does not change the total energy consumed by the wire by the last addition * ”.

• · ·

·.·.· 30

To terminate the plasma portion of the welding cycle in the arc mode, means are provided for generating a watt signal as an instantaneous input of the arc voltage: and the welding current for the welding process.

By integrating this signal from the beginning of the plasma acceleration pulse, the total energy value accumulated from 35 reaches a predetermined level which is used to terminate the high plasma current. A low base current is then used to maintain the molten metal ball until it reaches the workpiece of the molten metal pond welding cycle to create a short circuit. Thus, according to the invention, a high-current plasma acceleration pulse is used, followed by the plasma portion also at high current, until a fixed amount of energy has accumulated during the welding cycle. When this happens, the energy required to melt the ball is reached. The base current maintains the size and temperature of the ball.

As the elongation gradually changes, the amount of energy consumed by the resistance heating10 through the wire changes. This phenomenon does not affect the final heating of the wire head. As more heating occurs in the wire advancing toward the workpiece, less heating occurs as anode heating in the arc. According to the invention, the heating is stopped at a solid energy level just above the energy level necessary to convert the last addition of metal into a molten metal ball. For example, if the volume of metal requires 7.2 joules to melt the final addition, the energy cut-off used in the present invention would be slightly greater than this amount, such as about 7.25 joules.

According to another aspect of the present invention, a high frequency pulse circuit, such as a pulse width modulus 25 DC circuit breaker, is used in the DC power supply to control the current during the welding cycle. at a frequency such as greater than 10 KHz and preferably • · · about 2 0 KHz. In this way, all the convincing factors of the welding cycle are controlled and updated many • · · · '/ times during each welding cycle. There is no appreciable delay in compensating for the gradual change in elongation or protrusion. The total energy applied to the ball at the end of the wire before a short circuit is fixed. This va • · ·: the kio energy does not change even if the protrusion gradually changes. Given the high frequency of the supply power control device,

7/35 used in accordance with the preferred embodiment of the present invention, the real-time operation generates the same energy in the molten final addition regardless of the gradual change in the number of additions that make up the elongated portion of the weld wire. According to another aspect of the invention, the high energy plasma acceleration pulse is controlled to provide a fixed wattage state for at least the major portion of the plasma acceleration pulse. This solves the difficulties identified in the constant current or constant voltage form of operation and this is accomplished by introducing a system that has been used to control the energy during each welding cycle. This system generates a watt signal that sets the current pulse released by the DC pulse 10 modulated DC pulse interrupts. This principle results in a constant wattage during the plasma acceleration pulse. Thus, the plasma acceleration pulse is a constant wattage pulse with a fixed time. The energy cut-off time is adjusted during the next plasma arc mode of operation.

The method according to the invention has a current pulse after the start of the arc mode, wherein the current pulse has a first event portion or a plasma acceleration portion and a second event portion or a plasma portion. The energy reaches its full value20 sa during the current portions of these two monitored individual welding cycles. This current pulse is terminated so that the total energy has a predetermined value greater than the predetermined value. The determined value is the amount of energy required to melt the final addition at the end of the wire to form a predetermined molten metal ball. After that, eat. apply a low base current between the wire and the workpiece until the next short-circuit condition occurs. According to a preferred embodiment, the energy is achieved by creating a wattage signal as an instantaneous product of the arc voltage and the welding current,

By integrating this watt signal and collecting the integration values ​​until a preselected constant energy is reached.

• · · • · ·

According to another aspect of the invention, during the plasma acceleration current pulse, the current is selected to provide a plasma shadow at the tip of the wire or electrode. This results in a wide plasma jet extending transversely over the welding direction to heat a large area of ​​the plate into the surface melting space.

·; Molten metal binds metallurgically to the plate and spreads over a wide area without cold running. The current is then reduced for the plasma portion of the cycle, usually to form a conical arc. The energy cut-off can take place by generating a differential signal to change the length of the plasma portion of the current pulse or by the actual cut-off signal. In any case, this principle is defined to terminate the current pulse of the welding cycle when the full energy reaches a preselected value greater than a given melting value. This disconnection is implemented in a preferred embodiment by selecting a time difference with a time delay circuit. It can be done with an actual cut-off signal when the energy reaches a predetermined accumulated value. The second approach works during the period covered.

It is an object of the present invention to control the total female energy supplied during the plasma portion of the arc space of a given welding cycle and to cause the operation of many spatter control devices or methods in a manner that compensates for the varying elongations observed in semi-automatic welding. Equipment or methods previously used to control spatter have been successful primarily in automatic welding. Less success has been found in semi-automatic welding because the wire end was not always properly melted during a given welding cycle. As a result, the main object of the present invention is to improve a short-circuit arc welding device or method having a spatter control feature, which improvement allows the device or method to be used in semi-automatic welding as well as in automatic welding.

Another object of the invention is to control the plasma acceleration current pulse at a given period at the start of the arc mode to provide a constant watt pulse. This solves the problems identified in constant voltage control systems and constant voltage constant current control systems. According to this object of the invention, fewer splashes are generated during the plasma acceleration current pulse.

Il

Yet another object of the present invention is to provide an apparatus or method that uses constant energy control during the arc period of a welding cycle to compensate for variations in welding wire protrusion or elongation and uses a wat5 signal to control energy and current level during a plasma acceleration current pulse to reduce random spatter.

Yet another object of the present invention is to provide an apparatus or method in which the same total energy is supplied to the welding wire during the last addition of wire to ensure the formation of a molten metal ball regardless of the amount of wire protrusion in the holder. Thus, it is not necessary for the welder to position the wire protrusion accurately and skillfully to achieve the benefits of the latest spatter control circuits.

It is a further object of the present invention to provide an apparatus or method which directs the energy supplied to the end of a welding wire in a short-circuit arc welding to create a repetitive intermittent operation with less spatter.

It is an object of the present invention to provide an apparatus or method for short-circuit arc welding using light from a given cycle of a plasma acceleration current pulse._; at the start of the arc mode, in which case the plasma acceleration pulse • · ·. ' the current level is adjusted to produce a constant instantaneous wattage «· · for the plasma acceleration pulse. This wattage value is monitored and · · set many times for each plasma acceleration current pulse • · ♦

*. *. * 3 0 sin using a high frequency input power supply such as a pulse width modulator that adjusts the power switch.

It is an object of the present invention to provide an apparatus or method as described above which uses a DC power supply using a plurality of high frequency pulses modulated with respect to width to adjust the current at different times during the welding cycle.

Yet another object of the present invention is to provide an apparatus or method as defined above that uses an instantaneous watt signal that is integrated and collected to set welding energy during a welding cycle.

This same signal is used without integration to adjust the power supply so that the current level during the plasma acceleration current pulse maintains a constant instantaneous wattage level.

Yet another object of the invention is to provide an apparatus or method for short-circuit arc welding that controls the total energy consumed during the arc mode in each welding cycle.

Yet another object of the present invention is to provide an apparatus or method for short-circuit arc welding in which the constant energy principle is applied during an arc mode to maintain a substantially constant period length. This goal prevents the occurrence of a premature short circuit condition to maintain substantially constant welding conditions during each of its 20 welding cycles.

The device and method according to the application are characterized by what is clear from the claims.

These and other objects and advantages will become apparent from the following description taken in conjunction with the accompanying drawings.

• · • · · ·; Figure 1 is a combined block diagram and schematic wiring • · ·, ·. a diagram showing a preferred embodiment of the present invention;

. Fig. 2 is a series of graphical figures and tabular features used in a preferred embodiment of the present invention.

In the form '. ·';

; Fig. 3 is a wiring diagram illustrating a preferred embodiment of the invention for generating a watt signal and a accumulated energy signal for controlling the amount of energy applied to a welding wire during one welding cycle; Fig. 4 is a representative timing pulse at the output of the circuit shown in Fig. 3;

Fig. 5 is a simplified view of a portion of the wiring diagram of Fig. 3 and shows a sampling and holding feature; Fig. 6 is a diagram showing the operation curve of Fig. 5; Fig. 7 is a block diagram showing two embodiments of a watt output signal generated in accordance with a preferred embodiment of the invention;

Fig. 8 is a side view in which certain tags are used to explain the operating characteristics of the present invention in summary form;

Fig. 9 is a partial view showing an increase in the end of the welding wire before a short circuit; and Fig. 10 is a diagram illustrating an operation curve used in explaining the present invention.

Considering now only a preferred embodiment of the invention, the purpose of which is not to limit it, Fig. 1 shows a device A for short-circuit welding using control circuits for reducing spatter in the manner described in the previous application 135 832 of 21 December 1987. The present invention is directed to an improvement in the type of short-circuit arc welding implemented by device A having a unique principle implemented by the advantageous feature shown in Figure 3. The device A shown in Figure 1 is inherently illustrative and includes a power supply supply diagram that uses various separate current controls to create different current portions of the cycle for short-circuit arc welding. The welding wire 10 is spaced from the workpiece 12 by the electrical connection or holder 14. The yarn 12 can be passed through the holder 14 by a suitable wire feeder 16 from the feed roll 18 at a speed determined by the user. Holder 14 is connected to one terminal of the DC power transmitter PS. The amount of elongation of the wire projecting from the holder above the arc A determines the elongation or protrusion of the welding wire 10. The power supply PS includes a positive output terminal 20 and a negative output terminal 22 according to standard practice. The power switch 30 is cycled to approximately 20 KHz by a standard structured demodulator 32 with a control line 34. Thus, the voltage on the control line 34 indicates the width of the 20 KHz current pulses that are allowed to pass through the switch 30. In this way, the welding current flowing through the welding wire 10 and the arc is controlled by various input control circuits C1-C6, which are used separately or together as described below.

The width of the pulse that controls the voltage on line 34 is the DC voltage level at the output of the differential amplifier 40, which is given a suitable bias voltage by a resistor 42. The bypass or parallel circuit 44 acts in response to the logic of the inverting choke line 50. The input of the differential amplifier 40 and the circuit 44 is the voltage at the summing connection 52, which is controlled by a series of switches SW1-SW6 on the output side of the control circuits C1-C6. The upper circuits C1-C3 are used in conjunction with the lower circuits C5, C6 to supply and draw current from the connection 52 so that the current drawn from the differential amplifier controls the voltage of the modulator 32. The base current is maintained at a low level I_B by common closing of switches SW4, SW6. In accordance with previous practice, the splash control circuit 60 is used in response to an approaching melt with a signal on line 62. This melting signal is generated by the dv / dt pre-warning circuit so that the logic output on line 64 takes the power switch 17 non-conducting immediately before melting occurs during the short circuit condition. The operation of the switch 70 changes the flow of welding current through the choke or inductance 72 from a large current through the switch 70 to a small current through the deceleration circuit 74. As the short circuit portion of the cycle continues, the constant dv / dt circuit, not shown, begins to follow the arc of the arc25. When dv / dt exceeds the set value indicating the onset of melting, the logic of line 62 shifts. The voltage on line 64 causes the switch 70 to be in a non-conductive state. The welding current from switch 70 goes low to reduce the energy released by melting to reduce spatter. This principle does not form part of the improvement encompassing the present invention, which operates during the arc mode of the welding cycle.

The width of the high frequency pulses that the output of the pulse width modulator 32 allows to pass through the switch 30 is determined by the voltage at the sum connection 52 controlled by switches SW1-SW6 operating according to a standard method to control the welding current in different sections of the total welding cycle. -T6. As described below, modifications may be made to this scheme in accordance with a preferred embodiment of the present invention. To describe the operation of switches SW1-SW6, the cycle time or cycle 5 is assumed to start from time T1. At that time, a molten metal ball B, shown in Fig. 9, has formed at the end of the wire 10, and the wire moves toward the workpiece 12 toward the pool of molten metal formed. Since the plasma acceleration pulse and the plasma pulse have not yet been generated, the AND gate

84 the logic states of input lines 50, 80, 82 deactivate switches SW1, SW2, SW3 and SW5, while they activate switches SW4 and SW6. As a result, the basic current control C4 is active. This control circuit is connected to the output of the current control switch SW6 used by the current control circuit C6. The pulse width of the 20 KHz pulses passing through the switch 30 is thus at the base current level I_B. The short-circuit detection causes the switch SW1 caused by the logic of the reverse throttle line 50 to take over to control the current flow through the throttle-modified feedback circuit 44. The pulse width modulator 32 is controlled by circuits C1, C6 during the short circuit mode. Due to the short-circuit mode, there is a tendency for a large welding current. The pulse width modulator attempts to limit the amount of current, as described in the throttling portion of Figure 2. In the illustrated and preferred embodiment, there are two clear ramps; however, other forms of throttling may be controlled by circuit C1. As soon as melting occurs, the logic on line 62 changes. This opens the switch 70, which causes a significant reduction in current due to the use of the retarder 74. This is illustrated during T3 in Figure 2. Basic current I_B may be the same as this low level; however, in the described embodiment, the value I_Bis controlled by circuit C4 and is not identical to the current at time T3. Immediately thereafter, a standard plasma acceleration current pulse 100 is generated. This pulse is controlled by switch SW2, which is closed in response to a change in logic on line 80. Since the throttle state is not maintained, switch SW1 is disconnected and bypass circuit 44 is deactivated. Thus, during the plasma acceleration current pulse state 100, the switch SW2 allows the circuit C2 to control the pulse width modulator 32 to control the welding current pulses by the switch 30. In the illustrated embodiment, the plasma acceleration current pulse 100 includes a leading edge 102 controlled by the plasma acceleration control C2. In a preferred embodiment of the invention, the upper portion 104 is a constant wattage instead of the constant current control shown in Figure 2. When the device A has to adjust the plasma acceleration pulse at a constant power, the switch SW5 is closed so that the instantaneous watt signal is monitored by a circuit C5 which provides an input to the connection 52 via the switch SW5.

During constant power operation, the current control circuit C6 is deactivated by logic on line 80 which opens the switch SW6.

According to a preferred embodiment of the invention, during the standard plasma acceleration current pulse, the current passing through the switch 30 is adjusted by a circuit C2, C5 to produce a constant instantaneous watt which is updated at a sampling frequency of 20 KHz. During the other parts of the welding cycle, the watt signal control circuit C5 is inoperative, so then the current control takes place via the switches SW6 and the input circuit C6. At a fixed time T4, the plasma acceleration current pulse 100 is terminated by the control circuit C2. The current control is transferred from circuit C5 to circuit C6. At this time, the switch SW3 supplies the plasma control circuit C3 to the modulator 32 so that at the time T3, when the arc state began to follow the melting, the large current flow includes the first started plasma acceleration portion 100 and the second. ; si of the plasma portion 110. The large current of the plasma portion,. ·· controlled by circuit C3, terminates at time T5. The integrated area of ​​the pulses 100, 110 is the total energy supplied to the wire 10 during the welding cycle between time points T1 and T6 .

Iillä. After the high current plasma pulse 110, switch SW4,. is closed again so that the basic current control circuit C4 takes over the operation of the differential amplifier 40.

• ·

As a summary of the operation of the welding cycle at time T2, there is a short seal, whereby the molten metal ball B contacts the molten metal in the pool in the workpiece 12. When this occurs, the throttle control circuit C1 controls the switch 30 through the switch SW1 and the parallel branch or circuit 44. Direct flow control

II is needed to limit the current during a short circuit. The approaching melting causes a signal to line 62. This interrupts the throttle at time T3. Switch 70 is open and retarder 74 is placed in series with choke 72. Thereafter, an arc condition occurs that begins with a plasma acceleration current pulse 100 followed by a plasma current pulse 110. The plasma acceleration current pulse 100 has a fixed time T3 to T4 and the plasma current pulse 110 ends at time T5. According to the invention, the energy supplied to the welding operation during the pulses 100, 110 is constant. This is accomplished by setting the time T5, which is expressed as a decrease or increase in time T5. As will be explained below, the end of the plasma pulse or the end of the second event portion between the time points T3 to T5 of the total current pulse is made so that a constant energy is applied during each arc mode of the welding cycle. Energy produced during strangulation and base cycles is not counted. It is ignored because this energy does not produce a control function and is almost negligible because it only produces resistance heating to the wire 10 for a relatively short period of time and a pie20 square power.

Figure 2 depicts the current voltage, watts, and accumulated Joules to some extent in a straightforward manner to clarify the matter. In addition, the holding portion of the welding cycle that occurs after the two major plasma current portions of the cycle may include a third high current energy supply pulse that combines with the current pulses 100, 110 to create the desired amount of accumulated energy during the arc mode. When this occurs, both pulse 100 and pulse 110 both have a fixed time. The hold period then has an additional current pulse that causes the circuit to move to the ground level at time T6. At that moment, the time T6 is adjusted to control the total energy supplied to the wire during the arc mode. In a preferred embodiment of the invention, only two current pulses constitute the large current used to heat the wire 10 during the arc mode. However, a third large current state may exist, which is marked as a hold in the upper curve of Figure 2. In the preferred embodiment, the leading edge 102 of the pulse 100 is substantially vertical18 and the portion 104 is horizontal but adjusted to constant power by setting the current and allowing a corresponding variation in voltage. Only wattage is used. The curves in Figure 2 are only of principle in principle. Vertical lines

P in the lower current curve of Figure 2 illustrate switch 30 20

KHz frequency. Switch 30 operates many times during the welding cycle between times T1 and T6. Thus, precise and real time control is performed for the flow of power from the power supply PS through the switch 70 to the welding station determined by the workpiece

12 welding wire 10. As described, except for setting the time T5 when two high current pulses are applied or the time T6 when three high current pulses are applied, the spatter control principle of Figure 2 implemented by the schematically illustrated device A is based on the teachings of prior patent applications incorporated herein by reference.

The present invention is directed to controlling the end of thermal energy supplied to the welding wire 10 during each arc of the welding cycle. According to further features of the invention, the switch 30 is adjusted to provide a constant instantaneous level during the pulse 100. Both of these principles are realized by the special circuit illustrated in Figure 3, which is used to open the switch SW3 when a predetermined amount of energy has been applied during the arc mode of the welding cycle.

If energy is supplied by the third high current section, as described above, the time at which the switch SW4 opens can be adjusted by the circuit of Fig. 3. The multiplier 120 generates a signal on line 130 that is proportional to the product of the arc voltage on line 122 and the welding current on line 124. These levels are the voltage levels identified by suitable devices for measuring the total voltage over the elongation and for measuring the current through the welding operation as adjusted by the high frequency current pulses passing through the power switch 30. The output line 130 of the multiplier 120 is directed to the input of the integrator 150. Thus, the instantaneous watt signal on line 130 is integrated in a single welding cycle during the portion of the welding cycle determined by the operation of switch 152. In a preferred embodiment of the invention

II switch 152 is closed between times T3 and T5 so that the accumulated energy as a direct current level on line 154 is completed between times T3 and T5. Accumulated energy E_T line 154 could be used to stop the flow of current directly to the weld5 whenever all the summed accumulated energy from a given period E_T is equal to the reference energy E_r. This reference energy is just slightly greater than the energy required to melt a ball of the desired size at the end of the wire 10. Thus, the integrator 150 can provide an accumulated or summed energy signal or voltage level to line 154, which is used directly for timer alternation to move switch 130 to basic control circuit C4 via switch SW4 as shown in Figure 1. This principle uses state (a) in Figure 3. The pulse TP in Fig. 4 is the output of the circuit shown in Fig. 3. If a third current pulse is used, state (b) can be utilized, with switch 152 operating between times T3 and T6. In this case, the total summed or accumulated energy on line 154 controls the position at time T6. If desired, the total energy, which still includes the crossover circuit, can be used by integrating the instantaneous watt signal on line 130 between time points T1 to T6. This is state (c) and is not used in the two preferred embodiments of the present invention.

As described so far, the total energy is applied as a voltage level to line 154 during each welding cycle to provide a signal representing the accumulated amount of energy applied to the welding wire during plasma acceleration current pulse 100 and plasma current pulse 110 as illustrated in Figure 2. is shown in both Figure 3 and Figure 5. The logic on line 162 takes a sample and holds the accumulated energy determined by the voltage level on line 154 at the end of the plasma current pulse 110. This voltage level is maintained at line 164, on a scale of 0.2 volts corresponding to each 2.0 Joules of accumulated energy according to the voltage level at line 154. The voltage level maintained on line 154 is directed to a collecting capacitor 170 which forms a voltage divider with potentiometer 172 which is used at the energy set point E_R set taking parameters. In this way, a substantially DC signal or voltage level is applied to the control terminal 180 of the differential amplifier. This results in a softer operation than using a signal that varies between zero energy and accumulated energy during each period.

The output of differential amplifier 180 has a variable voltage level 10 on output line 182 which is applied to time delay capacitor 184 in time delay circuit 190. Line 182 determines the voltage in capacitor 184 to switch switch SW2 to start plasma acceleration 32 to switch to timeout between time T3 and switch SW3 opening. Thus, the pulse switch modulator maintains the control by the plasma acceleration control and then by the plasma control itself until the output 192 of the time delay device 190 stops the plasma control operation at time T5. This generates a time signal, whereby the energy E accumulated during the period_T is equal to the reference energy E_R, which is only slightly higher than the energy required to melt the last addition of wire by a combination of resistance heating and arc or anode heating.

As illustrated in Figure 7, the total energy E_T can be compared with the reference energy E_R intended to terminate the plasma pulse at time T5. Energy accumulated according to the invention E_T is kept constant by causing the T5 to occur when the accumulated energy reaches the reference energy. The means for carrying out this function in the preferred embodiment are illustrated in Figure 3, where the total energy E accumulated at the end of the plasma pulse_T is sampled and transferred as a voltage level to line 164. During each period, this voltage either increases or decreases the voltage at capacitor 170 to increase or decrease the DC level at line 182. As a result, the previously accumulated energy is averaged by capacitor 170 to determine the amount of time delay for the next period. The voltage at capacitor 184 is reset at the end of each plasma current pulse. Differential amplifier 180 is a standard device with high gain so that variations on line 164 can be amplified to obtain the necessary degree of voltage change in time delay device 190. Thus, the end of current pulse, whether it includes a fixed plasma acceleration pulse 100 and a variable plasma pulse 110 or an additional high current holding pulse , occurs at a time to create a fixed constant energy supply to the wire 10 during the arc mode of each cycle. Changes in the voltage of capacitor 170 are illustrated in Figure 6 and indicate that the capacitor maintains an overall voltage level that indicates the average accumulated energy per cycle from previous welding cycles. Thus, each cycle changes only slightly the average energy in capacitor 170. This principle regulates the voltage in the time delay device 190 as previously described. It is similar to provide the control circuit shown in Figure 3 or the schematically illustrated circuit shown in the upper part of the figure to provide means for terminating the high current portion of each welding cycle to provide a constant heating energy.

The lower part of Figure 7 illustrates a further feature of a preferred embodiment of the invention. Since the instantaneous watt signal is generated at line 130, this watt signal can be used to control the current emitted by the switch 30 during the plasma acceleration pulse 100 shown in Figure 2. Preferably, the watt control operates throughout the pulse 100, so that portion 104 extends between T3 and T4. Line 130 is routed to the wattage control circuit C5 on the input side of switch SW5 shown in Fig. 1 so that the pulse width modulator 32 is controlled at the output of switch SW5 instead of the output of current control switch SW6. As a result, in accordance with this aspect of the invention, the current flowing through the switch 30 during the plasma acceleration pulse is adjusted to maintain constant instantaneous watts. This solves the disadvantages described previously with regard to the use of a constant voltage during the plasma acceleration current pulse or the use of a variable voltage and a constant current state during this high-energy pulse. Thus, the high energy applied to the wire during the plasma acceleration current pulse 100 is adjusted to prevent the arc from driving the pond away from the ball or allowing the pond to randomly touch the molten metal ball. This is a further advantage of the present invention.

Referring now to Figures 8-10, the characteristics of the operation of the present invention are shown graphically. The elongation from the wire holder 14 is shown schematically in Figure 8 divided into a series of individual protrusions, each equal to the volume of molten metal at the end of the wire 10 to form the sphere B shown in Figure 9. This ball has an effective diameter of about 1.2 times the diameter of the wire 10.

During each welding cycle, the last addition, i.e. Appendix 1, is raised to a melting temperature of about 1535 ° C by the combined heating effect caused by the heat accumulated in Appendix 1 as it moves down from holder 14 and the heat generated by arc a in anode region 200._T the current welding cycle is constant and set to E_R, which value gives the melting temperature of the metal in Appendix 1. During this heating, in a single welding cycle, Appendix 1 melts and the subsequent additions heat I²R with heating effect. Thus, the total heating generated during a given welding cycle is divided between the anode heating in the anode region 200 and the resistance heating extending through all the extensions extending from the holder 14. As more li30 strands are included as the protrusion increases, the total resistance increases, transferring more heating to the resistance heating section. As the resistance increases with temperature, the heating of the lower additions contributes to the increase of their resistance. The energy constant of the last addition at the end of the wire is the sum of the resistance heating that occurs during successive welding cycles as the individual addition progresses downward. Assuming that the protrusion or elongation remains constant, the total heat in the last addition before being subjected to the tode of anode heating includes heat that is substantially accumulated by resistance heating from previous heating cycles. This is when the small change in resistance, the product of the resistance heating per cycle and the protrusion additions are ignored. In view of this phenomenon, the total heating energy applied to the wire during the welding cycle is divided between the anode heating and the resistance heating. The accumulated resistance heating in the addition as it progresses downward is the residual energy of the last addition. The resistance heating of all increments 10 in the cycle is substantially equal to the difference between the anode heating and the total energy introduced between times T3 and T5. Thus, keeping the total energy constant between times T3 and T5, there is always a regulated energy that is introduced as accumulated resistance heating and implemented as the heating of the usual period to raise the temperature of Appendix 1 to the fixed total energy E selected._T.

The welding cycles occur 30-100 times per second and the current is controlled during the welding cycle at a rate of 10 KHz, as illustrated by the vertical lines P in the current curve in Figure 2. As a result, the individual increments move from the holder 14 at a rate of 30-100 per second. This speed is substantially greater than any ordinary change that occurs in the protrusion by manual handling of the holder 14 during welding operation. Thus, when the protrusion or elongation changes, all the accumulated energy E_T the phenomenon created by the adjustment during the arc mode of any period does not change accordingly. The various accumulated resistance heating events are substantially slower than any change in the number of additions. Therefore, in the example of Figure 8, the heat H1 = H2 = H3 = H4 = H5, etc. Thus, the amount of energy in Appendix 1 before it melts is essentially the total resistance heating of the last welding cycle, despite being derived from Appendix 1 by increasing over the last several cycles.

An example illustrating this distribution between resistance heating and anode heating as the number of protrusion additions is shown below:

1.143 mm

2.565 mm / min

12.2 mm

EXAMPLE

Electrode diameter Electrode speed

Projection

Frequency

Increase

Standard addition S standard plasma time

plasma Power

Hz 0.6807 mm 17

0.00089 s 160 A

<td>Plasma Accelerator current</td><td>330 A</td>

<td>Plasma Acceleration time</td><td> 0,00140</td>

<td>Additional-</td><td>Trapped</td><td>Anode-</td><td>Kokonaiskuu-</td>

<td>main in</td><td>vastuskuumen-</td><td>heating</td><td>go (setting)</td>

<td>size-</td><td>increase</td><td>nus</td><td>joules</td>

<td>female -</td><td>Sessa</td><td>joules</td><td>(Cycles)</td>

<td>heating</td><td>joules</td><td></td><td>melting</td>

<td>nuksessa</td><td></td><td></td><td>7.2 Joules</td>

<td> 4</td><td> 0,1997</td><td> 7,0704</td><td> 7,2701</td>

<td> 6</td><td> 0,3138</td><td> 6,9563</td><td> 7,2701</td>

<td> 8</td><td> 0,4372</td><td> 6,8329</td><td> 7,2701</td>

<td> 10</td><td> 0,5691</td><td> 6,7010</td><td> 7,2701</td>

<td> 12</td><td> 0,7088</td><td> 6,5613</td><td> 7,2701</td>

<td> 14</td><td> 0,8550</td><td> 6,4151</td><td> 7,2701</td>

<td> 16</td><td> 1,0066</td><td> 6,2635</td><td> 7,2701</td>

<td> 17</td><td> 1,0839</td><td> 6,1862</td><td> 7,2701</td>

<td> 18</td><td> 1,1639</td><td> 6,1062</td><td> 7,2701</td>

<td> 20</td><td> 1,3364</td><td> 5,9337</td><td> 7,2701</td>

<td> 22</td><td> 1,5164</td><td> 5,7537</td><td> 7,2701</td>

<td> 24</td><td> 1,7004</td><td> 5,5697</td><td> 7,2701</td>

·»· ·

<img file="FI97030B_D0001.tif" />

<img file="FI97030B_D0002.tif" />

In any period, the total resistance heating per Joule heated increment is equal to the total resistance heating in the previous period. By adjusting the total energy setpoint E_T anode heating In Joules for each welding cycle added to the resistance heating accumulated in the fusible addition adjusts both the actual anode heating and the accumulated resistance heating of the last addition. These two heating sources for the last addition are always equal to the set total energy E_T and as permitted by the present invention. This principle is schematic

II is illustrated in the curve of Figure 10, which illustrates an example of 12 protrusion increments 24 for the prolongation of the increment with the last increment (increment reaching bottom and arc state) having accumulated a resistance heat content of 0.7088 Joules in this particular increment. Thus, by setting a reference value for the accumulated energy E_R to 7.2701, the anode heating is 6.5613 Joules before the time T5 is cut off by a pulse TP from the delay device 190 or the real-time plasma time control schematically shown in Fig. 10 sa 7. It does not matter how many increments are included in the protrusion. This principle always applies. The total energy is selected E_T divided into resistance and anode heating. At position 12 in Figure 10, the molten addition has accumulated a heat content of 0.7088 Joules due to resistance heating. During the plasma excitation current pulse, a fixed amount of energy is applied, which fixed amount is not sufficient to melt this increase, which requires 7.2 Joules. However, the total energy accumulated during the plasma acceleration pulse 100 and the plasma current pulse 110 transfers the temperature of the metal temperature change zone 210 through the heat so that the molten metal forms in the end as a sphere. Reference Energy E_R, which is adjusted during each welding cycle, should be only slightly above that required to melt the ball. This can be done manually by the user by changing the power setpoint with the voltage divider 172 in the figure

3 or with a reference potentiometer 172a in Figure 5. Each of these setpoint circuits allows voltage level adjustment on line 182 for the purpose described above.

In summary, by using a high frequency power supply and adjusting the total energy of each welding cycle during the arc state of the cycle, the protrusion or elongation can vary normally without altering the welding operation. Thus, special systems for reducing spatter developed in accordance with previous efforts can be used with equal success35 in semi-automatic welding.

Since the present invention uses an instantaneous watt signal, this signal can be used to adjust the current 104 during the plasma acceleration pulse 100 to achieve a constant wattage that overcomes the disadvantages resulting from either constant voltage control or constant current control during a high energy plasma acceleration current pulse.

The individual current control circuits shown in Figure 1 for controlling the throttle C1, controlling the plasma acceleration C2, controlling the plasma C3, controlling the base current to either two levels or only one level C4, and controlling the current C6 are used in previous systems to control the current for short-circuit arc welding. The present invention adds a wattage control circuit C6 implemented by the switch SW5 for controlling the current during the control of the plasma acceleration pulse by the switch SW2. This principle of wattage control is in accordance with the aspect of the invention.

A preferred embodiment of the invention is shown in Figure 3 and a small modification thereof is schematically illustrated in Figure 7. In both cases, the total energy E_T, which results from both the effective current consumption for anode heating and the total resistance heating of the protrusion additions during each arc mode of the welding cycle, is constant.