Forward and reverse feed control arc welding method and forward and reverse feed control arc welding apparatus

Abstract

In a forward / reverse feed control arc welding method in which the welding wire feed speed Fw is set to the forward feed peak value during the arc period and to the reverse feed peak value during the short-circuit period, the welding state is stabilized during the period from time t4 to t6 when the short circuit is released, the arc is regenerated and the feed speed Fw changes from the reverse feed peak value to the forward feed peak value. [Solution] In a forward / reverse feed control arc welding method in which the welding wire feed speed Fw is set to the forward feed peak value during the arc period and to the reverse feed peak value during the short circuit period, and welding is performed by applying a welding current Iw with positive electrode polarity, at the start of the arc period, the feed speed Fw is reduced from the reverse feed peak value to 0 during the reverse feed deceleration period from time t4 to t5, and the electrode polarity is switched to negative for at least the duration of the reverse feed deceleration period.

Description

Technical Field

[0001] The present invention relates to a forward and reverse feeding control arc welding method and a forward and reverse feeding control arc welding apparatus for welding by setting the feeding speed of a welding wire to a forward feeding peak value during the arc period and to a reverse feeding peak value during the short circuit period.

Background Art

[0002] In general consumable electrode type arc welding, a welding wire, which is a consumable electrode, is fed at a constant speed, and an arc is generated between the welding wire and the base material to perform welding. In consumable electrode type arc welding, the welding state where the welding wire and the base material alternately repeat the short circuit period and the arc period often occurs.

[0003] In order to further improve the welding quality, a forward and reverse feeding control arc welding method is used in which the feeding speed of the welding wire is set to a forward feeding peak value during the arc period and to a reverse feeding peak value during the short circuit period, and welding is performed by passing a welding current with electrode positive polarity (see, for example, Patent Document 1). In this forward and reverse feeding control arc welding method, compared with the prior art of a constant feeding speed, the cycle of repetition of short circuit and arc can be stabilized, so that improvement in welding quality such as reduction in the amount of spatter generation and improvement in bead appearance can be achieved.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] In the conventional forward / reverse feed control arc welding method described above, when a short circuit is released and the arc is regenerated, and the feed rate changes from the reverse feed peak value to the forward feed peak value, the cathode point of the arc moves in search of the oxide film on the surface of the base material, causing the arc to fluctuate and the welding state to become unstable. This problem is particularly pronounced when the base material is aluminum or an alloy thereof. Therefore, the present invention aims to provide a forward / reverse feed control arc welding method and a forward / reverse feed control arc welding apparatus that can stabilize the welding state when a short circuit is released, the arc is regenerated, and the feed rate changes from the reverse feed peak value to the forward feed peak value. [Means for solving the problem]

[0006] A forward / reverse feed control arc welding method provided by a first aspect of the present invention is a forward / reverse feed control arc welding method in which the feeding speed of the welding wire is set to the forward feed peak value during the arc period and to the reverse feed peak value during the short-circuit period, and welding is performed by applying a welding current with positive electrode polarity, wherein at the start of the arc period, the feeding speed transitions to a reverse feed deceleration period in which it is reduced from the reverse feed peak value to 0, and the electrode polarity is switched to negative for at least the duration of the reverse feed deceleration period.

[0007] In a preferred embodiment of the present invention, the electrode is returned to positive polarity with a delay from the end of the reverse deceleration period.

[0008] In a preferred embodiment of the present invention, the switching to the negative polarity of the electrode occurs before the start of the arc period.

[0009] In a preferred embodiment of the present invention, when constriction of the molten droplet is detected during the short-circuit period, the welding current is reduced, and the switching to the negative polarity of the electrode occurs at the point when the welding current is reduced.

[0010] In a preferred embodiment of the present invention, the welding current is controlled to 100A or less during the period when the electrode is negatively polarized.

[0011] A forward / reverse feed control arc welding apparatus provided by a second aspect of the present invention is a forward / reverse feed control arc welding apparatus that sets the welding wire feed speed to a forward feed peak value during the arc period and to a reverse feed peak value during the short-circuit period, and performs welding by applying a welding current with positive electrode polarity, wherein at the start of the arc period, the feed speed transitions to a reverse feed deceleration period in which it is reduced from the reverse feed peak value to 0, and the electrode polarity is switched to negative for at least the duration of the reverse feed deceleration period. [Effects of the Invention]

[0012] According to the present invention, the welding state can be stabilized when the short circuit is released, the arc is regenerated, and the feed rate changes from the reverse feed peak value to the forward feed peak value. [Brief explanation of the drawing]

[0013] [Figure 1] This is a block diagram of a forward and reverse feed control arc welding apparatus for implementing a forward and reverse feed control arc welding method according to an embodiment of the present invention. [Figure 2] Figure 1 shows the timing chart of each signal in the forward / reverse feed control arc welding apparatus, illustrating a forward / reverse feed control arc welding method according to an embodiment of the present invention. [Modes for carrying out the invention]

[0014] Embodiments of the present invention will be described below with reference to the drawings.

[0015] Figure 1 is a block diagram of a forward / reverse feed control arc welding apparatus for implementing a forward / reverse feed control arc welding method according to an embodiment of the present invention. In this figure, the circuit for applying a high voltage of several hundred volts for a short time between the welding wire 1 and the base material 2 in order to facilitate polarity switching is omitted. The following describes each block with reference to this figure.

[0016] The power control circuit PM takes a commercial power supply such as 3-phase 200V (not shown) as input, performs output control by inverter control etc. according to the error amplification signal Ea described later, performs constriction detection control by the drive signal Dr described later, and switches between the electrode positive polarity EP and the electrode negative polarity EN by the polarity switching signal Spn described later to output a welding voltage Vw and a welding current Iw between the welding wire 1 and the base material 2. This power control circuit PM, although not shown, includes a primary rectifier for rectifying the commercial power supply, a smoothing capacitor for smoothing the rectified DC, an inverter circuit driven by the error amplification signal Ea for converting the smoothed DC to a high-frequency AC, a high-frequency transformer for stepping down the high-frequency AC to a voltage value suitable for welding, a secondary rectifier for rectifying the stepped-down high-frequency AC to DC, a reactor for smoothing the rectified DC, a current-reducing resistor connected in series with the reactor, a transistor connected in parallel with the current-reducing resistor and driven by the drive signal Dr, and a secondary inverter circuit for switching the polarity of the smoothed DC based on the polarity switching signal Spn. The value of the current-reducing resistor described above is set to a value (approximately 0.5 to 3 Ω) that is more than 50 times larger than the short-circuit load (approximately 0.01 to 0.03 Ω). When the transistor described above is turned off, the current-reducing resistor is inserted into the current-carrying circuit, causing the welding current Iw to decrease sharply.

[0017] The feed motor WM receives the feed control signal Fc (described later) as input and feeds the welding wire 1 at a feed speed Fw by alternately feeding forward and backward. A motor with fast transient response is used for the feed motor WM. In order to speed up the rate of change of the feeding speed Fw of the welding wire 1 and the reversal of the feeding direction, the feed motor WM may be installed near the tip of the welding torch 4. In addition, two feed motors WM may be used to create a push-pull type feed system.

[0018] The welding wire 1 is fed through the welding torch 4 by the rotation of a feed roll 5 coupled to the feed motor WM, and an arc 3 is generated between it and the base material 2. A welding voltage Vw is applied and a welding current Iw is passed between the welding wire 1 and the base material 2. Stainless steel wire, aluminum wire, etc., are used for the welding wire 1. Shielding gas (not shown in the figure) is ejected from the tip of the welding torch 4.

[0019] The current detection circuit ID detects the absolute value of the above-mentioned alternating welding current Iw and outputs a current detection signal Id.

[0020] The voltage detection circuit VD detects the absolute value of the above-mentioned alternating welding voltage Vw and outputs a voltage detection signal Vd. The voltage setting circuit VR outputs a voltage setting signal Vr for setting the welding voltage Vw during the second arc period.

[0021] The voltage error amplification circuit EV takes the above-mentioned voltage setting signal Vr and the above-mentioned voltage detection signal Vd as inputs, amplifies the error between the two values, and outputs a voltage error amplification signal Ev.

[0022] The short-circuit discrimination circuit SD takes the above-mentioned voltage detection signal Vd as an input. When this value is less than a predetermined short-circuit discrimination value (about 10 V), it is determined that the short-circuit period is in progress and becomes High level. When it is above this value, it is determined that the arc period is in progress and becomes Low level, and outputs a short-circuit discrimination signal Sd.

[0023] The forward feed acceleration period setting circuit TSUR outputs a predetermined forward feed acceleration period setting signal Tsur.

[0024] The forward feed deceleration period setting circuit TSDR outputs a predetermined forward feed deceleration period setting signal Tsdr.

[0025] The reverse feed acceleration period setting circuit TRUR outputs a predetermined reverse feed acceleration period setting signal Trur.

[0026] The reverse feed deceleration period setting circuit TRDR outputs a predetermined reverse feed deceleration period setting signal Trdr.

[0027] The forward feed peak value setting circuit WSR outputs a predetermined forward feed peak value setting signal Wsr.

[0028] The reverse feed peak value setting circuit WRR outputs a predetermined reverse feed peak value setting signal Wrr.

[0029] <The feed speed setting circuit FR takes the above-mentioned forward acceleration period setting signal Tsur, forward deceleration period setting signal Tsdr, reverse acceleration period setting signal Tru, reverse deceleration period setting signal Trdr, forward peak value setting signal Wsr, reverse peak value setting signal Wrr, and short-circuit detection signal Sd as inputs and outputs the feed speed setting signal Fr and reverse deceleration period signal Srd of the feed speed pattern generated by the following processing. When this feed speed setting signal Fr is 0 or greater, it is the forward period, and when it is less than 0, it is the reverse period. 1) During the forward acceleration period Tsu, which is determined by the forward acceleration period setting signal Tsur, a feed speed setting signal Fr is output that accelerates from 0 to a positive forward peak value Wsp, which is determined by the forward peak value setting signal Wsr. 2) Next, during the positive transmission peak period Tsp, a transmission speed setting signal Fr is output to maintain the above positive transmission peak value Wsp. 3) When the short-circuit detection signal Sd changes from a low level (arc period) to a high level (short-circuit period), the system transitions to the forward deceleration period Tsd determined by the forward deceleration period setting signal Tsdr, and outputs a feed speed setting signal Fr that decelerates the feed speed from the forward peak value Wsp to 0. 4) Next, during the reverse acceleration period Tru, which is determined by the reverse acceleration period setting signal Trur, a feed speed setting signal Fr is output, which accelerates from 0 to a negative reverse peak value Wrp, which is determined by the reverse peak value setting signal Wrr. 5) Next, during the reverse transmission peak period Trp, a transmission speed setting signal Fr is output to maintain the above reverse transmission peak value Wrp. 6) When the short-circuit detection signal Sd changes from a high level (short-circuit period) to a low level (arc period), the system transitions to the reverse-speed deceleration period Trd, determined by the reverse-speed deceleration period setting signal Trdr, and outputs a feed speed setting signal Fr that decelerates the reverse-speed from the peak value Wrp to 0. During this period, the reverse-speed deceleration period signal Srd, which is at a high level, is output. 7) By repeating steps 1) to 6) above, a feed rate setting signal Fr is generated, which has a feed pattern that changes in a positive and negative trapezoidal wave shape.

[0030] The feed control circuit FC takes the above feed speed setting signal Fr as an input and outputs a feed control signal Fc for feeding the welding wire 1 at a feed speed Fw corresponding to the value of the feed speed setting signal Fr to the above feed motor WM.

[0031] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr.

[0032] The current comparison circuit CM takes the above low-level current setting signal Ilr and the above current detection signal Id as inputs and outputs a current comparison signal Cm that becomes High level when Id < Ilr and becomes Low level when Id ≥ Ilr.

[0033] The constriction detection circuit ND takes the above short-circuit discrimination signal Sd as an input and outputs a constriction detection signal Nd that becomes High level when the elapsed time from the time when the short-circuit discrimination signal Sd changes to High level (short-circuit period) reaches a predetermined reference time, and then becomes Low level when the short-circuit discrimination signal Sd changes to Low level (arc period). When the elapsed time from the occurrence of the short circuit reaches the reference time, it is determined that the state of the constriction formed in the droplet has progressed to the reference state, and the constriction detection signal Nd is set to High level. The reference time is set so that the time during which the constriction detection signal Nd is High level is about 0.5 to 1.0 ms.

[0034] The drive circuit DR takes the above-mentioned current comparison signal Cm and the above-mentioned constriction detection signal Nd as inputs and outputs a drive signal Dr to the base terminal of the transistor in the power control circuit PM. When the constriction detection signal Nd changes to a high level, the drive signal Dr changes to a low level, and then when the current comparison signal Cm changes to a high level, the drive signal Dr changes to a high level. Therefore, when constriction is detected, the drive signal Dr becomes low, the transistor turns off, and a current-reducing resistor is inserted into the current-carrying path, causing the welding current Iw that energizes the short-circuit load to decrease sharply. When the value of the sharply decreased welding current Iw falls to the value of the low-level current setting signal Ilr, the drive signal Dr becomes high, the transistor turns on, the current-reducing resistor is short-circuited, and the system returns to its normal state.

[0035] The short-circuit current setting circuit ISR takes the above-mentioned short-circuit detection signal Sd, the above-mentioned low-level current setting signal Ilr, and the above-mentioned constriction detection signal Nd as inputs, performs the following processing, and outputs the short-circuit current setting signal Isr. 1) From the moment the short-circuit detection signal Sd changes to a high level (short circuit), a short-circuit current setting signal Isr, which is a predetermined initial current setting value, is output for a predetermined initial period. 2) Subsequently, the short-circuit current rises at a predetermined short-circuit gradient, and when it reaches a predetermined short-circuit peak value, it outputs a short-circuit current setting signal Isr to maintain that value. 3) Subsequently, when the constriction detection signal Nd changes to a high level (constriction detected), a short-circuit current setting signal Isr, which is equal to the value of the low-level current setting signal Ilr, is output.

[0036] The polarity switching circuit SPN takes the above-mentioned reverse-drive deceleration period signal Srd and the above-mentioned constriction detection signal Nd as inputs, performs one of the following processes 1) to 4), and outputs a polarity switching signal Spn. 1) The polarity switching signal Spn is output, which is at a high level (electrode negative polarity EN) during the reverse deceleration period Trd when the reverse deceleration period signal Srd is at a high level, and at a low level (electrode positive polarity EP) during other periods. 2) In the above 1), a polarity switching signal Spn is output, which returns to a low level after a predetermined delay period has elapsed from the time the reverse deceleration period Trd ends when the reverse deceleration period Srd is at a low level. 3) In either 1) or 2) above, a polarity switching signal Spn is output that changes to a high level before the start of the reverse deceleration period Trd, when the reverse deceleration period signal Srd becomes high. 4) In either 1) or 2) above, a polarity switching signal Spn is output that changes to a high level before the reverse deceleration period Trd starts, when the constriction detection signal Nd becomes high level.

[0037] The first arc period setting circuit TA1R outputs a predetermined first arc period setting signal Ta1r.

[0038] The first arc period circuit STA1 takes the above-mentioned short-circuit detection signal Sd and the above-mentioned first arc period setting signal Ta1r as inputs and outputs the first arc period signal Sta1, which is at a high level from the moment the short-circuit detection signal Sd changes to a low level (arc period) until the first arc period Ta1 set by the first arc period setting signal Ta1r.

[0039] The first arc current setting circuit IA1R outputs a predetermined first arc current setting signal Ia1r.

[0040] The third arc period circuit STA3 takes the short-circuit detection signal Sd as input and outputs a third arc period signal Sta3 that becomes high when a predetermined current drop time Td has elapsed from the moment the short-circuit detection signal Sd changes to a low level (arc period), and then becomes low when the short-circuit detection signal Sd becomes high level (short-circuit period).

[0041] The third arc current setting circuit IA3R outputs a predetermined third arc current setting signal Ia3r.

[0042] The current control setting circuit ICR takes the above polarity switching signal Spn, the above short circuit detection signal Sd, the above low-level current setting signal Ilr, the above short-circuit current setting signal Isr, the above first arc period signal Sta1, the above third arc period signal Sta3, the above first arc current setting signal Ia1r, and the above third arc current setting signal Ia3r as inputs, performs the following processing, and outputs the current control setting signal Icr. 1) From the moment the short-circuit detection signal Sd changes to a low level (arc period) and the first arc period signal Sta1 changes to a high level until the polarity switching signal Spn changes to a low level, a current control setting signal Icr, which is equal to the value of the low-level current setting signal Ilr, is output. 2) Subsequently, a current control setting signal Icr, which is the value of the first arc current setting signal Ia1r, is output. 3) During the period from when the first arc period signal Sta1 changes to a low level until the third arc period signal Sta3 changes to a low level (the second and third arc periods), a current control setting signal Icr, which is equal to the value of the third arc current setting signal Ia3r, is output. 4) When the short-circuit detection signal Sd is at a high level (short-circuit period), the current control setting signal Icr, which is equal to the value of the short-circuit current setting signal Isr, is output.

[0043] The current error amplification circuit EI takes the above-mentioned current control setting signal Icr and the above-mentioned current detection signal Id as inputs, amplifies the error between the two values, and outputs a current error amplification signal Ei.

[0044] The power supply characteristic switching circuit SW takes the above-mentioned current error amplification signal Ei, the above-mentioned voltage error amplification signal Ev, the above-mentioned first arc period signal Sta1, and the above-mentioned third arc period signal Sta3 as inputs, performs the following processing, and outputs the error amplification signal Ea. 1) During the second arc period Ta2, from when the first arc period signal Sta1 changes to a low level until the third arc period signal Sta3 changes to a high level, the voltage error amplification signal Ev is output as the error amplification signal Ea. 2) During other periods, the current error amplification signal Ei is output as the error amplification signal Ea. With this circuit, the welding power supply characteristics become constant current during the short-circuit period, the first arc period Ta1, and the third arc period Ta3, and constant voltage during the second arc period Ta2.

[0045] Figure 2 is a timing chart of each signal in the forward / reverse feed control arc welding apparatus shown in Figure 1, which illustrates a forward / reverse feed control arc welding method according to an embodiment of the present invention. Figure (A) shows the time variation of the feed rate Fw, Figure (B) shows the time variation of the welding current Iw, Figure (C) shows the time variation of the welding voltage Vw, Figure (D) shows the time variation of the short-circuit detection signal Sd, Figure (E) shows the time variation of the first arc period signal Sta1, Figure (F) shows the time variation of the third arc period signal Sta3, Figure (G) shows the time variation of the polarity switching signal Spn, and Figure (H) shows the time variation of the necking detection signal Nd. The operation of each signal will be explained below with reference to the figure.

[0046] The feed speed Fw shown in Figure (A) indicates a forward feed state where the welding wire 1 is fed forward toward the base material 2 when it is a positive value, and a reverse feed state where it is fed backward toward the base material 2 when it is a negative value. The feed speed Fw is controlled by the value of the feed speed setting signal Fr output from the feed speed setting circuit FR in Figure 1. The feed speed Fw is formed from the forward feed acceleration period Tsu determined by the forward feed acceleration period setting signal Tsur in Figure 1, the forward feed peak period Tsp which continues until a short circuit occurs, the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr in Figure 1, the reverse feed acceleration period Tru determined by the reverse feed acceleration period setting signal Tru in Figure 1, the reverse feed peak period Trp which continues until an arc occurs, and the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Tdr in Figure 1. Furthermore, the positive feed peak value Wsp is determined by the positive feed peak value setting signal Wsr in Figure 1, and the negative feed peak value Wrp is determined by the negative feed peak value setting signal Wrr in Figure 1. As a result, the feed speed setting signal Fr has a feed pattern that changes in a roughly trapezoidal wave shape between positive and negative. The welding current Iw shown in Figure (B) and the welding voltage Vw shown in Figure (C) show the waveform when the electrode is positive polarity EP when they are positive values, and the waveform when the electrode is negative polarity EN when they are negative values.

[0047] [Operation during the short-circuit period from time t1 to t4] Up until partway through the short-circuit period, as shown in Figure (G), the polarity switching signal Spn is at a low level, so the output of the welding power supply is electrode positive polarity EP. Therefore, during the short-circuit period, the welding current Iw shown in Figure (B) and the welding voltage Vw shown in Figure (C) are positive values. When a short circuit occurs at time t1 during the positive feed peak period Tsp, as shown in Figure (C), the welding voltage Vw drops sharply to a short-circuit voltage of a few volts, and as shown in Figure (D), the short-circuit discrimination signal Sd changes to a high level (short-circuit period). In response to this, the system transitions to a predetermined positive feed deceleration period Tsd from time t1 to t2, and as shown in Figure (A), the feed rate Fw is reduced from the positive feed peak value Wsp to 0.

[0048] As shown in Figure (A), the feed rate Fw enters a predetermined reverse acceleration period Tru from time t2 to t3, accelerating from 0 to the reverse peak value Wrp. The short-circuit period continues during this period.

[0049] When the reverse acceleration period Tru ends at time t3, the feed rate Fw enters the reverse peak period Trp, as shown in Figure (A), and becomes the reverse peak value Wrp. The reverse peak period Trp continues until an arc occurs at time t4. Therefore, the period from time t1 to t4 is the short-circuit period.

[0050] As shown in Figure (B), the welding current Iw during the short-circuit period from time t1 to t4 is controlled to a constant current value equal to the value of the short-circuit current setting signal Isr shown in Figure 1.

[0051] As shown in Figure (B), the welding current Iw during the short-circuit period from time t1 to t4 is a predetermined initial current value during a predetermined initial period. Thereafter, the welding current Iw increases at a predetermined short-circuit slope, and once it reaches a predetermined short-circuit peak value, it maintains that value. The above initial period is approximately 0.5 ms, the initial current value is approximately 40 A, the short-circuit slope is approximately 260 A / ms, and the short-circuit peak value is approximately 300 A.

[0052] As shown in Figure (C), the welding voltage Vw increases when the welding current Iw reaches its short-circuit peak value. This is because the reverse feeding of the welding wire 1 and the pinching force caused by the welding current Iw gradually form a constriction in the molten droplet at the tip of the welding wire 1.

[0053] Subsequently, when the elapsed time since the short circuit occurred at time t1 reaches a predetermined reference time, it is determined that the constriction formation state has reached the reference state, and as shown in Figure (H), the constriction detection signal Nd changes to a high level at time t31. In response to this, the drive signal Dr in Figure 1 becomes low, and the transistor in the power control circuit PM in Figure 1 turns off, so the current reducing resistor in the power control circuit PM in Figure 1 is inserted into the current path. At the same time, the value of the short-circuit current setting signal Isr in Figure 1 becomes small enough to be the value of the low-level current setting signal Ilr. As a result, as shown in Figure (B), the short-circuit current rapidly decreases to a low-level current value (approximately 50A). When the short-circuit current decreases to the low-level current value, the drive signal Dr returns to a high level, the transistor turns on, and the current reducing resistor is short-circuited. As shown in Figure (B), the short-circuit current setting signal Isr remains at the low-level current setting signal Ilr, so the short-circuit current maintains a low-level current value until time t4 when the arc re-occurs. Therefore, the transistor is only in the off state during the period from when the constriction detection signal Nd changes to a high level until the short-circuit current decreases to a low level. As shown in Figure (C), the welding voltage Vw decreases because the short-circuit current becomes smaller. Since the current value when the arc is re-generated can be reduced by constriction detection control, spatter generation can be reduced.

[0054] At time t32, when the welding current Iw is at a low current level, the polarity switching signal Spn changes from a low level to a high level, as shown in Figure (G), and the output of the welding power supply switches to the negative electrode polarity EN. In response to this, as shown in Figure (B), the welding current Iw changes from a positive low current level to a negative low current level. Similarly, as shown in Figure (C), the welding voltage Vw changes from a positive short-circuit voltage level to a negative short-circuit voltage level.

[0055] At time t4, when the welding wire is reversed, constriction progresses and an arc is generated. As shown in Figure (C), the welding voltage Vw rapidly increases to a negative arc voltage value of several tens of volts, and as shown in Figure (D), the short-circuit detection signal Sd changes to a low level (arc period). In response to this, as shown in Figure (H), the constriction detection signal Nd changes to a low level. Simultaneously, as shown in Figure (E), the first arc period signal Sta1 changes to a high level, and the period from time t4 to t61 becomes the predetermined first arc period Ta1. Constant current control continues during the first arc period Ta1.

[0056] Simultaneously, the period from time t4 to t5 becomes a predetermined reverse-drive deceleration period Trd. As shown in Figure (A), the feed rate Fw is reduced from the reverse-drive peak value Wrp to 0.

[0057] When the reverse deceleration period Trd ends at time t5, the system transitions to a predetermined forward acceleration period Tsu from time t5 to t6. During this forward acceleration period Tsu, as shown in Figure (A), the feed rate Fw accelerates from 0 to the forward peak value Wsp. The arc period continues during this period.

[0058] When the forward acceleration period Tsu ends at time t6, the feed rate Fw enters the forward peak period Tsp, as shown in Figure (A), and becomes the forward peak value Wsp. The arc period continues during this period as well. The forward peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to t7 is the arc period. When a short circuit occurs, the operation returns to that of time t1.

[0059] At time t51 during the forward acceleration period Tsu, which is a predetermined delay period after the end of the reverse deceleration period Trd at time t5, the polarity switching signal Spn changes from a high level to a low level, as shown in Figure (G), and switches to the positive electrode polarity EP. In response to this, as shown in Figure (B), the welding current Iw changes from a negative low-level current value to a positive low-level current value. Similarly, as shown in Figure (C), the welding voltage Vw changes from a negative arc voltage value to a positive arc voltage value. Therefore, as shown in Figure (G), the polarity switching signal Spn is at a high level during the period from time t32 to t51, and the electrode polarity is negative EN. As shown in Figure (B), the welding current Iw maintains the value of the low-level current setting signal Ilr in Figure 1 during the period of negative electrode polarity EN.

[0060] The period of the negative electrode polarity EN described above is set by the polarity switching circuit SPN in Figure 1 as follows. 1) The period of negative electrode polarity EN shall include at least the reverse drive deceleration period Trd from time t4 to t5. 2) The end of the period with negative electrode polarity EN is set to time t51, which is delayed from the end of the reverse-speed deceleration period Trd. 3) The start time of the period with negative electrode polarity EN is set to a point earlier than the start time of the arc period at time t4. 4) The start of the period with negative electrode polarity EN is defined as the point at time t31 when constriction is detected and at time t32 when the welding current Iw decreases to a low current value.

[0061] In conventional forward and reverse feed control arc welding methods, there is a problem in that during the reverse feed deceleration period Trd, when the short circuit is released and the arc is regenerated and the feed speed changes from the reverse feed peak value to the forward feed peak value, the cathode point of the arc moves in search of the oxide film on the base metal surface, causing the arc to fluctuate and the welding state to become unstable. In this embodiment, the electrode polarity is set to negative EN at least during the reverse feed deceleration period Trd. In this way, the cathode point of the arc is fixed to the tip of the welding wire, so the arc does not fluctuate and the arc generation state can be stabilized. Furthermore, since the welding current Iw is at a low current value during the period of negative electrode polarity EN, melting of the welding wire can be suppressed, and the arc length which would rapidly increase and the arc generation state which would become unstable can be suppressed.

[0062] At time t51, when the period of negative electrode polarity EN ends, as shown in Figure (B), the welding current Iw increases from time t51 to the first arc current value Ia1 set by the first arc current setting signal Ia1r, and is maintained until the first arc period Ta1 ends at time t61. As shown in Figure (C), the welding voltage Vw also has a waveform similar to that of the welding current Iw.

[0063] When the first arc period Ta1 ends at time t61, the period from time t61 to t62 becomes the second arc period Ta2, and the welding power supply is switched to constant voltage control. As shown in Figure (B), the second arc current value Ia2 is a value corresponding to the arc load, and as shown in Figure (C), the welding voltage Vw is a value controlled by the voltage setting signal Vr in Figure 1. By controlling this second arc period Ta2 with constant voltage, the arc length is controlled to an appropriate value.

[0064] At time t62, after a predetermined current drop time Td has elapsed since the arc generation time t4, the third arc period signal Sta3 changes to a high level, as shown in Figure (F). The period from this point until time t7, when the next short circuit occurs, is the third arc period Ta3. During the third arc period Ta3, constant current control is applied. As shown in Figure (B), a predetermined third arc current value Ia3, determined by the third arc current setting signal Ia3r in Figure 1, is applied. As shown in Figure (C), the welding voltage Vw is a value determined by the current value and the arc load. By setting the third arc current value Ia3 immediately before a short circuit to a small value, it is possible to induce a short circuit and suppress spatter generation when a short circuit occurs.

[0065] Numerical examples for each of the above parameters are shown below: Short circuit period (not a specified value): 3ms, Arc period (not a specified value): 4ms, Period of negative electrode polarity EN (not a specified value): 1ms, Delay period (specified value): 0.1ms, First arc period Ta1 (specified value): 1.5ms, Second arc period Ta2 (not a specified value): 2ms, Third arc period Ta3 (not a specified value): 0.5ms, Current drop time (specified value): 3.5ms, Low-level current value (specified value): 50A, First arc current value Ia1 (specified value): 300A, Third arc current value Ia3 (specified value): 50A, Forward feed peak value Wsp (specified value): 30m / min, Reverse feed peak value Wrp (specified value): -25m / min

[0066] The effects of this embodiment will now be explained. According to this embodiment, in a forward / reverse feed control arc welding method in which the welding wire feed speed is set to the forward feed peak value during the arc period and to the reverse feed peak value during the short-circuit period, and welding is performed by applying a welding current with positive electrode polarity, at the start of the arc period, the feed speed transitions to a reverse feed deceleration period in which it is reduced from the reverse feed peak value to 0, and the electrode polarity is switched to negative for at least the duration of the reverse feed deceleration period. In the conventional forward / reverse feed control arc welding method, there is a problem that the arc fluctuates and the welding state becomes unstable because the cathode point of the arc moves in search of the oxide film on the surface of the base material during the reverse feed deceleration period when the short circuit is released, the arc is regenerated and the feed speed changes from the reverse feed peak value to the forward feed peak value. In this embodiment, the electrode polarity is negative for at least the duration of the reverse feed deceleration period. In this way, the cathode point of the arc is fixed to the tip of the welding wire, so the arc does not fluctuate and the arc generation state can be stabilized.

[0067] More preferably, according to this embodiment, the electrode is returned to positive polarity with a delay from the end of the reverse deceleration period. Since the arc may still fluctuate immediately after the end of the reverse deceleration period and the start of the forward acceleration period, the arc generation state can be stabilized by returning to positive polarity with a delay.

[0068] More preferably, according to this embodiment, the switching to the negative electrode polarity is performed before the start of the arc period. If the switching to the negative electrode polarity is performed during the arc period, there is a risk of arc interruption occurring due to the polarity switching. In this embodiment, since the polarity switching is performed during the short-circuit period before the start of the arc period, there is no concern about arc interruption and the process can be carried out smoothly.

[0069] More preferably, according to this embodiment, if a constriction of the molten droplet is detected during the short-circuit period, the welding current is reduced, and the switching to the negative polarity of the electrode is performed at the point when the welding current decreases. In this way, the polarity can be switched when the welding current is small, so the polarity can be switched smoothly.

[0070] More preferably, according to this embodiment, the welding current is controlled to 100A or less during the period when the electrode is negatively polarized. In this way, since the welding current is small during the period when the electrode is negatively polarized, melting of the welding wire can be suppressed, and the rapid increase in arc length and the resulting instability of the arc generation state can be prevented.

[0071] Furthermore, according to this embodiment, the forward / reverse feed control arc welding apparatus transitions to a reverse feed deceleration period at the start of the arc period in which the feed speed is reduced from the reverse feed peak value to 0, and switches to negative electrode polarity at least during the reverse feed deceleration period. The forward / reverse feed control arc welding apparatus according to this embodiment achieves the above-described effects. [Explanation of symbols]

[0072] 1: Welding wire, 2: Base metal, 3: Arc, 4: Welding torch, 5: Feed roll, CM: Current comparison circuit, Cm: Current comparison signal, DR: Drive circuit, Dr: Drive signal, Ea: Error amplification signal, EI: Current error amplification circuit, Ei: Current error amplification signal, EV: Voltage error amplification circuit, Ev: Voltage error amplification signal, FC: Feed control circuit, Fc: Feed control signal, FR: Feed speed setting circuit, Fr: Feed speed setting signal, Fw: Feed speed, Ia1: First arc current, IA1R: First arc current setting circuit, Ia1r: First arc current setting signal, Ia2: Second Arc current, Ia3: Third arc current, IA3R: Third arc current setting circuit, Ia3r: Third arc current setting signal, ICR: Current control setting circuit, Icr: Current control setting signal, ID: Current detection circuit, Id: Current detection signal, ILR: Low level current setting circuit, Ilr: Low level current setting signal, ISR: Short circuit current setting circuit, Isr: Short circuit current setting signal, Iw: Welding current, ND: Narrowing detection circuit, Nd: Narrowing detection signal, PM: Power control circuit, SD: Short circuit discrimination circuit, Sd: Short circuit discrimination signal, SPN: Polarity switching circuit, Spn: Polarity switching Signal, Srd: Reverse deceleration period signal, STA1: First arc period circuit, Sta1: First arc period signal, STA3: Third arc period circuit, Sta3: Third arc period signal, SW: Power supply characteristic switching circuit, TA1R: First arc period setting circuit, Ta1r: First arc period setting signal, Td: Current drop time, Trd: Reverse deceleration period, TRDR: Reverse deceleration period setting circuit, Tdr: Reverse deceleration period setting signal, Trp: Reverse peak period, Tru: Reverse acceleration period, TRUR: Reverse acceleration period setting circuit, Tru: Reverse acceleration period setting signal, Tsd : Forward feed deceleration period, TSDR: Forward feed deceleration period setting circuit, Tsdr: Forward feed deceleration period setting signal, Tsp: Forward feed peak period, Tsu: Forward feed acceleration period, TSUR: Forward feed acceleration period setting circuit, Tsur: Forward feed acceleration period setting signal, VD: Voltage detection circuit, Vd: Voltage detection signal, VR: Voltage setting circuit, Vr: Voltage setting signal, Vw: Welding voltage, WM: Feed motor, Wrp: Reverse feed peak value, WRR: Reverse feed peak value setting circuit, Wrr: Reverse feed peak value setting signal, Wsp: Forward feed peak value, WSR: Forward feed peak value setting circuit, Wsr: Forward feed peak value setting signal

Claims

1. In a forward / reverse feed controlled arc welding method in which the welding wire feed speed is set to the forward feed peak value during the arc period and to the reverse feed peak value during the short-circuit period, and welding is performed by applying the welding current with positive electrode polarity, At the start of the arc period, the feed rate transitions to a reverse deceleration period in which it decreases from the reverse peak value to 0, and the electrode polarity is switched to negative for at least the duration of the reverse deceleration period. A forward and reverse feed control arc welding method characterized by the following features.

2. The electrode is returned to positive polarity with a delay from the end of the aforementioned reverse deceleration period. The forward and reverse feed control arc welding method according to feature 1.

3. The switching of the electrode to negative polarity occurs before the start of the arc period. The forward and reverse feed control arc welding method according to feature 1.

4. If a constriction of the molten droplet is detected during the short-circuit period, the welding current is reduced, and the switching to the negative polarity of the electrode occurs at the point when the welding current decreases. The forward and reverse feed control arc welding method according to feature 3.

5. During the period when the electrode is negatively polarized, the welding current is controlled to 100 A or less. The forward and reverse feed control arc welding method according to any one of claims 1 to 4.

6. In a forward / reverse feed control arc welding apparatus that sets the welding wire feed speed to the forward feed peak value during the arc period and to the reverse feed peak value during the short-circuit period, and performs welding by applying welding current with positive electrode polarity, At the start of the arc period, the feed rate transitions to a reverse deceleration period in which it decreases from the reverse peak value to 0, and the electrode polarity is switched to negative for at least the duration of the reverse deceleration period. A forward and reverse feed control arc welding apparatus characterized by the following features.

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