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, when a short circuit is released and the arc is regenerated, causing the feed rate to change from the reverse feed peak value to the forward feed peak value, the arc may ignite, the arc length may become excessively long, and the welding state may become unstable. [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 when a constriction of the molten droplet is detected at time t31 during the short circuit period, the welding current Iw is reduced and the arc is regenerated at time t4 to perform welding, the feed speed Fw starts to change from the reverse feed peak value to 0 at time t31 before the arc is regenerated, and is at 0 at the time of arc regeneration t4.

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 for welding by setting the feeding speed of the welding wire to a forward feeding peak value during the arc period and to a reverse feeding peak value during the short circuit period is used (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 conventional forward / reverse feed control arc welding methods, 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 arc ignites, the arc length becomes excessively long, and the welding state becomes unstable. Therefore, the present invention aims to stabilize the welding state in a forward / reverse feed control arc welding method 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 when a constriction of the molten droplet is detected during the short-circuit period, the welding current is reduced and the arc is restarted to perform welding, wherein the feeding speed starts to change from the reverse feed peak value to 0 before the restart of the arc and is at a state of 0 at the time of the restart of the arc.

[0007] In a preferred embodiment of the present invention, the start time of the change from the reverse peak value to 0 is defined as the time when the constriction is detected.

[0008] In a preferred embodiment of the present invention, the feed rate begins to change from 0 to the positive feed peak value at the time the arc is regenerated.

[0009] In a preferred embodiment of the present invention, the feed rate starts to change from 0 to the positive feed peak value after a delay period has elapsed from the time the arc is regenerated.

[0010] In a preferred embodiment of the present invention, the welding current is maintained in the reduced state until the delay period has elapsed.

[0011] A forward / reverse feed control arc welding apparatus provided by a second aspect of the present invention 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 when a constriction of the molten droplet is detected during the short-circuit period, reduces the welding current to restart the arc and perform welding, wherein the feed speed starts to change from the reverse feed peak value to 0 before the restart of the arc and is at 0 at the time of the restart of the arc. [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. Each block will be described below with reference to the same figure.

[0016] The main power supply circuit PM takes a commercial power supply such as 3-phase 200V (not shown) as input and controls the output by inverter control etc. according to the error amplification signal Ea described later, and outputs an output voltage E. This main power supply circuit PM, although not shown, includes a primary rectifier that rectifies the commercial power supply, a smoothing capacitor that smooths the rectified DC, an inverter circuit driven by the above error amplification signal Ea that converts the smoothed DC into high-frequency AC, a high-frequency transformer that steps down the high-frequency AC to a voltage value suitable for welding, and a secondary rectifier that rectifies the stepped-down high-frequency AC into DC.

[0017] The reactor WL smooths the output voltage E mentioned above. The inductance value of this reactor WL is, for example, 100 μH.

[0018] 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.

[0019] The welding wire 1 is fed through the welding torch 4 by the rotation of the 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 between the power supply tip (not shown) inside the welding torch 4 and the base material 2, and a welding current Iw is passed through. Shielding gas (not shown) is ejected from the tip of the welding torch 4.

[0020] The welding current setting circuit IR outputs a predetermined welding current setting signal Ir to set the average value of the above-mentioned welding current Iw.

[0021] The welding voltage reference value setting circuit VSR takes the above-mentioned welding current setting signal Ir as an input and outputs a welding voltage reference value setting signal Vsr according to a predetermined voltage calculation function. The voltage setting function is a function that calculates the value of the welding voltage reference value setting signal Vsr corresponding to the value of the welding current setting signal Ir to obtain an appropriate arc length, and is defined by experiments in advance.

[0022] The welding voltage fine adjustment circuit DVR outputs a predetermined welding voltage fine adjustment signal Dvr with positive and negative values for correcting the value of the above-mentioned welding voltage reference value setting signal Vsr.

[0023] The welding voltage setting circuit VR takes the above-mentioned welding voltage reference value setting signal Vsr and the above-mentioned welding voltage fine adjustment signal Dvr as inputs, corrects the value of the welding voltage reference value setting signal Vsr by adding the two values, and outputs a welding voltage setting signal Vr. Assume that the welding voltage reference value setting signal Vsr = 21V when the welding current setting signal Ir = 200A. Also, if the welding voltage fine adjustment signal Dvr = -2V, then the welding voltage setting signal Vr = 21 - 2 = 19V.

[0024] The welding voltage detection circuit VD detects the above-mentioned welding voltage Vw and outputs a welding voltage detection signal Vd.

[0025] The voltage error amplification circuit EV takes the above-mentioned welding voltage setting signal Vr and the above-mentioned welding voltage detection signal Vd as inputs, amplifies the error between the two values, and outputs a voltage error amplification signal Ev.

[0026] The welding current detection circuit ID detects the above-mentioned welding current Iw and outputs a welding current detection signal Id.

[0027] The short-circuit discrimination circuit SD takes the above-mentioned welding voltage detection signal Vd as an input. When this value is less than a predetermined short-circuit discrimination value (about 10V), 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.

[0028] The forward transmission acceleration period setting circuit TSUR outputs a predetermined forward transmission acceleration period setting signal Tsur.

[0029] The forward / decelerate period setting circuit TSDR outputs a predetermined forward / decelerate period setting signal Tsdr.

[0030] The reverse acceleration period setting circuit TRUR outputs a predetermined reverse acceleration period setting signal True.

[0031] The reverse drive deceleration period setting circuit TRDR outputs a predetermined reverse drive deceleration period setting signal Tdr.

[0032] The forward peak value setting circuit WSR outputs a predetermined forward peak value setting signal Wsr.

[0033] The reverse peak value setting circuit WRR outputs a predetermined negative reverse peak value setting signal Wrr.

[0034] The power supply interruption period circuit PS takes the short-circuit detection signal Sd and the constriction detection signal Nd (described later) as inputs, performs one of the following processes 1) to 3), and outputs a power supply interruption period signal Ps that is at a high level for the period during which power supply is stopped. 1) Output a power supply interruption period signal Ps that goes to a high level before the arc re-occurs after the short circuit period, maintains a high level at the time of arc re-occurrence, and then goes to a low level. For example, the power supply interruption period signal Ps is set to a high level after a predetermined elapsed time has elapsed from the time the short circuit detection signal Sd changes to a high level (short circuit period). Since the short circuit period is approximately a predetermined value, the elapsed time is set to the predetermined value minus 0.7 ms. 2) When the constriction detection signal Nd changes to a high level, a feed stop period signal Ps is output, which becomes high level, and when the constriction detection signal Nd changes to a low level (arc re-generation), it becomes low level. 3) When the constriction detection signal Nd changes to a high level, a supply stop period signal Ps is output, which becomes high level. When the constriction detection signal Nd changes to a low level (arc re-generation) and a predetermined delay period Tc has elapsed, a supply stop period signal Ps is output, which becomes low level.

[0035] 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, short circuit detection signal Sd, and feed stop period signal Ps as inputs and outputs a feed speed pattern generated by the following process as the feed speed setting signal Fr. When this feed speed setting signal Fr > 0, it is in the forward transmission state; when Fr = 0, it is in the feed stop state; and when Fr < 0, it is in the reverse transmission state. 1) When the feed stop period signal Ps changes to a low level (after arc regeneration), a feed speed setting signal Fr is output, which accelerates from 0 to the feed peak value Wsp determined by the feed peak value setting signal Wsr during the feed acceleration period Tsu, which is determined by the feed acceleration period setting signal Tsur. 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 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 the 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 feed stop period signal Ps changes to a high level (just before arc re-initiation), the system transitions to the reverse deceleration period Trd, determined by the reverse deceleration period setting signal Trdr, and outputs a feed speed setting signal Fr that decelerates the feed speed from the reverse peak value Wrp to 0. 7) When the short-circuit detection signal Sd changes to a low level (the point at which the arc re-starts), the feed rate setting signal Fr, which is 0, is output. 8) By repeating steps 1) to 7) above, a feed rate setting signal Fr is generated, which has a feed pattern that changes in a positive and negative trapezoidal wave shape.

[0036] The feed control circuit FC takes the feed speed setting signal Fr as input and outputs a feed control signal Fc to the feed motor WM for feeding the welding wire 1 at a feed speed Fw corresponding to the value of the feed speed setting signal Fr.

[0037] The current-reducing resistor R is inserted between the reactor WL and the welding torch 4. The value of this current-reducing resistor R 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 this current-reducing resistor R is inserted into the current-carrying circuit, the energy stored in the reactor WL and the reactor of the external cable is rapidly discharged, causing a sharp decrease in the welding current Iw.

[0038] The transistor TR is connected in parallel with the current-reducing resistor R mentioned above and is controlled to be turned on or off according to the drive signal Dr described later.

[0039] The constriction detection circuit ND takes the above-mentioned short-circuit discrimination signal Sd, the above-mentioned welding voltage detection signal Vd, and the above-mentioned welding current detection signal Id as inputs. When the short-circuit discrimination signal Sd is at the High level (short-circuit period), when the voltage increase value of the welding voltage detection signal Vd reaches the reference value, it determines that the constriction formation state has reached the reference state and becomes High level, and outputs a constriction detection signal Nd that becomes Low level when the short-circuit discrimination signal Sd changes to the Low level (arc period). Also, the constriction detection signal Nd may be changed to High level when the differential value of the welding voltage detection signal Vd during the short-circuit period reaches the corresponding reference value. Further, the value of the welding voltage detection signal Vd is divided by the value of the welding current detection signal Id to calculate the resistance value of the droplet, and the constriction detection signal Nd may be changed to High level when the differential value of this resistance value reaches the corresponding reference value.

[0040] The low-level current setting circuit ILR outputs a predetermined low-level current setting signal Ilr. The current comparison circuit CM takes this low-level current setting signal Ilr and the above-mentioned welding 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.

[0041] 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 above-mentioned transistor TR that changes to Low level when the constriction detection signal Nd changes to High level, and then changes to High level when the current comparison signal Cm changes to High level. Therefore, this drive signal Dr becomes Low level when constriction is detected, the transistor TR becomes off, and the current limiting resistor R is inserted into the conduction path, so the welding current Iw passing through the short-circuit load rapidly decreases. And when the value of the rapidly decreasing welding current Iw decreases to the value of the low-level current setting signal Ilr, the drive signal Dr becomes High level, the transistor TR becomes on, so the current limiting resistor R is short-circuited and returns to the normal state.

[0042] The first arc period setting circuit TA1R outputs a predetermined first arc period setting signal Ta1r.

[0043] 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 during the first arc period Ta1 predetermined by the first arc period setting signal Ta1r, from the time when the short-circuit detection signal Sd changes to a low level (arc period) and a predetermined delay period Tc has elapsed.

[0044] The first arc current setting circuit IA1R outputs a predetermined first arc current setting signal Ia1r.

[0045] 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).

[0046] The third arc current setting circuit IA3R outputs a predetermined third arc current setting signal Ia3r.

[0047] The current control setting circuit ICR takes the above-mentioned short-circuit detection signal Sd, low-level current setting signal Ilr, constriction detection signal Nd, first arc period signal Sta1, third arc period signal Sta3, first arc current setting signal Ia1r, and third arc current setting signal Ia3r as inputs, performs the following processing, and outputs the current control setting signal Icr. 1) During the delay period Tc from the moment the short-circuit detection signal Sd changes to a low level (arc period) until the first arc period signal Sta1 changes to a high 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, when the first arc period signal Sta1 is at a high level (first arc period), a current control setting signal Icr, which becomes 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 becomes the third arc current setting signal Ia3r, is output. 4) When the short-circuit detection signal Sd changes to a high level (short-circuit period), the current will be set to a predetermined initial current setting value for a predetermined initial period, and thereafter, a current control setting signal Icr will be output, which rises to a predetermined short-circuit peak setting value with a predetermined short-circuit slope and maintains that value. 5) Subsequently, when the constriction detection signal Nd changes to a high level, a current control setting signal Icr is output, which is equal to the value of the low-level current setting signal Ilr.

[0048] The current error amplification circuit EI takes the above-mentioned current control setting signal Icr and the above-mentioned welding current detection signal Id as inputs, amplifies the error between the two values, and outputs a current error amplification signal Ei.

[0049] 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, delay period Tc, first arc period Ta1, and third arc period Ta3, and constant voltage during the second arc period Ta2.

[0050] 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, and Figure (G) shows the time variation of the feed stop period signal Ps. The operation of each signal will be explained below with reference to the figure.

[0051] The feed rate Fw shown in Figure (A) is controlled by the value of the feed rate setting signal Fr output from the feed rate setting circuit FR in Figure 1. The feed rate Fw is formed from the forward acceleration period Tsu, determined by the forward acceleration period setting signal Tsur in Figure 1 after arc regeneration; the forward peak period Tsp, which continues until a short circuit occurs; the forward deceleration period Tsd, determined by the forward deceleration period setting signal Tsdr in Figure 1; the reverse acceleration period Tru, determined by the reverse acceleration period setting signal Tru in Figure 1; the reverse peak period Trp, which continues until just before arc regeneration; and the reverse deceleration period Trd, determined by the reverse deceleration period setting signal Tdr in Figure 1 from just before arc regeneration. Furthermore, the forward peak value Wsp is determined by the forward peak value setting signal Wsr in Figure 1, and the reverse peak value Wrp is determined by the reverse peak value setting signal Wrr in Figure 1. As a result, the feed rate Fw is positive during the forward feed period and negative during the reverse feed period, resulting in a feed pattern that changes in a roughly trapezoidal wave shape between positive and negative values.

[0052] [Operation during the short-circuit period from time t1 to t4] If a short circuit occurs at time t1 during the forward feed peak period Tsp, the welding voltage Vw will rapidly decrease to a short-circuit voltage of a few volts, as shown in Figure (C), and the short-circuit detection signal Sd will change to a high level (short-circuit period), as shown in Figure (D). In response to this, the system will transition to a predetermined forward feed deceleration period Tsd from time t1 to t2, and the feed rate Fw will decelerate from the forward feed peak value Wsp to 0, as shown in Figure (A). For example, the forward feed deceleration period Tsd is set to 1 ms.

[0053] 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. For example, the reverse acceleration period Tru is set to 1 ms.

[0054] When the reverse acceleration period Tru ends at time t3, as shown in Figure (A), the feed rate Fw enters the reverse peak period Trp and becomes the reverse peak value Wrp. The reverse peak period Trp is not a predetermined value, but it is approximately 3 ms. For example, the reverse peak value Wrp is set to -40 m / min.

[0055] At time t31, as shown in Figure (G), when the feed stop period signal Ps changes to a High level, the predetermined reverse feed deceleration period Trd is entered, and as shown in Figure (A), the feed rate Fw begins to change from the reverse feed peak value Wrp to 0. The feed rate Fw is then 0 when the arc is regenerated at time t4, and this state continues until time t5, when the delay period Tc has elapsed and the feed stop period signal Ps changes to a Low level. In the conventional technology, when the 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, there is a problem in that the arc ignites, the arc length becomes excessively long, and the welding state becomes unstable. This is because the feed rate Fw is still in the reverse feed state when the arc is regenerated, so the arc length is increased and becomes excessively long. In this embodiment, the feed rate Fw is 0 when the arc is regenerated, and thereafter it is in the forward feed state, so the length of the arc can be suppressed. As a result, in this embodiment, 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. The period from time t1 to t4 is the short circuit period. For example, the reverse feed deceleration period Trd is set to 0.5 ms.

[0056] The above-mentioned power supply interruption period signal Ps is set by the power supply interruption period circuit PS in Figure 1 as follows. 1) The power supply interruption period signal Ps goes to a high level from the short-circuit period until the arc re-occurs, maintains a high level at the time of arc re-occurrence, and then goes to a low level. For example, the power supply interruption period signal Ps is set to a high level after a predetermined elapsed time has elapsed from the time the short-circuit detection signal Sd changes to a high level (short-circuit period) at time t1. Since the short-circuit period from time t1 to t4 is approximately a predetermined value, the elapsed time is set to the predetermined value minus 0.7ms. 2) The feed stop period signal Ps becomes high when the constriction detection signal Nd in Figure 1 changes to a high level at time t31, and becomes low when the constriction detection signal Nd changes to a low level (arc re-generation) at time t4. 3) The feed stop period signal Ps becomes high when the constriction detection signal Nd changes to high level at time t31, and becomes low at time t5 when the constriction detection signal Nd changes to low level (arc re-generation) and a predetermined delay period Tc has elapsed.

[0057] 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 the 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.

[0058] As shown in Figure (C), the welding voltage Vw increases from around the point where 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.

[0059] Subsequently, when the voltage rise of the welding voltage Vw reaches the reference value, it is determined that the neck formation state has reached the reference state, and at time t31, the neck detection signal Nd in Figure 1 changes to a high level.

[0060] In response to the constriction detection signal Nd reaching a high level, the drive signal Dr in Figure 1 goes to a low level, so the transistor TR in Figure 1 turns off and the current reducing resistor R in Figure 1 is inserted into the current path. At the same time, the current control setting signal Icr in Figure 1 decreases to the value of the low-level current setting signal Ilr. As a result, as shown in Figure (B), the welding current Iw rapidly decreases from the short-circuit peak value to the low-level current value. When the welding current Iw decreases to the low-level current value, the drive signal Dr returns to a high level, so the transistor TR turns on and the current reducing resistor R is short-circuited. As shown in Figure (B), the welding current Iw remains at a low level until time t5, when a predetermined delay period Tc has elapsed since arc regeneration, because the current control setting signal Icr remains at the low-level current setting signal Ilr. Therefore, the transistor TR is off only during the period from when the constriction detection signal Nd changes to a high level until the welding current Iw decreases to the low-level current value. As shown in Figure (C), the welding voltage Vw decreases as the welding current Iw decreases, and then rises sharply. The parameters mentioned above are set to the following values, for example: initial current = 40A, initial period = 0.5ms, short-circuit slope = 180A / ms, short-circuit peak value = 400A, low-level current value = 50A, delay period Tc = 0.5ms.

[0061] [Operation during the arc period from time t4 to t7] At time t4, as the welding wire is reversed and the pinching force caused by the application of the welding current Iw causes constriction to progress and an arc is generated, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, as shown in Figure (C), and the short-circuit detection signal Sd changes to a low level (arc period), as shown in Figure (D).

[0062] After a delay period Tc has elapsed from the time t4 when the arc re-occurs, 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. For example, the forward acceleration period Tsu is set to 1 ms.

[0063] When the forward acceleration period Tsu ends at time t6, as shown in Figure (A), the feed rate Fw enters the forward peak period Tsp and becomes the forward peak value Wsp mentioned above. 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. The forward peak period Tsp is not a predetermined value, but it is approximately 5ms. Also, for example, the forward peak value Wsp is set to 50m / min.

[0064] When an arc is generated at time t4, the welding voltage Vw rapidly increases to an arc voltage value of several tens of volts, as shown in Figure (C). On the other hand, as shown in Figure (B), the welding current Iw remains at a low level during the delay period Tc from time t4 to t5. This is because increasing the current value immediately after arc generation can cause the arc length to increase rapidly due to the melting of the welding wire by the welding current, potentially leading to an unstable welding state.

[0065] At time t5, when the delay period Tc ends, as shown in Figure (E), the first arc period signal Sta1 changes to a high level, and the system transitions to a predetermined first arc period Ta1 from time t5 to t61. During this first arc period Ta1, constant current control continues, and as shown in Figure (B), a predetermined first arc current Ia1 determined by the first arc current setting signal Ia1r in Figure 1 is supplied. As shown in Figure (C), the welding voltage Vw becomes a large value determined by the current value and arc load. For example, the first arc period Ta1 is set to 0.5 ms, and the first arc current Ia1 is set to 400 A.

[0066] 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 time t61 to t62 is the second arc period Ta2. During this second arc period Ta2, the welding voltage Vw is controlled to a constant voltage so that the value of the welding voltage setting signal Vr in Figure 1 and the value of the welding voltage detection signal Vd in Figure 1 are equal. The welding voltage setting signal Vr is calculated by adding the welding voltage fine adjustment signal Dvr in Figure 1 to the welding voltage reference value setting signal Vsr, which is calculated by a predetermined voltage calculation function using the welding current setting signal Ir in Figure 1 as input. That is, Vr = Vsr + Dvr. As shown in Figure (B), the second arc current Ia2 changes depending on the arc load, but it is smaller than the first arc current Ia1 and larger than the third arc current Ia3. In other words, the output is controlled so that Ia1 > Ia2 > Ia3. As shown in Figure (C), the welding voltage Vw is controlled to a predetermined value by constant voltage control, and is an intermediate value between the voltage value during the first arc period Ta1 and the voltage value during the third arc period Ta3. The voltage during the second arc period Ta2 is not a predetermined value, but is approximately 6 ms.

[0067] The period from time t62, when the third arc period signal Sta3 changes to a high level, until time t7, when a short circuit occurs, is the third arc period Ta3. During this third arc period Ta3, constant current control is applied. As shown in Figure (B), a predetermined third arc current 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. For example, the third arc current Ia3 is set to 60A. The third arc period Ta3 is not a predetermined value, but is approximately 0.5ms.

[0068] 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 when a constriction of the molten droplet is detected during the short circuit period, the welding current is reduced to regenerate the arc and weld, the feed speed starts to change from the reverse feed peak value to 0 before the arc is regenerated, and is at 0 when the arc is regenerated. In the conventional technology, 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, there is a problem that the arc ignites and the arc length becomes excessively long, making the welding state unstable. This is because the feed speed is still in the reverse feed state when the arc is regenerated, so the arc length is increased and becomes excessively long. In this embodiment, the feed speed is 0 when the arc is regenerated and thereafter becomes the forward feed state, so it is possible to suppress the arc length from becoming long. As a result, in this embodiment, 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.

[0069] More preferably, according to this embodiment, the start of the change from the reverse feed peak value to 0 is set to the time when necking is detected. If the start of the change from the reverse feed peak value to 0 is too early, the transition of the molten droplet to the molten pool will be insufficient, and the welding state will become unstable. As in this embodiment, setting the start of the change from the reverse feed peak value to 0 to the time when necking is detected results in an appropriate timing before arc regeneration. As a result, in this embodiment, the welding state can be made more stable 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.

[0070] More preferably, according to this embodiment, the feed rate begins to change from 0 to the positive feed peak value at the time the arc is re-initiated. In this way, the feed rate is accelerated over time to the positive feed peak value after the arc is re-initiated, which can suppress the arc length from becoming longer and the welding state from becoming unstable.

[0071] More preferably, according to this embodiment, the feed rate begins to change from 0 to the positive feed peak value after a delay period has elapsed from the time the arc is re-initiated. In this way, since the feed rate remains 0 immediately after the arc is re-initiated, the occurrence of re-short circuits can be suppressed and the welding state can be stabilized.

[0072] More preferably, according to this embodiment, the welding current is kept at a reduced state until the delay period has elapsed. In this way, since the welding current is at a reduced state immediately after the arc is re-generated, melting of the welding wire is suppressed. As a result, it is possible to suppress the melting of the welding wire and the lengthening of the arc, and thus the welding state can be stabilized.

[0073] Furthermore, according to this embodiment, in a forward / reverse feed control arc welding apparatus, the feed rate begins to change from the reverse feed peak value to 0 before the arc is regenerated, and is at 0 at the time the arc is regenerated. The forward / reverse feed control arc welding apparatus according to this embodiment achieves the above-mentioned effects. [Explanation of symbols]

[0074] 1: Welding wire, 2: Base material, 3: Arc, 4: Welding torch, 5: Feeding roll, CM: Current comparison circuit, Cm: Current comparison signal, DR: Drive circuit, Dr: Drive signal, DVR: Welding voltage fine adjustment circuit, Dvr: Welding voltage fine adjustment signal, E: Output voltage, Ea: Error amplification signal, EI: Current error amplification circuit, Ei: Current error amplification signal, EV: Voltage error amplification circuit, Ev: Voltage error amplification signal, FAR: Feeding speed average value setting circuit, Far: Feeding speed average value setting circuit, FC: Feeding control circuit, Fc: Feeding control signal, FR: Feeding speed setting circuit, Fr: Feeding speed setting signal, Fw: Feeding 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: Welding current detection circuit, Id: Welding current detection signal, ILR: Low-level current setting circuit, Ilr: Low-level current setting signal, IR: Welding current setting circuit, Ir: Welding current setting signal, Iw: Welding current, ND: Narrowing detection circuit, Nd: Narrowing detection signal, PM: Power supply main circuit, PS : Power supply stop period circuit, Ps: Power supply stop period signal, R: Current reducing resistor, SD: Short circuit detection circuit, Sd: Short circuit detection 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, Tc: Delay period, Td: Current drop time, TR: Transistor, Trd: Reverse deceleration period, TRDR: Reverse deceleration period setting circuit, Trdr: Reverse deceleration period setting signal, Trp: Reverse peak period, Tru: Reverse acceleration period TRUR: Reverse acceleration period setting circuit, Trur: Reverse acceleration period setting signal, Tsd: Forward deceleration period, TSDR: Forward deceleration period setting circuit, Tsdr: Forward deceleration period setting signal, Tsp: Forward peak period, Tsu: Forward acceleration period, TSUR: Forward acceleration period setting circuit, Tsur: Forward acceleration period setting signal, VD: Welding voltage detection circuit, Vd: Welding voltage detection signal, VR: Welding voltage setting circuit, Vr: Welding voltage setting signal, VSR: Welding voltage reference value setting circuit, Vsr: Welding voltage reference value setting signal, Vw: Welding voltage, WL: Reactor, WM: Feed motor, Wrp: Reverse peak value,WRR: Reverse peak value setting circuit, Wrr: Reverse peak value setting signal, Wsp: Forward peak value, WSR: Forward peak value setting circuit, Wsr: Forward peak value setting signal.

Claims

1. In a forward / reverse feed controlled arc welding method, 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 when a constriction of the molten droplet is detected during the short-circuit period, the welding current is reduced to regenerate the arc and weld, The feed rate begins to change from the reverse feed peak value to 0 before the arc is regenerated, and is at 0 at the time the arc is regenerated. A forward and reverse feed control arc welding method characterized by the following features.

2. The starting point of the change from the reverse peak value to 0 is defined as the time when the constriction is detected. The forward and reverse feed control arc welding method according to feature 1.

3. The feed rate begins to change from 0 to the positive feed peak value at the time the arc is regenerated. The forward and reverse feed control arc welding method according to claim 1 or 2, characterized by the above.

4. The feed rate begins to change from 0 to the forward feed peak value after a delay period has elapsed from the time the arc is regenerated. The forward and reverse feed control arc welding method according to claim 1 or 2, characterized by the above.

5. The welding current shall maintain the reduced state until the delay period has elapsed. The forward and reverse feed control arc welding method according to feature 4.

6. In a forward / reverse feed control arc welding apparatus, the welding wire feeding 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 when a constriction of the molten droplet is detected during the short-circuit period, the welding current is reduced to regenerate the arc and weld, The feed rate begins to change from the reverse feed peak value to 0 before the arc is regenerated, and is at 0 at the time the arc is regenerated. A forward and reverse feed control arc welding apparatus characterized by the following features.

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