Arc welding device

Abstract

An arc welding device is provided. A formation state of a neck of a droplet is estimated without detecting a voltage of an arc generation portion. The arc welding device includes a short-circuit determination portion (SD), a current reduction timer portion (ND) that outputs a current reduction signal (Nd) if a reference time (Tnr) elapses from a start time point of a short-circuit period, a power control portion (PM) that supplies an output terminal-to-terminal voltage (Vw) and a welding current (Iw) between a welding wire (1) and a base material (2), and repeatedly a short-circuit period and an arc period, and that reduces the welding current (Iw) and shifts to the arc period if the current reduction signal (Nd) is input in the short-circuit period, an average short-circuit time calculation portion (TSA) that calculates an average short-circuit time for each given period and outputs an average short-circuit time calculation signal (Tsa), and a reference time setting portion (TNR) that sets the reference time (Tnr) based on the average short-circuit time calculation signal (Tsa).

Description

Technical Field

[0001] This invention relates to an arc welding apparatus, which feeds welding wire and performs welding during repeated short circuits and during the arc. Background Technology

[0002] In typical consumable electrode arc welding, the welding wire, which serves as the consumable electrode, is fed at a fixed speed, generating an arc between the welding wire and the base material for welding. In consumable electrode arc welding, the welding wire and the base material are often in alternating short-circuit and arc phases during welding.

[0003] To improve weld quality, necking detection control is commonly used. If necking of the molten droplet is detected during a short circuit, the welding current is reduced to a low level, and the arc is regenerated. Since necking detection control significantly reduces spatter, it yields high-quality weld results. To perform this necking detection control, the necking state of the molten droplet needs to be accurately detected based on the voltage at the arc generation point. For this purpose, dedicated detection lines are laid on the base material and welding torch to detect the voltage at the arc generation point. However, setting up these detection lines is time-consuming. Furthermore, because the welding torch moves during welding, the detection lines sometimes break, causing malfunctions. Moreover, in the case of welding large structures, it is difficult to detect the voltage at the arc generation point.

[0004] To address the aforementioned problems, in the invention of Patent Document 1, if a predetermined reference time has elapsed since the start of the short circuit, it is estimated that the necking state of the molten droplet has reached a reference state, thus reducing the welding current. In this way, since it is not necessary to detect the voltage at the arc-generating part, a detection wire is not required. However, in this control, setting the reference time to a suitable value becomes a problem. The necking state of the molten droplet varies depending on various welding conditions such as the material of the welding wire, the type of shielding gas, the welding current, the welding voltage, the welding speed, the welding posture, and the wire protrusion length, making it difficult to pre-set a suitable reference time experimentally. If the reference time is shorter than the suitable value, the welding current is reduced before the molten droplet formation state is sufficient, resulting in a delayed arc regeneration timing and an unstable welding state. Conversely, if the reference time is longer than the suitable value, the arc will regenerate before the welding current has been sufficiently reduced, leading to more spatter. Therefore, setting the reference time to a suitable value is a challenge in the prior art.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: JP Patent No. 5974984 Summary of the Invention

[0008] Therefore, the objective of this invention is to provide an arc welding apparatus that can perform high-quality welding with minimal sputtering under various welding conditions without detecting the voltage of the arc generating part.

[0009] To address the aforementioned issues, technical solution 1 is an arc welding apparatus comprising: a feed motor that feeds welding wire; a short-circuit detection unit that determines whether a short circuit has occurred between the welding wire and the base material and outputs a short-circuit detection signal; a current reduction timer unit that takes the short-circuit detection signal as input and outputs a current reduction signal if a reference time has elapsed since the start of the short-circuit period; and a power control unit that supplies welding voltage and welding current between the welding wire and the base material, repeats the short-circuit period and the arc period, and reduces the welding current and shifts to the arc period if the current reduction signal is input during the short-circuit period. The arc welding apparatus further comprises: an average short-circuit time calculation unit that takes the short-circuit detection signal as input, calculates the average short-circuit time for each given cycle, and outputs an average short-circuit time calculation signal; and a reference time setting unit that sets the reference time based on the average short-circuit time calculation signal.

[0010] The invention of technical solution 2 is based on the arc welding apparatus described in technical solution 1, wherein the reference time setting unit sets the value obtained by subtracting a given time from the value of the signal calculated from the average short-circuit time as the reference time.

[0011] The invention of technical solution 3 is based on the arc welding device described in technical solution 1 or 2, wherein the feed motor feeds the welding wire in the forward direction during the arc and in the reverse direction during the short circuit.

[0012] The effects of the invention

[0013] According to the arc welding apparatus of the present invention, high-quality welding with minimal sputtering can be performed under various welding conditions without detecting the voltage of the arc generating part. Attached Figure Description

[0014] Figure 1 This is a block diagram of an arc welding apparatus according to an embodiment of the present invention.

[0015] Figure 2 yes Figure 1 Timing diagram of various signals in the arc welding device.

[0016] Explanation of reference numerals in the attached figures

[0017] 1 Welding wire

[0018] 2. Base Material

[0019] 3. Electric arc

[0020] 4 Welding torch

[0021] 5 feed rollers

[0022] CM current comparator circuit

[0023] Cm current comparison signal

[0024] DR drive circuit

[0025] Dr drive signal

[0026] E Output voltage

[0027] Ea Error Amplification Signal

[0028] ED output voltage detection circuit

[0029] Ed output voltage detection signal

[0030] EI current error amplifier circuit

[0031] Ei Current Error Amplification Signal

[0032] ER output voltage setting circuit

[0033] Er output voltage setting signal

[0034] EV voltage error amplifier circuit

[0035] Ev Voltage Error Amplification Signal

[0036] FC feed control circuit

[0037] Fc feed control signal

[0038] FR feed rate setting circuit

[0039] Fr feed rate setting signal

[0040] Fw feed rate

[0041] Ia1 First arc current

[0042] IA1R First Arc Current Setting Circuit

[0043] Ia1r1 First Arc Current Setting Signal

[0044] Ia2 Second arc current

[0045] Ia3 Third arc current

[0046] IA3R Third Arc Current Setting Circuit

[0047] Ia3r Third Arc Current Setting Signal

[0048] ICR current control setting circuit

[0049] Icr current control setting signal

[0050] ID current detection circuit

[0051] Id Current Detection Signal

[0052] ILR low-level current setting circuit

[0053] Ilr low-level current setting signal

[0054] Iw welding current

[0055] ND current reduction timer circuit

[0056] Nd current reduction signal

[0057] PM Power Control Department

[0058] R Current-reducing resistor

[0059] SD Short Circuit Detection Circuit

[0060] Sd Short Circuit Detection Signal

[0061] STA1 Circuit during the first arc period

[0062] Sta1 Signal during the first arc

[0063] STA3 Circuit during the third arc period

[0064] Sta3 Signal during the third arc

[0065] SW power characteristic switching circuit

[0066] Tc delay period

[0067] TA1R First Arc Period Setting Circuit

[0068] Ta1r Signal setting during the first arc period

[0069] Td Current fall time

[0070] Tn reference time

[0071] TNR reference time setting circuit

[0072] Tnr reference time setting signal

[0073] TR transistor

[0074] During Trd reverse feed deceleration

[0075] TRDR reverse feed deceleration period setting circuit

[0076] Trdr reverse feed deceleration setting signal

[0077] Trp reverse feed peak period

[0078] Tru during reverse feed acceleration

[0079] TRUR reverse feed acceleration period setting circuit

[0080] Trur reverse feed acceleration setting signal

[0081] TSA (Mean Short Circuit Time) is used to calculate the circuit.

[0082] Tsa is used to calculate the signal based on the average short-circuit time.

[0083] During Tsd forward feed deceleration

[0084] TSDR forward feed deceleration period setting circuit

[0085] Tsdr forward feed deceleration setting signal

[0086] During the peak period of Tsp positive feed

[0087] Tsu positive feed acceleration period

[0088] TSUR forward feed acceleration period setting circuit

[0089] Tsur forward feed acceleration period setting signal

[0090] VD voltage detection circuit

[0091] Vd voltage detection signal

[0092] Vw Output terminal voltage

[0093] WL Reactor

[0094] WM feed motor

[0095] Wrp Reverse Feed Peak

[0096] WRR Reverse Feed Peak Setting Circuit

[0097] Wrr Reverse feed peak setting signal

[0098] Wsp peak positive feed

[0099] WSR Forward Feed Peak Setting Circuit

[0100] Wsr positive feed peak setting signal Detailed Implementation

[0101] The embodiments of the present invention will be described below with reference to the accompanying drawings.

[0102] Figure 1 This is a block diagram of an arc welding apparatus according to an embodiment of the present invention. The following description refers to this diagram.

[0103] The power control unit PM takes a 3-phase 200V commercial power supply (not shown) as input and performs output control based on inverter control, etc., according to the error amplification signal Ea described later, thereby outputting the output voltage E. This supplies the output terminal voltage Vw and welding current Iw between the welding wire 1 and the base material 2. Although the illustration is omitted, the power control unit PM includes: a primary rectifier that rectifies the commercial power supply; a smoothing capacitor that smooths the rectified DC; an inverter circuit driven by the aforementioned 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 suitable for welding; and a secondary rectifier that rectifies the stepped-down high-frequency AC into DC.

[0104] The reactance WL smooths the aforementioned output voltage E. The inductance value of this reactance WL is 100 μH.

[0105] The feed motor WM takes the feed control signal Fc (described later) as input and alternately feeds forward and backward at a feed speed Fw to feed the welding wire 1. Forward feed advances the welding wire towards the base material, while reverse feed moves it backward away from the base material. The feed motor WM uses a motor with fast transient response. To accelerate the rate of change of the feed speed Fw of the welding wire 1 and the reversal of the feed direction, the feed motor WM may be positioned near the tip of the welding torch 4. Furthermore, there are cases where two feed motors WM are used to create a push-pull feed system.

[0106] The welding wire 1 is fed into the welding torch 4 by the rotation of the feed roller 5, which is connected to the aforementioned feed motor WM, generating an arc 3 between itself and the base material 2. An output terminal voltage Vw is applied between the conductive nozzle (not shown) inside the welding torch 4 and the base material 2, and a welding current Iw is applied. Shielding gas (not shown) is ejected from the front end of the welding torch 4.

[0107] The output voltage setting circuit ER outputs a predetermined output voltage setting signal Er. The output voltage detection circuit ED detects the output voltage E, smooths it, and outputs an output voltage detection signal Ed.

[0108] The voltage error amplifier circuit EV takes the above-mentioned output voltage setting signal Er and the above-mentioned output voltage detection signal Ed as inputs, amplifies the error between the output voltage setting signal Er (+) and the output voltage detection signal Ed (-), and outputs the voltage error amplified signal Ev.

[0109] The current detection circuit ID detects the welding current Iw and outputs a current detection signal Id. The voltage detection circuit VD detects the voltage Vw between the output terminals of the welding power supply and outputs a voltage detection signal Vd. The short-circuit discrimination circuit SD takes the voltage detection signal Vd as input and outputs a short-circuit discrimination signal Sd. This short-circuit discrimination signal Sd is high when the value of the voltage detection signal Vd is less than a predetermined short-circuit discrimination value (around 10V), and low when the value of the voltage detection signal Vd is above the predetermined short-circuit discrimination value (around 10V), indicating that an arc is in progress.

[0110] The forward feed acceleration period setting circuit TSUR outputs a predetermined forward feed acceleration period setting signal Tsur.

[0111] The forward feed deceleration period setting circuit TSDR outputs a predetermined forward feed deceleration period setting signal Tsdr.

[0112] The reverse feed acceleration period setting circuit TRUR outputs a predetermined reverse feed acceleration period setting signal Trur.

[0113] The reverse feed deceleration period setting circuit TRDR outputs a predetermined reverse feed deceleration period setting signal Trdr.

[0114] The forward feed peak setting circuit WSR outputs a predetermined forward feed peak setting signal Wsr.

[0115] The reverse feed peak setting circuit WRR outputs a predetermined reverse feed peak setting signal Wrr.

[0116] The feed rate setting circuit FR takes the aforementioned forward feed acceleration period setting signal Tsur, forward feed deceleration period setting signal Tsdr, reverse feed acceleration period setting signal Trur, reverse feed deceleration period setting signal Trdr, forward feed peak setting signal Wsr, reverse feed peak setting signal Wrr, and short-circuit discrimination signal Sd as inputs, and outputs a feed rate pattern generated through the following processing, which serves as the feed rate setting signal Fr. When the feed rate setting signal Fr is 0 or higher, it constitutes the forward feed period; when it is less than 0, it constitutes the reverse feed period.

[0117] 1) During the forward feed acceleration period Tsu, which is determined by the forward feed acceleration period setting signal Tsur, the feed rate setting signal Fr is output, which accelerates from 0 to the positive value of the forward feed peak value Wsp, which is determined by the forward feed peak value setting signal Wsr.

[0118] 2) Next, during the peak period of the forward feed Tsp, a feed rate setting signal Fr is output to maintain the aforementioned peak forward feed Wsp.

[0119] 3) If the short circuit discrimination signal Sd changes from low level (during the arc period) to high level (during the short circuit period), it will switch to the forward feed deceleration period Tsd determined by the forward feed deceleration period setting signal Tsdr, and output the feed speed setting signal Fr that decelerates from the above-mentioned forward feed peak Wsp to 0.

[0120] 4) Next, during the reverse feed acceleration period Tru, which is determined by the reverse feed acceleration period setting signal Tru, the feed speed setting signal Fr is output, which accelerates from 0 to the negative value of the reverse feed peak value Wrp determined by the reverse feed peak value setting signal Wrr.

[0121] 5) Next, during the peak reverse feed period Trp, output the feed rate setting signal Fr that maintains the aforementioned peak reverse feed Wrp.

[0122] 6) If the short circuit discrimination signal Sd changes from high level (short circuit period) to low level (arc period), it will switch to the reverse feed deceleration period Trd determined by the reverse feed deceleration period setting signal Trdr, and output the feed speed setting signal Fr which decelerates from the above-mentioned reverse feed peak value Wrp to 0.

[0123] 7) By repeating steps 1) to 6) above, a feed speed setting signal Fr is generated to produce a feed pattern with positive and negative trapezoidal wave variations.

[0124] The feed control circuit FC takes the aforementioned feed speed setting signal Fr as input and outputs the feed control signal Fc, which is used to feed the welding wire 1 at a feed speed Fw equivalent to the value of the feed speed setting signal Fr, to the aforementioned feed motor WM.

[0125] A current-reducing resistor R is inserted between the aforementioned reactor WL and the welding torch 4. The value of this current-reducing resistor R is set to be more than 50 times the short-circuit load (0.01 to 0.03 Ω) (0.5 to 3 Ω). When this current-reducing resistor R is inserted into the circuit, the energy stored in the reactor WL and the reactance of the external cable is rapidly discharged.

[0126] The transistor TR is connected in parallel with the aforementioned current-reducing resistor R, and is turned on or off according to the drive signal Dr described later.

[0127] The average short-circuit time calculation circuit TSA takes the aforementioned short-circuit discrimination signal Sd as input. The short-circuit discrimination signal Sd is a moving average of the short-circuit time during the high-level period (during the short circuit) across a given period, and outputs the average short-circuit time calculation signal Tsa. The given period is the period during which a short circuit occurs, and is set to a range of 3 to 10 periods. Therefore, whenever a short circuit occurs, the average short-circuit time of the nearest given period is calculated.

[0128] The reference time setting circuit TNR takes the average short-circuit time calculation signal Tsa as input, subtracts a given time from the value of the average short-circuit time calculation signal Tsa, and outputs the reference time setting signal Tnr. The given time is, for example, set to 1 ms. When the short circuit ends and the arc re-generates before the given time, the necking formation state becomes the reference state. If the welding current is reduced at this timing, the welding current will reach the desired low-level current value at the arc re-generation time.

[0129] The current reduction timer circuit ND takes the short-circuit discrimination signal Sd and the reference time setting signal Tnr as inputs and outputs a current reduction signal Nd. When the time elapsed from the point when the short-circuit discrimination signal Sd is high (during the short circuit) and changes to high level reaches the reference time Tn determined by the reference time setting signal Tnr, it becomes a short-term high level.

[0130] 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 aforementioned current detection signal Id as inputs and outputs a current comparison signal Cm, which becomes high when Id < I1r and low when Id ≥ Ilr.

[0131] The drive circuit DR takes the aforementioned current comparison signal Cm and the aforementioned current reduction signal Nd as inputs, and outputs the drive signal Dr to the base terminal of the aforementioned transistor TR. Regarding this drive signal Dr, if the current reduction signal Nd changes to a high level, it changes to a low level; if the current comparison signal Cm subsequently changes to a high level, it changes to a high level. Therefore, if necking is detected, the drive signal Dr becomes low, the transistor TR becomes off, and a current-reducing resistor R is inserted into the circuit, thus rapidly reducing the welding current Iw connected to the short-circuit load. Then, if the rapidly reduced welding current Iw decreases to the value of the low-level current setting signal Ilr, the drive signal Dr becomes high, the transistor TR becomes on, and the current-reducing resistor R is short-circuited, returning to the normal state.

[0132] The circuit TA1R for setting the first arc period outputs a predetermined signal Ta1r for setting the first arc period.

[0133] The circuit STA1 takes the short-circuit discrimination signal Sd and the first arc period setting signal Ta1r as inputs and outputs the first arc period signal Stal. The first arc period signal Stal becomes high during the first arc period Ta1 predetermined by the first arc period setting signal Ta1r, starting from the time point when the short-circuit discrimination signal Sd changes to a low level (arc period) and a predetermined delay period Tc has elapsed.

[0134] The first arc current setting circuit IA1R outputs a predetermined first arc current setting signal Ia1r.

[0135] During the third arc period, circuit STA3 takes the aforementioned short-circuit discrimination signal Sd as input and outputs the third arc period signal Sta3. This third arc period signal Sta3 becomes high after a predetermined current drop time Td from the point when the short-circuit discrimination signal Sd changes to a low level (during the arc period). If the short-circuit discrimination signal Sd becomes high level (during the short circuit period) thereafter, it becomes low level.

[0136] The third arc current setting circuit IA3R outputs a predetermined third arc current setting signal Ia3r.

[0137] The current control setting circuit ICR takes the short-circuit discrimination signal Sd, the low-level current setting signal Ilr, the current reduction signal Nd, the first arc period signal Sta1, the third arc period signal Sta3, the first arc current setting signal Ia1r, and the third arc current setting signal Ia3r as inputs, performs the following processing, and outputs the current control setting signal Icr.

[0138] 1) During the delay period from the point when the short-circuit discrimination signal Sd changes to a low level (during the arc) until the signal Sta1 changes to a high level during the first arc period, the current control setting signal Icr is output as the value of the low-level current setting signal Ilr.

[0139] 2) After that, when the signal Sta1 is high during the first arc period (during the first arc period), the output becomes the current control setting signal Icr, which is the first arc current setting signal Ia1r.

[0140] 3) During the period from the time when the signal Sta1 changes to a low level during the first arc period to the time when the signal Sta3 changes to a low level during the third arc period (the second and third arc periods), the current control setting signal Icr, which becomes the third arc current setting signal Ia3r, is output.

[0141] 4) Output current control setting signal Icr. Regarding this current control setting signal Icr, if the short circuit discrimination signal Sd changes to a high level (during the short circuit period), it becomes a predetermined initial current setting value during a predetermined initial period, and then rises to a predetermined short circuit peak setting value with a predetermined short circuit slope, and maintains that value.

[0142] 5) If the current reduction signal Nd changes to a high level afterward, the current control setting signal Icr is output as the value of the low-level current setting signal Ilr.

[0143] The current error amplifier circuit EI takes the aforementioned current control setting signal Icr and the aforementioned current detection signal Id as inputs, amplifies the error between the current control setting signal Icr(+) and the current detection signal Id(-), and outputs the current error amplified signal Ei.

[0144] The power characteristic switching circuit SW takes the aforementioned current error amplification signal Ei, the aforementioned voltage error amplification signal Ev, the aforementioned first arc period signal Sta1, and the aforementioned third arc period signal Sta3 as inputs, performs the following processing, and outputs the error amplification signal Ea.

[0145] 1) During the second arc period Ta2, from when signal Sta1 changes to a low level during the first arc period to when signal Sta3 changes to a high level during the third arc period, the output voltage error amplification signal Ev is used as the error amplification signal Ea.

[0146] 2) During the period outside of this, the output current error amplification signal Ei is used as the error amplification signal Ea.

[0147] Through this circuit, the characteristics of the welding power supply become constant current characteristics during the short circuit period, the delay period, the first arc period Ta1, and the third arc period Ta3, and constant voltage characteristics during the second arc period Ta2.

[0148] Figure 2 yes Figure 1 The following is a timing diagram of the signals in the arc welding apparatus. Diagram (A) shows the time variation of the feed speed Fw; (B) shows the time variation of the welding current Iw; (C) shows the time variation of the output terminal voltage Vw; (D) shows the time variation of the short-circuit detection signal Sd; (E) shows the time variation of the signal Sta1 during the first arc; (F) shows the time variation of the signal Sta3 during the third arc; and (G) shows the time variation of the current reduction signal Nd. The operation of each signal will be explained below with reference to this diagram.

[0149] The feed rate Fw shown in Figure (A) is controlled from... Figure 1The feed rate setting circuit FR outputs the value of the feed rate setting signal Fr. The feed rate Fw is formed during the following period: Figure 1 The forward feed acceleration period Tsu is determined by the forward feed acceleration setting signal Tsur, and the forward feed peak period Tsp lasts until a short circuit occurs. Figure 1 The forward feed deceleration period Tsd is determined by the setting signal Tsdr. Figure 1 The reverse feed acceleration period is determined by the reverse feed acceleration period setting signal Tru, the reverse feed peak period Trp lasting until the arc is generated, and the reverse feed acceleration period is determined by the reverse feed acceleration period setting signal Tru. Figure 1 The reverse feed deceleration period Trd is determined by the setting signal Trdr. Furthermore, the forward feed peak value Wsp is determined by... Figure 1 The forward feed peak value setting signal Wsr is determined, and the reverse feed peak value Wrp is determined by... Figure 1 The reverse feed peak setting signal Wrr is determined. As a result, the feed rate setting signal Fr becomes a feed pattern with approximately trapezoidal wave variations of positive and negative values.

[0150] [Actions during the short circuit period from time t1 to t4]

[0151] After a short circuit occurs at time t1 during the peak forward feed period Tsp, as shown in Figure (C), the voltage Vw between the output terminals drops sharply to a short-circuit voltage of several V. Therefore, as shown in Figure (D), the short-circuit detection signal Sd changes to a high level (during the short circuit). In response to this, the system shifts to a predetermined forward feed deceleration period Tsd between times t1 and t2, as shown in Figure (A), and the feed rate Fw decelerates from the aforementioned peak forward feed Wsp to 0. For example, the forward feed deceleration period Tsd is set to 1 ms.

[0152] As shown in Figure (A), the feed rate Fw enters the predetermined reverse feed acceleration period Tru at times t2 to t3, accelerating from 0 to the aforementioned reverse feed peak value Wrp. During this period, the short-circuit period continues. For example, the reverse feed acceleration period Tru is set to 1 ms.

[0153] After the reverse feed acceleration period Tru ends at time t3, as shown in Figure (A), the feed rate Fw enters the reverse feed peak period Trp, becoming the aforementioned reverse feed peak Wrp. The reverse feed peak period Trp continues until an arc is generated at time t4. Therefore, the period from time t1 to t4 is the short-circuit period. Although the reverse feed peak period Trp is not a given value, it is approximately 3 ms. Furthermore, for example, it can be set to reverse feed peak Wrp = -40 m / min.

[0154] As shown in Figure (B), the welding current Iw during the short-circuit period from time t1 to t4 has a predetermined initial current value during a predetermined initial period. Afterward, the welding current Iw increases at a predetermined short-circuit rate, and if it reaches a predetermined short-circuit peak value, it maintains that value.

[0155] As shown in Figure (C), the output terminal voltage Vw rises from near the peak value when the welding current Iw becomes short-circuited. This is because, through the reverse feed based on welding wire 1 and the clamping force of welding current Iw, the molten droplet at the tip of welding wire 1 gradually forms a neck.

[0156] If the elapsed time from the start of the short-circuit period at time t1 reaches the reference time Tn, it is estimated that the necking formation state becomes the reference state. At time t31, as shown in (G) of the figure, the current reduction signal Nd changes to a short-term high level. The reference time Tn passes through Figure 1 The reference time setting signal Tnr is used to set the time. Furthermore, the reference time setting signal Tnr is set to... Figure 1 The average short-circuit time is calculated by subtracting the given time from the value of the signal Tsa. The average short-circuit time signal Tsa is calculated by moving average the short-circuit time over a given period. For example, if the short circuit starting at time t1 is the m-th short circuit, and the given period is set to 3, with the short-circuit times in the given period set as Ts(m-3), Ts(m-2), and Ts(m-1), then the reference time setting signal Tsa(m) during the m-th short circuit is calculated as follows.

[0157] Tsa(m)=(Ts(m-3)+Ts(m-2)+Ts(m-1)) / 3

[0158] For various welding conditions, the short-circuit time becomes approximately a fixed value. Therefore, by calculating the average short-circuit time, the short-circuit time under the current welding conditions can be estimated. Furthermore, if a reference time Tm is set by subtracting a given time from this average short-circuit time, the state in which the short circuit ends and the arc re-emerges a given time earlier can be estimated as the reference state for necking formation. For example, if the average short-circuit time calculates the signal Tsa to be around 5 ms, the given time is 0.5 ms, and the reference time Tn becomes around 4.5 ms. As described above, the reference time Tn can be automatically set to a suitable value under various welding conditions.

[0159] At time t31, as shown in (G) of the figure, the current reduction signal Nd becomes a short-term high level in response to this. Figure 1 The drive signal Dr becomes low, therefore Figure 1 The transistor TR is turned off. Figure 1 The current-reducing resistor R is inserted into the circuit. Meanwhile, Figure 1 The current control setting signal Icr decreases to the value of the low-level current setting signal Ilr. Therefore, as shown in Figure (B), the welding current Iw decreases rapidly from its peak value during short circuit to a low-level current value. Then, if the welding current Iw decreases to the low-level current value, the drive signal Dr returns to a high level, thus the transistor TR becomes on, and the current-reducing resistor R is short-circuited. As shown in Figure (B), since the current control setting signal Icr is kept at the low-level current setting signal I1r, the welding current Iw maintains a low-level current value from the regeneration of the arc until a predetermined delay period Tc has elapsed. Therefore, the transistor TR is only off during the period from the time the current reduction signal Nd changes to a high level until the welding current Iw decreases to the low-level current value. As shown in Figure (C), because the welding current Iw decreases, the voltage Vw between the output terminals increases sharply after a decrease. The above parameters are set to, for example, the following values. Initial current = 40A, initial period = 0.5ms, short circuit tilt = 180A / ms, short circuit peak value = 400A, low-level current value = 50A, delay period Tc = 1ms.

[0160] [Actions during the arc from time t4 to t7]

[0161] At time t4, after the necking process, caused by the reverse feed of the welding wire and the clamping force of the welding current Iw, resulting in an arc, as shown in Figure (C), the voltage Vw between the output terminals surges to tens of V, the arc voltage value. Therefore, as shown in Figure (D), the short-circuit detection signal Sd changes to a low level (during the arc). In response, the system shifts to a predetermined reverse feed deceleration period Trd between times t4 and t5, as shown in Figure (A), where the feed rate Fw decelerates from the aforementioned reverse feed peak value Wrp to 0. For example, the reverse feed deceleration period Trd is set to 1 ms.

[0162] After the reverse feed deceleration period Trd ends at time t5, the process transitions to a predetermined forward feed acceleration period Tsu from time t5 to t6. During this forward feed acceleration period Tsu, as shown in Figure (A), the feed rate Fw accelerates from 0 to the aforementioned forward feed peak value Wsp. The arc period continues during this period. For example, the forward feed acceleration period Tsu is set to 1 ms.

[0163] After the forward feed acceleration period Tsu ends at time t6, as shown in Figure (A), the feed rate Fw enters the forward feed peak period Tsp, becoming the aforementioned forward feed peak Wsp. During this period, the arc period also continues. The forward feed peak period Tsp continues until a short circuit occurs at time t7. Therefore, the period from time t4 to t7 is the arc period. Furthermore, if a short circuit occurs, the operation returns to time t1. The forward feed peak period Tsp is not a given value, but is approximately 5 ms. For example, the forward feed peak Wsp is set to 60 m / min.

[0164] After the arc is generated at time t4, as shown in Figure (C), the voltage Vw between the output terminals increases sharply to an arc voltage value of tens of V. 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. This is because if the current value is increased immediately after the arc is generated, the reverse feed of the welding wire and the melting of the welding wire based on the welding current will be added together, the arc length will increase rapidly, and the welding state may become unstable.

[0165] At time t51 during the forward feed acceleration period Tsu, after the end of the delay period Tc, as shown in Figure (E), the signal Sta1 for the first arc period changes to a high level, shifting to the predetermined first arc period Ta1 from time t51 to t61. Constant current control continues during this first arc period Ta1, as shown in Figure (B), by switching on the current... Figure 1 The given first arc current Ia1 is determined by the first arc current setting signal Ia1r. As shown in Figure (C), the voltage Vw between the output terminals becomes a value determined by the current value and the arc load, and becomes a larger value. For example, the delay period Tc is about 1 ms, the first arc period Ta1 is about 1 ms, and the first arc current Ia1 is about 400A.

[0166] At time t62, after a predetermined current drop time Td from the arc generation time t4, as shown in Figure (F), the signal Sta3 changes to a high level during the third arc period. The period from time t61 to t62 is called the second arc period Ta2. Constant voltage control is performed during this second arc period Ta2. As shown in Figure (B), the second arc current Ia2 varies according to the arc load, becoming a value smaller than the first arc current Ia1 and larger than the third arc current Ia3. That is, the output is controlled to Ia1 > Ia2 > Ia3. As shown in Figure (C), the voltage Vw between the output terminals is controlled at a given value through constant voltage control, becoming the midpoint between the voltage value of Ta1 during the first arc period and the voltage value of Ta3 during the third arc period. Although Ta2 during the second arc period is not a given value, it is around 4.5 ms.

[0167] The period from the moment t62 when the signal Sta3 changes to a high level during the third arc period to the moment t7 when a short circuit occurs is called the third arc period Ta3. During this third arc period Ta3, constant current control is performed. As shown in Figure (B), the circuit is switched on... Figure 1 The given third arc current Ia3 is determined by the third arc current setting signal Ia3r. As shown in Figure (C), the output terminal voltage Vw becomes 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 given value, but is around 0.5ms.

[0168] In the above embodiments, the case of feeding the welding wire in the forward direction during the arc period and in the reverse direction during the short circuit period is described, but constant speed feeding can also be performed throughout the entire period.

[0169] The arc welding apparatus according to this embodiment described above includes: an average short-circuit time calculation unit that takes a short-circuit detection signal as input, calculates the average short-circuit time for each given cycle, and outputs an average short-circuit time calculation signal; and a reference time setting unit that sets a reference time based on the average short-circuit time calculation signal. In this embodiment, a reference time is automatically set based on the average short-circuit time to determine when the estimated necking formation state becomes a reference state, thereby reducing the welding current. Therefore, the reference time can be automatically set to a suitable value for various welding conditions. As a result, in this embodiment, without detecting the voltage of the arc generating unit, high-quality welding with less sputtering can be performed under various welding conditions.

[0170] Furthermore, according to this embodiment, the reference time setting unit preferably sets the value obtained by subtracting a given time from the value of the signal calculated from the average short-circuit time as the reference time. In this way, since the welding current can be kept at a low level before the arc regeneration point, the amount of sputtering can be reduced, and the transition during the phase arc can be made smooth.

[0171] Furthermore, according to this embodiment, the feed motor preferably feeds the welding wire in the forward direction during the arc period and in the reverse direction during the short circuit period. By controlling the forward and reverse feed of the welding wire, the deviation in short circuit time is reduced compared to constant speed feed control. Therefore, the estimation accuracy of the necking formation state based on the reference time is improved. As a result, the amount of sputtering can be further reduced.

Claims

1. An arc welding apparatus, comprising: The feed motor feeds the welding wire; The short-circuit detection unit determines that the welding wire and the base material are in a short-circuit period and outputs a short-circuit detection signal; The current reduction timer unit takes the short-circuit discrimination signal as input and outputs a current reduction signal if a reference time has elapsed since the start time of the short-circuit period. and The power control unit supplies welding voltage and welding current between the welding wire and the base material, repeats the short-circuit period and the arc period, and if the current reduction signal is input during the short-circuit period, the welding current is reduced and shifted to the arc period. The arc welding apparatus is characterized in that it further comprises: The average short-circuit time calculation unit takes the short-circuit discrimination signal as input, calculates the average short-circuit time every 3 to 10 cycles, and outputs the average short-circuit time calculation signal. and The reference time setting unit automatically sets the reference time based on a signal calculated from various welding conditions and the average short-circuit time, which changes over time whenever a short circuit occurs during welding.

2. The arc welding apparatus according to claim 1, characterized in that, The reference time setting unit sets the value obtained by subtracting a given time from the value of the signal calculated from the average short-circuit time as the reference time.

3. The arc welding apparatus according to claim 1 or 2, characterized in that, The feed motor feeds the welding wire in the forward direction during the arc and in the reverse direction during the short circuit.

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