JPH09271944A - Submerged arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a submerged arc welding method which starts arc discharge by bringing a consumable electrode and an object to be welded into contact with each other once and then separating them from each other. SOLUTION: Welding is performed so that, by a weld starting command, a consumable electrode is fed in the direction of the object to be welded in accordance with a signal for setting a slowdown by means of a constant speed control; that, after the contact between the consumable electrode and the object is detected, the feeding direction and speed of the electrode is controlled by the difference of code and size of a signal between a weld voltage setting signal and a weld voltage detection signal, in place of the constant speed control; and that an electric power required for welding is also supplied simultaneously.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a consumable electrode (hereinafter,
The invention relates to a submerged arc welding method in which an arc discharge is started by first contacting a wire) with an object to be welded and then separating them from each other.

[0002]

2. Description of the Related Art A conventional arc starting method for submerged arc welding is disclosed in Japanese Examined Patent Publication No. 54-309.
The one disclosed in Japanese Patent Publication No. 75 is known. This arc starting method detects the wire once contacting the work piece and stops feeding the wire, and after the wire contacts the work piece, the work piece and the wire are energized and the work piece is welded. A spark is generated between the wire and the wire, and after the spark is generated, the wire is pulled up from the work piece by a predetermined amount to grow an arc discharge between the wire and the work piece, and after the arc discharge is grown, the wire is pulled up. It is a method of stopping the action and feeding the wire in the steady welding state. Further, in the steady welding state, the welding voltage is detected, the detected value is compared with the set value, and the wire feeding speed is increased or decreased in the direction of decreasing the difference.

[0010]

In such a conventional starting method, an activator such as a metal fine wire or metal powder for starting an arc is not required, so that material cost and man-hours are reduced. However, the pull-up duration is constant when the wire is pulled up after the wire and the workpiece are in contact with each other and sparks are generated, so the pull-up duration is constant even when the welding current or the wire diameter changes. Is. Therefore, when the welding current is large with respect to the wire diameter, the wire burns up excessively within the pulling time of the wire and arc breakage occurs, and conversely, when the welding current is small with respect to the wire diameter, There was a problem that the wire and the object to be welded were welded to each other due to insufficient burning.

Further, even in the steady welding state, the processing accuracy of the work piece is low, the step between the work piece and the end tab,
Or, if the arc length fluctuates due to the fluctuation of the welding current, etc., the wire feed speed is only increased or decreased according to the fluctuation amount.In an extreme case, for example, when the wire short-circuits with the work piece, the wire Was only temporarily stopped. As a result, there is a problem that it is not possible to sufficiently cope with a sudden change in the arc length, and the arc is broken or the wire and the workpiece are welded.

The present invention has been made to solve such a problem, and its purpose is to:
A submerged arc welding method that always enables optimum arc starting even if the welding current or wire diameter changes, and that arc breakage and welding do not occur even when the arc length suddenly changes due to external fluctuations during welding. To provide.

[0020]

DISCLOSURE OF THE INVENTION According to the present invention, a consumable electrode is fed toward a work piece at a low speed, the feed is stopped when the consumable electrode comes into contact with the work piece, and then the welding electrode is welded. In the submerged arc welding method, which starts welding by pulling the consumable electrode from the work piece while supplying the necessary power to start welding, the consumable electrode is controlled at a constant speed according to the slowdown speed setting signal by the welding start command. After sending the signal to the direction of the welding target by the, and detecting the contact between the consumable electrode and the welding target, instead of constant speed control, the sign and magnitude of the signal of the difference between the welding voltage setting signal and the welding voltage detection signal are changed. Is a submerged arc welding method in which the feed direction and speed of the consumable electrode are controlled by means of and the welding power is supplied to perform welding.

[0030]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be specifically described below with reference to the drawings showing the embodiments. FIG. 1 is a flowchart explaining the submerged arc welding method of the present invention. Turn on the welding start switch in step ST1.
Then, a relatively low voltage for contact detection is applied between the wire and the object to be welded. At the same time, the wire is fed at a low speed toward the object to be welded (step ST2). Next, when the wire and the object to be welded come into contact with each other, the voltage between the wire and the object to be welded becomes substantially zero, so that the contact is detected and the feeding of the wire is stopped (step ST3). When the wire feeding is stopped, the flux is sprinkled (step ST
4).

After that, the welding power in the steady welding state is supplied and the short-circuit current starts to flow (step ST5). At this time, since the wire and the object to be welded are in contact with each other, the welding voltage detection value is substantially zero. Therefore, (welding voltage detection value) <
(Welding voltage setting value), (Welding voltage detection value)-(Welding voltage setting value) <0, the wire feed motor reverses according to this sign, (Welding voltage detection value)-(Welding voltage setting value) The wire is pulled up at a speed according to () (step ST6). Due to the reverse rotation of the wire feeding motor, an arc is generated at the moment when the wire separates from the workpiece (step S
T7), the welding voltage detection value starts to increase from zero. While (Welding voltage detection value)-(Welding voltage setting value) <0, the wire is continuously pulled up, whereby an arc grows, and (Welding voltage detection value)-(Welding voltage setting value) ≥ 0. When this happens, the wire feed motor changes from reverse rotation to normal rotation.
After that, when (welding voltage detection value)-(welding voltage setting value) ≧ 0, the wire feeding motor is normally rotated to feed the wire toward the workpiece. On the contrary, (welding voltage detection value)-
When (welding voltage set value) <0, the wire feeding motor is reversed to pull up the wire (steps ST8 to ST10). By repeating these steps ST8 to ST10, the welding voltage detection value is maintained at the welding voltage setting value. In step ST11, welding is completed.

[0034]

FIG. 2 is a block diagram showing an example of an apparatus for carrying out the welding method of the present invention. In the figure, reference numeral 8 is a welding power source, which supplies a welding power between the power feed tip 3 of the wire 1 and the object to be welded 2 when the time setting signal Td described later is input with the commercial power source as an input. A welding power source with a drooping characteristic or a constant current characteristic that generates an arc. Wire 1
Is supplied from a wire feeding roll 4 rotated by a wire feeding motor 5. Reference numeral 7 denotes a wire feeding speed detection circuit, which detects the feeding speed of the wire 1 and outputs a wire feeding speed detection signal Wd. A welding voltage detection circuit 9 detects the welding voltage and outputs a welding voltage detection signal Vd. Reference numeral 10 denotes a contact determination circuit, which is a start signal S described later.
After 1 is input, when the welding voltage detection signal Vd drops below a certain value, it is considered that the wire 1 and the workpiece 2 are in contact with each other, and the contact determination signal Sd is output.

A welding start switch 11 outputs a start signal S1 to the contact determination circuit 10 and the welding power source 8.
Reference numeral 17 denotes a timer, which outputs the time limit setting signal Td after the time T after the contact determination signal Sd is input. Fifteen
Is a wire slowdown speed setting circuit, which outputs a wire slowdown speed setting signal Ws which is a slow feeding speed until the wire 1 comes into contact with the workpiece 2 at the time of starting.
Reference numeral 16 is a welding voltage setting circuit, which is a welding voltage setting signal V
Output s. A detection signal switching circuit 12 switches between the wire feeding speed detection signal Wd and the welding voltage detection signal Vd by the time limit setting signal Td and outputs the signal S2.
A setting signal switching circuit 13 switches the wire slowdown speed setting signal Ws and the welding voltage setting signal Vs by the time setting signal Td and outputs the signal S3. Reference numeral 14 denotes a comparison circuit, which is an output signal S of the setting signal switching circuit 13.
3 and the output signal S2 of the detection signal switching circuit 12 are input, and the comparison signal Δs of the difference is output. Reference numeral 6 denotes a wire feeding control circuit, which receives the comparison signal Δs and determines the rotation direction and speed of the wire feeding motor 5 in accordance with its sign and value.

FIG. 3 is a diagram showing the time course of each signal in the block diagram shown in FIG. In FIG.
(A) shows the output S1 of the welding start switch 11,
(B) shows the output Sd of the contact determination circuit, (C) shows the output S2 of the detection signal switching circuit 12, (D) shows the output S3 of the setting signal switching circuit 13, and (E) shows the wire feeding. The output Wc of the control circuit 6 is shown, and (F) shows the output Vd of the welding voltage detection circuit 9.

When the welding start switch 11 is pressed at the time t1 shown in FIG. 3, the welding start switch 11 outputs the start signal S1 shown in FIG. The welding power source 8 inputs the activation signal S1 and supplies a low voltage for detecting the contact between the wire 1 and the workpiece 2 as shown in FIG. The contact determination circuit 10 receives the activation signal S1 and enters a state in which the contact between the wire 1 and the workpiece 2 can be determined. At time t1, the contact determination circuit 10 has not yet determined the contact, so the contact points of the detection signal switching circuit 12 and the setting signal switching circuit 13 are on the A side. Therefore, the detection signal switching circuit 12 outputs the wire feeding speed detection signal Wd as the detection switching signal S2, as shown in FIG. The setting signal switching circuit 13 also outputs a wire slowdown speed setting signal Ws as a signal S3, as shown in FIG. The comparison circuit 14 obtains the difference between the wire slowdown speed setting signal Ws and the wire feeding speed detection signal Wd, and outputs the comparison signal Δs. The wire feeding control circuit 6 inputs the comparison signal Δs and outputs the wire feeding control signal Wc to the wire feeding motor 5 as shown in FIG. As a result, the wire 1 is fed toward the workpiece 2 at a speed corresponding to the wire slowdown speed setting signal Ws.

Since a voltage is supplied from the welding power source 8 between the wire 1 and the object to be welded 2, when the wire 1 and the object to be welded 2 come into contact with each other, a voltage drop occurs and the welding voltage detection signal Vd becomes Since it becomes substantially zero, the contact determination circuit 10 can determine the contact. At time t2 shown in FIG. 3, when the wire 1 and the workpiece 2 contact each other, the contact determination circuit 10
Outputs the contact determination signal Sd shown in FIG. 7B to the timer 17 and the wire slowdown speed setting circuit 15, the timer 17 starts the time limit, and the wire slowdown speed setting circuit 15 is cut off. As shown in the figure (D), the wire slowdown speed setting signal Ws is turned off. Therefore, as shown in FIG. 7E, the wire feeding control signal Wc is also turned off, and the feeding of the wire 1 toward the workpiece 2 is stopped. Then, the flux is sprinkled. At a time t3 when the time limit of the timer 17 ends after a predetermined time T that is considered to sufficiently disperse the flux, the welding power source 8 generates an output sufficient to supply welding power, and the detection signal switching circuit 12 is set. Signal switching circuit 1
The contact with 3 is switched from A to B. As a result, the detection signal switching circuit 12 outputs the welding voltage detection signal Vd as the signal S2 as shown in FIG. 7C, and the setting signal switching circuit 13 outputs the welding voltage as shown in FIG. The voltage setting signal Vs is output as the signal S3.

At time t3 in FIG. 3, since the wire 1 is in contact with the object to be welded 2, the welding voltage detection value becomes substantially zero and (welding voltage detection value)-(welding voltage setting value) <0. . Therefore, the wire feed control circuit 6 inputs the difference signal Δs between the welding voltage setting signal Vs and the welding voltage detection signal Vd, and as shown in FIG.
To reverse. As a result, when the wire 1 is pulled up and the contact between the wire 1 and the workpiece 2 is eliminated, an arc is generated and welding is started. When the arc length is increased by pulling up the wire 1 and melting the wire 1, the difference voltage between (welding voltage detection value) and (welding voltage setting value) decreases, so the pulling speed of the wire 1 slows down and the welding voltage detection Value reaches the welding voltage setting value (welding voltage detection value) −
When (welding voltage setting value) ≧ 0, the wire feeding motor 5
Rotates normally, and the wire 1 is fed again in the direction of the workpiece 2. The forward or reverse rotation of the wire feeding motor 5 is determined by the sign of the difference voltage of (welding voltage detection value)-(welding voltage setting value), and the wire feeding speed is determined by the value of this difference voltage. . In FIG. 2, the speed at which the wire 1 is fed toward the workpiece 2 after the welding start switch 11 is turned on is the wire slowdown speed setting circuit 1
The speed of the wire feeding motor 5 was fed back so as to obtain the set value of 5, and constant speed control was performed. However, when the wire 1 comes into contact with the object to be welded, the speed may be such that a large impact is not received. In particular, the constant speed control by the feedback method may not be necessary.

[0050]

The submerged arc welding method of the present invention comprises:
Even when the welding current or the wire diameter or the like changes, since the wire can be pulled up with the welding voltage always set as a target, the wire burn-up does not become excessive or insufficient, A stable arc can be activated. Furthermore, in the steady welding state, when the arc length suddenly becomes shorter due to the step of the work piece, etc., the wire and the work piece are prevented from welding by positively pulling up the wire. This has the effect that the responsiveness of the wire feeding speed to the fluctuation of the arc voltage is extremely good.

[Brief description of drawings]

FIG. 1 is a flowchart illustrating a submerged arc welding method of the present invention.

FIG. 2 is a block diagram showing an example of an apparatus for carrying out the welding method of the present invention.

FIG. 3 is a diagram showing a time course of each signal in the block diagram of FIG.

[Explanation of symbols]

 1 Consumable Electrode (Wire) 2 Welding Object 3 Power Supply Tip 4 Wire Feeding Roll 5 Wire Feeding Motor 6 Wire Feeding Control Circuit 7 Wire Feeding Speed Detection Circuit 8 Welding Power Supply 9 Welding Voltage Detection Circuit 10 Contact Discrimination Circuit 11 Welding Start switch 12 Detection signal switching circuit 13 Setting signal switching circuit 14 Comparison circuit 15 Wire slowdown speed setting circuit 16 Welding voltage setting circuit 17 Timer Δs Comparison signal S1 Start signal S2 signal S3 signal Sd Contact discrimination signal Td Time limit setting signal Vd Welding voltage Detection signal Vs Welding voltage setting signal Wc Wire feeding control signal Wd Wire feeding speed detection signal Ws Wire slowdown speed setting signal

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toshimitsu Doi 2-1-11, Tagawa, Yodogawa-ku, Osaka City Daihen Corporation

Claims (1)

[Claims] 1. A consumable electrode is fed toward a work piece at a low speed, and when the consumable electrode comes into contact with the work piece, the feeding is stopped, and thereafter, power is consumed while supplying electric power required for welding. In the submerged arc welding method in which the electrode is pulled up from the work piece and an arc is generated to start welding, the consumable electrode is sent to the work piece by constant speed control in response to a slowdown speed setting signal in response to a welding start command. After detecting the contact between the consumable electrode and the object to be welded, instead of the constant speed control, the consumable electrode is fed by the sign and magnitude of the signal of the difference between the welding voltage setting signal and the welding voltage detection signal. A submerged arc welding method in which welding is performed by controlling the direction and speed and supplying electric power necessary for welding.