Welding power supply system

Abstract

This invention provides a welding power supply system that automates the initial operation of submerged arc welding and suppresses the introduction of impurities into the weld bead after welding. The welding system (A1) for submerged arc welding includes: a welding power supply device (2) having an inverter circuit (25) and providing power; a wire feed device (5) for feeding welding wire; and a control device (1) for controlling the welding power supply device (2) and the wire feed device (5). The control device (1) feeds the welding wire in the forward direction via the wire feed device (5) at the start of welding. When the tip of the welding wire contacts the workpiece (W), the welding power supply device (2) outputs an initial current. From the contact of the welding wire until the start of forward feeding at a first welding speed, a second forward feeding speed slower than the first speed is provided as the initial current.

Description

Technical Field

[0001] This invention relates to a welding power supply system for submerged arc welding. Background Technology

[0002] Submerged arc welding has been known for a long time. Submerged arc welding involves distributing granular flux onto the workpiece, feeding the welding wire into the flux, and creating an electric arc between the tip of the wire and the workpiece to perform welding. In submerged arc welding, by flowing a large current through a thick-diameter welding wire, thick plates can be welded efficiently.

[0003] When starting submerged arc welding, the operator inserts steel wool between the welding wire and the workpiece, and ignites the steel wool by applying electricity, thereby generating an electric arc between the welding wire and the workpiece. However, in this case, since the steel wool needs to be inserted every time welding is performed, it requires operator work. In order to automate this operation, Patent Document 1 discloses a method of distributing metal powder before distributing flux, instead of inserting steel wool.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: JP Japanese Patent Application Publication No. 64-34581

[0007] According to the method disclosed in Patent Document 1, the welding start-up process can be automated because the insertion of steel wool by the operator is not required. However, since metal powder that is not needed in the welding process is consumed every time welding is performed, unnecessary costs are incurred. In addition, metal powder will be mixed into the weld bead as an impurity. These disadvantages are the same as those when using steel wool. Summary of the Invention

[0008] The present invention was conceived based on the above-mentioned matters, and its object is to provide a welding power supply system that automates the operation at the beginning of submerged arc welding and can suppress the mixing of impurities into the weld bead after welding.

[0009] The welding power supply system provided by the present invention is a welding system for submerged arc welding, characterized in that it comprises: a welding power supply device having an inverter circuit and providing power; a welding wire feed device for feeding welding wire; and a control device for controlling the welding power supply device and the welding wire feed device, wherein the control device causes the welding wire feed device to feed the welding wire in the forward direction at the start of welding, and when the tip of the welding wire contacts the workpiece, the welding power supply device outputs a start current, and during the period from the contact of the welding wire to the start of the forward feed at a first speed for welding, a start current for feeding in the forward direction at a second speed slower than the first speed is set.

[0010] In a preferred embodiment of the present invention, the second speed is the speed at which the welding wire stops.

[0011] In a preferred embodiment of the invention, the start current period is the period up to a predetermined first time.

[0012] In a preferred embodiment of the invention, the welding power supply system further comprises: a voltage sensor for detecting the voltage applied between the tip of the welding wire and the workpiece to be welded, wherein the start current period is the period until the detected voltage detected by the voltage sensor becomes above a preset voltage threshold.

[0013] In a preferred embodiment of the invention, the start current period is a longer period between the period until the detection voltage becomes above the voltage threshold and the period until a predetermined second time has elapsed.

[0014] In a preferred embodiment of the invention, the control device causes the welding wire to be fed in the forward direction at a third speed when welding begins, and then feeds in the reverse direction for a given length when the tip of the welding wire contacts the workpiece. After that, until the tip of the welding wire contacts the workpiece again, it feeds in the forward direction at a fourth speed slower than the third speed.

[0015] In a preferred embodiment of the invention, the control device sets a termination current period at the end of welding, from stopping the feeding of the welding wire by the welding wire feeder to stopping the termination current by the welding power supply device.

[0016] The effects of the invention

[0017] According to the present invention, the control device contacts the tip of the welding wire with the workpiece at the start of welding and outputs a starting current during the start current period. The welding wire ignites upon the application of the starting current, generating an electric arc. The feed speed of the welding wire during the start current period is a second speed, slower than the first speed during welding. Therefore, the phenomenon of the welding wire tip being pressed against the workpiece and sticking together without generating an electric arc is suppressed. Furthermore, since no other materials such as metal powder or steel wool are used, the welding start operation can be automated, and the introduction of impurities into the weld bead after welding can be suppressed. Attached Figure Description

[0018] Figure 1 These are diagrams used to illustrate the welding system according to the first embodiment. (a) is a block diagram showing the overall structure of the welding system, and (b) is a block diagram showing the internal structure of the welding power supply device.

[0019] Figure 2(a) is an example of a flowchart representing the start of control processing, and (b) is an example of a flowchart representing the end of control processing.

[0020] Figure 3 This is a timing diagram showing the various states during welding in the welding system according to the first embodiment.

[0021] Figure 4 This is a timing diagram showing the various states during welding in a modified example of the welding system according to the first embodiment.

[0022] Explanation of reference numerals in the attached figures

[0023] A1: Welding system; 1: Control device; 2: Welding power supply device; 25: Inverter circuit; 27: Voltage sensor; 5: Welding wire feed device; 7: Distributor device. Detailed Implementation

[0024] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0025] [First Embodiment]

[0026] Figure 1 This is a diagram used to illustrate the welding system according to the first embodiment. Figure (a) is a block diagram showing the overall structure of the welding system. Figure (b) is a block diagram showing the internal structure of the welding power supply device.

[0027] Welding system A1 is a welding system used for submerged arc welding. For example... Figure 1 As shown in (a), the welding system A1 includes a control device 1, a welding power supply device 2, a trolley 4, a wire feed device 5, a welding tray 6, a distribution device 7, and an electrode 8. While moving the trolley 4 along the welding line of the workpiece W, the welding system A1 distributes granular flux stored in the distribution device 7, and the wire feed device 5 feeds the welding wire into the flux. The welding wire is supplied from the welding tray 6. The welding power supply 2 converts the AC power supplied from a commercial power source P into welding-appropriate power and outputs it, generating an electric arc between the tip of the welding wire, i.e., the electrode 8, and the workpiece W within the flux. Welding is performed by the heat of this electric arc. Welding is thus performed along the welding line of the workpiece W. Alternatively, the workpiece W can be moved or rotated instead of using the trolley 4.

[0028] Control device 1 performs various controls on welding system A1. Control device 1 can be a control device obtained by installing programs for various controls of welding system A1 on a general-purpose computer, or it can be a dedicated device for controlling welding system A1. Control device 1 moves the trolley 4 at a given speed. The speed is set according to the material and thickness of the workpiece W being welded. Control device 1 instructs the flux dispensing device 7 to distribute flux. Control device 1 instructs the wire feed device 5 to start and stop the wire feeding. It also instructs the wire feed speed, which is set according to a predetermined welding current. Control device 1 instructs the welding power supply device 2 to output power. Details regarding the controls performed by control device 1 at the start and end of welding will be described later.

[0029] The welding power supply 2 converts the AC power supplied from the commercial power supply P into AC power of the desired frequency and outputs it. Alternatively, a structure in which multiple welding power supply 2 are connected in parallel can be used instead of the welding power supply 2 (specifically, the output terminals a of each welding power supply 2 are connected to each other and connected to the workpiece W, and the output terminals b are connected to each other and connected to the welding wire).

[0030] like Figure 1 As shown in (b), the welding power supply device 2 includes a rectifier smoothing circuit 21, an inverter circuit 22, a transformer 23, a rectifier smoothing circuit 24, an inverter circuit 25, a current sensor 26, a voltage sensor 27, and a control circuit 28.

[0031] The rectifier-smoothing circuit 21 converts the AC power input from the commercial power supply P into DC power and outputs it. The rectifier-smoothing circuit 21 includes a rectifier circuit for rectifying the AC current and a smoothing capacitor for smoothing the current. In addition, the structure of the rectifier-smoothing circuit 21 is not limited.

[0032] Inverter circuit 22 is, for example, a unidirectional full-bridge PWM-controlled inverter with four switching elements. Inverter circuit 22 converts the DC power input from rectifier-smoothing circuit 21 into high-frequency power and outputs it by switching the switching elements according to the output control drive signal input from control circuit 28. Alternatively, inverter circuit 22 can be any circuit that converts DC power into high-frequency power; for example, it can be a half-bridge type or other inverter circuit structures.

[0033] Transformer 23 transforms the high-frequency voltage output from inverter circuit 22 and outputs it to rectifier smoothing circuit 24. Transformer 23 has a primary winding 23a and a secondary winding 23b. Each input terminal of the primary winding 23a is connected to each output terminal of inverter circuit 22. Each output terminal of the secondary winding 23b is connected to each input terminal of rectifier smoothing circuit 24. The output voltage of inverter circuit 22 is transformed according to the turns ratio of primary winding 23a and secondary winding 23b and input to rectifier smoothing circuit 24. Since the secondary winding 23b is insulated from the primary winding 23a, it prevents current from the commercial power supply P from flowing into the secondary circuit. In addition, since transformer 23 transforms the high-frequency voltage output from inverter circuit 22, it is smaller and lighter than transformers that transform the AC voltage of commercial power supply P.

[0034] The rectifier-smoothing circuit 24 converts the high-frequency power input from the transformer 23 into DC power and outputs it. The rectifier-smoothing circuit 24 includes a rectifier circuit for rectifying the high-frequency current and a DC reactor for smoothing. Furthermore, the structure of the rectifier-smoothing circuit 24 is not limited.

[0035] The inverter circuit 25 is, for example, a unidirectional full-bridge PWM-controlled inverter with four switching elements. The inverter circuit 25 converts the DC power input from the rectifier-smoothing circuit 24 into AC power and outputs it by switching the switching elements according to the switching drive signal input from the control circuit 28. The inverter circuit 25 switches between a state where the potential of output terminal a (connected to the workpiece W) is higher than that of output terminal b (connected to the solder wire), i.e., positive polarity, and a state where the potential of output terminal a is lower than that of output terminal b, i.e., opposite polarity. Furthermore, the inverter circuit 25 can be any circuit capable of converting DC power to AC power; for example, it can be a half-bridge type or other inverter circuit structures.

[0036] The current sensor 26 detects the output current of the welding power supply device 2. In this embodiment, it is disposed on the connecting line that connects one output terminal of the inverter circuit 25 to output terminal a. The output current of the welding power supply device 2 detected by the current sensor 26 is approximately equal to the current flowing through the electrode 8. The current sensor 26 outputs a current value signal corresponding to the detected instantaneous current value to the control circuit 28 and the control device 1. Furthermore, the structure of the current sensor 26 is not limited, as long as it detects the output current from the connecting line. Also, the placement location of the current sensor 26 is not limited. For example, the current sensor 26 can be disposed on the connecting line that connects the other output terminal of the inverter circuit 25 to output terminal b. Alternatively, the current sensor 26 can be disposed externally to the welding power supply device 2.

[0037] Voltage sensor 27 detects the output voltage of welding power supply device 2. In this embodiment, it detects the voltage between output terminals a and b. This voltage is approximately equal to the voltage applied between the workpiece W and the front end of electrode 8. Voltage sensor 27 outputs a voltage value signal corresponding to the detected instantaneous voltage value to control circuit 28 and control device 1. Furthermore, the structure of voltage sensor 27 is not limited, as long as it detects the voltage between output terminals a and b. The placement location of voltage sensor 27 is also not limited. For example, voltage sensor 27 can be placed outside welding power supply device 2.

[0038] The control circuit 28 is a circuit used to control the welding power supply device 2, and is implemented, for example, by a microcomputer. The control circuit 28 receives current value signals from the current sensor 26, voltage value signals from the voltage sensor 27, and various command signals from the control device 1. Then, the control circuit 28 outputs drive signals to the inverter circuit 22 and the inverter circuit 25 respectively.

[0039] When the control circuit 28 receives a command signal from the control device 1 indicating the start of power output, it starts power output by outputting start drive signals to the inverter circuit 22 and the inverter circuit 25 respectively. Conversely, when the control circuit 28 receives a command signal from the control device 1 indicating the stop of power output, it stops power output by stopping the output of the drive signals.

[0040] Furthermore, the control circuit 28 calculates the effective value of the current based on the current value signal input from the current sensor 26. Then, based on this effective current value and the current command value input from the control device 1, the control circuit 28 generates an output control drive signal for controlling the switching elements of the inverter circuit 22, and outputs it to the inverter circuit 22. That is, the control circuit 28 performs feedback control to ensure that the effective current value matches the current command value. Additionally, the control circuit 28 can also generate an output control drive signal based on the voltage value signal input from the voltage sensor 27 and the voltage command value.

[0041] Furthermore, the control circuit 28 generates a switching drive signal for controlling the switching elements of the inverter circuit 25 based on the current value signal input from the current sensor 26 and a waveform command signal generated internally, and outputs it to the inverter circuit 25. That is, the control circuit 28 performs feedback control so that the waveform of the output current matches the waveform commanded in the waveform command signal. In this embodiment, the waveform command signal is a sine wave signal. The control circuit 28 generates the switching drive signal based on the waveform command signal and outputs it to the inverter circuit 25, thereby causing the inverter circuit 25 to output a sinusoidal alternating current corresponding to the waveform command signal. Alternatively, the control circuit 28 may generate the switching drive signal based solely on the waveform command signal without using the instantaneous value of the output current.

[0042] Furthermore, when the control circuit 28 receives a DC output command signal from the control device 1, it sets the switch drive signal output to the inverter circuit 25 to a signal that fixes a given switching element in the on state and other switching elements in the off state. For example, if the states of each switching element are fixed such that the output terminal on the positive side of the rectifier smoothing circuit 24 is connected to output terminal a, and the output terminal on the negative side of the rectifier smoothing circuit 24 is connected to output terminal b, then the welding power supply device 2 outputs DC power with output terminal a as the positive terminal and output terminal b as the negative terminal. That is, the welding system A1 is a dual-purpose AC / DC welding system that can output both AC and DC power. In addition, the welding power supply device 2 can control the output current based on the current command value input from the control device 1. Therefore, the welding system A1 can appropriately control the output current.

[0043] The control processes performed by control device 1 at the start and end of welding will be described next. Figure 2 This is a flowchart illustrating the control processing performed by control device 1.

[0044] Figure 2 (a) is an example of a flowchart illustrating the start control process when welding begins. The start control process begins, for example, when the operation button that initiates welding is pressed.

[0045] First, the wire feeding begins (S1). Specifically, the control device 1 instructs the wire feeding device 5 to begin wire feeding. At this time, the control device 1 issues an instruction to feed the wire in the forward direction (from the welding tray 6 to the trolley 4) at a given micro-speed (not limited, but for example, around 5 m / min). The micro-speed corresponds to the "third speed" of this invention. Next, a DC voltage (not limited, but for example, around 15V) is applied between the workpiece W and the electrode 8 (S2). Specifically, the control device 1 instructs the welding power supply device 2 to output a DC voltage. In this embodiment, the welding power supply device 2, under the control of the control circuit 28, causes the inverter circuit 25 to output a DC voltage. Alternatively, the welding power supply device 2 may also have a DC power supply connected in parallel with the output terminals a and b, from which the DC voltage applied between the workpiece W and the electrode 8 is output.

[0046] Next, it is determined whether electrode 8 is in contact with the workpiece W and short-circuited (S3). Specifically, control device 1 makes the determination based on the voltage value signal input from voltage sensor 27. In the case of short circuit between electrode 8 and workpiece W, the voltage between electrode 8 and workpiece W drops sharply and approaches "0". Control device 1 determines a short circuit if the voltage detected by voltage sensor 27 (hereinafter referred to as "detection voltage") is below the short circuit detection threshold. In addition, the method of short circuit determination is not limited. For example, control device 1 can determine a short circuit based on the current value signal input from current sensor 26. If no short circuit is detected (S3 "No"), return to step S3 and repeat the determination in step S3. That is, control device 1 remains in standby mode until a short circuit is detected.

[0047] If a short circuit is detected (S3 "Yes"), the reverse feeding of the welding wire (from the trolley 4 to the welding tray 6) begins (S4). Specifically, the control device 1 instructs the welding wire feeding device 5 to begin the reverse feeding of the welding wire. As a result, the welding wire travels in the reverse direction, pulling away from the electrode 8 in contact with the workpiece W and retracting it. Next, it is determined whether the electrode 8 has retracted a given length (though not limited, but for example, around 3 mm) (S5). Specifically, the control device 1 times the time since the start of the reverse feeding and determines whether the time required for the given retraction length has elapsed. If the retraction is not complete (S5 "No"), the process returns to step S5, and the determination in step S5 is repeated. That is, the control device 1 remains in standby mode until the retraction is complete. If the retraction is complete (S5 "Yes"), the forward feeding of the welding wire at a decelerated speed begins (S6). The deceleration speed is a speed sufficiently slow compared to the micro-motion speed (though not limited, but for example, around 0.1 m / min). The deceleration speed is equivalent to the "fourth speed" of this invention.

[0048] Through steps S1 to S6, the welding wire is fed at a relatively fast speed until the electrode 8 makes initial contact with the workpiece W, and then fed at a relatively slow speed after retraction following contact. This shortens the time until the electrode 8 makes contact with the workpiece W and prevents the electrode 8 from being pressed against the workpiece W with strong stress. Furthermore, if the micro-motion speed is sufficiently slow to prevent the electrode 8 from being pressed against the workpiece W with strong stress upon contact, steps S3 to S6 can be omitted. That is, retraction and slowed-down feeding can be omitted.

[0049] Next, it is determined whether electrode 8 has short-circuited due to renewed contact with the workpiece W (S7). If no short circuit is detected (S7 "No"), the process returns to step S7 and repeats the determination. That is, control device 1 remains in standby mode until a short circuit is detected. If a short circuit is detected (S7 "Yes"), the wire feed is stopped (S8). Specifically, control device 1 instructs the wire feed device 5 to stop the wire feed.

[0050] Next, flux is distributed at and around the welding start point where the welding wire of the workpiece W is in direct contact with the workpiece (S9). Specifically, the control device 1 instructs the distributing device 7 to distribute the flux. The distributing device 7 distributes a pre-set appropriate amount of flux.

[0051] Next, the output of the starting current is initiated (S10). Specifically, the control device 1 instructs the welding power supply device 2 to output the starting current. The starting current is, for example, a direct current of around 1000A. Furthermore, the value of the starting current is not limited and can vary depending on the material and diameter of the welding wire used. Also, the starting current is not limited to direct current; it can also be alternating current.

[0052] Next, timing begins for the elapsed time T used to determine the start current period (S11). The start current period is the time during which the start current flows while the welding wire feed is stopped. Next, the standby time T becomes a preset first time T1 (not limited, but for example, around 400ms) (S12), and the first time T1 is a set time used to define the start current period by time. The first time T1 is the time from when the start current ignites the electrode 8, an arc is generated between the tip of the electrode 8 and the workpiece W, until the arc becomes stable, and is set based on experiments and simulations. That is, the start current period is the period from when the electrode 8 short-circuits again when it comes into contact with the workpiece W, during which the start current flows through the electrode 8 to generate and stabilize the arc. In addition, the first time T1 can be set according to the different materials and diameters of the welding wire used, or it can be set as a single time applicable to all welding wires that can be used in the welding system A1.

[0053] During the welding process executed after the initial control process has concluded, control device 1 feeds the welding wire via wire feeder 5, outputs welding power via welding power source 2, and moves trolley 4 according to the welding conditions. Additionally, control device 1 distributes flux via flux distribution device 7 according to the movement of trolley 4. The welding power output by welding power source 2 can be either alternating current (AC) or direct current (DC). Further details regarding the specific control of the welding process are omitted.

[0054] Figure 2 (b) is an example of a flowchart illustrating the end-of-weld control process. For instance, the end-of-weld control process begins when the welding end point of the workpiece W is reached and the welding end button is pressed.

[0055] First, the wire feed is stopped (S21). Specifically, the control device 1 instructs the wire feed device 5 to stop the wire feed. Next, the output of the termination current begins (S22). Specifically, the control device 1 instructs the welding power supply device 2 to output the termination current. The termination current is, for example, a direct current of about 500A. Furthermore, the value of the termination current is not limited and can vary depending on the material of the welding wire used. Also, the termination current is not limited to direct current and can be alternating current. By applying the termination current to the electrode 8 while the wire feed is stopped, the electrode 8 ignites. Next, a standby state is maintained until the detection voltage V detected by the voltage sensor 27 reaches or exceeds a preset termination voltage threshold Ve (though not limited, it is, for example, about 35V) (S23). The termination voltage threshold Ve is the threshold used to detect the start of electrode 8 ignition, thus causing the detection voltage V to begin to rise. As the electrode 8 ignites and the arc length increases, the higher the detection voltage V, the larger the diameter of the tip of the electrode 8. The end-of-life voltage threshold Ve is set to the voltage at which electrode 8 reliably begins to ignite and the diameter of the tip of electrode 8 has not yet become too large. Alternatively, in step S23, instead of comparing the detection voltage V and the end-of-life voltage threshold Ve, the amount of change in the detection voltage V since the start of the end-of-life current output, or the rate of change of the detection voltage V, can be compared with the threshold.

[0056] Next, the output of the termination current is stopped (S24). Specifically, the control device 1 instructs the welding power supply device 2 to stop the output of the termination current. The period during which the termination current flows through the electrode 8 from the stop of the welding wire feed until the termination current stops is the termination current period. Next, the flux distribution ends (S25), and the termination control process ends.

[0057] in addition, Figure 2 The process shown in the flowchart is an example, and the start control process and end control process performed by the control device 1 are not limited to the above.

[0058] Figure 3 This is a timing diagram showing the various states of welding in welding system A1. Diagram (a) shows the time variation of the welding state. Diagram (b) shows the time variation of the detection voltage detected by voltage sensor 27. Diagram (c) shows the time variation of the detection current detected by current sensor 26. Diagram (d) shows the time variation of the wire feed speed. The feed speed is positive when the wire is feeding in the forward direction and negative when feeding in the reverse direction. Diagram (e) shows the time variation of the flux distribution state. It is ON when the flux is being distributed. Additionally, Figure 3 The vertical and horizontal axes of the timing diagrams shown have been appropriately magnified or reduced for ease of understanding. Furthermore, the waveforms shown have been simplified, exaggerated, or emphasized for ease of comprehension. (Regarding...) Figure 4 (The same applies).

[0059] At time t0, by pressing the operation button to start welding, the welding state becomes ON (reference). Figure 3 (a) begins the control process. At this point, the welding wire of the micro-motion speed system begins to feed in the positive direction (see reference). Figure 3 (d)), start the DC voltage output (reference) Figure 3 (b)). In addition, the feed rate increases at an angle after being indicated by control device 1 due to inertia. The same applies when the feed rate is changed later.

[0060] At time t1, due to electrode 8 coming into contact with and short-circuiting the workpiece W, the detection voltage drops sharply (reference). Figure 3 (b)). This detects a short circuit and initiates a reverse feed of the welding wire, resulting in a negative feed rate (see reference). Figure 3 (d)). By feeding the welding wire in the reverse direction, electrode 8 is pulled away from the workpiece W, the detection voltage returns to its original state, the given length of retraction is completed at time t2, and the welding wire begins to feed in the forward direction at a deceleration speed (refer to...). Figure 3 (d)

[0061] Then, due to the short circuit caused by electrode 8 re-contacting the workpiece W at time t3, the detection voltage drops sharply (see reference). Figure 3 (b) indicates a sharp increase in the detection current (see reference). Figure 3 (c)). Therefore, a short circuit is detected, the wire feed stops, and the feed speed becomes "0" (see reference). Figure 3 (d)), the flux begins to spread (see reference). Figure 3 (e)). Additionally, the current output begins (see reference). Figure 3(c) When electrode 8 ignites, an electric arc is generated between the tip of electrode 8 and the workpiece W, and the detection voltage becomes a given voltage (refer to...). Figure 3 (b)). From time t3 to time t4 after the first time T1, the starting current period continues, and the starting current is applied to electrode 8. As a result, electrode 8 ignites and the arc length gradually increases, and the detection voltage gradually increases accordingly (see reference). Figure 3 (b)

[0062] Then, at time t4, during the end of the start current period, the start control process ends, and the welding process corresponding to the welding conditions begins. Consequently, the welding current corresponding to the current command value is output (see reference). Figure 3 (c)), begin feeding the welding wire (refer to...) Figure 3 (d)

[0063] At time t5, by pressing the button to end the welding process, the welding status is changed to OFF (reference). Figure 3 (a) begins the termination control process. At this point, the wire feed is terminated (see reference). Figure 3 (d)), start and end current output (reference) Figure 3 (c)). By ending the current flow, electrode 8 ignites smoothly, and the detection voltage begins to rise (see reference). Figure 3 (b)). At time t6, when the detected voltage becomes above the end voltage threshold Ve, the output of the end current during the end current period (refer to...) Figure 3 (c)) End flux distribution (see reference) Figure 3 (e)) and end the end control process. In addition, even if the control device 1 instructs the wire feed device 5 to stop the feed, the wire feed will not stop immediately due to inertia. The control device 1 can also start the output of the end current and start the end current period when the actual wire is detected by the signal from the encoder (not shown) from the wire feed device 5.

[0064] The function and effect of the welding system A1 involved in this embodiment will be explained next.

[0065] According to this embodiment, the control device 1 contacts the tip of the welding wire with the workpiece W at the start of welding. During the initial current period, the welding power supply device 2 outputs an initial current while the welding wire feed device 5 stops feeding the welding wire. The electrode is ignited by the first time T1 of the initial current, thereby generating an arc between the tip of the electrode 8 and the workpiece W, and this arc becomes stable. During this period, since the welding wire is not fed, the adhesion phenomenon of the tip of the electrode 8 being pressed against the workpiece W is suppressed. Furthermore, since other materials such as metal powder and steel wool are not used to generate the arc, the welding start-up operation can be automated, and impurities can be prevented from entering the weld bead after welding. When welding is started by inserting metal powder or steel wool, the distance between the welding wire and the workpiece at arc ignition, and the amount of metal powder or steel wool, vary depending on the operator, which can sometimes affect the success rate of arc ignition and the welding result at the start. However, according to this embodiment, since the operation at the start of welding can be automated, deviations caused by the operator will not occur, and welding results with high reproducibility can be obtained.

[0066] Furthermore, according to this embodiment, when welding begins, the control device 1 feeds the welding wire at a micro-speed, and after the tip contacts the workpiece W, it retracts a given length and then feeds it at a deceleration speed. This shortens the time until the electrode 8 contacts the workpiece W and prevents the electrode 8 from being pressed against the workpiece W with strong stress.

[0067] Furthermore, according to this embodiment, the control device 1 stops the wire feeder 5 at the end of welding and outputs a termination current to the welding power supply device 2 until the detection voltage V reaches or exceeds the termination voltage threshold Ve. By applying the termination current to the electrode 8 while the wire feed is stopped, the electrode 8 ignites; if ignition begins, the termination current is immediately stopped. Therefore, the diameter of the tip of the electrode 8 does not increase significantly, remaining sharp. Consequently, during subsequent welding, the contact area between the tip of the electrode 8 and the workpiece W is reduced, allowing for increased current density and suppressing arc failure. Furthermore, it is not necessary to cut the tip of the electrode 8 with pliers or the like to make it sharp.

[0068] Furthermore, this embodiment describes the case where the welding wire feed is stopped during the initial current input, but it is not limited to this. The welding wire can also be fed forward at a second speed, which is sufficiently slower than the first speed during welding, during the initial current input. In this case, adhesion caused by the tip of the electrode 8 pressing against the workpiece W is also suppressed. The welding wire feed is stopped when the second speed is the speed at which the welding wire stops, i.e., "0". Furthermore, a slower second speed is desirable, and it is even more desirable to stop the feed (the second speed being "0").

[0069] Furthermore, this embodiment describes the case where the start current period is defined by time, but it is not limited to this. Since the start current period is the period during which the start current flows to generate an arc between the electrode 8 and the workpiece W and to stabilize the arc, it can end when the stabilization of the arc can be detected. Figure 4 This is a timing diagram showing the various states during welding in different variations of the prescribed method for representing the start-up current period. In this variation, the start-up current period ends when the detection voltage V detected by the voltage sensor 27 reaches or exceeds a preset start-up voltage threshold Vs (though not limited, but for example, around 20V). The start-up voltage threshold Vs is a threshold used to detect arc stability, set when the generated arc length reaches a given length. Figure 4 In the timing diagram shown, at time t4, the start-up current period ends because the detection voltage V becomes above the initial voltage threshold Vs (reference). Figure 4 (b)) The start control process ends and the welding process corresponding to the welding conditions begins. According to this modified example, since the start current period is ended when the arc length becomes a given length based on the detection voltage V, adhesion can be suppressed if the start current period is ended when the arc length is still short, or electrode 8 can be suppressed from burning too much and depositing on the welding torch (not shown).

[0070] Furthermore, if the detection voltage V quickly exceeds the initial voltage threshold Vs, the arc may not yet be stable. In this case, the initial current period will end and welding will begin while the arc is unstable. To prevent this, the initial current period can be extended until a given second time T2 (not limited, but for example, around 100 ms) occurs after the detection voltage V exceeds the initial voltage threshold Vs. That is, the initial current period can be set to be a longer period between the period until the detection voltage V exceeds the initial voltage threshold Vs and the period until the second time T2. The second time T2 is the minimum time required for arc stabilization and is preset according to the material and diameter of the welding wire used.

[0071] The welding system involved in this invention is not limited to the embodiments described above. The specific structure of each part of the welding system involved in this invention can be freely modified in various ways.

Claims

1. A welding power supply system for submerged arc welding, characterized in that, have: A welding power supply device with an inverter circuit that provides power; A wire feeding device for feeding welding wire; A control device for controlling the welding power supply device and the welding wire feeding device; and A voltage sensor that detects the voltage applied between the tip of the welding wire and the workpiece. The control device, at the start of welding, causes the wire feed device to feed the welding wire in the forward direction. When the tip of the welding wire contacts the workpiece, the welding power supply device outputs a start current. From the moment the welding wire contacts the workpiece until the start of the forward feed at a first welding speed, a start current is provided for the forward feed at a second speed, slower than the first speed. The start current period is the period until the detected voltage detected by the voltage sensor becomes above a preset voltage threshold.

2. The welding power supply system according to claim 1, characterized in that, The second speed is the speed at which the welding wire stops.

3. The welding power supply system according to claim 1, characterized in that, The start current period is a longer period between the period until the detected voltage becomes above the voltage threshold and the period until a predetermined second time has elapsed.

4. The welding power supply system according to any one of claims 1 to 3, characterized in that, At the start of welding, the control device feeds the welding wire in the forward direction at a third speed. When the tip of the welding wire contacts the workpiece, it feeds it in the reverse direction for a given length. Then, until the tip of the welding wire contacts the workpiece again, it feeds it in the forward direction at a fourth speed, which is slower than the third speed.

5. The welding power supply system according to any one of claims 1 to 3, characterized in that, The control device, at the end of welding, sets a termination current period from when the wire feed device stops feeding the wire to when the welding power supply device stops the termination current.

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