Welding power supply system

Abstract

The present invention provides a submerged arc welding power source system capable of stabilizing the shape of the tip of an electrode after welding. In a welding system (A1) for performing submerged arc welding, there are provided a welding power source device (2) provided with an inverter circuit (25) and supplying electric power; a welding wire feeding device (5) feeding a welding wire; and a control device (1) controlling the welding power source device (2) and the welding wire feeding device (5). The control device (1) causes the welding power source device (2) to output an alternating current during welding, causes the welding wire feeding device (5) to stop the feeding of the welding wire at the end of welding, and causes the welding power source device (2) to output an end current as a direct current at the end of welding, and sets an end current period from the start of the output of the end current to the stop.

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 some time. Submerged arc welding involves distributing granular flux onto the workpiece, feeding a welding wire into the flux, and generating an electric arc between the tip of the wire and the workpiece to perform welding. In submerged arc welding, thick plates can be welded efficiently by passing a large current through a thick-diameter welding wire. Patent Document 1 discloses an example of a submerged arc welding apparatus for performing submerged arc welding.

[0003] Alternating current (AC) is supplied from the welding power source to the workpiece between the tip of the welding wire (hereinafter referred to as the "electrode") and the workpiece. The welding power source is equipped with a transformer, which outputs AC power transformed from the AC power input from a commercial power source. When submerged arc welding ends, if the welding current output is stopped simultaneously with the cessation of wire feed, the tip of the welding wire, due to inertia, may come into contact with the workpiece and stick together. To prevent this, an anti-sticking measure is implemented that delays the cessation of welding current output after the wire feed stops.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: JP 2000-117442

[0007] However, because the welding wire feed is stopped and the welding current, which is temporarily energized as alternating current, is later stopped, the shape of the electrode tip becomes different each time welding ends. Summary of the Invention

[0008] The present invention is proposed based on the above circumstances, with the aim of providing a welding power supply system that can stabilize the shape of the electrode tip after welding.

[0009] The welding power supply system provided by the present invention is a welding system for submerged arc welding, comprising: a welding power supply device having an inverter circuit and providing power; a welding wire feeding device for feeding welding wire; and a control device for controlling the welding power supply device and the welding wire feeding device. During welding, the control device causes the welding power supply device to output alternating current, and at the end of welding, causes the welding wire feeding device to stop feeding the welding wire and causes the welding power supply device to output a termination current as direct current. The control device also sets a termination current period from the start of the output of the termination current until its cessation.

[0010] 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 termination current period is the period until the detected voltage detected by the voltage sensor becomes above a preset voltage threshold.

[0011] 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 termination current period is the period until the rate of change of the detected voltage detected by the voltage sensor reaches or exceeds a preset rate of change threshold.

[0012] In a preferred embodiment of the invention, the termination current period is the period until a predetermined first time has elapsed.

[0013] The effects of the invention

[0014] According to the present invention, the control device stops the wire feed and outputs the finishing current during the finishing current period at the end of welding. If the finishing current is set to stop just after the electrode tip has ignited due to the current, adhesion will not occur, and the electrode tip will have a sharp shape. This stabilizes the shape of the electrode tip after welding. Furthermore, since the finishing current is direct current, arc depletion, which occurs with alternating current, can be suppressed, and the ignition of the electrode during the finishing current period can be appropriately controlled. Attached Figure Description

[0015] 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.

[0016] 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.

[0017] Figure 3 This is a timing diagram showing the various states during welding in the welding system according to the first embodiment.

[0018] Figure 4 This is an example of a flowchart illustrating the end control process in a variation of the welding system according to the first embodiment.

[0019] Figure 5 This is a timing diagram showing the various states during welding in a modified example of the welding system according to the first embodiment.

[0020] Explanation of reference numerals in the attached figures

[0021] 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

[0022] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings.

[0023] [First Embodiment]

[0024] 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.

[0025] 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 trolley 4 can be used instead of the welding system to move or rotate the workpiece W.

[0026] 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.

[0027] 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).

[0028] 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.

[0029] 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.

[0030] 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.

[0031] 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.

[0032] 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.

[0033] 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.

[0034] 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.

[0035] 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.

[0036] 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.

[0037] 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 signal.

[0038] 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.

[0039] 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.

[0040] Furthermore, when the control circuit 28 receives a DC output command signal from the control device 1 during the start current period and end current period (described later), 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.

[0041] 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.

[0042] 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.

[0043] 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). 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 the 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 the 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.

[0044] 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 a short circuit between electrode 8 and workpiece W, the voltage between electrode 8 and workpiece W drops sharply and approaches "0". If the voltage detected by voltage sensor 27 (hereinafter referred to as "detection voltage") is below the short circuit detection threshold, control device 1 determines that a short circuit has occurred. In addition, the method for determining a short circuit 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"), the process returns to step S3 and repeats the determination in step S3. That is, control device 1 remains in standby mode until a short circuit is detected.

[0045] 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).

[0046] 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.

[0047] 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.

[0048] 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.

[0049] 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.

[0050] 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.

[0051] During the welding process executed after the initial control process has concluded, control device 1 feeds the welding wire via wire feeder 5 according to the welding conditions, outputs AC welding power via welding power supply 2, and moves trolley 4. Additionally, control device 1, in response to the movement of trolley 4, distributes flux via flux distribution device 7. The welding power output by welding power supply 2 can be either AC or DC. Further details regarding the specific control of the welding process are omitted.

[0052] 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.

[0053] First, the wire feed is stopped (S21). Specifically, control device 1 instructs the wire feed device 5 to stop the wire feed. Next, the output of AC welding power is stopped, and the output of DC termination current is started (S22). Specifically, control device 1 instructs the welding power supply device 2 to output the termination current. The termination current is, for example, a DC current of about 500A. In addition, the value of the termination current is not limited and can vary depending on the material of the welding wire used. By energizing the electrode 8 with the termination current while the wire feed is stopped, the electrode 8 ignites. Next, standby is performed until the detection voltage V detected by voltage sensor 27 reaches or exceeds a preset termination voltage threshold Ve (not limited, but for example, about 35V) (S23). The termination voltage threshold Ve is the threshold used to detect the start of electrode 8 ignition, thereby detecting the rise of the detection voltage V. As the electrode 8 ignites and the arc length increases, the larger the detection voltage V, the larger the diameter of the tip of the electrode 8. At the end, the voltage threshold Ve is set to the voltage at which electrode 8 actually begins to ignite and the diameter of the tip of electrode 8 has not yet become too large.

[0054] As described above, the control device 1 brings the electrode 8 into contact with the workpiece W at the start of welding and generates an arc by applying an initiating current to the electrode 8. The larger the diameter of the tip of the electrode 8, the larger the contact area with the workpiece W, resulting in a lower current density and a higher probability of arc generation failure. To suppress arc generation failure, it is desirable for the tip of the electrode 8 to have a small diameter and a sharp shape. Therefore, in this embodiment, the control device 1 applies a direct current as a termination current at the end of welding and stops the termination current immediately after the electrode 8 ignites, thereby making the tip of the electrode 8 have a small diameter and a sharp shape.

[0055] 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 termination current period is the period during which the electrode 8 is energized from the start of the termination current output until it stops, when the welding wire feed stops. The larger the value of the termination current is set, the shorter the termination current period can be. Next, the flux distribution ends (S25), and the termination control process ends.

[0056] 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.

[0057] Figure 3This 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. Figure 5 (The same applies).

[0058] 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.

[0059] 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)

[0060] 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)

[0061] 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, an AC welding current corresponding to the current command value is output (reference). Figure 3 (c)), begin feeding the welding wire (refer to...) Figure 3 (d)

[0062] 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) Stop the output of AC welding current and start the output of DC end current (refer to...) 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.

[0063] The function and effect of the welding system A1 involved in this embodiment will be explained next.

[0064] According to this embodiment, when welding ends, the control device 1 stops the wire feeder 5 and the welding power supply device 2 outputs a termination current 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. Because the electrode 8 ignites, adhesion does not occur. Furthermore, since the termination current is stopped immediately after the electrode 8 ignites, the diameter of the electrode 8's tip does not increase significantly, remaining sharp. That is, the shape of the electrode 8's tip remains sharp and stable after welding. Therefore, during subsequent welding, the contact area between the electrode 8's tip and the workpiece W is reduced, allowing for increased current density and suppressing arc failure. Additionally, it is not necessary to cut the electrode 8 with pliers or similar devices to make its tip sharp.

[0065] Furthermore, according to this embodiment, the control device 1 stops the termination current when the detection voltage V reaches or exceeds the termination voltage threshold Ve. This allows for proper detection of the start of ignition on the electrode 8, thereby stopping the termination current.

[0066] Furthermore, 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. In addition, 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 suppressed from entering the weld bead after welding.

[0067] 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.

[0068] In addition, this embodiment describes a situation where the control device 1 detects the electrode 8 starting to ignite when the detection voltage V becomes above the end voltage threshold Ve, but it is not limited to this.

[0069] For example, the control device 1 can also detect the start of ignition of electrode 8 when the voltage change ΔV of the detection voltage V at the start of the energization and the end of the current becomes a change threshold ΔVe. Figure 4(a) is an example of a flowchart representing the end control process in this variation. Figure 4 The flowchart shown in (a) is in Figure 2 In the flowchart shown in (b), step S23 is changed to steps S31 and S32. In step S31, the voltage change ΔV is calculated. Specifically, the control device 1 stores the detection voltage V detected by the voltage sensor 27 when the current is turned on to end, and calculates the voltage change ΔV by subtracting it from the current detection voltage V. Next, in step S32, it is determined whether the voltage change ΔV is above a preset change threshold ΔVe (though not limited, it is, for example, around 15V) (S32). The change threshold ΔVe is the threshold used to detect the start of the electrode 8 ignition, thereby detecting the start of the rise in the voltage V. If the voltage change ΔV is less than the change threshold ΔVe (S32 "No"), the process returns to step S31 and repeats the steps S31 and S32. On the other hand, if the voltage change ΔV is above the change threshold ΔVe (S32 "Yes"), the process proceeds to step S24. In this modified example, the current is stopped immediately if the electrode 8 starts to ignite. Therefore, no adhesion occurs, and the tip of electrode 8 becomes sharp.

[0070] In addition, the control device 1 can also detect that the electrode 8 has started to ignite when the rate of change of the detection voltage V is above the rate of change threshold. Figure 4 (b) is an example of a flowchart representing the end control process in this variation. Figure 4 The flowchart shown in (b) is in Figure 2 In the flowchart shown in (b), step S23 is changed to steps S41 and S42. In step S41, the voltage change rate is calculated. Specifically, the control device 1 stores the detected voltage V detected by the voltage sensor 27 and calculates the voltage change rate of the current detected voltage V. Next, in step S42, it is determined whether the voltage change rate is above a preset change rate threshold (though not limited, but for example, around 10V / 100mssec) (S42). The change rate threshold is a threshold used to detect the start of ignition of the detection electrode 8, thereby detecting the start of voltage V rising. If the voltage change rate is below the change rate threshold (S42 "No"), the process returns to step S41 and repeats the steps S41 and S42. On the other hand, if the voltage change rate is above the change rate threshold (S42 "Yes"), the process proceeds to step S24. In this modified example, the current is immediately stopped if the electrode 8 starts to ignite.

[0071] Alternatively, the control device 1 can define the termination current period using elapsed time, rather than based on the detected voltage. The termination current period only needs to ensure that the electrode 8 is fully ignited and that the termination current is stopped before it over-ignites and the diameter of the tip of the electrode 8 increases. Therefore, depending on the material and diameter of the welding wire used, a second time T2 can be preset based on experiments and simulations to ensure that the electrode 8 is fully ignited when the termination current is applied and before it over-ignites and the diameter of the tip of the electrode 8 increases. The termination current is stopped when this second time T2 has elapsed since the start of the termination current output. Figure 4 (c) is an example of a flowchart representing the end control process in this variation. Figure 5 This is a timing diagram showing the various states during welding in this modified example.

[0072] Figure 4 The flowchart shown in (c) is in Figure 2 In the flowchart shown in (b), step S23 is changed to steps S51 and S52. In step S51, timing begins for the elapsed time T during the determination of the end current. Next, in step S52, a standby period is entered until time T reaches a preset second time T2, after which the process proceeds to step S24. Figure 5 In the timing diagram shown, the current termination period lasts from time t5 until time t6, after the second time interval T2, when electrode 8 is energized to terminate the current. As a result, electrode 8 ignites smoothly, and the detection voltage begins to rise (reference). Figure 5 (b)). Then at time t6, the termination current is stopped, and the termination control process ends. In this modified example, the termination current is also stopped immediately if electrode 8 starts to ignite.

[0073] 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 a start current flows to generate an arc between the electrode 8 and the workpiece W and to stabilize the arc, it can end when arc stabilization can be detected. For example, the control device 1 can also end the start current period when the detection voltage V detected by the voltage sensor 27 reaches or exceeds a preset start voltage threshold Vs (not limited, but for example, around 20V). The start voltage threshold Vs is a threshold used to detect arc stabilization, set to the voltage at which the arc length of the generated arc reaches a given length. According to this modified example, since the start current period ends when the arc length reaches a given length based on the detection voltage V, it is possible to suppress adhesion caused by ending the start current period when the arc length is still short, or to suppress excessive burning of the electrode 8 and deposition in the welding torch (not shown). Alternatively, control device 1 can continue the current initiation period until a given third time T3 (though not limited, but for example, around 100 ms) has elapsed, so that the current initiation period does not end even if the detected voltage V exceeds the initial voltage threshold Vs before the arc stabilizes. The third time T3 is the minimum time required for arc stabilization and can be preset according to the material and diameter of each welding wire used.

[0074] 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; The wire feeding device for feeding welding wire; and A control device for controlling the welding power supply and the welding wire feed device. During welding, the control device causes the welding power supply to output alternating current. At the end of welding, the wire feed device stops feeding the welding wire, and the welding power supply outputs a direct current as the termination current. The termination current period is set from the start of the termination current output until it stops, so that the termination current stops as soon as the electrode is ignited.

2. The welding power supply system according to claim 1, characterized in that, The welding power supply system also features: A voltage sensor that detects the voltage applied between the tip of the welding wire and the workpiece. The terminus current period is the period until the detected voltage detected by the voltage sensor becomes above a preset voltage threshold.

3. The welding power supply system according to claim 1, characterized in that, The welding power supply system also features: A voltage sensor that detects the voltage applied between the tip of the welding wire and the workpiece. The terminus current period is the period until the rate of change of the detected voltage detected by the voltage sensor reaches or exceeds a preset rate of change threshold.

4. The welding power supply system according to claim 1, characterized in that, The terminus current period is the period up to the point where a preset time has elapsed.

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