JP2006026667A - Resistance welding equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide resistance welding equipment with which a welding result of stable quality can be obtained through extremely simple structure. <P>SOLUTION: Voltage measured by a voltage measuring circuit 32 is controlled to be voltage set by a welding parameter and the voltage-controlled electricity is supplied. Then, after current measured by a current measuring circuit 30 reaches welding current set by the welding parameter, welding is performed by making the fixed welding current to flow through during the electricity supply time set by the welding parameter. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resistance welding apparatus that performs a welding process on a workpiece by controlling a welding current and an energization time thereof.

  In a resistance welding apparatus, two metal plates that are materials to be welded are sandwiched between welding electrodes, a predetermined welding current is passed between these welding electrodes for a predetermined time, and the metal plates are melted by the generated Joule heat. Join. In resistance welding using the heat generated by the contact resistance of the material to be welded as a heat source, if the contact resistance varies due to the influence of the surface roughness of the material to be welded or the oxide film, welding failure due to the fact that the desired welding current does not flow, Alternatively, there is a risk that problems such as the occurrence of sparks due to excessive welding current may occur.

  Therefore, a resistance welding apparatus disclosed in Patent Document 1 has been proposed as a technique capable of ensuring a desired welding current.

  This resistance welding device applies a constant set voltage between the welding electrodes according to the voltage set value and monitors the welding current. When the welding current reaches the current critical value, it switches from voltage control to current control and sets the current. According to the value, welding is performed by supplying a constant set welding current and the voltage between the electrodes is monitored, and when the voltage between the electrodes reaches the voltage critical value, switching from current control to voltage control and applying the constant set voltage again This process is to be repeated.

Japanese Patent No. 3484457

  By the way, the welding quality not only decreases due to excessive voltage or excessive current, but also greatly depends on the time during which the welding current is applied to the material to be welded. That is, the Joule heat required for welding is determined by the product of the welding current and its energization time. Therefore, in order to obtain an appropriate welding state, it is necessary to manage not only the welding current but also the energization time.

  An object of this invention is to provide the resistance welding apparatus which can obtain favorable welding quality with a very simple structure.

  Moreover, an object of this invention is to provide the resistance welding apparatus which can detect the presence or absence of abnormality, such as the state of a to-be-welded material.

The resistance welding apparatus of the present invention is a welding parameter setting means for setting a welding parameter including a welding current and an energization time of the welding current,
Voltage control means for controlling the voltage between the welding electrodes;
Current monitoring means for monitoring current supplied to the workpiece by voltage control by the voltage control means;
Welding current control means for supplying and controlling the welding current to the material to be welded for the energization time;
Control switching means for switching from voltage control by the voltage control means to current control by the welding current control means when the current monitored by the current monitoring means becomes the welding current;
It is characterized by providing.

  In this case, voltage control is performed by applying an inter-electrode voltage between the welding electrodes, and when the current supplied to the welded material becomes the set welding current, the energization that sets the welding of the welded material by the welding current By continuing for a certain amount of time, a welding process with constant Joule heat is performed.

  In addition, generation | occurrence | production of a splash can be avoided in advance by setting the voltage between electrodes until it reaches the set welding current as a voltage which increases gradually.

  In addition, when performing voltage control by the voltage control means, the time for reaching the set welding current is monitored, and it is determined whether or not the welding current is reached within a predetermined time range. It is possible to detect the presence or absence of abnormality such as. This time range can be set as the lower limit time and the upper limit time by the welding parameter setting means.

  Furthermore, the presence or absence of abnormality during the welding process can also be detected by determining whether or not the welding current by the welding current control means exceeds the upper limit welding current.

  In the resistance welding apparatus of the present invention, a desired welding current can be supplied to a material to be welded for a desired energization time to obtain good welding quality. Further, it is possible to recognize the presence / absence of an abnormality such as a set state of the material to be welded based on a time required to reach a desired welding current. This makes it possible to avoid the occurrence of welding defects in advance.

  FIG. 1 is a block diagram showing a circuit configuration of a transistor type resistance welding apparatus 10 of the present embodiment. The resistance welding apparatus 10 includes an AC power supply 12, an AC / DC conversion circuit 16 that converts an AC current supplied from the AC power supply 12 via the main power switches 14 a and 14 b into a DC current, and an AC / DC conversion circuit 16. Large capacitors 18a and 18b that store the current converted into direct current as electric charges, welding electrodes 20a and 20b connected between the positive and negative electrodes of the large capacitors 18a and 18b, and one of the large capacitors 18a and 18b. A plurality of transistors 22a, 22b,..., 22n connected in parallel between the electrode and one welding electrode 20a. In addition, two overlapped materials to be welded 24a and 24b are sandwiched between the welding electrodes 20a and 20b.

  Further, the resistance welding apparatus 10 includes a control unit 26 that controls the welding operation. The controller 26 supplies a drive signal to the gates of the respective transistors 22a, 22b,..., 22n, and simultaneously controls on / off of the transistors 22a, 22b,. , 24b, a current measuring circuit 30 (current monitoring means) for measuring a current (monitor current mi), a voltage measuring circuit 32 for measuring a voltage (monitor voltage mv) between the welding electrodes 20a, 20b, and a welding parameter Between the input unit 34 for inputting the current, the display unit 36 for displaying the state of the resistance welding apparatus 10 including the monitor current mi and the monitor voltage mv, and the large-capacity capacitors 18a and 18b and the welding electrodes 20a and 20b. A welding interruption switch 37 provided is connected.

  FIG. 2 is a detailed configuration block diagram of the control unit 26. Based on the welding parameters supplied from the input unit 34, the control unit 26 sets a reference waveform for the interelectrode voltage and the welding current, and sets the time based on the command from the setting unit 38. Switching of voltage control or current control on the basis of the time measuring circuit 40 for measuring the current, the monitor current mi, the monitor voltage mv, the welding parameter from the setting unit 38 and the elapsed time t supplied from the time measuring circuit 40, and A switching control circuit 42 (control switching means, welding current determination means) for determining the setting state of the welding materials 24a, 24b, a voltage control or current control selection signal se from the switching control circuit 42, a timing circuit 40 A reference waveform generation circuit 44 that generates a reference waveform according to the elapsed time t and the welding parameters supplied from the setting unit 38, and a switching control circuit 42 A comparison circuit 46 that compares the nita current mi or monitor voltage mv with the reference waveform signal from the reference waveform generation circuit 44, and a voltage generation circuit 48 that outputs a transistor control signal DG to the drive circuit 28 according to the comparison result by the comparison circuit 46. (Voltage control means, welding current control means).

  A display output circuit 50 is connected to the setting unit 38. The display output circuit 50 displays the monitor current mi, the monitor voltage mv, and the like on the display unit 36, or outputs a display signal for displaying the determination result such as the set state of the workpieces 24a and 24b on the display unit 36. To do.

  The resistance welding apparatus 10 of the present embodiment is basically configured as described above. Next, the operation will be described based on the flowchart shown in FIG.

  First, the operator sets welding parameters using the input unit 34 (step S1). In this case, the welding parameters are set as each data shown in FIG. That is, a squeeze time ST for clamping and pressurizing the workpieces 24a and 24b with the welding electrodes 20a and 20b is set, and the welding parameters of the interelectrode voltage by voltage control immediately after the start of energization are set as time T1, voltage P1 and P2. To do. In this case, the set interelectrode voltage is set as a reference voltage waveform that gradually increases from voltage P1 to voltage P2 at time T1. Moreover, the welding current i1 by current control and its energization time T2 are set. Furthermore, the welding parameters of the current for ending the current control are set as time T3, currents i2 and i3, as in the case of the interelectrode voltage. In this case, the set current is set as a reference current waveform that gradually decreases from current i2 to current i3 at time T3. Furthermore, a hold time HT for holding and pressurizing the workpieces 24a and 24b with the welding electrodes 20a and 20b is set.

  In addition, the lower limit time TLL and the upper limit time TUL for the state determination at the time of voltage control can also be set as a welding parameter. It is also possible to set an upper limit value Δi of the welding current i1 during the welding current control.

  After setting the welding parameters as described above, the main power switches 14a and 14b are closed, and energization of the resistance welding apparatus 10 is started (step S2). The current supplied from the AC power supply 12 is converted into a DC current by the AC / DC conversion circuit 16, and then supplied to the large-capacitance capacitors 18a and 18b to accumulate charges.

  Next, the workpieces 24a and 24b are sandwiched between the welding electrodes 20a and 20b, and the state is continued for the squeeze time ST (step S3). By this squeeze treatment, the welding electrodes 20a and 20b can be pressed against the workpieces 24a and 24b in a stable state. During the squeeze process, the transistors 22a, 22b,..., 22n disposed between the large-capacitance capacitors 18a, 18b and the welding electrodes 20a, 20b are turned off, and the welding electrodes No current flows between 20a and 20b.

  When the squeeze time ST has elapsed, the reference waveform generation circuit 44 supplies the comparison circuit 46 with a gradually increasing reference voltage waveform generated based on the welding parameter time T1 and the voltages P1 and P2 (step S4). The voltage increase rate in the reference voltage waveform is set as (P1-P2) / T1. On the other hand, the switching control circuit 42 supplies the monitor voltage mv between the welding electrodes 20 a and 20 b measured by the voltage measurement circuit 32 to the comparison circuit 46.

  The comparison circuit 46 compares the reference voltage waveform at the elapsed time t from the start of voltage control supplied from the reference waveform generation circuit 44 with the monitor voltage mv supplied from the switching control circuit 42, and the voltage according to the difference. A control signal is output to the voltage generation circuit 48 to perform voltage control (step S5). The voltage generation circuit 48 outputs a transistor control signal DG to the drive circuit 28 based on the voltage control signal from the comparison circuit 46, and the drive circuit 28 turns on the transistors 22a, 22b,..., 22n simultaneously according to the transistor control signal DG. Control off / on. As a result, the charges accumulated in the large-capacitance capacitors 18a, 18b are discharged through the transistors 22a, 22b,..., 22n, and a voltage corresponding to the reference voltage waveform is applied between the welding electrodes 20a, 20b.

  When a voltage is applied between the welding electrodes 20a and 20b, the current flowing between the workpieces 24a and 24b is measured by the current measurement circuit 30 and supplied to the switching control circuit 42 as the monitor current mi. During the voltage control, the switching control circuit 42 compares the measured monitor current mi with the welding current i1 that is a welding parameter supplied from the setting unit 38 (step S6).

  When the monitor current mi has not reached the welding current i1 and the elapsed time t = t1 from the start of voltage control does not exceed the predetermined upper limit time TUL (step S7), the switching control circuit 42 Continue voltage control based on the voltage waveform.

  On the other hand, if the monitor current mi has not reached the welding current i1 and the elapsed time t = t1 from the start of voltage control exceeds the upper limit time TUL (see FIG. 5), a welding interruption signal is output. Then, the welding interruption switch 37 is opened to interrupt the energization of the welding electrodes 20a and 20b, and the display unit 36 displays that the elapsed time t1 exceeds the upper limit time TUL via the display output circuit 50 (step S8). ). As a result, for example, a situation in which appropriate welding cannot be performed due to a defect in the joining state or surface state of the materials to be welded 24a, 24b, or a state in which no power is supplied is avoided in advance, and the situation occurs for the operator. Can be notified.

  Further, when the monitor current mi reaches the welding current i1 (step S6), the switching control circuit 42 determines that the elapsed time t = t1 after starting the voltage control has not reached the lower limit time TLL (step S9). In the same manner, a welding interruption signal is output to open the welding interruption switch 37 to interrupt the energization of the welding electrodes 20a and 20b, and the elapsed time t1 is set to the lower limit time via the display output circuit 50. The display unit 36 displays that the TLL has not been reached (step S10). Thereby, for example, the welded materials 24a and 24b do not exist, or only one of the welded materials 24a and 24b exists, or inappropriate welded materials 24a and 24b that do not correspond to the welding parameters are present. When it is set and there is a possibility that excessive welding current i1 flows, the situation can be avoided in advance and the operator can be notified that the situation has occurred.

  On the other hand, the switching control circuit 42 determines that the monitor current mi has reached the welding current i1 (step S6), and the elapsed time t = t1 from the start of voltage control is the lower limit time TLL and the upper limit time TUL. When it is determined that the time is appropriate (steps S9 and S11), the voltage control is switched to the current control, and the welding process is started (see FIG. 7). In step S11, when the elapsed time t = t1 from the start of voltage control exceeds the upper limit time TUL, the energization to the welding electrodes 20a and 20b is interrupted as in steps S8 and S10, and The state is displayed on the display unit 36 (step S12).

  When the monitor current mi reaches the welding current i1 within an appropriate time range between the lower limit time TLL and the upper limit time TUL, the reference waveform generation circuit 44 is a welding parameter according to the selection signal se from the switching control circuit 42. A first reference current waveform based on the welding current i1 and the energization time T2 is supplied to the comparison circuit 46 (step S13). The switching control circuit 42 supplies the monitor current mi flowing between the welding electrodes 20 a and 20 b measured by the current measurement circuit 30 to the comparison circuit 46.

  The comparison circuit 46 compares the constant welding current i1 which is the first reference current waveform supplied from the reference waveform generation circuit 44 with the monitor current mi supplied from the switching control circuit 42, and a voltage according to the difference. Current control is performed by outputting a control signal to the voltage generation circuit 48 (step S14).

  When the voltage control is switched to the current control, there is a possibility that the current flows excessively due to overshoot. Therefore, the switching control circuit 42 compares the monitor current mi with the upper limit welding current (i1 + Δi) obtained by adding the upper limit limit Δi to the welding current i1, and when mi> (i1 + Δi) is satisfied (step S15), Since the increase rate (P1-P2) / T1 may be set inappropriately, for example, the display unit 36 displays "Please review the welding parameters." A review can be suggested (step S16).

  On the other hand, when mi ≦ (i1 + Δi), the switching control circuit 42 compares the elapsed time t = t2 from the start of the current control with the energization time T2, and welds until the elapsed time t2 = the energization time T2. The welding with the current i1 is continued (step S17). As a result, the welding current i1 flows between the welding electrodes 20a and 20b for the energization time T2, and the workpieces 24a and 24b are welded.

  After the energization time T2 has elapsed, the reference waveform generation circuit 44 supplies the comparison circuit 46 with the gradually decreasing second reference current waveform generated based on the welding parameter time T3 and the currents i2 and i3 (step S18). ), Current control based on the second reference current waveform is continued (step S19). The switching control circuit 42 compares the elapsed time t = t3 after the start of the current control with the second reference current waveform with the time T3 (step S20), and when the elapsed time t3 = time T3, the welding is performed. The energization to the electrodes 20a and 20b is terminated (step S21).

  Next, in a state where no power is supplied, the workpieces 24a and 24b are sandwiched between the welding electrodes 20a and 20b during the hold time HT that is a welding parameter (step S22), and then the welding electrodes 20a and 20b are opened to open the workpiece 24a. , 24b is taken out to complete the entire welding process.

  Here, in this embodiment, after the current flowing between the welding electrodes 20a and 20b reaches the welding current i1, welding is performed by flowing a constant welding current i1 through the workpieces 24a and 24b for a certain energization time T2. Like to do. In this case, as shown in FIGS. 8 and 9, even if the elapsed time t1 from the start of energization until reaching the constant welding current i1 varies depending on the state of the materials to be welded 24a and 24b. The Joule heat actually applied to the materials to be welded 24a and 24b can be constant regardless of the elapsed time t1, as shown by the hatched portion. Therefore, a stable welding state can always be realized.

  In the above-described embodiment, during voltage control, it is determined whether or not the monitor current mi reaches the welding current i1 within a predetermined time range (between the lower limit time TLL and the upper limit time TUL). For example, the welding time can be determined by comparing the elapsed time from the start of voltage control to the end of current control with a predetermined time range.

  FIG. 10 is a circuit configuration block diagram when the present invention is applied to an inverter type resistance welding apparatus 60. The same components as those of the transistor type resistance welding apparatus 10 shown in FIG. 1 are denoted by the same reference numerals, and the description thereof is omitted.

  This resistance welding apparatus 60 is provided with four switching elements 62a to 62d, a welding transformer 64, and a rectifier circuit 66 in place of the transistors 22a, 22b,. The current flowing between the welding electrodes 20a and 20b is configured to be detected by a current sensor 68.

  The drive circuit 28 alternately switches the switching elements 62a, 62d and 62b, 62c, and supplies the electric charge discharged from the large capacity capacitor 18 to the welding transformer 64 as a high frequency current. The high-frequency current is adjusted to a predetermined voltage by the welding transformer 64, then rectified by the rectifier circuit 66, and supplied to the workpieces 24a and 24b, whereby desired welding is performed.

  FIG. 11 is a circuit configuration block diagram when the present invention is applied to a chopper type resistance welding apparatus 70. The same components as those of the inverter type resistance welding apparatus 60 shown in FIG. 10 are denoted by the same reference numerals, and the description thereof is omitted.

  In this resistance welding apparatus 70, a high-frequency alternating current is directly supplied between the welding electrodes 20a and 20b via the four switching elements 62a to 62d, and desired welding is performed.

It is a circuit block diagram of the resistance welding apparatus of this embodiment. FIG. 2 is a configuration block diagram of a control unit shown in FIG. 1. It is a flowchart of the processing operation in the resistance welding apparatus of this embodiment. It is explanatory drawing of the welding parameter set in the resistance welding apparatus of this embodiment. It is explanatory drawing of the welding current determination by the voltage control in the resistance welding apparatus of this embodiment. It is explanatory drawing of the welding current determination by the voltage control in the resistance welding apparatus of this embodiment. It is explanatory drawing of the welding current determination by the voltage control in the resistance welding apparatus of this embodiment. It is explanatory drawing of the relationship between the welding current and energization time in the resistance welding apparatus of this embodiment. It is explanatory drawing of the relationship between the welding current and energization time in the resistance welding apparatus of this embodiment. It is a circuit block diagram of the inverter type resistance welding apparatus which is other embodiment. It is a circuit block diagram of the resistance welding apparatus of the chopper system which is further another embodiment.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10, 60, 70 ... Resistance welding apparatus 16 ... AC / DC conversion circuit 18, 18a, 18b ... Large-capacitance capacitor 20a, 20b ... Welding electrodes 22a-22n ... Transistor 24a, 24b ... Material to be welded 26 ... Control part 28 ... Drive Circuit 30 ... Current measurement circuit 32 ... Voltage measurement circuit 34 ... Input unit 36 ... Display unit 37 ... Welding interruption switch 38 ... Setting unit 40 ... Timer circuit 42 ... Switching control circuit 44 ... Reference waveform generation circuit 46 ... Comparison circuit 48 ... Voltage Generating circuit 50... Display output circuits 62a to 62d... Switching element

Claims (5)

Welding parameter setting means for setting a welding parameter including a welding current and an energization time of the welding current;
Voltage control means for controlling the voltage between the welding electrodes;
Current monitoring means for monitoring current supplied to the workpiece by voltage control by the voltage control means;
Welding current control means for supplying and controlling the welding current to the material to be welded for the energization time;
Control switching means for switching from voltage control by the voltage control means to current control by the welding current control means when the current monitored by the current monitoring means becomes the welding current;
A resistance welding apparatus comprising: The apparatus of claim 1.
The welding parameter setting means sets a gradually increasing voltage between electrodes as the welding parameter. The apparatus of claim 1.
A resistance welding apparatus comprising welding current determination means for determining whether or not the welding current is reached within a predetermined time range during voltage control by the voltage control means. The apparatus of claim 3.
The resistance welding apparatus, wherein the welding parameter setting means sets a lower limit time and an upper limit time of the time range as the welding parameters. The apparatus of claim 1.
The current monitoring means monitors the welding current by the welding current control means,
A resistance welding apparatus comprising welding current determination means for determining whether or not the welding current exceeds an upper limit welding current.

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