JP2001225173A - Resistance welding equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent resistance welding equipment from generating expulsions and surface flashes at the time of welding. SOLUTION: By making a DC input Vw a square wave AC output S1 by a chopper circuit 35, and by applying this square wave AC output S1 to works W through welding electrodes 24, the works W are welded. By applying the square wave AC output S1 to the works W, almost no generation of the expulsions and surface flashes is observed on the works after welding.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to, for example, a method in which electricity is supplied through a contact portion between works (members) to be joined,
The present invention relates to a resistance welding apparatus that heats by utilizing resistance heat generated in a contact portion and applies pressure to weld the work.

[0002]

2. Description of the Related Art Conventionally, a DC resistance welding apparatus has been widely used for joining metal works to each other.

With this DC resistance welding apparatus, for example,
A ribbon-shaped workpiece made of stainless steel and having a thickness of 0.1 [mm], and a nickel-made oxide film having a diameter of 5.0 [m]
m], the output voltage is +2 [V] and the output time (also referred to as energization time or welding time) is 2 [ms] as shown in FIG.
Is applied between the welding electrodes sandwiching the work in a pressurized state.

[0004]

However, the above welding conditions (DC welding, output voltage +2 [V], output time 2
[Ms]), when the ribbon-shaped work and the stem-shaped work are welded, there is a problem that the work after the welding is scattered (dust).

It is to be noted that the output voltage is increased from +0.1 [V] to +3.
Between 0 [V], the output time is 0.1 [ms] to 9.99.
Even when welding was performed while changing the time within [ms], the occurrence of the scattering could not be avoided.

SUMMARY OF THE INVENTION The present invention has been made in consideration of such problems, and has as its object to provide a resistance welding apparatus that hardly causes scattering of a workpiece after welding.

[0007]

According to the present invention, a DC input is made into a rectangular wave AC output by a chopper circuit, and the rectangular wave AC output is applied to a work through a welding electrode.
The work is welded (the invention according to claim 1).

As a result, almost no scattering occurs on the workpiece after welding.

In this case, a control circuit connected to the chopper circuit feedback-controls at least one of a current flowing to the work through the welding electrode, a voltage applied to the work, or electric power of a product of the current and the voltage. (The invention according to claim 2).

Further, by connecting the display device and the input device to the control circuit, the type and value of elements (voltage, current or power) and the chopping frequency, duty, output time, etc. can be set between the display device and the input device. Can be set (the invention according to claim 3).

[0011]

An embodiment of the present invention will be described below with reference to the drawings.

FIG. 1 shows the configuration of a resistance welding apparatus 10 to which an embodiment of the present invention is applied.

The resistance welding apparatus 10 basically comprises a welding power supply 12 which is a rectangular wave AC output power supply, and a welding head 14 to which a rectangular wave AC output S1 from the welding power supply 12 is supplied. .

One end of a power supply line 16 (16a, 16b) is connected to output terminals 21 and 22 of the welding power supply 12, and the other end of the power supply line 16 (16a, 16b) is connected to an electrode constituting the welding head 14. Holder 20 (20a, 20b)
Is connected.

A welding electrode 24 (24a, 24b) comprising a pair of electrodes is detachably attached to the electrode holder 20. A work W as a welding member is arranged facing the welding electrodes 24 (24a, 24b).

The welding power supply 12 includes a power supply circuit 32. The power supply circuit 32 is supplied with a DC voltage of welding voltage Vw from an AC power supply such as 100 [V] or 200 [V] introduced through a power switch 33. A voltage (DC power supply) is generated, and ± 12 supplied as a power supply for the control circuit 50 and the like.
A DC low voltage power supply (not shown) such as [V] is generated.

The electrolytic capacitor 34 is charged by the DC voltage Vw for welding, and the DC voltage Vw charged in the electrolytic capacitor 34 is supplied to the input side of the chopper circuit 35 as a DC input.

The chopper circuit 35 includes a MOSFET 36 serving as a power switching element, and a MOSFET 3
6 and a DC drive voltage Vw
Is chopped to output a square wave AC output S1.

Here, as shown in FIG. 2, the rectangular wave AC output S1 is defined as a value 0 (unit: voltage [V], current [A] or power [W]) as a reference, from time t1 to time t2. , A chopped rectangular wave output having an amplitude + Q (unit: voltage [V], current [A] or power [W]) during the output time (welding time) Tout.

FIG. 2 shows an example of a positive power supply (positive power supply means a positive value when the square wave AC output S1 is integrated). ,
As shown in FIG. 3, a rectangular wave AC output S1 of a chopped negative power supply having an amplitude −Q based on the value 0 may be used.

The voltage V1, which is the welding voltage generated between the output terminals 21 and 22, is detected by the voltage detector 52 and supplied to the control circuit 50 as a feedback voltage (this symbol is also referred to as V1 because it becomes complicated). Is done.

The power supply lines 16 (16a, 16b)
The current I1 which is a welding current flowing through the current detector 48 is detected by the current detector 48, and is fed back through the current-voltage converter 54 (this symbol is also referred to as I1 because it becomes complicated).
Is supplied to the control circuit 50.

The control circuit 50 includes a microcomputer functioning as drive / control / processing / judgment means. As is well known, the microcomputer is a microprocessor (MPU) corresponding to a central processing unit (CPU).
Read in which an AD (analog-digital) conversion circuit or DA (digital-analog) conversion circuit as an input / output device connected to the microprocessor, an I / O port, a control program, a system program, a look-up table, etc. are written in advance A dedicated memory (ROM), a random access memory (R) for temporarily storing processing data, etc.
AM, a write / read memory), a timer circuit, a counter, and the like.

The control circuit 50 is connected to the input side of a gate drive circuit 58 constituting the chopper circuit 35, and the output side of the gate drive circuit 58 is connected to the gate terminal of the MOSFET 36.

A display device 56 such as a CRT display and an input device 62 are connected to the control circuit 50, and the types of welding elements that can be set by the control circuit 50 {FIG.
In the example, the voltage V1, the current I1, or the power P1 (V1 × I1)｝ which is the product of the voltage V1 and the current I1, the chopping frequency f, the duty D, the output time Tout, and the like are selectable on the display device 56. Input device 62
Can be set. The input device 62 is provided with a welding start switch 64.

The duty D is an on-duty in this embodiment, and in the rectangular wave AC output S1 shown in FIG. 4 (an enlarged view of FIG. 2), the output time Tout between the time points t1 and t2.
The duty D is defined as D [%] = (Ton / T) × 100, where T is the period of repetition between T and Ton the period during which the amplitude is + Q during this period T. .

In this embodiment, the voltage detector 52
Are designed so that the envelope of each instantaneous value can be obtained as the voltage V1 obtained at the output of the current and the current I1 obtained at the output of the current-voltage converter 54. The envelope of the instantaneous value is, for example, a voltage V1 and a current I1 supplied to the control circuit 50 by the rectangular wave AC output S1 shown in FIG.
Is assumed to be the voltage V1 until time t1.
= 0 [V] or current I1 = 0 [A], voltage V1 = + Q [V] or current I1 = + Q [A] during time t1 to t2, which is the output time, and voltage V1 after time t2.
= 0 [V] or current I1 = 0 [A], and these voltage V1 and current I1 are supplied to the control circuit 50.

The power P1 is actually obtained as the product of the effective value of the voltage V1 and the effective value of the current I1, but in this embodiment, the control circuit 50 determines the power from the detected voltage V1 and the current I1. P1 is calculated for convenience as P1 = V1 × I1. Of course, the power P1 may be calculated as P1 = V1 × I1 × (D / 100) in consideration of the duty D.

The control circuit 50 sets at least one element of the detected voltage V1, the current I1, or the power P1 calculated from the voltage V1 and the current I1, and sets the corresponding element by the input device 62 in advance. The set voltage (sign is Vs), set current (sign is Is) or set power (sign is Ps) is compared with the detected voltage V1, the detected current I1, or the detected power P1. To perform feedback control.

In this feedback control, slow-up control and the like can be selected by setting.
In the slow-up control, the slope may be automatically set according to the magnitude of the load (set power).

Next, an operation example of the resistance welding apparatus 10 configured as described above will be described. First, the operator as a user turns on the power switch 33 of the welding power source 12.

In this state, on the display device 56, the set voltage Vs, the set current Is, and the output time (also referred to as energization time or welding time) Tout shown on the upper side of FIG.
Is displayed.

Here, the workpiece W is a ribbon-shaped workpiece W made of stainless steel and having a thickness of 0.1 mm as described above.
A workpiece W made of nickel having an oxide film and having a diameter of 5.0 mm is used.

Therefore, the operator sets the values of the respective elements (welding conditions) on the setting screen 70 by using the not-shown up / down keys, cursor keys and the like in the input device 62.

Here, a setting screen 72 shown in the lower part of FIG.
As shown in the figure, constant voltage welding is performed at the set voltage Vs = 2.00 [V], and the output time Tout is set to Tout = 4.
Set to 00 [ms]. When only the set voltage Vs is set and the set current Is is not set (Is = “*. **” [kA]) as shown in the figure, the welding conditions in the constant voltage feedback control are automatically set. .

On the other hand, when the set current Is is set and the set voltage Vs is not set, the welding conditions in the constant current feedback control are automatically set, and both the set voltage Vs and the set current Is are set. In such a case, the welding conditions in the constant power feedback control are automatically set.

When a decision key (not shown) in the input device 62 is pressed in the state of the setting screen 72 (constant voltage welding condition), a selection screen 73 for chopping frequency f [kHz] and duty D [%] shown in FIG. Can be switched. On this selection screen 73, the values of the chopping frequency f and the duty D are selected.

As can be seen from the setting conditions in the selection screen 73 in FIG. 6, in this embodiment, the chopping frequency f can be set to either f = 10 [kHz] or f = 20 [kHz]. As the duty D, D = 25
Either [%], D = 50 [%] or D = 75 [%] can be set.

In the selection screen 73 in the example of FIG. 6, the chopping frequency f is set to f = 10 [kHz] using the cursor key.
z] is selected, and D = 50 [%] is selected and determined as the duty D by the operator. In the selection screen 73, a cursor ">" corresponding to this determination is displayed. The screen displays shown in FIGS.
It is possible to display on the same screen (one screen).

After setting the welding conditions, the operator
A welding start switch 64 on the input device 62 is pressed. This allows the electrode holder 20 to pass through a cylinder or the like (not shown).
The workpiece W is sandwiched between the welding electrodes 24a and 24b. When the work W is sandwiched between the welding electrodes 24a and 24b, the pressure applied to the work W is appropriately maintained by a cylinder (not shown).

In this state, the control circuit 50 sets the welding condition set value / voltage V1 = 2.00 [V], welding time T
out = 4.00 [ms], chopping frequency f = 1
The welding operation is performed by constant voltage feedback control based on 0 [kHz] and duty D = 50 [%].

The waveform 10 corresponding to the set value of the welding condition
2 is shown in the upper part of FIG. A waveform 2 on the lower side of FIG. 7 is a waveform (a waveform shown in FIG. 18) of the constant voltage feedback control of the rectangular wave DC output 2 according to the related art, which is shown again for reference.

In this case, the control circuit 50 controls the MOSFET 36 on and off through the gate drive circuit 58 based on the set values of the welding conditions according to the upper waveform in FIG. As a result, the rectangular wave AC output S1 = V1 obtained by chopping the DC voltage Vw by the chopper circuit 35 is applied to the work W via the welding electrodes 24a and 24b. The voltage V1 between the welding electrodes 24a and 24b applied to the work W is detected by the voltage detector 52 and introduced into the control circuit 50.

The control circuit 50 performs constant voltage feedback control during the welding time Tout so that the detected voltage V1 and the set voltage (welding voltage) Vs become equal.

Set value of welding condition / voltage V1 = 2.00
[V], welding time Tw = 4.00 [ms], chopping frequency f = 10 [kHz], duty D = 50
[%], The pressing pressure on the workpiece W by the welding head 14 is released, and the welding electrode 24
When the workpieces a and 24b are separated from the workpiece W, the welding process on the workpiece W is completed. In this embodiment, the actual welding current I1 detected by the current detector 48 during welding of the workpiece W was about 500 [A].

By performing such a welding process, no scattering (dust) was recognized on the workpiece W after welding.

The reason for this is that in the welding using the rectangular wave DC output 2 according to the prior art shown in the lower part of FIG. 7, the welding time is short (on the order of ms) (in this example, the welding time Tout = 2).
[Ms]), when the workpiece W having an oxide film is to be welded, the following of the welding head 14 is insufficient, and the welding time ends during the following of the welding head 14, resulting in scattering or the like. It is conceivable that a defect at the welding location occurs.

On the other hand, in the welding using the rectangular-wave AC output waveform 102 according to this embodiment shown in the upper part of FIG. 7, the welding voltage V1 is intermittently applied to the work W. The sudden change in voltage and current as at time t11 disappears. Further, since the welding time Tout becomes longer according to the value of the duty D (for example, in the case of the duty D = 50 [%] in the example of FIG. 7, the output time To
ut is Tout = 4 [ms], which is twice the conventional output time Tout = 2 [ms], and it is determined that the welding head 14 can sufficiently follow and the stable welding is performed.

Although it is a more qualitative explanation, the welding in the present invention is described as follows. "If the pulse constituting the square wave AC output S1 (102) is regarded as a hammer, the work W with the oxide film is reduced by the hammer. It can be said that it is "welding that removes the oxide film by hitting."

In the resistance welding apparatus 10 of FIG. 1, the welding voltage V1 is actually +0.10 [V].
To +3.00 [V].
The welding time Tout is 0.5 [ms] to 100.
[Ms]. Also, the welding current I1 can be varied between 0.1 [kA] and 8.0 [kA]. As the welding power P,
It can be varied between 0.1 [kVA] and 64 [kVA].

For reference, voltage current waveforms under various welding conditions by the resistance welding apparatus 10 of FIG. 1 will be described below.

In the voltage and current waveforms described below, the welding electrodes 24a and 24b are short-circuited. In the case of the voltage waveform, it is measured by a waveform measuring device between the output terminals 21 and 22, and in the case of the current waveform, A 1 [mΩ] resistor is inserted between the power supply line 16b and the output terminal 22, and a voltage waveform generated at both ends of the resistor is measured by a waveform measuring instrument.

First, the waveform in FIG. 8 is a voltage V1 = + 2 [V] and a chopping frequency f = 5 [kHz] by constant voltage control.
z] and duty D = 50 [%]. The upper side shows the waveform of the voltage V1, and the lower side shows the waveform of the current I1. Voltage V
It is understood from the waveform 1 that the voltage V1 is accurately feedback-controlled.

The waveform of FIG. 9 is a constant voltage control, and the voltage V1 =
+2 [V], chopping frequency f = 10 [kHz],
The duty D is 50 [%]. Upper side is voltage V
1 is the waveform of the current I1 on the lower side.

The waveform of FIG. 10 is a constant voltage control, and the voltage V1
= + 2 [V], chopping frequency f = 15 [kHz]
z] and duty D = 50 [%]. The upper side shows the waveform of the voltage V1, and the lower side shows the waveform of the current I1.

The waveform in FIG. 11 is a constant voltage control, and the voltage V1
= 2 [V], chopping frequency f = 20 [kHz],
The duty D is 50 [%]. Upper side is voltage V
1 is the waveform of the current I1 on the lower side.

The waveform of FIG. 12 shows the constant current control and the current I1
= 500 [A], chopping frequency f = 3 [kHz]
z] and duty D = 50 [%]. It is understood that the waveform of the lower current I1 is accurately feedback-controlled.

The waveform of FIG. 13 is a constant power control, and the power P =
2 [kVA], chopping frequency f = 10 [kHz]
z] and duty D = 50 [%]. Feedback control is performed so that a waveform obtained by multiplying the waveform of the upper voltage V1 and the waveform of the lower current I1 has a constant value (constant power).

The waveform of FIG. 14 is a constant power slope control.
Power P = 2 [kV], chopping frequency f = 10 [k]
Hz] and a duty D = 50 [%]. It is understood that the slope is applied from the time of rising.

Next, a waveform according to the prior art as a comparative example will be described.

The waveform shown in FIG. 15 is obtained by constant voltage control and the voltage V is V = 2 [V].

The waveform shown in FIG. 16 is a constant current control, and the current I is I = 650 [A].

The waveform in FIG. 17 is for constant power control, and the power P is P = 2 [kVA].

It should be noted that the present invention is not limited to the above-described embodiment, but can adopt various configurations without departing from the gist of the present invention.

[0065]

As described above, according to the present invention, a rectangular wave AC output is applied to a work through a welding electrode to weld the work.

As a result, it is possible to obtain a work with almost no occurrence of scattering after welding.

[Brief description of the drawings]

FIG. 1 is a circuit block diagram showing a configuration of a resistance welding apparatus to which an embodiment of the present invention has been applied.

FIG. 2 is a waveform chart for explaining a positive square wave AC output.

FIG. 3 is a waveform chart for explaining a negative square wave AC output.

FIG. 4 is a waveform chart for explaining a duty in a rectangular wave AC output.

FIG. 5 is an explanatory diagram of a screen used for setting welding conditions.

FIG. 6 is an explanatory diagram of a screen provided for setting welding conditions.

FIG. 7 is a waveform diagram for explaining a welding waveform according to the present embodiment in comparison with a welding waveform according to the related art.

FIG. 8 is a waveform diagram showing an example of constant voltage welding.

FIG. 9 is a waveform diagram showing another example of constant voltage welding.

FIG. 10 is a waveform diagram showing still another example of constant voltage welding.

FIG. 11 is a waveform diagram showing still another example of constant voltage welding.

FIG. 12 is a waveform chart showing an example of constant current welding.

FIG. 13 is a waveform chart showing an example of constant power welding.

FIG. 14 is a waveform diagram showing an example of constant power slope welding.

FIG. 15 is a waveform diagram showing an example of constant voltage welding as a comparative example.

FIG. 16 is a waveform diagram showing an example of constant current welding as a comparative example.

FIG. 17 is a waveform diagram showing an example of constant power welding as a comparative example.

FIG. 18 is a waveform diagram showing an example of constant voltage welding according to the related art.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Resistance welding apparatus 12 ... Welding power supply 14 ... Welding head 16 (16a,
16b) Power supply line 20 (20a, 20b) Electrode holder 21, 22 Output terminal 24 (24a, 24b) Welding electrode 32 Power supply circuit 33 Power switch 34 Electrolytic capacitor 35 Chopper circuit 36 MOSF
ET 48 current detector 50 control circuit 52 voltage detector 54 gate drive circuit 56 display device 62 input device 64 welding start switch 70, 72 setting screen 73 selection screen S1 rectangular wave AC output W …work

Claims (3)

[Claims] 1. A chopper circuit for chopping a DC input to produce a rectangular wave AC output, and a rectangular wave AC output of the chopper circuit is supplied to an input side.
A resistance welding apparatus, comprising: a welding electrode on the output side with which the workpiece is in contact, and applying the rectangular wave AC output to the workpiece via the welding electrode to weld the workpiece. 2. The resistance welding apparatus according to claim 1, further comprising a control circuit having an input side connected to said welding electrode side and an output side connected to said chopper circuit. A feedback welding control of at least one of a current flowing through the work through the workpiece, a voltage applied to the work, and an electric power supplied to the work. 3. The resistance welding apparatus according to claim 2, wherein a display device and an input device are connected to the control circuit, and the type of the feedback element is selectable on the display device by the input device. The resistance welding apparatus is displayed so that the value of the feedback element and the chopping frequency, duty, and output time can be set by the input device.