JP2512428B2 - DC arc welding machine - Google Patents

Description

TECHNICAL FIELD The present invention relates to an improvement in a DC arc welder.

[Background technology]

A direct current arc welding machine, which performs constant voltage control during arcing and outputs a welding current according to a preformed reference waveform during a short circuit, has already been disclosed, for example, in JP-A-57-124570. Various types have been developed.

However, the conventional ones have not yet been sufficiently taken into consideration for reducing the amount of spatter generated at a large current and increasing the number of short circuits at a small current, and there is room for improvement.

Generally, since the amount of spatter generated is small at a small current, there is no problem even if the number of short circuits is increased, but conversely, the amount of sputter generated extremely increases at a large current. by the way,
In order to increase the welding work efficiency, it is extremely desirable to increase the number of short circuits at a small current and to suppress the generation of spatter at a large current.

[Object of the Invention] An object of the present invention is to provide a DC arc welding machine that can meet the above-mentioned demands.

[Disclosure of Invention]

The present invention proposed to achieve the above object comprises an arc / short circuit judging means, a constant voltage control section, and a current control section. During arcing, the constant voltage control section is operated to perform constant voltage control. A DC arc welder that controls a welding current based on a pre-formed reference waveform by operating a current control unit when a short circuit occurs, wherein the current control unit sets a welding current setting device. Depending on the value, the di / dt change point setting circuit that changes the change point level of the reference waveform and the change point level set by this di / dt change point setting circuit
A first rising portion and a second rising portion (the second rising portion is set to have a gentler slope than the first rising portion) starting from the zero level are formed, and when the arc occurs, the zero rising level is reached. A current control reference waveform generation circuit for generating a reference waveform to be lowered, a feedback signal according to the welding current detected from the welding circuit, and a current control for inputting the reference waveform generated by the current control reference waveform generation circuit as a reference signal. It is configured to control the waveform of the welding current by inputting it to the error amplifier.
The change point setting circuit is characterized in that the change point level is also changed as the welding current set by the welding current setter increases. More specifically, such a reference waveform is achieved by utilizing the charge / discharge output of the capacitor or the output of the linear circuit.

[Embodiment] An embodiment of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 shows a system diagram of the DC arc welding machine of the present invention.

In the figure, A indicates an arc / short circuit determination means, B indicates a constant voltage control unit, and C indicates a current control unit. Output control of the DC arc welding machine is performed by PWM control using the inverter circuit 1, and the output of the inverter circuit 1 is supplied to the welding circuit D via a transformer and a rectifier circuit. A DC reactor 14 and a shunt 15 are provided in the welding circuit D so that the input voltage of the DC reactor 14 during an arc and the shunt 15 during a short circuit.
The output current of each becomes a feedback signal.

The constant voltage control unit B includes a voltage fine adjustment setting device 12 and a voltage control error amplifier 5, a reference voltage of the voltage control error amplifier 5 is set by a welding current setting device 13, and the voltage fine adjustment setting device 12 is This allows fine adjustment of the set reference voltage. In the illustrated example, the unitary control in which the reference voltage can be simultaneously set by the current setting is performed, but the reference voltage of the voltage control error amplifier 5 may be set only by the welding voltage setter (not shown). good.

The current control section C comprises a current control error amplifier 6, a current control reference waveform generating circuit 10, a dI / dt change point setting circuit 9 and an amplifier 7. The welding current setting device 13 is a wire feed device for the motor speed control circuit 11. The feed rate is specified and the change point of the dI / dt change point setting circuit 9 is set. The change point level increases as the welding current set by the welding current setting device 13 increases. It is configured to change.

The arc / short circuit detection circuit 8 constituting the arc / short circuit determination means A takes out the welding voltage, and the voltage value (when short circuit) occurs when the welding wire 16 short-circuits with the welding base metal 17 and the welding wire 16 welds. Voltage value when separated from the base material 17 (voltage output)
It is judged whether it is a short circuit or an arc by the difference with.

The inverter circuit 1 drives the drive circuit 2 by the control output from the PWM control circuit 3, and the PWM control circuit 3
Selectively inputs the output signal from the voltage control error amplifier 5 or the current control error amplifier 6 by the switching operation of the voltage / current control switch 4. The voltage / current control switch 4 performs a switching operation in response to a determination signal from the arc / short circuit detection circuit 8. When a short circuit occurs, current control as described below is performed and during arcing, a constant voltage control is performed. In addition,
In the constant voltage control shown in the embodiment, the input voltage of the DC reactor 14 is controlled to a constant level, but it goes without saying that the present invention is not limited to such an example.

FIG. 2 shows the main configuration of the current control circuit section C.

The displacement point defining signal set by the welding current setting device 13 is input to the non-inverting input terminal of the comparator COMP via the amplifier AMP1. The inverting input terminal of the comparator COMP is
The charge / discharge output of the CR circuit CR is input via the amplifier AMP2. The CR circuit CR has a configuration in which a parallel circuit composed of a capacitor C and a zener diode ZD is connected to two resistors R1 and R2, and one of the two resistors R2 can be connected / disconnected by a contact SW1. Has been done. In addition, the capacitor C has a contact point
SW2 and a resistor R3 are provided, and this contact SW2 is closed when an arc is generated to discharge the electric charge stored in the capacitor C.

In such a configuration, the arc / short circuit detection circuit 8
When the short circuit is detected, the contact SW2 is opened and the capacitor C
Starts charging.

However, since the terminal voltage of the capacitor C has not reached the displacement point level defined by the welding current setting device at this point, the output of the comparator COMP becomes "H" level and the contact SW1 is closed. Therefore, the time constant of the CR circuit CR becomes small, and the capacitor C is charged with a steep rising characteristic (see the part (I) in FIG. 3).

Then, when the terminal voltage of the capacitor C increases and reaches the change point level Vt defined by the welding current setting device, the output of the comparator COMP becomes "L" level and the contact SW1 is opened. The time constant of the circuit CR becomes large, and the capacitor C is charged with a gentle rising characteristic (see the part (II) in FIG. 3).

As a result, sufficient power is supplied to the welding wire, a constriction occurs at the welding wire tip, and the contact SW2 closes when the arc re-forms, so that the capacitor C is instantly discharged (Fig. 3 (III)). See section).

The curve shown by the broken line in FIG. 3 shows the reference waveform when no arc occurs, and its maximum value Vpmax
Is set by the zener voltage V _ZD of the zener diode ZD provided in the CR circuit CR and the gain of AMP2.

FIGS. 2a and 2b show another example of the reference waveform generating circuit 10, both of which are configured so that the value of the resistance R1 of the CR circuit CR can be changed to arbitrarily set the inclination of the reference waveform from the outside. It is a thing.

FIG. 3 shows a reference waveform diagram generated by the current control reference waveform generating circuit 10 and a welding current waveform diagram corresponding to FIG. In these figures, Ip large and Ip small indicate the peak values when the welding current is large and small, and It large and It small indicate the displacement point of the welding current, and (I) is (I
I) correspond to respectively. Incidentally, in FIG.
The reference waveform is instantly lowered to the zero level when an arc occurs, but may be lowered to the zero level before the next short circuit is started. As shown in Fig. 4, when the arc is generated, the constant voltage control is performed, so that the DC reactor 14
The current waveform has a dull curve characteristic due to the induction component L of. The degree of current drop at the start of a short circuit is also dependent on the DC reactor
It is defined by 14 induction components.

According to the experiments by the present inventors, when such control is performed, an example thereof is dI / dt of the first rising portion.
Good results were obtained by setting (see FIG. 4 portion) to 100 to 200 A / ms and setting the dI / dt of the second rising portion (see FIG. 4 portion) to 25 to 50 A / ms. Further, it is desirable to set the change point It to about the average value of the welding current in order to shorten the short circuit time and suppress the amount of spatter generated when the arc is reformed.

In the above embodiment, the reference waveform generating circuit 10 utilizing the charging / discharging of the capacitor C is shown, but in the present invention, the reference waveform may be formed utilizing the output characteristic of the linear circuit. An example of the configuration will be shown.

Also in this embodiment, the threshold value of the comparator COMP that defines the displacement point It is set to about the average value of the welding current, and the inverting amplifier AMP connected to the feedback capacitor Cf is connected.
The output waveform Vo of the linear amplifier AMPl is changed through the connection / disconnection of the additional resistor R'provided on the inverting input side. Contact SW3 provided at both ends of the feedback capacitor Cf
Are closed during an arc and open during a short circuit. The contact SW4 is opened and closed by the output signal of the comparator COMP,
The contact SW4 is closed at the "H" level, and the contact SW4 is opened at the "L" level.

With such a configuration, since the output of the comparator COMP is at the “H” level at the start of the short circuit, the contact SW4
Is closed, and at the same time, contact SW3 is opened at the time of short circuit. As a result, the capacitor Cf is charged by the output of the AMP set via the parallel circuit composed of the two resistors R and R ', and its charging current flows into the inverting amplifier AMP. Thus, when the output of the linear amplifier AMPl reaches the displacement point level Vt, the comparator COMP becomes "L" level output,
The contact SW4 is opened, and the charging speed of the capacitor Cf becomes slow. Then, when an arc is generated between the welding wire 16 and the base material 17, the contact SW3 is closed and the output waveform of the linear amplifier AMPl instantly becomes zero.

In the description of the DC arc welding machine of the present invention, the application examples of the short-circuit transfer type arc welding are shown in the above embodiments, but it goes without saying that it can be applied to the globule transfer and spray transfer welding methods. .

〔The invention's effect〕

According to the present invention, the shape of the reference waveform actuated during a short circuit has a first rising portion that rises sharply from the 0 level at the time of a short circuit, and the value at this first rising portion reaches a predetermined reference value. By the way, since it is composed of three parts, a second rising part that increases with a gentler slope than the first rising part and a descent part that sharply drops the reference waveform at the time of occurrence of an arc, There is a unique effect.

1) When the current is small, the rising slope of the welding current in the portion corresponding to the second rising portion is large (steep), and the time for narrowing down the current at the time of short circuit is short, so that the number of short circuits can be increased and therefore high speed welding It will be possible.

2) When the current is medium to large, the rising slope of the welding current in the portion corresponding to the second rising portion is small (gradual) and the time for narrowing the current is long, so the instantaneous molten pool where the wire contacts the molten pool. More scattered spatter is significantly reduced. Further, since the rising slope dI / dt of the welding current in the portion corresponding to the rising portion becomes small, the peak value of the peak current at which the arc re-forms becomes smaller than that in the conventional waveform control, and the occurrence of spatter can be significantly reduced.

3) Because the current waveform rises smoothly when a short circuit occurs,
It is resistant to changes in the protruding length of the welding wire, and the wire does not repel at the mounting part.

4) When the wire is short-circuited, the degree of rise in the current waveform can be completely controlled, so the DC reactor can be made compact.

[Brief description of drawings]

FIG. 1 is a system diagram of a DC arc welding machine of the present invention, FIG. 2 is an example diagram showing a configuration of a reference waveform generating circuit of a current control circuit,
2a and 2b show another example of the reference waveform generating circuit, FIG. 3 shows the reference waveform diagram, FIG. 4 shows the welding current waveform diagram, and FIG. 5 shows the configuration of the reference waveform generating circuit of the current control circuit. The other example figure is shown. (Explanation of Codes) A ... Arc / Short Circuit Determining Means B ... Constant Voltage Control Section C ... Current Control Section (I) ... First Rise of Reference Waveform (II) ... Second Rise of Reference Waveform (III) ... Descent part of reference waveform

Claims (4)

(57) [Claims] 1. An arc / short circuit determination means, a constant voltage control section, and a current control section are provided, and the constant voltage control section is operated to perform constant voltage control during an arc, while the current control section is operated during a short circuit. A DC arc welding machine which is operated to control a welding current based on a preformed reference waveform, wherein the current control unit is set by a welding current setting device.
By the di / dt change point setting circuit that changes the change point level of the reference waveform and the change point level set by this di / dt change point setting circuit, the first rising portion and the second rising portion starting from the zero level are set. A current control reference waveform generation circuit that forms a rising portion (the slope of the second rising portion is set to be gentler than that of the first rising portion), and generates a reference waveform that reduces to a zero level when an arc occurs; A configuration in which a feedback signal corresponding to a welding current detected from a welding circuit and a reference waveform generated by the current control reference waveform generating circuit are input to a current control error amplifier for inputting as a reference signal to control the waveform of the welding current. The above di / dt change point setting circuit changes the change point level as the welding current set by the welding current setter increases. DC arc welder, characterized in that it is configured to. 2. The DC arc welding machine according to claim 1, wherein the current reference waveform generating circuit is configured to generate a reference waveform by utilizing a charge / discharge characteristic of a capacitor. 3. The DC arc welding machine according to claim 1, wherein the current reference waveform generating circuit is configured to generate a reference waveform by utilizing an output characteristic of a linear circuit. 4. The method according to claim 1, wherein the slopes of the first and second rising portions of the reference waveform generated by the current reference waveform generating circuit can be arbitrarily and variably set from the outside. DC arc welding machine.