JPH03297560A - Method for starting ac arc - Google Patents

Abstract

PURPOSE:To smoothly start the arc and to improve stability of the arc by setting impressed output higher than stationary output at the time of starting the arc and till a specified time elapses after the arc is started and then, changing over the polarity. CONSTITUTION:In AC gas shielded arc welding, the output impressed on between consumption electric power and base metals is set higher than the stationary output before the AC gas arc is started and for a period of time till a specified time elapses after the arc is started. After a specified time elapses after the arc is started, the polarity is changed over. The polarity is fixed on one polarity and changeover is executed to the ordinary AC output so as to suit a welding purpose. Consequently, smooth arc starting can be carried out and stability of the arc and welding workability are improved.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to an AC arc starting method that is effective for improving arc starting characteristics in AC gas-shielded arc welding using a consumable electrode.

[Conventional technology]

For example, in non-consumable electrode type AC gas shielded arc welding, as described in Japanese Utility Model Application Publication No. 1-100672, the polarity EP (electrode polarity is positive) or polarity EN (electrode polarity is positive) until the arc is started. A method is adopted in which the polarity of the arc is kept negative (negative polarity) and then switched to alternating current immediately after the arc starts.

Further, in a commercially available consumable electrode type DC gas shielded arc welding machine, as shown in FIG. 6, a method is adopted in which the output until the arc starts is set to a larger output value than the steady output during welding.

[Problem to be solved by the invention]

In the above-mentioned non-consumable electrode AC welding, the arc is started using high-frequency alternating current, so a method of starting the arc by bringing the consumable electrode into contact with the base material is not considered.

In addition, in consumable electrode DC welding, consideration has been given to starting the arc by bringing the consumable electrode into contact with the base metal.
This method is for polar EP DC welding,
No consideration is given to switching polarity.

By the way, if the polarity of the wire is switched to EN immediately after starting the arc, the penetration of the EN polarity is smaller than that of the EP polarity, so there is a risk that welding defects such as poor fusion or overlap may occur at the arc starting part. Also, if you change the polarity immediately after starting the arc, the output will go to O once and then switch to the next polarity.

The arc that has been generated will be extinguished and the arc will be generated again, which may make the unstable arc form immediately after the arc starts even more unstable.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for starting an alternating current arc that starts an arc smoothly and stabilizes the starting arc.

[Means to solve the problem]

In order to achieve the above object, the AC arc starting method of the present invention is an AC arc starting method for AC gas shielded arc welding performed by applying an AC output between a consumable electrode and a base metal. It is characterized in that the applied output until a predetermined time has elapsed after starting the arc is set to be larger than the steady output, and the polarity is switched after the predetermined time has elapsed after starting the arc. The polarity may be fixed to either EP or EN to suit the purpose of welding work, and the output may be switched to normal AC output after a predetermined arc starting time has elapsed.

[Effect]

Arc starting can be performed by setting the wire, which is a consumable electrode, as polarized EP and increasing the output setting from that during welding.

The polarity is not switched until the arc form is stabilized after the arc is started, and the polarity is switched after the stabilized arc continues.

〔Example〕

3 - Figure 1 shows an example of arc starting when a mild steel φ], 2 wire is used as the consumable electrode, and the voltage applied between the wire and the base metal is set to Voltage Vp during wire polarity EP in subsequent steady state
, the voltage V when the wire polarity is EN in the steady state
Vo = 40 V, where To is the time to maintain the initial setting voltage Vo after starting the arc, and TP and TN are the periods of wire polarity EP and EN, respectively.
.

Vp=30V, VN=20V, To=1-00. s, T
p'' was kept constant at 4 ms, and arc starting was performed by increasing and decreasing the period TN in approximately inverse proportion to the wire feeding speed.

As a result, good arc starting and stable AC arc were obtained at any wire feeding speed.

Figure 2 shows a φ1. An example of Omm MIG blaze wire, the set current Io at arc startup
, the current IP during the wire polarity EP in the steady state after starting the arc, and the wire polarity EN in the steady state as well.
It is indicated by the current IN when the arc starts, and the set current Io after starting the arc.
Io=300A, where the holding time TO and the period of wire polarity EP and EN are indicated by TP and TN, respectively.
, Ip=300A, IN=50A, TP=25. S, T
o = 50-s constant, polarity E depending on wire feeding speed
The period TN of N was increased or decreased. In MIG blaze welding, it is necessary to hardly melt the base metal, so the polarity is set to EN when starting the arc, which requires a large output, to suppress melting of the base metal as much as possible when starting the arc.

Figure 3 shows a method that is suitable for small diameter wires, aluminum wires, etc., which are prone to burning wires, and is used to change the output settings from the start of the arc until the time To elapses to the initial setting V.
o or less and by making it more than the setting Vp during welding,
The time To can be made longer than in the case of FIG. 1,
The arc starting characteristics are further improved.

Note that although Figures 1 and 3 explain the arc starting method in the case of a constant voltage characteristic power source, and Figure 2 explains the arc starting method in the case of a constant current characteristic power source, both arc starting methods are limited by the power supply characteristics. Needless to say, good results can be obtained no matter which characteristic is used.

An AC gas shielded arc welding machine that implements the AC arc starting method of the present invention will be described below.

FIG. 4 is a block diagram of an AC gas shielded arc welding machine to which the arc starting method shown in FIG. 1 is applied. In FIG. 4, an inverter circuit 2 converts the output of a DC power source 1 into AC, and a welding wire 3 is supplied with power from the inverter 2 and sent out by a feeding device 4 to weld a base material 5.

A voltage setting device 13° for setting the output of the DC power supply 1]. 4 respectively set the voltage value Vp when the polarity of the welding wire is EP and the voltage value VN when the welding wire is polarized EN, and the time setters 15 and 16 respectively set the period TP of Vp and the period T of VN.
Set N. The polarity setting device 12 is connected to the time setting device 15,1.
The TP and TN signals of 6 are transmitted to the inverter drive circuit 6 of the inverter circuit 2 and the output changeover switch 11 that switches the current setters 13 and 14. Output selector switch 1
1 switches the voltage setters 13 and 14 so that the voltage during period Tp becomes Vp and the voltage during period TN becomes VN.

Welding current setting device 1o issues a control command to wire drive circuit 9 that drives feeding device 4.

The voltage error amplifier 18 controls the time setting device 16 of the TN so that the output of the arc voltage detector 17 provided in the inverter circuit 2 matches the value set by the arc voltage setting device 19.

Now, when the arc starting operation is performed, the AC/DC switching signal generator 7 outputs a signal to the inverter circuit 2 to set the polarity EP of the welding wire 3, and at the same time, the setting value V of the output setting device 21 at the time of starting is set. is the welding wire 3 from the start signal changeover switch 24 via the DC power supply 1 and the inverter circuit 2.
and the base material 5. When an arc is ignited between the welding wire 3 and the base metal 5, the welding current detector 25 connected to the output side of the inverter circuit 2 detects the current, and the detection signal activates the current detection timer 26. The current detection timer 26 has a set time T of a timer time setter 27 connected thereto. Afterwards, an operating signal 7-- is issued to operate the AC/DC switching signal generator 7.

The AC/DC switching signal generator 7 outputs an AC operation signal to drive the drive circuit 6, and at the same time outputs an AC operation signal to drive the drive circuit 6.
4 to connect the output changeover switch 11 and the DC power supply 1. A normal welding current is thus supplied.

Further, in the AC gas shielded arc welding machine to which the AC arc starting method shown in FIG. 2 is applied, in the block diagram of FIG. 4, the initial setting voltage V is set in the starting output setting device 21. Set current engineer instead. By setting current setting devices in place of the voltage setting devices 13 and 14, the current I at the time of polarity EP is set.
p, it is only necessary to set the current IN when the polarity is EN, and the other components of the device are the same as those shown in FIG.
The explanation will be omitted.

FIG. 5 is a block diagram of an AC gas shielded arc welding machine to which the AC arc starting method shown in FIG. 3 is applied.

This device will be explained by comparing it with the one shown in FIG. 4.The initial setting voltage V of the starting output setting device 21 in FIG. Instead, an immediately after startup output setting device 22 is provided which sets the voltage V1 (V. or less, Vp or more), and a startup output setting device 21 is separately provided, and the voltage V is set in this startup output setting device 21. , and then set the voltage ■. A set value changeover switch 23 for switching the output of voltage (1) and voltage (1) is provided, and this is connected to a welding current detector 25.

〔Effect of the invention〕

According to the present invention, the AC arc starting method is such that the output applied between the consumable electrode and the base metal is greater than the steady output during welding at the time of arc starting and until a predetermined time elapses, and after the predetermined time elapses. Since the polarity is switched, even in consumable electrode type AC gas shielded arc welding, the arc can be started smoothly, the stability of the arc is improved, and welding work efficiency is improved.

Furthermore, when it is desired to suppress the penetration of the base material, such as MIG blaze, by selecting the polarity at the time of arc startup, good results can be obtained by selecting the polarity EP at the time of arc startup.

[Brief explanation of drawings]

Figures 1, 2 and 3 are diagrams showing respective embodiments of the AC arc starting method according to the present invention, and Figures 4 and 5 are diagrams showing the AC arc shown in Figures 1-3, respectively. A block diagram of an AC gas shielded arc welding machine to which the starting method is applied, and FIG. 6 is an explanatory diagram of the starting method of an AC arc according to the prior art. 1-: DC power supply, 2: Inverter circuit, 3: Welding wire, 4 : Feeding device, 5: Base material, 6: Inverter drive circuit, 7: AC/DC switching signal generator, 9: Wire perturbation circuit, 1-O: Welding current setting device, 1]: Output selection switch, 13 , 14: Voltage setting device, 1.5, 16: Time setting device, 17: Arc voltage detector, 18: Voltage error amplifier, 19: Arc voltage setting device, 21: Output setting device at startup, 22: Output immediately after startup Setting device, 23: Setting value changeover switch, 24: Starting signal changeover switch, 25: Welding current detector, 26: Current detection timer, 27: Timer time setting device.

Claims (1)

[Claims] 1. In a method for starting an AC arc in AC gas shielded arc welding performed by applying an AC output between a consumable electrode and a base metal, a predetermined period of time elapses before and after the arc starts. A method for starting an AC arc, characterized in that the applied output is set to be larger than the steady output during the period, and the polarity is switched after a predetermined time has elapsed after starting the arc. 2. The polarity until a predetermined time elapses after the arc starts is as follows:
2. The method for starting an AC arc according to claim 1, wherein the electrode is positive. 3. The polarity until a predetermined time elapses after the arc starts is as follows:
2. The method for starting an AC arc according to claim 1, wherein the electrode is negative.