JP6728022B2 - Arc start control method for plasma arc welding - Google Patents

Description

TECHNICAL FIELD The present invention relates to an arc start control method for plasma arc welding in which a plasma gas is caused to flow, a pilot arc is generated, and a main arc is generated when a start signal is output.

Plasma arc welding can perform high-speed welding of thin plates or penetration welding of thick plates by using a plasma arc having a high energy density. In plasma arc welding, a pilot arc is generated and the main arc is induced by this pilot arc to start welding. It is important for the main arc to be smoothly generated from the pilot arc at the start of welding in order to improve the welding quality and improve the efficiency of the welding operation.

The flow rate of plasma gas is important for smoothly inducing the main arc from the pilot arc. In the invention of Patent Document 1, the flow rate of the plasma gas at the start of welding is set to be higher than that during welding to extend the arc length of the pilot arc and smoothly generate the main arc.

JP 61-82975

If the flow rate of the plasma gas at the start of welding is made higher than that during welding as in the conventional technique, the generation of the main arc becomes smooth. In particular, when the distance between the welding torch tip and the base metal (hereinafter referred to as the standoff) becomes long, the main arc is less likely to occur. When the conventional technique is applied in such a state, the main arc can be smoothly generated.

However, when the flow rate of the plasma gas at the start of welding is increased, the arc pressure due to the pilot arc increases. For this reason, in thin plate welding, there is a problem that burn-through occurs due to the arc pressure of the pilot arc. Further, also in thick plate welding, there is a problem that the base metal surface is melted by the arc pressure of the pilot arc and the bead appearance at the start of welding is deteriorated.

Therefore, the present invention provides an arc start control method for plasma arc welding that can smoothly generate a main arc even when the standoff is long and that can improve the welding quality at the start of welding. The purpose is to

In order to solve the above-mentioned problems, the invention of claim 1 provides
In the arc start control method of plasma arc welding, in which a plasma gas is flown, a pilot arc is generated, and a main arc is generated when a start signal is output,
A first step of setting the flow rate of the plasma gas to a predetermined initial value from the time when the start signal is output until a predetermined initial period elapses;
A second step of gradually increasing the flow rate of the plasma gas when the main arc does not occur during the initial period;
A third step of changing the flow rate of the plasma gas to a predetermined steady value when the main arc occurs,
An arc start control method for plasma arc welding, which is characterized in that

The invention of claim 2 provides a predetermined upper limit value for the increase of the plasma gas in the second step,
The arc start control method for plasma arc welding according to claim 1, wherein.

According to a third aspect of the present invention, when the main arc does not occur even after a predetermined reference time has elapsed from the time when the activation signal was output, an arc start abnormality is notified.
The arc start control method for plasma arc welding according to claim 1 or 2, characterized in that.

According to the present invention, even if the standoff is long, the main arc can be generated smoothly, and the welding quality at the start of welding can be improved.

FIG. 3 is a block diagram of a welding device for carrying out the arc start control method of plasma arc welding according to the first embodiment of the present invention. It is a timing chart of each signal in the welding device described above in FIG.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[Embodiment 1]
FIG. 1 is a block diagram of a welding apparatus for carrying out an arc start control method for plasma arc welding according to a first embodiment of the present invention. Each block will be described below with reference to FIG.

The welding torch mainly comprises an electrode 1, a plasma gas nozzle 4 surrounding it and a shield gas nozzle 5 surrounding it. A tungsten electrode or the like is used for the electrode 1.

The pilot arc start circuit OP outputs a pilot arc start signal Op that becomes High level when the pilot arc 3p is generated. The pilot arc starting circuit OP is, for example, a switch provided on the front panel of the welding device. When this switch is turned on, the pilot arc start signal Op becomes High level and is output.

The starting circuit OM outputs a starting signal Om that becomes High level when the main arc 3m is generated. The starting circuit OM is a torch switch provided on the welding torch. Further, the activation circuit OM may be provided in the robot controller.

The plasma gas flow rate setting circuit FR receives the starting signal Om and the main arc current energization determination signal Cm described below as inputs, and outputs a plasma gas flow rate setting signal Fr for setting a plasma gas flow rate Fp described later in FIG. ..

The open/close state of the plasma gas solenoid valve GP is controlled by the pilot arc start signal Op. When the pilot arc start signal Op becomes High level, the plasma gas solenoid valve GP is opened and the plasma gas 7 from the plasma gas cylinder 6 flows.

The plasma gas flow rate regulator FP adjusts the flow rate of the plasma gas 7 to a value determined by the plasma gas flow rate setting signal Fr.

The shield gas flow rate adjuster FS adjusts the flow rate of the shield gas 9 from the shield gas cylinder 8. The flow rate is adjusted by manually operating the rotary knob of the main body of the shield gas flow rate regulator FS. The flow rate of the shield gas 9 is adjusted to, for example, 10 liters/minute.

The open/close state of the shield gas solenoid valve GS is controlled by the above-mentioned start signal Om. When the activation signal Om becomes High level, the shield gas solenoid valve Gs is opened and the shield gas 9 flows.

A plasma gas 7 flows through the plasma gas nozzle 4. Further, the shield gas 9 flows in the shield gas nozzle 5. Argon is often used for the plasma gas 7 and the shield gas 9. The pilot arc 3p is generated between the electrode 1 and the plasma gas nozzle 4, and the main arc 3m is generated between the electrode 1 and the base material 2. The main arc 3m is generated by being triggered by the pilot arc 3p. The pilot arc 3p is generated with the electrode 1 serving as a negative electrode and the plasma gas nozzle 4 serving as a positive electrode. The main arc 3m is generated with the electrode 1 serving as a negative electrode and the base material 2 serving as a positive electrode.

The pilot arc power source PPS is a power source having a constant current characteristic or a drooping characteristic, and the pilot arc 3P is generated by this power source. The pilot arc switch SP turns on/off the pilot arc power supply PPS according to the pilot arc start signal Op. A relay, a semiconductor switching element, or the like is used as the pilot arc switch SP.

The main arc current setting circuit IR outputs a predetermined main arc current setting signal Ir. The main arc power supply MPS receives the main arc current setting signal Ir and has a constant current characteristic or a drooping characteristic. The main arc current Im determined by the main arc current setting signal Ir is supplied to the main arc power source MPS 3M. Generate. The main arc switch SM turns on/off the main arc power source MPS according to the start signal Om. A relay, a semiconductor switching element, or the like is used as the main arc switch SM.

The main arc current conduction determination circuit CM outputs a main arc current determination signal Cm that becomes High level when the main arc current Im is conducted.

The notification circuit AR receives the above-mentioned starting signal Om and the above-mentioned main arc current energization determination signal Cm as input, and even if a predetermined reference time has elapsed from the time when the starting signal Om changed to High level (starting), the main arc When the current energization determination signal Cm does not change to the high level (energization), an arc start abnormality is notified. The notification means is a sound, an abnormal lamp is lit, an alarm signal is output to the outside, or the like. Further, in conjunction with this notification, the activation signal Om may be forcibly set to the low level to stop the output from the welding device.

FIG. 2 is a timing chart of each signal in the welding device described above with reference to FIG. The same figure (A) shows the time variation of the pilot arc start signal Op, the same figure (B) shows the time variation of the starting signal Om, the same figure (C) shows the time variation of the plasma gas flow rate Fp [liter/minute]. FIG. 6D shows the time change of the shield gas flow rate Fs [liter/min], and FIG. 7E shows the time change of the main arc current energization determination signal Cm. Hereinafter, description will be given with reference to FIG.

When starting the welding operation, the welding operator connects the commercial AC power supply to the welding device and turns on the switch of the pilot arc starting circuit OP. In response to this, the pilot arc start signal Op changes to High level and is output, so that the pilot arc switch SP is closed and a voltage is applied between the electrode 1 and the plasma gas nozzle 4. At the same time, the plasma gas solenoid valve GP is opened and the plasma gas 7 flows. The plasma gas flow rate Fp at this time becomes a predetermined initial value determined by the plasma gas flow rate setting signal Fr, and the flow rate is adjusted by the plasma gas flow rate regulator FP. As a result, a pilot arc 3p is generated between the electrode 1 and the plasma gas nozzle 4. The initial value is about 0.2 to 0.5 liter/minute. The current value of the pilot arc 3p is about 5 to 15A. During the period in which a plurality of works (base material 2) are welded, the state in which the pilot arc 3p is generated is maintained. That is, the preparation for welding is performed until the pilot arc 3p is generated.

From time t1, the process is started to start welding. From this time t1 onward, as described above, the pilot arc start signal Op is at the high level as shown in (A) of the figure, and the plasma gas flow rate Fp is the initial level as shown in (C) of the figure. It is a value.

(First step)
At time t1, when the welding operator turns on the switch of the starting circuit OM, the starting signal Om changes to the high level as shown in FIG. In response to this, the main arc switch SM is closed and a no-load voltage is applied between the electrode 1 and the base material 2. At the same time, the shield gas solenoid valve GS is opened and the shield gas 9 flows. As shown in FIG. 6D, the shield gas flow rate Fs has a value adjusted by the shield gas flow rate adjuster FS. The shield gas flow rate Fs is a constant value during welding and is about 10 liters/minute. Since the main arc 3m is not generated during the predetermined initial period from time t1 to time t2, the plasma gas flow rate Fp remains at the initial value as shown in FIG. The initial period is set to about 0.5 to 1.0 seconds.

(Second step)
From time t2, the plasma gas flow rate Fp increases at a predetermined increase rate. This increase will continue until the main arc 3 m is generated. The rate of increase is set to about 0.2 to 1.0 liter/minute per second. As the plasma gas flow rate Fp increases, the arc length of the pilot arc 3p becomes longer, and the generation of the main arc 3m is more strongly induced.

(Third step)
At time t3, when the main arc 3m is generated, the main arc current Im is energized, so that the main arc current energization determination signal Cm changes to High level as shown in FIG. In response to this, the plasma gas flow rate Fp changes to a predetermined steady value, as shown in FIG. This steady value is set to about 0.2 to 3.5 liters/minute depending on the plate thickness. The main arc current Im is set to about 50 to 250A.

At time t4, when the welding of the first work is completed, the welding operator turns off the switch of the starting circuit OM, so that the starting signal Om changes to the low level as shown in FIG. In response to this, the main arc switch SM is opened and the main arc current Im is stopped from being energized, so that the main arc current energization determination signal Cm becomes Low level as shown in FIG. At the same time, since the shield gas electromagnetic valve GM is closed, the shield gas flow rate Fs becomes 0 as shown in FIG. However, as shown in FIG. 7A, the switch of the pilot arc starting circuit OP remains on, so the pilot arc switch SP remains closed and the pilot arc 3p maintains the generated state. Further, since the plasma gas solenoid valve GP remains in the open state, the plasma gas 7 maintains the flow. However, as shown in FIG. 7C, the plasma gas flow rate fp changes from a steady value to an initial value. In the figure, the steady value is equal to the initial value, but it may be set to a different value. When the welding of the next work is started, the operation from time t1 is repeated again.

When the main arc 3m occurs during the initial period from time t1 to time t2, the operation immediately proceeds to time t3, and the plasma gas flow rate Fp changes to a steady value.

The effects of this embodiment will be described below. From the time when the activation signal Om changes to the High level at time t1, the plasma gas flow rate Fp is set to a small value during the initial period and the generation of the main arc 3m is waited for. If the main arc 3 m is generated during this initial period, the plasma gas flow rate Fp has a small value, so that the welding quality at the start of welding is good. When the standoff is within a proper distance (about 2 to 5 mm), the main arc 3 m is generated almost during this period. When the standoff is longer than the appropriate distance (about 5 to 9 mm), the main arc 3 m often does not occur during the initial period. In such a case, the operation is performed after the time t2, and the plasma gas flow rate Fp continuously increases at a predetermined increase rate. When the main arc 3m is generated, the plasma gas flow rate Fp is changed to a steady value. In this case, the plasma gas flow rate Fp is increased by a minimum amount necessary to generate the main arc 3m, so that the welding quality at the start of welding is not deteriorated. In addition, the main arc 3 m can be reliably generated.

In the figure, when the main arc 3m does not occur even when the time elapsed from the time t1 when the activation signal Om becomes High level reaches a predetermined reference time, the alarm circuit AR issues an alarm. At the same time, the activation signal Om is forcibly changed to the Low level, the main arc switch SM is opened, and the output is stopped. The reference time is set to about 1.5 to 3 seconds.

In the figure, a predetermined upper limit value may be set for the plasma gas flow rate Fp from time t2. This can prevent the plasma gas flow rate Fp from becoming excessive.

1 Electrode 2 Base Material 3M Main Arc 3P Pilot Arc 4 Plasma Gas Nozzle 5 Shield Gas Nozzle 6 Plasma Gas Cylinder 7 Plasma Gas 8 Shield Gas Cylinder 9 Shield Gas AR Notification Circuit CM Main Arc Current Energization Discrimination Circuit Cm Main Arc Current Energization Discrimination Signal FP Plasma Gas Flow Rate Regulator Fp Plasma gas flow rate FR Plasma gas flow rate setting circuit Fr Plasma gas flow rate setting signal FS Shield gas flow rate regulator Fs Shield gas flow rate GP Plasma gas solenoid valve GS Shield gas solenoid valve Im Main arc current IR Main arc current setting circuit Ir main Arc current setting signal MPS Main arc power supply OM Start circuit Om Start signal OP Pilot arc start circuit Op Pilot arc start signal PPS Pilot arc power SM Main arc switch SP Pilot arc switch

Claims (3)

In the arc start control method of plasma arc welding, in which a plasma gas is flown, a pilot arc is generated, and a main arc is generated when a start signal is output,
A first step of setting the flow rate of the plasma gas to a predetermined initial value from the time when the start signal is output until a predetermined initial period elapses;
A second step of gradually increasing the flow rate of the plasma gas when the main arc does not occur during the initial period;
A third step of changing the flow rate of the plasma gas to a predetermined steady value when the main arc occurs,
An arc start control method for plasma arc welding, comprising: A predetermined upper limit value is set for the increase of the plasma gas in the second step,
The arc start control method for plasma arc welding according to claim 1, characterized in that. When the main arc does not occur even if a predetermined reference time has elapsed from the time when the start signal was output, an arc start abnormality is notified.
The arc start control method for plasma arc welding according to claim 1 or 2, characterized in that.

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