Patent ID: 12220772

DETAILED DESCRIPTION

Now, embodiments of the present disclosure will be described with reference to the drawings. The following description of advantageous embodiments is a mere example in nature, and is not at all intended to limit the scope, applications, or use of the present invention.

First Embodiment

FIG.1shows an arc welding device1according to a first embodiment of the present disclosure. The arc welding device1performs short-circuit arc welding of feeding a welding wire3held by a torch2, toward a base metal5at a constant feed velocity and alternating a short-circuit state and an arc state. In the short-circuit state, the welding wire3and the base metal5are short-circuited. In the arc state, arc A (seeFIG.3(d)) occurs between the welding wire3and the base metal5. The torch2is held by an operator. The welding wire3is made of mild steel or stainless steel (SUS). The welding wire3has a wire radius set within a range from 0.8 mm to 1.4 mm and preferably to 1.2 mm. Used as the base metal5is a thin plate (i.e., a plate member) made of mild steel. The base metal5has a plate thickness set within a range from 1.6 mm to 4.5 mm, for example, 2.3 mm. Used as the shield gas to be blown to the base metal5is carbon dioxide gas. The torch2has a tip6for supplying electric power to the welding wire3.

The arc welding device1includes an alternating current (AC) power supply7, a first rectifier element9, a first switching element11, a main transformer13, a second rectifier element15, a second switching element17, a resistor19, a reactor21, a current detector23, a voltage detector25, a wire feeding unit27, a welding output control unit29, and a wire feed velocity control unit31. The first rectifier element9, the first switching element11, the main transformer13, the second rectifier element15, the second switching element17, the resistor19, and the reactor21constitute a current supply unit33that supplies welding currents between the welding wire3and the base metal5.

The first rectifier element9rectifies the outputs from the AC power supply7.

The first switching element11adjusts the outputs from the first rectifier element9to outputs suitable for welding under the control of the welding output control unit29.

The main transformer13converts the outputs from the first switching element11into outputs suitable for welding.

The second rectifier element15rectifies the outputs from the main transformer13.

The second switching element17adjusts the outputs from the second rectifier element15to outputs suitable for welding under the control of the welding output control unit29.

The resistor19is connected in parallel to the second switching element17.

The reactor21is connected in series with the second switching element17and rectifies the outputs from the second switching element17to stabilize the welding currents.

The current detector23detects the welding currents supplied between the welding wire3and the base metal5.

The voltage detector25detects the welding voltages supplied between the welding wire3and the base metal5.

The wire feeding unit27feeds the welding wire3at a feed velocity based on the outputs from the wire feed velocity control unit31.

The welding output control unit29includes a constriction phenomenon detection unit29a, a state determination unit29b, and a welding current control unit29c.

The constriction phenomenon detection unit29acompares the change amount dVa/dt of a welding voltage Va detected by the voltage detector25per unit time to a preset threshold change amount. If the change amount dVa/dt of the welding voltage Va per unit time is larger than the threshold change amount, the constriction phenomenon detection unit29aoutputs a constriction determination signal Sn indicating a detection of the constriction phenomenon of a molten metal droplet D (seeFIGS.3(a) to3(c)). If the change amount dVa/dt is smaller than or equal to the threshold change amount, the constriction phenomenon detection unit29aoutputs a constriction determination signal Sn indicating no detection of any constriction phenomenon of the molten metal droplet D. In the constriction phenomenon, the molten metal droplet D constricts. As shown inFIG.3(c), at the time of detecting the constriction phenomenon, the constriction radius (the radius of the constricting section) is da2. The constriction phenomenon is detected at a time t5(seeFIG.2) which will be described later.

The state determination unit29bcompares the welding voltage Va detected by the voltage detector25to a preset threshold voltage Vth. If the welding voltage Va is lower than or equal to the threshold voltage Vth, the state determination unit29boutputs a state signal St indicating that the state is in the short-circuit state. On the other hand, if the welding voltage Va is higher than the threshold voltage Vth, the state determination unit29boutputs a state signal St indicating that the state is in the arc state.

The welding current control unit29ccontrols a welding current Ia based on the welding current Ia detected by the current detector23, the constriction determination signal Sn output by the constriction phenomenon detection unit29a, and the state signal St output by the state determination unit29b. The set current (the average of the welding currents Ia in each constant section) ranges from to 100 A to 250 A.

As shown inFIG.2, the wire feed velocity control unit31outputs signals indicating a constant wire feed velocity Wf.

Now, the control of the welding current Ia by the welding current control unit29cwill be described in detail. InFIG.2, each period of the short-circuit state is referred to as a “short-circuit period”, and each period of the arc state as an “arc period.”

As shown inFIG.2, at a time t1, once the state determination unit29boutputs the state signal St indicating the short-circuit state, the welding current control unit29cturns off the second switching element17to reduce the welding current Ia to an initial current Is.

After that, the welding current control unit29cturns on the second switching element17and controls the first switching element11so that the welding current Ia starts increasing from the initial current Is at the time t1and increases with a first slope S1between times t2to t3. The first slope S1is set in advance in accordance with the wire feed velocity Wf, for example, to 400 A/ms. Between the times t2to t3, the molten metal droplet D at the tip of the welding wire3shifts from the non-constricting state shown inFIG.3(a)to the slightly constricting state shown inFIG.3(b). InFIG.3(a), da corresponds to the wire radius of the welding wire3when there is no constriction in the molten metal droplet D, that is, when the molten metal droplet D does not constrict. InFIG.3(b), da1indicates the constriction radius at the occurrence of constriction in the molten metal droplet D at the tip of the welding wire3. At the time t3, the change amount dVa/dt of the welding voltage Va detected by the voltage detector25per unit time does not exceed the threshold change amount. As shown inFIG.3(b), the molten metal droplet D constricts slightly.

At the time t3, in accordance with an increase in the welding current Ia to a first peak value P1set in advance, the welding current control unit29cturns off the second switching element17to reduce the welding current Ia. Here, the welding current control unit29cperforms the control of turning off the second switching element17, once the welding current Ia reaches the first peak value P1. Alternatively, the control may be performed in response to (after) the lapse of a preset time from a predetermined reference time. Here, the predetermined reference time may be, for example, a start time of the short-circuit arc welding or the time t1or t2. The first peak value P1is preset within a range from 250 A to 450 A in accordance with the wire feed velocity Wf.

Next, at a time t4, once the welding current Ia reaches a preset first bottom value B1, the welding current control unit29cturns on the second switching element17and controls the first switching element11to increase the welding current Ia with a second slope S2from the first bottom value B1. Here, the welding current control unit29cperforms the control of increasing the welding current Ia with the second slope S2from the first bottom value B1, once the welding current Ia reaches the first bottom value B1. Alternatively, the control may be performed in response to (after) the lapse of a preset time from a predetermined reference time. Here, the predetermined reference time may be a start time of the short-circuit arc welding or any of the times t1to t3. The first bottom value B1is set within a range from 200 A to 350 A, and the second slope S2from 20 A/ms to 70 A/ms.

Here, the first bottom value B1is set to 200 A or more for the following reason. At a first bottom value B1smaller than 200 A, insufficient heat is input to the fed welding wire3to reduce the melting speed of the welding wire3and cause the welding wire3to plunge into the base metal5and bend, which may increase the period from the time t4to the opening of the short-circuit too much.

The first bottom value B1is set to 350 A or less for the following reason. A first bottom value B1greater than 350 A fails to sufficiently reduce the welding current Ia at the time of opening the short-circuit and to relatively reduce the spatter.

Next, at the time t5, as shown inFIG.3(c), the molten metal droplet D at the tip of the welding wire3constricts more than at the time t3. Once the constriction phenomenon detection unit29aoutputs then a constriction determination signal Sn indicating the detection of the constriction phenomenon, the welding current control unit29cturns off the second switching element17. InFIG.3(c), da2denotes the constriction radius at the occurrence of the constriction in the molten metal droplet D at the tip of the welding wire3at the time t5. Here, the values of da, da1, and da2satisfy the relationship da>da1>da2. As a result, the welding current Ia decreases to a second bottom value B2that is smaller than the first bottom value B1. As shown inFIG.3(d), the opening of the short-circuit shifts the state to the arc state. The second bottom value B2ranges from 50 A to 150 A. The welding current Ia at the time t5, that is, at the time of detecting the constriction phenomenon reaches a second peak value P2that is smaller than the first peak value P1.

As described above, in the first embodiment, the welding current control unit29cexecutes, in the short-circuit state, the first increase in the welding current Ia with the first slope S1, the first decrease in the welding current Ia to the first bottom value B1after executing the first increase, the second increase in the welding current Ia with the second slope S2after executing the first decrease, and the second decrease in the welding current Ia to the second bottom value B2that is smaller than the first bottom value B1after executing the second increase to shift the state to the arc state.

According to the first embodiment, the first decrease in the welding current Ia is executed during the period between the shift from the arc state to the short-circuit state and the detection of a constriction phenomenon. Thus, the amount of the welding current at the time of detecting the constriction phenomenon is smaller than in the case without any first decrease. Accordingly, the welding current Ia decreases at the time of opening the short-circuit, which reduces the occurrence of spatter.

The first slope S1is larger than the second slope S2. This reduces the time from the start of the short-circuit state to the shift to the arc state, and an increase in the welding current Ia at the time of opening the short-circuit that may be caused by a too large second slope S2. In addition, with an increase in the amount of heat given to the welding wire3from the start of the short-circuit state until reaching the first peak value P1, the welding current Ia decreases at the second peak value P2, that is, at the time of opening the short-circuit.

The first slope S1with 350 A/ms or more reduces the time from the start of the short-circuit state to the shift to the arc state more than a first slope less than 350 A/ms. This also reduces the failure in shifting from the short-circuit state to the arc state.

The second peak value P2is smaller than the first peak value P1. This reduces a time required from the start of the short-circuit state to the shift to the arc state, and the amount of the welding current Ia at the time of opening the short circuit, reducing the occurrence of spatter.

The second bottom value B2is smaller than the first bottom value B1. This reduces a time required from the start of the short-circuit state to the shift to the arc state, and the amount of the welding current Ia at the time of opening the short circuit, reducing the occurrence of spatter.

Second Embodiment

FIG.4corresponds toFIG.2and shows a second embodiment of the present disclosure.

In the second embodiment, short-circuit arc welding is performed with the torch2held by a robot (not shown). In addition to the function (i.e., the forward feeding function) of feeding the welding wire3toward the base metal5at a feed velocity based on the outputs from the wire feed velocity control unit31, the wire feeding unit27has a function (i.e., a reverse feeding function) of drawing the welding wire3away from the base metal5at a drawing velocity based on the outputs from the wire feed velocity control unit31.

The wire feed velocity control unit31outputs signals indicating the positive (forward) and negative (reverse) wire feed velocities Wf. The wire feed velocity control unit31sets the wire feed velocity Wf to a predetermined positive value if the state signal St indicates the arc state, and to the predetermined negative value if the state signal St indicates the short circuit state.

In the second embodiment, as shown inFIG.4, at the time t1, once the state determination unit29boutputs the state signal St indicating the short-circuit state, the wire feed velocity Wf changes from positive to negative, and the wire feeding unit27starts drawing the welding wire3away from the base metal5at a constant velocity. During the short-circuit period, the wire feeding unit27continues drawing the welding wire3at the constant velocity.

The first peak value P1is set in advance within a range from 100 A to 200 A. In this manner, in the second embodiment, the first peak value P1is set to be smaller than that in the first embodiment. At the time t3, the constriction occurs and the molten metal droplet D slightly constricts, although the molten metal droplet D at the tip of the welding wire3constricts at a smaller degree than at the time t3(seeFIG.2) in the first embodiment.

At the time t4, in response to (after) the lapse of a preset time from a predetermined reference time, the welding current control unit29cturns on the second switching element17and controls the first switching element11to increase the welding current Ia with the second slope S2from the first bottom value B1. Here, the predetermined reference time may be a start time of the short-circuit arc welding or any of the times t1to t3. The first bottom value B1ranges from 50 A to 150 A.

At the time t5, in response to (after) the lapse of a preset time from a predetermined reference time, the welding current control unit29cturns off the second switching element17. Here, the predetermined reference time may be a start time of the short-circuit arc welding or any of the times t1to t4. Alternatively, the second switching element17may be periodically turned off. At the time t5inFIG.4, the constriction occurs in the molten metal droplet D at the tip of the welding wire3, but at a smaller degree than at the time t5(seeFIG.2) in the first embodiment. The value of the welding current Ia at the time of shifting to the arc state, that is, the second bottom value B2is smaller than the second bottom value B2in the first embodiment. In this manner, even if less heat enters the welding wire3at the welding current Ia and a welding voltage Va in the reverse feeding operation of the welding wire3, the constriction occurs in the molten metal droplet D at the tip of the welding wire3. This reduces the welding current at the time of opening the short circuit more than the case of constantly feeding the welding wire3. Accordingly, the occurrence of spatter is reduced effectively.

The other configurations and operations are the same as those in the first embodiment, and detailed description thereof will thus be omitted.

In the second embodiment, in the short-circuit state, since the welding wire3is drawn (reversely runs) away from the base metal5, the short circuit of the welding wire3is easily open, and less welding current Ia is required to open the short circuit. Accordingly, the short-circuit period and the occurrence of spatter are reduced more effectively. In the arc state, the welding wire3is fed toward the base metal5(i.e., forward), the accuracy of the bead width and of the depth of weld penetration can be ensured.

In the first embodiment described above, at the time t5, the welding current control unit29cperforms the control of reducing the welding current Ia in response to detection of the constriction phenomenon of the molten metal droplet D. Alternatively, the control may be performed in response to (after) the elapse of a preset time from a predetermined reference time. The predetermined reference time may be a start time of the short-circuit arc welding or any of the times t1to t4.

In the second embodiment described above, at the time t5, the welding current control unit29cperforms the control of reducing the welding current Ia in response to (after) the elapse of a preset time from a predetermined reference time. Alternatively, the control may be performed in response to detection of the constriction phenomenon of the molten metal droplet D, like in the first embodiment.

In the second embodiment, the direction (i.e., positive or negative) of the wire feed velocity Wf changes in accordance with the state signal St. Alternatively, the short-circuit period and the arc period may be specified in advance by an experiment or other type of study, and the direction (i.e., positive or negative) of the wire feed velocity Wf may periodically change based on the specified short-circuit and arc periods.

In the first and second embodiments, the present invention is applied to carbon dioxide gas arc welding. In addition, the present invention is also applicable to metal active gas welding using, as a shield gas, a mixture of an inert gas and carbon dioxide gas.

In the first and second embodiments, the base metal5is mild steel. Alternatively, the base metal5may be other materials such as stainless steel, aluminum, and copper.

In the first embodiment, the welding is performed with the torch2held by the operator. Alternatively, the welding may be performed at a welding speed ranging from 0.3 m/min to 1.5 m/min with the torch2held by a robot.

The arc welding control method and arc welding device according to the present disclosure more reliably and effectively reduces the occurrence of spatter, and are useful as an arc welding control method and an arc welding device that control welding currents in arc welding.