WELDING APPARATUS

BACKGROUND

1. TECHNICAL FIELD

The present invention relates to a welding apparatus for performing the welding using shielding gas.

2. BACKGROUND ART

Recently, environmental and energy issues have become social issues, and awareness of the industrial environment and energy saving rises extremely. In such a situation, the energy saving effect of a welding machine is considered important.

As a conventional welding apparatus including a welding machine, a welding apparatus that has a valve for controlling the supply of shielding gas in a welding machine is known (for example, Patent Literature 1).

Some conventional welding apparatuses perform the welding while supplying shielding gas by maximally opening the gas regulator attached on a gas bomb or by opening the gas regulator in response to a maximum value of the required gas flow rate that varies during welding.

A conventional welding apparatus is described with reference to Fig. 8. Fig. 8 is a front view showing a schematic configuration of the conventional welding apparatus and its peripheral devices.

As shown in Fig. 8, welding machine 101 is connected to welding torch 114 and gas bomb 105. Welding machine 1 has gas valve 102 as a valve for controlling the supply of shielding gas. Gas bomb 105 has gas regulator 106 as a flow controller for controlling the flow rate of shielding gas.

Next, the operation of the welding apparatus of Fig. 8 is described.

As a preparation for welding, the flow rate of shielding gas is set by gas regulator 106. When a torch switch (not shown) disposed in welding torch 114 is pushed, a welding start signal is transmitted to welding machine 101. When welding machine 101 having received the welding start signal opens gas valve 102, shielding gas is supplied to welding torch 114.

Gas valve 102 undergoes an opening or closing operation, but has not a function such as half opening, for example.

In the conventional welding apparatus, when gas valve 102 is "opened" for starting the welding to supply shielding gas, shielding gas accumulated in the gas hose is released at a dash to cause outburst of shielding gas. This causes a problem that wasted shielding gas is released.

Furthermore, in the conventional welding apparatus, gas regulator 106 is set with reference to the time period that requires the highest gas flow rate in the welding period. Therefore, also in the time period that requires a low gas flow rate in the welding period, much gas is supplied uselessly to cause waste of gas.

The gas flow rate can be altered every time the welding is completed, but the work by workers is interrupted by the alteration and the efficiency becomes low because the distances to the installation places of concentrated piping and gas regulator 106 are long. Citation List Patent literature PTL 1 Unexamined Japanese Patent Publication No. HI 1-077309

SUMMARY

The present invention provides a welding apparatus capable of preventing gas outburst at the start of welding and suppressing waste of shielding gas.

In order to address the above-mentioned problem, the welding apparatus of the present invention has a welding machine in a midway of a shielding gas supply route from a gas supply source to a welding torch. In the welding apparatus of the present invention, at least two valves including a first valve and second valve are disposed in series in the shielding gas supply route, the first valve is arranged on the side close to the welding torch, and the second valve is arranged on the side close to the gas supply source. In the configuration of the welding apparatus of the present invention, for supplying the shielding gas to the welding torch, the first valve is opened, and the second valve is opened after a first predetermined time after the first valve is opened.

Thanks to this configuration, gas outburst at the start of welding can be prevented and waste of shielding gas can be suppressed.

BRIEF DESCRIPTION OF DRAWINGS

Fig. 1 is a front view showing a schematic configuration of a welding apparatus in accordance with a first exemplary embodiment of the present invention.

Fig. 2 is a front view showing a schematic configuration of a gas flow control device in accordance with the first exemplary embodiment of the present invention.

Fig. 3 is a plan view showing a schematic configuration of an essential part of the welding apparatus in accordance with the first exemplary embodiment of the present invention.

Fig. 4 is a perspective view showing the appearance of a welding machine in accordance with a second exemplary embodiment of the present invention.

Fig. 5 is a front view showing a schematic configuration of an operating section of a welding machine in accordance with the second exemplary embodiment of the present invention.

Fig. 6 is a characteristic diagram showing the relationship between welding current and gas flow rate in accordance with the second exemplary embodiment of the present invention.

Fig. 7 is another characteristic diagram showing the relationship between welding current and gas flow rate in accordance with the second exemplary embodiment of the present invention.

Fig. 8 is a front view showing a schematic configuration of a conventional welding apparatus.

DESCRIPTION OF EMBODIMENTS

Exemplary embodiments of the present invention will be described hereinafter with reference to the accompanying drawings. In the accompanying drawings, the same elements are denoted with the same reference marks, and the descriptions of those elements are omitted.

FIRST EXEMPLARY EMBODIMENT

A welding apparatus of a first exemplary embodiment of the present invention is described with reference to Fig. 1 through Fig. 3. Fig. 1 is a front view showing a schematic configuration of the welding apparatus and its peripheral devices in accordance with the first exemplary embodiment of the present invention. Fig. 2 is a front view showing a schematic configuration of a gas flow control device in accordance with the first exemplary embodiment of the present invention. Fig. 3 is a plan view showing a schematic configuration of an essential part of the welding apparatus in accordance with the first exemplary embodiment of the present invention.

As shown in Fig. 1, welding machine 1 is connected to welding torch 14 and gas flow control device 3. Gas flow control device 3 is connected to gas bomb 5 as a gas supply source via gas regulator 6. The welding apparatus includes at least welding machine 1 and gas flow control device 3. Pipe 5a is extended from gas bomb 5 to welding torch 14, and supplies shielding gas from gas bomb 5 to welding torch 14.

Welding machine 1 has gas valve 2 as first valve 2 for controlling supply of shielding gas. Gas flow control device 3 has gas valve 4 as second valve 4 for controlling supply of shielding gas. Gas bomb 5 has gas regulator 6 as a flow controller for regulating the flow rate of shielding gas.

As shown in Fig. 2, gas flow control device 3 includes gas valve 4 as second valve 4 for controlling supply of shielding gas, control section 7 for controlling gas flow control device 3, and flow sensor 8 for measuring the flow rate of shielding gas.

As shown in Fig. 3, welding machine 1 has welding control section 9 for controlling welding machine 1. As shown by arrow 19, information is exchanged between welding control section 9 of welding machine 1 and control section 7 of gas flow control device 3.

Welding machine 1, as shown in Fig. 3, includes storage section 16, welding current setting section 18, and flow determining section 17. Storage section 16 stores a characteristic curve indicating the quantitative relationship between the set welding current and shielding gas flow rate. Welding current setting section 18 sets a set welding current. Flow determining section 17 determines the shielding gas flow rate based on the set welding current set by welding current setting section 18 and the characteristic curve stored in storage section 16.

Thus, when a configuration for storing the characteristic curve is employed, shielding gas can be synchronized with the set welding current and can be controlled automatically. The required shielding gas flow rate differs between a region of high welding current and a region of low welding current. When the welding current is low, therefore, the amount of used shielding gas is small, wasted shielding gas is reduced, and hence the cost can be reduced.

The operation of the welding apparatus having such a configuration is described. The operation at the start of welding is firstly described, and the operation at the completion of the welding is secondly described.

First, the operation at the start of welding of the welding apparatus of the first exemplary embodiment is described.

As a preparation for welding, the flow rate of shielding gas is set by gas regulator 6 disposed in gas bomb 5. Thus, shielding gas flows via pipe 5a from gas bomb 5 to gas valve 4 of gas flow control device 3.

When a torch switch (not shown) of welding torch 14 is turned on and welding machine 1 starts the operation, the gas flow rate output value is determined based on a welding current command value set by welding current setting section 18 of welding machine 1. Specifically, welding control section 9 of welding machine 1 stores, in the form of a table or mathematical expression, the characteristic where the welding current command value is associated with the gas flow rate output value. Welding control section 9 determines the gas flow rate output value based on the set welding current command value. In other words, welding control section 9 has a function of storage section 16 for storing the characteristic where the set welding current is associated with the shielding gas flow rate and a function of flow determining section 17 for determining the shielding gas flow rate based on the set welding current and the stored characteristic curve. The determined gas flow rate output value is transmitted to control section 7 of gas flow control device 3, and then transmitted from control section 7 to gas valve 4.

When the torch switch (not shown) of welding torch 14 is turned on, the signal is transmitted to welding control section 9 of welding machine 1, welding control section 9 controls gas valve 2 so that gas valve 2 is "opened". Gas valve 2 performs only ON-OFF, and does not have a flow control function.

Welding control section 9 has a timer function, and measures the elapsed time after gas valve 2 is "opened". When a first predetermined time passes after it is "opened", welding control section 9 transmits, as information, the signal indicating that the first predetermined time has passed to control section 7 of gas flow control device 3. Here, the first predetermined time is between about 10 msec and 100 msec, for example.

On receiving the signal indicating that the first predetermined time has passed from welding control section 9, control section 7 controls gas valve 4 so that gas valve 4 is "opened". Here, gas valve 4 has the ON-OFF function and flow control function.

In this operation, shielding gas is supplied from gas bomb 5 to welding torch 14.

In the welding apparatus of the first exemplary embodiment, as discussed above, for supplying shielding gas to welding torch 14, gas valve 2 (first valve 2) of welding machine 1 is firstly "opened". Here, gas valve 2 is on the side close to welding torch 14. After a lapse of the first predetermined time, gas valve 4 (second valve 4) of gas flow control device 3 is "opened". Here, gas valve 4 is on the side close to gas bomb 5. Thus, comparing the conventional welding apparatus that does not include gas flow control device 3, the pressure of shielding gas can be suppressed and the outburst of shielding gas at the start of welding can be prevented. In other words, waste of shielding gas at the start of welding can be suppressed.

This is for the following reason. By "opening" gas valve 2, shielding gas in pipe 5a of the shielding gas supply route from gas valve 4 to welding torch 14 is discharged from the side of welding torch 14, and the amount of shielding gas remaining in the route, namely the amount of remaining shielding gas when the pressure is converted into the atmospheric pressure, is reduced. The fact that gas valve 4 is "opened" in this state means that gas valve 4 is not "opened" until gas valve 2 is "opened". In other words, the supply pressure of shielding gas is lower than that when gas valve 2 and gas valve 4 are simultaneously "opened". That is because the fact that gas valve 4 is "opened" after gas valve 2 is "opened" means that the amount of shielding gas remaining in pipe 5a has been reduced when gas valve 4 is "opened", as discussed above. Therefore, the outburst of shielding gas from pipe 5a can be prevented.

Another reason is as follows. Second shielding gas supply distance L2 from gas valve 4 of gas flow control device 3 to welding torch 14 is longer than first shielding gas supply distance LI from gas valve 2 of welding machine 1 to welding torch 14. The shielding gas supply distance in the conventional welding apparatus corresponds to first shielding gas supply distance LI, and the shielding gas supply distance in the welding apparatus of the first exemplary embodiment corresponds to second shielding gas supply distance L2. When shielding gas is supplied via pipe 5a, the pressure of shielding gas is reduced and suppressed as the length of pipe 5a is increased. Therefore, in the welding apparatus of the first exemplary embodiment, the effect of suppressing the pressure of shielding gas is enhanced and waste of shielding gas at the start of welding can be suppressed.

Welding machine 1 is sometimes used in a state where it is directly connected to gas bomb 5, so that welding machine 1 includes gas valve 2 in consideration of the general versatility. Thus, welding machine 1 including gas valve 2 is well known. The welding apparatus of the first exemplary embodiment is related to a welding apparatus including such welding machine 1 having gas valve 2.

In other words, the welding apparatus of the first exemplary embodiment is a welding apparatus including a welding machine in a midway of a shielding gas supply route from gas supply source 5 to welding torch 14. In the welding apparatus of the first exemplary embodiment, at least two valves including first valve 2 and second valve 4 are disposed in series in the shielding gas supply route, first valve 2 is arranged on the side close to welding torch 14 and second valve 4 is arranged on the side close to gas supply source 5. The welding apparatus of the first exemplary embodiment has the following configuration: for supplying shielding gas to welding torch 14, first valve 2 is opened, and second valve 4 is opened after the first predetermined time after first valve 2 is opened.

Thanks to this configuration, gas outburst at the start of welding can be prevented and waste of shielding gas can be suppressed.

Next, the operation at the completion of welding is described.

When the torch switch (not shown) in welding torch 14 is turned off for completing the welding, a signal indicating that it has been turned off is input to welding control section 9 of welding machine 1. Then, welding control section 9 transmits this signal to control section 7 of gas flow control device 3. On receiving the signal from welding control section 9, control section 7 controls gas valve 4 of gas flow control device 3 so that gas valve 4 is "closed".

Control section 7 has a timer function, and measures the elapsed time after gas valve 4 is "closed". When a second predetermined time passes after it is "closed", control section 7 transmits a signal indicating that the second predetermined time has passed to welding control section 9 of welding machine 1. Here, the second predetermined time is between about 10 msec and 100 msec, for example.

On receiving the signal indicating that the second predetermined time has passed from control section 7, welding control section 9 controls gas valve 2 so that gas valve 2 is "closed".

By this operation, the supply of shielding gas from gas bomb 5 to welding torch 14 is stopped.

In the welding apparatus of the first exemplary embodiment, as discussed above, for stopping the supply of shielding gas to welding torch 14, gas valve 4 (second valve 4) of gas flow control device 3 is "closed". Here, gas valve 4 is on the side close to gas bomb 5. After a lapse of the second predetermined time, gas valve 2 (first valve 2) of welding machine 1 is "closed". Here, gas valve 2 is on the side close to welding torch 14.
Thus, shielding gas whose pressure is sufficiently higher than the atmospheric pressure is released from welding torch 14 to the atmosphere without being contained in pipe 5a that is extended from gas valve 4 to gas valve 2, the pressure of the shielding gas in pipe 5a is reduced to a degree equivalent to the atmospheric pressure. This pressure reduction can decrease the amount of shielding gas remaining in pipe 5a of the shielding gas supply route from gas valve 4 of gas flow control device 3 to welding torch 14, namely the amount of remaining shielding gas when the pressure is converted into the atmospheric pressure. This reduction of the remaining shielding gas can suppress the outburst of shielding gas at the next start of welding. In other words, waste of shielding gas at the start of welding can be suppressed.

In the welding apparatus of the first exemplary embodiment, thus, gas flow control device 3 is disposed between welding machine 1 and gas bomb 5. In the example of the welding apparatus of the first exemplary embodiment, for supplying shielding gas to welding torch 14, gas valve 2 (first valve 2) disposed in welding machine 1 is "opened", and gas valve 4 (second valve 4) disposed in gas flow control device 3 is "opened" after the first predetermined time.

However, gas flow control device 3 may be disposed between welding machine 1 and welding torch 14. In this case, for supplying shielding gas to welding torch 14, gas valve 4 disposed in gas flow control device 3 is used as the first valve and is "opened", and gas valve 2 disposed in welding machine 1 is used as the second valve and is "opened" after the first predetermined time.

In other words, at least two valves including the first valve and second valve are disposed in series in a midway of the shielding gas supply route from gas bomb 5 to welding torch 14. For supplying shielding gas to welding torch 14, the first valve on the side close to welding torch 14 is "opened", and the second valve on the side close to gas bomb 5 is "opened" after the first predetermined time after the first valve is "opened".

For stopping the supply of shielding gas to welding torch 14, similarly, the second valve on the side close to gas bomb 5 is "closed", and the second valve on the side close to welding torch 14 is "closed" after the second predetermined time after the second valve is "closed".

In this configuration, gas outburst at the start of welding can be prevented and waste of shielding gas can be suppressed. The welding apparatus may further have a valve such as a gas valve in addition to the first valve and second valve.

SECOND EXEMPLARY EMBODIMENT

A second exemplary embodiment of the present invention is described with reference to Fig. 4 through Fig. 7. Fig. 4 is a perspective view showing the appearance of a welding machine. Fig. 5 is a front view showing a schematic configuration of an operating section of the welding machine. Fig. 6 is a characteristic diagram showing the relationship between welding current and gas flow rate. Fig. 7 is a characteristic diagram showing the relationship between welding current and gas flow rate, and is obtained by altering the characteristic of Fig. 6.

The welding apparatus of the second exemplary embodiment differs from that of the first exemplary embodiment in the following points:
the gas flow rate determined based on the set welding current command value can be altered; and
the characteristic where the welding current command value is associated with the gas flow rate output value is altered by altering the gas flow rate.

As shown in Fig. 4, welding machine 1 further includes operating section 15. Welding machine 1 includes welding control section 9 similarly to the first exemplary embodiment, and includes storage section 16, flow determining section 17, and welding current setting section 18.

As shown in Fig. 5, operating section 15 includes current setting button 10 as a part of welding current setting section 18, gas flow setting button 11 as a part of flow altering section 20 of shielding gas, display section 12, and jog dial 13. Display section 12 displays a welding current value and gas flow rate value. Jog dial 13 alters the welding current value and gas flow rate value. Welding current setting section 18 and flow altering section 20 may have, on the surface of operating section 15, a numeric keypad used for inputting the welding current value and gas flow rate value.

Therefore, welding machine 1 of Fig. 4 has flow altering section 20 that alters the shielding gas flow rate having been determined by flow determining section 17. Thanks to the configuration having flow altering section 20, the shielding gas flow rate corresponding to the set welding current can be set arbitrarily. Therefore, depending on the welding condition, the amount of used shielding gas can be reduced and the cost can be further reduced.

First, setting of the welding current and determination of the gas flow rate are described.

When current setting button 10 of Fig. 5 is pushed, mode for setting welding current is obtained. Then, by turning jog dial 13, the welding current displayed on display section 12 is adjusted to an intended value. When current setting button 10 is pushed again in this state, the welding current is set at the display value.

Welding control section 9 previously stores, in storage section 16, the characteristic (Fig. 6) showing the relationship between the current value of welding current and the gas flow rate of shielding gas in the form of a table or mathematical expression. Fig. 6 shows an example where the characteristic is expressed by a linear curve (straight line). Welding control section 9 determines a gas flow rate based on this characteristic and the set current value of welding current. The determined gas flow rate is displayed on display section 12.

Next, the case where the determined gas flow rate is altered is described.

For example, when the set welding current is 40 A, the gas flow rate is determined as 4 L/min based on Fig. 6. The case where the gas flow rate is intended to be altered to 1 L/min is described.

When the set welding current is set at 40 A as discussed above, the gas flow rate is determined as 4 L/min, and 40 A as the set welding current value and 4 L/min as the gas flow rate value are displayed on display section 12.

When gas flow setting button 11 is pushed in this state, mode for allowing the gas flow rate to be altered is obtained. Then, by turning jog dial 13, the gas flow rate displayed on display section 12 is adjusted to an intended value, 1 L/min in this case. When gas flow setting button 11 is pushed again in this state, a new gas flow rate is set as follows.

Welding machine 1 of the second exemplary embodiment has the following function:

when the gas flow rate is altered in that manner, the characteristic showing the relationship between the new welding current and gas flow rate is created based on the alteration and is stored in storage section 16 of welding control section 9, and welding is performed based on the new characteristic. The details of the function are described as follows.

When the gas flow rate for the 40-A welding current is altered to 1 L/min as discussed above, welding control section 9 creates a new characteristic of Fig. 7 and stores it in storage section 16 of welding control section 9, based on the altered gas flow rate value and the characteristic of Fig. 6.

More specifically, the position indicated by the 40-A welding current and the 1-L/min gas flow rate after the alteration is set as the second inflection point as shown in Fig. 7. The position indicated by the 2-L/min gas flow rate and the 20-A welding current, which is lower than the 40-A welding current by the 20-A predetermined value, is set as the first inflection point. The position indicated by the 6-L/min gas flow rate and the 60-A welding current, which is higher than the 40-A welding current by the 20-A predetermined value, is set as the third inflection point. After three inflection points are thus determined, a new polygonal-line-type characteristic curve is created by linearly interpolating the first inflection point and second inflection point and linearly interpolating the second inflection point and third inflection point. The created characteristic curve is then stored as the characteristic curve of Fig. 7 in storage section 16 of welding control section 9. The 20-A predetermined value is one example, and the present invention is not limited to this. An appropriate value is previously determined by experiment or the like. The predetermined value may be different between the decrease side and increase side of the welding current.

Then, the gas flow rate is determined based on the new characteristic curve of Fig. 7 until a set current is determined newly or the gas flow rate is altered.

In other words, in the welding apparatus of the second exemplary embodiment, the characteristic curve stored in storage section 16 is a linear curve. When the shielding gas flow rate is altered by flow altering section 20, the position indicated by the relationship between the set welding current and the altered shielding gas flow rate is set as the second inflection point. The intersection point between the linear curve and the welding current value that is lower than the set welding current by a first predetermined value is set as the first inflection point. The intersection point between the linear curve and the welding current value that is higher than the set welding current by a second predetermined value is set as the third inflection point. A new characteristic curve is created by linearly interpolating the first inflection point and second inflection point and linearly interpolating the second inflection point and third inflection point. After that, the welding apparatus of the second exemplary embodiment determines the shielding gas flow rate based on the new characteristic curve until the set welding current is altered.

This configuration has a function of altering the gas flow rate that has been determined based on a previously stored basic characteristic, and hence can set a gas flow rate corresponding to a welding object. Thus, waste of shielding gas can be reduced. A new characteristic curve is created based on the altered gas flow rate, the gas flow rate is determined in response to the set welding current based on the new characteristic curve, and thus welding can be performed. Thus, welding stabler than that when a new characteristic curve is not created can be performed.

Next, an example where the gas flow rate is determined based on the new characteristic curve is described.

First, using operating section 15 of welding machine 1, steady welding current (e.g. 40 A) in a steady welding period, initial welding current (e.g. 10 A) in an initial period, and terminal welding current (e.g. 50 A) in a terminal period are previously set. Here, the initial period is a period before the steady welding period, and the terminal period is a period after the steady welding period. When the gas flow rate for the 40-A steady welding current is altered from 4 L/min to 1 L/min, the characteristic curve of Fig. 7 is created based on the characteristic curve of Fig. 6 as discussed above.

Since the initial welding current is set at 10 A, the gas flow rate in the initial period is determined as 1 L/min based on the characteristic curve of Fig. 7. In this case, the gas flow rate value is the same as that in the characteristic curve of Fig. 6. Since the steady welding current is set at 40 A, the gas flow rate in the steady welding period is determined as 1 L/min based on the characteristic curve of Fig. 7. In this case, the gas flow rate is lower than that in the characteristic curve of Fig. 6. Since the terminal welding current is set at 50 A, the gas flow rate in the terminal period is determined as 3.5 L/min based on the characteristic curve of Fig. 7. In this case, the gas flow rate is lower than that in the characteristic curve of Fig. 6.

By creating a characteristic curve by linearly interpolating the inflection points in the above-mentioned manner, the gas flow rate that is determined in response to the welding current (in the range between 20 A and 60 A) near the welding current (40 A) at which the gas flow rate has been altered (gas flow rate is reduced, in this case) is also reduced. Thus, the ratio of the variation in gas flow rate to the variation in welding current (between 20 A and 60 A) is smaller than that in the characteristic curve of Fig. 6, and welding stabler than that when the characteristic curve of Fig. 6 is used can be performed.

In the welding apparatus of the second exemplary embodiment, welding current setting section 18 previously sets the steady welding current in the steady welding period, the initial welding current in the initial period before the steady welding period, and the terminal welding current in the terminal period after the steady welding period. When flow altering section 20 alters the shielding gas flow rate in the steady welding period, the welding apparatus of the second exemplary embodiment creates a new characteristic curve. The shielding gas flow rate corresponding to the initial welding current and the shielding gas flow rate corresponding to the terminal welding current may be determined based on the new characteristic curve.

Thanks to this configuration, welding can be performed in the following manner:

a new characteristic curve is created based on the altered gas flow rate, the gas flow rate is determined in response to the set welding current based on the new characteristic curve.

Thus, welding stabler than that when a new characteristic curve is not created can be performed.

Thus, welding machine 1 of the second exemplary embodiment can set the gas flow rate corresponding to the welding object, so that waste of shielding gas can be reduced. When the gas flow rate is altered, a new characteristic curve is created, and the gas flow rate is determined in response to the set welding current based on the new characteristic curve. Thus, the ratio of the variation in gas flow rate to the variation in welding current decreases, and stable welding can be performed.

In the first exemplary embodiment and second exemplary embodiment, gas flow control device 3 may be mounted on the surface of welding machine 1. Alternatively, gas flow control device 3 may be disposed at a position apart from welding machine 1. Alternatively, gas flow control device 3 may be disposed in welding machine 1. Such a configuration does not require large-scale construction work or equipment modification, thereby facilitating the installation.

In the first exemplary embodiment and second exemplary embodiment, first valve 2 is disposed in welding machine 1, and second valve 4 is disposed between gas supply source 5 and welding machine 1 and disposed in gas flow control device 3 for controlling the supply of shielding gas.

Such a configuration is an optimal combination in consideration that the gas outburst is suppressed, the interference to a torch or the like is suppressed, the time and effort for the installation work is reduced, and the cost is reduced.

INDUSTRIAL APPLICABILITY

The welding apparatus of the present invention can prevent gas outburst at the start of welding and can suppress waste of shielding gas. This welding apparatus is industrially useful as a welding apparatus including a welding machine that has a valve for controlling shielding gas.

REFERENCE MARKS IN THE DRAWINGS
1 welding machine
2 gas valve (first valve)
3 gas flow control device
4 gas valve (second valve)
5 gas bomb (gas supply source) 5a pipe
6 gas regulator (flow controller)
7 control section
8 flow sensor
9 welding control section
10 current setting button
11 gas flow setting button
12 display section
13 jog dial
14 welding torch
15 operating section
16 storage section
17 flow determining section
18 welding current setting section
19 arrow
20 flow altering section

What is claimed is:

1. A welding apparatus comprising:
a welding machine disposed in a midway of a supply route of shielding gas from a gas supply source to a welding torch,
wherein at least two valves including a first valve and a second valve are disposed in series in the supply route of the shielding gas,
wherein the first valve is arranged on a side close to the welding torch, and the second valve is arranged on a side close to the gas supply source, and
wherein, for supplying the shielding gas to the welding torch, the first valve is opened, and the second valve is opened after a first predetermined time after the first valve is opened.

2. The welding apparatus of claim 1, wherein
for stopping supply of the shielding gas to the welding torch, the second valve is closed, and the first valve is closed after a second predetermined time after the second valve is closed.

3. The welding apparatus of claim 1, wherein
the welding machine includes:
a storage section for storing a characteristic curve that indicates a quantitative relationship between set welding current and shielding gas flow rate;
a welding current setting section for setting the set welding current; and
a flow determining section for determining the shielding gas flow rate based on the set welding current set by the welding current setting section and the characteristic curve stored in the storage section.

4. The welding apparatus of claim 2, wherein
the welding machine includes:
a storage section for storing a characteristic curve that indicates a quantitative relationship between set welding current and shielding gas flow rate;
a welding current setting section for setting the set welding current; and
a flow determining section for determining the shielding gas flow rate based on the set welding current set by the welding current setting section and the characteristic curve stored in the storage section.

5. The welding apparatus of claim 3, wherein
the welding machine includes a flow altering section for altering the shielding gas flow rate that has been determined by the flow determining section.

6. The welding apparatus of claim 5, wherein
the characteristic curve stored in the storage section is a linear curve,
when the shielding gas flow rate is altered by the flow altering section, the position indicated by the relationship between the set welding current and the altered shielding gas flow rate is set as a second inflection point,
the intersection point between the linear curve and a welding current value that is lower than the set welding current by a first predetermined value is set as a first inflection point,
the intersection point between the linear curve and a welding current value that is higher than the set welding current by a second predetermined value is set as a third inflection point, and
a new characteristic curve is created by linearly interpolating the first inflection point and the second inflection point and linearly interpolating the second inflection point and third inflection point, and the shielding gas flow rate is determined based on the new characteristic curve until the set welding current is altered.

7. The welding apparatus of claim 6, wherein
the welding current setting section previously sets steady welding current in a steady welding period, initial welding current in an initial period, and terminal welding current in a terminal period, the initial period being a period before the steady welding period, the terminal period being a period after the steady welding period, and
when shielding gas flow rate in the steady welding period is altered by the flow altering section, a new characteristic curve is created, and shielding gas flow rate corresponding to the initial welding current and shielding gas flow rate corresponding to the terminal welding current are determined based on the new characteristic curve.

8. The welding apparatus of one of claim 1 through claim 7, wherein
the first valve is disposed in the welding machine, and the second valve is disposed between the gas supply source and the welding machine and disposed in the gas flow control device for controlling the supply of the shielding gas.

9. The welding apparatus of claim 8, wherein
the gas flow control device is mounted on the welding machine.