JP2014176865A - Arc spot welding apparatus and arc spot welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an arc spot welding apparatus and an arc spot welding method in which arc spot welding can be performed adequately even in a case of arranging a welding torch below a workpiece.SOLUTION: An arc spot welding apparatus 100 is arranged below a workpiece K which is formed by piling plural base materials K1, K2, and comprises a welding torch 10 which performs spot welding by arc-discharging with the workpiece K, a gas supply device 30 which supplies a shield gas to the workpiece K so as to surround the arc that is generated between the workpiece K and the welding torch 10, and a control device 50 which controls the welding torch 10 and the gas supply device 30. The control device 50 controls the gas supply device 30 so that oxygen or carbon dioxide of 1 to 30% of the whole flow rate is included in the shield gas.

Description

  The present invention relates to an arc spot welding apparatus and an arc spot welding method for performing arc discharge and spot welding between a workpiece and a welding torch.

  Arc welding is known in which an arc is generated and welded between a workpiece on which a plurality of base materials are superimposed and a welding torch arranged on one side of the workpiece. In particular, when spot welding is performed in a spot shape by concentrating the arc at a predetermined position of the workpiece, this is called arc spot welding. Compared with the case of continuous welding (that is, the welding points are connected in a line) while moving the welding torch, it is possible to improve productivity and reduce costs by performing arc spot welding. .

  For example, Patent Document 1 describes a plasma arc spot welding apparatus that spot welds a plurality of stacked metal plates with a plasma arc. This plasma arc spot welding apparatus includes a plasma torch for generating a plasma arc and filler supply means for supplying a filler to the plasma arc, and at least one of the plasma gas and the shield gas contains approximately 50% oxygen.

Japanese Patent No. 3723861

In the invention described in Patent Document 1, a plasma torch is arranged on the upper side with respect to a workpiece (a plurality of stacked metal plates), and a hole formed by melting with the heat of a plasma arc can be filled with a molten filler. It is a premise.
On the other hand, when manufacturing an automobile body or the like, a plasma torch may be disposed on the lower side with respect to the workpiece, and an arc may be generated and welded to the workpiece positioned above. In this case, convection is generated due to the temperature distribution in the molten part, and the molten metal may be melted down by the influence of the convection and gravity.

  For example, it is also conceivable to supply a filler from the lower side to the workpiece and fill the missing portion due to the above-mentioned melting with a molten filler. However, in this case as well, there is a problem that production efficiency is lowered because melting continues due to the influence of convection and gravity.

  Then, this invention makes it a subject to provide the arc spot welding apparatus and the arc spot welding method which can be appropriately arc spot-welded also when arrange | positioning a welding torch below with respect to a workpiece | work.

  In order to solve the above-mentioned problem, an arc spot welding apparatus according to the present invention is arranged on the lower side of a workpiece which is a plurality of superimposed base materials, and performs spot welding by arc discharge with the workpiece. A welding torch, a shield gas supply means for supplying a shielding gas toward the workpiece so as to surround an arc generated between the workpiece and the welding torch, and a control for controlling the welding torch and the shielding gas supply means And the control means controls the shield gas supply means so that the shield gas contains 1 to 30% of oxygen or carbon dioxide of the total gas flow rate.

According to such a configuration, the control means controls the welding torch to generate an arc between the workpiece. Here, the welding torch is arranged below the workpiece. Therefore, it melts from the lower surface of the work by the heat of arc discharge, and the melting proceeds upward in the vertical direction.
Further, the control means controls the shield gas supply means so that 1 to 30% of the total gas flow rate of oxygen or carbon dioxide is contained in the shield gas. Oxygen or carbon dioxide contained in the shielding gas becomes high in temperature due to the heat of the arc generated between the welding torch and the workpiece and becomes highly reactive. The shielding gas is supplied so as to surround the arc. Then, oxygen or carbon dioxide dissolves in the vicinity of the interface with the shield gas (annular interface as viewed from below) in the melted part (melted part) of the workpiece, and the interface of the part is activated.

As a result, due to the reaction heat with oxygen or carbon dioxide, the surface tension of the melted portion near the interface with the shield gas (medium temperature) becomes larger than the upper portion (low temperature) of the melted portion. In addition, the surface tension near the center of the outer surface (high temperature) where one end of the arc is located is higher than the surface tension near the interface with the shielding gas (medium temperature). In this way, Marangoni convection occurs due to non-uniform surface tension, and molten metal gathers from the edge of the outer surface of the melted portion toward the center, and a flow that rises upward in the vertical direction is generated.
Accordingly, it is possible to suppress the force that the molten metal tends to come out from the edge of the outer surface of the melted portion, and to prevent the melted-down due to its own weight. Further, the molten metal rises upward in the vertical direction, so that the workpiece can be smoothly melted and the efficiency of arc spot welding can be increased.

  Further, the arc spot welding method according to the present invention is such that a welding torch is arranged below a workpiece that is a plurality of superimposed base materials, and arc welding is performed between the workpiece and the welding torch. In this arc spot welding method, the shield gas supplied toward the workpiece so as to surround the arc contains 1 to 30% of the total gas flow rate of oxygen or carbon dioxide.

According to such a configuration, 1 to 30% of the total gas flow rate of oxygen or carbon dioxide is contained in the shield gas. Therefore, oxygen or carbon dioxide dissolves in the melted portion near the interface with the shield gas (annular interface as viewed from below), and the interface of the melted portion is activated to generate Marangoni convection. As a result, the molten metal gathers from the edge of the outer surface of the melted portion toward the vicinity of the center, and a flow that rises upward in the vertical direction is generated.
Accordingly, it is possible to suppress the force for the molten metal to come out from the edge described above, and to prevent the molten metal from being burned out by its own weight. Further, the melting of the workpiece proceeds smoothly upward, and the efficiency of arc spot welding can be increased.

  According to the present invention, it is possible to provide an arc spot welding apparatus and an arc spot welding method for appropriately performing arc spot welding even when a welding torch is disposed on the lower side with respect to a workpiece.

It is a lineblock diagram of the arc spot welding device concerning one embodiment of the present invention. (A) is a graph which shows the relationship between the surface temperature at the time of including carbon dioxide in shielding gas, and surface tension, (b) is a cross-sectional schematic diagram of the fusion | melting part at the time of including carbon dioxide in shielding gas. (C) is a graph showing the relationship between the surface temperature and the surface tension when carbon dioxide is not included in the shield gas, and (d) is the melting portion when carbon dioxide is not included in the shield gas. It is a cross-sectional schematic diagram. (A) is a cross-sectional schematic diagram which shows the flow of the molten metal at the time of using the arc spot welding apparatus which concerns on this embodiment, (b) is the molten metal at the time of using the arc spot welding apparatus which concerns on a comparative example. It is a cross-sectional schematic diagram which shows a flow. It is a graph which shows the relationship between the content rate of a carbon dioxide, and the penetration depth of a fusion | melting part.

Hereinafter, embodiments for carrying out the present invention will be described in detail with reference to the drawings as appropriate.
Hereinafter, as an example, a case where arc base welding is performed on the base material K1 and the base material K2 that are overlapped in the vertical direction will be described. Note that the base material K1 and the base material K2, which are members to be welded, may be referred to as “workpiece K”.

<Configuration of arc spot welding equipment>
FIG. 1 is a configuration diagram of an arc spot welding apparatus according to a first embodiment of the present invention. The arc spot welding apparatus 100 is an apparatus that performs arc spot welding of the superposed base material K1 and base material K2. In the present embodiment, as the base materials K1 and K2, plate-like metal members having a rectangular shape in plan view are used. The base material K1 is, for example, high tensile steel (High Tensile Strength Steel). The base material K2 is, for example, mild steel.

<Configuration of arc welding equipment>
As shown in FIG. 1, the arc welding apparatus 100 includes a welding torch 10, a robot drive device 20, a gas supply device 30, a power supply device 40, and a control device 50.

(Welding torch)
The welding torch 10 performs arc discharge by introducing a welding current to a non-consumable electrode 11 made of tungsten or the like, and supplies a shielding gas S in order to shield the welding portion from the outside air. The welding torch 10 includes a rod-shaped non-consumable electrode 11, a cylindrical nozzle 12 extending so that the non-consumable electrode 11 serves as an axis, and a collet body (not shown) that holds the non-consumable electrode 11 in the nozzle 12. And have.

  The welding torch 10 is held by a multi-axis articulated robot (not shown) so that the welding torch 10 is positioned below the workpiece K and the non-consumable electrode 11 and the workpiece K are kept at a predetermined distance. For example, the welding torch 10 is held by a multi-axis multi-joint robot such that its axis is along the vertical direction. The distance between the welding torch 10 and the workpiece K and the angle of the axis are set in advance.

(Robot drive)
The robot drive device 20 is an actuator or the like that drives the multi-axis multi-joint robot in response to a command from the control device 50, and has a function of moving the welding torch 10 or temporarily stopping at a predetermined welding location. Have. As described above, arc spot welding is a welding method in which arcs R are concentrated on a predetermined position of the workpiece K so that welding points are scattered.

(Gas supply device)
The gas supply device 30 injects an inert gas such as argon gas or helium gas from the nozzle 12 as the shield gas S. That is, the gas supply device 30 sets the opening degrees of the first control valve 32 connected to the gas cylinder 31 filled with argon gas and the second control valve 34 connected to the gas cylinder 33 filled with carbon dioxide. Adjust each one. Thus, the shield gas S in which argon and carbon dioxide are mixed at a predetermined flow rate ratio is supplied to the welding torch 10. This protects the arc R and prevents the molten metal from reacting with oxygen / nitrogen contained in the outside air.

(Power supply)
The power supply device 40 is a device that supplies electric power necessary for arc welding, and includes a TIG (Tungsten Insert Gas) power supply 41, a drive power supply 42, a current detector 43, and a voltage detector 44. .
The TIG power source 41 is a power source for converting commercial three-phase AC power into DC power using a transformer (not shown) and causing arc discharge in accordance with a command from the control device 50. The anode of the TIG power source 41 is electrically connected to the workpiece K, and the negative electrode of the TIG power source 41 is electrically connected to the non-consumable electrode 11 of the welding torch 10.

  The drive power source 42 is a power source that converts commercial three-phase AC power into DC power using a transformer (not shown) and supplies power to the gas supply device 30 and the robot drive device 20 in accordance with a command from the control device 50. . The anode of the drive power source 42 is electrically connected to the gas supply device 30 and the robot drive device 20, and the anode of the drive power source 42 is grounded.

The current detector 43 detects a current value or the like of arc discharge that occurs between the non-consumable electrode 11 of the welding torch 10 and the workpiece K. The current detector 43 outputs the detected current value to the control device 50.
The voltage detector 44 detects a voltage value or the like of arc discharge that occurs between the non-consumable electrode 11 of the welding torch 10 and the workpiece K. The voltage detector 44 outputs the detected voltage value to the control device 50.

(Control device)
The control device 50 controls driving of the robot drive device 20, the gas supply device 30, and the power supply device 40. The control device 50 includes electronic circuits such as a CPU (Central Processing Unit), a ROM (Read Only Memory), a RAM (Random Access Memory), a HDD (Hard Disk Drive), and various interfaces, and is stored therein. Various functions are demonstrated by operating according to the program.
The control device 50 includes an arc discharge control unit 51, a gas supply control unit 52, and a welding torch movement control unit 53.

  The arc discharge controller 51 has a function of generating an arc R between the non-consumable electrode 11 and the workpiece K (base material K1) by driving the power supply device 40. The arc discharge control unit 51 starts arc discharge at a timing at which the movement of the welding torch 10 is stopped at a predetermined welding location, and drives the power supply device 40 so as to continue the arc discharge for a predetermined time. The arc voltage / current, arc discharge time, and the like by the arc discharge control unit 51 are appropriately set according to the materials and applications of the base material K1 and the base material K2.

The gas supply control unit 52 generates the arc R and shield gas S for shielding the welded part from the outside air from the gas cylinders 31 and 32 to the welding torch 10 at a predetermined pressure and flow rate. A command signal is output to. The gas supply control unit 52 includes carbon dioxide: CO ₂ in the shielding gas S at a ratio of 1 to 30% of the entire flow rate, and the remaining shielding gas S is argon: Ar.

That is, the gas supply control unit 52 controls the flow rate of gas supplied from the gas cylinder 31 filled with argon and the gas cylinder 32 filled with carbon dioxide, and mixes carbon dioxide and argon at a predetermined ratio, and performs welding. Inject from the torch 10 toward the workpiece K.
Accordingly, the “shield gas supply means” for supplying the shield gas S toward the work K so as to surround the arc R generated between the work K and the welding torch 10 includes the gas cylinders 31 and 32 and the first control valve 32. And a second control valve 34, a gas supply device 30, and a gas supply control unit 52.

  The welding torch movement control unit 53 has a function of controlling the robot drive device 20 to move and stop the welding torch 10 in a predetermined direction below the workpiece K.

<Welding procedure>
(Welding process)
The control device 50 causes the welding torch movement control unit 53 to stop the movement of the welding torch 10 at a predetermined welding location. Further, the control device 50 supplies the arc R between the non-consumable electrode 11 and the work K by the arc discharge control unit 53 while supplying the shield gas S from the welding torch 10 toward the work K by the gas supply control unit 52. generate. As described above, the shield gas S whose flow rate and the like are controlled by the gas supply control unit 52 contains carbon dioxide of 1 to 30% of its volume flow rate.

  The time for performing arc spot welding at one welding point is set so that the melting of the workpiece K is advanced to a predetermined position of the base material K2 in the vertical direction (or the arc R penetrates the base material K2). . Incidentally, in this embodiment, the filler is not fed.

(Transfer process)
After a predetermined time has elapsed since the start of welding at the welding location, the control device 50 stops the arc discharge by the arc discharge control unit 51 and stops the supply of the shield gas S by the gas supply control unit 52. Next, the control device 50 causes the welding torch movement control unit 53 to move the welding torch 10 toward the next welding location.

  As described above, the control device 50 moves the welding torch 10 so as to sequentially perform arc spot welding at a plurality of preset welding locations, and executes the arc discharge and the supply of the shielding gas S.

<Flow of molten metal>
When an arc discharge occurs between the non-consumable electrode 11 and the workpiece K positioned thereabove, the heat of the arc R starts to melt from the lower surface (base material K1) of the welded portion, and the melting proceeds upward. Go. Here, surface tension acts on the interface of the melted part P that is in contact with the non-melted part or the shield gas S so as to reduce the surface area. In addition, the magnitude | size of above-described surface tension changes according to the temperature of the fusion | melting part P. FIG.

As described above, the shielding gas S contains carbon dioxide of 1 to 30% (for example, 15%) of the volume flow rate, and the carbon dioxide is heated by the heat of the arc R to increase the reactivity. Yes.
When the shield gas S is injected at a predetermined pressure so as to surround the arc R, carbon dioxide dissolves into the melting part P and activates the interface. As a result, as shown in FIG. 2A, the surface tension increases as the temperature of the melted portion P increases.

In addition, since one end of the arc R is positioned substantially at the center of the melted part P in the front-rear and left-right directions, the vicinity of the center of the outer surface of the melted part P becomes higher than the surroundings. Therefore, as shown in FIG. 2B, in the vicinity of the outer surface of the melted portion P, the surface tension increases toward the center (location where the arc R hits), and the molten metal collects from the periphery toward the center. Will occur. Thus, convection caused by non-uniform surface tension of fluid is called Marangoni convection.
When the molten metal collected at the center rises from the vicinity of the interface between the melting part P and the shield gas S, the workpiece K is melted upward by the heat of the melting part P (see FIG. 2B).

Hereinafter, a melted portion that is formed when the shield gas S does not contain carbon dioxide (for example, only argon) is referred to as a “melted portion Q”. As shown in FIG.2 (c), when carbon dioxide is not included in shield gas S, surface tension becomes weak, so that the temperature of the fusion | melting part Q is high.
As a result, as shown in FIG. 2 (d), a flow of molten metal from the center toward the periphery occurs in the vicinity of the outer surface of the melted portion Q. That is, in the comparative example, Marangoni convection in the opposite direction to the present embodiment occurs.
Thus, in the case of the comparative example, the molten metal flows so as to spread around the outer surface of the molten metal, so that the penetration depth (height) is shallower than that of the present embodiment. Further, in the vicinity of the interface (annular interface viewed from below) in contact with the shield gas S, a part of the molten metal flowing outward from the center may be melted by its own weight (FIG. 2). (See (d)).

By the way, the Marangoni number Ma [−] indicating the magnitude of the Marangoni convection is expressed by the following (Formula 1). In (Equation 1), σ _T is the surface tension temperature coefficient, ΔT is the temperature difference between the liquid column end faces [K], H is the liquid column length [m], ρ is the density [kg / m ³ ], and γ is the kinematic viscosity coefficient. [M ² / s], κ represents a temperature diffusion coefficient [m ² / s].

Ma = σ _T ΔT · H / (ρ · γ · κ) (Formula 1)

As described above, the value of the Marangoni number Ma is proportional to the temperature difference ΔT between the liquid column end faces (the end face temperature difference related to an arbitrary liquid column in the melting portion P).
As shown in FIG. 3A, the temperature in the vicinity of the outer surface center A of the melted part P where one end of the arc R is located is increased by the heat of the arc R (for example, 2000 ° C.).
In the melting part P, the vicinity B of the interface with the shield gas S is lower than the center A, but the temperature of the melting part P is raised by about 100 ° C. (for example, 1900 ° C.) by the heat of reaction with carbon dioxide. .
The temperature of the upper part C of the melting part P is lower than the vicinity B of the interface with the shield gas S (for example, 1800 ° C .: low temperature).

Accordingly, the surface tension of the melted part P is larger from the upper part C (low temperature region) to the vicinity B (intermediate temperature region) of the interface with the shielding gas S and to the vicinity of the center A (high temperature) than the vicinity of the interface B to the shielding gas S. Area) is larger. As a result, Marangoni convection in the direction shown in FIG. 3A is generated, and the molten metal flows and circulates in the direction of B → A → C → B →.
As described above, since the molten metal collected in the high temperature central region rises (A → C), the area of the melted portion P is narrowed as viewed from below, and the work K is melted (upward melting). .

  On the other hand, in the comparative example shown in FIG. 3B, the shield gas S1 does not contain carbon dioxide. Therefore, the molten metal changes from the vicinity of the center D at a high temperature (for example, 2000 ° C.) to the vicinity of the edge E at a low temperature (for example, 1800 ° C.) due to the relationship between the temperature and the surface tension described in FIG. Head. In addition, the temperature of the upper part F of the fusion | melting part Q is substantially equal to the temperature of the edge vicinity E mentioned above. As a result, Marangoni convection shown in FIG. 3B is generated, and the molten metal flows and circulates in the direction of D → E → F → D →.

As described above, since an outward flow is generated from the vicinity of the center D along the interface (D → E), there is a high possibility that the molten metal melts in the vicinity of the edge E due to the force and the weight of the flow. Become.
Further, since Marangoni convection in the direction shown in FIG. 3B is generated, the area of the melted portion Q is widened as viewed from below, and the speed at which the work K is melted (upward melting) is as shown in FIG. Compared with the case of a), it becomes slower.

FIG. 4 is a graph showing the relationship between the carbon dioxide content and the penetration depth of the melted portion. The penetration depth means the distance in the vertical direction between the lower surface of the base material K1 and the upper end of the melted portion P (the distance when a predetermined time has elapsed since the start of arc discharge).
As shown in FIG. 4, when the content rate of carbon dioxide contained in the shield gas S is gradually increased from 0%, the penetration depth value increases accordingly, and the penetration depth is around 17%. Is the maximum. In particular, in the region where the carbon dioxide content is in the range of 1% to 30%, it has been found that the value of the penetration depth is larger than that in the case where no carbon dioxide is contained.

<Effect>
According to the arc spot welding apparatus 100 according to the present embodiment, the shield gas S supplied so as to surround the arc R contains 1 to 30% of the volume flow rate of carbon dioxide. Since the melted portion P is activated at the interface when carbon dioxide dissolves, the vicinity of the center A (high temperature: see FIG. 3A) near the outer surface of the melted portion is near the interface B with the shield gas S. (Medium temperature: (see FIG. 3A)) The surface tension becomes larger than this, Marangoni convection is generated by making the surface tension of the melted portion P non-uniform in this way, and the molten metal is an interface with the shield gas S. It is possible to generate a flow (B → C: see FIG. 3A) that goes from the vicinity B to the center vicinity A and further upwards in the vertical direction.

Further, the above-mentioned Marangoni convection suppresses the force that the molten metal tends to go outward from the center A where one end of the arc R is located, and the molten metal melts down by its own weight near the interface B with the shield gas S. Can be prevented.
Further, the molten metal rises upward in the vertical direction by Marangoni convection, so that the workpiece K is smoothly melted, and the efficiency of arc spot welding can be increased.

≪Modification≫
As mentioned above, although the Kuspot welding apparatus 100 which concerns on this invention was demonstrated by embodiment, this invention is not limited to these description, A various change etc. can be performed.
For example, in the embodiment, the case where carbon dioxide is contained in the shield gas S has been described, but the present invention is not limited to this. That is, the shield gas S may contain 1 to 30% oxygen. Even in this case, the interface of the portion that receives the injection of the shield gas S in the melted portion P is activated and the temperature rises as in the above embodiment. Therefore, even when Marangoni convection in the direction shown in FIG. 3A is generated and the welding torch 10 is disposed below the workpiece K, arc spot welding can be appropriately performed.

Moreover, although the said embodiment demonstrated the case where an arc was generated between the welding torch 10 and the workpiece | work K and arc spot welding was carried out, it is not restricted to this. For example, it can be applied to other welding methods such as laser welding and plasma welding.
Moreover, although the said embodiment demonstrated the case where two base materials K1, K2 were welded, it is not restricted to this. That is, three or more plate-shaped base materials may be welded by the same method.

Moreover, although the said embodiment demonstrated the case where the base material K1 (high-tensile steel) and the base material K2 (soft steel) are different members, it is not restricted to this. That is, the same kind of the plurality of base materials may exist. Further, other types of metals may be used as the base materials K1 and K2.
Moreover, although the said embodiment demonstrated the case where it welded automatically using the robot drive device 30 and the control apparatus 50, it is not restricted to this. That is, a human may hold the welding torch 10 and manually weld from the lower side of the workpiece K.

Moreover, although the said embodiment demonstrated the case where the workpiece | work K was arrange | positioned so that a plate | board surface might become substantially parallel to a horizontal surface and arc spot welding was performed from the lower side of the workpiece | work K, it is not restricted to this. That is, the workpiece K may be arranged so that the plate surface has a predetermined angle with the horizontal plane, and the welding torch 10 may be arranged below the workpiece K.
Further, the welding torch 10 may be arranged on the upper side of the workpiece K, and arc spot welding may be performed by the same method as in the above embodiment. Even in this case, since the penetration proceeds rapidly by Marangoni convection, welding can be performed efficiently.

DESCRIPTION OF SYMBOLS 100 Arc spot welding apparatus 10 Welding torch 20 Robot drive apparatus 30 Gas supply apparatus (shield gas supply means)
31, 33 Gas cylinder (shield gas supply means)
32 1st control valve (shield gas supply means)
34 Second control valve (shield gas supply means)
40 power supply device 50 control device (control means)
51 Arc Discharge Control Unit 52 Gas Supply Control Unit (Shield Gas Supply Means)
53 Welding torch movement control part K1, K2 Base material K Work P Melting part

Claims (2)

A welding torch that is disposed on the lower side of the workpiece, which is a plurality of superposed base materials, and is spot-welded by arc discharge with the workpiece;
Shielding gas supply means for supplying a shielding gas toward the workpiece so as to surround an arc generated between the workpiece and the welding torch;
Control means for controlling the welding torch and the shield gas supply means,
The said control means controls the said shield gas supply means so that 1-30% of oxygen or carbon dioxide of the whole gas flow rate may be contained in shield gas. The arc spot welding apparatus characterized by the above-mentioned. An arc spot welding method in which a welding torch is arranged on the lower side of a workpiece that is a plurality of superimposed base materials, and spot welding is performed by arc discharge between the workpiece and the welding torch,
An arc spot welding method, wherein the shield gas supplied toward the workpiece so as to surround the arc contains 1 to 30% of oxygen or carbon dioxide of the total gas flow rate.

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