JP2016163900A - Gas shield arc welding method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain excellent weld quality, while suppressing generation of slag by lowering the ratio of carbon dioxide in shield gas.SOLUTION: A current value is increased after short circuit between a weld wire and a member to be welded until arriving at a first peak current value, to thereby set a time until release of short circuit at 0.005 second or shorter. After release of the short circuit, a time of a period after increasing a current value until arriving at a second peak current value, and until lowering it to a prescribed current value is set at 0.005 second or shorter.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a gas shielded arc welding method used when, for example, steel plates are welded.

  In gas shielded arc welding, a shielding gas is supplied from the tip of the welding torch, and an arc is generated between the welding wire and the work piece in the shielding gas to melt and solidify the welding wire and work piece in a short time. For example, it is widely used at the welding site of automobile parts.

  In Patent Document 1, a mixed gas in which 10 to 30% of carbon dioxide is mixed with argon is used as a shielding gas. In Patent Document 2, a pulse current in which the first pulse and the second pulse are alternately repeated is used as the welding current. The peak current is changed between the first pulse and the second pulse, and the peak period is also changed. In addition, when one droplet is transferred per cycle of the pulse current and the distance between the welding wire and the material to be welded changes, the peak current and the peak period are within a range that does not disturb one droplet transfer per cycle. By adjusting the arc length, the arc length is controlled to be constant.

  In general, in gas shielded arc welding, carbon dioxide in the shielding gas is separated by the heat of the arc to generate oxygen, and this oxygen enters the molten metal and tends to become pore defects after solidification. As a countermeasure, a deoxidizer such as silicon or manganese is added to the material to be welded to generate silicon or manganese oxides during welding, and these oxides appear as slag in the weld after welding.

JP 2007-98459 A JP 2007-237270 A

  By the way, since the slag which generate | occur | produces in a welding part worsens the appearance of a welding part, it is unpreferable. In addition, in the case of a part to be subjected to cationic electrodeposition coating such as an automobile part, there is also a problem that the paint does not electrodeposit on the portion where the slag is adhered because the slag is not energized if the surface is adhered. In particular, if it is an undercarriage part, slag is peeled off by chipping of stones and the like received during traveling, and a portion not electrodeposited is exposed, and rust progresses from there.

  The following three measures can be considered for the generation of slag. The first countermeasure is to scrape the slag after welding. However, it takes man-hours to scrape slag, and in the case of automated equipment using shot peening, etc., the capital investment is high and running costs such as replenishment of balls are high, which is effective in terms of cost. It is not a measure.

  The second measure is to reduce the amount of additives such as silicon and manganese in the material to be welded. However, if the amount of additives is decreased, the composition of the material to be welded will change and the deoxidizer will decrease. This increases the probability of pore defects and is not an effective measure.

  A third countermeasure is to reduce the volume ratio of carbon dioxide in the shield gas. For example, if the ratio of carbon dioxide is reduced until the ratio of argon: carbon dioxide is about 95: 5, slag is hardly generated, which is effective as a slag suppression measure.

  However, when the amount of carbon dioxide in the shield gas decreases, the amount of heat required for the carbon dioxide divergence during arc generation decreases, that is, the amount of heat taken away from the arc decreases, so that the arc energy increases and the arc temperature increases. The arc will spread.

  When the arc spreads, the material to be welded becomes less melted, the surplus is lowered, and the weld bead becomes flat. In particular, in the welding of a T-joint having a relatively large gap between materials to be welded, a hole is easily generated and the welding quality is deteriorated. For this reason, it is costly to modify the welding to fill the hole, and to correct the mold and jig to manage the gap narrowly. In addition, robotic teaching equipment must be corrected frequently. This also increases costs.

  Moreover, when the arc spreads, the arc length tends to be long. For this reason, there is also a problem that the droplets do not grow stably and the weld bead fluctuates and the weld quality deteriorates.

  The present invention has been made in view of such points, and the object is to obtain good welding quality while suppressing the generation of slag by reducing the ratio of carbon dioxide in the shielding gas. Is to be able to.

  In order to achieve the above object, in the present invention, by controlling the waveform of the welding current, the arc does not spread even if the ratio of carbon dioxide in the shield gas is low, and the arc length is shortened. did.

The first invention is
In a gas shielded arc welding method of welding an object to be welded by generating an arc between a welding wire supplied in a shielding gas containing argon and carbon dioxide and the member to be welded,
After the short-circuit between the welding wire and the member to be welded, the time until the current value is increased until the first peak current value is reached to open the short-circuit is 0.005 seconds or less. Welding the member to be welded by supplying a welding current having a waveform in which the time for increasing the current value to a peak current value of 2 and then decreasing the current value to a predetermined current value is set to 0.005 seconds or less. Features.

  According to this configuration, after the short-circuit between the welding wire and the member to be welded, the droplet transfer of the welding wire is promoted by increasing the current value until the first peak current value is reached. And a droplet moves to a molten pool and a short circuit is open | released. Since the time during this period is 0.005 seconds or less, the speed at which the current value is increased until the first peak current value is reached. Since the speed at which the current value is increased is increased, the disconnection of the short-circuited welding wire is promoted, so that the position where the welding wire is disconnected can be brought closer to the member to be welded. As a result, the arc length generated after opening the short circuit is shortened. And melting of the front-end | tip part of a welding wire is accelerated by increasing an electric current until it becomes a 2nd peak electric current, and welding current falls after that. Since the time from when the current value is increased until the second peak current value is reached until it is decreased is 0.005 seconds or less, the current value decreases rapidly from the second peak current. Thereby, since the supply amount of thermal energy is rapidly reduced, an increase in arc energy is suppressed and the arc is difficult to spread, and the arc length is shortened. Accordingly, when the generation of slag is suppressed by reducing the ratio of carbon dioxide in the shield gas, it is difficult for holes to be generated in the welded portion, and fluctuations in the weld bead are also reduced.

According to a second invention, in the first invention,
The volume ratio of carbon dioxide in the shielding gas containing argon and carbon dioxide is 5% or less.

  According to this configuration, when the volume ratio of carbon dioxide in the shield gas is 5% or less, the amount of slag generated is further reduced. Therefore, the appearance of the welded portion is improved, and the corrosion resistance is improved when the cationic electrodeposition coating is performed after welding as in an automobile underbody part, for example.

  And even if it is a case where the volume ratio of the carbon dioxide in shielding gas is 5% or less, the spread of an arc is suppressed by setting the waveform of a welding current like 1st invention, and arc length is short. Therefore, the welding quality is not adversely affected.

According to a third invention, in the first or second invention,
The current value is increased to a second peak current value and then decreased to a base current value.

  According to this configuration, by reducing the current value to the base current value, the amount of heat energy supplied is sufficiently reduced, and the effect of suppressing the spread of the arc is improved.

According to a fourth invention, in any one of the first to third inventions,
The second peak current value is maintained for a predetermined time.

  According to this configuration, it is possible to sufficiently melt the tip of the welding wire by maintaining the second peak current for a predetermined time.

  According to the first invention, the ratio of carbon dioxide in the shielding gas can be reduced to suppress the generation of slag, and the arc length can be shortened by suppressing the spread of the arc. Quality can be maintained.

  According to the second invention, since the volume ratio of carbon dioxide in the shielding gas is 5% or less, the amount of slag generated can be further reduced, the appearance can be improved, and, for example, an automobile undercarriage part Corrosion resistance can be improved.

  According to the third aspect of the present invention, the current value is increased until the second peak current value is reached, and then the base current value is decreased, thereby sufficiently reducing the supply amount of thermal energy and suppressing the spread of the arc. Can improve the effect.

  According to the fourth aspect of the invention, the tip end portion of the welding wire can be sufficiently melted by maintaining the second peak current value for a predetermined time, and the welding quality can be further improved.

It is a schematic block diagram of the gas shielded arc welding apparatus which concerns on embodiment. It is a figure which shows the shape of a welding current waveform. It is a schematic diagram of a welding wire and a member to be welded, (a) shows a state where the welding wire and the member to be welded are short-circuited, (b) shows a droplet transfer state, and (c) shows an arc when the short-circuit is opened. (D) shows a state in which the welding wire has been melted, and (e) shows a state in which the droplet is maintained by reducing the current.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.

  FIG. 1 shows a schematic configuration of a gas shielded arc welding apparatus 1 according to an embodiment of the present invention. By using this gas shielded arc welding apparatus 1, the gas shielded arc welding method of the present invention is executed. Can do.

  The gas shielded arc welding apparatus 1 is installed, for example, at a manufacturing site of undercarriage parts as automobile parts, and automatically welds a plurality of steel plates as welded members 10 (shown in FIG. 3) constituting the undercarriage parts by a robot 2. Used when Examples of the member to be welded 10 include a galvanized steel sheet. In addition to the robot 2, the gas shielded arc welding apparatus 1 includes a robot control device 3 that controls the robot 2, a welding power supply device 4, a gas cylinder 5, and a welding wire supply device 6. The gas shielded arc welding apparatus 1 can be used for welding a T-shaped joint.

  As the robot 2, a well-known articulated industrial robot can be used. A robot welding torch 2 b is attached to the tip of the arm 2 a of the robot 2. A welding wire W (shown in FIG. 3) is supplied from the tip of the robot welding torch 2b, and a shielding gas is supplied. Since the robot welding torch 2b is well known in the art, a detailed description thereof will be omitted.

  The robot control device 3 is connected to the robot 2 and includes a known arithmetic processing device and storage device. A predetermined operation program can be stored in the storage device of the robot control device 3. The robot control device 3 is configured to control the robot 2 according to an operation program. The operation program is created by teaching, for example.

  The gas cylinder 5 is filled with a shielding gas. The gas cylinder 5 is connected to the robot welding torch 2b of the robot 2 through a pipe. The shield gas is a mixed gas of argon and carbon dioxide. In this embodiment, the volume ratio of carbon dioxide in the shielding gas is 5%, but the volume ratio of carbon dioxide may be less than 5%.

  The welding wire supply device 6 accommodates the welding wire W and is configured to continuously supply the welding wire W. The feeding speed of the welding wire W can be arbitrarily adjusted according to the welding speed and the type of the material to be welded 10.

  The welding power source device 4 outputs a welding current supplied to the welding wire W, and includes a well-known welding current waveform generation unit 4a and an output unit 4b that outputs a welding current having a waveform generated by the welding current waveform generation unit 4a. And. The welding current waveform generation unit 4a is configured to generate a welding current waveform by digital control, and since the structure thereof is conventionally known, detailed description thereof is omitted.

  The welding waveform generated by the welding current waveform generation unit 4a is specifically the waveform shown in FIG. 2, and the welding waveform is generated continuously. The base current value Ib is set between 170A and 180A. Point A is a point representing the moment when the tip of the welding wire W contacts the member to be welded 10 and short-circuits. First, the current value is instantaneously reduced from point A to point B. The current value at point B is preferably 1/3 or less of the base current value Ib, and in this embodiment it is 50A. Then, the current value is increased from point B to point C. The current value at the point C is the first peak current value, and the first peak current value is preferably at least twice the base current value Ib. In this embodiment, the current value is 450A.

  After increasing the current value to the first peak current value, the current value is instantaneously decreased to point D. Point D is a point that opens the short circuit. The time from point A to point D is preferably 0.005 seconds or less, and may be 0.003 seconds or less. The current value at point D is lower than the base current value Ib and is preferably 1/3 or less of the base current value Ib. In this embodiment, the current value at point B is 50A. Thereafter, the current value is increased again from the point D to the point E. The current value at point E is the second peak current value, and the second peak current value is preferably at least twice the base current value Ib. In this embodiment, the current value is 450A, which is the same as the first peak current value. The second peak current value is maintained up to point F. The predetermined time for maintaining the second peak current value is, for example, 0.001 seconds.

  Thereafter, the current value is lowered from the F point to the G point and then lowered to the H point. The current value at point G is higher than the base current value Ib, and is 200 A in this embodiment. The current value at point H is the base current value Ib. The time required to decrease the current value from the F point to the G point is set to be the same as or shorter than the time required to decrease the current value from the G point to the H point. As a result, the current value can be reduced gradually after being instantaneously reduced from the F point to the G point. After releasing the short circuit, the time for increasing the current value until the second peak current value is reached and then decreasing to the predetermined current value, that is, the time from point E to point H is preferably 0.005 seconds or less, It may be 0.003 seconds or less. The time from the start point (point A) to the end point (point H) in one welding waveform is preferably 0.001 seconds or less, and may be 0.007 seconds or less.

  Next, a method for welding the workpiece 10 using the gas shield arc welding apparatus 1 configured as described above will be described. The material to be welded 10 is, for example, a press-molded plate material or the like. The robot 2 moves the robot welding torch 2b to a predetermined welding position. Further, the shield gas is supplied from the gas cylinder 5 and the welding wire W is supplied from the welding wire supply device 6. The welding power supply 4 supplies a welding current having a continuous waveform as shown in FIG. In this embodiment, since the volume ratio of carbon dioxide in the shield gas is reduced to 5% or less, slag is hardly generated.

  At the point A in FIG. 2, as shown in FIG. 3 (a), the tip of the welding wire W and the member to be welded 10 are short-circuited, and then the current value instantaneously decreases to the point B. The tip end portion of W and the member to be welded 10 are reliably short-circuited, and a stable short-circuit state in which the droplets are not easily scattered can be created.

  Thereafter, the current value increases up to point C, which is the first peak current value, thereby promoting droplet transfer of the welding wire W as shown in FIG. Then, as the current value decreases to point D, as shown in FIG. 3C, the droplets move to the molten pool, the short circuit is opened, and the arc 100 is generated. Since the time from the short-circuit between the welding wire W and the member to be welded 10 until the short-circuit is opened is 0.005 seconds or less, the speed of increasing the current value is sufficiently high until the first peak current value is reached. can do. By increasing the speed at which the current value is increased, disconnection of the short-circuited welding wire W is promoted, so that the position where the welding wire W can be disconnected can be brought closer to the member to be welded 10. As a result, the arc length generated after opening the short circuit is shortened.

  Next, the current value increases to the point E which is the second peak current value, and the current value is maintained up to the point F, thereby accelerating the melting of the tip of the welding wire W as shown in FIG. In addition, a sufficient amount of penetration of the workpiece 10 can be secured. Thereafter, the welding current decreases to the G point and the H point. Since the time from when the current value is increased to the second peak current value until the current value is decreased to the base current value Ib is 0.005 seconds or less, the current value rapidly decreases from the second peak current value. Will be reduced. Thereby, since the supply amount of thermal energy is rapidly reduced, an increase in arc energy is suppressed. Therefore, even when the volume ratio of carbon dioxide is 5% or less and the amount of heat required for carbon dioxide separation during arc generation is reduced, the arc energy can be appropriately controlled. Thereby, as shown in FIG.3 (e), while an arc becomes difficult to spread, the arc length becomes short. Since the arc is difficult to spread, it is difficult for holes to be generated in the welded portion, and because the arc length is shortened, the droplets become small and stable short-circuiting in the molten pool reduces the wobbling of the weld bead. The

  As described above, according to this embodiment, the ratio of carbon dioxide in the shield gas can be reduced to suppress the generation of slag, and the arc length can be shortened by suppressing the spread of the arc. And good welding quality can be maintained.

  By suppressing the slag, the appearance of the welded portion can be improved without performing the work of scraping off the slag, and the electrodeposited coating can be applied to the welded portion, so that a part having high corrosion resistance can be obtained.

  In addition, the gas shielded arc welding method according to the present invention can be used not only at a welding site for automobile parts but also at a welding site such as an electric product.

  The above-described embodiment is merely an example in all respects and should not be interpreted in a limited manner. Further, all modifications and changes belonging to the equivalent scope of the claims are within the scope of the present invention.

  As described above, the gas shielded arc welding method according to the present invention can be used, for example, when welding automobile parts.

DESCRIPTION OF SYMBOLS 1 Gas shield arc welding apparatus 2 Robot 2a Arm 2b Robot welding torch 3 Robot control apparatus 4 Welding power supply apparatus 5 Gas cylinder 6 Welding wire supply apparatus 10 To-be-welded member 100 Arc W Welding wire

Claims (4)

In a gas shielded arc welding method of welding an object to be welded by generating an arc between a welding wire supplied in a shielding gas containing argon and carbon dioxide and the member to be welded,
After the short-circuit between the welding wire and the member to be welded, the time until the current value is increased until the first peak current value is reached to open the short-circuit is 0.005 seconds or less. Welding the member to be welded by supplying a welding current having a waveform in which the time for increasing the current value to a peak current value of 2 and then decreasing the current value to a predetermined current value is set to 0.005 seconds or less. A characteristic gas shielded arc welding method. In the gas shielded arc welding method according to claim 1,
A gas shielded arc welding method, wherein a volume ratio of carbon dioxide in a shielding gas containing argon and carbon dioxide is 5% or less. In the gas shielded arc welding method according to claim 1 or 2,
A gas shielded arc welding method, wherein the current value is increased to a second peak current value and then decreased to a base current value. In the gas shielded arc welding method according to any one of claims 1 to 3,
A gas shielded arc welding method, wherein the second peak current value is maintained for a predetermined time.

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