JP3867164B2 - Welding method - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The invention of this application relates to a welding method. More specifically, in the invention of this application, welding is possible even with a super groove having a groove width of 10 mm or less, which could not be constructed due to arc instability in the prior art. The present invention relates to a new consumable electrode type arc welding method capable of freely controlling the arc heat density distribution.
[0002]
[Prior art and its problems]
Conventionally, in the welding of machine parts and structural materials, gas shielded arc welding (GMA), submerged arc welding (SAW), electrogas arc, from the viewpoint of preventing welding deformation and reducing heat input during welding. Known are the welding method (EGW), the covered arc welding method (MMAW), the self-shielded arc welding method (FCAW), etc., and a groove width of about 10 to 12 mm by the GMA method using these methods. A narrow groove welding method (narrow gap welding method / NGW) is also known.
[0003]
Among them, MIG welding methods such as CO ₂ , Ar—He, Ar—O ₂ , and Ar—CO ₂ shield, MAG welding methods, and SAW welding methods are representative.
In the method of narrow groove welding by consumable electrode arc welding, for example, as shown in FIG. 6, a DC or AC welding power source (1) is connected to a feeding welding wire (3) of a welding torch (2). A welding arc (5) is generated from the welding wire (3), and the workpiece (narrow groove joint) (4) is welded by the weld metal (6).
[0004]
However, this conventional consumable electrode arc welding method has a problem that welding is impossible when the groove gap is 10 mm or less. Securing of arc heat in the weld joint groove was not ensured, and the problem of poor welding efficiency was inevitable.
In addition, the conventional method is liable to cause deterioration of metallographic characteristics and melt deformation at the welded joint due to the concentration of arc heat, so that the distribution of arc heat on the groove surface should be controlled. It was.
[0005]
Therefore, in the consumable electrode type arc welding method, it is possible to reliably secure arc heat in the weld joint groove, perform stable and efficient welding, and freely control the concentration and dispersion of arc heat. Development of a welding method that can be performed has been an issue.
Under such circumstances, a method has been adopted in which arc heat is mechanically oscillated (vibrated) to ensure arc heat. For example, in a method known as the BHK system, an arc is oscillated by giving a wave-like bending crease continuously in the groove width direction. In the TWIST-ARC method, the arc is rotated by two twisted welding wires. In the bent welding wire method, the welding wire is bent by a welding wire bending gear to oscillate the arc.
[0006]
However, in such a conventional mechanical oscillation method, a device for oscillating the arc is required separately, and the actual solution is not a fundamental solution for securing the arc heat.
A completely different method from the mechanical oscillation method has also been proposed. In the narrow groove welding method disclosed in Japanese Patent Application Laid-Open No. 47-16357, when the welding current is generally increased, the pole of the arc moves from the tip of the welding wire along the surface of the welding wire. There is a case where it reaches the tip of the power supply fitting of the welding torch, etc., and there is a problem that the arc heat in the weld joint groove cannot be ensured reliably and the tip of the welding torch is also melted. Therefore, when conducting a gas shield consumable electrode arc welding (narrow groove MIG welding method) by inserting a welding torch into the abutting weld groove gap of the work piece, DC positive polarity with the welding wire as the negative electrode It is proposed that welding with a high current with a positive direct current polarity is prevented by periodically lowering the welding current to a low welding current to prevent arcing.
[0007]
However, since there is no theoretical background in this method, it depends on the operator's feeling and experience, and in fact, arc heat control such as concentration and dispersion of arc heat cannot be performed. It was.
Actually, even in this method, when the gap of the narrow groove is 10 mm or less, there is a problem that an arc is generated on the surface of the base material and the inside of the groove cannot be melted.
[0008]
Also in this method, the weldability of the structure preservation type that does not impair the properties of the material to be welded (base material) is not sufficient, and the problems of shape deformation and residual stress caused by welding have not been solved.
Therefore, the invention of this application has been made to eliminate the above-described drawbacks of the prior art, and does not require mechanical oscillation, and even if the gap of the narrow groove is 10 mm or less, the mother An object is to provide a new consumable electrode type arc welding method that enables stable and efficient welding by freely controlling the distribution and concentration of arc heat on the groove surface of the material. Yes.
[0009]
[Means for Solving the Problems]
In order to solve the above problems, the invention of this application increases or decreases the melting speed of the welding wire relative to the feeding speed of the welding wire by changing the arc current characteristics, and the arc at the melting end of the welding wire. Welding is characterized in that the generation position can be changed by swinging up and down without stopping the tip of the welding wire at one point within the groove, enabling control of the arc heat distribution on the groove surface of the material to be welded. Provide a method.
The invention of this application provides the above-described welding method for welding a very narrow groove having a groove width of 10 mm or less.
[0010]
In other words, the invention of this application is based on the groove surface of the material to be welded in order to enable stable and efficient welding obtained from detailed investigations by the inventors and structure-preserving welding without deterioration. It is indispensable to obtain the optimum arc heat distribution of the welding wire, and for that purpose, the melting rate of the welding wire is determined based on the behavior range of the arc pole (arc current conduction point), that is, the arc current conduction region and its moving speed. As for the knowledge that it is important to control in relation to the arc, and more specifically, regarding the position of the wire end related to the arc pole, the vertical amplitude width of the welding wire end is basically the frequency of the fluctuation current waveform. Depends on the ratio of the maximum current and the minimum current of the current waveform, and furthermore, the movement speed of the welding wire end is completed based on the knowledge that it strongly depends on the current change with time (current waveform gradient) There.
[0011]
In other words, in order to obtain the optimal arc heat distribution on the groove surface of the base metal, the welding wire melting rate is changed relative to the welding wire feed rate, and the arc current characteristics are changed as described above. As described above, there is a great feature in controlling the behavior range of the arc pole point, that is, the arc current conduction region, and the moving speed thereof without adding mechanical oscillation as in the conventional method.
[0012]
This is also based on a new idea by the inventor using the heat conduction theory from the viewpoint of controlling the heat affected zone (HAZ) region width in arc welding. More specifically, in the quasi-steady state of the moving line heat source (r = 0), the position where the highest temperature reaches the melting point (Tf) (rf: melting width) and the position where it becomes Acl (Tm) (rm: heat source) If the welding speed is high to some extent, this ratio is a constant determined only by the material property value.
[0013]
For example, the value of rm / rf for steel is about 2. This result means that the HAZ width (rm-rf) and the weld width (rf) are substantially equal, and it is shown that narrowing the melt width as much as possible leads to narrowing of the HAZ. In other words, in arc welding where the penetration depth is not as narrow as in electron beam or laser beam welding, welding a tight butt joint is not an optimal technique for narrowing the HAZ width. It is effective to use a joint having a tip gap, disperse the arc heat distribution on the groove wall, minimize the heat density there, and slightly weld the base metal.
[0014]
Therefore, by increasing or decreasing the welding wire melting speed relative to the constant welding wire feed speed, the welding wire melting end (arc generation principal point) enters the groove and is simultaneously swung in the plate thickness direction. The idea of trying was led.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
First, the basics of the present invention will be described with reference to FIG. In DC arc welding, as illustrated in FIG. 1, if the feeding speed of the welding wire is constant, when a large current flows through the welding wire, the welding wire melts and the end of the welding wire changes from A1 to A2. To rise.
[0016]
When the arc current is reduced after reaching A2, the amount of welding wire melted decreases and the end of the welding wire falls to A3.
The optimum value of A2 can be determined by the plate thickness and the number of welding passes. For example, in 2-pass welding with a plate thickness of 20 mm, A2 can be set to 10 to 15 mm. When the arc current is reduced after reaching A2, the amount of melting of the wire decreases and the wire width decreases to A3. In order to ensure penetration at the A3 point, the position of the A3 point is held. Thus, by moving the wire end to A1-A2-A3, the arc heat is dispersed by the poles of the arc, and the arc heat can be concentrated at the point A3. At this time, when the arc pole moves to A1-A2-A3, the melting region of the inner wall surface of the groove also moves to A1-A2-A3, and the arc heat can be dispersed on the inner surface of the groove. Similarly, a plate having a thickness of 70 mm can be welded.
[0017]
In the AC arc welding, as shown in FIG. 2, the wire end is at the A1 position when the welding wire has a small melting amount, and rises to the A2 position when the welding wire has a large melting amount. Thereafter, when the wire anode is made again, the wire end is lowered to A3. Similarly to the above, by moving the wire end to A1-A2-A3, the arc heat can be dispersed by the arc pole.
[0018]
Thereby, even narrow groove welding of 10 mm or less is possible. High-efficiency welding with a small number of layers can be realized as compared with the prior art. At the same time, the arc heat density can be greatly reduced, and thermal deformation can be suppressed. Further, stable backside welding can be performed by controlling the current waveform so as to increase the concentration of arc heat at the A3 position. Furthermore, depending on the weld joint shape, it is necessary to concentrate heat on the surface of the plate. In the method of the present invention, it is also possible to control the shape of the toe portion by concentrating heat on the surface while maintaining the position at A2 by appropriately selecting the current waveform in both direct current and alternating current. . Further, in a narrow groove joint, a mold crack may occur in the center of the bead. If there is a possibility that such a crack will occur, the amount of heat input can be increased in the vicinity of point A2.
[0019]
In the method of the present invention, various methods of consumable electrode arc welding are employed. Of these, MIG welding, MAG welding, and the like with a shield of Ar—He, Ar—O ₂ , Ar—CO ₂ , CO ₂ , etc. are suitable.
In addition, when using flux-cored welding wires, the flux component prevents welding defects by improving the wettability of the base metal groove wall and molten metal, and the arc heat density distribution is highly accurate by improving the controllability of the pole behavior. The range of oscillation during AC arc can be increased by improving the welding wire melting rate at the time of welding wire cathode, and the stability and controllability of the welding method of the present invention is further enhanced.
[0020]
Moreover, in this invention, since deformation is suppressed, it is possible to reduce the residual stress associated therewith.
In the present invention, it is also effective for a groove having a narrow groove width of 15 to 10 mm and a normal groove (U groove, V groove). In particular, the effect is very large in an extremely narrow groove having a groove width of 10 mm or less.
[0021]
There are no particular restrictions on the type of material to be welded that is the subject of this invention. Appropriate materials such as general steel, stainless steel, aluminum, heat resistant steel, and corrosion resistant steel may be used. The welding wire may be a general welding wire. Also, the GMA gas conditions may be MIG gas or MAG gas which are generally used.
Hereinafter, the present invention will be described in more detail with reference to examples.
[0022]
【Example】
Example 1
The current waveform was actually changed to measure how the welding wire end behaves. FIG. 3 shows the result when the voltage at high current is 0.2 seconds at 44 V and the voltage at low current is 0.3 seconds from 22 V to 25 V. The dotted line in the figure below shows the welding current at that time. In addition, the solid line indicates the wire tip position.
[0023]
Changing the voltage as shown in FIG. 3 increases the arc heat at the bottom of the groove to ensure melting and is applied to reverse wave welding.
On the other hand, FIG. 4 shows the result when the voltage at high current is changed from 50 V to sawtooth for 0.2 seconds, and the voltage at low current is set at 25 V for 0.3 seconds. The welding current at the time is shown, and the solid line shows the wire tip position.
[0024]
Changing the voltage as shown in FIG. 4 is applied when increasing the arc heat at the upper end of the swing to ensure melting and smoothing the bead shape of the toe.
Example 2
The voltage conditions in FIG. 3 of the first embodiment, that is, the voltage at the time of a large current is changed to 44 V, the voltage at the time of a small current is changed from 22 V to 25 V, and the frequency of the fluctuation current is changed to investigate the relationship of the wire vertical swing width. It was. The result was as shown in FIG. From this figure, it can be seen that when the frequency of the variable current is increased, the wire vertical swing width is reduced.
Example 3
DC arc GMA welding is performed under welding conditions of 0.06 second at 600A for large current, 0.3 second for 250A at small current, and 300A average arc current in a type I narrow groove with a groove width of 5mm and a plate thickness of 20mm. went. As a result, two layers of high-efficiency welding were possible with a penetration depth of 10 mm, a base material melted part piece width of 0.5 mm, and a heat-affected part piece width of 1 mm.
[0025]
Furthermore, in this method, high-efficiency welding was possible up to a plate thickness of 70 mm.
[0026]
【The invention's effect】
According to the present invention, it is possible to provide a welding system capable of freely controlling the distribution and concentration of arc heat on the groove surface of the base material.
Furthermore, in the present invention, since the heat density distribution in the groove can be freely controlled, the structure-preserving-type welding construction that does not impair the properties of the base material at the time of small heat input heat density distribution, or a groove that cannot be constructed conventionally. Ultra-narrow groove welding with a width of 10 mm or less and reverse wave welding such as V-shaped groove, melting area and heat affected zone at the time of welding can be minimized, so deformation, residual stress reduction and stress concentration control by toe shape control Reduction is also possible.
[Brief description of the drawings]
FIG. 1 is a schematic diagram showing a relationship between a welding wire position and a current during DC arc welding.
FIG. 2 is a schematic diagram showing a relationship between a welding wire position and current during AC arc welding.
FIG. 3 is a relational diagram showing a change in behavior of a wire end due to a change in a current waveform.
FIG. 4 is a relationship diagram showing a behavior change different from FIG. 3;
FIG. 5 is a relationship diagram showing the relationship between the frequency of the fluctuation current and the vertical swing width of the wire.
FIG. 6 is a schematic view showing a conventional welding apparatus.
[Explanation of symbols]
1 Welding power source 2 Welding torch 3 Welding wire 4 Work piece (narrow groove joint)
5 Welding arc 6 Weld metal

Claims (7)

The welding wire melting speed is increased or decreased relative to the welding wire feed speed by changing the arc current characteristics, and the arc generation position at the welding wire melting end is kept at one point within the groove. The welding method is characterized in that the arc heat distribution can be controlled on the groove face to be welded by changing it by swinging up and down . The welding method according to claim 1, wherein an extremely narrow groove having a groove width of 10 mm or less is welded. The welding method according to claim 1 or 2 , wherein DC arc welding is performed by changing an amount of current as arc current characteristics. The welding method according to claim 1 or 2 , wherein AC arc welding is performed by changing a wire polarity as an arc current characteristic. The welding method according to claim 1 or 2 , wherein arc welding is performed by changing a current waveform as an arc current characteristic . Either welding method of claims 1 to 5 perform groove welding. The welding method according to claim 1, wherein reverse wave welding is performed .

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