Dissimilar material welding method

Abstract

To provide a dissimilar material welding method that reduces spatter and smut to improve an appearance quality while achieving weight saving, and suppresses wear of an electrode and can perform efficient welding.SOLUTION: A dissimilar material welding method includes: an overlapping process in which a first component 11 comprising iron or steel and a second component 13 comprising aluminum or an aluminum alloy are overlapped; and a welding process in which an aluminum or aluminum alloy filler material 33 is molten and filled toward the second component 13 from an open hole 21 previously formed in the first component 11, whereby the first component 11 and the second component 13 are arc-spot welded. In the welding process, AC welding current is given with use of tungsten as an electrode 31 for generating an arc Ac, and after the start of welding, a ratio of a cathode time of the electrode 31 in one cycle of the welding current is so controlled as to be increased.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a dissimilar material welding method. [Background technology]

[0002] There has been a demand for improved safety for occupants in vehicles, and for this purpose, the strength of the vehicle body has been improved. On the other hand, against the background of the worsening of the global warming problem, the movement to improve the fuel efficiency of automobiles is accelerating. It is known that reducing the weight of the vehicle body is effective in improving fuel efficiency.

[0003] For example, in order to reduce weight by using aluminum material, a technique for joining a steel plate and an aluminum plate has been developed. A known technique for joining steel and aluminum materials is dissimilar metals arc spot welding (DASW), in which a through hole is formed in a steel plate in advance, the steel plate is placed on an aluminum plate, and molten aluminum material is filled into the through hole by MIG (Metal Inert Gas) welding using an aluminum welding wire to join the steel plate and aluminum plate.

[0004] However, the arc spot welding method using MIG welding is prone to producing spatter, in which molten droplets formed at the tip of the aluminum welding wire, which serves as a consumable electrode, fly out of the molten pool and adhere to the parts, and smut, in which the magnesium in the welding wire vaporizes, oxidizes, and solidifies, adhering to the base material like black soot.

[0005] In contrast, TIG (Tungsten Inert Gas) welding is generally considered to produce less spatter and smut. This is because a non-consumable tungsten electrode is used, and an arc is generated using inert argon gas, helium gas, or a mixture of these as a shielding gas, and an aluminum welding wire is inserted little by little into the arc to melt it, thereby suppressing evaporation of the wire. For this reason, TIG welding is often used for welding parts where appearance and quality are more important than cost, for example, in jet engines and nuclear power structures.

[0006] In TIG welding, if a tungsten electrode is used as the cathode (EN: Electrode Negative, negative rod), the arc concentrates directly under the electrode, resulting in a narrow and deep penetration. For this reason, TIG welding is usually performed using a tungsten electrode as the cathode.

[0007] In contrast, when a tungsten electrode is used as the anode (EP: Electrode Positive, rod positive) in TIG welding, a cleaning effect is obtained that removes the oxide film on the surface of the base material. The oxide film that covers the surface of aluminum base material has a higher melting point and specific gravity than aluminum itself, and if it is not removed before welding, the oxide remains in the molten pool and is likely to cause welding defects. For this reason, obtaining a cleaning effect by TIG welding with a tungsten electrode as the anode is effective for welding aluminum. However, since the cathode spot, which is the path of electricity formed on the base material, moves around violently on the surface of the base material, heat is not concentrated, resulting in a wide and shallow penetration, and the heat input to the tungsten electrode is large, making the electrode prone to wear, making it impractical.

[0008] Therefore, when welding to aluminum by TIG welding, it is preferable to use an AC welding current, which has the advantages of both using a tungsten electrode as the anode and using a tungsten electrode as the cathode.

[0009] Patent Document 1 discloses a TIG arc welding method for welding aluminum alloys by periodically switching the polarity of the welding current supplied between a non-consumable electrode and a workpiece. In this welding method, a positive polarity direct current is passed for 0.5 to 1.0 seconds at the end of welding to prevent burn-through due to heat concentration and crater cracking due to the arc force of the alternating current.

[0010] Furthermore, Patent Document 2 discloses a welding method for welding aluminum alloys by periodically switching the polarity of the welding current supplied between a non-consumable electrode and a workpiece, in which the penetration depth in thick aluminum alloy plates is increased by switching between an unbalanced square wave AC current and a pulse current in which the non-consumable electrode is only negative. [Prior art documents] [Patent documents]

[0011] [Patent Document 1] Patent No. 3158545 [Patent Document 2] Patent No. 3421014 Summary of the Invention [Problem to be solved by the invention]

[0012] However, as in Patent Documents 1 and 2, even when TIG welding is performed using AC welding current, the tungsten electrode is consumed significantly, and a part of the molten part at the tip of the tungsten electrode breaks off and scatters, and the tungsten, which is the main component of the electrode, may mix with the welded part and reduce the quality of the weld. In addition, when the tungsten electrode is consumed, the arc becomes unstable. For this reason, it is necessary to frequently grind the tungsten electrode, which leads to a decrease in efficiency and an increase in cost.

[0013] Furthermore, the welding methods of Patent Documents 1 and 2 are both techniques for line welding aluminum alloys, and it is difficult to apply them to dissimilar metal arc spot welding, in which a through hole is formed in a steel plate in advance, the steel plate is placed on an aluminum plate, and molten aluminum material is filled into the through hole to join the steel plate and the aluminum plate.

[0014] Therefore, an object of the present invention is to provide a dissimilar material welding method that can reduce weight, reduce spatter and smut to improve appearance quality, and suppress electrode wear to enable efficient welding. [Means for solving the problem]

[0015] The present invention comprises the following configurations. A dissimilar metal welding method for joining a first member made of iron or steel and a second member made of aluminum or an aluminum alloy, comprising: a superposing step of superposing the first member and the second member; a welding process for arc spot welding the first member and the second member by melting and filling a filler material of aluminum or an aluminum alloy from a through hole previously formed in the first member toward the second member; Including, In the welding process, an AC welding current is applied using tungsten as an electrode for generating an arc, and after the start of welding, the proportion of the cathode time of the electrode in one cycle of the welding current is controlled to be high. Dissimilar material welding methods. Effect of the Invention

[0016] According to the present invention, it is possible to reduce the weight, reduce spatter and smut to improve the appearance quality, and suppress electrode wear to perform efficient welding. [Brief description of the drawings]

[0017] [Figure 1] FIG. 1 is a cross-sectional view of a welded joint between a first member and a second member joined to each other. [Figure 2A] FIG. 2A is a cross-sectional view showing a state in which a first member and a second member are joined together. [Figure 2B] FIG. 2B is a cross-sectional view showing how the first member and the second member are joined together. [Figure 2C] FIG. 2C is a cross-sectional view showing how the first member and the second member are joined together. [Figure 2D] FIG. 2D is a cross-sectional view showing how the first member and the second member are joined together. [Diagram 3] FIG. 3 is a diagram showing a waveform of a welding current in the first embodiment. [Figure 4] FIG. 4 is a diagram showing a waveform of a welding current in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] Hereinafter, an embodiment of the present invention will be described in detail with reference to the drawings. (First embodiment) First, a dissimilar material welding method according to a first embodiment will be described. FIG. 1 is a cross-sectional view of a welded joint 15 between a first member 11 and a second member 13 that are joined to each other. 1, the dissimilar material welding method according to this embodiment is a method for welding a first member 11 and a second member 13. The first member 11 and the second member 13 are joined in a superposed state to form a welded joint 15. In this embodiment, the first member 11 and the second member 13 are joined by TIG welding.

[0019] The first member 11 is a metal plate made of iron or steel and formed into a flat plate shape. The second member 13 is a metal plate made of aluminum or an aluminum alloy and formed into a flat plate shape.

[0020] A through hole 21 is formed in advance in the first member 11. The through hole 21 is filled with a weld metal 23, and the first member 11 and the second member 13 are joined together by this weld metal 23.

[0021] The weld metal 23 is formed by melting and hardening a filler material by an arc, and is a metal made of aluminum or an aluminum alloy. The weld metal 23 is melted into the second member 13. The weld metal 23 has an excess portion 25 that protrudes from the through hole 21 in the first member 11 upward from the surface of the first member 11, and a peripheral portion 25a of the excess portion 25 extends outward from the periphery of the through hole 21.

[0022] In this way, in the welded joint 15, the first member 11 and the second member 13 are joined by a dissimilar metal arc spot welding method in which an aluminum or aluminum alloy filler material is melted and filled into the through hole 21 formed in the first member 11.

[0023] Next, a case where the first member 11 and the second member 13 are joined by TIG welding will be described. 2A to 2D are cross-sectional views showing how a first member 11 and a second member 13 are joined together.

[0024] (Layering process) As shown in FIG. 2A, the through hole 21 is formed in the first member 11 in advance, and the first member 11 and the second member 13 are overlapped with each other and placed in a welding device. The welding device includes an electrode 31, which is placed directly above the through hole 21. The electrode 31 is a non-consumable electrode made of tungsten or a tungsten alloy (containing 1% to 2% of thorium oxide, lanthanum oxide, cerium oxide, etc.). The welding device also includes a filler material supplying section 35 that supplies a filler material 33 made of aluminum or an aluminum alloy, and the tip of the filler material 33 is placed above the through hole 21. The welding device also includes a power supply device, which is capable of applying a welding current between the second member 13 as a base material and the electrode 31.

[0025] The power supply of the welding device can apply either AC or AC / DC welding current between the base material and the electrode 31. The AC frequency of the applied welding current can be as high as 500 Hz. When the AC frequency is high, the arc concentration is improved, and the penetration can be made deeper. The AC frequency of the welding current can be a high frequency exceeding 500 Hz.

[0026] (Welding process) 2B, the second member 13 is used as a base material, and a welding current is applied between the base material and an electrode 31 by a power supply device of a welding device, and an arc Ac is generated between the electrode 31 and the second member 13 serving as the base material. Note that an inert gas such as argon, helium, or a mixture thereof is used as a shielding gas when generating the arc Ac.

[0027] 2C, the filler material 33 is melted and welded by the generated arc Ac. In this manner, the second member 13 is melted by the arc Ac, and the molten weld metal 23 of the filler material 33 is filled into the through hole 21 of the first member 11 above the second member 13.

[0028] 2D, the weld metal 23 overflowing from the through hole 21 of the first member 11 extends outward beyond the periphery of the through hole 21. Then, by ending the welding, the molten weld metal 23 hardens. As a result, the first member 11 and the second member 13 are joined to each other by the weld metal 23 having an excess weld portion 25 that protrudes upward from the surface of the first member 11, forming a weld joint 15. Note that a back excess weld may be formed on the back side of the weld joint 15.

[0029] In the welding process, the electrode 31 is raised as the welding progresses, and welding is performed while maintaining an appropriate arc length. Also, the filler material 33 is fed by a filler material supply unit 35 as the welding progresses.

[0030] In this embodiment, in the above welding process, the welding current applied by the power supply device is controlled in accordance with each period. FIG. 3 is a diagram showing a waveform of a welding current in the first embodiment.

[0031] (1) Welding start period (T1 in Figure 3) At the start of welding (see FIG. 2B), an AC current is applied as the welding current. During this start of welding, the ratio of the cathode time of electrode 31 in one cycle of the welding current (Tn1 / (Tp1+Tn1)) is controlled so that a good cleaning effect is obtained when electrode 31 is the anode (EP) and good penetration is obtained by the concentration of arc Ac when electrode 31 is the cathode (EN).

[0032] (2) Intermediate welding period (T2 in Figure 3) During the intermediate welding period (see FIG. 2C), an AC current is also applied as the welding current. At this time, the ratio of the cathode time of electrode 31 in one cycle of the welding current (Tn2 / (Tp2+Tn2)) is controlled to be high.

[0033] Here, after the start of welding when the base metal has been cleaned, if the electrode 31 is used as an anode (EP), the electrode 31 will be worn out more than the cleaning effect obtained. Therefore, the ratio of the cathode time of the electrode 31 in one cycle of the welding current (Tn2 / (Tp2+Tn2)) is controlled to be high. This makes it possible to obtain good penetration by the concentration of the arc Ac while suppressing the wear of the electrode 31.

[0034] (3) Welding completion period (T3 in Figure 3) Even during the final welding period (see FIG. 2D), an AC current is applied as the welding current. At this time, the ratio of the cathode time of electrode 31 in one cycle of the welding current (Tn3 / (Tp3+Tn3)) is controlled to be even higher.

[0035] In this manner, by controlling the ratio of the cathode time of electrode 31 in one cycle of the welding current (Tn3 / (Tp3+Tn3)) to be even higher at the end of welding, it is possible to further reduce wear of electrode 31 while further increasing the penetration due to the concentration of arc Ac, thereby improving welding efficiency.

[0036] As described above, according to the dissimilar material welding method of the first embodiment, in the welding process, an AC welding current is applied to generate an arc Ac and perform welding. Therefore, while a good cleaning effect is obtained when the electrode 31 is an anode (EP), good penetration is obtained due to the concentration of the arc Ac when the electrode 31 is a cathode (EN).

[0037] In addition, after the start of welding when the base metal consisting of the second member 13 has been cleaned, by controlling so that the proportion of the cathode time of the electrode 31 in one cycle of the alternating current welding current is increased, it is possible to obtain good penetration by the concentration of the arc Ac while suppressing wear of the tungsten electrode 31.

[0038] This allows the aluminum or aluminum alloy filler material 33 to be melted and filled from the through hole 21 formed in advance in the first member 11 toward the second member 13, thereby smoothly welding the first member 11 and the second member 13 by dissimilar metal arc spot welding. Therefore, the weight of the structural material of the vehicle can be reduced by using aluminum material, and fuel efficiency can be improved.

[0039] Here, the cleaning action of making the electrode 31 an anode (EP) also has the effect of removing smut adhering to the base metal and the cleaning effect on the filler material 33. For this reason, instead of setting the ratio of the cathode (EN) in the electrode 31 to 100% immediately after removing the oxide film on the base metal, by gradually increasing the ratio of the cathode (EN) after the start of welding, the effect of removing smut adhering to the base metal and the cleaning effect on the filler material 33 can be obtained.

[0040] In the above welding process, the duration of each of the welding start period (T1), welding middle period (T2) and welding end period (T3) may be, for example, 0.5 seconds or less.

[0041] Second embodiment Next, a dissimilar material welding method according to a second embodiment will be described. The same components as those in the first embodiment are given the same reference numerals and the description thereof will be omitted. FIG. 4 is a diagram showing a waveform of a welding current in the second embodiment.

[0042] (1) Welding start period (T1 in Figure 4) In the welding start period (see FIG. 2B), an AC current is applied as the welding current, as in the first embodiment. In this welding start period, the ratio of the cathode time of electrode 31 in one cycle of the welding current (Tn1 / (Tp1+Tn1)) is controlled so as to obtain a good cleaning effect and good penetration.

[0043] (2) Intermediate welding period (T2 in Figure 4) During the intermediate welding period (see FIG. 2C), an AC current is applied as the welding current, as in the first embodiment. At this time, the ratio of the cathode time of electrode 31 in one cycle of the welding current (Tn2 / (Tp2+Tn2)) is controlled to be high.

[0044] As a result, after the start of welding when the base material has been cleaned, good penetration due to the concentration of the arc Ac can be obtained while suppressing wear of the electrode 31.

[0045] (3) Welding completion period (T3 in Figure 4) In the welding end period (see FIG. 2D), the welding current is controlled to be a direct current with the electrode 31 as the cathode (EN). The applied direct current welding current is a pulse current whose current value periodically changes.

[0046] In this manner, in the welding completion period, a direct current welding current is applied with the electrode 31 as the cathode (EN). In other words, by controlling the ratio of the cathode (EN) in the electrode 31 to 100% in the welding completion period, it is possible to further suppress wear of the electrode 31 while further increasing the penetration due to the concentration of the arc Ac, thereby improving the welding efficiency.

[0047] In the above embodiment, the through hole 21 formed in the first member 11 is not limited to a circular shape, and may be an elliptical or rectangular shape. When an elliptical or rectangular through hole 21 is formed, a short line weld is formed along the longitudinal direction of the through hole 21, and welding can be performed by swinging the electrode 31. The swinging of the electrode 31 may be repeated. Even when the through hole 21 is circular, welding may be performed by swinging the electrode 31.

[0048] The present invention is also applicable to plasma arc welding using a tungsten electrode 31, similar to TIG welding. It is also applicable to welding methods that can generate a more concentrated arc Ac to obtain deeper penetration, such as plasma jet TIG welding in which an inner gas is made to flow inside a nozzle to generate a high-velocity airflow, and constriction TIG welding using a constriction nozzle.

[0049] As such, the present invention is not limited to the above-described embodiments, and the present invention also contemplates mutual combinations of the various components of the embodiments, as well as modifications and applications by those skilled in the art based on the descriptions in the specification and well-known technologies, and these are included in the scope of protection sought.

[0050] As described above, the present specification discloses the following: (1) A dissimilar metal welding method for joining a first member made of iron or steel and a second member made of aluminum or an aluminum alloy, comprising: a superposing step of superposing the first member and the second member; a welding process for arc spot welding the first member and the second member by melting and filling a filler material of aluminum or an aluminum alloy from a through hole previously formed in the first member toward the second member; Including, a welding current supplying step for supplying an alternating current to the welding electrode using tungsten as an electrode for generating an arc; and controlling the proportion of the cathode time of the electrode in one cycle of the welding current to be high after the start of welding. According to this dissimilar material welding method, in the welding process, an AC welding current is applied to generate an arc and perform welding, so that when the electrode is an anode, a good cleaning effect is obtained, while when the electrode is a cathode, good penetration is obtained due to the concentration of the arc. In addition, after the start of welding when the base material has been cleaned, by controlling the proportion of the cathode time of the electrode in one cycle of the welding current to be high, it is possible to suppress wear of the tungsten electrode while obtaining good penetration due to the concentration of the arc. This allows the first and second members to be smoothly welded by dissimilar metal arc spot welding by melting and filling the aluminum or aluminum alloy filler material from the through hole previously formed in the first member toward the second member. Therefore, the weight of the structural material of the vehicle can be reduced by using aluminum material, and fuel efficiency can be improved.

[0051] (2) The dissimilar material welding method according to (1), wherein in the welding step, at a welding end stage, the welding current is controlled to be a direct current with the electrode as a cathode. According to this dissimilar material welding method, in the final stage of welding, it is possible to further reduce electrode wear while further increasing the penetration due to arc concentration, thereby improving welding efficiency.

[0052] (3) The dissimilar material welding method according to (2), wherein the welding current consisting of DC in the welding end period is a pulse current. According to this dissimilar material welding method, the wear of the electrodes can be further suppressed by applying a direct current welding current consisting of a pulse current. [Explanation of symbols]

[0053] 11 First member 13 Second member 21 Through hole 31 electrode 33 Filler material AC Arc EN cathode EP anode

Claims

1. A dissimilar metal welding method for joining a first member made of iron or steel and a second member made of aluminum or an aluminum alloy, comprising: a superposing step of superposing the first member and the second member; a welding process for arc spot welding the first member and the second member by melting and filling a filler material of aluminum or an aluminum alloy from a through hole previously formed in the first member toward the second member; Including, In the welding process, an AC welding current is applied using tungsten as an electrode for generating an arc, and after the start of welding, the proportion of the cathode time of the electrode in one cycle of the welding current is controlled to be high. Dissimilar material welding methods.

2. In the welding process, at a welding end period, a direct current is applied as the welding current with the electrode as a cathode. The dissimilar material welding method according to claim 1 .

3. The welding current consisting of a direct current at the end of the welding period is a pulse current. The dissimilar material welding method according to claim 2 .

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