A three-arc plasma-arc hybrid welding method

Abstract

The application discloses a three-arc plasma-arc hybrid welding method, which comprises the following steps: S1, igniting a first arc between a melting electrode welding wire and a workpiece; S2, a first plasma gas flows through an inner channel between a conductive nozzle and an inner plasma nozzle, and a second plasma gas flows through an outer channel between the inner plasma nozzle and an outer plasma nozzle; S3, igniting a third arc between the outer plasma nozzle and the workpiece; S4, igniting a second arc between the inner plasma nozzle and the workpiece; and S5, forming a liquid metal pool on the surface of the workpiece under the joint action of the first arc, the second arc and the third arc. The application adds an additional non-melting electrode arc outside, and can work under a large current without burning the electrode; the hybrid arc has stronger penetration capacity and faster welding speed; the welding seam obtained by the application has high forming quality, low porosity and lower requirement for a welding gap.

Description

Technical Field

[0001] This invention relates to the field of welding, and in particular to a plasma-arc composite welding method with three electric arcs. Background Technology

[0002] US Patent No. 3818175: Welding Torch. Inventors: W.G. G. Jelmorini, USPhilips Corporation (New York, NY); International Patent Classification: B23K9 / 00; 18.06.1974] discloses a welding torch comprising a housing, a copper contact tube placed along the torch axis, and a welding wire passing through the torch axis. A tungsten electrode is placed on the side of the copper contact tube, and the welding wire passes through a copper nozzle and is agitated by an inert gas flow. A consumable electrode arc burns between the welding wire tip and the workpiece, and a non-consumable electrode arc also burns between the tungsten electrode and the workpiece. A drawback of this design is that the positive polarity of the non-consumable electrode arc and the opposite polarity of the consumable electrode arc interfere with each other; when welding aluminum and magnesium alloys, the non-consumable electrode arc has poor destructive effect on the surface oxide layer.

[0003] The closest in technical essence to the aforementioned patent is a welding torch for plasma-MIG welding ② [European Patent No. 0168810: A welding torch for plasma-MIG welding. Inventors: Hans-Herbert Wilhelm, Suddeutsche Kuhlerfabrik Julius Fr.Behr GmbH&Co.KG. (Stuttgart, DE); International Patent Classification: B23K28 / 00; 22.01.1986], which serves as a prototype method. In this method, the welding torch comprises a copper contact tube located inside a DC reverse-polarized plasma electrode (anode), through which the consumable electrode welding wire passes. A non-consumable electrode arc originates from the plasma electrode and reaches the workpiece. It passes through a copper nozzle and is compressed by an inert gas flow. In this case, the compressed arc of the non-consumable electrode overlaps the arc of the consumable electrode. Both the non-fusible electrode compression arc and the fusible electrode arc burn under reverse polarity direct current (positive electrode). The focusing gas, plasma gas, and protective gas can be adjusted independently. Argon is used as both the focusing and protective gas; a mixture of argon with carbon dioxide or oxygen can also be used as the protective gas. The plasma anode has a beveled annular sealing ring. A disadvantage of this method is that the reverse polarity direct current used in the non-fusible electrode compression arc causes intense heating of the non-fusible electrode, which can easily lead to strong arc discharge and electrode damage under high current conditions.

[0004] In view of the shortcomings of existing technologies, it is necessary to improve the plasma-arc hybrid welding method. Summary of the Invention

[0005] The purpose of this invention is to solve the problems of existing plasma-arc composite welding torches being unable to operate under high current and the electrodes being easily burned out. This invention provides a three-arc plasma-arc composite welding method.

[0006] The technical solution adopted in this invention is:

[0007] A plasma-arc hybrid welding method with three electric arcs, the method comprising the following steps:

[0008] S1, ignite the first electric arc, i.e., the consumable electrode arc (MIG / GMAW), between the consumable electrode welding wire and the workpiece; the consumable electrode welding wire passes coaxially through the contact tip via the wire feeding device, and the contact tip is located on the central axis of the plasma welding gun;

[0009] S2, outside the conductive nozzle, is arranged in sequence from the inside to the outside, with a coaxial hollow inner plasma nozzle, an outer plasma nozzle and a protective nozzle. The first plasma gas flow passes through the inner channel between the conductive nozzle and the inner plasma nozzle, and the second plasma gas flow passes through the outer channel between the inner plasma nozzle and the outer plasma nozzle.

[0010] S3, ignite the second arc between the inner plasma nozzle and the outer plasma nozzle. Under the action of the first plasma gas flow, the second arc between the inner plasma nozzle and the workpiece is ignited, namely the internal plasma arc (PAW).

[0011] S4, under the action of the second plasma gas flow, ignites the third electric arc between the external plasma nozzle and the workpiece, namely the externally assisted non-consumable electrode electric arc.

[0012] S5, under the combined action of the first, second and third electric arcs, forms a liquid metal pool on the surface of the workpiece; the consumable electrode welding wire melts to form molten metal for welding, surfacing or additive manufacturing.

[0013] The method may further include step S6, in which protective gas passes through the protective gas channel between the outer plasma nozzle and the protective nozzle to protect the molten metal pool.

[0014] In this invention, the second electric arc heats the workpiece surface and compresses the first electric arc, increasing its energy density. The third electric arc heats the workpiece and compresses the second electric arc, replacing the function of a traditional compression nozzle; the third electric arc also ionizes the second plasma gas flow in the external channel, increasing the efficiency of the second electric arc.

[0015] Preferably, both the inner and outer plasma nozzles are non-melting electrodes, with the inner plasma nozzle recessed within the outer plasma nozzle, and the distance between the end faces of the two nozzles being 1.0–1.5 mm.

[0016] Preferably, the current value of the inner plasma nozzle is 1.5 to 2.0 times that of the outer plasma nozzle.

[0017] Preferably, the first and second plasma gas flows in the inner and outer channels are inert gases, namely argon, helium, or a mixture of both.

[0018] The gas flow rate of the second plasma gas stream is 4 to 6 times that of the first plasma gas stream.

[0019] The total gas flow rate of the first plasma gas flow and the second plasma gas flow is 3 to 9 L / min.

[0020] Preferably, the width of the outer channel, i.e. the gap width between the inner plasma nozzle and the outer plasma nozzle, is 1 / 10 of the diameter of the outer plasma nozzle. The inert gas passes through the inner channel to form a first plasma flow, and the inert gas passes through the outer channel to form a second plasma flow.

[0021] Preferably, the two non-fusible electrode arcs, namely the inner plasma nozzle and the outer plasma nozzle, are powered by two synchronous power supplies, which provide reverse polarity modulated DC power with a modulation frequency of 100-200Hz.

[0022] Preferably, the three electrodes of the first, second, and third arcs are all connected to a reverse polarity direct current. The effective energy of the first arc (fusible electrode arc) can be less than, equal to, or greater than the effective energy of the second arc (internal plasma arc), without any particular limitation. The effective energy of the third arc (externally assisted non-fusible electrode arc) is 0.5 to 0.75 times the effective energy of the second arc.

[0023] Preferably, the welding current supplied to the first electric arc (consumable electrode arc) is in the range of 50A-400A.

[0024] Preferably, the molten electrode welding wire is coaxially passed through the conductive nozzle by a wire feeding device and continuously fed along the central axis of the plasma welding gun at a speed of 2 to 20 m / min.

[0025] The diameter of the metal arc welding wire ranges from 0.8 to 3 mm.

[0026] Preferably, both the inner and outer plasma nozzles are made of copper-tungsten composite material containing 10-20% copper. This material is obtained by pressing and sintering tungsten powder into a porous sintered body, then contacting it with molten copper in hydrogen and heating it to 1200-1800°C.

[0027] Preferably, the protective gas in step S6 is argon, helium, or a mixture of both, or a mixture of argon and hydrogen, argon and oxygen, or argon and carbon dioxide, and the flow rate of the protective gas is 30-50 L / min.

[0028] Preferably, the distance between the end of the inner or outer plasma nozzle and the surface of the workpiece to be welded is 5 to 8 mm.

[0029] This invention combines three types of electric arcs, wherein the internal plasma arc is compressed by an additional external auxiliary third electric arc, and the heat of the external third electric arc is also introduced into the weld pool. Therefore, the composite arc has a stronger penetration capability, a faster welding speed, and reduces the porosity in the weld, improves the weld formation quality, and has lower requirements for welding gap during welding.

[0030] Compared with the prior art, the beneficial effects of this invention are: (1) The core of this invention is to add an auxiliary non-consumable electrode arc outside the consumable electrode arc and the inner plasma compression arc. The inner arc is compressed by the outer arc, resulting in higher energy density and the ability to work under high current without burning the electrode; (2) The composite arc of the three arcs has stronger penetration capability and faster welding speed; (3) The weld formation quality obtained by using this invention is high and the porosity is low; (4) The requirements for welding gap are lower when using this invention. Attached Figure Description

[0031] Figure 1 This is a schematic cross-sectional view of the equipment for a plasma-arc composite welding method with three electric arcs according to the present invention.

[0032] Figure 2 The images show the experimental equipment used in this invention, where a is the robotic arm, b is the plasma spray gun of this invention, and c is the control system.

[0033] Figure 3 The images show the appearance of joints welded with Q235 steel using different methods. Figure a shows the appearance of a joint welded with Q235 steel using the prototype method; Figure b shows the appearance of a joint welded with Q235 steel using the method of this invention.

[0034] Figure 4 The images show cross-sectional photos of joints welded from 1561 aluminum alloy using different methods. Figure a shows a cross-sectional photo of a joint welded from 1561 aluminum alloy using the prototype method, and Figure b shows a cross-sectional photo of a joint welded from 1561 aluminum alloy using the method of this invention.

[0035] Figure 1In the middle: 1. First arc, 2. Consumable electrode welding wire, 3. Workpiece, 4. Liquid metal pool, 5. Conductive nozzle, 6. Second arc, 7. Inner plasma nozzle, 8. Inner channel, 9. Outer plasma nozzle, 10. Outer channel, 11. Third arc, 12. Protective nozzle, 13. Protective gas channel. Detailed Implementation

[0036] The technical solution of the present invention will be further described below with reference to the accompanying drawings and specific embodiments, but the scope of protection of the present invention is not limited thereto.

[0037] To test the effectiveness of the proposed method, we used... Figure 1 and Figure 2 The experimental equipment shown verifies this method.

[0038] The method steps of the present invention are as follows:

[0039] S1, ignite the first electric arc 1, i.e., the consumable electrode arc (MIG / GMAW), between the consumable electrode welding wire 2 and the workpiece 3; the consumable electrode welding wire 2 passes coaxially through the conductive nozzle 5 via the wire feeding device, and the conductive nozzle 5 is located on the central axis of the plasma welding gun.

[0040] S2, the outer ring of the conductive nozzle 5 is provided with a coaxial hollow inner plasma nozzle 7, an outer plasma nozzle 9 and a protective nozzle 12 from the inside to the outside. The first plasma gas flow passes through the inner channel 8 between the conductive nozzle 5 and the inner plasma nozzle 7, and the second plasma gas flow passes through the outer channel 10 between the inner plasma nozzle 7 and the outer plasma nozzle 9.

[0041] S3, ignite the arc between the inner plasma nozzle 7 and the outer plasma nozzle 9, and under the action of the first plasma gas flow, ignite the second arc 6 between the inner plasma nozzle 7 and the workpiece 3, namely the internal plasma arc (PAW).

[0042] S4, under the action of the arc and the second plasma gas flow, the third electric arc 11 between the external plasma nozzle 9 and the workpiece 3 is ignited, namely the externally assisted non-consumable electrode electric arc.

[0043] S5, under the combined action of the first arc 1, the second arc 6 and the third arc 11, a liquid metal pool 4 is formed on the surface of the workpiece 3; the consumable electrode welding wire 2 melts to form molten metal for welding, surfacing or additive manufacturing.

[0044] S6, the protective gas passes through the protective gas channel 13 between the outer plasma nozzle 9 and the protective nozzle 12 to protect the liquid metal pool 4.

[0045] Photographs of the experimental equipment used in this invention are shown below. Figure 2 As shown, where Figure 2 'a' represents the robotic arm. Figure 2 b is the plasma spray gun of the present invention. Figure 2 c represents the control system.

[0046] The second electric arc 6 heats the surface of the workpiece 3 and compresses the first electric arc 1, increasing its energy density. The third electric arc 11 heats the workpiece 3 and compresses the second electric arc 6, replacing the function of the traditional compression nozzle; the third electric arc 11 also ionizes the second plasma gas flow in the external channel 10, increasing the efficiency of the second electric arc 6.

[0047] In this embodiment, both the inner plasma nozzle 7 and the outer plasma nozzle 9 are non-melting electrodes. The inner plasma nozzle 7 is recessed inside the outer plasma nozzle 9, and the distance between the end faces of the two nozzles is 1.0 to 1.5 mm.

[0048] Furthermore, the current value of the inner plasma nozzle 7 is 1.5 to 2.0 times that of the outer plasma nozzle 9.

[0049] Furthermore, both the first and second plasma gas streams are inert gases, namely argon, helium, or a mixture of both. The flow rate of the second plasma gas stream is 4 to 6 times that of the first plasma gas stream.

[0050] The total gas flow rate of the first plasma gas flow and the second plasma gas flow is 3 to 9 L / min.

[0051] Furthermore, the width of the outer channel 10, that is, the gap width between the inner plasma nozzle 7 and the outer plasma nozzle 9, is 1 / 10 of the diameter of the outer plasma nozzle 9. The inert gas passes through the inner channel 8 to form a first plasma flow, and the inert gas passes through the outer channel 10 to form a second plasma flow.

[0052] Furthermore, the two non-fusible electrode arcs, namely the inner plasma nozzle 7 and the outer plasma nozzle 9, are powered by two synchronous power supplies, which provide reverse polarity modulated DC power with a modulation frequency of 100-200Hz.

[0053] Furthermore, the three electrodes of the first arc 1, the second arc 6, and the third arc 11 are all connected to a reverse polarity direct current. The effective energy of the first arc (melting electrode arc) can be less than, equal to, or greater than the effective energy of the second arc (internal plasma arc), without any particular limitation. The effective energy of the third arc (externally assisted non-melting electrode arc) is 0.5 to 0.75 times the effective energy of the second arc.

[0054] Furthermore, the welding current provided to the first electric arc (consumable electrode arc) is in the range of 50A-400A, preferably 100-400A.

[0055] Furthermore, the current value of the internal plasma nozzle 7 is preferably 50 to 400 A, more preferably 100 to 200 A.

[0056] Furthermore, the molten electrode welding wire passes coaxially through the conductive tip via a wire feeding device and is continuously fed along the central axis of the plasma welding torch at a speed of 2 to 20 m / min, preferably at a wire feeding speed of 5 to 10 m / min.

[0057] The diameter of the metal arc welding wire ranges from 0.8 to 3 mm.

[0058] Furthermore, both the inner and outer plasma nozzles are made of copper-tungsten composite material containing 10-20% copper. This material is obtained by pressing and sintering tungsten powder into a porous sintered body, then contacting it with molten copper in hydrogen and heating it to 1200-1800°C.

[0059] The protective gas in step S6 is argon, helium, or a mixture of both, or a mixture of argon and hydrogen, argon and oxygen, or argon and carbon dioxide. The flow rate of the protective gas is 30-50 L / min.

[0060] The distance between the end of the internal or external plasma nozzle and the surface of the workpiece to be welded is 5 to 8 mm.

[0061] Butt welding experiments were conducted on Q235 steel (shielding gas: 82% Ar + 18% CO2) and 1561 aluminum alloy (shielding gas: Ar) using both the prototype method and this method. The shielding gas flow rate was approximately 30 L / min. The specimen dimensions were 100 × 50 × δ and 100 × 400 × δ mm, with specimen thicknesses δ of 4, 5, 8, and 10 mm, respectively. The prototype method is the one disclosed in European Patent No. 0168810, excluding the third arc.

[0062] The experimental parameters are shown in Table 1-3.

[0063] In Tables 1 to 3, the inert gas is argon. The inert gas passes through the inner channel 8 to form the first plasma flow, and the inert gas passes through the outer channel 10 to form the second plasma flow. The gas flow rate of the second plasma flow is 5 times that of the first plasma flow.

[0064] Table 1. Process parameters for butt welding 1561 aluminum alloy (δ=5mm) under argon protection using the prototype method and this method.

[0065]

[0066] Note: MIG / GMAW and PAW processes can be implemented independently in both the prototype method and this method; they are used in experiments. ER5356 metal arc welding wire (mm).

[0067] Table 2. Process parameters for butt welding 1561 aluminum alloy (δ=8mm) under argon protection using the prototype method and this method.

[0068]

[0069] Note: Used in the experiment ER5356 metal arc welding wire.

[0070] Table 3. Process parameters for butt welding Q235 steel (δ=10mm) under 82% Ar + 18% CO2 protection using the prototype method and this method.

[0071]

[0072]

[0073] Note: Used in the experiment ER-70S metal arc welding wire.

[0074] Photos of the appearance of joints welded using different methods on Q235 steel are shown below. Figure 3 As shown, Figure a is a photograph of the appearance of a joint welded with Q235 steel using the prototype method; Figure b is a photograph of the appearance of a joint welded with Q235 steel using the method of the present invention.

[0075] Photographs of joint cross-sections of 1561 aluminum alloy welded using different methods are shown below. Figure 4 As shown, Figure a is a photograph of the joint cross-section of 1561 aluminum alloy welded using the prototype method, and Figure b is a photograph of the joint cross-section of 1561 aluminum alloy welded using the method of the present invention.

[0076] Figure 3 and Figure 4 The results show that the penetration depth of this method is increased by about 50% compared with the prototype method, and the porosity is reduced by 20-30%. Furthermore, the experimental results in Tables 1 and 3 show that this method can increase the welding speed by 20-25% compared with the prototype method.

[0077] This invention combines three types of electric arcs, wherein the internal plasma arc is compressed by an additional external auxiliary third electric arc, and the heat of the external third electric arc is also introduced into the weld pool. Therefore, the combined electric arc has a stronger penetration capability, a faster welding speed, reduces the porosity in the weld, and improves the weld formation quality.

Claims

1. A plasma-arc hybrid welding method with three electric arcs, characterized in that... The method includes the following steps: S1, ignite the first electric arc, i.e., the consumable electrode arc, between the consumable electrode welding wire and the workpiece; the consumable electrode welding wire passes coaxially through the conductive tip via the wire feeding device, and the conductive tip is located on the central axis of the plasma welding gun; S2, outside the conductive nozzle, is arranged in sequence from the inside to the outside, with a coaxial hollow inner plasma nozzle, an outer plasma nozzle and a protective nozzle. The first plasma gas flow passes through the inner channel between the conductive nozzle and the inner plasma nozzle, and the second plasma gas flow passes through the outer channel between the inner plasma nozzle and the outer plasma nozzle. S3, ignite the arc between the inner plasma nozzle and the outer plasma nozzle, and under the action of the first plasma gas flow, ignite the second arc between the inner plasma nozzle and the workpiece, namely the inner plasma arc. S4, under the action of the second plasma gas flow, ignites the third electric arc between the external plasma nozzle and the workpiece, namely the externally assisted non-consumable electrode electric arc. S5, under the combined action of the first, second and third electric arcs, forms a liquid metal pool on the surface of the workpiece; the consumable electrode welding wire melts to form molten metal for welding, surfacing or additive manufacturing.

2. The method as described in claim 1, characterized in that... The method further includes step S6, in which protective gas passes through the protective gas channel between the outer plasma nozzle and the protective nozzle to protect the molten metal pool.

3. The method as described in claim 1, characterized in that... The second electric arc both heats the surface of the workpiece and compresses the first electric arc, increasing its energy density; The third electric arc not only heats the workpiece and compresses the second electric arc, but also ionizes the second plasma gas flow in the external channel, increasing the efficiency of the second electric arc.

4. The method as described in claim 1, characterized in that... Both the inner and outer plasma nozzles are non-melting electrodes. The inner plasma nozzle is recessed inside the outer plasma nozzle, and the distance between the end faces of the two nozzles is 1.0 to 1.5 mm.

5. The method as described in claim 1, characterized in that... The current value of the inner plasma nozzle is 1.5 to 2.0 times that of the outer plasma nozzle.

6. The method as described in claim 1, characterized in that... The first and second plasma gas flows in the inner and outer channels are inert gases, namely argon, helium, or a mixture of both; the gas flow rate of the second plasma gas flow is 4 to 6 times that of the first plasma gas flow.

7. The method as described in claim 6, characterized in that... The width of the outer channel is 1 / 10 of the diameter of the outer plasma nozzle. Inert gas passes through the inner channel to form a first plasma flow, and inert gas passes through the outer channel to form a second plasma flow.

8. The method as described in claim 1, characterized in that... The inner and outer plasma nozzles are powered by two synchronous power supplies, which provide reverse polarity modulated DC power with a modulation frequency of 100-200Hz.

9. The method as described in claim 1, characterized in that... The three electrodes of the first, second, and third electric arcs are all connected to a reverse polarity direct current, wherein the effective energy of the third electric arc is 0.5 to 0.75 times that of the second electric arc.

10. The method as described in claim 1, characterized in that... The welding current range for the first electric arc is 50A to 400A.

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