CN114247962A

CN114247962A - Multi-electrode time-sharing conduction and polarity-changing alternating arc welding and material adding method

Info

Publication number: CN114247962A
Application number: CN202111557788.2A
Authority: CN
Inventors: 闫朝阳; 胡青松; 陈树君; 郭凯伟
Original assignee: Beijing University of Technology
Current assignee: Beijing University of Technology
Priority date: 2021-12-16
Filing date: 2021-12-16
Publication date: 2022-03-29
Anticipated expiration: 2041-12-16
Also published as: CN114247962B

Abstract

A multi-electrode time-sharing conduction polarity-variable alternating arc welding and material additive method belongs to the field of welding methods and arc fuse material additives. A time-sharing conducting device with two conducting channels of a power supply is established, wherein one electrode of the power supply is connected to a welding gun, the other electrode is divided into two paths and is respectively connected to a welding wire and a workpiece, a diode, preferably a large-capacity diode with relatively large capacity, is respectively connected in series with the wiring of the welding wire and the workpiece, the directions of the two diodes are opposite, and the power supply is a power supply with variable polarity and periodic alternation; by utilizing the characteristic of instantaneous electrode conversion, time-sharing conduction electric arcs are established, and heat transfer, force transfer and mass transfer of the electric arcs are decoupled by utilizing alternate electric arcs, so that the welding and material increase quality is improved.

Description

Multi-electrode time-sharing conduction and polarity-changing alternating arc welding and material adding method

Technical Field

The invention relates to a multi-electrode time-sharing conduction polarity-variable alternating arc welding and material increasing method, and belongs to the field of welding methods and arc fuse material increasing.

Background

The additive manufacturing technology is a technology for generating a three-dimensional entity by continuously increasing materials layer by layer, and can manufacture a large-scale metal integral structural part at one time without processes such as forming, welding, assembling and the like. Metal additive manufacturing techniques can be classified into lasers, electron beams, and arcs according to the type of heat source. The arc fuse wire additive manufacturing technology takes an arc as a heat source, adopts a layer-by-layer surfacing mode to manufacture a metal solid component, is high in forming speed, is developed mainly based on TIG (tungsten inert gas), MIG (metal-inert gas), SAW (surface acoustic wave) and other welding technologies, and the formed component is formed by a full weld joint, is uniform in chemical composition and high in density, and has the advantages of high strength, good toughness and the like compared with an integral forged component.

However, most of the existing arc fuse additive manufacturing technologies are simply transplanted from arc surfacing to additive manufacturing, and a 3D entity is formed by layer-by-layer accumulation in a mode that high-temperature liquid metal droplets continuously and smoothly transit to the surface of a formed piece. Along with the increase of the number of layers of overlaying welding, the heat accumulation of a formed part is increased, the heat dissipation condition is worsened, so that the solidification time of a molten pool is increased, the shape of the molten pool is difficult to control, and particularly, the shape and the forming size of the end part are difficult to control due to the existence of a liquid molten pool at the end part of a part. In addition, the manufacturing process of the arc fuse additive of the metal material has the defects of low geometric precision, rough surface and the like, secondary machining is often needed, and for the machining of complex components, the inner walls interfere with each other and cannot be operated. The reason for this is that the traditional welding heat source can not realize the decoupling of heat transfer, mass transfer and force transfer for the free combination of heat and mass transfer. The heat diffusion form of welding and additive process gradually changes from heat conduction to the substrate to heat convection and heat radiation to the surrounding air, resulting in difficulty in controlling the stability of the molten pool, so that the stacking forming precision is difficult to guarantee in the additive process.

Therefore, the traditional concept that the rapid forming of metal parts is increased and not reduced is abandoned, a novel heat source is developed, and the material increase is realized in the manufacturing process

In the current industrial production, welding technology has become an important material processing technology. In a traditional welding heat source, the heat and mass transfer of electric arcs has deep coupling, when multilayer repeated welding is carried out, more welding wire materials are needed for filling, layer-by-layer welding action is carried out, when mass transfer meets the welding requirement, overhigh heat input can be caused, the welding quality is lower, and the welding stress and the welding thermal deformation are increased. The reason for this is that conventional welding heat sources cannot achieve decoupling of heat transfer, mass transfer and force transfer for free combination of heat and mass transfer. The heat diffusion form of the welding and additive process gradually changes from heat conduction to the substrate to heat convection and radiation to the surrounding air, resulting in difficulty in controlling the weld pool stability.

In recent years, inherent constraints of a traditional heat source in the aspects of heat transfer, mass transfer and force transfer are overcome by the multi-electrode coupling electric arc, and the heteroarmy projection is realized. The multi-electrode electric arc can be divided into three types according to coupling carriers, the multi-electrode electric arc taking a molten pool as a carrier adjusts the heat output of a heat source to a certain degree, but does not decouple the heat and mass fundamentally; the multi-electrode electric arc with the welding gun as a carrier can effectively change the inherent collocation of a heat source in heat input, mass filling and molten pool stress, but has difficulty in active control; the multi-electrode electric arc using the electric arc as a carrier can realize the decoupling of thermal mass, but a polar region effect and an arc winding action exist, and the stability is influenced.

The invention provides a method for alternating arc welding and material addition by multi-electrode time-sharing conduction and polarity-changing on the basis of research at home and abroad, which breaks through the traditional concept that electric arc is a strong and durable discharge phenomenon between two electrodes. Electric arcs are alternately generated in the three electrodes through polarity-changing current polarity conversion and diode cutoff action, heat generated by the anode is mainly used for melting wires at the stage of the anode of the wires and the cathode of the tungsten electrode, and electric arc plasma heats a base material, so that the heat required by the base material is met and the cladding rate is increased; by utilizing the characteristic of cathode cleaning, the tungsten electrode anode-substrate cathode in the stage is used for smashing an oxide film on the periphery of the substrate molten pool by utilizing cathode spots to release hydrogen substances, so that the probability of generating air holes when the molten pool is solidified is reduced. The method and the device can meet the deep decoupling control of the thermal mass force of the electric arc, can realize the low-momentum mass transfer of the wire material and the dynamic infiltration solidification of the weak constraint molten pool, and provide an ideal heat source for the high-quality welding and material increase of the aluminum alloy.

Disclosure of Invention

The invention relates to a device for establishing a multi-electrode time-sharing conduction variable-polarity alternating arc, which aims to provide a high-efficiency and high-quality welding and material increase method with independently controllable heat and mass. Breaking through the traditional concept that 'electric arc is a strong and lasting discharge phenomenon between two electrodes', decoupling heat and mass transmission control of the electric arc, developing a set of welding and material increasing methods with heat and mass active control and coordination to adapt to the change of heat dissipation conditions of a deposition layer and the increase of heat accumulation effect, and determining interactive solidification cooperative control parameters of molten drops and a molten pool to realize active control of the morphology of the deposition layer.

The method takes multi-electrode time-sharing conduction polarity-changing alternating arcs as research objects to mutually disassemble a tungsten electrode and a wire arc and a tungsten electrode and a base material arc so as to decouple heat source thermal mass transmission, realizes the active control of molten drop quantitative distribution and weak momentum transition by utilizing the corresponding characteristics of an arc electrode area, and realizes the self-stabilization and self-adaptive control of welding and fuse additive manufacturing on the basis of no need of external sensing, thereby making up the constraint of the traditional heat source thermal depth coupling.

In order to achieve the purpose, the invention adopts the following technical scheme:

in the welding and material adding method of the multi-electrode time-sharing conduction variable-polarity alternating arc, a time-sharing conducting device with two conducting channels of a power supply is established, wherein one electrode of the power supply is connected to a welding gun, the other electrode is divided into two paths and is respectively connected to a welding wire and a workpiece, a diode, preferably a relatively large-capacity diode, is respectively connected in series to the wiring of the welding wire and the workpiece, and the directions of the two diodes are opposite, as shown in figure 1. The power supply is a power supply with variable polarity and periodic alternation; by utilizing the characteristic of instantaneous electrode conversion, time-sharing conduction electric arcs are established, and heat transfer, force transfer and mass transfer of the electric arcs are decoupled by utilizing alternate electric arcs, so that the welding and material increase quality is improved.

In the period of changing polarity of the welding power supply, due to the cut-off action of the diode, the welding gun can only be burnt with one electrode of the welding wire or the workpiece at the same time; when the DCEN direct current is reversely connected, the current cannot pass through the workpiece under the action of the diode, and the current is forced to be conducted between the welding gun and the welding wire at the moment, as shown in (III) in fig. 2, the welding gun is a negative electrode at the moment, and the welding wire is a positive electrode; when the DCEP direct current is connected in the positive direction, the current cannot pass through the welding wire due to the action of the diode, and the current is forced to be conducted between the welding gun and the workpiece, as shown in (two) in fig. 2, the welding gun is the positive electrode, and the welding wire is the negative electrode; thus, during one period of varying polarity, the two arcs are alternately ignited to form alternating arcs of varying polarity, as shown in fig. 2 (one).

The electric arc quantitative fixed-point heating of the wire is realized by controlling the pulse amplitude, the pulse frequency and the polarity duty ratio of the variable polarity current corresponding to the power supply, and the tungsten electrode and the wire electric arc and the tungsten electrode and the base material electric arc are mutually disassembled to decouple the heat source heat mass force transmission.

The variable polarity current controls the current pulse amplitude, pulse frequency and polarity duty cycle through the current controller. When the power current is transmitted normally, the base material becomes a cathode, and the tungsten electrode becomes an anode; when the power current changes polarity, the tungsten electrode becomes the cathode and the wire becomes the anode. The alternating generation of the arc is realized. The method utilizes the rapid melting of the wire material when the tungsten electrode is the cathode during the heat generating efficiency of the anode, and the active impact of the electric arc when the tungsten electrode is switched to the anode of the substrate cathode to realize the weak momentum transition of molten drops. And the active control of the size and the temperature of the molten drop is realized by utilizing the heating of wire materials and the adjustment of the time sequence of molten drop impact.

In the stage of wire anode-tungsten electrode cathode, heat generated by the anode is mainly used for melting the wire, the electric arc plasma heats the base material, the heat required by the base material is met, the cladding rate is increased, and electric arc thermal decoupling and weak restraint of a molten pool are realized.

In the tungsten electrode anode-substrate cathode stage, cathode spots are used for cleaning and smashing an oxide film on the periphery of the substrate molten pool, hydrogen substances are released, the probability of generation of air holes during molten pool solidification is reduced, and meanwhile, wire material weak momentum mass transfer and molten pool dynamic infiltration solidification are realized.

The invention can obtain the following beneficial effects:

the method for multi-electrode time-sharing conduction and polarity-variable alternating arc welding and material addition breaks through the traditional concept that electric arc is a phenomenon of strong and durable discharge between two electrodes by establishing a power supply and a three-electrode time-sharing conduction device, the alternating electric arc is generated between the three electrodes, and the characteristic that the electric arc can be separated is utilized to ensure that at the stage of wire anode-tungsten electrode cathode, the heat generated by the anode is mainly used for melting wire materials, the electric arc plasma heats the base material, the heat required by the base material is satisfied, and the thermal decoupling and weak restraint molten pool of the electric arc are realized while the cladding rate is increased; by utilizing the characteristic of cathode cleaning, at the stage of tungsten electrode anode-substrate cathode, the cathode spot is used for cleaning and smashing an oxide film on the periphery of a substrate molten pool, hydrogen substances are released, the probability of air hole generation during molten pool solidification is reduced, and meanwhile, the weak momentum mass transfer of wire materials and the dynamic infiltration solidification of the molten pool are realized. Based on the method, the deep decoupling control of the multi-electrode time-sharing conduction alternating arc heat source on wire melting, droplet transition, cathode cleaning, weak restraint molten pool and solidification is realized, and an ideal heat source is provided for high-quality welding and material increase of aluminum alloy.

Drawings

FIG. 1 is a schematic diagram of an apparatus for implementing a multi-electrode time-sharing conduction polarity-changing alternating arc welding and additive method.

FIG. 2 is a schematic diagram of current conduction of multi-electrode time-sharing conduction alternating-polarity arc welding and additive material.

Fig. 3 is a schematic diagram of a multi-electrode time-sharing conduction polarity-variable alternating arc welding and additive manufacturing method according to an embodiment of the invention.

In fig. 1: 1. the welding method comprises the following steps of polarity-changing welding power supply, 2, a cooling water tank, 3, a non-consumable electrode welding gun, 4, a workpiece to be welded, 5, a wire feeder, 6, a wire material, 7, shielding gas/ion gas, 8, shielding gas/ion gas, 9, a shielding gas meter/ion gas meter, 10, a shielding gas meter/ion gas meter, 11, an IGBT/large-capacity diode, 12, an IGBT/large-capacity diode, 13 and a tungsten electrode.

Detailed Description

The present invention will be described in detail with reference to examples, which are only preferred embodiments of the present invention and are not intended to limit the present invention.

Example 1

Firstly, before welding or material adding, performing surface treatment on a workpiece to be welded, polishing the workpiece one by using sand paper, removing an oxide film on the surface, cleaning the workpiece by using acetone, drying the workpiece in the air and fixing the workpiece on a welding tool;

keeping the welding gun perpendicular to the workpiece all the time in the welding or material adding process, enabling the welding wire to be located beside the welding gun and not to be in contact with the workpiece, and setting the geometric parameters as follows, wherein the distance from the welding gun to the welding wire is 2-4 mm; the welding gun is 5mm-8mm away from the workpiece.

Thirdly, welding or material increasing specific operation:

the embodiments of the present invention will be described in detail below, and the drawings are only illustrative and only represent the connection method of the method with respect to the electric circuit, and the gas and water connections necessary for the welding gun are conventional connections, and therefore, the description thereof will not be repeated. The method comprises non-consumable electrode welding guns such as plasma welding, TIG welding and the like.

The steps of the welding method are explained in detail below:

firstly, the work before welding is ready, the position of a non-consumable electrode welding gun (3) is adjusted to be vertical to a workpiece to be welded, and the posture is kept unchanged in the welding process. The wire feeder (5) is opened in advance before welding so that the wire (6) is fed to a preset position; before the ion gas (7) and the protective gas (8) are opened and the cooling water tank (2), the correct connection of a welding gun and other necessary gas and water paths is ensured. And opening the ion gas meter (9) and the protective gas meter (10), and connecting various switches of the welding system according to requirements. Adjusting parameters of a welding power supply, setting pulse amplitude, frequency and polarity duty ratio of the variable polarity current, and outputting preset current parameters to the welding gun. According to the requirement of the multi-electrode time-sharing conduction polarity-variable alternating arc welding method, a direct-current maintaining arc is started in advance through high frequency, after the maintaining arc is stable, a direct-current main arc is started, and finally a polarity-variable main arc is started to perform welding material increase.

When the polarity of the polarity-changing current is switched, only one arc is forced to be formed in the three electrodes through the cut-off action of the IGBT or the large-capacity diode. In the DCEN stage, the tungsten electrode (13) is conducted with the wire material (6) to form a wire material anode-tungsten electrode cathode arc, anode heat generation is mainly used for melting the wire material in the DCEN stage, and the arc plasma heats the base material, so that the heat required by the base material is met and the cladding rate is increased. Then, when the current polarity is changed, namely in a DCEP stage, the tungsten electrode (13) is conducted with the substrate (4) to form an arc of a tungsten electrode anode-substrate cathode, and in the stage, an oxide film at the periphery of a molten pool of the substrate is broken by using a cathode spot to release hydrogen substances, so that the probability of generating pores when the molten pool is solidified is reduced. The method and the device can meet the deep decoupling control of the thermal mass force of the electric arc, can realize the low-momentum mass transfer of the wire material and the dynamic infiltration solidification of the weak constraint molten pool, and provide an ideal heat source for the high-quality welding and material increase of the aluminum alloy.

The foregoing is a more detailed description of the invention in connection with specific embodiments thereof, and it is not intended that the invention be limited to the specific embodiments thereof. For those skilled in the art to which the present invention pertains, the frame configuration can be flexible and varied without departing from the concept of the present invention, and can be used to derive a series of products. But rather a number of simple derivations or substitutions are made which are to be considered as falling within the scope of the patent protection of the invention as defined by the claims as filed.

Claims

1. A multi-electrode time-sharing conduction and polarity-changing alternating arc welding and material adding method is characterized in that a time-sharing conduction device with two conduction channels of a power supply is established, wherein one electrode of the power supply is connected to a welding gun, the other electrode is divided into two paths and is respectively connected to a welding wire and a workpiece, a diode, preferably a relatively large-capacity diode, is respectively connected in series to the connection wires of the welding wire and the workpiece, and the directions of the two diodes are opposite; the power supply is a power supply with variable polarity and periodic alternation; by utilizing the characteristic of instantaneous electrode conversion, time-sharing conduction electric arcs are established, and heat transfer, force transfer and mass transfer of the electric arcs are decoupled by utilizing alternate electric arcs, so that the welding and material increase quality is improved.

2. The method for multi-electrode time-sharing conduction polarity-variable alternating arc welding and material addition according to claim 1, wherein in the polarity-variable period of the welding power source, due to the cut-off action of the diode, the welding gun can only be burnt with one electrode of the welding wire or the workpiece at the same time; when DCEN direct current is reversely connected, current cannot pass through a workpiece under the action of a diode, the current is forced to be conducted between a welding gun and a welding wire, the welding gun is a negative electrode, and the welding wire is a positive electrode; when DCEP direct current is in direct connection, current cannot pass through a welding wire due to the action of a diode, the current is forced to be conducted between a welding gun and a workpiece, the welding gun is an anode, and the welding wire is a cathode; whereby during one period of alternating polarity the two arcs are alternately ignited to form alternating arcs of alternating polarity.

3. The method for multi-electrode time-sharing conduction variable-polarity alternating arc welding and material addition according to claim 1, wherein electric arc quantitative spot heating of the wire is realized by controlling the pulse amplitude, the pulse frequency and the polarity duty ratio of the variable-polarity current corresponding to a power supply, and a tungsten electrode and a wire electric arc and a tungsten electrode and a base material electric arc are mutually disassembled to decouple heat source thermal mass transmission.

4. The method for multi-electrode time-sharing conduction variable polarity alternate arc welding and material adding according to claim 1, wherein the variable polarity current is controlled by a current controller for current pulse amplitude, pulse frequency and polarity duty cycle; when the power current is transmitted normally, the base material becomes a cathode, and the tungsten electrode becomes an anode; when the polarity of the power current is changed, the tungsten electrode becomes a cathode, and the wire becomes an anode; the alternating generation of the electric arc is realized; the method comprises the steps of utilizing the rapid melting of wires when a tungsten electrode is a cathode during the heat production efficiency of the anode, and realizing the weak momentum transition of molten drops through the active impact of electric arcs when the tungsten electrode is switched to a substrate cathode and the tungsten electrode anode; and the active control of the size and the temperature of the molten drop is realized by utilizing the heating of wire materials and the adjustment of the time sequence of molten drop impact.

5. The method for multi-electrode time-sharing conduction polarity-variable alternating arc welding and material increase as claimed in claim 1, wherein in the stage of wire anode-tungsten electrode cathode, heat generated by the anode is mainly used for melting the wire, and the electric arc plasma heats the substrate, so that the required heat of the substrate is satisfied while the cladding rate is increased, and electric arc thermal decoupling and weak confinement molten pool are realized;

in the tungsten electrode anode-substrate cathode stage, cathode spots are used for cleaning and smashing an oxide film on the periphery of a substrate molten pool, hydrogen substances are released, the probability of generation of air holes during solidification of the molten pool is reduced, and meanwhile, weak momentum mass transfer of wires and dynamic infiltration solidification of the molten pool are realized.