RU2401726C2 - Method of welding in protective gas by infusible electrode and magnet-controlled arc - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to method of welding in protective gas by infusible electrode and magnet-controlled arc. Current is fed via conductor with its contacts moving over article surface on the side facing welding torch and in synchronism with it. During welding, points of current connection to article are intermittently and multiply changed, arc being deflected under action of its own magnetic field. Arc is held in every deflected position, while when its moves between its extreme positions, standby mode is set up. Operating and standby currents are controlled independently. Welding current is controlled on its flowing through each point of its feed to the article, while minimum current is set to be no less than: I=4.466·h-0.4·h²+0.0147·h³-0.225·10^-3·h⁴+1.236·10^-6·h⁵, where h is distance from current feed point to electrode axis, mm. Frequency of current switching between separate feed points may not exceed 4 Hz. Varying aforesaid distance from 0 to 100 mm allows varying angle of arc deflection from electrode axis. When current flows through every current feed point, current value may be constant in time or vary periodically in the form of pulses.

EFFECT: higher quality and stability of welded joint.

3 cl, 9 dwg, 1 ex

Description

The proposed method relates mainly to mechanical engineering and construction and can be used for welding units and parts of various metals and alloys.

A known method of welding by a magnetically controlled arc (USSR author's certificate No. 1581503, MKI (5) V23K 9/08, A.N. Sergeev, G.V. Osyankin, V.M. Burdykin, A.V. Klementyev, priority date 09/22/87 , publ. 30.07.90, Bull. No. 28), according to which during the welding process, the arc is moved across the seam by an external transverse magnetic field created using an electromagnetic system. The arc during welding is delayed in the extreme deflected position, on one of the edges to be welded, for a given period of time. When moving the arc from one extreme position to another, located on the other welded edge, set the standby mode of arc burning. When the arc reaches its extreme position, it is transferred to the welding mode, while the arc moves in the welding direction in the extreme deflected position. The magnitude of the welding current and the current of the arc on duty is controlled independently. The arc is held in an extreme deflected position by adjusting the magnetic field strength. To implement the method, a set of equipment is used, which includes, in addition to the welding power source itself, a separately placed electromagnetic system next to the torch, as well as a control signal generating unit, an amplifier and a multiplier. As follows from the description of the invention, the use of the method allows a wide range to change the shape of the melt, without changing the width of the seam, and also allows you to perform high-quality welds in hard to reach places. However, the use of this method is associated with the need to use additional complex equipment, which increases the complexity and cost of the necessary equipment. In addition, the effectiveness of the method for welding in hard-to-reach spots will either be very small, or additional expensive specialized equipment should be used to achieve high efficiency. When welding in inaccessible places, such as narrow cutting, the welding arc together with the torch are located below the surface level of the product. To ensure high efficiency, and most importantly stability, the impact of an external transverse magnetic field on the arc, the electromagnetic system should be located, in height, at the level of the arc. When welding in hard-to-reach spots (for example, as described in the description of the invention, when welding the butt of sheets with a thickness of 18 mm without cutting edges and a gap of 8 mm), to ensure the location of the electromagnetic system at the arc level is difficult to solve, expensive, and the resulting equipment will be highly specialized. The location of the magnetic system outside the cutting, i.e. above the surface of the product, of course, it will allow creating a magnetic field in the groove, however, its parameters will be unstable and depend on the amount of burner immersion in the groove, the parameters and design of the product in the welding zone, and the material properties of the product.

There is also a known method of arc welding (USSR author's certificate No. 465291, MKI V23K 9/08, AM Makara, A.T. Nazarchuk, A.V. Gordon, A.T. Dibets, priority date 04/19/73, publ. 30.03.75 , Bull. No. 12), adopted as a prototype, according to which during the welding process produce a programmed deflection of the arc under the influence of a magnetic field. A feature of the method is that it is not the external magnetic field, but the intrinsic magnetic field of the arc, that controls the position of the magnetic field arc. The change in the spatial position of the arc is based on the application of the magnetic "blast" effect, which consists in displacing the arc from a zone with a higher magnetic field strength to a zone with a lower intensity. T.O. The change in the spatial position of the arc occurs due to the zonal change in the intrinsic magnetic field of the arc. For purposeful changes in the zonal magnetic field strength in the method, it is proposed to use a change in the place where the current is connected to the product. Changing the current connection place is carried out during the welding process automatically or manually according to the specified program. Applying various schemes for connecting current to the product and changing the order of connecting current at different points of the product, various arc paths are achieved. Using the approach proposed in the method for controlling the spatial position of the arc allows you to adjust the heat input process in the product and control the quality of the connection depending on the welding conditions. The equipment used for this is greatly simplified and cheapened. The need to use an external magnetic field disappears, for the creation and control of which it is necessary to use additional equipment in the form of electromagnetic systems, as well as equipment to control the operation of these systems. In addition, according to the equation with the previously discussed method, the process controllability is increased and the dependence of the process control efficiency on the product parameters and welding conditions (such as the amount of torch immersion in the groove, product parameters and design in the welding zone, product material properties, etc.) is reduced. . However, the method under consideration has a number of disadvantages that significantly reduce the effectiveness of the effect on the quality of the welded joint and contribute to a decrease in the reliability and performance of the equipment used. Firstly, the method does not provide any specific recommendations on the scope of its application, in terms of the processes used and the parameters of these processes. The method does not contain data limiting the possibility of its use, which creates significant obstacles, and sometimes the impossibility of its practical application. Due to the complete uncertainty of the conditions under which the method can be implemented, its implementation does not allow the planned achievement of the declared technical result, i.e. improve the quality of the compounds. The possibility of achieving this result is probabilistic, stochastic. Those. for certain process parameters, it is impossible to say in advance whether the effect of arc deflection will be achieved at all, and whether (how and how much) it will be possible to improve the quality of the welded joint. So, for example, the magnitude of the deflection of the arc under the influence of magnetic "blast" is largely determined by the distance from the axis of the electrode to the point where the current is connected to the product. The effect of magnetic blasting is observed at relatively small distances from the axis of the electrode to the current lead, and at large distances it does not appear at all. Also, the possibility and magnitude of arc deflection under the influence of magnetic “blast” significantly depends on the strength of the welding current. At a certain distance from the axis of the electrode to the current lead, there is a certain minimum threshold value of the current strength at which the effect of arc deflection begins to appear. When the current is less than the threshold, the effect of arc deflection is not observed. Moreover, this minimum threshold value will be different for each distance from the axis of the electrode to the current lead, i.e. is not constant. An important factor is the frequency of switching the direction of the current supply. In the considered method, it is indicated that the frequency can vary over a wide range. However, it should be borne in mind that the electric arc has a certain reaction rate to changes in the magnetic field, i.e. inertia is observed. Moreover, the electric welding arc is a fairly inertial system. When the frequency of changing the direction of the current lead reaches a certain maximum critical frequency, the arc ceases (or rather, does not have time) to respond to changes in the magnetic field. If we consider the possibility of implementing the proposed method depending on the welding processes, it can be noted that the description of the method indicates that it can be used both for welding with a consumable and non-consumable electrode. However, due to the specific characteristics of the arc during welding with a consumable electrode (shorter and constantly changing arc lengths, shorter burning times per welding cycle, transfer of molten electrode metal through the arc), the effectiveness of the method under consideration for welding with a consumable electrode will be much less than for a non-consumable one. Considering that the use of the method for welding with a consumable electrode will affect not only the change in the nature of heat input, but also on the nature of metal transfer through the arc, the use of this method without recommendations on its effective field of application may lead not to an improvement, but to a deterioration in the quality of the welded joint . Secondly, in the method under consideration, it is proposed to use electromechanical devices — contactors and electromechanical relays — to change the direction of the current supply. The application of this approach significantly reduces the efficiency and reliability of the equipment used for the method. The control system has a low operating life, high susceptibility to various kinds of interference (due to the lack of galvanic isolation of the input and output), and the ability to work only with low-power equipment (even modern solid-state relays are limited by open-circuit voltage and are suitable only for low-power power sources welding arc).

The technical result of the proposed method is to improve the quality of the welded joint and quality stability, achieved by increasing the efficiency of controlling the heat input into the base metal and the seam, and reducing the negative impact of disturbances during welding on the quality of the welded joint, and also using the method improves the quality and reliability of the equipment used for the implementation of the welding process by an arc deflected by its own magnetic field.

The essence of the proposed method of arc welding with a non-consumable electrode in a protective gas is that before welding one pole of the power source is connected to a non-consumable electrode, and the second to the product. During the welding process, periodic and multiple changes are made in the place where the current is connected to the workpiece, which allows the program to deflect the arc under the influence of its own magnetic field. The arc is delayed in the extreme deflected position for a predetermined period of time, supplying current to one of the points of current supply to the product. When the arc passes from one extreme position to another, the standby mode of arc burning is established. The magnitude of the welding current and the current of the arc on duty is controlled independently. To ensure continuity of arc burning, or for technological purposes, in the process of changing the place where the current is connected to the product, at each moment of time, the current to the product is applied to one or several points on the surface of the product. To supply current to the product, a current supply is used, which is moved synchronously with the electrode, while the sequence and frequency of switching the current supply between individual points and the duration of the current connection to each point are regulated. The switching parameters are adjusted and adjusted using the control device - the switch, and the energy parameters of the process are adjusted and regulated, controlling the operation of the welding power source.

Unlike the prototype, the contacts of the device supplying current to the product are placed on the surface of the product from the side facing the welding torch. By changing the distance from the axis of the electrode to a certain point of the current supply, at a given value of the welding current, the angle of deviation of the arc from the axis of the electrode is adjusted when the current is applied to this point. In this case, the maximum distance from the axis of the electrode to any point of the current supply should be no more than 100 mm. The value of the welding current is regulated separately when current flows through each point of current supply to the product, while the minimum allowable working value of the welding current must be no less than the value determined by the expression

I = 4.466 · h-0.4 · h ² + 0.0147 · h ³ -0.225 · 10 ^-3 · h ⁴ + 1.236 · 10 ^-6 · h ⁵ ,

where I is the minimum welding arc current at which the effect of deflection of the arc column, A, is observed;

h is the distance from the point of current supply to the product to the axis of the electrode, mm

When current flows through each individual point of current supply to the product, the value of the welding working current may remain unchanged with time or periodically change, in the form of pulses, according to a predetermined law.

The switching frequency of the current supply between the points is selected no more than 4 Hz.

When implementing the method, the current to each current supply point on the product surface is supplied via a separate current supply channel from the power source. At the same time, the switching parameters between the individual current supply channels are controlled using an electronic programmable switch that controls the operation of the power source itself.

It is also possible to implement a method in which a change in the place where the current is connected to the product, relative to the axis of the non-consumable electrode, occurs due to the mechanical movement of the current lead contact over the product surface along a predetermined path. In this case, the switching parameters between the individual channels of the current supply are regulated by the appointment of the corresponding law of movement of the contact of the current supply over the surface of the product.

Such a combination of new features with the known ones makes it possible to increase the efficiency of controlling the heat input into the base metal and the seam, which, in turn, makes it possible to improve the quality of the welded joint, and, most importantly, stability in obtaining the planned quality. The efficiency of heat input control and stability in obtaining the planned weld quality is increased by clearly indicating the ranges of the process parameters or their significant boundaries, within which a method of welding by an arc deflected by its own magnetic field can be implemented. Those. the field of effective application of the method is clearly described. The quality of the welded joint and the efficiency of heat input control are also increased because, in contrast to the known analogues, it becomes possible to control the arc deflection angle to each of the possible deflection sides, as well as the possibility of separately controlling the current value when it is supplied through different points (contacts) of the current supply, which in addition to a simple effect on the shape of the weld, it reduces the negative impact of disturbances during welding on the quality of the welded joint. Improving the quality and reliability of equipment used to implement the arc welding process, deflected by its own magnetic field, is achieved through the use of electronic current switching between current points instead of switching using electromechanical devices. This allows you to increase the noise immunity, reliability and functionality of the process control equipment.

The invention is illustrated by drawings, where figure 1 shows a diagram of an implementation of the proposed welding method; figure 2 shows the sequence diagram of the welding process; figure 3 shows a diagram of the process when applying current to each point on the surface of the product through a separate channel for supplying current from a power source; figure 4 shows a process diagram for the mechanical movement of the contact of the current supply over the surface of the product; figure 5 shows the design of the current lead located on the welding torch; figure 6 shows an example of an electrical circuit diagram of a power source for implementing the method according to the circuit for supplying current to each point on the surface of the product through a separate channel for supplying current from the power source; 7 shows an example of a design of a moving roller current lead for implementing the method according to the scheme of mechanical movement of the contact of the current lead over the surface of the product.

The proposed method of arc welding with a non-consumable electrode in a shielding gas is that before welding one pole of the power source 1 (Fig. 1) is connected to the non-consumable electrode 2, and the second to the product 3, for which a current lead is used, which is moved synchronously with the electrode. Contacts 4 and 5 of the current supply are placed on the surface of the product from the side facing the welding torch 6. During welding, periodically and repeatedly change the place where the current is connected to the product, according to the specified program, using the switch 7. At least two points of current to the product are used (at the locations of contacts 4 and 5 of the current supply). Such switching between the individual points of the current supply to the product allows you to programmatically deflect the arc 8 in the opposite direction from the current supply to the product, under the influence of its own magnetic field due to the use of the "magnetic blowing out of the arc" effect. In this case, it is possible to independently change the distance from the axis of the electrode to each of the points of current supply to the product (h1 and h2).

With the passage of current I _p1 through one of the points of current supply to the product (Fig. 2), the arc deviates by an angle α1, away from the current supply in the plane passing through the axis of the electrode and the current supply point. The arc is held in this deflected position for a predetermined and adjustable time interval T ₁ , supplying current I _p1 to one of the points of current supply to the product. When changing the location of the current to the product, i.e. when the arc moves from one extreme position to another, the standby mode of arc burning is set for the time T _dezh , passing through the welding circuit the current of the standby arc I _d.d. Moreover, to ensure continuity of arc burning or for technological purposes, in the process of switching circuits, at each moment of time, the current to the product is supplied to one or several points on the surface of the product, as, for example, this is done for the current of the duty arc I _d.d . At the end of the switching process, i.e. at the end of the burning phase of the “standby” arc, a working current I _{p2 is} passed through the new current supply point for an adjustable time T ₂ , which causes the arc column to deviate to the side from the new current supply point, by angle α2, and burning it at such an angle in the flow of time T ₂ . Next, re-switching occurs, i.e. changing the place of current supply to the product, accompanied by burning of the arc in the “standby” mode I _dd for a time T _dezh. . After that, the described cycle is repeated many times. The above cycle illustrates the simplest embodiment of the proposed welding method, in which the switching channel for supplying current to the product occurs between two points of current supply. By a similar principle, cycles can be built with any number of current supply points, the number of which is assigned based on technological needs.

The value of the welding operating current (I _p ) and the current of the standby arc (I _dd ) are separately regulated, and the value of the welding working current is regulated separately when the current flows through each current supply point to the product (I _p1 and I _p2 ), while the minimum allowable the value of the welding current flowing through each point of the current supply should not be less than the value determined by the expression

I = 4.466 · h-0.4 · h ² + 0.0147 · h ³ -0.225 · 10 ^-3 · h ⁴ + 1.236 · 10 ^-6 · h ⁵ ,

where I is the minimum welding current in the circuit at which the effect of deflection of the arc column, A, is observed;

h is the distance from the point of current supply to the product to the axis of the electrode, mm

When current flows through each individual point of the current supply to the product, the value of the welding working current may either remain unchanged with time, i.e. welding is performed by a continuous welding arc (see current I _p2 ), or periodically change, in the form of pulses, according to a predetermined law, i.e. welding is performed by a pulsed arc (or modulated current). In this case, the main parameters of the law of change in current are set: pulse current I _p2i , pause current I _p2p , pulse time t _and pause time t _p .

The angle of deviation of the arc column from the axis of the electrode (α), for a given value of the welding current, is controlled by changing the distance from the axis of the electrode to a certain point of current supply. The smaller the distance from the axis of the electrode to the point of current supply, the ceteris paribus, the greater the angle of deviation of the arc from the axis of the electrode (see α1 and α2 of FIGS. 1 and 2 for the corresponding distances h1> h2 of FIG. 1). In this case, the maximum distance from the axis of the electrode to any point of the current supply should be no more than 100 mm.

Adjustable parameters of the switching process are the sequence and frequency of switching the current supply between the individual points of the current supply, as well as the duration of the current connection to each point (duty cycle). The switching frequency of the current supply between the points is selected no more than 4 Hz.

The switching parameters are adjusted and regulated using the control device - the switch, and the energy parameters of the process, such as the magnitude of the welding current, when current flows through each channel for supplying current to the product, the value of the arc current on duty, the arc voltage, etc., are adjusted and adjusted by controlling work of a welding power source.

When implementing the method, the current to each point on the surface of the product 3 (Fig. 3) can be supplied via its own separate channel for supplying current 4 and 5 from the power source 1. At the same time, the switching parameters between the individual channels of the current supply are regulated using an electronic programmable switch 7 that controls the operation the power source itself.

It is also possible to implement a method in which a change in the place where the current is connected to the product 3 (Fig. 4), relative to the axis of the non-consumable electrode 2, occurs due to the mechanical movement of one contact of the current lead 4 along the surface of the product along a predetermined path. In this case, the switching parameters between the individual points of the current supply to the product from the power source 1 is regulated by the appointment of the corresponding law of the movement of the contact of the current supply on the surface of the product, using the switch 7.

This set of features allows you to:

- increase the efficiency of heat input control in the base metal and seam;

- improve the quality of the welded joint;

- increase stability in obtaining the planned quality.

The efficiency of heat input control is increased due to two significant factors. Firstly, the proposed welding method clearly defines and indicates the ranges of variation of the process parameters, and their significant boundaries, within which the method of welding by an arc deflected by its own magnetic field can be implemented. Those. the area of effective application of the method is clearly described, which leads to the disappearance of the inherent uncertainty in the prototype in achieving the planned result. Secondly, the functionality of the welding method is greatly expanded, which leads to an increase in the efficiency of heat input control. An increase in the efficiency of heat input control is achieved due to the fact that the known analogues implement the principle of heat input control only due to the controlled spatial movement of the arc heating spot, and in the proposed method, in addition to the specified principle of heat input control, the heat input control principle is applied due to the controlled change in the arc energy parameters in depending on its spatial position. So, for example, in well-known analogues, the welding working current when passing it through different points of the current supply to the product has the same quantitative value, which does not change over time. In this situation, the heat input can be controlled by adjusting the amplitude of the spatial oscillations of the arc, and most importantly, by passing the working current through different points of current supply to the product. This limits the ability to control heat input. In the proposed welding method, the magnitude of the welding current flowing through each individual point of the current supply to the product can be adjusted independently of the current flowing through other points of current supply to the product. Moreover, in the proposed method, it is possible to control the law of change in the magnitude of the welding current in time, by passing current through each individual point of the current supply to the product. Those. either a continuous process of arc burning, or arc burning in a pulsed mode, with predetermined parameters of the pulses (current and time of the pulse and pause) can be implemented. Thus, in the welding method under consideration, it is proposed to use two principles of heat input control (due to the controlled spatial movement of the arc heating spot, and due to a controlled change in the energy parameters of the arc depending on its spatial position), and four heat input control mechanisms (due to the spatial amplitude adjustment arc oscillations; due to the time the working current passes through different points of current supply to the product; due to the independent adjustment of the force current flowing through separate points of current supply to the product; by controlling the law of change in the value of the welding current in time, while passing current through each separate point of current supply to the product). In well-known analogues, one principle and two mechanisms for controlling heat input are used. A significant expansion of the possibilities of controlling heat input significantly increases the efficiency of this process.

The quality of welded joints made using the proposed welding method is improved due to the increase in the method’s functionality described above, which makes it possible to better perform complex joints, such as joints of heterogeneous or different thickness elements, and also due to a significant reduction in the negative impact of various disturbing factors on the quality of the welded connections. For example, using the possibility of separate regulation of the welding current when passing it through different points of the current supply significantly simplifies the process of welding dissimilar metals (for example, carbon steel with high alloy austenitic steel), which are significantly different in their thermal conductivity. Using the possibility of pulsed welding when passing welding current through separate points of the current lead leads to an increase in the quality of the connection of sheet material with thicker elements. When the arc is deflected towards the thin metal, the pulse mode is activated, and when the arc is burning on thick metal, a continuous mode of arc burning is used. This makes it much easier to obtain high-quality penetration of the seam and sharply reduce the risk of burn-through of thin metal. Using the additional functionality of the proposed welding method allows you to get symmetrical welded joints with high-quality penetration in complex joints of heterogeneous or heterogeneous elements.

Stability in obtaining the planned quality increases due to two factors. Firstly, the application of the proposed method allows at the stage of preparation for production and development of the welding process to clearly indicate the operating parameters of the welding process, depending on the desired result, and more clearly predict the planned result, in contrast to the prototype, which is characterized by a high degree of uncertainty in achieving the planned result, due to the inability to clearly indicate the process parameters at which the application of the method can lead to the achievement of this result, and the impossibility of show the process parameters at which the method can generally be implemented. Secondly, at the stage of the welding process, the stability of the quality of the welded joint, when using the proposed method, can be significantly improved by reducing the negative impact of disturbances on the quality of the welded joint. This is achieved due to the possibility of independent control of the process parameters when passing current through each individual point of current supply to the product. The main disturbances are:

- non-uniformity of the parameters for preparing the edges along the length of the joint (uneven bevel angle, uneven blunting of the edges, etc.);

- unevenness of the parameters of the assembly of the edges along the length of the joint (uneven clearance at the joint, the offset of the edges, etc.);

- exposure to external magnetic fields and ferromagnetic masses.

Using the welding method adopted as a prototype would probably reduce the negative impact of such disturbances as the unevenness of the edge preparation parameters along the joint length due to the continuous movement of the heating spot along the welded edges, which makes the process less susceptible to such disturbances. However, we can talk about this only tentatively, since the method adopted for the prototype does not have any clear recommendations for its practical application.

The application of the proposed welding method, due to the clearly adjustable movement of the arc heating spot along the edges to be welded (i.e., the controlled value of the arc pressure on the metal of the weld pool) and the adjustable energy parameters of the arc, depending on its spatial position, can significantly reduce the susceptibility of the welding process to such disturbances as the unevenness of the edge preparation parameters along the joint length and the unevenness of the edge assembly parameters along the joint length. And, most importantly, the application of the proposed welding method can drastically reduce the negative impact of external magnetic fields and ferromagnetic masses on the quality of the welded joint. Neither the analogue considered above, nor protopit allow achieving such a technical result. Exposure to external magnetic fields or ferromagnetic masses causes arc deflection in space. Application of the proposed welding method due to the choice of the current supply to the product and the possibility of adjusting the arc deflection angle (by changing the distance from the axis of the electrode to the current supply) allows you to compensate for the deviation caused by the action of an external magnetic field by creating an adjustable "counter-deflection" of the arc.

All of the above confirms that the application of the proposed welding method, in comparison with the prototype, can improve the efficiency of heat input control in the base metal and seam, the quality and stability of the quality of the welded joint.

The location of the contacts of the device supplying current to the product on the surface of the product, precisely from the side facing the welding torch, is due to the fact that with this arrangement of the contacts of the current supply, the maximum possible arc deflection under the action of its own magnetic field is achieved. The deviation of the arc under the influence of its own magnetic field (ie, “magnetic blast”) occurs due to a violation of the symmetry of the magnetic field of the arc (its curvature), the cause of which is the curvature of the conditional path for supplying current to the welding zone. If you place the contact of the current supply on the surface of the product from the side opposite to the one above which the welding torch is located (contact 9 of figure 1), this will cause less curvature of the conditional path for supplying current to the welding zone (see conditional current path 2 in figure 1) than if the current supply contact is located on the surface of the product from the side facing the welding torch (contact 5) (see conditional current path 1). A greater curvature of the conditional path of supplying current to the welding zone causes a greater asymmetry of the magnetic field of the arc and, accordingly, ceteris paribus, a large amount of deflection of the arc to the side from the current supply. Therefore, when the contacts of the device supplying current to the product are located on the surface of the product, namely from the side facing the welding torch, the greatest effect is achieved on the spatial position of the arc due to the use of the “magnetic blast” effect.

The distance from the axis of the electrode to any point of the current supply is set to not more than 100 mm. Such a quantitative value of the maximum permissible distance from the axis of the electrode to the point of current supply follows from the results of experimental studies conducted by the authors of the method, which show that when the distance from the axis of the electrode to the point of current input into the product is greater than 100 mm, the deviation of the welding arc is not observed. This is due to the fact that, at the indicated distances, there is practically no violation of the symmetry of the intrinsic magnetic field of the arc caused by the curvature of the conditional path for supplying current to the welding zone.

The minimum allowable working value of the welding current is assigned no less than the value determined by the expression

I = 4.466 · h-0.4 · h ² + 0.0147 · h ³ -0.225 · 10 ^-3 · h ⁴ + 1.236 · 10 ^-6 · h ⁵ ,

where I is the minimum welding arc current at which the effect of deflection of the arc column, A, is observed;

h is the distance from the point of current supply to the product to the axis of the electrode, mm

The above expression for determining the minimum allowable working value of the welding current is obtained as a result of experimental studies conducted by the authors of the method. The studies show that if, at a certain distance from the current supply point to the product to the electrode axis, the value of the welding working current is less than the value determined from the above dependence, then the effect of the welding arc deviating to the side from the current supply will not be observed. The arc deviation visually begins to be determined only when the values of the welding operating current are greater than the value determined from the above dependence. This is explained by the fact that for small values of the welding current, the magnitude of the magnetic induction of the intrinsic magnetic field of the arc is so small that the curvature (i.e., symmetry breaking) of this field is not able to cause a change in the spatial position of the arc. By reducing the distance from the axis of the electrode to the point of current input into the product, at a constant value of the welding current, it is possible to achieve a significant curvature of the intrinsic magnetic field of the arc, which will become sufficient to affect the welding arc, and its deviation.

The switching frequency of the current supply between individual points is assigned no more than 4 Hz. Such a quantitative value of the maximum allowable switching frequency of electrical circuits follows from the results of experimental studies conducted by the authors of the method, which show that when the switching frequency of the current supply between the individual points of the current supply is more than 4 Hz, the effect of arc deflection is not observed. This is due to the inertia of the welding arc. At a frequency of changes in the spatial position of the arc of more than 4 Hz, the arc does not have time to respond to the changes and ceases to change its spatial position, burning in the center of the junction.

An example of the application of the proposed method may be the process of automatic argon-arc welding of the root layer of the seam with a non-consumable electrode arc controlled by its own magnetic field of the connection of plates of steel 10 with a thickness of 5 mm and a length of 150 mm.

The plates have the following parameters for preparing and assembling edges for welding:

- the bevel angle of each edge varies along the length of the joint from 25 to 30 °;

- the gap in the assembled joint varies in length from 0 to 2 mm;

- blunting of the edge along the length of the joint varies from 0 to 0.5 mm;

- on a section with a length of 50 mm there is an offset of the edges up to 0.5-1 mm in size.

For welding, a current lead with two separate points of current supply to the product is used. The current lead is structurally connected to the welding torch and moves with it along the surface of the product facing the torch at a welding speed. The current lead design is shown in Fig.5. The current lead consists of two symmetrical parts. Each part consists of a steel base 10, which is mounted through an insulator 11 on the body of the welding torch 6. To reliably press the graphite contacts of the current supply 4 and 5 to the surface of the product (in particular, when the edges are offset), steel springs 12 are used. On one side, the spring is attached to the base 10, and to the other side of the spring with a bolt, washer and nut, a graphite contact 4 or 5 of a cylindrical shape is attached. The terminal of the wire 13 from the power source is attached to each part of the current supply with a bolt and nut 14. The graphite contact 4 or 5 with the spring 12 can be moved along the base 10 to adjust the distance from the axis of the burner electrode 6 to each graphite contact.

The method described in the example is implemented according to the scheme, when the current to each of the two graphite contacts, through which the current is introduced into the product, is supplied through its own separate channel for supplying current from the power source (Fig. 3). To implement this approach, a power source with a modified rectifier unit circuit is used. Schematic diagram of such a rectifier is shown in Fig.6. The voltage from the power transformer T1 is supplied to the rectifier unit. In the rectifier block, instead of six thyristors, as in conventional rectifiers, nine VS1-VS9 are used (one thyristor in each of the three additional arms of the rectifier block). The operation of the rectifier unit of the power source is controlled by an electronic control unit 7 (electronic switch). To increase noise immunity, the control unit is galvanically isolated from the power unit by means of galvanic isolation elements T2-T7. The voltage from one pole of the rectifier unit is supplied, via the stabilizing inductor L1, to the non-consumable electrode 2, and two outputs of the second pole of the rectifier block are connected to the product 3 through movable contacts 4 and 5. The control unit controls both the energy parameters of the process (current, arc voltage and etc.), as well as the parameters of the current switching between the channels for supplying current to the product through contacts 4 and 5. Due to the absence of electromechanical elements (relays) in the control circuit and the presence of galvanic isolation of the control circuits control and power circuits, the control unit has high noise immunity, and the power supply itself is more reliable in operation than the equipment used in the prototype.

The negative pole of the power source is connected, using a power cable, with the electrode 2 (Fig.6) of the welding torch. Each of the two graphite contacts 4 and 5 of the current supply is connected to one of the two positive poles of the power source, using a power cable.

In order to obtain a high-quality welded joint and compensate for the negative effect of the unevenness of the parameters of preparation and assembly of the joint along its length, the following parameters of the welding mode are set:

- the distance from the axis of the electrode to the axis of the cylindrical graphite contact of the current supply is set the same for each of the two arms of the current supply and equal to 30 mm;

- the frequency of the current switching between the two contacts of the current supply 1.5 Hz (which corresponds to the cycle time T _St = 0.67 s (see figure 2));

- the burning time of the duty arc T _d.d. = 0.1 s;

- switching duty - 50% (i.e., the arc burning time in each of its two extreme deflected positions is the same), which, when the duty arc burns for 0.1 s, corresponds to the arc burning time in each extreme deflected position T ₁ = T ₂ = 0.28 s;

- the value of the welding operating current for each of the two channels is the same and is I _p1 = I _p2 = 130 A (with a minimum permissible current of 19 A). The value of the operating current in time is unchanged (i.e., welding in continuous mode);

- the magnitude of the current on-duty arc, passed simultaneously on each of the two channels, is I _dd = 40 A;

- diameter of the tungsten electrode 3 mm;

- arc length 3 mm (which corresponds to an arc voltage of approximately 12 V);

- welding speed 16.5 cm / min;

- argon flow rate of 6 l / min.

A graphical representation of the welding cycle corresponds to that shown in figure 2, with the equality of the arc deflection angles α1 and α2.

The specified mode is basic and allows you to fully compensate for the negative effect of the unevenness of the bevel angles, blunting of the edge and the unevenness of the gap along the length of the joint.

As soon as during welding there is a section with a displacement of the edges, this immediately causes an extension of the arc, when burning to an edge farther from the electrode, by 0.5-1 mm. This, in turn, causes an increase in arc voltage, i.e. increase in its thermal power. There is a danger of burn-through of the edge. The formation of a single weld pool is also difficult, since the geometry of the joint is broken. Therefore, in order to exclude the occurrence of burns in the area with a displacement of the edges, it is necessary to adjust the welding mode. In the above welding mode, the following parameters are changed:

- the welding working current when burning the arc to an edge farther from the electrode is reduced to I _p1 = 120 A (this is done in order to maintain a constant value of the thermal power of the arc and to exclude burn through of the farther edge);

- when current flows through the second channel, when the arc burns to the edge closest to the electrode, set the pulse mode of arc burning: assign two pulses with the following parameters:

- pulse current I _p2i = 150 A, pause current I _p2 = 40 A; duty cycle of 60% (which corresponds to a pulse time of t _and = 0.09 s, and a pause time of t _p = 0.06 s). The process flow diagram, see figure 2 (dashed line).

The remaining parameters of the welding process remain unchanged. The current flowing through the second channel was made pulsed in order to simplify the process of forming a monolithic weld pool between two welded edges, in the presence of an offset between them (namely, in order to reduce the instantaneous volume of liquid metal in the weld pool). The value of the operating pulse current was increased to 150 A to provide the necessary penetration of the edge, since when switching to the pulse mode, the heat input to the edge decreases. The transition from the basic mode to the corrected one and vice versa takes place according to a command given by the control unit (initialization of the command can be performed automatically or when the operator presses a button).

In these modes, the root layer of the seam of the plates was welded without the use of filler wire. The resulting weld in the root layer of the seam turned out without defects (without burns or lack of penetration). The width of the root layer of the suture was 7 ± 0.5 mm.

To demonstrate the effectiveness of the method, two more plates were assembled with the same parameters for preparing and assembling edges for welding (with the same clearance, bevel angle, blunting, and edge displacement), as indicated earlier. The welding of the new joint was performed by the classical method of automatic argon-arc welding, without changing the spatial position of the arc (i.e., when the arc burns in the center of the joint). The welding current was 130 A, the arc length was 3 mm (which corresponds to an arc voltage of about 12 V), the welding speed was 16.5 cm / min, and the argon flow rate was 6 l / min. As a result of welding the root layer of the joint of the plate joint, a root layer with an uneven width of 7 to 10 mm and with a burn-through of the welded edges with a total length of 45% of the joint length was obtained (the burn section coincided with the section where the edges were displaced, as well as the section without displacement but with a gap at the joint of 1-2 mm). Those. the seam turned out to be of poor quality at 45% of its length. In this case, the span of the seam width was from 7 to 10 mm, i.e. within 3 mm, while on the first sample made by the proposed welding method, the span of the seam width was only 1 mm in the absence of defects in the weld.

Thus, the possibility of practical implementation of the proposed welding method using methods known in the art and the possibility of achieving a positive technical effect in the form of increasing the quality of the welded joint and increasing the dimensional stability of its dimensions (which indicates an increase in the quality stability and reducing the degree of influence of various perturbations on the quality welded joint).

The described example of the proposed welding method can also be implemented according to the scheme in which the change in the current connection to the product, relative to the axis of the non-consumable electrode, occurs due to the mechanical movement of the current lead contact along the surface of the product along a predetermined path. Such a scheme of the welding method can be implemented if, for example, a current lead in the form of a disk rolling on the surface of a product is used as a current lead while moving along a circular path relative to the axis of the non-consumable electrode. An example of the implementation of such a current supply is shown in Fig.7. The shape of the current lead in the form of a disk is best suited because when a disk moves from one edge to another, it touches two edges simultaneously (at points 3 and 4 respectively), which ensures the required, according to the description of the method, current input in several points in the switching process, and the absence of arc breaks. The movable contact of the current lead 4, in the form of a copper disk, rolls along the surface of the welded edges 3 (either along the already welded edges or along the still welded edges) along a certain path relative to the axis of the non-consumable electrode 2 of the burner 6. The disk is mounted on the burner using a cylindrical sleeve 15 connected to the burner through a bearing. The holder and the disk are interconnected by a lever 16. To set various trajectories of the disk relative to the axis of the non-consumable electrode, a lever system can be used, the design of which can be as shown in Fig. 8. The system consists of a lever 16 and a shoulder 17, interconnected through a hinge 18. The lever 16 is located so that its axis of rotation coincides with the axis of the non-consumable electrode. The axis of the hinge 18 is simultaneously the axis of rotation of the shoulder 17. The lever system is mounted on the burner 6 using a cylindrical cage 15 connected to the burner through a bearing. The rotation of the lever 16 is made periodically when you want to change the path of the disk. As soon as the lever 16 has taken the required position, its rotation stops, and it is rigidly fixed in the position that it took. The rotation of the shoulder 17 around the hinge 18 occurs cyclically during the welding process. The rotation cycle is determined by the extreme points of the trajectory, which determine the distances h1 and h2 from the movable disk to the axis of the electrode. The parameters of the rotation cycle are the angle of rotation of the shoulder between the extreme points, the speed of movement between the extreme points, the delay time of the disk at each extreme point. By changing the angle of rotation of the lever 16 around the hinge 18 on the axis of the burner 6, it is possible to assign various trajectories of the copper disk 4 and thereby change the distances h1 and h2 of the extreme working points of the current input into the product to the axis of the non-consumable electrode 2. The parameters of the motion cycle can be set by the law of the drive engine. For these purposes, for example, a stepper motor can be used, which allows you to set (program) the law of your work. On Fig shows the state of the mechanical system, providing equal distances h1 and h2 from the extreme points of the trajectory to the axis of the non-consumable electrode. Figure 9 shows the state of the mechanical system, providing different distances h1 and h2 from the extreme points of the trajectory to the axis of the non-consumable electrode. Management of the energy parameters of the process (current strength, the law of current change in time, etc.) occurs due to the programmable control unit of the power source, which allows you to implement a sequence diagram of the equipment according to the sequence diagram shown in figure 2. In this case, the energy parameters are regulated depending on the angle of rotation of the stepper motor in a certain direction.

Using the proposed equipment, it is possible to fully implement the process described in the above example of welding two plates.

This embodiment of the method is simpler in execution (since it does not require a change in the design of the power source), however, it is less reliable than that described in the previous example, because it is implemented through the use of a movable mechanical system, the presence of which reduces the reliability of the equipment.

Thus, the proposed method of welding a non-consumable electrode in a protective gas provides a positive technical effect and can be carried out using means known in the art. Therefore, the proposed method has industrial applicability.

Claims (3)

1. A method of welding in a shielding gas by a non-consumable electrode with a magnetically controlled arc, comprising connecting one pole of the power source through one channel for supplying current to a non-consumable electrode and a second pole through another channel for supplying current to the product by means of current supply and welding, during which current is supplied at each moment of time to one or at the same time to several points on the surface of the product by means of current supply and periodically and repeatedly change the place of connection of current to the product for the programmer arc deflection under the influence of its own magnetic field, characterized in that when the arc is deflected under the influence of its own magnetic field, it is delayed in the extreme deflected position for a predetermined period of time and when the arc moves from one extreme position to another, the standby mode of arc burning is set, while independently they control the magnitude of the welding current and the current of the arc on duty, in the process of changing the place where the current is connected to the product, the current lead is moved synchronously with the non-consumable electrode, controlled by by a switch included in the current supply channel from the power source to the product, the sequence and frequency of switching the current supply between individual points and the duration of the current connection to each point, which are the switching parameters, the contacts of the current supply to the product are placed on the surface of the product from the side facing the welding torch, adjust the angle of the arc deviation from the axis of the electrode, changing the distance from the axis of the electrode to a certain point of current supply to the product at a given value of the welding current, the maximum distance from the axis of the electrode to any current supply point to the product is set to not more than 100 mm, and the current supply switching frequency between individual points is not more than 4 Hz, the welding current is regulated separately when current flows through each current supply point to the product, minimum allowable working value of the welding current is set not less than the value determined by the expression:
I = 4.466 · h-0.4 · h ² + 0.0147 · h ³ -0.225 · 10 ^-3 · h ⁴ + 1.236 · 10 ^-6 · h ⁵ ,
where I is the minimum welding arc current at which the effect of deflection of the arc column is observed, A, h is the distance from the current supply point to the product to the axis of the non-consumable electrode, mm, and when the current flows through each separate current supply point to the product, the value of the welding operating current over time, maintain unchanged or periodically in the form of pulses change. 2. The method according to claim 1, characterized in that the current to each point of its supply to the product is supplied via a separate channel of the corresponding pole of the power source, and the parameters of the current switching between the individual channels of the current supply to the product are controlled by the power supply control unit. 3. The method according to claim 1, characterized in that the change in the place where the current is connected to the product is carried out by mechanically moving the current supply contact over the product surface along a predetermined path, and the current switching parameters between the individual points of current supply to the product are regulated depending on the path of the current supply contact on the surface of the product.

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