RU2735847C1 - Method for controlling penetration depth during arc automatic welding - Google Patents

Abstract

FIELD: welding.

SUBSTANCE: invention can be used in automatic argon-arc welding by nonconsumable electrode to stabilize welding speed and arc voltage. To control the penetration depth, a mathematical model of a point source of heat of a plate moving on the surface is used. Widths and depths of penetration of the reference seam are used to calculate two coefficients of the mathematical model: the ratio of the specific effective power to the volumetric heat capacity and the thermal diffusivity. Obtained values are used to determine the position of the temperature measurement point on the surface of the plate. Point of measurement shall ensure stability of adjustment of penetration depth. In the process of regulation, the difference between the calculated and measured point temperatures is determined. Initial temperature of the plates to be welded is varied and the welding current required for stabilization of penetration depth is calculated.

EFFECT: method provides elimination of uncontrolled disturbances, increases accuracy of control, which increases stability of quality of welded joints.

1 cl, 4 ex, 14 dwg

Description

The invention relates to the field of arc welding and can be used in mechanical engineering in the production of welded structures when welding butt joints without cutting edges and surfacing layers with special properties on plates and pipes.

There is a method for automatic control of the penetration depth in automatic arc welding, in which reference values of the welding current, welding speed, welding voltage are set, during the welding process, the current values of these parameters are measured, the difference between the current and their specified parameters is calculated, and the process is controlled according to the obtained differences, the temperature of the point of the surface of the weld is measured, the calculated value of the temperature of the same point of the weld surface is calculated, simultaneously with the differences between the current and specified parameters of the welding current, welding voltage, welding speed, the difference between the current and calculated values of temperature and the value of the controlled parameter of the welding process are adjusted according to equation

where K l, m, n are known constants depending on the specific welding process,

I _O - reference welding current,

I - current welding current,

V _O - reference welding speed,

V - current welding speed,

U _O - reference welding voltage,

U - current welding voltage,

Т - current temperature value,

T _P - calculated temperature value,

moreover, the welding current is selected as the control parameter of the process. (see the description to the author's certificate of the USSR No. 10131363, published on April 23, 1983).

The disadvantage of this method is that for regulation it is necessary to develop two empirical mathematical models for calculating the depth of penetration and temperature at the measurement point, which require numerous experiments to determine the coefficients of the models. One model associates the change in the surface point temperature with respect to the nominal temperature with the deviations of only the mode parameters. The second model relates the maximum penetration depth with the parameters of the mode and the change in the temperature of the point under the action of all disturbances. Both models have 7 empirical coefficients. The resulting equations must be solved together as a system.

This method does not take into account the possibility of the opposite influence of some uncontrolled disturbances on the temperature of the measuring point and on the penetration depth. Such disturbances include the coefficient of thermal diffusivity of the metal of the product. This leads to the fact that in some cases the stability of the process of controlling the penetration depth is disturbed.

There is a known method for automatic control of the penetration depth during non-consumable electrode welding, in which the nominal values of the welding current, welding speed and arc voltage are set, during the welding process, the current values of these parameters are measured, as well as the temperature at a given point on the surface of the product, which characterizes the effect of uncontrolled disturbances during welding and the obtained information is used to maintain the specified penetration depth by adjusting the welding current in accordance with the deviations of the measured parameters from the specified ones, taking into account uncontrolled disturbances, and in order to improve the quality of the weld by compensating for the effect on the penetration depth of uncontrolled disturbances of various physical nature behind the welding arc, at a distance from it, the controlled cross-section of the weld is pre-selected and the temperature on the surface is measured at the center of this section, the temperature is additionally set obviously lower The width of the zone heated above this temperature is measured in the center and during the welding process in the specified section, and when adjusting the welding current to take into account uncontrolled disturbances, a mathematical expression is used that takes into account the obtained difference between the measured and calculated zone widths (see. description to the USSR inventor's certificate for the method SU No. 1346369 dated 23.10.1987).

When implementing this method, a number of technical problems arise. The most serious problem is that to take into account uncontrolled (immeasurable) deviations of parameters, for example, the thermal diffusivity of parts, which, according to the description of this patent, with a different sign can affect the adjustable penetration depth and the measured point temperature, it is necessary to measure and the width of the zone heated above the set temperature. This requires special sensors that scan the heat-affected zone and determine the border with this temperature and the width of the zone. Sensors are necessary on each side of the joint axis, since during welding, for a number of reasons, the symmetry of the sought isotherm relative to the joint can be violated.

Also, when calculating the criterion parameter K, which ensures the stability of the regulation, it is necessary to make a calculated correction for the change in the welding speed by means of a special empirical coefficient, which complicates the regulation.

To calculate the parameter characterizing the condition of regulation stability, it is necessary to experimentally determine three coefficients. With the simplest way of performing experiments - their mathematical planning, it is necessary to perform 2 ³ = 8 experiments, not counting their repetitions, which are necessary to obtain an adequate model.

In the mathematical formula for a distributed heat source in a flat layer, on which this method is based (2nd paragraph of column 3 of the description), the concept of the effective power of the welding arc is used. However, the description does not indicate a method for determining such power. Usually, to determine the effective power of the welding arc in welding, the effective efficiency is used, which has a significant scatter of values, and the specified method does not provide signs of determining this coefficient with the accuracy necessary for regulation (see, for example, A.A. Erokhin, Fundamentals of fusion welding. .: Mechanical engineering, 1973, 448 p. 13, table 1.2). The authors of the known method incorrectly call the effective efficiency of the process - thermal efficiency (see description annotation). Thermal efficiency is usually understood as the ratio of the power consumed to melt the metal to the total power of the heat source, and the effective efficiency is the entire fraction of the power of the heat source transferred to the product.

Another option for determining the effective power is to perform calorimetry of the plates to be welded, however, this method is also not indicated. In the known method, in the mathematical formula used, which is not given in the description of the method, when calculating the control effect, the volumetric heat capacity of the metal of the product and the thermal diffusivity coefficient (2nd paragraph 1 of the description column) are used, but the methods for their selection are also not given.

It is known that the thermophysical coefficients used in the prototype and any analytical formula depend on the temperature of the metal. The temperatures in the parts to be welded are always extremely unevenly distributed. In the literature, however, only the recommended values of the coefficients for some averaged temperatures are given, which can be used for calculations that are of a qualitative nature. The same applies to the coefficient of thermal diffusivity of metal (see the monograph by V.A.Karkhin "Thermal processes in welding." St. Petersburg: Izd-e Polytechnic University, 2015. - 572 p., P. 86, table 2.7. 1).

Also, in the known method, it is impossible to take into account the concentration of the heat flux from the arc to the product, since no signs are given of how the concentration should be determined. Concentration is unambiguously associated with such process parameters as welding current and arc length (voltage); however, the available data on the concentration of the heat flux of welding arcs are few and contradictory. Since in the known method the welding current and arc length can vary significantly, this affects the concentration of the heat flux from the arc to the product and the calculated point temperature and creates a significant error in calculating the temperature of the measuring point.

In the known method, changes in the arc voltage are allowed, which leads to a decrease in the control accuracy. Arc voltage when welding with a non-consumable electrode is practically independent of the arc current, but depends on its length. When changing the length of the arc, its effective power and the concentration of the heat flux from the arc to the product change simultaneously. And as noted in the description of the known method, this can affect the depth of penetration and the temperature of the measuring point in different ways. In the literature, there is practically no data on the effect of the arc length on the effective power and concentration of the heat flux simultaneously.

In the known method for controlling the penetration depth in automatic nonconsumable electrode welding of butt joints without cutting edges with or without filler wire, including maintaining the penetration depth at a given constant level by adjusting the welding current, while the welding process measures and calculates temperatures at a point on the surface connections and the difference of these temperatures, measure the actual values of the regulated current in the welding process, which are corrected in accordance with their calculated values according to the specified mathematical relationship.

In contrast to the prototype, with nominal welding parameters, the maximum depth of penetration and the width of the weld are additionally measured, the melting point of the metal and the reference initial temperature and thickness of the parts to be welded are set, the coordinates of the point of measuring the temperature of the surface point are found, for which the influence on the temperature of the thermal diffusivity by the sign coincides with their influence on the adjustable depth of penetration of the weld, in the process of regulation they stabilize the welding speed and arc voltage and calculate the adjustable welding current according to the formula

where I is the welding current, A,

T _L - product melting point, ° С,

T ₀ - nominal initial temperature of the product, ° С,

Т _И - measured temperature of the surface point, ° С,

Т _Р - design temperature of the surface point, ° С,

- коэффициент температуропроводности изделия, см²/с,

- coefficient of thermal diffusivity of the product, cm²/from,

Q is the ratio of the specific effective power of the welding arc q _Y to the volumetric heat capacity of the product cρ, (cm ³ ⋅ ° C) / (A⋅s), where q _Y is the ratio of the effective power of the welding arc to the welding current, W / A.

x ₀ - coordinate of the point with the maximum penetration depth at nominal welding parameters, in the direction opposite to the direction of the welding speed, cm,

V _C - welding speed, cm / s,

t - current time since the beginning of the action and movement of the arc, s,

δ - nominal product thickness, cm,

Н ₀ - nominal maximum penetration depth, cm,

n - integers from -10 to +10,

и коэффициент пропорциональности Q рассчитывают по значениям ширины и глубины проплавления эталонного шва.for which the thermal diffusivity

and the proportionality factor Q is calculated from the values of the width and depth of penetration of the reference weld.

и коэффициента пропорциональности Q и использовать их впоследствии для отыскании координат подходящей точки поверхности, отвечающей необходимому требованию устойчивости регулирования и расчета тока сварки для стабилизации глубины проплавления с учетом разности измеренной и вычисленной температур.The technical result of the proposed method consists in eliminating the need to measure the width of the heating zone above a predetermined temperature, less than the melting temperature, significantly reducing experiments to determine the coefficients of the mathematical dependence, increasing the accuracy of controlling the penetration depth by reducing the dependence of the coefficients determined experimentally on the welding mode parameters. In fact, only one experiment is needed for welding a reference seam and measuring after it the depth of penetration of the seam and the width of the seam. This result is achieved due to the established dependence that an adequate description of the shape of the temperature field using an analytical dependence representing the action of a moving point heat source on the plate surface allows, when measuring two dimensions of a weld, to find the exact values of the corresponding thermal diffusivity

and the proportionality coefficient Q and use them subsequently to find the coordinates of a suitable point on the surface that meets the necessary requirement for control stability and calculate the welding current to stabilize the penetration depth, taking into account the difference between the measured and calculated temperatures.

Stabilization of the welding speed and arc voltage makes it possible to eliminate significant changes in the temperature of the measuring point associated with a change in these parameters, which can occur in this method only from the action of uncontrolled disturbances and arc current. Also, minor deviations of the stabilized parameters, due to the accuracy of the operation of the supporting devices, are also reflected in the change in the temperature of the measuring point and, accordingly, are taken into account when calculating the correction welding current. This significantly improves the accuracy and ensures the stability of the regulation.

This result is also achieved because the deviation of the measured point temperature from the calculated one is equivalent to a change in the initial temperature of the plates being welded and allows one to take into account the effect of all uncontrolled disturbances and small deviations of the stabilized mode parameters at the maximum penetration depth.

In addition, the technical result is also the fact that the method can be used for automatic welding of butt joints without cutting edges and surfacing on plates with filler wire feeding into the weld pool, since the effect of the filler wire on heat propagation is taken into account while simultaneously measuring the penetration depth and weld width when welding, the values of the coefficients used and, therefore, to the penetration depth and temperature of the controlled point.

The method can be used for automatic welding of butt joints without cutting edges and surfacing on plates with a welding arc with a consumable electrode, since when simultaneously measuring the depth of penetration and width of the weld, the effect of molten electrode metal on heat propagation during welding, the values of the coefficients used and, consequently, on penetration depth. For this variant of the welding method, in addition to the welding speed and arc voltage, it is necessary to stabilize the rate of melting and feeding of the electrode wire.

There are a number of widely used methods for stabilizing the arc voltage with a non-consumable electrode by controlling the arc length. Also, modern motors used in welding machines make it possible to stabilize the number of shaft revolutions with high accuracy and provide a similar stabilization of the welding speed. Therefore, there is no need to measure all measurable process parameters while simultaneously adjusting the penetration depth with only one of them. At the same time, a number of uncontrollable (immeasurable) disturbances act on the welding zone, which are difficult to measure and stabilize during the welding process. They can only be estimated by measuring the temperature of a point on the surface of the product in comparison with the calculated value. To ensure the stability of the control system, the correct selection of the temperature measuring point is necessary. For this, using the mathematical formula for the temperature propagation in the plate and the coefficients found from the dimensions of the reference weld, a number of points are checked for compliance with the regulation stability condition.

, на фиг. 7 - зависимость размеров шва от скорости сварки, на фиг. 8 - зависимость глубины проплавления и ширины шва от начальной температуры пластины, на фиг. 9 - зависимость глубины проплавления и ширины шва от толщины пластины, на фиг. 10 - схема получения изолиний, на фиг. 11 - изолиния «коэффициент пропорциональности - коэффициент температуропроводности», на фиг. 12 - зависимости температуры точек поверхности от коэффициента температуропроводности, на фиг. 13 - схема регулирования процесса сварки по предлагаемому способу, на фиг. 14 - схема сварки пластин со скачкообразным изменением толщины деталей.FIG. 1 shows a cross-section of the penetration, FIG. 2 shows a longitudinal profile of penetration, FIG. 3 - semi-isotherm of the weld pool, Fig. 4 - the dependence of the specific effective power of the arc on the arc current; in fig. 5 - dependences of the depth of penetration and the width of the seam on the proportionality coefficient Q, in Fig. 6 - the dependence of the dimensions of the seam on the coefficient of thermal diffusivity

, in FIG. 7 - the dependence of the dimensions of the seam on the welding speed, in Fig. 8 - the dependence of the depth of penetration and the width of the seam on the initial temperature of the plate, Fig. 9 - the dependence of the depth of penetration and the width of the seam on the thickness of the plate, in Fig. 10 is a diagram of obtaining isolines, in Fig. 11 - isoline "proportionality coefficient - thermal diffusivity coefficient", in Fig. 12 - the dependence of the temperature of the surface points on the coefficient of thermal diffusivity, in Fig. 13 is a diagram for regulating the welding process according to the proposed method, FIG. 14 is a diagram of welding plates with an abrupt change in the thickness of the parts.

FIG. 1 shows a cross-sectional view of the first layer of a double-sided butt joint made of non-grooved plates with incomplete penetration depth. B ₀ is the maximum width of the weld pool (seam) on the outer surface of the plates (from the side of the welding arc). Н ₀ - nominal (reference) weld penetration depth. When regulating, it is required to stabilize the penetration depth H ₀ . The value of H ₀ should ensure overlapping of the seams when welding a similar seam from the opposite plane of the plate.

FIG. 1 shows the axes when calculating temperatures - the Y-axis is perpendicular to the direction of the welding speed V _C and the Z-axis directed perpendicular to the outer surface of the plate from the side of the welding arc from the point of action of a point heat source. The X axis coincides with the direction of welding (not shown in Fig. 1). The coordinate system is movable, moving at the welding speed. The penetration depth H ₀ has a permissible positive and negative deviations from the nominal depth + ΔH ₀₁ , and (-ΔH ₀₁ ), which may be equal or unequal in absolute value. Nominal penetration and permissible deviations can be established by the developer of the welding technology or given in regulatory documents. The maximum penetration depth takes place along the weld axis at the transverse coordinate y = 0. The weld can also be produced using filler wire, so it has a convex g.

On the basis of the permissible deviations of the maximum penetration depth, the permissible deviations of the welding parameters can be established with the required accuracy. In the proposed method, these are mode parameters such as welding speed and arc voltage. The method for determining the permissible deviations of the parameters of double-sided welding is described in the article by V.P. Sidorov, A.V. Melzitdinova. Study of permissible deviations of parameters of double-sided arc welding / Welding production, 2016, No. 3, pp. 11-15.

The danger of a deviation of any parameter during welding should be assessed by the relative disturbance transfer coefficient (RTR). This is the ratio of the relative permissible deviation of the controlled parameter of the weld to the relative deviation of the process variable. For example, when assessing the influence of the deviation of the welding current from the nominal value I on the maximum penetration depth.

OKPV = (ΔН ₀ / Н ₀ ) / (ΔI / I)

The GCWS is a dimensionless quantity, the sign of which can be either positive or negative. For example, with an increase in the welding speed, the penetration depth decreases, therefore, the GWPW will be negative. It shows how many times more or less the controlled parameter of the weld seam changes when one of the welding parameters is changed. The GWVS can be greater than 1 or less than 1. If the GWWS = 0, this means that this parameter does not affect the weld parameter. The larger the TWCS, the greater the deviation of the controlled parameter causes the considered welding parameter, the more dangerous the disturbance. The sum of the absolute values of TWCF for all parameters of the welding process characterizes the difficulty of ensuring the stability of the controlled value, for example, the maximum penetration depth. PCWS can be defined for both measurable welding parameters (modes) and non-measurable (welding conditions). To determine the permissible deviation of each of the process parameters, it is most expedient to use the principle of equal contribution. The principle of equal contribution means that the permissible relative deviation of the weld parameter ΔН ₀ should be divided by the number of welding parameters N and each of them must provide its own equal share of the permissible deviation ΔН _0П

ΔН _0П = ΔН ₀ / N.

With this approach, it is not difficult to stabilize the two controlled parameters of the welding mode, the arc voltage and the welding speed, so that the unfavorable combination of their permissible deviations does not exceed the specified permissible deviation of the adjustable weld penetration depth ΔН ₀ . For example, if we assign the permissible deviation of the maximum penetration depth H ₀ = 3.6 mm to ± 0.6 mm, then the relative permissible deviation will be ± 16.7%. Assuming that ± 6.7% of them can introduce uncontrollable deviations, the remaining ± 10% falls on the arc speed and voltage, ± 5% for each parameter. Modern equipment provides a significantly higher stabilization accuracy, even taking into account the fact that the RCSV can be greater than unity in absolute value.

FIG. 2 shows the longitudinal profile of penetration through the thickness of the plate along the X axis at the transverse coordinate y = 0, calculated using the formula for a point heat source moving along the surface of a flat layer (plate).

The formula for calculating the temperature increment ΔT at a point on the plate from the action of such a heat source has the form

where Т is the temperature of the point of the plate, ° С,

Т ₀ - initial temperature of the plate, ° С,

q _And - effective power of the heat source, W,

сρ - volumetric heat capacity of the plate metal, J / (cm ³ ° С),

- коэффициент температуропроводности пластины, см²/с,

- coefficient of thermal diffusivity of the plate, cm ² / s,

x - coordinate in the direction of movement of the heat source, measured from the heat source, cm,

V _C - speed of movement of the heat source, cm / s,

t is the current time since the beginning of the action and movement of the heat source, s,

y - coordinate perpendicular to the direction of movement of the heat source, measured from the heat source, cm,

z is the coordinate perpendicular to the direction of movement of the heat source and the plane of the plate on which the heat source acts, cm,

δ - plate thickness, cm,

n - integers from -∞ to + ∞.

Formula (3) is given in the textbook "Theory of welding processes" / V.N. Volchenko M. et al. Ed. V.V. Frolov. - M: Higher school, 1988 .-- 559 p. P. 186.

The specific number of numbers n specifies the number of terms in the series (the number of integrals) to be calculated. It depends on the required accuracy of calculations of the last term of the series in formula (3). The larger the number n in absolute value, the smaller the last integral of the series. That is, the series in (3) is convergent. The accuracy of calculating the temperature at a point rapidly increases with increasing n in absolute value. When calculating temperatures, the number n is limited by specifying the ratio of the last term of the series to the sum of all previous members of the series. When calculating temperatures in steels and aluminum alloys, the number n = N does not exceed 10 in absolute value. The first term of the series is calculated at n = 0 and the number n ceases to increase in absolute value when the required accuracy of temperature calculations is achieved. Therefore, we can recommend limiting the number n = ± 10 when calculating by formula (3). This will provide the necessary accuracy in temperature calculations, both for welding steels and aluminum alloys. All other alloys have intermediate thermophysical properties and this recommendation is universal.

The upper limit of integration of time t is chosen such that the temperature field in the plate is steady-state (quasi-stationary). This is a state of the temperature field when the temperature of all points of the body in the welding zone changes by a negligible amount. In this condition, the penetration depth and weld width reach the nominal values with high accuracy. The t value, like the n value, is selected based on the required computational accuracy. Experiments and calculations show that in conditions of double-sided welding of butt joints (plate thickness 6-8 mm), this state is achieved in about 10 seconds for steels and 15 seconds for aluminum steels with a very high relative accuracy of temperature calculation of at least 0.1%. Therefore, it can be recommended to limit the upper limit of integration in integrals to 15 seconds when calculating by formula (3). This will provide the necessary accuracy in temperature calculations, both for welding steels and aluminum alloys and other alloys.

The value of the effective power q _And in the formula (3) for the welding arc should be determined by the formula

where I is the welding current (arc), A;

q _Y - specific effective arc power, equal to the quotient of dividing the experimental value of the effective power by the welding current, W / A.

Therefore, in formula (2), instead of the effective power of the arc q _AND , expression (4) is used. This form makes it possible to isolate and present more clearly the direct effect of the welding current as a mode parameter on the temperature of the product and, consequently, on the penetration depth, and to obtain formula (2) for calculating the regulating welding current.

From formula (3) it can be seen that the temperature of the points of the body is proportional to the effective power of the heat source and inversely proportional to the volumetric heat capacity of the plate. Therefore, the temperature will be proportional to the ratio of these values. This makes it possible to determine experimentally and further use in formula (3) not each of these values separately, but their ratio, and in the future, when adjusting the penetration depth, operate with this ratio. Let us denote this ratio Q, excluding the welding current, which can change during welding due to the action of disturbances

The dimension of the coefficient Q is (cm ³ ⋅ ° С) / (А⋅с). When multiplying Q by the welding current I, we get the dimension (cm ³ ⋅ ° C) / (s).

. Для их однозначного определения на номинальном (эталонном) режиме нужно знать две независимые температуры в двух точках тела при известных координатах этих точек х, у, z. Тогда из формулы (3) можно составить систему уравнений относительно неизвестных коэффициентов. Так как известно, что на границе шва с основным металлом при сварке температура всегда равна температуре плавления, можно использовать ширину шва и глубину проплавления для отыскания постоянных коэффициентов Q и

в формуле (3), а затем применять эти коэффициенты при расчете регулирующего параметра - тока сварки. При этом обеспечивается высокая точность определения регулирующего воздействия, так как полученные коэффициенты изменяются очень незначительно при имеющих место возмущениях параметров сварки, в том числе вследствие их стабилизации.In this case, it turns out that only two unknowns remain in formula (3): the proportionality coefficient Q and the thermal diffusivity

... For their unambiguous determination in the nominal (reference) mode, you need to know two independent temperatures at two points of the body with the known coordinates of these points x, y, z. Then from formula (3) it is possible to compose a system of equations for unknown coefficients. Since it is known that at the interface of the weld with the base metal during welding, the temperature is always equal to the melting temperature, you can use the width of the weld and the depth of penetration to find constant coefficients Q and

in the formula (3), and then apply these coefficients when calculating the control parameter - welding current. At the same time, a high accuracy of determining the control action is ensured, since the obtained coefficients change very insignificantly when there are disturbances in welding parameters, including due to their stabilization.

.Instead of the z coordinate in formula (3), when compiling formula (2), the nominal (reference) penetration depth H _{0 was used} , since it is used to calculate the welding control parameter - the welding current, that is, when regulated, it is a known set value, and unknown is the value of the control parameter - welding current. The value of the y coordinate is taken to be zero (y = 0), since the maximum penetration depth occurs at such a value of y due to the symmetry of the temperature distribution about the X axis. The value of the x ₀ coordinate is determined numerically during the calculation of the Q and

...

The value of q _Y in the literature is called the volt equivalent of effective power or specific heat flux. The last name does not quite accurately reflect the essence of this parameter, since the concept of heat flux density includes the area over which the power acts. It is more accurate to call this value the specific effective power. The value of q _{Y is} weak, but still depends on the current and arc length, and, consequently, on the arc voltage. This is due to the fact that the effective power when welding with a non-consumable electrode is mainly transferred to the product from the near-electrode region of the arc at the product. In this regard, the stabilization of the arc voltage in the proposed method has a positive effect on the accuracy of control of the penetration depth.

It is known that the effective power of the welding arc is often determined by the formula

where U is the voltage of the welding arc, V,

η _И - effective efficiency of the welding arc.

Comparing formulas (4) and (6), it can be noted that in fact

From formula (7) it follows that the joint change in the arc voltage and the effective welding efficiency can be such that with an increase in one of them (voltage, arc length), the second will decrease, and in general, the product of these values will be stable. This is actually the case in practice when changing the arc length.

The effective efficiency of a welding arc of straight polarity in argon with a nonconsumable tungsten electrode in the literature is recommended to be taken in the range of 0.65-0.75 (see, for example, A.A. Erokhin, Fundamentals of fusion welding. M .: Mashinostroenie, 1973, 448 p. P. 13, table 1.2). The deviation from the mean here is ± 8%. In many cases, it is much larger. Such a scatter of efficiency values is due to changes in conditions such as arc length, welding speed, electrode sharpening angle, metal thickness, quality of its surface, etc. With an increase in the arc length, the effective efficiency usually decreases. This is caused by an increase in the voltage in the arc column and the constancy of the useful (effective) power transmitted by the arc to the product by its near-electrode region. With the lengthening of the arc, the increase in arc power occurs mainly due to an increase in the release of energy in the arc column, and almost all of it is lost to the environment. In contrast to the efficiency, the specific effective power q _{Y is} practically independent of the current. This makes it possible, by calculating the coefficient Q by the dimensions of the weld at nominal welding parameters, to take it constant and then use it to calculate the regulating welding parameter with disturbances in the arc current. At the same time, the influence of the volumetric heat capacity cρ is taken into account.

Based on the experiment to determine the dimensions of the weld in the proposed control method, not the value of q _Y itself is determined, but the proportionality coefficient Q, in which q _Y is a factor. Then the disturbing effect on the welding current will lead to a proportional change in the Q⋅I multiplier in formula (3) and it is possible to calculate the welding control parameter - the welding current. Knowing the current when welding a reference seam, it is easy to calculate by the coefficient Q and the value of q _Y.

Equating in formula (3) the temperature T equal to the melting temperature T _L , measured from zero degrees Celsius and taking into account the initial temperature of the plates T ₀ , we obtain an equation for finding the depth of penetration H at y = 0 along the X axis. Including can be found by the numerical method maximum penetration depth Н ₀ and its coordinate x ₀ .

Using equation (8), it is possible to calculate any size of the weld pool, including the depth of the weld pool H in any plane along the plate thickness, including the maximum one at the coordinate y = 0, that is, find the coordinates x, z at which the temperature increment ΔТ = ΔT _L. If we take a different value for y, we obtain the depth of penetration in a plane parallel to the Y axis. The value of the z coordinate is taken in this calculation to be equal to the penetration depth H and is the desired value when constructing the profile of the weld pool boundary in Fig. 2.

To find the z coordinate with a temperature equal to the melting temperature, for example, for each selected x coordinate, the method of dividing the segment between the planes of the plates in half (dichotomy method) can be used. This method calculates the temperature of a point in the middle plane of the plate first. The search for the maximum penetration depth and the x ₀ coordinates of its position can be carried out numerically by successive substitution of the x coordinates with a certain step Δx. When calculating the profile in FIG. 2 step Δx was chosen 0.1 cm = 1 mm. Thus, the profile shown in FIG. 2 is the reference design longitudinal profile of the weld pool along the weld axis X.

=0,0432 см²/с (см. Сидоров В.П. Двухдуговая двусторонняя сварка неплавящимися электродами в аргоне / В.П. Сидоров, С.А. Хурин. Тольятти: Изд-во ТГУ, 2015. - 191 с. - С. 67-68).The values of thermophysical coefficients when calculating the profile in Fig. 2 were taken as recommended for high-alloy steel 304L (USA): volumetric heat capacity cρ = 3.476 J / (cm ³ ° C), thermal diffusivity

= 0.0432 cm ² / s (see Sidorov V.P. Double-arc double-sided welding with non-consumable electrodes in argon / V.P. Sidorov, S.A. Khurin. Togliatti: TSU Publishing House, 2015. - 191 p. - S. 67-68).

The plate thickness was assumed when calculating δ = 0,6 cm, the effective power of the heat source _and q = 1350 W, the welding speed V _C = 0,43 cm / s. With a specific effective power q _Y = 6.0 W / A, this power corresponds to a welding current I = 225 A.

The value of the Q coefficient for the given calculation parameters

Q = q _Y / cρ = 6 / 3.476 = 1.726 (cm ³ ° C) / (A⋅s).

The melting temperature of high-alloy steel, measured from 0 ° C, was taken as T _L = 1440 ° C. The nominal temperature of the parts before welding was taken T ₀ = 20 ° C. Thus, the nominal (reference) calculated melting temperature ΔT _L = (T _L -T ₀ ) when calculating the dimensions of the weld pool was 1420 ° C. The upper limit of integration of the time t in the equation compiled according to the formula (3) was taken t = 15 seconds, as a result of a further increase in time, the penetration depth changed by less than 0.01%. The division of one second when calculating one integral from the series in the equation into segments was M = 50. In this case, the computation time for one point of the profile on an ordinary personal computer is less than one second. When optimizing a computer program and using a faster computer, the time for calculating the regulating parameter according to formula (2), composed from (3), can be of the order of 0.01 s or less. The maximum penetration depth for the profile in FIG. 2 Н ₀ = 0.36 cm, which is 60% of the plate thickness. The choice of the same value of H ₀ for the second weld provides overlapping of the seams in height during double-sided welding by 0.12 cm = 1.2 mm - 20% of the plate thickness. Since when welding two symmetrical seams on both sides, in order to avoid lack of penetration, they must be welded by at least 50% of the thickness, the permissible deviation (-ΔH ₀ = 0.36) = - 0.6 mm. A positive deviation can be taken equal to +0.6 mm and then the maximum allowable penetration depth will be H = 4.2 mm.

Calculations according to equation (8) were performed by programming the calculations by setting the required accuracy of calculating the penetration depth, which was 0.01 mm. In this case, the number of positive and negative terms of the series in equation (8) did not exceed n = N = ± 10. The program automatically stops calculating when the specified calculation accuracy of the last term of the series in (8) is reached.

The definition of the profile points in FIG. 2 was produced as follows. The Y-axis coordinate is set to y = 0, so that the maximum penetration depth is ensured. Then the starting point is set with the x = 0 coordinate and the dichotomy method is used to calculate the value of the z coordinate, which represents the endpoint with the melting point. After that, the x coordinate changes with a certain step and the calculation is repeated. In the calculations, for convenience, the positive direction of the x axis was chosen opposite to the direction of welding, which is achieved by changing the sign at x in equation (8). From the obtained values of the penetration depth, a point with a maximum value of H ₀ is selected and its coordinate x _{0 is} determined.

In the X coordinate region with the maximum penetration depth, the latter changes with a low intensity, that is, the dH / dx derivative is close to zero. It can be assumed that the maximum penetration depth takes place in this mode at x ₀ = 0.45 cm. Such a dependence of H (x) makes it possible not to take into account the change in the position of x ₀ at small perturbations of the parameters and to take its found value for the nominal process parameters.

Methods for solving nonlinear equations of type (8) are described in detail in special literature, for example, see V.P. Dyakonov. Reference book on algorithms and programs in the BASIC language for personal computers. - M .: Nauka, 1987 - 240 p., Pp. 86-91, programs 4.11 ... 4.19. In a certain place of such programs, calculations are programmed according to the original function, according to which the equation is formed. In our case, for the profile in FIG. 2 is function (3). The dichotomy method is described in Program 4.15 on page 89 of this handbook.

. При этом отпадает необходимость прямого измерения эффективной мощности дуги калориметрированием, которое заменяется более простым определением эталонной ширины шва В₀ и глубины шва Н₀. Одновременно устраняется неопределенность с назначением объемной теплоемкости сρ. Такой методикой устраняются неточности математической модели, вызванные принятием допущения о постоянстве теплофизических коэффициентов, отсутствии учета их зависимости от температуры, а также допущение о действии точечного источника тепла. При составлении системы уравнений для расчета коэффициентов Q и

второе уравнение будет иметь видUsually, the problem when using formulas like formula (3) for calculating temperatures during welding in a linear formulation of the problem (thermophysical coefficients are taken to be independent of temperature) is precisely the assignment of the values of these coefficients, since in reality they depend to a certain extent on temperature. Usually, the best convergence of the calculated and experimental thermal cycles of plate points is achieved by choosing the values of the coefficients for a certain average welding temperature. Recommendations for the selection of such an average welding temperature are not suitable for achieving the required accuracy of calculations with automatic control. However, if we use two parameters of the temperature field (in the proposed control method these are the penetration depth and the seam width), then we can obtain two exact values of the coefficients Q and

... This eliminates the need for direct measurement of the effective arc power by calorimetry, which is replaced by a simpler determination of the reference weld width B ₀ and the seam depth H ₀ . At the same time, the uncertainty with the assignment of the volumetric heat capacity cρ is eliminated. This technique eliminates the inaccuracies of the mathematical model caused by the assumption of the constancy of thermophysical coefficients, the lack of taking into account their dependence on temperature, as well as the assumption of the action of a point heat source. When compiling a system of equations for calculating the coefficients Q and

the second equation will be

, для заданных максимальной глубины проплавления и ширины шва.In equation (9), instead of the y coordinate, half of the nominal (reference) weld width B _{0 is used} , and z = 0 is substituted for the z coordinate, so the maximum seam width will take place on the plate surface from the side of the heat source. The x coordinate is variable and is fixed to the maximum width of the weld pool. Thus, the solution to the system of equations (8) and (9) consists in finding the unique values of the coefficients Q and

, for the given maximum penetration depth and weld width.

FIG. 3 shows the calculated half-isotherm of the weld pool on the surface of the plates from the side of the heat source, obtained using equation (9), compiled by formula (3). Heat source parameters and thermophysical coefficients are similar to the curve in Fig. 2. The z coordinate in equation (3) was taken z = 0. One half of the isotherm is shown, since such an isotherm is symmetric about the longitudinal axis X. The order of constructing the isotherm is similar to constructing the penetration profile for Fig. 2. The difference lies in the fact that when using the dichotomy method for calculating (dividing a segment in half), it is necessary to search for the weld pool boundary inside the Δу segment, the size of which must be chosen deliberately greater than the maximum width of the weld pool. This is done in such a way that the remote boundary of the calculation zone is taken in proportion to the thickness of the plates being welded, for example, 3δ, which is obviously more than half the reference seam width.

Another option is an approximate estimate of the seam width according to the known simpler formula for a point fast-moving heat source, which gives a slightly overestimated value of the seam width, in comparison with a heat source moving at a limited speed.

Then the point with the x coordinate is set and the value of the y coordinate, representing the boundary point with the melting point, is calculated using the dichotomy method. After that, the x coordinate changes with a certain step and the calculation is repeated. When constructing the isotherm, for convenience, the positive direction of the x axis was chosen opposite to the direction of welding, which is achieved by changing the sign at x in Eq. (9). From the obtained values of the width of the weld pool, the point with the maximum value of the seam width B ₀ is selected. This point is always in the direction opposite to the direction of welding, so the first value of x can be taken x = 0, and then change it with a certain step. When plotting the isotherm in FIG. 3 step along X Δх = 0.1 cm = 1 mm.

формулы (3) и уравнений (8), (9).In the X coordinate area with the maximum width of the weld pool (weld width), it changes with a low intensity, that is, the derivative dB / dx is close to zero. It can be assumed that the maximum width of the weld pool takes place at x ₀ = 0.40 cm. Such a dependence B (x) makes it possible not to take into account the change in the position of x ₀ at small perturbations of the parameters and to take its found value for the nominal process parameters. This is necessary when determining the coefficients Q and

formulas (3) and equations (8), (9).

From the graph in FIG. 3 it follows that the total length of the weld pool along the axis at y = 0 is L = ≈1.4 cm.The length of the pool in front of the heat source is ≈0.2 cm, and the length of the pool behind the heat source is ≈1.2 cm. These data are necessary, to locate the temperature measuring point on the weld axis outside the weld pool.

FIG. 4 shows the dependences of the specific effective power q _Y on the arc current of straight polarity in argon to the copper anode according to the literature data. In this case, the formula for q _Y has the form

where Wa is the effective power to the anode of the welding arc, W;

- ток дуги (сварки), А.

- arc current (welding), A.

Curve 1 shows the dependence when using pure tungsten with diameters of 3.2 mm and 1.6 mm as a tungsten electrode, curve 2 - dependence when using a thoriated tungsten electrode with a diameter of 3.2 mm. The largest change in the specific effective power takes place for curve 2 and is 0.2 W / A in the arc current range of 50-70 A, which with a deviation of the arc current by 10 A will lead to an error in determining the effective arc power by only 2 W, which is approximately 0.3%.

The dependencies in FIG. 4 and the designations of the quantities are given in the monograph by A.V. Savinova et al. "Non-consumable electrode arc welding." M .: Mechanical engineering. 2011 .-- 477 p. P. 82, fig. 1.57.

FIG. 5 shows the calculated dependences of the maximum penetration depth H and the weld width B on the coefficient Q, obtained using equations (8) and (9). The thermophysical parameters of the calculation remained the same as for the dependence in Fig. 2. Curve 3 represents the dependence for the depth of penetration H, and curve 4 for the width of the weld B. In the range of coefficients Q centered at the point of the nominal mode Q = 1.73 (cm ³ ° C) / (А⋅с), the average transmission coefficient for penetration depth k _PN = ΔH / ΔQ = 0.65 / 1.72 = 0.378 mm / [(cm ³ ° C) / (A⋅s)]. Dependence 3 shows the influence of the Q coefficient on the penetration depth. Therefore, an accurate determination of the coefficient Q, for given welding conditions, taking into account the effective power and heat capacity of the metal, is necessary for accurate control of the penetration depth.

. Остальные параметры расчета и коэффициенты были как для профиля на фиг. 2. Значение коэффициента Q=1,73 (см³°С)/(А⋅с), q_И=1350 Вт, чему соответствует ток сварки I≈225 А.FIG. 6 shows the dependences of the penetration depth and weld width on the thermal diffusivity coefficient calculated according to equations (8) and (9)

... The rest of the calculation parameters and coefficients were the same as for the profile in Fig. 2. The value of the coefficient Q = 1.73 (cm ³ ° C) / (A⋅s), q _И = 1350 W, which corresponds to the welding current I≈225 A.

на глубину проплавления. Поэтому точное определение

для данных условий сварки, необходимо для точного регулирования глубины проплавления.Curve 5 refers to the depth of penetration H, and curve 6 to the width of the weld B. From dependencies 5 and 6 it can be seen that an increase in the thermal diffusivity leads to a decrease in the depth of penetration and the width of the weld. Dependence 5 shows the influence of the thermal diffusivity

to the depth of penetration. Therefore, the precise definition

for given welding conditions, it is necessary to accurately control the penetration depth.

FIG. 7 shows the dependences of the maximum penetration depth H and the weld width B on the welding speed, calculated according to equations (8) and (9). The calculation parameters remained the same as for the weld pool profile in Fig. 2. Curve 7 represents the dependence for the depth of penetration, and curve 8 for the width of the seam B. The value of the coefficient Q = 1.73 (cm ³ ° C) / (А⋅с).

In the range of welding speeds V _C = 0.38-0.48 cm / s, the average transmission coefficient for the depth of penetration k _PN = ΔН / ΔV _C = (0.56) / 0.1 = 5.6 mm / (cm / s ).

FIG. 8 shows the calculated dependences of the maximum penetration depth and weld width on the difference ΔT _L between the melting temperature T _L and the initial temperature of the parts T ₀ , obtained according to equations (8) and (9). This difference characterizes the plate heating temperature, the initial plate temperature. From formula (3) it follows that heating the plate is equivalent to a decrease in the melting temperature of the metal. Curve 9 refers to the penetration depth, curve 10 to the weld width. Other calculation parameters correspond to the data for Fig. 2.

или объемной теплоемкости сρ. Уменьшение объемной теплоемкости будет эквивалентно увеличению удельной эффективной мощности и приведет к повышению реальной температуры изделия. Это отразится на измеренной температуре точки, которая также повысится. В связи с этим регулирующая система произведет уменьшение тока сварки. Для учета влияния возмущения по коэффициенту температуропроводности или объемной теплоемкости необходимо при расчете регулирующего воздействия с помощью формулы (2) изменить разность между температурой плавления T_L и номинальной начальной температурой пластины Т₀ на величину разности температур в точке замера измеренной Т_И и расчетной Т_Р. Эту разность (Т_И-Т_Р) нужно вычесть из (T_L-T₀). При положительной разности (Т_И-Т_Р) начальная температура в формуле (2) снизится, что означает снижение глубины проплавления приведет к повышению расчетного тока сварки I по формуле (2). При отрицательной разности (Т_И-Т_Р) начальная температура в формуле (2) повысится, что означает повышение глубины проплавления и приведет к уменьшению расчетного тока сварки I по формуле (2).The value of the coefficient Q = 1.73 (cm ³ ° C) / (А⋅s). The curves in FIG. 8 show that deviations in the plate temperature, if not taken into account in the regulation, will lead to errors in the control of the penetration depth. Transfer coefficient for curve 9 k _P = ΔН / ΔТ = 0.49 / 200 = 2.45⋅10 ^-3 mm / ° С. Deviations of the temperature at the measuring point from the nominal temperature will characterize the overall heating of the weldment. Since the arc voltage and welding speed in the proposed method are stabilized, the change in the temperature of the measuring point will characterize mainly the effect of only uncontrolled disturbances, for example, the thermal diffusivity

or volumetric heat capacity сρ. A decrease in the volumetric heat capacity will be equivalent to an increase in the specific effective power and will lead to an increase in the actual temperature of the product. This will affect the measured point temperature, which will also rise. In this regard, the control system will reduce the welding current. To account is necessary when calculating the regulatory impact of the perturbation effect on the coefficient of thermal or volume heat capacity using formula (2) to change the difference between the melting temperature T _L and nominal initial temperature of the plate T ₀ to the temperature difference value at the measuring point measured by T _{D and} the calculated T _R. This difference (T _AND -T _P ) must be subtracted from (T _L -T ₀ ). With a positive difference (T _AND -T _R ), the initial temperature in formula (2) will decrease, which means a decrease in the penetration depth will lead to an increase in the calculated welding current I according to formula (2). With a negative difference (T _AND -T _R ), the initial temperature in formula (2) will increase, which means an increase in the penetration depth and will lead to a decrease in the calculated welding current I according to formula (2).

FIG. 9 shows the calculated dependences of the penetration depth and weld width on the plate thickness, obtained using equations (8) and (9). Curve 11 shows the dependence for the penetration depth, and curve 12 for the weld width. The calculation parameters were used as when constructing the profile in Fig. 2. The value of the coefficient Q = 1.73 (cm ³ ° C) / (A⋅s).

The thickness of the plate should be attributed to uncontrolled process parameters, since its measurement during the welding process is difficult and it is unclear at what point of the plates being welded to be measured. With an increase in the thickness of the plate, the penetration depth and the width of the seam decrease, which will lead to a constant control error, if the welding current is not corrected and the change in plate thickness is not taken into account in the calculations when adjusting. This is done by measuring the temperature at the measuring point. A change in thickness always affects the penetration depth and temperature of any measuring point with the same sign. Therefore, for perturbations in thickness, the position of the temperature measurement point is indifferent.

и коэффициента Q. Кривая 13 представляет зависимость номинальной глубины проплавления Н₀ от коэффициента Q при коэффициенте температуропроводности

см²/с, кривая 14 при

см²/с, а кривая 15 при

см²/с. Через эти кривые проводится линия, параллельная оси коэффициента Q при значении Н=Н₀. Точки пересечения этой прямой с кривыми 13, 14, 15 дают координаты значений Q₁, Q₂, Q₃ при разных коэффициентах температуропроводности и дают возможность построить изолинию «коэффициент Q - коэффициент температуропроводности

» на фиг. 11, относящуюся к максимальной глубине проплавления.FIG. 10 shows a diagram of the construction of isolines to obtain the thermal diffusivity

and coefficient Q. Curve 13 represents the dependence of the nominal penetration depth H ₀ from the coefficient Q at the coefficient of thermal diffusivity

cm ² / s, curve 14 at

cm ² / s, and curve 15 at

cm ² / s. A line is drawn through these curves parallel to the axis of the coefficient Q at the value H = H ₀ . The points of intersection of this straight line with curves 13, 14, 15 give the coordinates of the values Q ₁ , Q ₂ , Q ₃ at different coefficients of thermal diffusivity and make it possible to construct the isoline "coefficient Q - coefficient of thermal diffusivity

"In FIG. 11 for the maximum penetration depth.

Similarly, the graph of the second isoline is plotted for the seam width B ₀ .

» для заданных значений номинальной глубины проплавления Н₀ и номинальной ширины шва В₀. Кривая 16 представляет изолинию для глубины проплавления Н₀, а кривая 17 - изолинию для ширины шва В₀. Изолиния - это такая кривая, на которой любая точка с различными коэффициентами Q и

дает одинаковое значение исследуемого параметра. В данном случае любая точка на кривой 16 дает одинаковую номинальную глубину проплавления Н₀, а любая точка на кривой 17 дает одинаковую номинальную ширину шва В₀. Поскольку сочетание номинальной глубины проплавления и номинальной ширины шва для номинального режима единственное, то изолинии 16 и 17 имеют одну точку пересечения, которая дает единственные значения искомых коэффициентов Q и

. Эти значения необходимо использовать для расчета величины регулируемого тока сварки при его расчете по формуле (2), что обеспечивает высокую точность регулирования глубины проплавления. Кривые строились на основе эксперимента по сварке стали марки 0Х18Н9Т толщиной 6 мм. Ток сварки I=200 А, скорость сварки V_C=0,4 см/с. Ширина шва В₀=6,8 мм Максимальная глубина проплавления Н₀=3,6 мм. Согласно фиг. 11 можно принять

=0,05 см²/с, Q=1,87 (см³°С)/(А⋅с). Полученным значениям соответствует эффективная мощность дуги q_И=1650 Вт и удельная эффективная мощность q_У=8,25 Вт/А.FIG. 11 shows two isolines "coefficient Q - coefficient of thermal diffusivity

»For the given values of the nominal penetration depth H ₀ and the nominal weld width B ₀ . Curve 16 represents the isoline for the penetration depth H ₀ , and curve 17 is the isoline for the weld width B ₀ . An isoline is a curve on which any point with different coefficients Q and

gives the same value of the investigated parameter. In this case, any point on curve 16 gives the same nominal penetration depth H ₀ , and any point on curve 17 gives the same nominal weld width B ₀ . Since the combination of the nominal penetration depth and the nominal weld width for the nominal mode is the only one, the isolines 16 and 17 have one intersection point, which gives the only values of the sought coefficients Q and

... These values must be used to calculate the value of the adjustable welding current when calculating it according to formula (2), which ensures high accuracy of control of the penetration depth. The curves were constructed on the basis of an experiment on welding steel grade 0Kh18N9T with a thickness of 6 mm. Welding current I = 200 A, welding speed V _C = 0.4 cm / s. Joint width B ₀ = 6.8 mm Maximum penetration depth H ₀ = 3.6 mm. As shown in FIG. 11 can be taken

= 0.05 cm ² / s, Q = 1.87 (cm ³ ° C) / (A⋅s). The obtained values correspond to the effective arc power q _I = 1650 W and the specific effective power q _Y = 8.25 W / A.

принимается постоянной, найденной для номинального режима. В обоих уравнениях, решаемых численным методом с помощью изолиний, координата по оси X изменяется с небольшим шагом Δх.The construction of isolines actually represents a graphical method for solving a system of two nonlinear equations (8) and (9), compiled according to formula (3). In this case, in one of the equations, the coordinate is y = 0, az = H ₀ , and in the other z = 0, and y = B _0/2 . The value of the longitudinal coordinate x ₀₁ with the maximum penetration depth when finding the Q coefficient is assumed constant, found for the nominal mode. Similarly x ₀₂ for the width of the weld pool (seam) when finding the thermal diffusivity

is assumed to be the constant found for the nominal mode. In both equations, solved numerically using isolines, the coordinate along the X axis changes with a small step Δх.

. Параметры расчета аналогичны зависимости глубины проплавления от коэффициента температуропроводности

на фиг 6. (кривая 5). Параметры расчета такие же, как для фиг. 2 и фиг. 6. Кривая 18 представляет зависимость для точки замера с координатами у=0, z=0 х=1,4 см. Это точка на оси шва со стороны действия источника тепла на расстоянии 0,2 см от конца сварочной ванны. Кривая 19 для точки у=0, z=0,6 х=0,5 см. Это точка на противоположной плоскости пластины. Координата х близка к координате х₀=0,45 см с максимальной глубиной сварочной ванны. Кривая 20 для точки у=0, z=0,6 х=1,2 см. Это точка также на противоположной плоскости пластины, более удалена от источника тепла. Координаты точек указаны в подвижной системе координат, центр которой в точке действия точечного источника тепла.FIG. 12 shows the dependences of the temperature of three points of the plate surface on the thermal diffusivity

... The calculation parameters are similar to the dependence of the penetration depth on the thermal diffusivity

in Fig. 6. (curve 5). The calculation parameters are the same as for FIG. 2 and FIG. 6. Curve 18 represents the dependence for the measuring point with coordinates y = 0, z = 0 x = 1.4 cm. This is a point on the weld axis from the side of the heat source at a distance of 0.2 cm from the end of the weld pool. Curve 19 for the point y = 0, z = 0.6 x = 0.5 cm. This is a point on the opposite plane of the plate. The x coordinate is close to the x ₀ = 0.45 cm coordinate with the maximum weld pool depth. Curve 20 for the point y = 0, z = 0.6 x = 1.2 cm. This point is also on the opposite plane of the plate, more distant from the heat source. The coordinates of the points are indicated in a moving coordinate system, the center of which is at the point of action of the point heat source.

глубина проплавления и температура точки замера могут изменяться с одинаковым знаком или с противоположным знаком. При регулировании, в случае влияния отклонения коэффициента

на температуру с противоположным знаком, по отношению к глубине проплавления это приведет к нарушению устойчивости регулирования. Точки замера температуры для кривой 18 и 20 подходят для регулирования глубины проплавления, а точка для кривой 19 - не подходит. Для нее с увеличением коэффициента температуропроводности

происходит увеличение температуры точки, в то время как максимальная глубина проплавления уменьшается (кривая 5 на фиг. 6).By comparing graphs 18, 19 and 20 in FIG. 12 and graph 5 in Fig. 6, it can be seen that with a decrease or increase in the thermal diffusivity

penetration depth and measuring point temperature can vary with the same sign or with the opposite sign. During regulation, in case of influence of coefficient deviation

to a temperature with the opposite sign, in relation to the penetration depth, this will lead to a violation of the stability of the regulation. The temperature measuring points for curve 18 and 20 are suitable for adjusting the penetration depth, but the point for curve 19 is not. For it, with an increase in the thermal diffusivity

the point temperature increases, while the maximum penetration depth decreases (curve 5 in Fig. 6).

FIG. 13 shows a diagram of automatic control according to the proposed method. The work piece 21 to be welded moves relative to the welding arc 22 at a speed V _C burning from the electrode of the welding torch 23, which is stationary. The power source 24 is connected with the positive pole to the product 21, and the negative pole to the non-consumable electrode of the welding torch 23. The welding arc 22, burning from the non-consumable electrode of the torch 23 to the product 21, melts the edges of the product to be welded 21. A weld pool 25 is formed and after solidification of the molten metal occurs weld 26 with a nominal maximum depth of penetration H ₀ and a nominal width B ₀ . Their values are measured after welding at nominal welding parameters of the reference sample. The welding current is measured by a 27 current sensor connected to the welding circuit. In the weld puddle 25, between the nonconsumable electrode of the welding torch 23 and the weld puddle 25, filler wire 28 is fed at a speed V _P equal to the rate of its melting by the heat of the arc 22. Welding speed V _C , arc voltage 22 U and speed V _P of filler wire 28 are stabilized by separate devices with a given accuracy. These devices in FIG. 13 are not shown.

On the bracket 29, mounted on the welding torch 23, a temperature sensor 30 of the surface of the product 21 is attached at point A on the axis of the seam 26 outside the weld pool 25.

During welding, the welding current is measured using the current sensor 27. The current values from the sensor 27 are transmitted to the computing unit 31, in which, on the basis of the given constants, a constant stabilized welding speed value and the measured value of the welding current I _AND , the calculated value of the temperature T _{P of} the measuring point is calculated And according to the formula (3).

и Q определяется координата подходящей точки замера температур А на поверхности изделия 21(z, у, х)_А. В вычислительном блоке 31 используются следующие необходимые для расчета коэффициенты: температуропроводность

, коэффициент Q, начальная номинальная температура изделия Т₀, толщины пластин изделия δ, значения координат точки замера температуры, скорость сварки V_C.Before welding according to the above procedure after welding the reference seam and determining the coefficients

and Q, the coordinate of a suitable temperature measurement point A on the surface of the product 21 (z, y, x) _{A is} determined. The computing unit 31 uses the following coefficients necessary for the calculation: thermal diffusivity

, coefficient Q, the initial nominal temperature of the product T ₀ , the thickness of the plates of the product δ, the values of the coordinates of the temperature measurement point, the welding speed V _C.

The calculated temperature T _P is transmitted to the temperature comparison unit 32. The measured temperature of point A from the temperature sensor 30 is also transferred to the comparison unit 32. The comparison unit 32 calculates the difference between the measured T _AND and the calculated temperatures T _P. The obtained temperature difference (T _P -T _And ) from the comparison unit 32 is transmitted to the second computing unit 33, in which the initial temperature of the welded product is first changed from T ₀ by the value of the obtained difference, and then the required welding current I _{P is} calculated using the formula (2 ). The constants necessary for the calculation are also stored directly in the block 33. The calculated value of the welding current I _P is transmitted from the computing unit 33 to the welding power source 24, in which the welding current I _P required to stabilize the penetration depth is set. Due to the rather high inertia of penetration during welding with respect to the action of disturbances, the measurement of the welding current and the surface temperature of the product and the calculation of the required current are performed discretely, for example, with a frequency of 0.05 seconds.

In the computing unit 33, in addition to the constants stored in the computing unit 32, the value of the melting temperature of the metal of the product T _L and the nominal maximum penetration depth H ₀ , coordinates of the point x ₀ with the maximum penetration depth are stored. At the same time, the computational unit 32 does not store the coordinates of point A.

As a welded product 21, plates can be used when surfacing layers with special properties or parts of a butt joint without cutting edges during welding, for example, joining pipe blanks.

Example 1.

The determination of the regulating welding current was carried out according to the proposed method. The power source had a control system for setting the required welding current.

For welding, plates of steel 20 with a thickness of δ = 6 mm were used. The regulation was considered for the case of welding the first layer of a double-sided weld. The nominal penetration depth was 60% of the plate thickness H ₀ = 3.6 mm. The permissible deviations from this value were chosen ΔH ₀ ± 0.6 mm, that is, ± 10% of the thickness. To obtain the nominal penetration depth, the mode of argon-arc welding with a non-consumable tungsten electrode without filler wire was selected on the straight arc polarity: welding voltage (arc) U = 14.0 V, welding current (arc) I = 275 A, welding speed V _C = 0, 25 cm / s (nominal modes). The welding speed and arc voltage were stabilized with an accuracy of ± 0.5% of the nominal values.

The nominal joint width at this amounted B ₀ = 0.653 cm = 6.53 mm.

и на точке пересечения изолиний получены расчетные значения Q=1,2 (см³°С)/(А⋅с) и температуропроводности

=0,08 см²/с. Координата точки в направлении движения источника тепла, в которой глубина проплавления максимальна при у=0 составила x₀=0,2 см. Эта координата используется при расчете регулирующего тока сварки. Длина сварочной ванны на поверхности пластины составила L=0,9 см, а координата точки конца сварочной ванны позади дуги x_L=0,6 см. Последняя координата необходима для поиска точки замера температуры, так как точка замера должна располагаться за пределами сварочной ванны.The initial temperature of the plates was T ₀ = 20 ° C. According to the experimental values of the nominal penetration depth H ₀ = 0.36 cm and the nominal weld width B ₀ = 0.653 cm and the melting temperature of low-carbon steel, measured from 0 ° C T _L = 1520 ° C at the nominal parameters of the welding process according to equations (8) and (9) with the help of a computer program written in the BASIC programming language, isolines were constructed “coefficient Q - coefficient of thermal diffusivity

and at the point of intersection of isolines, the calculated values of Q = 1.2 (cm ³ ° С) / (А⋅с) and thermal diffusivity were obtained

= 0.08 cm ² / s. The coordinate of the point in the direction of movement of the heat source, in which the penetration depth is maximum at y = 0 was x ₀ = 0.2 cm. This coordinate is used to calculate the control welding current. The length of the weld pool on the surface of the plate was L = 0.9 cm, and the coordinate of the point of the end of the weld pool behind the arc x _L = 0.6 cm.The last coordinate is necessary to find the temperature measuring point, since the measuring point must be located outside the weld pool.

After that, the position of the temperature measurement point was determined, at which the same sign of the change in the penetration depth and temperature of the point with coordinates on the surface from the side of the heat source z = 0, y = 0, x = 0.8 cm is ensured.The nominal design temperature of this point T _AP = 1196 ° C. In the course of another experiment, the real temperature of the point was determined at the nominal mode T _AI . The calculated temperature turned out to be + 5 ° C higher than the actual temperature. The relative error of the calculated temperature value relative to the experimental one is 0.04%, which fully meets the requirements for the accuracy of controlling the penetration depth. To take into account this error, an amendment was made to the welding current calculation program. The calculated temperature value was reduced by the obtained error of 5 ° C.

After completing the first seam, the second seam was immediately welded on the other side. The process parameters remained the same. As a result of welding the first seam, the plates were heated on average by 50 ° C, and the temperature was not quite uniformly distributed over the plate.

When performing test welding, the welding current after the formation of the weld pool of the plate is automatically carried out using the control device described for FIG. 13 decreased by 8 A and amounted to I = 267 A. Subsequently, the current gradually increased, which is associated with a decrease in the temperature of the plates due to heat removal into the lining. The depth of penetration along the length of the seam varied within ± 0.05 mm.

Example 2.

With the parameters of example 1, welding was carried out with an abrupt increase in the welding current and control of the penetration depth. The welding current was reduced using a ballast rheostat connected in series with the welding power source. The welding current was reduced by ΔI = 20 A, which first led to a slight decrease in temperature at the measuring point from the nominal 1196 ° C to 10 ° C. The temperature at the measuring point during welding with the control system turned off dropped to 1110 ° C. After that, due to the action of the control system, the current at the power source began to increase due to its own current regulator and after 0.5 seconds it returned to its original position I = 275 A. On the longitudinal macrosection, a slight decrease in the penetration depth by 0.3 mm was observed from the moment the current decreased. Then the penetration depth returned to its original state H ₀ = 3.6 mm.

Example 3.

The determination of the regulating welding current was carried out according to the proposed method.

For welding, plates of aluminum alloy AD0 with a thickness of 8 mm and 7.5 mm were used. The regulation was considered for the case of welding the first layer of a double-sided weld. The nominal penetration depth was 60% of the plate thickness of 8 mm H ₀ = 4.8 mm. The permissible deviations from this value were chosen ± 0.8 mm, that is, ± 10% of the thickness. This ensures, while maintaining the nominal parameters, the overlap of the two joints in height by 1.6 mm. To obtain the nominal penetration depth, the mode of automatic argon-arc welding with a non-consumable tungsten electrode with a filler wire Sv-AD0 with a diameter of 2 mm was selected by an alternating current arc (reference mode): welding (arc) voltage U = 14.0 V, welding (arc) current I = 380 A, welding speed V _C = 0.5 cm / s. Argon consumption 12 l / min, tungsten electrode diameter 6 mm. The filler wire feed speed V _P = 30 m / h = 0.83 cm / s. In this mode, the width of the seam from the front side B ₀ = 0.884 cm = 8.84 mm, the depth of penetration H ₀ = 0.48 cm, and the seam bulge g = 0.5 mm were obtained.

The initial temperature of the plates was T ₀ = 20 ° C. The melting point of the AD0 alloy was taken according to the reference data T _L = 660 ° C. Then the calculated difference between the melting temperature and the initial temperature of the parts T ₀ ΔT _L = T _L -T ₀ = 660-20 = 640 ° C.

» значения этих коэффициентов. Q=2,6 (см³°С)/(А⋅с), а=0,75 см²/с.After that, it was calculated by plotting isolines "coefficient Q - coefficient of thermal diffusivity

»The values of these coefficients. Q = 2.6 (cm ³ ° C) / (A⋅s), a = 0.75 cm ² / s.

The coordinate of the point in the direction opposite to the arc movement, in which the penetration depth is maximum at y = 0 was x ₀ = 0.1 cm. This coordinate is used to calculate the welding control current. The total length of the weld pool on the surface of the product was 1.0 cm, and the coordinate of the end point of the weld pool x _L = 0.6 cm. This coordinate is necessary to find the temperature measuring point, since the measuring point must be located outside the weld pool.

After that, the position of the temperature measurement point was determined, at which the same sign of change in the penetration depth and temperature of the point with coordinates on the surface from the side of the heat source z = 0, y = 0, x = 1.0 cm at a distance of 0.4 cm from the end of the welding baths. The nominal design temperature of this point is T _0I = 491 ° C. In the course of another experiment, the real temperature of the point was determined at the nominal mode. The calculated temperature turned out to be + 3 ° C higher than the actual temperature. The relative error of the calculated temperature value relative to the experimental one is 0.06%, which fully meets the requirements for the accuracy of controlling the penetration depth. To take into account this error, an amendment was made to the welding current calculation program. The calculated temperature value was decreased by the obtained error of 3 ° C.

FIG. 14 shows a diagram of a sample for welding with a deviation in plate thickness. To plate 34 with a nominal thickness of 8 mm, plate 36 with a thickness of 7.5 mm was attached using manual argon-arc welding with a seam 35, which together constituted one of the halves of the entire sample. Plates 34 and 36 were joined when aligning the face planes on which the welding arc 22 acted. Thus, a shoulder 37 was formed in the middle along the length of the plates. The shoulder was directed to the side opposite to the welding side of the control seam. The ledge 37 of both abutting plates 34 and 36 is aligned over their entire width. The welding arc 22 generated by the welding torch 23 first moved over the surface of the specimen 34 of greater thickness, and when the middle of the length of the joint was reached, its thickness abruptly decreased. With the control system turned off, after the arc transitioned from a thicker plate to a thinner one, the maximum penetration depth on the thin plate reached 5.4 mm. With the control system turned on, when the arc 22 passed to half of the specimen of reduced thickness, the temperature of the measuring point gradually increased from 491 ° C to 520 ° C, and the welding current began to decrease and settled at a value of 367 A, decreasing by 13 A. macrosection along the weld axis, the depth of penetration of the plates in the half, where their thickness was 7.5 mm, first gradually increased by 0.3 mm, amounting to 5.1 mm, then began to decrease and reached 4.9 mm, increasing compared to the nominal value for a thickness of 8 mm by 0.1 mm. Therefore, the system reduced the penetration depth by 0.5 mm for the 7.5 mm plate. In this case, the nominal penetration depth for a thickness of 7.5 mm with a 10% tolerance, the maximum penetration depth in this mode is 4.5 mm, the maximum penetration is 5.25 mm. The resulting maximum penetration depth of 4.9 mm fell within the acceptable range for 7.5 mm from 4.5 to 5.25 mm. It turns out that the system did not adjust to the ideal state 4.5 mm penetration at a thickness of 7.5 mm by ΔH = 4.9-4.5 = 0.4 mm, but adjusted it by 0.5 mm in relation to the 8 mm plate, that is, it adjusted by 55%. Incomplete adjustment for 7.5 mm is due to the fact that the influence of the plate thickness on the penetration depth and the temperature of the measuring point have different relative disturbance transfer coefficients (RTR). Plate thickness has a greater influence on the penetration depth than on the temperature of a given measuring point. This does not lead to complete processing of the disturbance in the case of deviations in the thickness of the plates.

Example 4.

For the parameters of example 4, surfacing was carried out on a special composite specimen of aluminum alloys AD0 and AMts with a thickness of 8 mm. The samples were welded together with a welded seam at the ends using argon-arc welding to maintain the conditions of thermal conductivity between the plates during welding. Nominal welding conditions were obtained for AD0. They are given in example 3. When surfacing in the same mode on a plate made of AMts alloy, the maximum penetration H = 5.65 mm was obtained, and the nominal temperature at the measuring point was 527 ° C, which is 46 ° C higher than the nominal value on the AD0 alloy ... Control welding of docked samples was started on the AD0 alloy with regulation according to the proposed method.

When the arc transitions to half of the AMts alloy samples under the control system, the temperature of the measurement point began to increase and its maximum reached 510 ° C, which is 19 ° C higher than the nominal value for AD0, and the welding current decreased to I = 370 A. In the study of the longitudinal macrosection along the weld axis, the depth of penetration of the plates in the half where the AMts alloy was located first increased by 0.3 mm, and then reached the value H ₀ = 4.9 mm.

Thus, the overall increase in maximum penetration depth was only 0.1 mm in relation to the nominal value. Was adjusted 5.65-4.9 = 0.75 mm of a possible change in the penetration depth. The increase in the temperature of the measuring point was apparently caused by the fact that, with a close value of the volumetric heat capacity of the AD0 and AMts alloys, their thermal conductivity and thermal diffusivity coefficients differ, since the thermal diffusivity is determined by the formula

where λ is the thermal conductivity of the metal, W / (cm⋅ ° С).

достаточно близки. Аналогичная ситуация будет иметь место при сварке производственных стыков вследствие неоднородности теплофизических свойств свариваемого металла.This leads to an increase in the maximum penetration depth and the temperature of the measuring point when surfacing on the AMts alloy. When surfacing the control joint, a decrease in the point temperature reacted to a change in the thermal diffusivity of the second half of the sample, and the control system restored the maximum penetration depth almost to the nominal value. In this case, the current even decreased slightly. This is due to the fact that the relative perturbation transfer coefficient (RTR) for the point temperature and penetration depth by the coefficient

close enough. A similar situation will take place when welding production joints due to the inhomogeneity of the thermophysical properties of the metal being welded.

The proposed control method makes it possible to avoid additional measurement of the width of the heating zone during welding to a temperature higher than the specified one, to reduce the number of preliminary experiments to one and significantly reduce the complexity of determining the coefficients of the mathematical model while increasing the control accuracy, which improves the quality and its stability in welded joints. Experimentally, it is necessary to determine before regulation only the maximum penetration depth and the width of the seam in the nominal welding mode, and also to find by calculation the position of the measuring point that ensures the stability of regulation. Due to the stabilization of all parameters of the mode, except for the adjustable welding current, the accuracy of regulation of the maximum penetration depth is increased. In this method, it is possible to correct the welding current when the nominal initial temperature of the product changes and take into account the change in the thickness of the parts without conducting new experiments to determine the coefficients of the equation used. The method can be used with equal efficiency both in welding and surfacing without filler wire, and with filler wire. In the case of stabilization of the rate of melting and electrode feeding, the method can be used in consumable electrode welding.

The method can also be used in plasma welding, both without feed and with filler wire feed. In this case, in addition to the length of the open section of the arc column (compressed arc voltage) and the welding speed, it is necessary to stabilize the plasma-forming gas flow rate, which affects the effective arc power and the Q coefficient.

The method can be implemented using known devices - digital ammeters and current sensors for measuring the welding arc current, welding speed meters based on measuring the number of revolutions of the welding machine drive electric motor for moving the welding torch, remote sensors for measuring surface temperature. Almost all modern welding machines are equipped with a system for stabilizing the length and arc voltage. Many modern welding power sources allow microprocessor-based current control. Modern means of microprocessor technology and software allow high-speed calculation of the temperature of the measuring point and the calculation of the regulating value of the welding current. Therefore, the method has industrial applicability.

Claims (16)

A method for controlling the penetration depth in automatic nonconsumable electrode argon-arc welding of butt joints without cutting edges with or without filler wire, including maintaining the penetration depth at a predetermined constant level by regulating the welding current, while welding a reference seam is preliminarily performed, and in the process of performing argon-arc welding, it is measured and calculate the current temperature at a point on the joint surface and its deviation from the reference temperature, and measure the actual values of the controlled current in the welding process, which are corrected in accordance with their calculated values according to a given mathematical relationship, characterized in that said point on the joint surface is selected from the conditions for the coincidence in it by the sign of the influence of the coefficients of the mathematical dependence

and Q on the temperature with their influence on the adjustable depth of penetration of the weld, while at the nominal welding parameters, the maximum penetration and width of the weld are additionally measured, the melting point of the metal and the reference initial temperature and thickness of the parts to be welded are set, and in the process of regulation, the welding speed is stabilized and arc voltage and calculate the adjustable welding current according to the formula:

where I is the welding current, A, T _L - product melting point, ° С, T ₀ - nominal initial temperature of the product, ° С, Т _И - measured temperature of the surface point, ° С, Т _Р - design temperature of the surface point, ° С,

- coefficient of thermal diffusivity of the product, cm ² / s, Q is the ratio of the specific effective power of the welding arc q _Y to the volumetric heat capacity of the product cρ, (cm ³ ⋅ ° C) / (A⋅s), where q _Y is the ratio of the effective power of the welding arc to the welding current, W / A. x ₀ - coordinate of the point with the maximum penetration depth at nominal welding parameters, in the direction opposite to the direction of the welding speed, cm, V _C - welding speed, cm / s, t - current time since the beginning of the action and movement of the arc, s, δ - nominal product thickness, cm, Н ₀ - nominal maximum penetration depth, cm, n - integers from -10 to +10, and the thermal diffusivity

and the proportionality factor Q for said formula is calculated from the values of the width and depth of penetration of the reference weld.

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