RU2691824C1 - Method for controlling penetration depth during arc automatic welding - Google Patents

Abstract

FIELD: technological processes.SUBSTANCE: invention relates to the field of welding production. Method comprises maintaining penetration depth at a given constant level by controlling welding parameter, wherein actual values of controlled parameter are measured during welding. Besides, at nominal parameters of welding, width of welded seam is additionally measured, metal melting point and reference initial temperature of welded parts are set. As the controlled parameter, welding current is used, the values of which are corrected in accordance with the values calculated from the given mathematical relationship, including said temperatures, coordinates of the point with maximum penetration depth, rate of welding, nominal penetration depth, thickness of plates to be welded, as well as coefficient of thermal conductivity and coefficient of proportionality, which are calculated from values of width and depth of penetration of reference seam.EFFECT: use of the invention improves accuracy of welding current control and accordingly quality of welded joints.1 cl, 14 dwg

Description

The invention relates to the welding industry and can be used when argon-arc welding with non-consumable electrode butt joints without cutting edges and during argon-arc surfacing of the filler wire on the plate.

A known method of regulating the depth of penetration in automatic argon-arc welding with a non-consumable electrode without filler wire, in which one of the mode parameters is measured - welding current, arc voltage, welding speed, the difference between the measured and reference mode values is calculated and the measured parameter is adjusted, eliminating the difference. This method can be used to control simultaneously several parameters of the mode (see Gladkov, EA Automation of welding processes / EA Gladkov, VN Brodyagin, RA Perkovsky. - M .: MGTU Publishing House named after NE Bauman, 2014. - 421 p. p. 294, Fig. 6.4 a).

A technical problem when using this method is the need to regulate simultaneously all the measured mode parameters, which makes the control system difficult. With such a system of regulation, there are high demands on the accuracy of maintaining each of the measured and controlled values. When determining the accuracy of maintaining each of the mode parameters, the total tolerance of the controlled penetration depth should be divided by the number of modes and the resulting deviation should be provided by each mode parameter separately.

The known method of regulating the depth of penetration during automatic argon-arc welding with a non-consumable electrode without filler wire butt joints without edge cutting, at which mode parameters are measured - welding current, arc voltage, welding speed, and the change of these parameters due to external disturbances is compensated by changing one of the measured parameters calculated from the condition of maintaining the constancy of a given depth of penetration H, which is determined by the previously obtained exp experimentally depending

where M, p, q, r - coefficients determined on the basis of experiments,

I is the arc current

U - arc voltage,

V _C - welding speed.

(see Japanese Patent No. 50-3987, Cl. 12В112.4, Cl. W23K 9/12, published on February 13, 75). This method of automatic control is taken as a prototype.

In this case, the requirements for the accuracy of maintaining the regulatory mode of welding are reduced by three times, which significantly reduces the cost of the equipment used. The main technical problem when using this method is the high complexity of the experimental determination of the coefficients of dependence (1) and insufficient regulation accuracy, due to the substantial dependence of these coefficients on the welding mode parameters. For the latter reason, the stability of the penetration depth and other parameters of the quality of the welded joint connected with it is insufficient.

To determine each of the four coefficients of formula (1), it is necessary to perform at least three independent experiments, with the remaining parameters remaining constant, including the point with nominal mode parameters, to determine the dependence of the depth of penetration on the parameter values. When conducting such experiments, it is necessary to maintain the two remaining parameters of the mode of three at a constant level, which is rather difficult for the welding arc, since, for example, the arc voltage depends not only on the arc length, but also on its current. In total, to determine only the exponents in formula (1), at least 9 different experiments will be required, without taking their repetitions into account, in order to increase the accuracy of the determination.

The technical problem is also that the dependence (1) does not take into account the effect on the penetration depth of the initial temperature of the parts to be welded, which requires additional experiments when the temperature at which the welding is carried out, for example, with preliminary or concurrent heating of the parts being welded, changes from the previously performed weld. or another significant change in ambient temperature. The presence of deviations of the temperature of the parts known from before the welding at which the coefficients were determined will lead to a deviation of the nominal value of the controlled penetration depth and cannot be taken into account using formula (1).

With this method of regulating the depth of penetration, the possibility of reducing the number of controlled parameters of the welding mode by eliminating the arc voltage measurement without compromising the control accuracy is not taken into account, since it has little effect on the depth of penetration within its possible disturbances.

A technical problem is also the fact that in a known method of regulation it is impossible to take into account the deviations in thickness used for welding plates, which affect the depth of penetration. The metal used in welding for blanks has significant thickness tolerances. This requires the determination of new values of the coefficients in the formula (1). In the case of regulation without taking into account changes in the thickness of the rolled stock, a substantial systematic error occurs with respect to the nominal penetration depth.

Also, the method cannot be applied in argon-arc welding and surfacing with a filler wire, since it does not take into account its effect on the controlled parameters.

In the known method of regulating the depth of penetration during automatic argon-arc welding by non-consumable electrode of butt joints without edge cutting with filler or without filler wire, at which current and speed of welding are measured and their change due to external disturbances is compensated by adjusting one measured parameter calculated from the condition of maintaining constant depth melting, which is determined by mathematical dependence.

Unlike the prototype, with the nominal welding parameters, the nominal initial temperature of the parts to be welded and their thickness, the width of the weld is additionally measured, the melting temperature of the metal is set and the mathematical dependence of the temperature in the plate is used to calculate the welding control parameter when a point heat source acts on its surface

where T _L is the melting point of the metal of the product, ° C;

T ₀ - the nominal initial temperature of the plates of the product, ° C;

K - coefficient of proportionality, equal to

K = 2q _Y / [cρ (4π) ^1.5 ], (cm ³ ° С) / (А⋅с), in which q _Y is the ratio of the effective power of the welding arc to the welding current, W / A,

I - welding current, A,

сρ is the volumetric heat capacity of the product material, J / (cm ³ ° С),

a - coefficient of thermal diffusivity of the material of the product, cm ² / s,

x - coordinate, positive in the direction of welding, measured from the axis of the heat spot of the welding arc, cm,

V _C - welding speed, cm / s,

t is the time from the beginning of the arc, to the onset of the steady state penetration of the product, s;

y is the coordinate perpendicular to the direction of welding, cm

H ₀ - the nominal depth of penetration, cm;

δ is the nominal thickness of welded plates, cm;

n - integers from -∞ to + ∞,

for which the coefficient of thermal diffusivity a and the coefficient of proportionality K are calculated from the values of the width and depth of penetration of the reference weld.

The technical result of the proposed method is to significantly reduce experiments to determine the coefficients of the mathematical dependence of the depth of penetration on welding parameters, improving the accuracy of controlling the depth of penetration by reducing the dependence of the coefficients determined experimentally on the welding mode parameters and taking into account the effect of the temperature of the parts to be welded to the depth of penetration experiments. In fact, only one experiment is needed on welding the reference weld and measuring after it the penetration depth of the weld and the width of the weld. This result is possible due to the established dependence that an adequate description of the temperature field shape using an analytical dependence representing the action of a moving point heat source on the plate surface allows, when measuring two weld dimensions, to find the exact values of the corresponding thermal diffusivity a and the proportionality coefficient K and use them later for the calculation of the regulatory parameter mode to stabilize the depth of penetration during welding. This allows with sufficiently high accuracy to determine the transfer coefficients for regulating any of the parameters of the mode in relation to the penetration depth.

In addition, the technical result is achieved, which consists in not measuring and regulating the arc voltage by using the concept of the specific effective arc power at the nominal welding current, which is due to the weak dependence of this parameter on the arc voltage in the region of possible disturbances in welding current and length arc.

The technical result is also the fact that the method allows to take into account, prior to welding, known changes in the thickness of the parts to be welded within the limits of rolling tolerances without additional experiments.

The technical result can also be attributed to the fact that the method makes it possible to take into account, prior to welding, known changes in the temperature of the parts being welded without additional experiments.

In addition, the technical result is also the fact that the method can be used when welding butt joints without cutting edges and surfacing on the plate with the filing wire in the weld pool, as the simultaneous measurement of the penetration depth and weld width takes into account the effect of the filler wire welding, the values of the coefficients used and, consequently, the depth of penetration.

FIG. 1 shows a penetration cross section; FIG. 2 shows the longitudinal profile of penetration; FIG. 3 - welding bath isotherm; FIG. 4 - dependence of the specific effective power of the arc on the arc current; in fig. 5 shows the dependence of the effective efficiency of the arc on the arc current; FIG. 6 - dependence of the depth of penetration and the width of the seam on the coefficient of proportionality K, FIG. 7 shows the dependence of the seam size on the thermal diffusivity a, in FIG. 8 - dependences of the depth of penetration and the width of the weld on the welding speed, in FIG. 9 - dependence of the depth of penetration and the width of the seam on the initial temperature of the plate; FIG. 10 - dependences of the depth of penetration and the width of the seam on the thickness of the plate; FIG. 11 is a circuit for producing contour lines; FIG. 12 - isoline "proportionality coefficient - thermal diffusivity", in FIG. 13 - the “current - welding speed” isoline; in FIG. 14 is a diagram of the regulation of the welding process according to the proposed method.

FIG. 1 shows a cross-section of the first layer of double-sided welding seam of a butt joint of plates without edge cutting with an incomplete penetration depth. In ₀ - the maximum width of the weld pool (seam) on the outer surface of the plates (from the action of the welding arc). H ₀ - nominal (reference) penetration depth of the seam. When adjusting it is required to stabilize the depth of penetration H ₀ . FIG. Figure 1 shows the axes in the calculation of temperatures — the Y axis is perpendicular to the direction of the welding speed and the Z axis directed from the outer surface of the plate from the side of the action of the welding arc. The depth of penetration H ₀ has permissible deviations from the nominal depth ± ΔН ₀ , which should ensure the overlap of the seams in the thickness of the plates after welding the second similar seam. Nominal penetration and tolerances can be set by the developer of the welding technology or given in regulatory documents. The maximum depth of penetration takes place along the axis of the weld with the transverse coordinate y = 0. The seam can be obtained using filler wire, therefore it has a bulge g.

FIG. Figure 2 shows the longitudinal profile of penetration along the plate thickness along the X axis with the transverse coordinate y = 0, calculated using the formula for a point source of heat acting on the surface of a flat layer.

The formula for calculating the temperature increment ΔT at the point of the body from the action of such a heat source is

where T is the temperature point of the product, ° C;

T ₀ - the initial temperature of the plate, ° C;

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

сρ is the volumetric heat capacity of the plate material, J / (cm ³ ° С);

a is the coefficient of thermal diffusivity of the plate, cm ² / s;

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

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

t is the time since the beginning of the action of the moving heat source, s;

y is the coordinate perpendicular to the direction of movement of the heat source, measured from the axis of 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: High School, 1988. - 559 p. P. 186.

The specific number of numbers n specifies the number of members of the series (the number of integrals) to be calculated. It depends on the required accuracy of the calculations of the last member of the series in formula (3). The greater the number n in absolute value, the smaller the last integral of the series. The accuracy of calculating the temperature at a point increases rapidly with increasing n in absolute value. When calculating temperatures, the limitation of the number n is made by setting the ratio of the last member of the series to the sum of all previous members of the series. When calculating temperatures in steels, the number n = N does not exceed 10 in absolute value. The first term of the series is calculated when n = 0 and the number n ceases to increase in absolute value when the required accuracy of temperature calculations is reached.

The upper limit of integration of time t is chosen such that the temperature field in the plate is steady (quasistationary). This is a state of the temperature field when the temperature of all points of the body in the weld zone changes to a negligible value. In this condition, the depth of penetration and the width of the seam reach the nominal values with high accuracy. The value of t, as well as the value of n, is selected on the basis of the required accuracy of calculations. Experiments and calculations show that under conditions of double-sided welding of butt joints (plate thickness 6-8 mm), this condition is achieved in about 10 seconds for steels and 15 seconds for aluminum steels with a very high relative accuracy of temperature calculation not lower than 0.1%.

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 is the 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 equation (2) should also be used instead of the effective power of the arc q _{And the} expression (4). This form allows you to select directly the influence of the welding current as a mode parameter on the product temperature and penetration depth.

It can be seen from formula (3) that the temperature of the body points 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 use in the formula (3) not each of these quantities separately, but their ratio, and later in regulating the depth of penetration to operate with this ratio. Taking into account constant numbers, we denote this coefficient K, not including the welding current in it, which may change during the welding process due to the effect of perturbations

The dimension of the coefficient K - (cm ³ ⋅- ° С) / (А⋅с). When multiplying K by the welding current, we obtain the dimension (cm ³ ⋅ ° C) / s.

In this case, it turns out that only two unknowns remain in formula (3): the coefficient of proportionality K and the coefficient of thermal diffusivity a. To determine them uniquely at the nominal (reference) mode, you need to know two independent temperatures at two points of the body with known coordinates of these points x, y, z. Then from the formula (3) you can make a system of equations for the unknown coefficients. Since it is known that the temperature at the boundary of the weld with the base metal is always equal to the melting temperature, you can use the weld width and penetration depth to find constant coefficients K and a in formula (3), and then apply these coefficients when calculating the control parameter - current or welding speed. This ensures high accuracy in determining the regulatory impact, since the coefficients obtained change very little when welding parameters are disturbed.

Instead of the z coordinate in the formula (3), the equation (2) used the nominal (reference) penetration depth H ₀ , because it is used to calculate the welding control parameter — the welding current or welding speed, that is, when adjusting, it is a known target value , and the unknown is the value of the control parameter - welding current or welding speed.

The value of q _V in the literature is called the volt equivalent of the effective power or specific heat flux. The latter name does not quite accurately reflect the essence of this parameter, since the concept of heat flow density includes the area on which power acts. More precisely, to call this value the specific effective power. The quantity q _Y is weakly dependent on the current and the arc length and hence the arc voltage. This is due to the fact that the effective power during welding with a non-consumable electrode is predominantly transferred to the product from the near-electrode area of the arc at the product.

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 _And - effective efficiency of the welding arc.

The effective efficiency of a welding arc of direct polarity in argon with a non-consumable tungsten electrode is recommended in the literature to be taken in the range of 0.65-0.75 (see, for example, Erokhin AA, Fundamentals of fusion welding. M .: Mashinostroenie, 1973, 448 p. P. 13, table 1.2). Here the deviation from the mean value is ± 8%. In many cases, it is much larger. Such a spread of efficiency values is due to changes in conditions such as arc length, welding speed, electrode sharpening angle, etc. With increasing arc length, the effective efficiency usually decreases. This is caused by the increase in voltage in the arc column and the constancy of the useful (effective) power transmitted by the arc to the product near its electrode area. With the lengthening of the arc, the increase in arc power occurs mainly due to an increase in the energy release in the arc column and almost all is lost to the environment. In contrast to the efficiency, the specific effective power q _{Y is} practically independent of the current, length and voltage of the arc. This allows the automatic adjustment of the depth of penetration according to equation (2), having previously determined the coefficient K, which includes q _Y as a factor, from the test, not to measure and regulate the arc voltage during the welding process. The specific effective power q _Y also very weakly depends on the arc current. This allows us, by calculating the coefficient K from the size of the weld at the nominal welding parameters, to accept it constant and then use it to calculate the regulating welding parameter in case of arc current disturbances.

The effective efficiency of the arc is approximately estimated by the formula

where U _P is the voltage corresponding to the contribution to the effective power of the near-electrode areas of the arc (cathodic or anodic).

On the straight arc polarity

where U _A is the anode voltage drop of the arc at the product, V;

U _In - voltage corresponding to the numerical value of the electron work function of the metal product anode, V.

On the reverse polarity of the arc

where U _K is the cathode voltage drop of the arc at the product, V;

U _In - voltage corresponding to the numerical value of the electron work function of the metal product cathode, B.

In the arc of single-phase alternating current U _P is equal to the half-sum of (8) and (9)

Formulas (7-10) are given in the monograph by G.I. Leskov "Electric welding arc", M .: Mashinostroenie, 1970. - 335 p.

U _P in formulas (7-10) is actually a fairly accurate estimate of the specific effective power q _Y.

Due to the fact that the near-electrode voltage drops of the arc are practically independent of the length of the arc and weakly dependent on the arc current, then q _Y depends very little on them. This allows you to include and use q _Y in equation (2) and formula (3) as a constant value in the coefficient K. On the basis of the experiment, the proposed control method determines not the value of q _{У itself} , but the proportionality coefficient K, into which q _Y is a factor. Then the perturbing effect on the welding current will lead to a proportional change in the multiplier К⋅I in equation (2) and it is possible to calculate the welding parameter regulating current or welding speed.

Equating the expression (3) 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 equation (2), and using it, we can calculate the depth of the weld pool in any plane through the thickness of the plate, including the maximum at the coordinate y = 0, that is, find the coordinates x, z, for which T = T _L. The value of the z coordinate is taken in formula (3) equal to the nominal penetration depth H ₀ . In this case, formula (3) turns into equation (2). For finding the z coordinate with a temperature equal to the melting point, for example, for each selected x coordinate, the method of dividing the segment between the plate planes in half (dichotomy method) can be used. Finding the maximum depth of penetration can be done by a numerical method by successively substituting the x coordinates with a certain step Δx. When calculating the profile in FIG. Step 2 Δh was chosen 0.1 cm = 1 mm. Thus, the profile shown in FIG. 2 is a reference design longitudinal profile of the weld pool along the weld axis.

The recommended values of thermophysical coefficients when calculating the profile in FIG. 2 were adopted for high-alloy steel 304L (USA): the volumetric heat capacity was ρ = 3.476 J / (cm ³ ° C), the thermal diffusivity a = 0.0432 cm ² / s.

(see Sidorov, VP. Two-arc two-sided welding with non-consumable electrodes in argon / V.P. Sidorov, S.A. Khurin. Togliatti: TSU, 2015. 191 p. p. 67-68).

The thickness of the plates in the calculation was taken δ = 0.6 cm, the effective power of the heat source q _И = 1350 W, welding speed V _С = 0.43 cm / s. _{With a} specific effective power q _У = 6.0 W / A, this power corresponds to welding current I = 225 A.

The value of the coefficient K with the given calculation parameters

K = 2q _Y / cρ (4π) ^1.5 = 2⋅6 / (3.476⋅44.54) = 7.75⋅10 ^-2 (cm ³ ° С) / (А⋅с).

The melting point of high-alloyed steel, measured from 0 ° C was taken to T _L = 1440 ° C. The nominal temperature of the parts before welding was taken T ₀ = 20 ° C. Thus, the nominal (reference) calculated melting point (T _L –T ₀ ) when calculating the size of the weld pool was 1420 ° C. The upper limit for the integration of time t in the equation compiled by formula (3) was taken t = 40 seconds; as a result of a further increase in time, the depth of penetration changed by less than 0.01%. The division of one second in the calculation of one integral from the series in the equation into segments was M = 50. At the same time, the calculation of one profile point on an ordinary personal computer is 1-2 seconds. When optimizing a computer program and using a faster computer, the calculation time of the regulating parameter according to equation (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 seam ensures the overlapping of the seams in height with double-sided welding by 0.12 cm = 1.2 mm - 20% of the plate thickness.

Calculations according to equation (3) were made by programming calculations by specifying the required accuracy of calculation of the depth of penetration, which was 0.01 mm. At the same time, the number of positive and negative terms in the series in equation (3) did not exceed n = N = ± 10. The program automatically stops the calculations when the specified accuracy of the calculations of the last member of the series (2) or (3) is reached.

The definition of the profile points in FIG. 2 was made as follows. The coordinate along the Y axis is given by y = 0, thus ensuring the maximum penetration depth. Then a point with a coordinate x = 0 is set and the value of the coordinate z 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. In the calculations, the positive direction of the x axis for convenience was chosen opposite to the direction of welding, which is achieved by changing the sign when x in equation (3). From the obtained values of the depth of penetration, a point with a maximum value of H ₀ is selected.

Methods for solving nonlinear equations of type (2 or 3) are described in detail in the specialist literature, for example, see VP Diakonov. Handbook of algorithms and programs in the BASIC language for personal computers. - M .: Nauka, 1987 - 240 p., P. 86-91, programs 4.11 ... 4.19. In a certain place such programs are programmed to calculate the original function, which is the equation. In our case, for the profile in FIG. 2 is a function (3). The dichotomy method is described in program 4.15 on page 89 of this handbook.

Usually, the problem when using formulas like formula (3) for calculating temperatures during welding in a linear formulation of the problem (thermophysical coefficients are taken independent of temperature) is precisely the assignment of the values of these coefficients, since in reality they depend to some extent on temperature. Usually, the best convergence of the calculated and experimental thermal cycles is achieved by choosing the values of the coefficients for a certain average welding temperature. Recommendations for choosing such an average welding temperature are not yet sufficiently substantiated. However, if you use two parameters of the temperature field (in the proposed method of regulation it is the depth of penetration and the width of the weld), then you can get two exact values of the coefficients K and a. In this case, there is no need to measure the effective welding power, which is replaced by a simpler determination of the reference weld width B ₀ . This is the basis of the main technical result of the proposed technical solution. Such a technique eliminates inaccuracies of the mathematical model, caused by the adoption of the assumption of the constancy of thermophysical coefficients, the absence of taking into account their dependence on temperature.

In compiling the second equation of the system of equations for calculating the coefficients, formula (3) will take the form

In equation (11), instead of the y coordinate, half the nominal (reference) seam width B _{0 is used} , and z = 0 is substituted for the z coordinate, so the maximum seam width will occur on the surface of the plate from the side of the heat source.

FIG. 3 shows the calculated semi-isotherm of the weld pool on the surface of the plates from the side of the action of the heat source, obtained using the equation composed by the formula (3). The parameters of the heat source 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 given, since such an isotherm is symmetric about the longitudinal axis X. The order of construction of the isotherm is similar to the construction of the penetration profile for FIG. 2. The difference is that when using the dichotomy method (dividing a segment in half) to calculate, it is necessary to search for the boundary of the weld pool inside the segment ∆y, the size of which should be chosen to be obviously greater than the maximum width of the weld pool. This is done in such a way that the remote border of the calculation zone is taken in proportion to the thickness of the plates being welded, for example, 3δ, which is certainly more than half of the standard weld width.

Another option is to approximate the width of the seam using a well-known simple formula for a point-like, fast-moving heat source, which gives a slightly overestimated value of the seam width compared to a heat source moving at a limited speed.

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

FIG. 4 shows the dependences of the specific effective power q _Y on the arc current of direct polarity in argon into the copper anode according to the literature data.

In this case, the formula for q _Y has the form

q _Y = Wa / Id,

where Wa - effective power in the anode of the welding arc, W;

Id - arc current (welding), A.

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

The dependencies in FIG. 4 and designations of values are given in the monograph by A.V. Savinov and others. "Arc welding with non-consumable electrode." M .: Mechanical Engineering. 2011. - 477 s. P. 82, fig. 1.57.

FIG. 5 shows the dependence of the effective efficiency of an arc of direct polarity in argon with a non-consumable electrode on the arc current. An EVI brand electrode with a diameter of 2 mm was used with a sharpening angle of 30 degrees and an arc length of 1 mm. When changing the arc current from 10 to 40 A, the effective efficiency of the arc increased from 0.5 to 0.7.

This dependence is also given in the monograph by A.V. Savinov and others. "Arc welding with non-consumable electrode." M .: Mechanical Engineering. 2011. - 477 p., P. 94, fig. 1.71.

The dependency in FIG. 5 indicates a significant effect of current on the effective efficiency and that this factor should not be used when determining the effective arc power in the case of adjusting the depth of penetration according to the mathematical dependence (2). In this case, the deviation of the effective efficiency from the average value is about 17%, which is much more than the error when using the specific effective power q _Y. To determine the approximate value of the effective power using the effective efficiency, it is necessary to know the arc voltage, which also depends on the arc current and its length. The dependence of the specific effective power on the arc current and the arc length is much less. Similarly, other parameters of the arc (diameter, angle of sharpening of the electrode) have little effect on the specific effective power, unlike the efficiency of the arc. This allows for adjusting the penetration depth of the proposed method, determining the coefficient K and the thermal diffusivity a in the reference mode by calculating on the basis of experience, not to determine the effective arc power q _I , to include in the coefficient K the specific effective power q _Y , and use the latter for disturbances not only welding current, but also arc voltage.

FIG. 6 shows the calculated dependences of the maximum penetration depth H ₀ and the weld width B ₀ on the coefficient K. The calculation of the thermophysical parameters 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 seam B. The values of the coefficient K in FIG. 6 magnified 100 times.

In interval K coefficients centered at the nominal mode K = 7,75⋅10 ^{-2 (cm3} ° C) / (A⋅s) the average transmission coefficient for the penetration depth k _PN =? H / ΔK = 0.65 / 1 72⋅10 ^-2 = 0.378⋅10 ² mm / [(cm ³ ° С) / (А⋅с)]. The average transmission coefficient for the seam width is k _PW = ΔВ / ΔК = 0.94 / 1.72⋅10 ^-2 = 0.547⋅10 ² mm / [(cm ³ ° С) / (А⋅с)].

FIG. 7 shows the dependences of the depth of penetration and the width of the weld on the thermal diffusivity coefficient calculated by the formula (3). The remaining calculation parameters and coefficients were the same as for the profile in FIG. 2

The value of the coefficient K = 7.75⋅10 ^-2 (cm ³ ° С) / (А⋅с), q _И = 1350 W, which corresponds to the welding current I = 225 A.

Curve 5 refers to the penetration depth H, and curve 6 to the seam width B. From dependences 5 and 6, it can be seen that an increase in the thermal diffusivity leads to a decrease in the penetration depth and the seam width.

FIG. 8 shows the dependences of the maximum penetration depth H and the width of the seam B on the welding speed calculated by the formula (2). 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 K = 7.75⋅10 ^-2 (cm ³ ° С) / (А⋅с).

In the interval of welding speeds, V _C = 0.38-0.48 cm / s, the average transfer coefficient for the penetration depth k _PN = ΔH / ΔV _C = (0.56) / 0.1 = 5.6 mm / (cm / s ). For the width of the seam, k _PV = ΔAB / ΔV _C = (0.75) /0.1 = 7.5 mm / (cm / s).

FIG. 9 shows the calculated dependences of the maximum penetration depth and the weld width on the difference ΔT between the melting temperature T _L and the initial temperature of the parts T ₀ This difference characterizes the temperature of heating the product. Curve 9 refers to the depth of penetration, curve 10 - to the width of the seam. Other calculation parameters correspond to the data for FIG. 2

The value of the coefficient K = 7.75⋅10 ^-2 (cm ³ ° С) / (А⋅с). The curves in FIG. 9 show that deviations of the temperature of the parts will lead to errors in the regulation of the depth of penetration. The transmission coefficient for the curve 9 k _П = ΔН / ΔТ = 0.49 / 200 = 2.45⋅10 ^-3 mm / ° С, for the curve 10 k _П = ΔВ / ΔТ = 0.61 / 200 = 3.05⋅ 10 ^-3 mm / ° C. With significant changes in the initial temperature of the parts, such as, for example, with preliminary or concurrent heating during the regulation according to a known method, it will be necessary to conduct new experiments to determine the empirical coefficients in formula (1), which is very laborious. When adjusting for the proposed method, it is possible by calculation to adjust the welding modes: current and welding speed and verify experimentally the value of the penetration depth.

FIG. 10 gives the calculated dependences of the depth of penetration and the width of the seam on the thickness of the plate. Curve 11 shows the relationship for the depth of penetration, and curve 12 for the width of the seam. The calculation parameters were used as in the construction of the profile in FIG. 2. As the plate thickness increases, the penetration depth and weld width will decrease, which will lead to a constant regulation error, if the welding mode is not corrected and the change in plate thickness is not taken into account in the calculations when adjusting.

FIG. 11 shows the construction of contour lines. Curve 13 represents the dependence of the penetration depth H ₀ on the coefficient K at the thermal diffusivity a = 0.03 cm ² / s, curve 14 at a = 0.04 cm ² / s, and curve 15 at a = 0.05 cm ² / s . Through these curves, a line is drawn parallel to the axis of the coefficient K with the value H = H ₀ . The points of intersection of this straight line with curves 13, 14, 15 give the coordinates of the values of K ₁ , K ₂ , K ₃ at different thermal diffusivity and make it possible to draw the isoline “coefficient K - coefficient of thermal diffusivity a” in FIG. 12.

The graph of the second contour for the seam width B ₀ is constructed similarly.

FIG. 12 shows the contour "coefficient K - thermal diffusivity a" for given values of the nominal penetration depth H ₀ and the nominal width of the weld B ₀ . Curve 16 represents the isoline for the penetration depth of H ₀ , and curve 17 represents the isoline for the seam width B ₀ . An isoline is a curve on which any point with different coefficients K and a gives the same value of the parameter being studied. 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 width of the weld B ₀ . Since the combination of the nominal penetration depth and the nominal weld width for the nominal mode is the only one, contour lines 16 and 17 have one intersection point, which gives the only values of the desired coefficients K and a. These values should be used to calculate the value of the welding control parameter when calculating it using equation (2), which ensures high accuracy of the penetration depth control. According to FIG. 12 you can take a = 0.05 cm ² / s, K = 8.4⋅10 ^-2 (cm ³ ° С) / (А⋅с).

The construction of isolines actually represents a graphical method for solving a system of two nonlinear equations (2) and (11), 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 . In both equations, solved numerically using contour lines, the coordinate along the X axis changes with a small step Δx.

FIG. Figure 13 shows the calculated “current – welding rate” isoline for the nominal penetration depth. In the calculation, the parameters were the same as in the calculation of the profile in FIG. 2. The boundary values of the currents on the isolines 208 A - 242 A. The boundary values of the welding speeds 0.4-0.47 cm / s. The dependencies of the required current for several welding speeds were built at nominal penetration. Then a line was drawn parallel to the axis of welding speeds and the coordinates of the sought points of the isoline were obtained at the intersection of this line with the curves. Any point on the contour (values of currents and welding speeds) gives the same maximum depth of penetration H ₀ . The isoline can be considered as an adjustment curve for the proposed method of regulation. The nominal parameters of the process correspond to the point A on the isolines, the current I _A and the welding speed V _CA. When positioned due to the effect of perturbations of the working point of the process at point B, outside the isoline, the current values of current I _B and welding speed V _CB generally have deviations from nominal values. When regulating the proposed method, it is necessary to change only the welding speed or the welding current. When adjusting the welding speed, the working point of the process will be point C with the measured current I _B and the new value of the welding speed V _CC .

To simplify the regulation system, the resulting isoline can be approximated with high accuracy before welding and instead of equation (2) used for regulation. This will significantly reduce the amount and time of calculations in the regulatory process. The isoline shown in FIG. 13 approximated by a parabola

where B ₀ , B ₁ , B ₂ are the approximation coefficients determined by the points of the curve in FIG. 13. As a result, the approximations obtained the values of the coefficients

B ₀ = 0.842 cm / s, B ₁ = -5.72⋅10 ^-3 cm / (сА), В ₂ = 17.28⋅10 ^-5 cm / (сА ² ).

The analytical and approximating values for these coefficients coincide with an accuracy above 0.01%.

A computer program for calculating the coefficients for parabolic regression is given in the reference: VP Diakonov. Handbook of algorithms and programs in the BASIC language for personal computers. - M .: Nauka, 1987 - 240 p., P. 142 program 5.24.

FIG. 14 shows the automatic control scheme for the proposed method. The welded product 18 is supplied to the welding zone at a rate of V _C. The power source 19 is connected to the product 18 by the positive pole, and the non-consumable electrode of the welding torch 20 is connected to the non-consumable electrode. An electric arc 21 is excited between the non-consumable electrode of the burner 20 and product 18, and the edges of the product to be welded melt 18. A weld is formed and the weld metal solidifies. 23 with a nominal penetration depth H ₀ and a nominal width B ₀ . Measurement of their values is carried out after welding the reference sample. In the welding bath 22 in the gap between the non-consumable electrode of the welding torch 20 and the welding bath 22 is fed the filler wire 24 with a speed V _P equal to the speed of its melting heat arc. The welding process is monitored using a welding speed sensor 25, a welding current strength sensor 26. Data on welding speed and welding current from sensors 25,26 are fed to a computing device 27. In the memory unit 28, the values determined in advance and transmitted to the computing device 27 are received physical characteristics: thermal diffusivity a, the coefficient K, the metal melting temperature T _L and its initial temperature T _0, the plate thickness δ, the value of the x coordinate for the nominal maximum penetration depth H _0, to rdinaty y = 0. The device 29 provides control of the welding speed. In the computing device 27, first, the proportionality coefficient in equation (2) K ¹ = K⋅I is calculated from the measured welding current. Then, using the coefficients transferred from the memory unit 28 and the reference penetration depth H ₀ , the value of the welding speed V _{CP is} calculated by equation (2), which provides the specified value of the penetration depth H ₀ . The calculated value of the welding speed V _{CP is} compared with the measured, V _SI and the difference ΔV _C is fed to the welding speed control device 29, which sets the required speed V _CC = V _CP .

Example 1

Conducted the determination of the regulatory parameter of welding on the proposed method.

For welding, plates of steel 20 with a thickness of 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. Permissible deviations from this value were chosen ± 0.6 mm, that is ± 10% of the thickness. To obtain the nominal penetration depth, we selected the argon-arc welding method with non-consumable tungsten electrode without filler wire on the direct polarity of the arc: welding voltage (arc) U = 14.0 V, welding current (arc) I = 275 A, welding speed V _C = 0, 25 cm / s (nominal modes). The nominal width of the seam was B ₀ = 0.653 cm = 6.53 mm. The welding speed V _C was chosen as the control parameter.

The initial temperature of the plates was T ₀ = 20 ° C. According to 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 ° С T _L = 1520 ° С at the nominal parameters of the welding process according to the equation (3) using the computer program compiled in the BASIC programming language, the contour lines were constructed; the K coefficient — the thermal diffusivity coefficient a; and the calculated values of K = 5.39⋅10 ^-2 (cm ³ ° С) / (А⋅ c) and thermal diffusivity a = 0.08 cm ² /with.

In the process of trial welding using a ballast rheostat, the arc current was reduced. The arc voltage decreased by 0.5 V. As a result, the arc current decreased by 30 A and amounted to I = 245 A, the welding speed V _C did not change. The change in the coefficient K1 = K⋅245 A from the reduction of the arc current to K1 = 13.2 (cm ³ ° C) / s was calculated. The calculated value of the maximum penetration depth decreased by equation (2) by ΔН ₀ = 0.5 mm. On the longitudinal section of the seam, a gradual decrease in the maximum penetration depth of ΔН ₀ = 0.6 mm was obtained.

Given the nominal penetration depth, the calculated coefficients, the melting temperature of the parts and their initial temperature were calculated using equation (2) the value of the welding speed, which allows to leave the penetration depth H ₀ unchanged. Received V _C = 0.20 cm / s.

After this, the experiment was repeated with a decrease in the arc current by the same amount. After reducing the current by 30 A, the welding speed was reduced by 0.05 cm / s. As a result, on the longitudinal section of the seam after reducing the penetration by 0.6 mm, it increased by the same amount. As a result, the penetration deviation from the nominal value was 0.1 mm, that is, it differs by only 1.4% from the nominal penetration depth.

Example 2

Conducted the determination of the regulatory parameter of welding on the proposed method.

For welding, plates of aluminum alloy AD0 8 mm thick 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 = 4.8 mm. Tolerances from this value were chosen ± 0.8 mm, that is ± 10% of the thickness. This ensures, while maintaining the nominal parameters, the overlap of two joints in height by 1.6 mm. To obtain the nominal penetration depth, we selected the argon-arc welding method with a non-consumable tungsten electrode with an Sv-AD0 filler wire with a diameter of 2 mm AC arc (reference mode): welding voltage (arc) U = 14.0 V, welding current (arc) I = 340 A, welding speed V _C = 0.4 cm / s. Argon consumption 12 l / min, the diameter of the tungsten electrode 5 mm. The filing wire feed speed is V _П = 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, the convexity of the seam g = 0.5 mm, was obtained. After that, the values of these coefficients were calculated by constructing isolines "coefficient K - coefficient of thermal diffusivity a". K = 0.132 (cm ³ ° С) / (А⋅с), а = 0.85 cm ² / s. The welding current was selected as the controlled welding parameter. The initial temperature of the plates was T ₀ = 20 ° C.

During the welding process, the welding speed was reduced to 0.29 cm / s. Welding current has not changed. The coefficient K also has not changed. The calculated maximum penetration depth increased by ΔН ₀ = + 1.2 mm. On the longitudinal section of the seam, a gradual decrease in the maximum penetration depth of ΔН ₀ = + 1.2 mm was obtained. Therefore, using equation (2), a decrease in the welding current was calculated, which should compensate for the decrease in the welding speed ΔV _С.

Given the nominal penetration depth, the known coefficients K and a, the melting temperature of parts T _L and their initial temperature T ₀ , the welding current was calculated using equation (2), which allows the penetration depth to remain unchanged. Received I = 315A.

After this, a repeated experiment was carried out, as a result of which, after reducing the welding speed to 0.29 cm / s, the welding current was reduced to the calculated value I = 315 A. As a result, a decrease in the weld longitudinal section after an increase in penetration of 1.2 mm occurred by the amount of 1.2 mm. As a result, the penetration deviation from the nominal value within the limits of measurement accuracy was absent.

Example 3

For the parameters of example 1, it was found that the initial temperature of parts increased by 30 ° C. Such a situation is possible, for example, when welding the second layer of a two-sided joint immediately after welding the first layer and in a number of other cases. To reduce the loss of working time required to bring parts to the nominal welding temperature, the arc current welding mode was adjusted. To do this, when calculating the penetration depth H by the formula (3), the value of T _L -T ₀ was not taken as 1420 ° С, as for the reference mode, but 1390 ° С. Received by calculating that the maximum penetration depth in this case will increase by 0.15 mm. After that, using the known value of the coefficient K = 5.39⋅10 ^-2 (cm ³ ° С) / (А⋅с) and the thermal diffusivity a = 0.08 cm ² / s, the reduced value of the welding current was calculated by formula (3) providing the nominal (reference) penetration H ₀ = 0.36 cm. We obtained the welding current value 10 A less than the nominal value. Due to the fact that, as the dependences in Fig. 5 show, such small deviations of the effective power do not affect the values of the transfer coefficient, then the correction of the value of the thermal diffusivity coefficient and K is not required. To take into account the heating of parts, it is advisable to reduce the reference welding current at the power source by 10 A before welding or to increase the reference welding speed using the device 29 in FIG. 14. When adjusting for the proposed method in the memory block 28 in FIG. 14, a new value of the initial temperature of the parts must be entered and regulation during welding will be performed automatically.

Example 4

For the parameters of example 1, it was found that the thickness of the metal increased to δ = 0.64 cm in a batch of rolled products for billets. When adjusting by a known method, a new nominal penetration value and time-consuming determination of four coefficients in the formula (1) would be required. When adjusting for the proposed method, it is necessary to introduce new values of plate thickness δ = 0.64 cm and a new value of reference penetration H ₀ = 0.384 cm into the memory block. Before welding using the computing unit 27 in FIG. 14, it is possible to calculate the adjusted welding speed value and set it. It was calculated by the formula (3) that the nominal welding speed at a new plate thickness and a new maximum penetration depth should be V _C = 0.205 cm / s. In connection with the dependences in FIG. 8 such small deviations of the welding speed do not affect the values of the transfer coefficient, then the correction of the value of the coefficients of thermal diffusivity and volumetric heat capacity is not required. When adjusting for the proposed method in the memory block 28 in FIG. 14, new values of thickness and reference depth must be entered and the welding speed will be pre-adjusted automatically, and automatic adjustment will occur during the welding process.

The proposed method of regulation allows to reduce the number of experiments and the complexity of determining the coefficients of the mathematical model while increasing the accuracy of regulation, which allows to increase the stability of welded joints. Experimentally, it is necessary to determine before the regulation only the penetration depth and the width of the seam at the nominal welding mode. The method also allows the measurement of two welding parameters instead of three by a known method. In this method, it is possible to correct the nominal initial temperature of the product and to 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 the same efficiency as in welding and surfacing without filler wire, and with filler wire.

The method can be implemented using known devices - digital ammeters and current sensors for measuring the current of the welding arc, measuring the speed of welding based on measuring the number of revolutions of the electric motor driving the automatic welding machine for moving the welding torch. Modern means of microprocessor technology and software allow solving the equation (2) with high speed and calculating the required welding speed or arc current to control the penetration depth. Therefore, the method has industrial applicability.

Claims (15)

The method of regulating the depth of penetration in automatic argon-arc welding with non-consumable electrode butt joints without edge cutting with filler or filler wire, which includes maintaining the depth of penetration at a given constant level by adjusting the welding parameter selected from the welding current and welding speed, while measuring the actual values of the controlled parameter in the process of welding, which is adjusted in accordance with their calculated according to a given mathematical dependence of Achen, characterized in that at the nominal welding parameters further measure the width of the weld, define the metal melting temperature and the initial temperature reference parts being welded, and as a control parameter used welding current whose calculation is based on a mathematical function

where I is the welding current, A, T _L - the melting point of the metal products, ° C T ₀ - the reference initial temperature of the plates of the product, ° C, K is a proportionality coefficient equal to K = 2qy / [cρ (4π) ^1.5 ], (cm ³ ° С) / (А⋅с), where q _y is the ratio of the effective power of the welding arc to the welding current, W / A, сρ is the volumetric heat capacity of the product material, J / (cm ³ ° С), a - coefficient of thermal diffusivity of the material of the product, cm ² / s, x ₀ is the coordinate of the point with the maximum penetration depth at the nominal welding parameters, in the direction opposite to the direction of the welding speed, cm, V _C - welding speed, cm / s, t is the current time since the beginning of the action and movement of the source, s, H ₀ - the nominal depth of penetration, cm δ is the thickness of the welded plates, cm n - integers from -10 to +10, for which the coefficient of thermal diffusivity a and the coefficient of proportionality K are calculated from the values of the width and depth of penetration of the reference weld.

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