RU2632751C1 - Method of control of arc deflection from joint of fusion edges - Google Patents

Abstract

FIELD: technological processes.

SUBSTANCE: invention can be used to automatically control the defection of the welding arc from the joint of fusion edges. In the process of welding, the indicators of the intensity of the physical state of the surface of the welded product in the welded connection zone along the joint axis in two points located at a constant distance from each other are measured. As an indicator, the temperature of the surface heating by the welding arc at the mentioned measuring stations is used. Before welding, a reference temperature distribution is obtained in the location section of the measuring stations perpendicular to the welding direction. When the product is moved relative to the welding torch, the temperature at the measuring stations located symmetrically relative to the welding torch is measured, and when the welding torch is moved relative to the product, it is symmetrical relative to the joint of the fusion edges. The temperatures half-difference in each of two symmetrical measuring stations is calculated and the deflection of the arc from the joint is determined, taking into account the reference temperature distribution.

EFFECT: high sensitivity to arc deflections from the joint and the possibility to choose the temperature measuring stations at a considerable distance from the welding bath.

6 dwg, 1 tbl

Description

The invention relates to the field of welding and can be used in mechanical engineering with automatic control of the deviation of the welding arc from the joint of the welded edges.

A known method of controlling the deviation of the torch from the junction of the welded edges using an electromagnetic sensor that measures the electromotive force induced by alternating current in the measuring windings with an asymmetric arrangement of the sensor associated with the welding torch relative to the joint (see E. A. Gladkov. Automation of welding processes / E .A. Gladkov, V.N. Brodyagin, R.A. Perkovsky. - Moscow: Publishing House of MSTU named after Bauman, 2014.S. 219-220).

This method allows you to control the impact of only the deviation of the arc from the joint and does not allow you to control the effect of other disturbances on the welding process. The output of the sensor is affected by the coordinates of the junction; deviations of the geometric parameters of the welded joint; material properties of the product; differences in electrical and magnetic properties of workpiece materials. When welding butt welds, the mutual excess of the edges has a significant effect on the output signal of the sensor.

There is also a method of controlling the deviation of the arc from the joint of the welded edges, in which ultrasonic vibrations are excited in the weld zone by applying current pulses of 10 ^-6 -10 ^-5 s and a repetition period of 10 ^-3 -10 ^-2 s on the arc and determine the difference the intensities of these vibrations on the surface of the welded product at points equidistant from the welding torch (see the description of the invention to the copyright certificate SU 1042924 from 29. 09.1983). This method of controlling the deviation of the arc from the junction is taken as a prototype.

This method allows you to control the impact also only the deviation of the arc from the joint and does not allow you to control the effect of other disturbances on the welding process, affecting the change in surface temperature of the parts being welded. Therefore, to control the action of such disturbances, it is necessary to carry out additional measurements of the state of the surface by other physical methods.

In the proposed method for monitoring the deviation of the arc from the junction of the welded edges in the welded joint area, the intensities of the physical state of the surface of the welded product are measured at two points at a constant distance between them and the difference in the intensities of the physical condition is determined.

In contrast to the prototype, a reference distribution of the temperature of the surface of the welded joint in the direction perpendicular to the direction of welding in the cross section of the location of the measuring points is obtained before welding, during the welding process, the location of the measuring points on the surface of the product depending on the type of relative movement of the welding torch and the product is measured, temperatures are measured at points , calculate the half-difference of temperatures at points and determine from it and the reference temperature distribution the deviation of the arc from the junction.

When moving during welding the product relative to the welding torch, the temperature measuring points are symmetrically relative to the welding torch.

When moving during welding of the welding torch relative to the product, the temperature measuring points are located symmetrically with respect to the joint.

The technical result of the proposed control method is that when the welding arc or joint is shifted relative to each other, the type of temperature dependence in the transverse direction of the welded joint does not change, but only its position with respect to a fixed object changes. This makes it possible to control the deflection of the arc relative to the joint. It was found that the magnitude of such a deviation characterizes the half-difference of the measured temperatures at the measurement points. In addition to measuring the deviation of the arc from the butt, temperature measurement at two points can be used to evaluate the effect of other disturbances on the welding process.

In FIG. 1 shows a cross section of a welded joint; in FIG. 2 - reference temperature distribution; in FIG. - 3 a similar temperature distribution at a different welding speed; in FIG. 4 shows a diagram of measuring temperatures at measuring points by the proposed method; in FIG. 5 presents a methodology for determining the deviation of the arc from the junction; in FIG. 6 - dependence of the deviation of the arc from the joint on the half-difference of temperatures at the measurement points.

In FIG. Figure 1 shows the cross section of the weld of a product from plates without cutting edges with a full penetration depth when welding on one side of the butt joint with a non-consumable electrode without filler wire feeding. E1 - the maximum width of the weld pool (seam) on the outer surface (from the side of the welding arc) in cross section with a maximum penetration width. E2 - width of the reverse roller. In FIG. Figure 1 shows the axes when calculating temperatures — the Y axis 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 welding arc. X axis coincides with the direction of the welding speed. The weld in FIG. 1 obtained without offset welding arc relative to the joint.

In FIG. 2, curves 1 and 2 represent the calculated temperature distribution in the directions of the Y axis on the outer surface of the welded parts (from the side of the welding arc) at a point with the coordinate x = 0.5 cm along the X axis, in the region of the maximum width of the weld pool. The distribution is obtained in the absence of deflection of the arc relative to the joint, that is, it is a reference. The temperature distribution along the Y axis is symmetrical with respect to the origin.

Curves 1 and 2 are obtained using the formula for calculating the temperatures in a plate under the action of a heat source on its surface with a normally circular distribution of heat flux (NKI).

The formula for calculating the temperatures during welding from NKI of heat acting on the surface of the plate has the form

where x, y, z are the coordinates of the point relative to the moving coordinate system

heat source, cm; the x coordinate is in this case

positive in the opposite direction to the welding speed.

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

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

t is the time from the moment the moving heat source began to act, s;

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

q _and - effective arc power, W;

δ is the plate thickness, cm;

a is the thermal diffusivity, cm ² / s;

t ₀ = 1 / 4ak - time constant characterizing the concentration of the heat flux from the heat source to the product, s;

k is the concentration coefficient of the welding heat source, cm ^-2 ;

V _C is the velocity of the heat source, cm / s;

N is the number of fictitious heat sources that take into account the reflection of heat from the surfaces of a flat layer (plate).

By the formula (1), you can calculate the temperature at any point on the plates.

The value of the effective power in the formula (1) is determined, for example, by the formula

where η _and are the effective efficiency of the welding heat source, U _C is the welding voltage, I _C is the welding current.

Nominal values of thermophysical coefficients were taken into account for high alloyed steel: volumetric heat capacity cρ = 3.476 J / (cm ³ ° С), thermal diffusivity a = 0.0432 cm ² / s. The density of the axial heat flux was selected according to the literature q ₀ = 4200 W / cm ² . The concentration coefficient of the welding heat source was k = 11 cm ^-2 , the diameter of the heating spot D _n = 1.04 cm. This concentration coefficient corresponds to a time constant t ₀ = 0.526 seconds. The melting point of high alloy steel, measured from 0 ° C was taken T ₁ = 1440 ° C. The nominal temperature of the parts before welding was taken T ₀ = 20 ° C. Thus, the nominal (reference) calculated melting temperature (T ₁ -T ₀ ) when determining the size of the weld pool was 1420 ° C.

The heat source parameters for curves 1 and 2 in FIG. 2: effective power q _and = 1194 W, welding speed V _C = 0.495 cm / s, plate thickness δ = 0.4 cm. This effective power corresponds to approximately the welding current I _C ≈200 A, with a volt equivalent of the effective arc power in argon direct polarity with non-consumable electrodes U _E = 6 W / A. The volt equivalent of effective power is determined by the formula

The following relationship exists between the volt equivalent and effective efficiency

When the arc is displaced from the axis of the joint X by Δу = 0.1 cm, to estimate the temperature displacement, temperature curves 1 and 2 must also be shifted in the same direction. The maximum temperature will be located already at the coordinate y = 0.1 cm.The position of the measuring points A and B on the parts should remain unchanged when the burner moves relative to the product, or they must move around the product with the burner stationary and the product moving relative to the burner.

To determine the displacement of the arc from the axis of the joint, it is necessary to divide the temperature difference at the measurement points by 2 and find the value of the displacement of the heat source relative to the joint from the reference temperature curves 1 or 2.

Let initially the temperature measuring points A and B be located at coordinates y = ± 0.6 cm, which is greater than the width of the weld pool of the front roll E1 = 0.775 cm at x = 0.5 cm. Then the calculated nominal temperature of the controlled points is T _A = T _B = T _T = 479 ° C. With a shift of the axis of the heat source relative to the Y axis by Δy = 0.1 cm, the temperatures at the measurement points will change to T _A = 831 ° C at y = 0.5 cm and T _B = 270 ° C at y = 0.7 cm. The difference temperatures will be ΔТ = 831-270 = 561 ° С. The semi-difference is ΔТ / 2 = 280.5 ° С.

In FIG. Figure 3 shows similar curves 3 and 4 of the calculated temperature distribution with a decrease in the welding speed to V _C = 0.48 cm / s. They represent the temperature distribution in the absence of a shift in the axis of the heat source relative to the joint. Despite the change in welding speed and temperature distribution, the difference between the point temperatures y = 0.5 cm and y = 0.7 cm did not change and amounted to 561 ° C. Therefore, regardless of the perturbation in the welding speed with the same occurrence of the arc displacement relative to the joint, this displacement will be determined to be the same. Similarly, for example, perturbations in effective power (arc current) will act.

In FIG. 4 presents a diagram of the measurement of the deviation of the arc from the junction of the proposed method.

Plates 1 and 2 without grooving are assembled in a butt joint. On the axis of the junction, a welding torch 3 with a non-consumable electrode 4 performs welding with a welding arc 5, resulting in a welding seam 6. When welding, the welding torch remains stationary relative to the direction of welding using fastening 7, and the welded plates 1 and 2 move in the direction of welding, which corresponds, for example, to welding pipes or shells during their rotation. Initially, at the same distance from the joint and the welding torch 3, points A and B are located for measuring the temperature on the outer surface of plates 1 and 2, temperatures are measured using non-contact temperature sensors 8 and 9, mounted on the welding torch 3 fixed above the plates 1 and 2 using brackets 10 and 11 at the same distance relative to the torch 3. When the plates 1 and 2 move, the welding arc 5 moves along them in the welding direction with a welding speed V _C (along the X axis, not shown in Fig. 4), with the same speed of the displacement plate are relative to non-contact temperature sensors 8 and 9. During welding, due to inaccuracy in the manufacture of plates and other reasons, the axis of the junction of the plates relative to the torch and the arc can shift by a value of ± Δy, which leads to a shift of the temperature field in the plates relative to the axis of the joint. In the absence of a deviation of the torch relative to the joint, various perturbations of the welding process will lead to the same temperature change at the measuring points A and B and there will be no difference in the measured temperatures. When the joint deviates relative to the welding arc, the measuring points A and B will move on the surface of the plates 1 and 2 and at the measuring points a temperature difference will occur due to the asymmetry of the temperature field. The measured temperatures T _A and T _B from the measuring points A and B are transferred from the temperature sensors 8, 9 to the computing device 12, into which, before the start of welding, the reference temperature distribution T (y) is introduced in the cross section with the x coordinate at which points A and B measurement of temperatures. In the device 12, the difference between the temperature of point A and the temperature of point B is calculated. The sign of the difference is also determined. If the difference sign is positive (the temperature at point A is greater than the temperature at point B), this will mean that the welding arc has shifted relative to the joint in the direction of point A. If the difference sign will be negative (the temperature at point A is less than the temperature at to point B), this will mean that the welding arc has shifted relative to the joint in the direction of point B. After this, half of the obtained temperature difference is calculated and the value of the arc deviation 5 rel respect to the joint.

In FIG. 5 shows a diagram for obtaining the magnitude of the deviation of the arc from the junction by changing the measured temperatures graphically. Curve 5 is a conditional reference temperature distribution curve T (y) at nominal process parameters for one of the plates to be welded. Point A on curve 5 corresponds to the nominal temperature at the measuring point A. When the plate is shifted towards the welding torch and arc, the temperature measuring point will become closer to the joint axis. The temperature at the measuring point will rise. Upon receipt of half the temperature difference between point A and point B, this half on the corresponding scale of the temperature axis T is laid off from point A in the form of a segment perpendicular to the axis Y. A straight line parallel to the axis Y is drawn from the end of this segment D until it intersects curve 5 at point C From point C, we need to lower the perpendicular to the Y axis, we get point G. The difference in the coordinates along the Y axis between point A and the intersection point T of temperatures T (y) gives the value of the joint deviation from the arc Δy = y (A) -y (G). Since the measurement point A approached the burner and the arc, then y (A)> y (C). The sign Δy will be positive. The direction of postponement of the AD segment, on a scale equal to half the temperature difference, corresponds to the sign of the temperature difference. If the temperature at point A is greater than at point B, the segment is delayed in the positive direction of the temperature axis T. If the temperature at point A is less than at point B, the segment is delayed in the negative direction of the temperature axis T.

In FIG. 6, curve 6 shows the relationship between the half-difference of temperatures at the measurement points and the deviation of the arc from the joint, obtained according to the procedure described for FIG. 5. The dependence is built on the basis of the reference dependence shown in FIG. 2 or curve 5 in FIG. 5. Given the value of the deviation Δy of the arc from the junction, using the reference temperature distribution, we obtain the values of the temperature half-difference. This dependence can be directly used to determine the deviation of the arc from the axis of the joint in the computing device 12 of FIG. 4. Curve 6 of the dependence of the arc deviation from the joint on the temperature half-difference at the measurement points in FIG. 6 is constructed using formula (1) with parameters q _and = 1200 W; V _C = 0.5 cm / s. Plate thickness δ = 0.4 cm.

Example

The influence of the perturbation by the initial temperature of the welded parts on the deviation of the heat source from the joint was determined. The thermophysical calculation parameters and the thickness of the parts remained the same as in the calculation of the reference temperature distribution in FIG. 2. The effective power of the welding source changed and amounted to q _and = 1210 watts. The coordinate x for calculating temperatures was chosen along the axis of the welding heat source x = 0. The welding speed was V _C = 0.5 cm / s. The initial temperature of the parts T ₀ = 20 ° C. The reference design temperature distribution is presented in the table.

If temperature points are used as measuring points, the coordinates with coordinates ± у = 0.5 cm will result in a temperature difference of points T (0.4) -T (0.6) = 439-123 = 316 ° when the arc is shifted by 0.1 cm FROM. The semi-difference is 158 ° C. According to it, as shown for FIG. 5 methodology, we determine that this value corresponds to the deviation of the arc from the junction Δу = 0.1 cm.

Increased the initial temperature of the parts by 50 ° C. This means that in the formula (1), the temperature of the parts before welding was taken T ₀ = 70 ° C. All point temperatures along the Y axis increased by 50 ° C. In this case, the temperature differences with the deviation of the arc from the junction did not change. Also, the deviation of the arc from the junction Δy = 0.1 cm will correspond to a half-difference of temperatures of 158 ° C.

The method has a high sensitivity to arc deflection relative to the joint, which is due to the fact that in most cross sections on the surface of the welded joint during welding there is a high temperature gradient in the transverse direction dT / dy.

The method can be implemented using known instruments and devices: obtaining a reference temperature distribution on the surface of parts can be performed by installing 2-3 thermocouples or other temperature sensors when they are fixed on the plate. To determine the temperature during welding, you can use known devices for non-contact measurement of surface temperature. The calculation of the deviation of the arc relative to the joint according to the reference temperature distribution can be performed using programmable microprocessor devices. The method is most effectively applicable when moving when welding the product relative to the welding torch.

Claims (1)

A method for controlling the deviation of the arc from the joint of the edges to be welded, including measuring during the welding process the indicators of the intensity of the physical state of the surface of the welded product in the zone of the welded joint along the joint axis at two points located at a constant distance from each other and determining the differences of the indicators of this intensity, characterized in that as an indicator of the physical state of the surface of the welded product, the temperature of its heating by the welding arc at the mentioned measurement points is used, while By welding, a reference temperature distribution is obtained in the cross section of the location of the measuring points perpendicular to the direction of welding, and during welding, the temperature is measured at the measuring points located symmetrically with respect to the welding torch when moving the product relative to the welding torch or symmetrically with respect to the joint of the welded edges when moving the welding torch relative to the product, in this case, the half-difference of the temperatures measured at every two symmetric measuring points is calculated, and the deviations are determined e arcs from the joint, taking into account the reference temperature distribution.

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