JPH05142B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to an arc welding method, and more particularly to a method for compensating and controlling non-uniformity in bead height due to groove gap changes when performing arc welding by oscillating an arc within a groove and performing profile control. Prior Art Japanese Patent Publication No. 52-29973 was developed as a welding method that traces the weld line and groove width of the material to be welded while controlling the arc length and oscillating the welding torch in the groove width direction within the groove. However, when the groove gap changes, if welding is performed with the welding speed and wire feed rate constant using the above-mentioned welding method, the bead height will fluctuate, and welding across multiple layers may occur. Sometimes, height differences occur on the bead surface during the final pass. Conventionally, in order to eliminate such differences in bead height, a welding operator would adjust welding conditions such as wire feed rate during the final pass of welding to eliminate the differences in height. Examples of methods for automating this are JP-A-59-130683 and JP-A-57.
-109575 etc. Problems of the prior art to be solved by the invention In the above two prior art, the bead height is controlled to be kept constant by changing the groove cross-sectional area derived from the displacement of the torch height every half cycle of the oscillation. I was doing it. Generally, a servo system that controls welding speed uses a motor with relatively large inertia to maintain a stable welding speed against load fluctuations due to changes in welding posture. Therefore, frequent speed changes are undesirable because they tend to become unstable. In the conventional method, since control was performed every half cycle of the oscillation rate, the welding speed reacted sensitively to local unevenness within the groove, resulting in sudden changes in welding speed and loss of control. In addition, when the nozzle is located in the welding line and the direction in which the welding machine moves as shown in Figure 6, the welding torch will not move even though the oscillation width is constant as shown in Figures 7 and 8. The cross-sectional area to be drawn is
Since Snr≠Snl, the welding speed had to be changed every half cycle of the oscillation, making speed control likely to become unstable. In addition, since the control reference is always the previous value, errors in calculations each time are accumulated, resulting in errors when welding a long welding line. Furthermore, in order to obtain the cross-sectional area drawn by the torch, it is necessary to continuously integrate the amount of positional deviation of the torch in the vertical direction, and the detection section must be configured with a complex and expensive atrolog system, which requires control and computing power. In order to incorporate it into a microprocessor with high processing power, means such as an A/D converter were required, which caused the problem that it was not suitable for using a microprocessor with excellent processing power. OBJECTS OF THE INVENTION The present invention has been made to solve the problems of the prior art described above, and an object of the present invention is to provide a welding method that performs stable bead height control with a simple configuration. Structure of the Invention The welding method of the present invention traces the weld line and groove width of the material to be welded while oscillating the welding torch in the groove width direction, detects the oscillation width, and determines the bid height using the oscillation width. In the arc welding method for controlled automatic welding, when the average value of the detected oscillation widths n times (n is a natural number) is the oscillation width la for calculation, the reference oscillation width l ₀ and the reference welding speed are V ₀ , (l ₀
It is characterized in that the welding speed Va found by ÷la)×VV ₀ is set as the welding speed for the next n oscillation periods. This invention will be described below with reference to examples. In the present invention, while performing constant arc length control to maintain a constant distance between the welding torch and the groove surface of the welded material,
In a welding method in which the welding torch is oscillated in the groove width direction within the groove, an optical pulse generator detects the rotation amount of the drive motor that controls the oscillation rate reversal of the welding torch and constant arc length control. When the number of output pulses reaches a certain value based on the position of the bottom of the groove, the oscillation is reversed, and the oscillation stop position at both ends of the groove is set as P ₁ r ，
As P ₁ s,..., (Pnr, Pns, the values of the y-axis (axis in the direction of welding progress) of the components are stored.Then, using the above stored values, calculate as follows. First, equation (1) Find l ₁ r ~ lnr, and use equation (2) to obtain
Find l ₁ s~lrs. lmr=Pms −Pmr(m=1,2,…,n) …(1) lms=Pms−P(m+ ₁ )r(m=1,2,…,n)
...(2) Also, l ₁ ...ln is determined by equation (3). In the next preferred embodiment, according to equation (4),
Find the average la of n oscillation widths. la=( _o 〓 ^m=1 lm)/n...(4) Here, the value of n is experimentally determined to be 8 to 12.
However, if the groove gap fluctuates slowly, increase n, and if it fluctuates suddenly, n
All you have to do is reduce it. Generally, the weld bead height h in arc welding
Assuming that the groove shape is as shown in Figure 4a, (cm) is determined by the relationship between the groove volume to be filled with weld metal per unit time t (sec) and the fed weld metal to be filled. ) formula holds true. V・t・h・(lu−h/tanθ)=W・t……(5) V: Welding speed (cm/sec) W: Wire feed rate (cm ³ /sec) Here, the actual oscillation width The relationship between l and lu is
In order to perform welding under conditions that do not cause cuts at both ends of the groove, l = lu - α (α > 0),
The locus of this electrode tip is as shown in FIG. 4b. At this time, if the groove gap is wide to some extent, the cross-sectional area Sa in FIG. 4a can be approximated by a rectangular parallelepiped with two sides l and h. In this case, equation (5) becomes equation (6). V・h・l=W...(6) Here, by transforming the 6th equation, the 7th equation is derived. hW/V・l...(7) From formula (7), in order to keep the bead height h constant,
Either the wire feed rate W can be kept constant and the welding speed V can be varied in inverse proportion to the oscillation width l, or the welding speed V can be kept constant and the wire feed rate W can be varied in proportion to the oscillation width l. I understand that. Therefore, as a practical method for controlling the bead height to a constant value from the oscillation width l, first, the reference oscillation width l ₀ , welding speed V ₀ , and wire feeding speed W ₀ are set. In addition to the method of directly setting the reference value, there is also a method of performing welding without performing the bead height control described above, and using each value at a time deemed appropriate by the operator as the reference. Here, as an example, a method will be described in which the wire feeding speed is fixed and the welding speed is controlled. At the time when calculating la (that is, when n oscillations are completed), calculate the following formula (8) to determine the welding speed during the next n oscillations.
Determine V′. V′=l ₀ /laV ₀ ……(8) By continuing this operation, the bead height can be kept constant. Next, a method of fixing the welding speed and controlling the wire feeding speed will be described. It is sufficient to calculate Equation 9 instead of Equation 8, and continue the operation to control the wire feeding speed W' during the next n oscillation operations. W′=la/l ₀ W ₀ ………(9) In the above explanation, an optical type Although this can be done using the output of a pulse generator, a similar control system can also be constructed using other position detection means such as a potentiometer or an integral value of the output of a tachogenerator. By the way, when performing the above-mentioned control, when the bevel gap is 5 mm or more, constant bead height control can be achieved, but when the gap becomes narrow,
When the groove angle θ varies, the approximation of equation (6) no longer holds true, resulting in decreased control accuracy and errors. A method for correcting this will be described below. This method is a method of controlling without approximating equation (5) to equation (6). That is, correct the average value la of the oscillation width as shown in equation (10), calculate la′,
This method uses la' in place of la in equation (8) or equation (9) to determine V' or W' and control the bead height. la'=la+α-h/tanθ...(10) α: Difference between oscillation width and bead width as shown in Figure 4b. In equation (10), a constant value can be used for α as long as welding is performed under appropriate welding conditions that do not cause cuts. According to experiments, α is about 2 mm under normal welding conditions. Also, the bead height h can be calculated by solving equation (5), so by inputting θ,
Equation (10) can be transformed into equation (11) with β as a constant. la′=la+β...(11) By using la′ obtained in this way in place of the above-mentioned la, bead height control could be achieved with high accuracy even in the case of a narrow groove. In addition, in general, servo systems that perform constant arc length control have a
It has a fast response. For this reason, the oscillation frequency (the number of oscillations per unit time) is limited by the permissible range of the frequency response of the servo system.
When the frequency exceeds this limit, the locus of the electrode tip rises upward as shown in Figure 5a, and the oscillation width l ₂ becomes larger than the original oscillation width l ₁ due to the groove, which is due only to the inability to control. This results in a welding defect with cuts at both ends of the groove. A method for stable control even when the groove becomes narrow in this way will be described below. That is, the la,
Alternatively, there is a method of automatically setting the oscillation speed from la' to an appropriate value that does not exceed the frequency response of the servo system that controls the arc length. This value varies depending on the performance of the servo system, but an example is shown in Table 1.

[Table] In the above explanation, only the method of calculating the average of n times was described as a method of calculating la, but of course it is also possible to calculate the average of only the first m times out of n times, or only an even or odd number of times. . Furthermore, if the groove of the workpiece is a straight line, it may be possible to perform control using the oscillation width of either the forward or backward path. Although the above-mentioned control method can be applied to any of MIG, MAG, TIG, and CO ₂ welding methods, an example for TIG welding will be described here. FIG. 1 is an overall block diagram of the mechanism of one embodiment of the present invention. In the figure, A indicates a material to be welded, which is to be welded along a groove K. 1 is a non-consumable electrode that generates an arc with the material to be welded A, 2 is a welding torch, and 3 is a welding torch 2 that is driven in the vertical direction (Z-axis direction in the figure) to perform constant arc length control. 4 is a Z-axis motor, 5 is an optical pulse generator directly connected to the axis of the motor 4, and the output of the pulse generator 5 is transferred to a motor driver 6. The position of the welding torch 2 in the Z-axis direction is controlled. 7 is a mechanical transmission device that drives the welding torch 2 in the Y-axis direction in order to oscillate the welding torch 2, 8 is a motor for oscillation, and 9 is an optical encoder that outputs a number of pulses according to the amount of rotation of the motor 8. occurs. 10
is the driver. Reference numeral 11 denotes a moving mechanism for moving the welding torch 2 in the direction The moving mechanism 11 is adapted to move in the X direction in the figure along the rail 11a.
14 is a pulse generator that outputs a signal according to the rotation of the motor 13, and 15 is a driver that drives the motor 13. With the above 3 to 15 devices, welding torch 2 is
Drive in three orthogonal directions of Y and Z. Also, 16
1 is a wire feeding tip, 17 is a filler wire, and this filler wire 17 is fed into the arc between the non-consumable electrode 1 and the groove K by a mechanical feeding device 18 to form a bead. 19 is a wire feed motor, and 20 is a tacho generator which feeds back its output to a wire motor feed driver 21 to control the wire feed speed. Next, FIG. 2 shows a block diagram of the electrical system for driving the motor of the present invention. Components with the same numbers as in FIG. 1 are the same devices. In FIG. 2, first, the part that performs constant arc length control will be explained. 22 is a welding power source. 23 is a voltage detector that detects the voltage between the welding torch 2 and the material to be welded A, 24 is a reference arc voltage setting device, 25 is a differential amplifier, 26 is a control element that performs PID compensation, 27
is a V/F converter that outputs a pulse train with a frequency proportional to the speed command analog output voltage of the control element 26, and the output is used to rotate the motor 4 using the driver 6 to move the welding torch 2 in the Z-axis direction. Performs arc length control. Further, 29 is an up-down counter in the Z-axis direction that counts the pulse train output from the pulse generator 5 and outputs the position of the welding torch 2 in the Z-axis direction to the microprocessor 30. The output of up-down counter 29 is used within microprocessor 30 to detect the oscillation reversal position. The microprocessor 30 includes a CPU, memory, etc., and has oscillation operation stop positions P ₁ r, P ₁ l,
...Position data such as Pnr, Pns, etc. and Y of those components
By storing the values necessary to carry out the present invention, such as values on the axes, and calculating equations (1) to (10), etc., the speed commands for driving the motors of the X to Z axes and the wire feeding motor are generated. Output. To explain the X-axis drive system, 32 is a command pulse generator, which proportionally adjusts the frequency of pulse attenuation and the total number of pulses to the digital speed command and movement distance command output from the microprocessor 30. generates a pulse train. As a result, the motor 13 is driven by the driver 15 to move the welding torch 2 in the X-axis direction. Regarding the Y-axis drive system, 34 is a command pulse generator similar to 32, which drives the motor 8 via the driver 10 to drive the welding torch 2 in the Y-axis direction to perform an oscillating operation. Also, 33
is an up-down counter similar to 29,
The count is increased or decreased in accordance with the movement of the welding torch 2 in the Y-axis direction. This updown counter 3
From the contents of 3, the above P ₁ r, P ₁ s,..., Pnr, Pns,
The microprocessor 30 reads the value of P(n+ ₁ )r. Finally, I would like to explain about the wire feeding system.
35 is a D/A converter that converts the wire feed speed command output in digital quantity output from the microprocessor 30 into an analog quantity.
will be sent. In the above embodiment, the bead height is controlled only by detecting the oscillation width, and the means for detecting the oscillation width is an up-down counter that counts pulses from a pulse generator that operates based on the oscillation amount. Since the required data can be input into the microprocessor through the output of the microprocessor, there is no need for a complex analog system and a device for converting analog quantities into digital quantities, which were required in the past. Therefore, the bead height can be controlled with a simple and inexpensive device configuration. In addition, by taking the average of n times as the oscillation amount, it is not affected by small irregularities in the groove, and by keeping the reference constant without determining the previous value, it is stable even at the largest weld line without accumulating errors. Bead height control is possible. Effects of the Invention As detailed above, in this invention, the bead height is controlled only by detecting the oscillation width of the welding torch, so the bead height can be controlled regardless of the local unevenness within the groove. Control is easier, and it is no longer necessary to continuously integrate the vertical positional deviation of the torch in order to obtain the cross-sectional area drawn by the torch, and the detection section can be configured with a complicated and expensive analog system. This also eliminates the need for the device, which simplifies the device.

[Brief explanation of the drawing]

FIG. 1 is a block diagram of a welding device used in an embodiment of the present invention, FIG. 2 is a circuit diagram of an electric circuit used in the device shown in FIG. 1, and FIG. 3 is a graph showing one state of the oscillation rate. Figure 4 a, b and Figure 5 a,
6 is a graph showing one state of the oscillation, and FIGS. 7 and 8 are sectional views showing the cross-sectional area drawn by the welding torch in the oscillation of FIG. 6. K...Bevel, 1...Non-consumable electrode, 2...Welding torch,
17... Filler wire.

Claims (1)

[Scope of Claims] 1. An automatic system that traces the welding line and groove width of the material to be welded while oscillating the welding torch in the groove width direction, detects the oscillation width, and controls the bead height based on the oscillation width. In the arc welding method for welding, the average value of the detected oscillation widths n times (n is a natural number) is the oscillation width la for calculation, the reference oscillation width l ₀ and the reference welding speed are V ₀ , (l ₀
An arc welding method characterized in that the welding speed Va found by ÷la)×V ₀ is set as the welding speed for the next n oscillation periods. 2. The arc welding method according to claim 1, wherein the oscillation width is an average value of the oscillation widths of the outward and return passes of the oscillation process. 3 The welding speed is kept constant and the standard wire feed rate is
When W ₀ , the wire feeding speed Wa determined by (la÷l ₀ )×W ₀ is the wire feeding speed for the next n oscillation periods. Arc welding method described. 4 Claims that control the parameters using the oscillation width la for the calculations corrected by a bead height calculation method that is calculated from parameters that control the groove angle of the material to be welded and the bead height. The arc welding method according to any one of items 1 to 3. 5. Claims 1 to 4 set the oscillation speed during oscillation to a value suitable for the response of constant arc length control from the oscillation width for calculation.
The arc welding method described in any of paragraphs.