JPH0431799B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to seam welding using a laser in the manufacture of metal pipes and the like. Prior Art Welding methods other than laser welding (Fig. 2a) (e.g.
A major feature different from TIG welding (Figure 2b) is that the bead width is narrower. Therefore, when welding for a long period of time, welding defects are likely to occur due to seam misalignment, but as a countermeasure, detect seam misalignment at one point in front of the welding point, and adjust the machining head at the welding point by the amount of that misalignment. There is a seam tracing control method that returns the direction to the welding point.
Publication No. 148089). This method has been tried so far for plate welding (for example, coil seam welding), but when this technique is applied to pipe welding, the following problems arise. That is, FIG. 3a shows an ideal weld without seam displacement, and FIG. 3c shows the groove portion viewed from directly above. On the other hand, Figure 3b shows how the pipe is twisted and the seam is shifted, and Figure 3d is a view of the groove seen from directly above, as in Figure 3c. If we now consider the midpoint M of the gap AB as the detection point, the deviation of M from the reference line (indicated by a broken line) and the deviation of the welding point W are different in direction and magnitude. That is, the deviation of the seam caused by the twisting of the pipe is different from the parallel deviation from the reference line such as when welding plates, and it is not possible to predict the deviation vector at the welding point by detecting only one point. Problems to be Solved by the Invention As described above, the conventional technology has a problem in that it cannot cope with twisting of the pipe. In view of the above, it is an object of the present invention to provide a seam tracing control method that can accurately track the laser irradiation position during pipe seam welding using a laser and can prevent defects in the welded portion. Means for Solving the Problems In order to solve the above problems, the following inventions were made. That is, in pipe seam welding using a laser, the present invention uses two detection positions that are located in front of the welding point and are spaced apart from each other by a predetermined distance in the welding direction, and detects the welding reference line at the midpoint of the gap at the detection positions. Based on each deviation vector and the distance of each detected position from the welding point, the deviation of the welding point from the welding reference line is calculated, and the laser irradiation position is matched to the welding point accordingly. This will be described in detail below with reference to the drawings. Effect W in FIG. 4 represents the welding point, and δ represents the deviation vector (one-dimensional) from the reference line 9. Also, the first detection point is the midpoint M ₁ of the gap A ₁ B ₁ , the second detection point is the midpoint M ₂ of the gap A ₂ B ₂ , and the deviation vectors of M ₁ and M ₂ from the reference line are C ₁ and C ₂ , furthermore, if the distances between the welding point and the first detection point, the first detection point and the second detection point, and the respective welding directions are D ₁ and D ₂ , δ is approximately C ₁ , C ₂ ,
It can be expressed as a function of D ₁ and D ₂ . δ=(C ₁ , C ₂ , D ₁ , D ₂ ) Especially when the first detection point and the second detection point are not far from the welding point, W, A ₁ , A ₂ and W, B ₁ , B ₂
Since we can assume that each is on a straight line, we can express it as follows. (C ₁ , C ₂ , D ₁ , D ₂ ) = sgn [(1+D ₁ /D ₂ )C ₁ ² −(D ₁ /D ₂ )C ₁ C ₂ ] | (1+D ₁ /D ₂ )C ₁ − (D ₁ /D ₂ )C ₂ | ...(1) Here, the directions of the vectors δ, C ₁ and C ₂ are as shown in FIG. 4, with the upward direction being + and the downward direction being -. From this, for example, when sgn(δ) = -1, the welding point is deviated from the reference line in one direction |δ|, so
It is sufficient to control the machining head to move in one direction |δ|, and when sgn(δ)=+1, the welding point is deviated from the reference line in the + direction |δ|, so the machining head can be controlled in the + direction |δ| | All you have to do is control the movement. Further, FIG. 5 shows an example of the detection system. The laser beams emitted from the two slit light sources 5-1 and 5-2 move in the x direction on the rail 5-4 at two locations A ₁ M ₁ B ₁ and A ₂ M ₂ B ₂ in Fig. 4. While being irradiated, this reflected light is simultaneously placed within the field of view of the CCD camera 5-3 by a cylindrical lens 5-5 that widens the field of view in the x direction in FIG. FIG. 6 shows an example of the signal flow from detection to drive in which the controller calculates and controls the amount of movement of the processing head based on the output signal of the CCD camera. EXAMPLE An experiment based on the present invention was conducted under the above conditions (FIG. 1). D ₁ = D ₂ = 100 (mm), pipe making speed v = 5 (m/min),
Tube thickness t = 3 (mm), laser power P = 5 (kw),
Initial value of seam deviation δ ₀ =5 (mm). Experiment 1: Detect the positions of M ₁ and M ₂ and control using the method of the present invention. Experiment 2: Detect only the position of _M1 and control using the conventional method. The results of Experiment 1 and Experiment 2 are shown below.

【table】

[Table] As can be seen from the above, in the case of one-point control (Experiment 2), the deviation increases and reaches the movement limit (±10 mm) of the machining head (this is because the initial value of M ₁ is −1.5 (This is due to the fact that control was performed to set it to 0.) On the other hand, in the two-point control (Experiment 1) of the present invention, the deviation quickly becomes small, and when L is 1500 mm or more, the deviation is ±0.25 mm.
It is stable within Effects of the Invention As described above, according to the present invention, it is possible to prevent seam deviation welding defects caused by twisting of the tube, which could not be achieved with conventional techniques, and the effect is extremely large.

[Brief explanation of drawings]

FIG. 1 is a schematic diagram of a system in which the present invention is implemented. Figure 2 shows pipes with the same thickness.
A cross-sectional view comparing TIG welding bead width a and laser welding bead width b, Figure 3 a is a perspective view showing an ideal welding condition without seam deviation, and Figure 3 b shows a welding condition when seam deviation occurs. Perspective views c and d are views of the groove portion in each welded state viewed from directly above. Further, FIG. 4 is a plan view showing detection positions, control positions, and quantitative points in two-point detection control, and FIG. 5 is a schematic diagram of the detection system. FIG. 6 is a signal flow chart from position detection to drive. 1...pipe, 2...squeeze roll, 3...
Processing head, 4... Controller, 5-1, 5-
2... Laser light, 5-3... CCD camera, 5-
4...Rail, 5-5...Cylindrical lens, 7...Drive, 8...Position detection, 9...Reference line.

Claims (1)

[Claims] 1. In pipe seam welding using a laser, two detection positions are defined as two locations in front of the welding point with a predetermined interval in the welding direction, and welding at the midpoint of the gap is performed at the detection positions. The deviation vector from the reference line is measured, and the deviation of the welding point from the welding reference line is calculated based on each deviation vector and the distance from the welding point of each detected position, and the processing head is placed at the welding point accordingly. A seam tracing control method in laser welding characterized by matching. 2. A seam tracing control method in laser welding according to claim 1, wherein a deviation vector is measured by reflecting laser light from a slit light source at a measurement position and receiving the light with a CCD camera. 3. A seam tracing control method in laser welding according to claim 2, characterized in that two detection positions are placed within the same field of view and measured simultaneously using a cylindrical lens that widens the field of view in the direction of movement of the workpiece.