JPH02211987A - Method and device for monitoring welding state at time of manufacturing resistance welded tube - Google Patents

Abstract

PURPOSE:To reduce variance of welding strength by detecting an interval between squeeze rolls and monitoring variation of the quantity of welding upset and detecting set load of a pressure reducing spring and also monitoring variation of a weld bead. CONSTITUTION:A couple of squeeze rolls 1a and 1b hold and press a tube 2. The pressing force is made to F1-F2 which is determined by the load F1 of a pressing spring 4 and the load F2 of the pressure reducing spring 5b generated by abutting of a squeeze roll holder 8 on a pressure reducing plate 5a. The quantity of welding upset is measured by a position sensor 9a to detect the position of the holder 8 to move together with the squeeze roll 1a. Even if the quantity of welding upset is maintained in the prescribed range, when the counterforce F2 is low, a bead shape is small and the counterforce F2 is high, the bead shape becomes large. The counterforce F2 is measured by a load sensor 13a and control is carried out so that the bead shape becomes optimum and variance of welding strength is reduced.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a welding monitor for monitoring the welding state used in the manufacturing process of electric resistance welded tubes, particularly thin-walled welded tubes for automobile heat exchangers.

[Conventional technology]

In the conventional electric resistance welding pipe manufacturing process using high frequency welding or the like, the welding condition was monitored by visually inspecting the welded area by a skilled worker. For this reason, the criteria for welding quality may vary slightly from worker to worker, and even for the same worker, the criteria for welding may vary, resulting in large variations in welding quality and stability. It was difficult to obtain a suitable weld.

As a conventional method for manufacturing electric resistance welded pipes, the joints of metal plates bent into a tubular shape are melted, and the metal plates are pressed from both sides with squeeze rolls placed opposite each other to form the joints of the metal plates. When welding continuously, the pressing force of the squeeze rolls is set to the set load of the pressure spring when the distance between the squeeze rolls is more than a predetermined amount, and when the distance between the squeeze rolls is less than a predetermined amount, A method of setting the pressing force of the squeeze roll to a pressure that is equal to the set load of the decompression spring less than the set load of the pressure spring was published in Japanese Patent Publication No. 57-
It is known from the publication No. 39878.

In order to solve the above-mentioned problems in the above-mentioned manufacturing method, the present inventors have already disclosed in Japanese Patent Application Laid-Open No. 61-46383 the fact that welding quality is correlated with the amount of welding upset, and the fact that the amount of welding upset is a pair of Focusing on the fact that it depends on the relative spacing of the squeeze rolls, 1
A method for monitoring the variation in welding absorpt amount by measuring the variation in the relative spacing of a pair of squeeze rolls was proposed.

However, as a result of more detailed research conducted by the present inventors, it was found that the state of weld bead formation changes slightly even in a region where the amount of weld upset is stable. The thinner the material, the greater the influence of this subtle change in the state of bead formation on the welding quality. Therefore, in manufacturing thin-walled electric resistance welded pipes, even with the above method, it is not possible to monitor subtle changes in the state of bead formation, and subtle variations in welding quality are unavoidable. In particular, in the case of thin-walled electric resistance welded pipes with a wall thickness of 0.15 s or less, the influence of welding and welding fluctuations on welding quality is large, and a solution to this problem has been strongly desired.

[Problem to be solved by the invention]

The present invention provides a welding condition monitoring method that can monitor not only changes in the amount of upset during the manufacture of ERW pipes, but also subtle changes in welding and welding in the stable region of the amount of upset, and an apparatus for implementing the same. The purpose is to

[Means to solve the problem]

According to the present invention, the above object is achieved by melting the joints of metal plates bent into a tubular shape and pressing the metal plates from both sides with squeeze rolls arranged opposite to each other to join the metal plates. When continuously welding parts, if the distance between the squeeze rolls is more than a predetermined amount, the pressing force of the squeeze rolls is set to the set load of the pressure spring, and if the distance between the squeeze rolls is less than a predetermined amount, A method for monitoring the welding condition in an electric resistance welding pipe manufacturing method in which the pressing force of a squeeze roll is set to a pressure obtained by subtracting the set load of a pressure reduction spring from the set load of a pressure spring, the method comprising: detecting the interval between the squeeze rolls; By comparing this detected value with a predetermined value, fluctuations in the amount of weld upset are monitored, and by detecting the set load of the decompression spring and comparing this detected value with a predetermined value, fluctuations in the weld bead can also be monitored. This is achieved by a method for monitoring welding conditions during the manufacture of ERW pipes, which is characterized by:

A welding condition monitoring device suitable for carrying out the method of the present invention includes a device for melting the joint of a metal plate bent into a tubular shape, and a device disposed facing the downstream of this device that melts the joint of the metal plate on both sides. The device includes a pair of squeeze rolls that press against the metal, a pressure spring that applies a pressing force to the squeeze roll, and a decompression spring that applies a counterforce to the squeeze roll in the opposite direction to the pressing force. A device for monitoring welding conditions in an electric resistance welding pipe manufacturing device consisting of a press joining device that continuously welds joints of plates, the device comprising a position sensor that detects the position of at least one of the squeeze rolls, and a position sensor that detects the position of at least one of the squeeze rolls; A position signal output circuit that operates in response to a signal, a reference value setter that sets the upper and lower limits of the preferred welding upset amount, and a signal from the position signal output circuit that sets the upper and lower limit values set in the reference value setter. a device for monitoring fluctuations in the amount of welding upset, comprising a comparison indicator that indicates when the amount of welding upset exceeds an upper or lower limit value, and detecting the counterforce applied by the decompression spring; A load sensor, a load signal output circuit that operates in response to a signal from the load sensor, a reference value setter that sets the upper and lower limits of preferred counterforce, and a reference value setter that sends the signal from the load signal output circuit to the reference value setter. It is characterized by comprising a device for monitoring fluctuations in the weld bead, which comprises a comparison indicator that displays when the counter force exceeds the upper and lower limit values by comparing it with set upper and lower limit values. do.

〔Example〕

FIG. 2 schematically shows the welding process in manufacturing thin-walled ERW tubes. The metal tube 2, which is continuously formed into a circular shape, is made to flow stably by guiding its edge end face with a seam guide 12.Both end faces 2a of the circular tube 2 are connected to a high frequency oscillator 3a. The material is heated and melted by a heating coil 3, and pressed by a squeeze roll 1 to weld both end surfaces 2a to form a welded tube 2'.

Figures 3a and 3b show cross sections of the tube immediately before and after welding, respectively. In Figure 3b, molten metal is pushed up and down the welded part 2a by the pressing force of the squeeze roll 1 (Figure 2). This is the state in which one door 2a1 is formed. Here, the amount of absent is generally the difference between the total circumferential length of tube 2 and the total circumferential length of tube 2', but this is approximately proportional to the difference d in the tube lateral diameter8. Utilizing this fact, in Japanese Patent Application Laid-Open No. 61-46383, a method was proposed for monitoring the welding condition by defining the above-mentioned d as an upset amount and measuring d. In the present invention, the above method has been further improved to prevent subtle variations in welding quality.

FIG. 1 shows an example of a welding mechanism to which the present invention is applied.

A pair of squeeze rolls 1a and 1b hold a circular metal tube 2. The squeeze roll 1b rotates around a spindle 7b fixed to the squeeze roll stand 6,
The squeeze roll 1a rotates around a support shaft 7a fixed to a squeeze roll holder 8 that can move horizontally within a roll stand 6. The pressure spring 4 has one end held by the squeeze roll stand 6 and the other end brought into contact with the squeeze roll holder 8. Set load F of pressure spring 4
, is transmitted to the movable squeeze roll la via the squeeze roll holder 8 and the support shaft 7a, and the squeeze roll la and the fixed squeeze roll lb cooperate to press the circular tube 2 from both sides. Decompression spring 5
One end of b is held by the squeeze roll stand 6, and the other end is connected to the pressure reducing plate 5a. squeeze roll 1a
When the distance between and 1b becomes less than a predetermined amount, the squeeze roll holder 8 is arranged so as to come into contact with the pressure reducing plate 5a.

In that case, the pressing force applied to the squeeze roll holder 8 and transmitted to the squeeze roll 1a becomes Ft-F, which is obtained by subtracting the set load F2 of the pressure reduction spring 5b from the set load F+ of the pressure spring 4. In this way, the pressed state of the joint is prevented from becoming extremely excessive.

Regarding the welding mechanism itself up to this point, please refer to the above-mentioned
This is detailed in Japanese Patent No.-39878.

The welding upset amount is determined by the position sensor 9a as the distance between the squeeze rolls 1a and 1b, that is, as the position of the squeeze roll holder 8 that moves with the squeeze roll 1a.
This detected value is appropriately converted into a signal by the position measuring device 9 and input to the comparator 11. The comparator 11 compares the lower limit value (dI) and upper limit value (dI) of d set by the setting device 10 with the measured value of d,
If the measured value exceeds the lower or upper limit, this is displayed to the operator.

In the above-mentioned Japanese Patent Application Laid-Open No. 61-46383, welding quality was controlled by monitoring the amount of upset as described above. However, even if the amount of upset is stabilized within the predetermined upper and lower limits in this manner, slight fluctuations in the weld bead cannot be avoided.

Therefore, in the present invention, the counter force F by the decompression spring 5b is also monitored to prevent subtle changes in the weld bead.

FIGS. 4(a) and 4(b) respectively show a change in the upset amount (a) and a change in the counterforce F2 by the decompression spring 5b (b) with respect to the elapsed welding time (horizontal axis).

Upset (traditionally done)! In monitoring only, the fourth
Only the changes shown in Figure (a) are observed.

In Fig. 4(a), A indicates a good welding area, B indicates a small upset amount due to insufficient welding heat input, and insufficient strength due to non-welding.
The area where leakage failure occurs and C is an area where the upset amount becomes excessive due to excessive welding heat input, and pinhole leakage failure occurs due to scattering of welding spatter.

However, in region A, the amount of upset (d) is the upper and lower limit values (d
z, dt), the weld bead is stable near the center of A1. Subtle changes as shown in At and As occur. (B and C in FIG. 5 correspond to the weld bead states in areas B and C in FIG. 4(a).)
Here, At is a region where the opposing force F3 shows a small value,
The bead shape is small, which causes variations in weld strength. Ag is a region in which the opposing force exhibits a value approximately at the center value of the set value F2, and the bead shape has an optimal size. Therefore, the welding strength is stable with almost no variation. A3 is counter force F! The bead shape becomes larger in the region where is the upper limit of the set value.

This may result in insufficient pressurization, resulting in variations in welding strength.

These areas A+, Ax, and As correspond to each other as shown in Fig. 4(a), but since there is no change in the amount of upset that allows these areas to be identified, monitoring of the amount of upset does not involve these subtleties. etc., no changes are detected at all.

The inventor of the present invention solved the above problem by monitoring the change in the counter force F8 by the decompression spring 5b in addition to monitoring the amount of upset.

As shown in Fig. 4(b), even in the stable region of the welding upset amount (At, Ax, As), the opposing force Ft
has clearly changed. In the present invention, by monitoring this clear change and setting appropriate upper and lower limits for the counterforce F2, we can always maintain the optimal A! can be controlled to the state of

A counterforce monitoring device suitable for carrying out the monitoring method of the present invention includes, for example, as shown in FIG. 1, a load sensor 13a that detects F2, a load meter 13 that appropriately converts the detected value into a signal, A setter 14 sets the upper limit (rmcr, > and lower limit (fl) of F2, and the measured F2 value is set to these f
t and ft and a comparator 15 for displaying the result to the operator.

The welding mechanism of FIG. 1 including the monitoring device of the present invention operates, for example, as follows.

By setting the position when no welding heat input is applied (that is, when the upset amount is zero) as the zero point, and measuring the amount by which the squeeze roll holder 8 moves left and right when welding heat input is applied, the upset amount can be determined. Measure d. The comparator 11 outputs a signal indicating which state it is in, A, B, or C in FIG. It is then removed as a defective tube. In the state before welding shown in FIG. 3a, only the pressing force F+ by the pressing spring is applied to the welding part 2a by the squeeze roll 1a. When welding heat input is applied and the appropriate upset amount is reached, the squeeze roll holder 8 moves and comes into contact with the load sensor 13a, and a counterforce F2 begins to act. Then, before welding, a pressing force of F r F z is applied, and Abcera I is stabilized. The set load of the decompression spring 5b that applies the counterforce F8 is set to about 4 to 6 kg (taax) for a thin-walled electric resistance welded pipe made of brass, for example. From the load sensor 13a installed on the pressure reducing plate 5a to the load meter 13
A signal is sent to , and the load change exhibits the behavior shown in FIG. 4(b). Counter force Ft value is OK when welding heat input is insufficient
gf, and increases gradually as heat input is gradually given,
When the heat input becomes excessive, the setting value of the decompression spring Fztaa
It comes to show the same value as x.

In other words, within the range of upset upper and lower limit values dz, d+ (Af
In region II), the load cell will indicate σ from 0 to F gllaX. When the value of the load cell is close to O, the heat input during welding is small, and the weld bead becomes small.

Furthermore, if the value of the load cell is close to F, max, the welding heat input will be large and the weld bead will be large. When the value indicated by the load cell is between O and F fillaχ, the weld bead shape shows the optimum amount. From this, from 0 to fI, the bead is small, between fI and f2, the bead is good, and between f2 and F twa.
The bead becomes large between x. This is AI and Asfil
Although the welding is good in the area, the variation in welding strength is A2
becomes larger than . Therefore, the setting device 14 sets fI and f.
2 is set, and the value measured by the load cell 13 is compared with the value measured by the comparator 15, and between or and fz -F,
A caution signal is displayed between a and ax to notify the operator. The operator adjusts the output of the oscillator according to the condition.
ft as shown on the load cell. As a result, the good welded shape 11 region A can be further stabilized, and a high quality welded pipe can be provided.

The embodiment shown in Fig. 1 is a method in which one side of the squeeze roll is fixed, but it can also be applied to a pressurizing method in which both squeeze rolls move, as in the embodiment of Japanese Patent Publication No. 57-39878, or to other embodiments. It can also be applied to

In this example, it has been explained that the operator can adjust the oscillator output based on the measurement result of the opposing force F2 and a stable weld bead can be obtained.However, it is possible to automatically feed back the oscillator output based on the measurement result of F□. is also possible.

〔Effect of the invention〕

In addition to monitoring the amount of welding upset, the present invention also monitors the counterforce that reduces the pressing force applied to the squeeze roll, thereby preventing subtle changes in the weld bead that occur in the stable area of the amount of welding upset. , thereby making it possible to further reduce variations in welding strength and significantly improve welding quality.

[Brief Description of the Drawings] Fig. 1 is a configuration diagram showing an example of an ERW pipe welding mechanism to which a welding condition monitoring device according to the present invention is applied; 3a and 3b are sectional views showing the state of the circular tube before and after welding, respectively. ) a graph showing changes in welding upset amount and (b) changes in counterforce;
and FIG. 5 is a sectional view showing the state of formation of a weld bead. la, lb... squeeze roll, 2... tube, 4... pressure spring, 5
b...Decompression spring, 9...Position measuring device, 9a...Position sensor, 10.
...Setter, 11...Comparator. Procedural amendment (method) % formula % Display of the case 1999 Patent Application No. 31102 Name of the invention Person who makes corrections to the method and device for monitoring welding conditions during the manufacture of ERW pipes Relationship with the case Patent applicant name ( 426) Nippondenso Co., Ltd. Agent address: 8-10 Toranomon-chome, Minato-ku, Tokyo 105 Contents of the amendment Subject to amendment Figure 4 will be amended as shown in the attached sheet. One list of attached documents

Claims (1)

[Claims] 1. Melting the joints of metal plates bent into a tubular shape, and pressing the metal plates from both sides with squeeze rolls arranged opposite to each other to continuously form the joints of the metal plates. When welding, when the distance between the squeeze rolls is more than a predetermined amount, the pressing force of the squeeze rolls is set to the set load of the pressure spring, and when the distance between the squeeze rolls is less than a predetermined amount, A method for monitoring a welding state in an electric resistance welding tube manufacturing method in which the pressing force of the squeeze roll is set to a pressure obtained by subtracting the set load of the pressure reduction spring from the set load of the pressure spring, the method comprising: By detecting and comparing the detected value with a predetermined value, fluctuations in the amount of welding upset are monitored, and by detecting the set load of the decompression spring and comparing this detected value with a predetermined value, fluctuations in the weld bead can be monitored. A method for monitoring welding conditions during the manufacture of ERW pipes, the method comprising: also monitoring 2. A device for melting the joint of a metal plate bent into a tubular shape, a pair of squeeze rolls that are placed opposite to each other downstream of the device and press the metal plate from both sides, and a pressing force on the squeeze roll. a pressurizing spring that applies a pressure force to the squeeze roll, and a decompression spring that applies a counterforce in the opposite direction to the pressing force to the squeeze roll, and press joining that continuously welds the joint portion of the metal plate by the press force. A device for monitoring a welding state in an electric resistance welded pipe manufacturing device comprising a position sensor that detects the position of at least one of the squeeze rolls, and a position signal output circuit that operates in response to a signal from the position sensor. and a reference value setter for setting the upper and lower limits of the preferable welding upset amount, and a signal from the position signal output circuit is compared with the upper and lower limit values set in the reference value setting device to determine the welding upset amount. a device for monitoring fluctuations in the amount of welding upset, comprising a comparison indicator that displays when the upper and lower limits are exceeded; and a load sensor that detects the counterforce applied by the decompression spring;
A load signal output circuit that operates in response to a signal from the load sensor, a reference value setter that sets upper and lower limits of preferable counterforce, and a reference value setter that sets the signal from the load signal output circuit to the reference value setter. The welding bead is characterized by comprising a device for monitoring fluctuations in the weld bead, comprising a comparison indicator that compares the counterforce with the upper and lower limit values and displays it when the counterforce exceeds the upper and lower limit values. A device that monitors welding conditions during the manufacture of ERW pipes.