JP3681964B2 - Arc welding method and arc welding equipment - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
[0002]
The present invention relates to an arc welding method and an arc welding apparatus suitable for arc welding of thin plate-like base materials such as automobile bodies.
[0003]
[Prior art]
[0004]
As a welding method that firmly welds sheet metal panels such as the upper panel of an automobile body by overlapping each other, spot welding is performed by sandwiching the front and back surfaces of the sheet metal panel with a pair of electrodes, and welding is performed only from the surface side of the sheet metal panel. There is an arc welding method in which a wire is used to generate an arc for welding. The spot welding method is employed only when there is enough space for the pair of electrodes to enter the front and back sides of the sheet metal panel. In the arc welding method, the welding wire is approached from the front surface side of the sheet metal panel to melt the sheet metal panel itself, and droplets from the welding wire are attached to the melted portion for welding. Welding is possible regardless of whether there is room or not, and the degree of freedom for the shape of the base metal that can be welded is higher than that of spot welding. For this reason, the arc welding method tends to be frequently used for welding between sheet metal panels of automobile bodies whose shapes are remarkably diversified.
[0005]
[Problems to be solved by the invention]
[0006]
When arc-welding a base material of a thin steel plate such as a sheet metal panel of an automobile body, if the thickness of the base material exceeds 2 mm, the possibility that the melted portion of the base metal melted by the arc is less likely to melt down. As the thickness becomes thinner at 2 mm or less, the possibility that the base material melted portion melts increases. This base metal melting phenomenon will be described with reference to FIGS.
[0007]
As shown in FIG. 5A, a welding voltage is applied between the wire 2 brought close to the surface of the base material 1 and the base material 1 to generate an arc 3, and the surface of the base material 1 is generated by arc heat. The tip of the wire 2 is melted to form a molten portion 4 that is a molten metal pool on the surface of the base material 1. The molten portion 4 is a portion called a molten pool or a molten film, and is hereinafter referred to as a molten pool 4 as necessary. Note that the base material 1 is obtained by superposing the front surface side base material 1a and the back surface side base material 1b of two thin steel plates, and in FIG. 5A, the molten pool 4 is formed on the front surface side base material 1a. The first half of welding is shown. When arc welding is continued from FIG. 5 (A), the molten pool 4 reaches the back surface side base material 1b as shown in FIG. 5 (B), and the bottom of the molten pool 4 slightly touches the back surface of the back surface side base material 1b. Exposed. FIG. 5B shows the latter half of welding. When arc welding is further continued, the area and volume of the molten pool 4 increase as shown in FIG. Note that if arc welding is terminated at the time of FIG. 5 (B) or at the timing of transition from FIG. 5 (B) to (C), there is little possibility of the base material 1 being burned out and a good arc is achieved. Welding is possible. As shown in FIG. 5C, when both the area and volume of the molten pool 4 are increased, the molten pool 4 hangs down due to the arc force acting on the surface of the molten pool 4 and the weight of the molten metal in the molten pool 4. As shown in FIG. 5 (D), the molten pool 4 melts from the base material 1, and a hole portion 5 is formed in the base material 1. Such melting of the base material 1 at the arc welding portion is promoted by external vibration and impact force applied to the base material 1.
[0008]
The above melt-down of the base material 1 can be surely avoided if the end of the arc welding is performed at the timing of transition from FIG. 5A to FIG. 5B. Insufficient melting of the side base material 1b results in poor welding quality. As a measure to prevent any melting of the base material 1 by applying arc welding termination treatment at the time of FIG. 5 (B) or at the time of transition from FIG. 5 (B) to (C), Control property stabilization measures, welding wire speed control measures, welding wire material change measures, shield gas type change measures at arc welding, and the like have been tried. However, the shape and strength of the arc during welding varies, and it is difficult to grasp the high-accuracy condition of the molten pool itself, which is formed by melting the base material. Can not do it. Therefore, when the base metal melts down, the welded hole opening is manually welded and corrected. However, if the number of post-weld parts increases manually, workability is poor and the cost of arc welding is reduced. Down is difficult.
[0009]
An object of the present invention is to provide an arc welding method and an arc welding apparatus capable of preventing burn-off with high reliability even when arc welding a base material such as a thin steel plate having a thickness of 2 mm or less.
[0010]
[Means for Solving the Problems]
[0011]
In order to achieve the above object, the method of the present invention is based on a detection signal of at least one of an arc voltage and an arc current during arc welding in which a welded portion of a base material is melted by an arc generated between the base material and a welding wire. The pulsation level on the surface of the melted part that is arc welded is detected, and this pulsation level detection signal is used as a control signal that suppresses burn-out during arc welding. According to another aspect of the present invention, there is provided an arc welding apparatus for melting a welded portion of a base metal with an arc generated between the base metal and a welding wire in order to achieve the above-described object. And a burn-out suppression unit for detecting a pulsation level on the surface of the base metal melted part by arc welding and outputting this pulsation level detection signal as a control signal for suppressing burn-off during arc welding.
[0012]
It is known that the natural vibration of the molten pool is determined by the size, material, and the like. The present inventor has verified this from various angles, paying attention to the change in the frequency from the generation of the arc to the melt-off, and in particular, has found a phenomenon in which the vibration appears as pulsation immediately before the melt-down. Furthermore, the inventors found that the pulsation level can be grasped by measuring arc voltage and arc current, and developed the method and apparatus of the invention.
[0013]
More specifically, the present invention is characterized in that the pulsation level of the surface of the melted part where the base metal is arc welded is detected by detecting the degree of variation in the peak value of the arc voltage.
[0014]
Furthermore, the present invention achieves the purpose of preventing the base material from being melted down with a further degree of reliability, so that the exposed shape on the back surface side of the base material of the molten part that is arc welded on the surface side of the base material, It is measured by a laser distance sensor disposed on the back side of the base material, and this measurement signal is used as one of control signals for suppressing burn-off during arc welding.
[0015]
The laser distance sensor here measures the size of the melted portion that appears on the back side of the base material and is arc welded to the back side of the base material. From the measurement value signal of the melted part on the back of the base metal measured by the laser distance sensor, it can be determined whether or not it is a stage just before the melted part melts, and this judgment signal can be obtained from the arc voltage or arc current. By using the control signal as a control signal for suppressing burn-off, it is possible to prevent burn-out with higher accuracy. As the laser distance sensor, a commercially available small and inexpensive optical sensor can be used. Between such a laser distance sensor and a base material, a filter that cuts extraneous light and increases measurement accuracy is installed as necessary.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
[0017]
A first embodiment of the method of the present invention will be described in order with reference to FIGS. 1 to 3 and a second embodiment with reference to FIG.
[0018]
FIG. 1 shows an arc welder for arc-welding the base material 1 of FIG. 5 and its power supply unit 10. The power supply unit 10 has an arc welding function similar to that in the past in which an arc voltage Vx having an output waveform is applied to the base material 1 and the welding wire 2 to generate an arc 3 between the surface of the base material 1 and the tip of the welding wire 2. Have. The power supply unit 10 includes an arc voltage detection unit 11 that detects an arc voltage Vx during arc welding, an arc current detection unit 12 that detects an arc current Ix during arc welding, and a burn-out during arc welding. A burn-off suppression unit 20 is provided to prevent this. The burn-off suppression unit 20 pulsates the surface of the molten pool 4 that is the molten portion of the base material 1 that is arc-welded based on the detection signal of either or both of the arc voltage Vx and the arc current Ix detected during arc welding. The level (such as the upper and lower levels of the pulsating surface) is detected, and this pulsation level detection signal is output to the power supply unit 10 as a control signal Cx for preventing burnout during arc welding.
[0019]
That is, the present inventor is able to accurately determine the physical conditions such as the size and fluidity of the molten pool 4 in the arc welded portion of the base material 1 in the stage of FIGS. 5 (B) and 5 (C). As a result of verifying the means and methods to be understood from various angles, the pulsation phenomenon that finely vibrates finely with arc force etc. starts to stand out as the molten pool 4 increases in both area and volume, and the pulsation phenomenon fluctuates vertically and horizontally. When the arc voltage Vx and arc current Ix at the time of arc welding substantially follow the pulsation level of the surface of the molten pool 4 that changes, and further when temporal variations start to be noticeable in the varying pulsation level of the surface of the molten pool 4 It has been found that the possibility that the molten pool 4 melts from the base material 1 due to its own weight and pulse power increases rapidly. FIG. 3 shows an example of the relationship between the pulsation level that fluctuates on the surface of the molten pool 4 and, for example, the arc voltage Vx that varies in a proportional relationship with the pulsation level.
[0020]
Molten pool 4 ₁ in the base material 1 at the time of arc welding shown in FIG. 3 (b), equivalent to the molten pool 4 of FIG. 5 (B), the molten pool 4 ₁ to the back surface of the back side base material 1b The bottom has reached, and when the arc welding is terminated here, the best arc welding is performed in both strength and appearance. The molten pool 4 ₂ shown in FIG. 3 (c) is equivalent to the molten pool 4 of FIG. 5 (C), and the molten pool 4 ₂ is on the verge of being melted down due to excessive expansion of both area and volume. . The pulsation in which the molten metal in the molten pool sways due to arc force or other external vibration starts to become noticeable as the transition from the molten pool 4 ₁ to the molten pool 4 ₂ occurs, and the distance between the molten pool surface and the tip of the welding wire 2 Fluctuates. When the arc voltage Vx of the output waveform during the transition from the molten pool 4 ₁ to the molten pool 4 ₂ is detected, a pulse waveform of about 100 Hz as shown in FIG. When obtaining the peak value interval P of the arc voltage Vx of example 1 cycle of the pulse waveform, is a value less relatively stable variation interval P ₁ when the molten pool 4 _1, when the molten pool 4 ₂ The interval P ₂ is larger than the interval P ₁ on average, and the variation among the individual intervals P ₂ is conspicuously large. Such a variation state of the intervals P ₁ and P ₂ represents the magnitude of the pulsation level on the surface of the corresponding weld pool 4 ₁ , 4 ₂ , and the magnitude of the pulsation level is obtained with high accuracy from the arc voltage Vx. It is.
[0021]
FIG. 2 shows a circuit example of the burn-out suppression unit 20 that detects the arc voltage Vx and suppresses burn-out. This includes a pulsation determination circuit 21, a limit pulsation detection circuit 22, and a limit pulsation setting unit 23. When the arc voltage Vx detected from the arc voltage detection means 11 is output to the pulsation determination circuit 21, the pulsation determination circuit 21 calculates the data of the size and variation of the interval P and outputs it to the limit pulsation detection circuit 22. . The limit pulsation detection circuit 22 compares the data of the inputted interval P, the variation data with the data set in advance by the limit pulsation setting unit 23, etc., so that the area and volume of the welding pond 4 during arc welding are both the same. Detects whether the allowable limit before melting is reached. For example, it is determined that the pulsation level of the weld pool 4 surface when the data interval P ₁ of the arc voltage Vx in Figure 3 does not reach the tolerance limit, the interval P ₂ when changing from data interval P ₁ in the data interval P ₂ And the variation degree data are compared with the interval size and variation degree tolerance limit data set in advance by the limit pulsation setting unit 23. If it is determined from the comparison result to the limit pulsation level close to the situation of the molten pool 4 ₂ of FIG. 3 (c), the control signal Cx of burn suppressing the power supply unit 10 from the limit pulsation detection circuit 22 is output .
[0022]
The output timing of the control signal Cx is set to a point in time until the migration to the situation of the molten pool 4 ₂ if the last point of the molten pool 4 ₁ situation, at the latest FIG 3 (c) shown in FIG. 3 (b) .
When the control signal Cx is output to the power supply unit 10, for example, the power supply unit 10 lowers both the arc voltage Vx and the arc current Ix or performs an operation of interrupting the arc welding itself to prevent melting.
[0023]
The arc welding operation in FIG. 3 is based on fixed point welding. In line welding in which the straight portion of the base metal is continuously arc welded, melting is performed by controlling the line welding speed with the control signal Cx. It is also possible to prevent dropping.
[0024]
The above is an arc welding method that detects the peak value interval P of the arc voltage Vx and suppresses burn-through, but the frequency fluctuations in the arc voltage Vx and the arc current Ix are caused by the pulsation of the molten pool 4 where the base material 1 is arc welded. Since a component appears, this frequency variation component may be detected to obtain a control signal Cx that suppresses burnout.
[0025]
In the arc welder of the embodiment of FIG. 4, a laser distance sensor 30 and a filter 31 are arranged on the back surface side of the base material 1 for the purpose of preventing the base material 1 from being melted down with higher reliability. . The laser distance sensor 30 measures and inspects the appearance of the weld pool 4 that is arc-welded on the surface side of the base material 1 on the back side of the base material, and the filter 31 receives unnecessary external light on the laser distance sensor 30. And the measurement accuracy of the laser distance sensor 30 is increased.
[0026]
That is, when the molten pool 4 ₁ As shown in FIG. 3 (b) the base material 1 and arc welding is formed, the bottom of the molten pool 4 ₁ slightly exposed on the back surface of the base material 1, the exposed melt pool 4 ₁ laser distance sensor 30 the width w of the bottom surface is output to the power supply unit 10 measurements. Power supply unit 10 to determine whether there progressing into the molten pool 4 ₂ of the molten pool 4 ₁ or 3 shown in FIG. 3 (b) from the data of the input width w (c), Ya arc voltage Vx The operation of preventing burn-off is performed in cooperation with the control signal Cx based on the arc current Ix. In this way, the data from the laser distance sensor 30 is also used in combination with the double triple tripping prevention measure to increase the reliability of the burnout prevention.
[0027]
The laser distance sensor 30 and the filter 31 are simple in structure, inexpensive, and can be applied to small commercial products. They can be used easily even when the space on the back surface of the base material 1 is narrow, and the arc welder can be used freely. Is hardly damaged.
[0028]
【The invention's effect】
In the present invention, as described above, the pulsation level of the molten portion (molten pool) that is melted by arc welding of the base metal is detected based on the detection signal of the arc voltage or arc current, and melting proceeds until the molten portion is melted down. By controlling so as not to melt, even if the base metal is a thin steel sheet of 2 mm or less, burn-off during arc welding can be prevented with high accuracy, and this high-precision burn-out prevention effect increases arc welding strength. Costs can be reduced by improving welding quality and improving yield. In particular, arc welding of a base material, which tends to be made thinner and thinner like a sheet metal panel of an automobile body, can be carried out with a high yield and low cost.
[0029]
Also, if the arc welded part is measured from the back side of the base metal with a laser distance sensor during arc welding of the base metal surface, the burn-out can be suppressed from this measurement result, and the reliability of the burn-out prevention effect is still low. Further increase.
[Brief description of the drawings]
FIG. 1 is a block diagram of an arc welder showing an embodiment of the present invention.
FIG. 2 is a block diagram of a burn-off suppression unit in FIG.
FIG. 3 is a cross-sectional view and a voltage waveform diagram for explaining a correlation between an arc welding portion of a base material and an arc voltage in the method of the present invention.
FIG. 4 is a block diagram showing another embodiment of the present invention.
FIGS. 5A and 5B are cross-sectional views for explaining a burn-out phenomenon in arc welding, where FIG. 5A is the first half of arc welding, FIG. 5B is the second half of arc welding, FIG. Sectional drawing at the time of falling.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 Base material 1a Front side base material 1b Back side base material 2 Welding wire 3 Arc 4 Molten part (molten pool)
DESCRIPTION OF SYMBOLS 10 Power supply part Vx Arc voltage 11 Arc voltage detection means Ix Arc current 12 Arc current detection means 20 Burn-off suppression part Cx Control signal for burn-off suppression

Claims (4)

The pulsation level at the surface of the base metal melted part by arc welding from the detection signal of at least one of arc voltage and arc current during arc welding in which the welded part of the base metal is melted by an arc generated between the base metal and the welding wire An arc welding method characterized in that this pulsation level detection signal is used as a control signal for suppressing burn-off during arc welding. 2. The arc welding method according to claim 1, wherein the pulsation level of the surface of the melted portion where the base metal is arc welded is detected by detecting the degree of variation in the interval between the peak values of the arc voltage. The exposed shape on the back side of the base metal of the melted part that is arc welded on the front side of the base material is measured with a laser distance sensor arranged on the back side of the base material, and this measurement signal is suppressed from melting during arc welding. The arc welding method according to claim 1 or 2, wherein the control signal is one of the control signals. In an arc welding device that melts the welded part of the base metal with an arc generated between the base metal and the welding wire, the pulsation on the surface of the base metal melted part by arc welding is detected from the detection signal of at least one of arc voltage and arc current. An arc welding apparatus comprising a burn-out suppression unit that detects a level and outputs this pulsation level detection signal as a control signal for suppressing burn-off during arc welding.

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