JPH0249829B2 - - Google Patents

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an arc welding method, and in particular to a consumable electrode in an inert gas such as argon or helium, or a gas mixed with an inert gas such as oxygen or carbon dioxide. The present invention relates to a gas-shielded pulsed arc welding method using a gas-shielded pulsed arc welding method.

[Conventional technology]

Generally, in this type of welding method, as shown in FIG. 1, the phenomenon in which the welding wire melts and transfers to the workpiece changes discontinuously after a certain current value.
This current value is called the critical current value, and below the critical current value, the size of the droplets (molten metal that falls from the tip of the wire, the same number as the number of particles in the figure) becomes a large lump larger than the wire diameter. The growth becomes irregular (that is, the timing of growth and fall is irregular). However, when the current exceeds the critical current value, the droplets become finer and fall, so the number of particles increases and spray transfer becomes relatively stable. Therefore, in order to perform stable welding, it is necessary to weld at a current higher than the critical current value, but if the workpiece to be welded has a relatively thin plate thickness, excessive heat input may occur, making it difficult to obtain a satisfactory welded workpiece. is not possible.

For this reason, a method is used in which a pulse current is superimposed on a direct current as shown in FIG. In this method, the base current value I _B is set below the critical current value,
By setting the peak current value I _P higher than the critical current value, the transfer of droplets is smoothed, and by lowering the average value I _n of the welding current, the amount of heat input to the workpiece is reduced, resulting in good welding. It is an attempt to obtain a division.

[Problem to be solved by the invention]

However, since conventional pulse arc welding methods and devices use thyristors to control the output current, the output current waveform is automatically controlled, making it difficult to weld with an optimal welding current waveform. In other words, most conventional devices use thyristor elements for phase control, and the pulse frequency corresponds to the primary power frequency as shown in Figure 3.
It can only output a frequency of 50/60Hz or an integral multiple thereof, and the rise speed of the peak current value I _P is also limited. Furthermore, if the peak current value is changed, the peak current time T _P also changes, so only a very limited waveform can be output. Furthermore, when changing the average value I _n of welding current, the peak current value I _P (or peak voltage value) and base current value I _B (or base voltage value) must be adjusted individually. There are also problems with the above.

By the way, there is a method that uses a welding power source with a transistor as a control element, changes the frequency arbitrarily to ensure the stability of the arc and droplet transfer, and increases the penetration depth with the same amount of heat input. be. However, with this method, as shown in Figure 4,
The droplet could be completely synchronized with the pulse cycle up to about 300 Hz (the linear relationship in the same figure), and it was impossible to synchronize it above that.

The present invention has been made in view of the above-mentioned problems, and is a pulsed arc welding method for welding using a consumable electrode in a shielding gas of an inert gas or a mixed gas in which oxygen, carbon dioxide, etc. are added to the inert gas. Under a wide range of welding conditions from very low current (e.g. 50A) to high welding current range (e.g. 600A), the optimal welding current waveform is always output under any condition, and one welding process can be performed with one pulse. It is an object of the present invention to provide a pulse arc welding method that allows droplets to be transferred reliably and has low noise.

[Means to solve the problem]

In order to achieve the above object, the present invention superimposes a pulse current defined by an on time T _P and an off time T _B on a DC component having a base current value I _B smaller than the critical current value, _and Apply a welding current with a peak current value I _P larger than the current value, select I _P , T _P or T _B as appropriate depending on the welding conditions, and set the average current I _n
In this method, I P and _{T P are} determined under the conditions that the product of I _P ^K (K = 1.9 to 2.5) and T _P is constant, and the average droplet is transferred per pulse. When the current I _n exceeds the critical current value, the base current value I _B is maintained below the critical current value and the I _B value is made larger than the current value.

Particularly when welding aluminum alloys, the time T from the start of the rise to the start of the fall of the pulse current value _P should be 0.2ms≦T≦4ms, and each of the above T _U and T _D should be 0.1ms≦T _U , It is preferable that T _D ≦4ms.

[Effect]

The present invention makes it possible to reliably transfer one droplet with one pulse by the above solution.

Furthermore, as will be described later, when the welding current (average current) value exceeds the critical current value, a so-called spray transfer phenomenon occurs. This is a phenomenon in which multiple droplets are transferred in one pulse, contrary to one droplet per pulse. Even in this case, the present invention is characterized by not only keeping the I _B value itself below the critical current value, but also making the I _B value larger than the current value. The current value means the value set in the welding current range of drop transition. In other words, the I _B set when the average current value is less than the critical current value
It means to be larger than the value. This is also effective in reducing arc noise.

〔Example〕

Embodiments of the present invention will be described below with reference to FIGS. 5 to 19.

Figure 5 is a definition diagram of the pulse current waveform, and is I _P
is the peak current value, T _P is the peak current time (on time), I _B is the base current value, T _B is the base current time (off time), and I _n is the average value of the welding current (hereinafter referred to as average current). be. At this time, the average current value I _n can be expressed by the following equation.

Influence of pulse current factors I _P , _{T P , I B , and T B on} droplet transfer, arc stability _, and weld quality This will be explained using aluminum alloy welding as an example.

FIG. 6 shows the influence of the peak current value I _P on the grain size of the welded portion, assuming that the average current value I _n and the heat input are constant. The crystal grain size was measured from the number of primary crystals at the central 3 mm position (A in the figure). The grain size tends to become finer as the peak current value I _P increases. Also T _P / T _B
The crystal grain size also becomes finer as it becomes smaller.

FIG. 7 shows the cross-sectional macrostructure of the welding beam at this time. In order to refine the grain size, which has a significant effect on the strength of the weld, especially the cracking resistance, it is necessary to at least increase the peak current value I _P.
It needs to be 300A, preferably 350A or more.

Figure 8 shows the relationship between the peak current value I _P and the peak current time T _P to ensure that the droplet moves in one pulse, which was determined from observation of the arc phenomenon photographed with a high-speed cine camera. It is shown in double logarithm based on common logarithm.

In the figure, in the region A below line A, the droplet does not transfer reliably with one pulse due to insufficient energy input, and the droplet size is 2 to 4 times the wire diameter, causing the droplet at the tip of the wire to This is a region where the arc becomes unstable because it fluctuates depending on its size. In area B above line segment RO, due to excessive input, several droplets may migrate,
This is the area where the tip of the welding wire becomes candy-like, creating a phenomenon similar to whiplash, where many spatters occur, and where the arc becomes unstable. When the wire diameter is 1.4 mm, the region C is an appropriate range in which one droplet is reliably transferred in one pulse.

When I _P ≧ 800 A, the appropriate range of T _P at I _P = 800 A is from 0.2 ms to 0.5 ms at most.
Therefore, a very fast rise of 800A/0.2 to 0.5ms is required, and to achieve this, the internal impedance of the power supply must be extremely low, and the circuit configuration must be made of multiple transistors. This is not a practical configuration for the welding machine in use.
Additionally, the arc noise becomes stronger, which poses a problem in welding work.

Furthermore, in the region between line segments A and B and where I _P ≦300A, one droplet transfers in one pulse, but the crystal grains in the weld become large, which poses a problem in terms of strength. This will be further explained with reference to FIG. FIG. 19 shows the relationship between the peak current value I _P and the grain size of the weld. The crystal grain size shows a tendency to become finer as the peak current increases. There is a close relationship between the grain size and the strength (especially cracking resistance) of the weld, for example, the peak current I _P = 430A in Figure 19.
(grain size approx. 0.18 mm) and I _P = 230A (crystal grain size approx. 0.35
When a cracking test was conducted using the reverse hold-craft method under the conditions of (mm), I _P =430A had approximately 1.5 times better cracking resistance than I _P =230A. In this cracking test, almost the same results were obtained when the peak current I _P was 300 A or more.

From Fig. 8, the upper limit of I _P is 800A, and from Fig. 19, the lower limit of I _P is 300A. From this, the peak current I _P
In this example, the appropriate range of is 300A≦I _P ≦
It is 800A. At that time, the peak current time T _P for transferring one droplet with one pulse is at I _P = 300A.
1.5ms≦T _P300 ≦4ms, 0.2ms≦T _P800 for I _P = 800A
≦0.5ms. Therefore, the appropriate range of T _P is
0.2ms≦T _P ≦4ms, and the lower and upper limits of the appropriate range shown by line segment A and line segment D in the figure are
I _P ^K ×T _P = C (however, k = 1.9 to 2.5 (for example, SUS304
If the wire diameter is 0.9 mm, k = 1.9; if the wire diameter is aluminum, k = 2.5), k is a constant determined by the wire diameter and material, but the possible range is
It is narrow, ranging from 1.9 to 2.5, and there is virtually no difference in wire material or wire diameter. C is also a constant determined by the wire diameter and wire material. ) can be expressed as
In other words, the product of I _P ^K and T _P is constant. For example, line segment A in the figure becomes I _P ^2.0543 ×T _P =184012, and line segment B in the figure becomes I _P ^2.12 ×T _P =714114.7. This formula was obtained through intensive study by the inventors, and the k value is a constant that depends only on the thermal conductivity of the wire. In short, the inventor believes that when transferring one droplet per pulse,
They discovered that there is a certain relationship between I _P and T _P , an idea that had never existed before. The material and diameter of arc welding wire are standardized, and the wire material and diameter are limited. When examining all of this range, the k value increases in the order of stainless steel, mild steel, and aluminum in terms of wire materials, and the k value increases as the wire diameter increases. Therefore, among commonly used arc welding wires, the one with the smallest k value is the stainless steel wire with a minimum wire diameter of 0.9 mm, which is 1.9.
On the other hand, the largest k value is for aluminum wire at 1.6 mm, which is the largest wire diameter commonly used for arc welding.
It becomes 2.5.

Based on the above, what governs droplet transfer is the peak current value and peak current time, and in order to reliably transfer one droplet with one pulse, the peak current I _P and the peak current time are It is necessary to set T _P so that the relationship I _P ^K ·T _P =C holds. In other words, I _P and T _P such that the product of I _P ^K and T _P is constant
With any of these combinations, one droplet transfer can be reliably performed with one pulse, and stable welding without spatter can be performed.

Figure 9 is based on this relationship, I _P = 600A, T _P =
0.5ms (i.e. located within area C in Figure 8)
The welding current I and voltage recorded with an electromagnetic oscilloscope when welding was performed under the following conditions are shown. When a droplet migrates, the arc length momentarily increases and the arc voltage rises, so the time at which the droplet migrates can be confirmed from the oscilloscope waveform.

In addition, Figure 10 shows the form of droplet transfer based on observation of the arc phenomenon, but actual confirmation confirms the results shown in Figure 9, and one droplet is reliably transferred with one pulse. I can see that you are doing it.
That is, if the point at which the peak ends at the position E in FIG. 9 is the start of frame number 1 in FIG. 10, then the position to the peak in FIG. 9 corresponds to the droplet falling from frame number 11 onward.

It has become clear that such droplet migration is controlled by the peak current value I _P and the peak current time T _P . Based on this, the base current value I _B is a current value low enough to maintain the arc stably (for example,
20 to 50 A), the average welding current I _n can be lowered, and excessive heat input to the base metal can be prevented.

From the results described above, as shown in Figure 11, the peak current value I _P , peak current time T _P , base current value
It is possible to change the average current I _n by setting I _B to a constant value and adjusting the base current time T _B , and an optimal pulse waveform can be obtained at any welding current.

As described above, we have established a simple and effective method for adjusting the average current I _n by simply changing the base current time T _B , but it is important to relate the wire feeding speed W _f to the base current time T _B. The average current I _n can be adjusted more easily by .

Figure 12 shows the average welding current I _n and base current time.
This is a diagram summarizing the relationship with T _B using common logarithms. At this time, base current value I _B = 50A,
Peak current value I _P = 600A, peak current time T _P =
It was set to 0.5ms. On the other hand, since there is a proportional relationship between the average welding current I _n and the wire feed speed W _f as shown in Fig. 13, the relationship between the wire feed speed W _f and the base current time T _B is determined from this. and as shown in Figure 14. FIG. 14 is shown in double logarithm based on common logarithm. Therefore, by setting the relationship between the wire feeding speed W _f and the base current time T _B in advance as shown in Fig. 14, the base current time can be adjusted.
If the average welding current I _n can be changed simply by changing T _B , the optimum wire feeding speed commensurate with the average current I _n at that time can be ensured, making adjustment very easy.

Furthermore, in the region where the average current I _n is higher than the critical current value (the welding current region for spray transition), the time of the base current I _B (base current time T _B ) becomes shorter and the pulse frequency becomes higher, which causes a considerably louder arc noise. issue. In this case, if the base current value I _B is increased in a range lower than the critical current value, the average current value I _n will increase, the base current time T _B will become longer, and the arc sound will shift to a lower range, so the arc sound will become smaller. .

Figure 15 shows a specific example of this, with 140A
In the following, the base current I _B is set to 50 A, and for currents higher than that, the base current is switched to I _B = 130 A. In the case of I _B =50A, the base current time T _B =1.4ms when the welding current is 200A. Therefore, the pulse frequency (1/T _P + T _B ) is 526 Hz, but when switching to I _B = 130 A, the welding current
The base current time at 200A is T _B = 3ms,
The pulse frequency is 285Hz, approximately 1/2 of that when I _B = 50A.
frequency, which can significantly reduce arc noise. In this case, when the base current I _B is made higher than the critical current,
This is undesirable because the droplets begin to migrate regardless of the pulse period.

In this example, in order to achieve the above-mentioned purpose, the 16th
As shown in the figure, a power supply based on analog control of transistors can be used. In Fig. 16, 1 is a rectifier, 2
is a transistor, 3 is a controller, 4 is a signal setting device, and 5 is a welding detector. Also, 6 is a wire,
7 is a workpiece to be welded, and 8 is a feed motor. With such a configuration, the above-mentioned waveform is output between the welding wire 6 and the workpiece 7.

In addition, the peak current value I _P and peak current time mentioned above
If the relationship T _P can be secured, the object of the present invention can also be achieved by a system in which a base current output circuit and a peak current output circuit are provided as shown in FIG. 17, and transistor 2 is controlled by switching.

In Fig. 17, 9 is a base current rectifier, 1
0 is a base current controller that sets external characteristics to appropriate values.

FIG. 18 shows an implementation example of the present invention. This figure shows the appearance of a bead when butt welding an aluminum alloy plate with a thickness of 1.6 mm using a 1.4 mmφ welding wire. The welding conditions at this time are average welding current I _n =54A, peak current value I _P =600A, peak current time T _P =0.5ms, base current value I _B =400A, and bake current time T _B =70ms.

As can be seen from the figure, beads with an extremely good appearance were obtained.

As described above, according to this embodiment, it is possible to weld thin aluminum plates of 0.8 to 1.6 mm thick to medium thick plates (6 to 12 mm) using large diameter wires (1.4 to 1.6 mmφ), which was previously impossible. A very stable arc and smooth droplet transfer can be achieved over a wide range of welding, resulting in high quality welds, and the average welding current can be adjusted very easily.

〔Effect of the invention〕

As described above, according to the present invention, the peak current
It is possible to reliably transfer one droplet with one pulse by setting I _P , the time T _P from the start of the peak current rise to the start of fall, and the product of these (I _P ×T _P ) to appropriate values. This enables low-noise pulsed arc welding.

[Brief explanation of the drawing]

Figure 1 is a basic explanatory diagram of the gas-shielded arc welding method, Figure 2 is a conventional peak current and base current relationship characteristic diagram, Figure 3 is a pulse frequency characteristic diagram of the conventional method, and Figure 4 is the same conventional method. Figure 5 shows the definition of peak current, base current, average current, peak current time, and base current time. Figure 6 shows the grain size of the welded area at peak current. A characteristic diagram showing the influence on
Figure 7 is a photograph of the metal macrostructure of the weld bead cross section.
Fig. 8 is a characteristic diagram explaining the relationship between peak current and peak current time in an embodiment of the arc welding method of the present invention, Fig. 9 is a characteristic diagram showing the results recorded with an electromagnetic oscillograph in the same embodiment, Figure 10 is a schematic diagram showing the transfer form of a droplet as observed by observing the arc phenomenon in the same example, Figure 11 is a schematic diagram of a pulse waveform obtained by the same example, and Figure 12 is a base diagram in an example of the present invention. A characteristic diagram showing the relationship between the current time and the average welding current, FIG. 13 is a characteristic diagram showing the relationship between the average welding current and the wire feed amount in the same example, and FIG. 14 is a characteristic diagram showing the relationship between the base current time and the average welding current in the same example. Figure 15 is a characteristic diagram showing the relationship with the wire feed amount, and Figure 15 is a characteristic diagram showing the relationship between base potential time and welding current when the base current value is changed.
Fig. 6 and Fig. 17 are both control circuit diagrams used in the embodiment of the present invention, Fig. 18 is a metal structure photograph showing the state of the bead obtained in the embodiment of the present invention, Fig. 19
The figure is a characteristic diagram illustrating the relationship between peak current and crystal grain size in an example of the present invention. DESCRIPTION OF SYMBOLS 1... Rectifier, 2... Transistor, 3... Controller, 4... Signal setting device, 5... Current detector, 6... Welding wire, 8... Feeding motor, 9...
... Rectifier for base current, 10... Controller for base current.

Claims (1)

[Claims] 1 A pulse current with an on time specified by T _P and an off time specified by T _B is superimposed on a DC component with a base current value I _B smaller than the critical current value, and at time T _P a peak current value I _P larger than the critical current value is superimposed. _{In the} arc welding method _, a ^welding _{current of}
If I _P and T _P are determined under the condition that the product of (K = 1.9 to 2.5) and T _P is constant, and the average current I _n exceeds the critical current value, the base current value I _B is changed to the critical current value. An arc welding method characterized by increasing the I _B value to a larger value than the current value while maintaining the I B value below the current value.