JPS6348633B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a pulsed arc welding method in which a pulsed welding current is passed. As a conventional pulse arc welding machine, there was one shown in FIG. In the figure, 1 is a pulse generation power source that supplies a pulsed welding current (hereinafter referred to as "pulse current"), 2 is a pulse gate circuit for giving a trigger signal to the gate of a thyristor, etc. in the pulse generation power source 1, and 3 is a base power supply for supplying a direct current (hereinafter referred to as "base current") so that arc breakage does not occur between pulse currents, 4 is a wire, and 5 is a wire 4 that is sent toward the base metal. 6 is a base material, and 7 is an arc lit between the wire 4 and the base material 6. Next, the operation will be explained. If the wire 4 is fed in the direction of the base material 6 by the wire feeding device 5, and the pulse current and base current are supplied from the pulse generating power source 1 and the base power source 3, respectively, a welding current with a waveform as shown in FIG. 2 can be obtained. flow, and the base metal is welded. Figure 2 a shows the case where the average welding current value is small, and b shows the case where the average welding current value is large, τ is the pulse width, I _p is the peak value of the pulse current (hereinafter referred to as "peak current value"),
I _B indicates the base current value. To change the energy amount of the arc (that is, the amount of heat input into the wire and the base metal), the firing phase of the thyristor in the pulse generating power source 1 is changed by the pulse gate circuit 2, and the pulse width τ and therefore the peak current value are changed. Adjustments are made by changing I _p and the base current value I _B depending on the time. That is, when the average welding current value is small, I _B , τ, and I _p are set small as shown in Figure 2 a, and conversely, when the average welding current value is large, the second
As shown in Figure b, I _B , τ, and I _p are set large. The pulse frequency is fixed to be equal to or twice the basic power frequency (50Hz, 60Hz in Japan). Now, in a welding method using such a pulse arc welding machine, usually once per pulse, the wire droplets become fine particles and transfer to the base metal (hereinafter referred to as "spray transfer"). . If a conventional pulse arc welding machine were to change the welding current waveform, the amount of heat injected into the wire per pulse would vary greatly. That is, when the average welding current value is small, the amount of heat injected into the wire per pulse is small, and the peak current value is less than the critical current value required to cause spray transfer.
If the droplets do not become large, they will not transfer to the base material. This situation is shown in FIG. 3a. Therefore, if the arc length is shortened, the wire and the base metal will be short-circuited, and the short-circuit current will cause the melted wire to become spatter and scatter around. In addition, if the average welding current value is large, the amount of heat input to the wire per pulse becomes too large, and the droplets droop as shown in Figure 3c.If the arc length is shortened, the wire This will cause a short circuit with the base material, resulting in spatter. In cases like Figure 3 a and c, if the arc length is made long to avoid spatter,
Undercut occurs and welding speed cannot be increased. Therefore, in order to transfer the droplet without spatter even with a short arc length as shown in FIG. 3b, the diameter of the droplet must be made as small as possible. That is, the amount of heat input to the wire must be kept at an appropriate value. However, in the conventional pulsed arc welding method, the current waveform is changed as shown in Figure 2a and b, so in order to obtain the appropriate droplet transfer form as shown in Figure 3b, it is necessary to I had to adjust the current value etc. very well. As mentioned above, in the conventional pulse arc welding method, it is difficult to make adjustments to achieve a proper droplet transfer state, and often spatter or weld defects such as undercuts occur.
It also had the disadvantage of poor work efficiency, such as the need for extra work steps such as removing spatter. This invention was made in order to eliminate the drawbacks of the conventional methods as described above.The welding current is detected moment by moment, integrated and calculated, and when the value becomes equal to a preset heat input amount or coulomb amount, a pulse is generated. By stopping the heat input into the wire per pulse, the heat input to the wire per pulse can be set to an appropriate value, and with simple adjustment,
It is an object of the present invention to provide a pulse arc welding method that allows a proper droplet transfer state to be obtained. Next, an embodiment of the method of this invention will be described with reference to the drawings. In Fig. 4, the pulse generating power supply 1 turns on DC current using a switching element such as a transistor.
It's off. 9 is a detector for detecting welding current;
10 is an integration circuit, which includes an integrator 11 that integrates the output of the detector 9 itself, an integrator 12 that integrates the square of the output of the detector 9, and an integrator 11 that multiplies the output of the integrator 11 by K (K is the wire material, a constant determined by the diameter and type of shielding gas), a multiplier 13, and an integrator 12.
a multiplier 14 that multiplies the output by Rl (R is the resistance value per unit length of the wire, l is the protrusion length), and an adder 15 that adds the outputs of the multipliers 13 and 14.
It is made up of. Reference numeral 16 is a setter for presetting a predetermined amount of heat W ₀ , and 17 is a comparator for comparing the output W of the adder 15 and the set amount W ₀ of the setter 16 . Next, before explaining the method of the embodiment, the principle of operation of the present invention will be described. When the wire melts and becomes fine particles and transfers to the base metal, the size of the droplet is determined by the following three forces acting on the droplet: (a) electromagnetic force (pinch force) in the direction of the base metal; ) Surface tension in the wire direction (c) Determined from the balance of gravity. When the wire material, diameter, and type of shielding gas are varied, the droplet diameter a during spray transfer as shown in Figure 3b is:
According to actual measurements, the results are as shown in Table 1 shown on the next page. Since droplet transfer occurs approximately once per pulse,
The amount of heat input to the wire per pulse must be sufficient to melt the wire for the number of droplets shown in the table. For example, if the wire is mild steel 1.2mmφ and the shielding gas is a mixed gas with a flow rate ratio of Ar/CO ₂ = 8/2, the room temperature is 0°C, the temperature of the droplet is 1535°C (melting point of iron), the density is 7.8g/cm ³ , and the specific heat is 0.15cal/g・℃, latent heat
If calculated as 65 cal/g, 2.08 cal (8.74 Joule) is required when the droplet diameter is 1.2 mmφ.

[Table] Table 1 also shows the required amount of heat input W ₀ to the wire under various conditions. The physical constants used for stainless steel and aluminum are shown in Table 2.

[Table] On the other hand, the amount of heat W injected into the wire by the welding current per pulse is considered to be equal to the sum of the arc heat W ₁ and the Joule heat W ₂ at the protruding portion. The arc heat W ₁ is larger than the Joule heat W ₂ and is considered to have a ratio of about 8:2 or 7:3. Further, the former is proportional to the current, and the latter is proportional to the square of the current. Therefore, the relationship between the area Q ₁ of the current waveform per pulse, the area Q ₂ of the square of the current waveform, and the above W is as follows. W=W ₁ +W ₂ =KQ ₁ +RlQ ₂ Therefore, by detecting the current waveform and performing the calculation shown in the above equation, the amount of heat being injected can be grasped moment by moment. Therefore, W is W ₀ shown in Table 1.
If the pulse generation is stopped when the pulse becomes equal to W, the amount of heat input W to the wire per pulse can be appropriately suppressed. A circuit configuration for concretely realizing the above operating principle is shown in FIG. 4, and its operation will be described below. First, the wire 4 is fed toward the base metal by the wire feeding device 5, and welding is performed by supplying welding current from the pulse generating power source 1 and the base power source 3. However, the welding current waveform is detected by the detector 9. They are detected moment by moment, and Q ₁ is calculated by an integrator 11, and Q ₂ is calculated by an integrator 12 (this integrator 12 integrates, for example, via a non-linear element). Therefore, the output of the multiplier 13 is the portion of the heat input W into the wire due to the arc heat, and the output of the multiplier 14 is the portion due to the Joule heat at the protruding portion. Adder 15 sums the outputs of multipliers 13 and 14, and its output indicates the total amount of heat input to the wire, W. Since the value of W ₀ shown in Table 1 is set in the setter 16, the output W of the adder 15 is set in the setter 16.
When the set amount W becomes larger than ₀ , a command is sent to the pulse trigger circuit 2 to turn off switching elements such as transistors in the pulse generation power supply 1.
Stop the pulse. Figure 5 shows the current waveform of this example. In the figure, the current waveform is detected and calculated from _t1 , and detected and calculated at time _t2 when the amount of heat input to the wire reaches the set value _W0 . The calculation is reset, and the detection and calculation for the next cycle of pulses is performed again. Next, let's try to calculate the optimal range of Q ₁ , which corresponds to the optimal calorific value range. At that time, it is necessary to set a peak current value I _p , but this peak current value I _p must be at least higher than the minimum necessary current value (critical current value) sufficient to cause spray transfer. However, if it is too large, the arc force on the base material will become strong and the bead will become disordered. Considering this, the value I _p is set as shown in Table 1.
Now, since the base current is small (approximately 10 to 30 A), it is ignored, and the current waveform is also approximated by a rectangular wave as shown in FIG. If the wire is mild steel 1.2mmφ and the shielding gas is a mixed gas with a flow rate ratio of 8/2, K = 4J/
AS, R = 3mΩ/cm, l = 20mm, and when the heat input is set to 8.74Joule, 400×τ×4+(400) ² ×τ×0.003×2 =8.74 ∴τ=3.41ms ∴Q ₁ = 400×3.41=1.37 coulombs. Table 1 also shows the appropriate range of _Q1 determined by the same procedure. Note that the values of the constants used are as shown in Table 3. The l is unified to 20mm for all.

[Table] Q ₁₀ set within the range shown in Table 1,
By comparing with the value of Q ₁ obtained from time to time,
It is also possible to determine the stop time of the pulse. FIG. 7 is a diagram showing a power supply circuit configuration for realizing this other embodiment method. In this example, the integrator 11 only needs to integrate the output of the detector 9;
Appropriate coulomb amount set with Q ₁ and setting device 16
Q ₁₀ is compared in comparator 17, and integrator 1
The pulse current is stopped when the output _Q1 becomes larger. The example shown in FIG. 7 has the advantage that the circuit is simpler than the example shown in FIG. This invention provides a pulsed arc welding method in which a welding current that superimposes a pulsed current on a base current that maintains arc discharge is supplied to a wire electrode, and droplets of the wire electrode are spray-transferred to a base material for welding. is detected moment by moment and integrated to calculate the Coulomb quantity, and the calculated value is set as 1.
When the optimum welding state per pulse is obtained and the amount of coulomb is exceeded, the pulse current is stopped and the heat input to the wire electrode per pulse is set to an appropriate value, or the welding current is changed from time to time. In addition to calculating the amount of coulomb by detecting and integrating the welding current moment by moment, the amount of Joule heat is calculated by squaring and integrating the detected welding current, and the amount of heat input is calculated by adding the amount of coulombs calculated above and the amount of Joule heat. , when the calculated heat input amount becomes larger than the preset value of the heat input amount that provides the optimum welding state per pulse, the pulse current is stopped, and the heat input to the wire electrode per pulse is increased. The welding current is detected moment by moment, and the pulse stop time is controlled to ensure that the amount of heat input to the wire is within the appropriate value, so even simple adjustments can always ensure proper welding. This has the effect that a droplet transfer form is obtained, no spatter occurs, and welding defects such as undercuts can be removed.

[Brief explanation of the drawing]

Fig. 1 is a diagram showing the power supply circuit configuration of a conventional pulse arc welding machine, Fig. 2 is a diagram showing a welding current waveform by a conventional pulse arc welding machine, Fig. 3 is a diagram showing the state of droplet transfer, FIG. 4 is a diagram showing the power supply circuit configuration of a pulse arc welding machine used in one embodiment of the method of the present invention, and FIGS. 5 and 6 show the welding current waveform and rectangular wave approximation of the pulse arc welding machine of FIG. 4, respectively. FIG. 7, which is a diagram showing waveforms, is a power supply circuit configuration diagram of a pulse arc welding machine used in another embodiment method of the present invention. In the figure, 1 is a pulse generation power supply, 2 is a pulse gate circuit, 3 is a base power supply, 9 is a detector, 10
is an integration circuit, 11 is a first integrator, 12 is a second integrator, 13 and 14 are multipliers, 15 is an adder, 1
6 is a setting device, and 17 is a comparator. In addition, in the figure,
The same reference numerals indicate the same or corresponding parts.

Claims (1)

[Claims] 1. Pulsed arc welding in which a welding current made by superimposing a pulse current on a base current that maintains arc discharge is supplied to a wire electrode, and droplets from the wire electrode are sprayed and transferred to the base material for welding. In the method,
Detecting and integrating the welding current from time to time to calculate a coulomb amount, and stopping the pulse current when the calculated value becomes larger than a preset coulomb amount for obtaining an optimal welding state per pulse; A pulse arc welding method characterized in that heat input to the wire electrode per one pulse is set to an appropriate value. 2. In a pulsed arc welding method in which a welding current made by superimposing a pulsed current on a base current that maintains arc discharge is supplied to a wire electrode, droplets from the wire electrode are sprayed and transferred to the base material for welding,
The amount of coulomb is calculated by momentarily detecting and integrating the welding current, and the amount of heat is calculated by squaring and integrating the detected welding current, and the amount of coulomb and the amount of heat calculated above are added. The amount of heat input is calculated, and when the calculated amount of heat input becomes larger than the preset value of the amount of heat input that provides the optimal welding state per pulse, the pulse current is stopped, and the wire is A pulsed arc welding method characterized by setting the heat input to the electrode at an appropriate value.