JPS5928432B2 - Constant current DC MIG welding method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a MIG welding method using a consumable electrode.
Constant current MI that maintains a good arc condition
This relates to the G welding method.

In the MIG welding method using a consumable electrode, when a constant current characteristic type welding power source is used, the welding current remains unchanged even if the welding voltage fluctuates due to the constant movement of the cathode spot on the base metal in a steady state. Therefore, the melting rate of the electrode remains constant. Therefore, if the electrode is fed at a constant speed, the apparent arc length (hereinafter simply referred to as "arc length"), which corresponds to the distance between the electrode tip and the base material surface, will be maintained at a constant length. . Therefore, it is a well-known fact that good welding results can be obtained because the weld penetration is uniform and the amount of weld metal is constant. However, when a constant current type power source is used, it is difficult to start an arc, and there are also the following drawbacks, so the above advantages are not widely used.

In other words, even if the arc length fluctuates for some reason during welding, such as when there is a step in the welding area and the arc length increases from 11 to 12, the current remains constant. Therefore, the melting rate of the electrode remains unchanged, and the protruding length of the electrode that is fed at a constant speed remains the same, so the lengthened arc length does not easily return to its original length.

This will be explained with reference to FIG. If Li and L2 are the load characteristic lines when the arc length is 11 and 12, and 2 is the external characteristic line of the constant current type power supply, even if the arc length increases from 11 to 12, Li and L2 are the constant current characteristic lines. 2, so it can be seen that the current is constant (11). That is,
Unlike the constant-voltage power supply described later, the power supply does not self-control the arc length (when the arc length fluctuates, it returns to its original length to maintain a constant arc length), so the arc Welding continues with the length remaining excessively long. As a result, penetration is insufficient, and shielding and
The disadvantage is that good welding results cannot be obtained because the shielding effect of the gas deteriorates. On the other hand, in a constant voltage type power supply, its external characteristic line is indicated by 1 in FIG. 2, so for example, as mentioned above, the arc length is l!
1 to J2, the intersection of the load characteristic line L2 and the external characteristic line 1 becomes the operating point, and a current 12 smaller than the current 11 when the arc length is 21 flows.

As a result, the melting rate of the electrode decreases, the electrode being fed at a constant rate protrudes, and the arc length recovers to its original length. That is, it is superior to a constant current type power source in that a constant arc length is maintained due to the self-control action of the arc length by the power source. Therefore, the reality is that constant voltage power supplies are generally used. However, since the welding current fluctuates greatly almost all the time, the amount of molten metal and penetration are unstable, and a good welding result cannot be obtained. This is an unavoidable drawback. In order to eliminate the above-mentioned drawbacks, one of the applicants previously proposed that ``the external characteristics of the welding power source are controlled to be constant voltage characteristics at the time of starting the arc, and at the point when the arc is established in a predetermined state. We proposed a "DC arc welding method that can be switched to a predetermined constant current characteristic."

That is, in the previous proposal, as shown in Figure 1, the external characteristics of the welding power source become constant voltage characteristic 1 when the arc starts, and switch to constant current characteristic 2 when the arc is established. It's becoming like that. This makes it possible to take advantage of the advantages of a power supply having constant voltage characteristics and constant current characteristics. However, in this method, the no-load voltage of constant current characteristic 2 is high enough to maintain the maximum arc length at any set current value within the rated current value of the power supply. ing.

Therefore, even if the arc causes parts back-up due to some reason (such as a decrease in wire feed speed) and the wire is fused to the contact tube, a constant arc current is maintained. means to be

This means that the arc current will not change at all even if the arc length changes, but the arc length will be maintained longer than necessary, so if the above trouble occurs, the wire tip will eventually reach the contact tube. It has the disadvantage that parts may back up and cause fusion. In general, in this type of welding machine, the longer the arc length, the worse the shielding ability of shielding gas such as argon, and the more likely pores will be formed in the welded part.

In addition, there are adverse effects such as poor arc concentration and reduced penetration. In addition, in order to eliminate the inconvenience of changing the power supply characteristics or using a separate power supply every time the object to be welded or the welding method changes, we have developed a constant voltage region and a constant current region that drops at a certain value. There has been provided an apparatus which automatically switches the arc operating point to one of the above ranges depending on the object to be welded or the welding method.

However, since this device has an arc operating point in one of each region, as mentioned above, in the constant voltage region, insufficient penetration is likely to occur due to current fluctuations, and even if the constant current region is simply set, There is a disadvantage that self-control of the arc length cannot be achieved.

The present invention cleverly eliminates the disadvantages of power supplies that use constant voltage characteristics, constant current characteristics, or a combination of both characteristics, and provides a welding method that provides a stable welding current and a stable arc length. This is what we provide.

This will be explained using FIG.

In Figure 3, 1 is the constant voltage characteristic when starting the arc, and 2 is the constant voltage characteristic (A) that changes after the arc is established.
B) and the constant current characteristic (B) that drops at a predetermined current value
C). If the intersection of 1 and 2 is D, and BD=α, then d is the voltage difference in the constant voltage section of characteristic 1 and characteristic 2, which will be explained later.

However, by selecting the value of α within a certain range, wonderful effects can be produced.

In other words, as shown in Figure 4a, even if the arc length varies slightly to the extent that it does not adversely affect the welding results, the operating point (the intersection of the power supply characteristics and the load characteristics) is always on the constant current characteristic line and the current value remains constant. remains unchanged. When the arc length becomes excessive to the extent that it adversely affects the welding result, L3 (load characteristic curve at excessive arc length 13) comes to intersect constant voltage characteristic line 2, and the operating point moves to the left. , the current value decreases to I2, the self-control action of the arc length works, the arc length rapidly shortens, the load characteristic curve moves to L2, and returns to the constant current region.

The arc length is always maintained within a range that does not adversely affect the welding result, and the welding current is maintained at a constant current value. Furthermore, the voltage value used when starting the arc shall be selected so that a constant arc length can be obtained at a predetermined arc current value.

Therefore, according to this method, welding can be performed using only the excellent characteristics of constant voltage characteristics, which are excellent in arc starting characteristics, and constant current characteristics, which provide good results during welding work.

In addition, the constant voltage value of the constant voltage constant current characteristic that switches after arc starting is set to a slightly higher value than the starting voltage, so even if the arc length becomes excessive, the arc length can be self-controlled. Within the range where the effect can be obtained, the V1 welding result will not be affected. Next, the value of the difference α between the voltage value at arc startup and the voltage value after arc establishment will be explained.

Fig. 4b is a characteristic diagram when the value of d is set to zero.As explained earlier, the welding current 11 changes to I2 only when the arc length L1 changes to the arc length L2, so the penetration is reduced. There will be a change in the

Figure 4c shows the case where the value of α is sufficiently large, but even in this case, the welding current remains unchanged even if the arc length changes significantly to L3, and self-control of the arc length cannot be obtained. It turns out. The inventors repeated experiments with this value α, and found that a minimum of 1 volt is necessary, and a value sufficient to obtain arc length self-control is 5 volts, and that outside this range, the welding current will fluctuate. (b), the arc length self-control function could not be sufficiently obtained.

As described above, according to the present invention, it is possible to provide a welding method that skillfully utilizes only the advantages of a power source having constant voltage characteristics or constant current characteristics.

The advantages of the method of the present invention are listed as follows.

(1) Since arc starting is performed using constant voltage characteristics, arc starting is reliable and easy.

Furthermore, the arc length is established in a short time because the current value is adjusted to the desired arc length voltage. (2
) A constant current can be maintained at all times even if slight load voltage fluctuations occur due to changes in the arc length or changes in the position of the cathode spot on the base metal side. (3) If a load voltage fluctuation occurs to the extent that it adversely affects the welding result, a self-control action is immediately activated to restore the load state to an unaffected range.

In this way, constant current welding can be performed effectively.

[Brief explanation of the drawing]

Figures 1 and 2 show the current-voltage characteristics of a conventional welding power source, Figure 3 shows the current and voltage characteristics of a power source with constant voltage and constant current characteristics according to the present invention, and Figure 4 A, b, and c. is a characteristic diagram when the voltage difference of the constant voltage section in FIG. 3 is changed, and FIG. 5 is a diagram showing the state of variation in arc length during welding.

Claims (1)

[Claims] 1 In the constant current type DC MIG welding method, the arc is started with constant voltage characteristics such that a constant arc length can be obtained at a predetermined arc current value, and after the constant arc length is established, the voltage at that time is 1 to 5 volts lower. Switching to characteristics that have both high constant voltage characteristics and constant current characteristics that droop at a predetermined current value,
When welding near a predetermined arc length, constant current characteristics are used, and when the arc length exceeds the preset arc length according to the voltage difference of 1 to 5 volts, a constant arc length is applied by self-control of the arc length using constant voltage characteristics. A constant current type MIG characterized in that the welding is continued based on constant current characteristics by returning to
Welding method.