JPS63152B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for detecting defects in high-speed carbon dioxide arc welding.

Normally, in carbon dioxide arc welding, in welding that uses a relatively large current, the molten metal melted at the tip of the electrode becomes large droplets, and the droplets irregularly separate from the tip of the electrode due to electromagnetic repulsion. On the other hand, in welding using a relatively small current, a contact transfer mode occurs in which droplets transfer when they come into contact with the molten pool surface (hereinafter referred to as short-circuit transfer). ) is known to be. In the latter type of short-circuit transfer welding, arc generation and short circuiting occur repeatedly, and each time a short circuit occurs, the droplets transfer to the molten pool, so when arc generation conditions are good, arc generation and short circuits repeat regularly. Good welding results can be obtained. The number of times this arc generation and short circuit occur within a certain period of time (hereinafter the number of times repeated per second is the "number of short circuits")
It is expressed in Hz. ) is approximately 30 to 120 Hz when the arc is in good condition, although it varies depending on the welding conditions such as the diameter of the welding electrode, its material, welding current, welding voltage, and wire protrusion length. If the welding conditions are constant, the number of short circuits will be 30 to 30 when the arc generation condition is good.
Although the number of short circuits is approximately constant within the range of 120 Hz, when the arc generation condition becomes poor and the welding result becomes poor, the number of short circuits changes. Therefore, in short-circuit transition welding,
The number of short circuits is outside the setting range, for example 10 to 30.
It is common practice to judge that welding is defective when the value drops to Hz. However, in the former type of droplet transfer welding, the droplets do not necessarily transfer due to a short circuit as in short-circuit transfer welding, so regular short circuits as in short-circuit transfer welding are not performed. Therefore, in droplet transfer welding, welding defects have not been determined based on an increase or decrease in the number of short circuits, unlike short circuit transfer welding.

In droplet transfer welding, as shown in Fig. 1 or 2, in the large current range, the molten pool 2a generated by generating the arc 3 between the electrode 1 and the workpiece 2 becomes large. , and since the depression 2b also becomes larger, welding (hereinafter referred to as "buried arc") is carried out by burying the electrode tip into the molten pool so that the molten part 1a of the electrode tip transfers within the large depression of the molten pool. It is being said. Even if the welding current is a buried arc with a large current, when the welding speed is low, for example 50 cm/min, the molten pool will have a large depression as shown in Figure 1, and the molten part 1a at the tip of the electrode will become a large lump. They grow and separate due to electromagnetic repulsion, resulting in irregular short circuits as described above. However, even in buried arc welding with a large current, when the welding speed is high, for example, 1 m/min or more, when the arc voltage is lowered, the depression in the molten pool 2a becomes narrower, as shown in Fig. 2. The tip of the electrode melts along the front 2c of the molten pool and becomes sharp.
Along with this, the molten portion 1a at the tip of the electrode flows down, so there is an advantage that there is less spatter. Moreover,
In this high welding speed buried arc welding, the molten metal of the workpiece directly under the arc is swept backwards by the strong arc force, exposing the solid exposed surface, making it possible to obtain deep penetration. Another drawback is that there is no molten metal in the welding process, and the arc directly hits the unmolten parts of the welded object, making it easy for the welded object to melt through. Even if such burn-through occurs, carbon dioxide arc welding uses a power source with constant voltage characteristics, so the welding voltage hardly changes, so this burn-through cannot be detected by changes in the welding voltage. .

On the other hand, in short-circuit transition welding, even if burn-through occurs, the surface condition of the molten pool of the workpiece changes, resulting in a repeating state of regular arc generation and short circuit before burn-through. This causes a clear change in the number of short circuits. Furthermore, because thin plates are used in short-circuit transition welding, when the molten metal that generated the arc flows out due to burn-through, the position of the arc changes, and sometimes the arc length becomes longer. Become,
Therefore, the welding current is reduced and the number of short circuits is also reduced. In this way, in short-circuit transition welding, burn-through is less likely to occur than in buried arc welding, and even if burn-through occurs, the arc becomes unstable, resulting in noticeable changes in the welding current, number of short circuits, etc. Since the drop could be detected easily and quickly, it was easy to automatically stop welding.

However, in high-speed buried arc welding, as shown in Figure 2, an arc 3 is generated between the electrode tip and the front 2c of the molten pool, that is, the unmelted part of the workpiece. molten pool 2
Even if the molten metal melts down and flows out from the object to be welded within a, the stability of the arc is hardly affected.
Therefore, even if burn-through occurs, the welding voltage and welding current are hardly affected. Therefore, even if burn-through occurs during buried arc welding, it is not possible to make a reliable judgment just by detecting changes in arc voltage and welding current, and detection is delayed because it is detected by visual inspection. This resulted in a large amount of burn-through, and excessive effort was required to repair it.

Therefore, the present inventor discovered that in high-speed carbon dioxide arc welding, the molten metal of the object to be welded easily melts down, and even if the molten metal melts down and flows out, the position of the arc does not change, and the arc is almost stable. The present invention proposes a high-speed carbon dioxide arc welding method that can detect burn-through early and reliably and stop welding even in buried arc welding where the welding voltage and welding current are approximately constant.

In high-speed buried arc welding, the current is larger than in short-circuit transition welding, and the arc continues to be generated, so short circuits do not occur as often as in short-circuit transition welding, and short circuits as shown in Figure 1 do not occur. There are no irregular short circuits that occur with low-speed buried arc welding. However, even under normal conditions in which burn-through does not occur during high-speed buried arc welding, short circuits occur due to a phenomenon completely different from the short circuit transfer phenomenon.
That is, short circuits occur relatively regularly between the droplet at the tip of the electrode and the molten metal of the object to be welded that has been swept backward, and the number of short circuits is 10 to 50 Hz. On the other hand, when a stable arc condition that meets various welding conditions in short-circuit transition welding continues, the number of short circuits is 30Hz to 120Hz, but when the arc condition becomes unstable, the number of short circuits decreases to 10Hz to 30Hz. do. Therefore, in buried arc welding,
Even in a normal arc generation state, the number of short circuits includes the range of the number of short circuits in an unstable arc state of short-circuit transition welding. However, if we consider the arc condition when burn-through occurs in buried arc welding, the arc continues stably as mentioned above, but the molten metal of the workpiece is swept away behind the molten pool. Since the molten metal flows out by melting through, the chance of short circuit between the droplet at the tip of the electrode and the molten metal swept backward is reduced, and the number of short circuits is reduced, and the number of short circuits is 0 to 5 Hz. In this way, in buried arc welding, short circuits occur based on a phenomenon completely different from that in short-circuit transition welding, so even if the number of short circuits is within the range where the arc becomes unstable in short-circuit transition welding By further analysis, it is possible to clearly distinguish between a range where burn-through has not occurred and a range where burn-through has occurred. In other words, in buried arc welding, the number of short circuits when no burn through occurs is 10 to 50.
Hz, and the number of short circuits when burn-through occurs is 0.
The frequency ranges from 5Hz to 5Hz.

Next, an example of the high-speed carbon dioxide gas arc welding method of the present invention will be shown.

Shielding gas CO ₂ 25/min Electrode Mild steel Diameter 1.6mm Material to be welded Mild steel Plate thickness 2.3mm Lateral position Lap fillet welding Example 1 Example 2 Welding current 390A 360A Welding voltage 32V 28V Welding speed 2m /sec 1.5m/sec Number of short circuits before burn-through occurs 20Hz 15Hz Number of short circuits after burn-through occurs 2Hz 0Hz As described above, according to the high-speed carbon dioxide arc welding method of the present invention, the short circuit phenomenon of buried arc welding and Due to the difference from the short circuit phenomenon in short-circuit transition welding, the arc is unstable in short-circuit transition welding when the number of short circuits is 10 to 30 Hz.
This range is the normal range in which burn-through of the welded object does not occur in buried arc welding, and
In addition, when the number of short circuits becomes 0 to 5 Hz, it is assumed that the welded object is in the range where burn-through occurs, and when burn-through occurs in the welded object, welding can be reliably and quickly stopped. The effect is great because it does not require excessive effort to repair.

[Brief explanation of the drawing]

FIG. 1 is a diagram illustrating the droplet transfer form in low-speed carbon dioxide arc welding, and FIG. 2 is a diagram explaining the droplet transfer form in a buried arc in high-speed carbon dioxide arc welding.

Claims (1)

[Claims] 1. In the carbon dioxide arc welding method, when the welding speed is high, exceeding 1 m/min, and welding is performed in a buried arc state, it is detected that the number of short circuits has become 5 cycles or less, and welding is stopped. Carbon dioxide arc welding method.