JPS5852744B2 - Crater treatment method in plasma keyhole welding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a crater treatment method in plasma keyhole welding, and provides a treatment sequence for reliably eliminating the keyhole in the crater portion at the welding end point.

In the plasma arc welding method, a plasma gas such as argon is injected from the nozzle of a welding torch toward the base metal (material to be welded), and at the same time, the plasma is injected between the negative electrode in the welding torch and the base metal, which is the anode. A plasma arc is generated through gas to create a plasma jet, and the base metal is melted by this plasma jet to perform the desired welding.

In this plasma arc welding method, the diameter of the plasma jet can be narrowed down by the magnetic Hiwochi effect of the plasma jet itself and the thermal pinch effect caused by the spraying of shielding gas, so it is possible to obtain high-density energy and Accurate and efficient welding can be achieved.

In the plasma arc welding method, during welding work,
A welding technique called plasma keyhole welding is used.

In other words, plasma keyhole welding involves welding using a high-temperature, high-speed plasma jet to drill a small hole called a keyhole that penetrates the front and back sides of the base material, and molten metal is deposited behind the keyhole as the welding progresses. The weld bead is formed by the welding going around the base metal, and as complete melt penetration is performed on both the front and back of the base metal, extremely good welding can be achieved.

In keyhole welding using such a plasma arc welding method, it is necessary to eliminate the keyhole in the crater area at the welding end point, and the crater is usually eliminated by weakening or stopping the plasma gas flow rate at the welding end point. The molten metal is controlled so that it fills the keyhole without being blown away by the plasma jet.

As a method of controlling the flow rate of this plasma gas, a piping configuration shown in FIG. 3 or 5 is adopted.

That is, the piping configuration shown in FIG. 3 supplies source pressure P from a gas cylinder or the like.

Plasma gas such as argon, which is sent by the Both electromagnetic on-off valves 1 and 2 are opened to send gas at a flow rate of d1+d2, and at the welding end point, electromagnetic on-off valve 2 is closed to send gas at a gas flow rate of d1.

According to the piping shown in FIG. 3, even if the electromagnetic on-off valve 2 is closed to weaken the flow rate of plasma gas at the welding end point, the flow rate will be reduced due to the plasma gas existing between the electromagnetic on-off valve 2 and the throttle valve 4. A delay as shown in FIG. 4 occurs in the characteristics, leading to unfavorable results in terms of control.

The piping configuration shown in FIG. 5 is obtained by reversing the arrangement of the electromagnetic on-off valve 1.degree. 2 and the throttle valves 3 and 4 shown in FIG. 3, and is a piping method generally employed at present.

Although the delay characteristic of the piping shown in FIG. 3 can be improved, the distortion in the piping shown in FIG.
Source pressure P between.

When the electromagnetic on-off valve 2 is opened again, the original pressure P is filled.

plasma gas is ejected all at once, causing an overshoot in the gas flow rate d3 as shown in FIG. 6, which has the disadvantage that the molten metal in the crater portion is blown away.

In automatic welding lines, it is necessary to start and stop the plasma arc many times in a short period of time, so a fifth
By adopting the piping configuration shown in the figure, the plasma gas is returned to its original high flow rate level immediately after filling the keyhole in the crater at the welding end point, but due to the overshoot mentioned above, the molten gas that filled the crater This has the drawback that the metal may be blown off before it solidifies, causing defects such as keyholes and recesses in the crater portion.

The present invention uses a treatment method having the configuration described in the claims, so that defects such as keyholes will not occur again in the crater portion when welding is completed.

The method of the present invention will be explained below with reference to FIGS. 1 and 2.

FIG. 1 shows the principle of an automatic plasma arc welding machine for carrying out the method of the present invention, and FIG. 2 shows the processing sequence of the method of the present invention.

First, to explain the outline of plasma arc automatic welding with reference to FIG. 1, we will introduce a welding torch 6 with a restraining nozzle 5 formed at its tip, and an electromagnetic shut-off valve 1 with the same piping configuration as shown in FIG.
, 2 and throttle valves 3 and 4 are connected to supply plasma gas such as argon.

Before starting the plasma jet, that is, before starting welding, the electromagnetic on-off valves 1 and 2 are opened, and plasma gas at a gas flow rate of d1+d2 is supplied to the negative electrode 7 in the welding torch 6 and the restraint nozzle 5. A pilot arc is constantly ignited by a pilot power source 8 between the two and ionizes the plasma gas to facilitate starting of the plasma jet.

To start welding, plasma gas is supplied at a gas flow rate of d1+d2, and at the same time, the welding power source 9 is energized to generate a plasma arc between the negative electrode 7 in the welding torch 6 and the base metal 10. Keyhole welding of the base material 10 is performed using a high temperature and high speed plasma jet 11.

Each component is sequentially controlled by a welding control circuit 12, and the welding torch 6 or base material 10 is controlled to be fed by a transfer mechanism.

In the plasma arc automatic welding machine having the above configuration, the crater treatment method of the present invention will be explained with reference to FIG.

The plasma jet 11 collides with the base metal 10 to create a keyhole in the front of the molten pool while keyhole welding progresses,
When the welding end point is reached after a predetermined operation, either the welding torch 6 or the base metal 10 is stopped, and if the welding torch 6 is moving, the welding torch 6 has a moving speed of 0 as shown in FIG. 2a. becomes.

When the welding torch 6 comes to a stop, backfilling of the crater portion is started.

First, the welding current (arc current) of the welding power source 9 is gradually decreased by slope-down control as shown in Fig. 2, and at the same time, the electromagnetic on-off valve 2 is closed, and the plasma gas is controlled as shown in Fig. 2C. The flow rate of the plasma jet 11 is reduced by reducing the gas flow rate from d1+d2 to dl to control so that the molten metal in the crater part is not blown away due to the injection pressure of the plasma jet 11.

By controlling the slope down of the welding current and controlling the plasma gas flow rate, the keyhole in the crater portion is covered and buried by the surrounding molten metal, and the crater portion is flattened back.

Next, after the slope down time T1 of the welding current ends and the arc is interrupted, the electromagnetic on-off valve 2 is opened with a delay of time T2 for the molten metal in the crater to completely solidify, and the second
As shown in Figure C, the plasma gas flow rate is returned to the original flow rate during welding.

The slope down time T1 and the solidification time T2 of the molten metal are set in advance in the welding control circuit 12 as a control sequence.

According to the above-mentioned method of the present invention, after the welding current slope down time T1 has elapsed, the return of the plasma gas flow rate is delayed until the molten metal in the crater part is completely solidified.
The molten metal in the crater portion is not blown away due to the overshoot at the time of return shown in Figure C, and there is no risk of a keyhole or recess forming again in the crater portion that has been backfilled at the welding end point.

Furthermore, by performing the sequence control of the method of the present invention, there is no need to eliminate overshoot when the plasma gas flow rate returns, so the inside of the nozzle of the welding torch can be cleaned by the injection pressure of the overshoot, and the overshoot Because of the injection pressure, the plasma gas flow rate is easily pushed out to the outside of the nozzle, which has the effect of ensuring the activation of the plasma arc.

[Brief explanation of drawings]

Fig. 1 is a diagram showing the principle of a plasma arc automatic welding machine for explaining the method of the present invention, Fig. 2 is a diagram showing the processing sequence of the method of the present invention, and Fig. 3 is a diagram showing an example of the first piping configuration for plasma gas. Figure 4 is a flow rate characteristic diagram of the piping configuration example shown in Figure 3, Figure 5 is a diagram showing the second piping configuration example of plasma gas, and Figure 6 is a flow rate characteristic diagram of the piping configuration example shown in Figure 5. It is a diagram. 1.2... Solenoid on-off valve, 3, 4... Throttle valve, 6... Welding torch, 9... Welding power source, 10... ...Base material, 11...Plasma jet, T1...Slope down time, T
2... Time for the molten metal in the crater to solidify.

Claims (1)

[Claims] 1 In keyhole welding using a plasma arc automatic welding machine configured to adjust the flow rate of plasma gas such as argon through a throttle valve and then supply it to the welding torch through an electromagnetic shut-off valve, the welding torch stops moving at the welding end point. When the welding current is shifted to slope-down control, the flow rate of plasma gas is reduced through the electromagnetic on-off valve at the same time, and after the slope-down time T1 has elapsed and the arc between the welding torch and the base metal is interrupted, a crater is generated. A crater treatment method in plasma keyhole welding, characterized in that the electromagnetic on-off valve is opened after a time T2 for solidification of the molten metal in the area, and the flow rate of plasma gas is returned to the flow rate during welding.