DE2534278C2 - Tungsten inert gas welding process - Google Patents

Description

The invention relates to a process for welding according to the tungsten inert gas process with the features of the preamble of claim I.

Such a process can run automatically. For the welding of pipes z. B. Devices (US-PS 34 00 237) are used, which are clamped onto the pipe ends. Via an engine With a gear, the tungsten electrode is guided around the tubes, with a step-by-step movement can be switched on via a corresponding control. The electrode is set to the radius of the am Pipe aligned clamping jaws. This means that their distance from the welding point cannot be changed. A jet of an inert gas is directed onto the arc through a gas nozzle. The devices can be equipped with and without feed of additional wire.

The slow reduction of the current after completion of the weld, the so-called current drop, serves to avoid the formation of end craters. In the known method, during the impulsive Withdrawal of the welding head during the passage of the basic current, the so-called Basic current time, moving forward at the same speed as when performing the Weld.

When welding pipes made of unalloyed or low-alloy steels, voids appeared in the End of the weld that started from the inside of the pipe and reached into the middle of the weld.

Such material defects are impermissible because they reduce the strength in the weld seam considerably. That known methods therefore did not allow automatic welding of pipes from unalloyed and low alloy steels too. It was also found that the burnt cavities always appeared when the

Material was just welded through, i.e. in

first or second falling point of the current drop.

Furthermore, DE-OS 22 15 646 is a

Known welding system, with the welding according to the tungsten-inert gas process and with inipulsinodulationscn Sehweißslrom can be carried out.

There is / was after reaching the predetermined ancillary welding current also the rate of return between welding head and workpiece

id stopped. But there / no matter; with decreasing welding current strength the relative speed between the welding head and the workpiece must be the same It can be expected that there will be cavities in the weld seam before the relative movement has ended have formed.

The invention is based on the object of applying the aforementioned method to the welding of Unalloyed or low alloy steels expand by the formation of voids in the end of the Weld seam is avoided.

This is done by the features specified in Palent claim 1 in the characterizing part.

This method avoids the disadvantages of the known method, but requires a certain amount of control effort. In a further development of the invention it is therefore proposed that during the current drop Weld head and workpiece are stopped. The speed of the welding head opposite the workpiece is therefore reduced to zero. In the case of a weld seam produced using this method the weld pool still has enough space to cool down at the last welding point. Wed! be of his help not only avoided the formation of end craters, but there are also no pores in the

v, approaching during the power failure. The method is, moreover, easy to carry out.

The invention was based on the knowledge that during the sirom drop of the impulse strci and the base current or the times corresponding to these currents and the movement between welding head and workpiece were no longer in the prescribed ratio.

As a result, it was considered that the weld pool cooled too quickly and that this resulted in voids, which lead to the formation of pores. A lower pulse current became a lower one Distance to the next welding point assigned so that the weld pool cooled down more slowly. The same The effect is achieved when the welding head is stopped the same point with a falling current pulse

so is melted and cooled again several times.

The invention is based on what is described below and exemplary embodiment shown in the drawing explained. It shows

Fig. 1 is the Stromslärkc-Zcit diagram.

FIG. 2 shows the visual wind speed-time diagram according to the method according to the invention and FIG

3 shows the speed-time diagram according to another embodiment.

For welding boiler tubes. for example

ho of steel quality St 35.8, with a diameter of 44.5 mm and 3.6 mm wall thickness became a manual welding device used without additional wire feed of known type, as it is in the Beschrcibiblcitung was mentioned. First is with a pulsed current

ir> with an amperage of Ip = 72 amperes at standstill Welding head is welded at the first weld of the seam. After that, the current is on the Grunclstrom with a current of Ig = 20 amps / u-

withdrawn. At this amperage, the arc just burns while the weld pool cools down at the same time. During this time T , as shown in FIG. 2 hervorgehl, the welding head at a speed Vum a predetermined path weilerge- ^r> rotates and then welded again with the Impulsstroni. In this step-impulse sequence, identified by the lines 1 and 2, one now welds point-door point, whereby the individual points overlap. IU

After the welding seam has been completed, the welding current is reduced in pulses to avoid end craters. During this, represented by the line 3, Strorsabfall is with constant Base current The pulse current is gradually reducedL So that after the last welding point of the seam If no cavities form, the welding head is stopped (line 4). The welding head speed is the same Zero.

In Fig. 3 the case is also indicated by the line 5. that the welding head also during the Stroniab case is rotated further. The speed of the welding head is in the same ratio of pulse current reduced to base current.

The method according to the invention can be used not only for welding pipes, but also for everyone other fully automatic tungsten inert gas welding be applied.

For this 1 blue drawings

Claims (2)

Patent claims: 1. Process for welding using the tungsten inert gas process, where there is a constant distance between the electrode and the workpiece is adhered to, in which a lower base current is periodically used to carry out the weld recurring current pulses are superimposed between the welding head and the workpiece there is an intermittent relative movement, the respective pause in movement in time coincides with the respective current pulse duration and in which, after completion of the weld seam, the Current is slowly reduced while continuing the welding process, characterized in that that immediately after the occurrence of a current pulse with one opposite the temporal previous current impulse reduced Imniilshöhe the speed of the relative movement is reduced according to the respective ratio of the pulse current level to the base current level. 2. The method according to claim 1, characterized in that that immediately after the occurrence of a current pulse with one opposite the temporal previous current pulse, pulse height reduced the speed of the relative movement Becomes zero.