CLASSIFICATION OF PULSE ARC WELDING PROCESSES

CLASSIFICATION OF PULSE ARC WELDING PROCESSES

Scientific article

Krampit A.G.¹, Krampit N.Y.², Krampit M.A.³, Dmitrieva A.V.⁴

^{1, 2,3,4} Yurga Institute of Technologies (branch) of Tomsk Polytechnic University, Yurga, Russia

Annotation

Pulse welding processes improve productivity; also they allow welding of thin sheets of metal without penetration. Splashing and expenses for cleaning surfaces from droplets are also reduced. Pulse welding processes have a wholesome effect on seam formation at the expenses of thermal exposure on welding puddle and HAZ.

Key words: pulsed arc welding, modulated current welding, beating arc welding, pulse feeding of filling wire. Ключевые слова: импульсная дуговая сварка, сварка модулированным током, импульсная подача проволоки.

Arc welding is still being developed. There are some stages of development such as improving of process stability and quality of products, increasing of productivity.

Mechanized methods of welding in the medium of protective gases, specifically carbon dioxide, were of great importance. But they had some disadvantages such as splashing of metal droplets, that needed further finishing and resulted a higher cost of a product. Also there was a problem of joining thin lists because burn-through probability was high.

In the 1960s methods of controlled transfer of electrode metal were developed. A method of short pulse pile-ups on the principal current sufficient for droplet detachment was developed. The lower limit of welding current decreased 2-3 times, that allowed to join thin materials [1].

Pulse processes can be classified as follows:

• modulated current welding;
• pulsed arc welding;
• beating arc welding;
• pulse feeding of filling wire.

The term “Modulated current welding (MCW)” is the most common term, and MCW is used for some purposes [2]:

- providing of controlled transfer of electrode wire; that increases stability of the process and reduce spraying;

- control of rate and crystallization of welding puddle; thermo-cyclic effect on HAZ;

- successful forming of welding seam in different positions.

Current strength modulating is useful at welding in CO₂; short circuit is applied to limit current strength at the moment when a metal droplet is near to drop. This method allows reducing splatter of metal to 40 – 50 per cent.

The two most applicable methods of welding are consumable electrode welding [3,4] and  pulsed arc welding [5].

Consumable electrode welding provides controlled transferring of electrode metal; pulse arc welding affects properties of joints at the expense of thermal effect on the welding puddle and heat affected zone. Current pulse at consumable electrode welding is f>25 Hz, at pulse arc welding it is f<25 Hz.

The main aspect of controlled transfer of welding metal is droplet detachment by every pulse and possibility to control the frequency of their transfer. It is considered that pulse duration should be as long as to detach a droplet.  If a droplet detaches at the current strength near to that of amplitude, metal transfer is attended by a higher splashing. Droplet detachment at the end of pulse act provides controlled metal transfer at all attitude positions with minimum loss of metal splashing. As compared with nonconsumable electrode welding, pulse arc welding increased productivity 3-8 times and reduced deformation with the same quality of welded joints. Pulse arc welding can be used for vital constructions made from different steels, nickel alloys and titanium of1 mmthickness; also it can be used for welding in all attitude positions.

Pulse arc welding provides high quality of joints. It allows controlling of electrode metal transfer and improves the stability of the process itself as well as the stability of arc burning and forming of joints in different attitude positions.

The most common protective gases are Ar and its mixture with carbon dioxide (CO₂) especially for welding of steels.

A number of investigations on process control of pulse arc welding were performed at Yurga Institute of technologies of Tomsk Polytechnic University. It was determined that the welding condition is to be stabilized for stable arc burning, joint forming and metallurgy reactions [6].

Synergetic control systems for pulse arc welding modes have been developed recently. At this method of control of consumable electrode welding, generated current pulses are correlated with rate of feeding of electrode wire. Amplitude, width and frequency of current pulses are programmed so that every pulse is attended by a droplet detachment at steady rate of electrode melting and constant arc length. In synergetic system only one or two parameters are varied [1].

Pulse arc welding has a disadvantage such as a higher cost of welding devices and need for care cleaning of welded edges.

At pulse welding wire feeding, and electrode is given a pulse to the puddle, under the pulse a droplet of melted metal on the butt end gets an accessory kinetic energy, that, at instant stop of electrode, enable to cause forced droplet detachment or transfer it to the puddle. Short-time feeding pulses are overlaid on steady component of wire feeding rate; discreet pulses of feeding and reverse feeding of electrode wire are used.

Steady process of welding with pulse wire feeding can be employed in protective gases CO₂, Ar and gas mixtures. At 100-400 A current and 1,2 and1,6 mm wire pulse feeding, waste of metal and losses from splashing decrease almost twice.

Seams are 20-30% wider and have more smooth transition with base metal. Welding with consumable electrode facilitates performing seams in different attitude positions and increases quality of metal sheets welding. The joints possess improved mechanical properties.

Pulse methods allow controlling of electrode metal transfer. The stability of welding process and arc burning are improved; welding joint formation in different attitude positions provides quality of joints.

Conclusion

Pulse welding processes improve productivity; also they allow welding of thin sheets of metal without penetration. Splashing and expenses for cleaning surfaces from droplets are also reduced. Pulse welding processes have a wholesome effect on seam formation at the expenses of thermal exposure on welding puddle and HAZ.

Literature

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