Improving the way of droplet transition in CO2 gas shielded welding

In The process of CO2 gas shielded welding, welding spatter is the biggest disadvantage, which is related to the transition form of welding wire droplet. Therefore, the best way to solve the droplet transition can improve the welding spatter, so we should improve the performance of welding equipment and choose different welding process to solve the problem.

Improvement of welding equipment

A new welding equipment, IGBT inverter low splash CO2 gas shielded welding machine, is developed based on the control principle of waveform control and short circuit current channel.with this welding machine, the spatter is less, the welding seam is beautiful, the welding quality is good, the main circuit and the control circuit are simple and reliable.

Waveform control of short circuit current In the PROCESS of CO2 gas shielded welding, according to the characteristics of the two stages of arc burning and wire droplet short circuit, the principle of variable structure circuit design is adopted to design the control circuit into arc burning circuit and short circuit current control circuit. According to the state of welding wire in the process of droplet, the judgment control circuit the directives issued by the timely switch: in short circuit phase, CO2 gas shielded welding system is designed to be a follower current, make the output welding current changes over a given value, and at the beginning of the short circuit, using the short circuit current channel circuit that welding arc part, in order to reduce short circuit welding splash in the early .

Short circuit current waveform control can be divided into instantaneous short circuit control normal short circuit control and short circuit overlength control and other three methods.

Instantaneous short-circuit control. When short circuit current waveform control detected wire short-circuit droplet with weld pool, after first instantaneous short circuit control, reduce the short circuit current, controls the speed of instantaneous short circuit current rise the welding wire melting drop at lower current value and the weld molten pool full contact, to slow transition and reduce instantaneous short circuit welding spatter.
Normal short-circuit control. After control of the instantaneous short circuit, the welding circuit of low current value to keep a certain amount of time, and then control in small current through the short circuit liquid bridge slope growth, while ensure adequate electromagnetic compression effect, reduce the peak of short circuit current to minimize late in short circuit, short circuit liquid bridge neck welding spatter produced during the blasting off.
short circuit control, time is too long when short circuit time is too long, is beyond the normal time of short circuit, immediately remove control of the short circuit current rise speed, made the current big at normal speed, accelerate the broken wire melting drops of necking, prompting rapid drop to the weld molten pool wave, avoid short-circuit time is too long, because wire drop excessive growth and affect the stability of welding process.

Selection of welding process

Mixed use of CO2 and O2
The welding process is not stable during CO2 gas shielded welding. For example, O2 with a volume fraction of 15%-20% is added to THE CO2 gas to enhance the oxidation of the protective gas. Through the metallurgical reaction in the welding process, greater heat is generated, so as to reduce the surface tension of liquid metal, improve the wire droplet transition and the fluidity of the weld pool metal. At the same time, because of the addition of O2, the metallurgical reaction in the welding process is more intense, the hydrogen content in the weld is lower, and the crack resistance of the welded joint is improved.

MIXED use of CO2 and Ar
Adding Ar into CO2 gas reduces the thermal conductivity of pure CO2 gas in the welding radian area and consumes a lot of heat in the welding arc, so that the arc column and arc spot contract strongly and produce welding splash. CO2 plus A mixture of gas welding, in addition to reduce the welding, but also can improve the weld shape, reduce the weld height and depth, increase the weld width.

using pulsing in the CO2 gas shielded welding wire feed system, using pulse wire feed system instead of the conventional SuSong silk, such as the welding wire melting drop in pulse into the case, and the weld molten pool of short-circuit, the short circuit transition frequency and the frequency of the wire feed, not only uniform short-circuit current peak, and the value is not high also, reducing welding spatter. If the pulse in the wire feed base on, and with current waveform control (which controls welding spatter), to ensure the stable transfer effect of welding wire droplet will be better.

When using pure CO2 gas cored wire welding process, the welding spatter is larger and the weld forming is worse than that of electrode arc welding. When using pure CO2 gas cored wire welding process, it is the welding process with gas slag combined protection, which overcomes the shortcoming of pure CO2 gas shielded welding.

Its main process characteristics are as follows:
(1) Small welding spatter. By changing the composition of flux cored wire, the surface tension of flux cored wire droplet and pool can be changed, and then the droplet product can be reduced, spray transition can be realized, and welding spatter can be reduced.
(2) fewer holes in weld seams. By increasing FeC2 of flux cored wire and reducing TiO2, the porosity of flux cored wire bead is less than that of solid cored CO2 bead.
(3) High toughness of weld. Use cored wire deoxidizer, reduce the oxygen content in the weld, improve the low temperature toughness of the weld.
(4) High deposition speed. Because the metal skin of flux cored wire is very thin, the welding current density is large, and the heat of the welding wire extending length is large, thus forming the welding characteristics of flux cored wire with high melting speed. Compared with electrode arc welding, flux cored wire continuous welding replaces the welding interrupted by changing the electrode, so that the welding deposition speed is obviously improved.
(5) The weld depth is large. Due to the high current density of flux-cored wire, not only the butt pass penetration depth is deeper, but also the penetration depth of fillet welding root is improved. Compared with CO2 shielded welding with solid cored wire, the workload of rework repair due to poor fusion is reduced.
(6) Vertical upward welding suitable for large welding speed. CO2 shielded flux cored wire for vertical welding, through the high viscosity, high freezing point slag, firmly support the molten metal to form a perfect weld. In the process of vertical welding with high welding speed, the welding current is about two times that of solid cored wire.
(7) Flux cored wire CO2 gas shielded welding can weld stainless steel. Because of the role of TiO2 and silicon sand and other acid oxides in flux cored wire, Cr and C in stainless steel no longer metallurgical reaction, try to use CO2 gas protection in the welding process, but the carbon content in the molten metal does not increase, so as to avoid the intergranular corrosion of stainless steel solid cored wire CO2 gas protection welding process.
(8) Welder operation technology is easy to master. Compared with solid cored wire CO2 gas shielded welding, in the process of flux cored wire CO2 gas shielded welding, due to the joint protection of slag and CO2 gas, not only the welding spatter is less, the weld is well formed, but also the welder’s operation technology is easy to master, and the training time required is correspondingly shortened.