Author: electrex

TIG pulsed arc welding is a variation of the TIG process, which switches between two levels: a peak current and a base current. Although this variant existed for several years, nowadays with electronic power control technologies we can achieve pulses per second (pulse frequency) much higher than those of a machine with conventional technology. For this, we need an inverter welding machine with pulsed Tig as such of the Electrex’s TP range (163, 203, 223, 253, 323, 403, 503 DC ou AC/DC).

PULSED TIG ADVANTAGES

This process allows the incensement of the quality of the welds, it reduces the costs of the process, obtaining narrower or wider arcs, it controls the temperature of the welding bath, it allows welding with more or less penetration or even reproduce the dimes effect more easily.
Besides these, allows:

• less heat input to the work piece, preventing the deformation of the work piece.
• an arc more concentrated, allowing more penetration.
• possibility of welding plates of different thicknesses
• More control of the welding bath.

PULSED TIG ADJUSTING PARAMETERS

Take the example of ELECTREX TP 323, for regulating the pulsed parameters and its consequences in the welding process.
After selecting process of TIG welding and pulsed mode, we have 4 specific parameters that can regulate pulsed TIG:
Main Current (Amperes), the base current (Ampere), pulse frequency (Hz) and peak current ratio time / Base current time (%).
The main current or peak current is the current with higher intensity, while the base current is the current at a lower intensity. The welding current value is the average of the two currents levels.
The pulsed rate is represented by the number of cycles per second between 0.5 and 200 cycles per second.
At a higher pulse rate corresponds to a more concentrated arc, producing narrower seams and decreasing the thermally affected zone.
The cadence of the dimes effect will also be proportional to the pulse frequency and a smooth seam with a very high pulse rate can also be obtained.
Finally, the pulse time or length can be adjusted at both current levels and the effects of pulse length identical to pulse rate can be adjusted.
The shorter the main current time, the lower the heat induction, there will be greater penetration and narrower seams will be obtained.

The old TIG machines with conventional technology used the sinusoidal waveform in TIG welding in alternating current (AC). Nowadays, the new inverter TIG AC/DC machines allow the selection of various waveforms in TIG welding in alternating current (AC). This selection, without changing other parameters of welding, allows to change the characteristics of the arc, the seam, and the cleaning / penetration effect.

Square wave:

Welding of light alloys with more penetration into thick plates. It forms a more “strong” arc, then more rough and noisy, where there is more heat transfer. It forms a broader and thicker seam.

Sine wave:

É usada na maioria das aplicações. 
O arco é mais suave e menos ruidoso, do que a onda quadrada. 

Triangular wave:

Welding of thin plates with little transference energy and thus, less penetration. It reduces the distortion of the parts and allows a fast solidification of the welding bath. It is especially recommended for thin-thickness aluminum.

There are many ways to inspect a weld, but one of the simplest, practical to do, is the visual inspection. This is surely a non-destructive testing, which lets you monitor what is happening on the surface with the naked eye or through a magnifying glass. There are other techniques such as radiographic testing or ultrasound testing, which should be part of the quality proceedings. The weld bead, its shape and form, is a major defect indicator in a weld, but not the only: the heat-affected zone, the presence of projections, cracks or distortions in the workpiece, among others are also indicators of welding quality. The most common defects in a weld joint may be due to the following causes:

Falta de penetração 
– corrente ou velocidade de soldadura muito baixas
– abertura excessiva da junta
– chanfro inadequado
– grande espessura da peça de trabalho
– distância excessiva entre o eléctrodo e a peça de trabalho
– posição ou movimento do eléctrodo inadequados
– diâmetro do eléctrodo inadequado

Mordedura: 
– corrente ou velocidade de soldadura demasiado elevadas

Preparação incorrecta da junta: 
– chanfro inadequado
– desalinhamento das peças a soldar

Fissuras: 
– Crateras no final da soldadura
– tipo de eléctrodo inadequado
– eléctrodo húmido
– grande espessura da peça de trabalho
– chanfro incorrecto

Excesso de respingos: 
– corrente de soldadura muito elevada
– grande distância entre eléctrodo e a peça de trabalho
– peça suja- eléctrodo húmido

Inclusão de escória: 
– escória não removida durante passes ou na troca de eléctrodo
– posição ou ângulo de eléctrodos inadequados
– diâmetro do eléctrodo muito elevado ou chanfro muito estreito

Porosidade: 
– Peça suja, enferrujada ou húmida
– corrente de soldadura incorrecta
– velocidade de soldadura elevada
– distância excessiva entre o eléctrodo e a peça de trabalho
– eléctrodo húmido

Distorção de contracção e angular: 
– corrente ou velocidade de soldadura demasiado elevadas