Hi Anil,
DC power sources for SAW are either of CV or CC type.
A constant-voltage power supply is self-regulating, so it can be used with a constant-speed wire feeder (relatively cheaper option). No voltage or current sensing is required. The current is controlled by the wire diameter, the electrical sickout, and the wire-feed speed, while the voltage is controlled by the power supply. Constant-voltage dc power is the best choice for the high-speed welding of thin steel. As you know GMAW/FCAW welding machines and majority of SAW machines are also of this type. The limitations of these machines are , they're sometimes unreliable is the current exceeds 1000A.
Unlike constant voltage, constant-current power supplies are not self-regulating, so they must be used with voltage sensing variable-wire-feed speed controls(more expensive). A constant-current wire feeder monitors arc voltage and adjusts the wire-feed speed in response to changes in the arc voltage. The wire-feed speed control attempts to maintain a constant arc length, while the power supply controls the arc current
The variations of SAW are as follows:-
Tandem SAW:-This process involves feeding two wires through 2 independent heads connected to 2 independent power sources.CC power source is preferred-choice since to get higher deposition one has to use of bigger diameter wire, typically 3.2 mm(1/8") dia upwards. for which CC type source is reliable. Tandem SAW ensures greater penetration and deposition. CC type power source ensures constant current, which is essential for melting of electrode. CV power source are good for smaller diameter wire(2.4 mm or below). Most of the high duty DC sub arc welding machines, e.g Lincoln Ideal arc or ESAB have both CV& CC features inbuilt in one system.
Note:-For tandem arc DC-DC combination is not advisable due to arc blow, so DC(lead)+ AC(trail) is the best choice or it could be AC+AC also.
Twin wire SAW:- involves feeding of two wires (typically 2.4 or 3.2 mm diameter max ) simultaneously through a common contact tip or head connected to single power source and feeds the same weld puddle. This process is not exactly recommended for thick wall welding. It could be accomplished with either with CV or CC type power source. CV power source is good for the above filler sizes.As the intention of this process is increased deposition, with amperage very seldom exceeding 1000-1100 Amps, a single power source of CV type of above capacity can meet the requirements.
The technology always changes. Hence the above limitations may not exists in the current generation of inverter type power sources. I would think it would be the best to get the recommendations of the welding equipment manufacturers to know the pros and cons of a specific SAW equipments.
Attached are two articles which explains the scenario
Thanks
Pradip Goswami,P.Eng.IWE
Welding & Metallurgical Specialist & Consultant
Ontario, Canada.
Email-pgoswami@sympatico.ca,
pgoswami@quickclic.net
-----Original Message-----
From: materials-welding@googlegroups.com [mailto:materials-welding@googlegroups.com] On Behalf Of Anil Kumar
Sent: Friday, February 24, 2012 3:18 PM
To: Materials & Welding
Subject: [MW:13778] Why constant Current (power source) used for Multi wire SAW
Respected All,
Generally continuous electrode wire welding is recommended to use with constant voltage (CV) power source characteristic i.e. GMAW ,FCAW and single wire SAW.
For multi wire SAW instead of CV mode why constant current (CC) power source characteristic is recommended ???
what will be the effect on welding if we use CV mode for multi wire SAW.
Regards.
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