Dear Debashish
Thank you very much for your answer
We are fabricating the structures of hydraulic excavators with MIG welding. we use ROBOT as well as manual welding. From our experience we know that pure Co2 is better for manual welding ( provided we can maintain the 1G and 1F position ) and for Robot Argo mixture is essential.
As rightly pointed by you , the economics of using Argo mix has to be ascertained. I feel that basically we are getting a mixed mode of transfer and not a pure spray transfer . The question is can we ascertain that from the variation of voltage with time as shown What is your experience ?In the shop floor the welders are trained to identify the correct setting by the sound, is there a more scientific method?
From: DEBASISH <debasish.uae@gmail.com>
To: materials-welding@googlegroups.com
Sent: Tuesday, 4 October 2011 3:06 PM
Subject: Re: [MW:12619] Mode of transfer
Dear Arijoy,
Basically the mode of metal transfer in GMAW is dependent on the arc current & arc voltage., and are subdivided into three basic modes of transfer:
i) Short Circuiting Mode: Low voltage Low Amps produces Short ckting mode ( called Dip transfer) and this mode is utilized for most out of position welding (overhead 4G/4For verical 3G/3Fwelding positions. It is also for any thinner gauge welding. Next is
ii) Globular tansfer: where in current & Voltage are such that it forms globules which detaches from the wire tip after forming critical dia., making a free fall due to gravity. Generally most of the 1G/1F flat /horizontal welding goes by this mode. Next is
iii) Spray transfer mode: where in the droplets bursts at the tip of the molten wire tip formed at Highest current and Voltage levels and is thus thrown on to the substrate in a higest speed impinging droplets.tThe doplet dia befor detaching is less than the wire dia.In this the deposition is heavy and is therefore used in flat /horz positions only.Also penetration is substantially on highest side amongs all other modes.
Apart from these basic modes there are other modes too, viz.: pulsed mode transfer with square wave or synergic wave etc. but these are all extentions of the three basic modes as said above. Pulse wave transfer is a Spray mode in each pulsed peaks.
Further, as far as shielding gas composition is concerned, the gas ionization potential plays a important role in this.
For example: SS MIG with pure Argon, the spray transfer mode is attained at a much lower current & voltage , than a Carbon steel MAG welding with CO2 as shielding gas, for a particular deposition rate.
Inferring it to the 80/20 mix gas (Argoshield) : Comparing with a plain CO2 gas used with a CS wire & a 80/20 mix., used with CS wire , the current/voltage setting required for a particular mode will be different. Argoshield gives higher productivity than plain CO2 , because of less spatter,more stabilized arc, because it requires a lesser current density in the same wire speed setting, thereby automaticall the wire speed kept by welder is more inorder to match the same level of current for a given weld procedure; and more importantly Argoshield is heavier than CO2 and so even at site/outdoor work is less porosity prone.
These are the advantages of Argoshield over CO2 shielding in CS/MS welding. Ofcourse one need to lookinto the economic aspect too in selecting this bit costlier Argoshield than plain CO2.
regards,
Debasish.
cell: +971504349936
Dubai.
On Sat, Oct 1, 2011 at 11:00 AM, arijoy roy <bhaitu1@yahoo.com> wrote:
--Dear ExpertsWe are interested to find out the mode of transfer during welding ( GMAW with 80% Argon and 20 % CO2 mix gas.) An oscilloscope was conneted in series to the invertor based welding machine and the waveform obtained is depicted in the photo. Please let me know from the wave form can we comment on the mode of transferWith regardsArijoy Roy.
Thanks & Regards
Posting on behalf of: Amit Pahuja
--
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