GMAW short circuit and spray transfer slope

Date 02-21-2013 20:28

Slope is the relationship between arc voltage and welding current.

A power supply that has a drooping slope simply means that a small increase in arc voltage produces a small drop in welding current. Conversely, a small drop in arc voltage produces a small increase in welding current. Power supplies used for manual welding processes typically utilize power supplies known as droopers.

A power supply with a flat slope produces a large drop in welding current with a small increase in arc voltage. It produces a large increase in welding current with a small decrease in arc voltage. Si-automatic welding processes typically use a power supply with a flat slope. In reality the slope is not truly flat, but in fact the graph, if you plot the arc voltage versus welding current, slopes gently down toward the right.

Best regards – Al

By jarsanb (***)

Date 02-21-2013 22:10

Equipment with slope adjustments vary depending on model. Get the owner's manual for your model. Here is an example:

http://www.millerwelds.com/pdf/spec_sheets/DC31-0.pdf
http://www.millerwelds.com/om/o456q_mil.pdf

By ssbn727 (*****)

Date 02-22-2013 03:11

Al, Deisel, Kara,

Al,that's an excellent definition of the term slope as it relates to both Constant Current & Constant Voltage welding power sources/supplies...
"Drooping Slope" "Flat/Linear Slope"

All I have to add is this link to ESAB's online school of welding and this is pertaining to GMAW which shows a flat/linear slope... Here's the link:

http://www.esabna.com/EUWeb/MIG_handbook/592mig3_3.htm

I'll make an exception for you Kara!

Respectfully,
Henry

By Shane Feder (****)

Date 02-25-2013 14:26 Edited 02-25-2013 14:29

deisel,
Just to add a bit to what the guys have stated.
A lot of the new fangled GTAW machines have a slope up / slope down capability.
You can pre-program the amps at ignition of the arc and also pre-program the duration of time before the required amps are available.
Example: When you strike the arc you have 50 amps and then you press the button on your TIG torch - in 5 seconds it will gradually increase to 100 amps.
Then you have slope down which works the opposite way - welding at 100 amps and when you press the button on your torch in 5 seconds your amps will reduce to 50 amps.

First time I experienced this was welding boiler tubes - one welder on either side of the tube bank.
As the access between the tubes was very limited and you had to try and get past halfway on the tube (to overlap the welder on the other side) the ability to strike an arc with low amps and then while you were getting yourself and your wire organised the amps would slowly increase made it so much easier.
Conversely, when you wanted to tail off you can just reduce the amps with a push of the button,
Hope that helps,
Regards,
Shane

Edit: Re-reading Als post I think we may be talking about different things - not sure what context your "slope" was meant in.

By 803056

Date 02-25-2013 15:25

Right you are Shane, two different things.

What you are talking about, up-slope and down-slope is a feature that some machines have to enhance the welding experience (market talk). However, to complicate issues even more, some programmable machines can change the slope of the pulse when using pulse mode. To make matters worse, some GMAW pulse programs actually utilize variable slope, i.e., constant current versus constant voltage, while pulsing.

The traditional constant voltage power supply maintains constant voltage as the welder varies the wire feed speed and/or contact tip to work distance. However, some pulse programs utilize constant current depending on the particulars of the manufacturer's program. In the latter case, the voltage can experience considerable variation as the welder varies the contact to work distance. It can catch the user off guard because the machine does not respond as expected. Add in the complexity of up-slope and down-slope, frequency, pulse width, variable inductance, etc. and one can easily see where programing these machines can be very frustrating to the average welder.

I’ve said it before and I’ll keep saying it, there are many situations where people get sold by sales people on the idea that pulsing is the best thing since sliced bread. I have been involved in too many cases where the customer would have been much further ahead if they had simply stayed with the traditional GMAW power supply. Pulsing is oversold. Only the sales people and the power supply manufacturer come out ahead in that game. To add icing to the cake, the fabricator becomes dependent on the power supply manufacturer to provide a new program when the materials change.

Qualifying WPSs using pulsing power sources is ridiculous. There is no way one can “record” the welding parameters without a multichannel oscilloscope. Once qualified, there is no way that WPS can be used with a different model power supply even if it is from the same manufacturer. Enough of a rant, you’ve heard it before.

Best regards - Al