another 'whats wrong with my weld'

dpv2010 · Apr 6, 2011

just started MIG today and tried to weld some sheet metal at 1mm and 2mm thick. the 1mm think welded ok, pooling well and penetrating ok (seen in the round weld power setting 3)

my other two attempts at welding on the 2mm steel were poor - not sure if its the wire speed or voltage (voltage remained the same as the round weld)

Is it the voltage or wire speed? (my wire speed knob is broken so i dont know what the speen is

going to make a new knob.

using a unimig 250 workshop series, using gassless wire

GrahamGKD · Apr 6, 2011

dpv2010, I think you would do better to experiment with some cleaner material - from the pictures it looks like the stuff you are using is covered with rust/crud which is never a good thing for MIG welding.

Sid · Apr 6, 2011

As Graham says really.

You can clean the area you are welding if that's all the material you have. Flap discs on angle grinders are good for this. Also it's likely your earth clamp will not be making great contact either, so clean up an area for that as well.

eddie49 · Apr 6, 2011

What the others said about cleaning the metal....
Without separating the two parts, or replacing the lower metal with new, it's going to be impossible to really get the rust out of the seam.
Additionally, the weld seems mostly to be attached to the upper edge, with little or no penetration on the lower sheet. Increase the voltage and aim the torch more at the lower sheet.

backpurge · Apr 6, 2011

As has been said above, there does not appear to be any fusion to the bottom piece of material, the weld is far too big and it is very peaky.
From the photograph it looks as if you need to alter your torch angle/positioning, increase your travel speed a lot and possibly either increase your voltage of decrease the wire feed speed
In addition to the above, as has been covered, you need to remove as much surface contamination from the plate as you can

dpv2010 · Apr 6, 2011

I was trying to clean it for my tests but my partner was sleeping before night shift - i was a little too keen then!
I wasn't sure with the penetration if its voltage or what. I increase the wire speed it feels as if the gun is being pushed back, so im assuming that is something to do with the voltage being too low?
Next test ill wait until shes awake!

backpurge · Apr 6, 2011

Re the wire speed, you are dead right, either increase the volts or decrease the wire feed speed

dpv2010 · Apr 16, 2011

I cleaned up the area and the welds are looking a bit better. Upped the power and wire speed but they still arent looking great. (will post pics tonight)

But my question is - I am using gasless at the moment until I have lots of welding to do in one hit to save on gas hire.
Is the polarity the same or do i need to change it?

Sean · Apr 16, 2011

torch-ve return +ve for gassless

dpv2010 · Apr 23, 2011

and for gas = torch +ve return -ve?
now the next question is how do i change the polarity? This is my welder below.
Using 0.8 gasless wire and a 0.9 tip to stop the wire catching.

dpv2010 · May 6, 2011

ok So i have contacted Unimig about the two ports on the bottom of my welder. They are the -ve outputs but the guy explained them as a choke or inducor. Are these just fancy names for -ve ports?

long coil used for low power - short coil for high power is this right?

eddie49 · May 6, 2011

Your Unimig looks like a nice machine. The photo shows that the existing setup, for gas, has the cable which goes back inside the machine ( with the Torch symbol - goes internally to the Euroconnector ) in the +ve Dinse socket. There is a choice of two Dinse sockets for the Earth lead, with low inductance ( short coil symbol ) or high inductance ( long coil ); select according to the work and results.
As Sean said, to go gasless: unplug the Torch cable from the +ve Dinse socket, and move it to either of the two "coil" sockets, so the Torch will be -ve. The Earth lead will then go into the +ve socket.

dpv2010 · May 7, 2011

Thanks for that eddie49. I changed it to the sort coil and it seems to be welding heaps better with less spatter too.

The only thing I dont really understand is the inductance stuff. ie- thick metal uses one and thin another?

eddie49 · May 7, 2011

An inductor or "choke" slows down the rate of change ( rise or fall ) of a current; it acts like a damper or a flywheel. A large inductance value will provide more of this "damping" effect, so actually I would have expected a smoother arc, with a flatter, lower bead and less spatter with the "long coil" setting than the short one.

another 'whats wrong with my weld'

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