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Posted by Eric R Snow on May 12, 2006, 11:44 am
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Greetings wire-heads (isn't that from Known Space?). Ernie Leimkuhler
gave me the advice that .035 wire is too big for my 115 volt wire-feed
welder. And if anyone knows, he does (Thanks Ernie). Well, the Lincoln
SP125 Plus that I recently bought came with a spool of .035 70S-6. The
wire has some rust in spots which leads to weld porosity. So I'm just
using it to practice technique. Last night I was welding hot rolled
mild steel angle, 2 x 2 x 3/16". When the clean part of the wire was
making the weld the penetration was just over 1/2 the thickness of the
angle. After welding a butt joint with square edges I beat the two
pieces apart and the weld nugget tore out of the angle. The weld
itself did not fracture. When the weld nugget came out you could see
that it had penetrated more than 1/2 the parent metal thickness. It
appeared that the weld had separated at the weld/parent metal
interface. If I used a smaller diameter wire will the penetration be
greater?
Eric
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Posted by =?ISO-8859-1?Q?Nick_M=FCller?= on May 12, 2006, 2:05 pm
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> If I used a smaller diameter wire will the penetration be
> greater?
If you look closer at the physics behind MIG/MAG, you will see what is
happening. There are some parameters (and more):
* voltage (some say current)
* wire diameter
* wire speed
* distance work / wire jet
I'll start with the last one, distance work / wire jet:
If you increase that parameter, the wire coming out of the jet (and
having to conduct all that current) gets hotter. That means, that more
energy is going into the wire and less into the work piece.
Wire speed:
If you increase the speed, the arc will get shorter and the length of
the wire having to conduct the current will get longer. So the wire will
get hotter. But if decrease the wire speed, the arc will get longer and
will spread the heat more, meaning that it will not be directly on spot.
Wire diameter:
Increasing the wire diameter will reduce the resistance of the wire and
thus get more eneergy to the work, but you also will have to decrease
wire speed and thus will not get a gain. A decreased wire speed means a
softer (wider) arc.
Note: the volume of melted wire will have to be constant.
voltage:
Increasing the voltage will melt the wire faster. If you don't
compensate that with a higher wire speed, the arc will get longer and
thus won't get the heat on spot.
Now if you combine all the parameters, you will see that a smaller wire
gets more heat to the spot.
If you need more penetration, get CO2 as shielding gas. It has a better
penetration compared to mix-gas.
I'm using a 0.8mm wire most of the time. But I'm wondering how many amps
your MIG/MAG can deliver.
Nick
--
DIY-DRO // Eigenbau-Digitalanzeige
Available now in USA / Canada
<http://www.yadro.de>
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Posted by RoyJ on May 13, 2006, 10:16 am
Please log in for more thread options I think some of those comments are misleading. Assuming that you are
running in "droplet mode" (not spray or short cirucit modes):
Wire speed: You are usuing a constant voltage power supply, the faster
the wire feed, the shorter the arc, the higher the current. So faster
wire feed increases the "heat"
Stickout distance: Yes the wire gets warmer with longer stickout which
seems to help certain flux wires but you also start losing your shield
gas protection.
Wire diameter: In droplet mode you are melting the wire as it goes to
the work. Cross sectional area times wire speed is the predominent
factor. (although some others are at work here)
Nick Müller wrote:
>
>
>>If I used a smaller diameter wire will the penetration be
>>greater?
>
>
> If you look closer at the physics behind MIG/MAG, you will see what is
> happening. There are some parameters (and more):
> * voltage (some say current)
> * wire diameter
> * wire speed
> * distance work / wire jet
>
> I'll start with the last one, distance work / wire jet:
> If you increase that parameter, the wire coming out of the jet (and
> having to conduct all that current) gets hotter. That means, that more
> energy is going into the wire and less into the work piece.
>
> Wire speed:
> If you increase the speed, the arc will get shorter and the length of
> the wire having to conduct the current will get longer. So the wire will
> get hotter. But if decrease the wire speed, the arc will get longer and
> will spread the heat more, meaning that it will not be directly on spot.
>
> Wire diameter:
> Increasing the wire diameter will reduce the resistance of the wire and
> thus get more eneergy to the work, but you also will have to decrease
> wire speed and thus will not get a gain. A decreased wire speed means a
> softer (wider) arc.
> Note: the volume of melted wire will have to be constant.
>
>
> voltage:
> Increasing the voltage will melt the wire faster. If you don't
> compensate that with a higher wire speed, the arc will get longer and
> thus won't get the heat on spot.
>
>
> Now if you combine all the parameters, you will see that a smaller wire
> gets more heat to the spot.
>
> If you need more penetration, get CO2 as shielding gas. It has a better
> penetration compared to mix-gas.
>
> I'm using a 0.8mm wire most of the time. But I'm wondering how many amps
> your MIG/MAG can deliver.
>
> Nick
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Posted by Don Foreman on May 13, 2006, 12:44 pm
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>I think some of those comments are misleading. Assuming that you are
>running in "droplet mode" (not spray or short cirucit modes):
>
>Wire speed: You are usuing a constant voltage power supply, the faster
>the wire feed, the shorter the arc, the higher the current. So faster
>wire feed increases the "heat"
>
>Stickout distance: Yes the wire gets warmer with longer stickout which
>seems to help certain flux wires but you also start losing your shield
>gas protection.
>
>Wire diameter: In droplet mode you are melting the wire as it goes to
>the work. Cross sectional area times wire speed is the predominent
>factor. (although some others are at work here)
>
Right. I t may just be a matter of weld quality. Miller's MIG
book points out that current is a function of voltage, wire speed
and wire diameter. For given voltage, larger wire fed at lower
speed results in current similar to smaller wire fed at higher speed.
The amount of heat delivered to the work depends on the voltage
setting, but also on the wire diameter and feed rate. In practice, we
adjust the feed rate so the MIG "runs right"; if we want more heat
we turn up the voltage and adjust the feed rate again so it "runs
right". It's still a discontinous process of transferring discrete
droplets, but when it's "running right" it sounds and feels somewhat
continous -- the familiar "frying bacon" sound of a happy MIG.
I speculate that in droplet transfer mode with a small welder with
lower instantaneous peak current capability, smaller wire results
in smaller droplets but more of them per second, producing a smoother
more homogenous weld more resembling the continuous material transfer
of the constant arc in a (constant current) stick weld.
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Posted by Eric R Snow on May 13, 2006, 10:36 am
Please log in for more thread options On Fri, 12 May 2006 20:05:30 +0200, muellernick@gmx.de (Nick Müller)
wrote:
>
>> If I used a smaller diameter wire will the penetration be
>> greater?
>
>If you look closer at the physics behind MIG/MAG, you will see what is
>happening. There are some parameters (and more):
>* voltage (some say current)
>* wire diameter
>* wire speed
>* distance work / wire jet
>
>I'll start with the last one, distance work / wire jet:
>If you increase that parameter, the wire coming out of the jet (and
>having to conduct all that current) gets hotter. That means, that more
>energy is going into the wire and less into the work piece.
>
>Wire speed:
>If you increase the speed, the arc will get shorter and the length of
>the wire having to conduct the current will get longer. So the wire will
>get hotter. But if decrease the wire speed, the arc will get longer and
>will spread the heat more, meaning that it will not be directly on spot.
>
>Wire diameter:
>Increasing the wire diameter will reduce the resistance of the wire and
>thus get more eneergy to the work, but you also will have to decrease
>wire speed and thus will not get a gain. A decreased wire speed means a
>softer (wider) arc.
>Note: the volume of melted wire will have to be constant.
>
>
>voltage:
>Increasing the voltage will melt the wire faster. If you don't
>compensate that with a higher wire speed, the arc will get longer and
>thus won't get the heat on spot.
>
>
>Now if you combine all the parameters, you will see that a smaller wire
>gets more heat to the spot.
>
>If you need more penetration, get CO2 as shielding gas. It has a better
>penetration compared to mix-gas.
>
>I'm using a 0.8mm wire most of the time. But I'm wondering how many amps
>your MIG/MAG can deliver.
>
>Nick
Greetings Nick and Roy,
Thanks for the explanations. It's good to know the real why behind the
process.
Eric R Snow
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