Subject: welder questions

From: Peter Lawrence <[email-masked]>
Date: Thu, 06 Jun 1996 06:50:04 -0700

I have a few questions regarding welders, answers to any and all will 
be welcome. Thanks in advance.

  I have been watching the newspaper classifieds for TIG welders and all
I see are MIG. Is there any difference other than the torch tip. Can a
MIG be used as a TIG just be leaving out the wire spool and putting on a
TIG tip (do they make such tips for MIGs?). Does the welder have to be
able to do both + and - polarities (doesn't TIG use - on the tip to keep
the tungsten from melting, and MIG us + on the tip to help melt the wire?).
Do MIGs generally have High Frequency start, or if not can they generally 
be adapted or is this very manufacturer make/model specific.  What else 
would or could be incompatible.

  I have heard that for thin sheet metal a larger unit (more amps) is
preferable, because even though you wont use the amps on thin metal you
will benefit from a more stable arc with a larger transformer. Is the
same true of the solid-state (inverter) type welders. What are peoples
experience and opinions on this.

  Is there a big difference between a plasma cutter and a TIG/MIG unit
other than the torch tip, are there tips available for TIG/MIG units for
doing cutting?

Thanks,
Peter Lawrence ([email-masked])

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From: [email-masked] (ErnieLeim)
Date: 9 Jun 1996 14:05:57 -0400

My best recommendation is to go down to your local library and check out a
welding textbook. Give it a read and you will find the answers to all of
your questions.

Best of luck
@}---------------------------------------------------{@
                    Ernie Leimkuhler                                      

                  Stagesmith Productions                                  
                                          
                 Custom Metal Fabrication                                 
               
*    ABANA   SCA     AWS    USITT   IATSE local 15, 488   *
                        Renton, WA                                        
   
*    "Death is like being on holiday with
          a group of germans" ---- Rimmer ( Red Dwarf )
@}------------------------------------------------------{@

---

From: [email-masked]
Date: Sun, 09 Jun 1996 23:06:08 GMT

Peter Lawrence <[email-masked]> wrote:

>I see are MIG. Is there any difference other than the torch tip. 

TIG welders generally use a constant current power supply, while MIG
uses constant voltage power.  Basically, the open circuit voltage on
the TIG will go very high to say... 50 to 90 V.  As the arc is
established, the voltage goes lower and maintains a constant current
flow.  MIG welder hold the voltage under control, and allow whatever
current is necessary to flow to melt the wire.  In addition, TIG
generally uses the negative terminal connected to the electrode, while
the MIG uses the positive terminal connected to the electrode.  There
are exceptions to this last statement.  

>Can a

I have used constant voltage supplies with TIG, and it will work.  The
reason that it works is probably due to the fact that the MIG supplies
have some constant current characteristics, and are not perfect
constant voltage sources.  Never try to use a constant current source
with MIG however.  The wire will not burn back precisely, and the wire
will be welded to the contact tip.  

You are generally correct about the polarity, but there are
exceptions.

>would or could be incompatible.

MIG machines do not use a high frequency start.  It is basic to the
MIG (short circuit) theory that the arc is started with contact
between the wire and weldment.  It is also basic that the arc voltage
is limited, which controls how far the arc can burn the wire back from
the point of contact. 

You would find it hard to start an arc with a TIG torch used on a MIG
supply.  The open circuit voltage is not high enough to enable easy
arcing.  However, once an arc is established, then you could probably
maintain it with a TIG torch on most MIG supplies.  Adding high
frequency would help with arc starting, but is not usable with MIG.  

>experience and opinions on this.

I have a Lincoln SP 100 and a Powcon Inverter with a wire feeder.  The
Lincoln SP 100 works better on really thin stuff.  The Powcon works
much better on heavier material.  The Powcon has a tendency to burn
through very light metal in the 20 ga range.  But it can supply enough
current to handle heavy wire, and spray arc techniques.  

>other than the torch tip, are there tips available for TIG/MIG units for

Plasma cutting uses high frequency high voltage power.  The open
circuit voltage will be several hundred volts.  

My Powcon inverter power supply has switches on the front panel to
change modes.  It will provide constant current power for TIG and
stick welding.  It will also provide constant voltage power for MIG.
You have to change torches as you switch modes.  The power supply also
has a third setting for plasma cutting and has a plasma torch attached
to the supply at all times.  

There are rods that are for cutting metal.  There are also carbon arc
gouging torches that will cut metal.  Both of these can be used on a
TIG Constant Current supply.  

J. M. Stuart

Engineer / Inventor / Patentee