Sonsivri
 
*
Welcome, Guest. Please login or register.
Did you miss your activation email?
December 07, 2016, 09:29:52 09:29


Login with username, password and session length


Pages: [1]
Print
Author Topic: Operational Difference between AC and DC Arc Welding Machine  (Read 19129 times)
0 Members and 1 Guest are viewing this topic.
tAhm1D
Senior Member
****
Offline Offline

Posts: 336

Thank You
-Given: 103
-Receive: 180



« on: December 04, 2009, 08:01:16 20:01 »

Hi,
In AC Arc Welding Machine,if Welding Voltage is less than 30v, then normally proper welding is difficult as with that sort of voltage, Arching becomes inconsistent. But I found in one German DC Arc Welding Machine, where the welding voltage is less than 18v. Now, the question is that is it actually possible to weld with that type of low voltage in DC Arc Welding Machine, which is otherwise not possible in AC type?

If it is true that with that sort of low voltage welding can be possible, then I must say that DC type Arc welding machine is far better than AC type as in that case overall power control will be much easier by applying pulse width modulation technique. If anybody is having clear cut idea regarding this, he is welcome to express his idea.
Logged
oldvan
V.I.P
Senior Member
*****
Offline Offline

Posts: 375

Thank You
-Given: 152
-Receive: 106


If the van is a Rockin'...


WWW
« Reply #1 on: December 05, 2009, 12:38:54 00:38 »

DC concentrates the majority of the heat at either the workpiece or the tip of the electrode,
depending on polarity.  AC does not have this benefit/detriment.

DC arcs don't like to break, AC or pulsed DC ones do.

Different methods of welding (TIG/MIG/Stick) require different application of voltage and
polarity to produce the desired best result.

With MIG welding mild steel, flux-cored filler requires the opposite polarity from gas shielded
welding to do a good job.

Two forums that make excellent sources of insight into welding:

http://www.practicalmachinist.com/
and
http://www.chaski.org/homemachinist/

A search of those forums for terms like welding voltage polarity current willl find many
discussions on the topic.
Logged

Give a man a fish and you feed him for a day.
Teach a man to fish and he will sit around in a boat drinking beer all day.
tAhm1D
Senior Member
****
Offline Offline

Posts: 336

Thank You
-Given: 103
-Receive: 180



« Reply #2 on: December 05, 2009, 01:35:06 13:35 »

Hi oldvan,
Different methods of welding or welding process is known. Do you have any idea about the minimum voltage required in AC and DC Welding Machine for keeping the arching constant without hinderence and any other operational/funcional difference? Requirement is for smps Arc Welding Machine, not for TIG or MIG welding.


Logged
oldvan
V.I.P
Senior Member
*****
Offline Offline

Posts: 375

Thank You
-Given: 152
-Receive: 106


If the van is a Rockin'...


WWW
« Reply #3 on: December 06, 2009, 05:17:58 05:17 »

From http://en.wikipedia.org/wiki/Shielded_metal_arc_welding
Quote
The power supply used in SMAW has constant current output, ensuring that the
current (and thus the heat) remains relatively constant, even if the arc distance and
voltage change.

...the power supplied by the transformer is around 17–45 V at currents up to 600 A.

Direct current with a negatively charged electrode (DCEN) causes heat to build up on
the electrode, increasing the electrode melting rate and decreasing the depth of the
weld. Reversing the polarity so that the electrode is positively charged and the
workpiece is negatively charged increases the weld penetration. With alternating
current the polarity changes over 100 times per second, ... providing a balance
between electrode melting rate and penetration.

Looks like you should try for current regulated and up to about 45 volts.
Were the choice mine, I'd use DC.

Logged

Give a man a fish and you feed him for a day.
Teach a man to fish and he will sit around in a boat drinking beer all day.
solutions
Hero Member
*****
Offline Offline

Posts: 1446

Thank You
-Given: 590
-Receive: 851



« Reply #4 on: December 06, 2009, 10:22:58 22:22 »

The heat is determined by I*I*R, so it is critical to maintain constant current to make the welding process consistent and controllable.  For arc welding there are three phases - starting the arc, maintaining the arc, then extinguishing the arc.

If you go with a low voltage machine, make sure you superimpose a high frequency on it to aid the starting process.  Once the plasma has been initiated, current control is critical, and on really nice machines current is variable with a pedal.  At some point you need to turn the arc off and in some welding like aluminum, you need to turn the arc on and off as you weld to allow the oxide to form as the shield for the weld.

There are also safety restrictions if you take the voltage beyond 48V, if I recall correctly.  Also, anything below 100% duty cycle for welding is for hobbyists and even for them it is a pain to weld a few minutes, then allow the machine to cool off for a few.

As others have already said, DC with reverse polarity capability is the way to go.

EMI is going to be a major pain in the butt in a switcher....create your children now before switching on the machine.
Logged
tAhm1D
Senior Member
****
Offline Offline

Posts: 336

Thank You
-Given: 103
-Receive: 180



« Reply #5 on: December 07, 2009, 04:03:43 16:03 »

Hi solutions,
I am not oriented with DC ARC Welding Machine and was not clear earlier regarding the requirement of reverse polarity capability in DC arc welding machine.  Do you know what minimum voltage will suffice in DC arc welding machine? What are the benefits in using DC arc welding machine instead of AC? Rather extra rectifiers are required for such high powered machine and also reverse polarity mechanism to be incorporated. Extra cost and complexity involved. What is your opinion?
« Last Edit: December 07, 2009, 04:32:35 16:32 by tAhm1D » Logged
solutions
Hero Member
*****
Offline Offline

Posts: 1446

Thank You
-Given: 590
-Receive: 851



« Reply #6 on: December 09, 2009, 04:34:44 04:34 »

Look here:  http://www.millerwelds.com/resources/articles/index?page=articles16.html
Logged
oldvan
V.I.P
Senior Member
*****
Offline Offline

Posts: 375

Thank You
-Given: 152
-Receive: 106


If the van is a Rockin'...


WWW
« Reply #7 on: December 09, 2009, 12:46:29 12:46 »

Reversing polarity is often accomplished by unplugging 2 wires and plugging them
into opposite holes, very low tech and low complexity.

Design for 48V open circuit output and allow current regulation to reduce this to a
couple volts.  Could you use it to weld if it maxes out at 20 Volts?  Certainly.  Will
you be pleased with its operation?  Likely not.

Too low a voltage and arcs will break and make welding annoying and low quality.
What "will suffice" is a relative term.  As long as you are designing and building this
yourself, best to have enough voltage available to do it right.  The pride and
satisfaction of using it for years to come will be immense.

With the economy in its sad state, complete used professional welders can be had
for a fraction of what they are worth, but that cuts out the chance to learn.
Logged

Give a man a fish and you feed him for a day.
Teach a man to fish and he will sit around in a boat drinking beer all day.
tAhm1D
Senior Member
****
Offline Offline

Posts: 336

Thank You
-Given: 103
-Receive: 180



« Reply #8 on: December 09, 2009, 06:39:08 18:39 »

Hi,
Do you consider it feasible to plug and unplug 2 wires all the time during welding?
Suffice in welding means a specific minimum welding voltage may be different for AC or DC Arc welding is required for proper welding Arc. Testing from 48v,yes that can be done because for learning, test and trial always bring some useful lessons.
I don't want to buy ready made one , as my aim is to make one for learning sake and that knowledge can be applied for other purpose if necessary.
Logged
oldvan
V.I.P
Senior Member
*****
Offline Offline

Posts: 375

Thank You
-Given: 152
-Receive: 106


If the van is a Rockin'...


WWW
« Reply #9 on: December 10, 2009, 04:41:57 04:41 »

Do you consider it feasible to plug and unplug 2 wires all the time during welding?

This would not be necessary DURING welding, only when changing from a job on thick
metal where penetration is more important to a job on thin stock where a flatter weld
and not destroying base metal is desireable.



Two matching connections, one for POSITIVE, one for NEGATIVE. 
http://www.millerwelds.com/about/news_releases/2005/articles128.html
Logged

Give a man a fish and you feed him for a day.
Teach a man to fish and he will sit around in a boat drinking beer all day.
tAhm1D
Senior Member
****
Offline Offline

Posts: 336

Thank You
-Given: 103
-Receive: 180



« Reply #10 on: September 09, 2011, 05:59:28 17:59 »

Hi oldvan,
Due to my study and engagement with different projects, I could not put proper attention to the welding machine and now I am putting my attention in making both Linear and SMPS type welding machine.I will test both DC and AC Type. Both will be dsPIC33 Micro controller based for which I made the Program,schematics and PCB Boards and will test soon. Your posts helped me alot.
Logged
yoda
V.I.P
Junior Member
*****
Offline Offline

Posts: 58

Thank You
-Given: 609
-Receive: 17


« Reply #11 on: September 21, 2011, 10:27:02 10:27 »

// Linear and SMPS type welding machine. I will test both DC and AC Type.//

Interesting tAhm1D, I'm looking forward to your test outcom's.
Logged
jstavene
Guest
« Reply #12 on: December 29, 2011, 07:26:56 19:26 »

Different metals and alloys require different voltage and current charcteristics, the big thing I see is switching from negative ground to positive ground for aluminum and using flux core wire (most common I see) as far as voltage and current settings,, the aforementioned miller website is good, and a few I also would add ,,

http://www.weldreality.com/
(explanations ,,weld processes,, some settings haha a good guy I know)

also the AWS site (American Welding Society) is our defacto,,but they are heavy on commercial charge money for their books but they set the standard in the USA,, they are one of 2 main standards as a American Welder I have had to meet (the other is US Military Spec.)

http://www.aws.org/w/a/


Another I googled (I don't like the site but a couple videos and explanations.)
http://www.weldingtipsandtricks.com/


My humble experience is that a good weld should be stronger then the material your welding.
Different alloys and metals,, its nice to know if its mild steel or stainless or aluminum or cast iron, the hardness, if it has chrome or other alloys or if its a high tensile ,,or uhm most large companies have a metallurgist ,,who can do scratch or etch tests to determine what,,a piece is,, if not known then what process is best (cost, time, technique,,) then proper settings usually the welding engineers determine what process,, if the company is big otherwise the welders usually individualy determine settings,, gas, wire or electrode sizes, and types,, then voltage and current,, or frequency ,trim,, etc

The majority of welding is now GMAW (Gas Metal Arc Welding) genericaly called mig (Metal Inert Gas, which it is not always,,so this is a misnomer) -think the guy holding a welding gun mostly mild steel, high tensile steel and stainless, you can do aluminum,,but this is often the cheap high volume production process most used in my experience.  (main transfer types are Spray -very good quality if done right but literally sprays material deposition on and requires most skill but very fast and high quality but due to high travel speed most tough to do repetitively, I used to make Helicopter parts using this then we had them x-rayed,
Pulsed spray is similar to Spray but less travel speed, and is gaining popularity here also called Rapid-Arc,, tough to set the welder unless the welder is a Pulse type, uhm great for high quality production,,
Most common used is Globular Transfer (imagine small balls of molten metal) Globular is okay for most steel and common,,  Then Short Circuit,, I have used this for welding odd out of position type robot welds,, on thin materials,, very sharp,,quick,, not often used by me anyway,,
(the videos and pics on welding reality will explain much better then I)

Tig is on tv alot, the shows where people build motorcycles,, tig can do most things GMAW can, with better quality but takes more practice more time and better skill, (Tungsten Inert Gas)

Arc is used most often for heavy thick (2 inches or more thick steel) Construction, or pipe and where a emergency exists that a alternative is impractical,,(maybe the second most primitive but a art unto itself,,)
Think a guy with 2 cables,,one grounded and a rod on the other ,,this is capable and can be good quality but takes the most skill, in my opinion,,,knowing which rod for the job,, (there are books and charts,, but no shielding gas,,can make things tough and the older welders had touchy heat controls,, uhm a powered unit I was taught to go gas engine powered, that diesel powered ones would idle up and down and the welder would suffer with heat,,deviations,, I am sure newer regulators may have solved some of this but,,

I like big solid state transformer style,,, the inverters are lighter, but a employee spilling a can of pop into one means big money,, and they last on average 3-6 years,,whereas the transformer style we had some from the 1950's open them up,, after unplugging them ,,spray soap and water,, oil the slide bicycle chain arm,, and they last ,,, cheap solid and heavy so hard to steal,,  

good luck, I remember people building small mig machines with flux core using transformors from,,(microwaves)? but usually like 90-120 amp machines,, so they could weld thin metal,,or medium if they layered,,
Logged
Pages: [1]
Print
Jump to:  


DISCLAIMER
WE DONT HOST ANY ILLEGAL FILES ON THE SERVER
USE CONTACT US TO REPORT ILLEGAL FILES
ADMINISTRATORS CANNOT BE HELD RESPONSIBLE FOR USERS POSTS AND LINKS

... Copyright 2003-2999 Sonsivri.to ...
Powered by SMF 1.1.18 | SMF © 2006-2009, Simple Machines LLC | HarzeM Dilber MC