About cold welding machine,

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
Hi,
The cold welding machine, its principle is to use a charging capacitor and discharge in an ultra-short time of 10-6 to 10-5 seconds in a cycle of 10-3 to 10-1 seconds. The contact part of the electrode material and the workpiece will be instantly heated to 8000°C~10000°C, the molten metal in the plasma state.
There are two questions to make it for now:
1. how to charge the large capacitor of ~ 200v- 150000uf, at 10^(-5) - 10^(-6) second?
2. how to control the large current of ~200A on/off?
Thanks
Adam
 

MisterBill2

Joined Jan 23, 2018
9,258
The vital concern with the capacitor discharge welder is to assure that the current drops below the SCR holding current so that the SCR power -time rating is not exceeded. And the big challenge with creating such a system is assuring that all of the discharge circuit has adequate current handling ability. In addition, that large current pulse will produce a large magnetic field pulse that must also be considered.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
The vital concern with the capacitor discharge welder is to assure that the current drops below the SCR holding current so that the SCR power -time rating is not exceeded. And the big challenge with creating such a system is assuring that all of the discharge circuit has adequate current handling ability. In addition, that large current pulse will produce a large magnetic field pulse that must also be considered.
Thanks.
Do you have a circuit for a 200A? may I just use large enough module say 300a SCR?
 
Last edited:

shortbus

Joined Sep 30, 2009
8,803
I wish one of the videos of that type would take a cross section of the resulting weld. The welds where they are making a 90 degree joint. From doing welding most of my adult life, of all types from oxy/accet to Tig and all in between, I can't understand where the fillet metal is coming from, when no filler rod is being used. I'm betting that if seen in cross section there is a void under the fillet, and that is not a strong weld.

When they showed building up an edge, they showed adding a filler, that is a normal procedure, but fillet welds with no filler rod??? I'm not believing it.
 

MaxHeadRoom

Joined Jul 18, 2013
23,612
The industrial versions I have worked on have been the projection welding types, that is the object being welded has small projections on the joint face, that melt and use as filler when the discharge occurs.
Also pressure had to be applied and sensed with a P.S. before the weld could occur to avoid arc splash.
200a SCR's were typical,
e.g. IR IR304RA60
 
Last edited:

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
I wish one of the videos of that type would take a cross section of the resulting weld. The welds where they are making a 90 degree joint. From doing welding most of my adult life, of all types from oxy/accet to Tig and all in between, I can't understand where the fillet metal is coming from, when no filler rod is being used. I'm betting that if seen in cross section there is a void under the fillet, and that is not a strong weld.

When they showed building up an edge, they showed adding a filler, that is a normal procedure, but fillet welds with no filler rod??? I'm not believing it.
Thanks.
I don't think the cold welder can have a deep penetration welder.
It is typically for the surface welding and connection welding, small thermal stress and thermal deformation is the benefit I guess.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
The industrial versions I have worked on have been the projection welding types, that is the object being welded has small projections on the joint face, that melt and use as filler when the discharge occurs.
Also pressure had to be applied and sensed with a P.S. before the weld could occur to avoid arc splash.
200a SCR's were typical,
e.g. IR IR304RA60
Thanks.
Properly I'll use IGBT instead of SCR, cause of the latter is just half control, SCR controlled the conduction not the disconnect。
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
Not sure what is meant by disconnect?
Or that SCR dumps the whole charge? i.e. there is no regulation unless caps are switched in as needed.
Thanks.
I mean: the silicon controlled rectifier (SCR) can only trigger the turn-on, but not the turn-off, which is called a semi-controlled device
 

strantor

Joined Oct 3, 2010
5,632
Hi,
The cold welding machine, its principle is to use a charging capacitor and discharge in an ultra-short time of 10-6 to 10-5 seconds in a cycle of 10-3 to 10-1 seconds. The contact part of the electrode material and the workpiece will be instantly heated to 8000°C~10000°C, the molten metal in the plasma state.
There are two questions to make it for now:
1. how to charge the large capacitor of ~ 200v- 150000uf, at 10^(-5) - 10^(-6) second?
2. how to control the large current of ~200A on/off?
1. to charge a 150,000uF capacitor from 0V to 200V in 0.00001 seconds would require a total circuit resistance lower than .0000135 Ω and supply capable of 14,814,814 Amps. This is practically impossible.
2. with an SCR or IGBT or MOSFET or ... there are lots of options

If these are specs provided by some manufacturer that you're trying to copy, you would be better off doing what they did: design the circuit around more reasonable numbers and then tell absurd lies about its performance.
 

MaxHeadRoom

Joined Jul 18, 2013
23,612
The commercial ones I worked on would dump the charge when fired, the firing circuit would then be delayed until the capacitor bank was ready.
The supply was then removed before next firing allowed.
These were in the automotive field so re-fresh/ready rate had to be fairly quick.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
The commercial ones I worked on would dump the charge when fired, the firing circuit would then be delayed until the capacitor bank was ready.
The supply was then removed before next firing allowed.
These were in the automotive field so re-fresh/ready rate had to be fairly quick.
Thanks.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
You missed my point. Where is the extra metal that is making the ripples, that kind of look like a TIG weld (stack of dimes) coming from? The ripples are robbing the metal from under the weld bead.

There is a member here that bought one of these I was hoping he would chime in. @cmartinez
Thanks.
It's right.
 

MisterBill2

Joined Jan 23, 2018
9,258
You missed my point. Where is the extra metal that is making the ripples, that kind of look like a TIG weld (stack of dimes) coming from? The ripples are robbing the metal from under the weld bead.

There is a member here that bought one of these I was hoping he would chime in. @cmartinez
The fact that a weld can look good to somebody who does not understand welds is unfortunate. S is certainly correct that every bit of that metal has to come from someplace. So just because it looks good does not mean that it has any strength. When I was able to rip apart a pretty weld with one hand the forman had to agree that it was not adequate. It was a very pretty fillet with no penetration. S undoubtedly understands what I men by that. And limit switch brackets do need to be strong.
 

Thread Starter

LAOADAM

Joined Nov 21, 2018
629
anywhere can find a simple IGBT or MOSFET switch circuit? I mean just simply turn on / turn off the large current, and the on/off time adjustable?
Some source said the IGBT burn right after turn on, and MOSFET better, is this right?
I like to do test for it.
BTW: what's the 6.3v means in the picture?
6.3v.PNG
 
Last edited:
Top