Resistance Soldering question

[Patrice LeméeParticipant @patricelemee72098]

Hi. My name is Patrice Lemée and I am a metal sculptor. I need help with resistance soldering and this seemed like a good place to ask. It’s hard to find people using this and I think you guys do. It’s not about models per say so I hope it is still ok to ask. Let me know if it’s not.

I have purchased a soldering unit from American Beauty. Very happy with it so far but I am having a small problem. Well I hope it’s small. I am trying to solder a small piece to a much larger piece as you can see in this picture.

The thing is I need to put a lot of heat into the larger piece for the solder to properly flow to it. The result is a perfect solder joint but the carbon electrodes leave marks. Since I am doing this on a near finished sculpture and in hard to reach places I need to minimize this scarring of the surface. Not sure how to do that or if it’s even possible. These are carbon electrodes and they glow red hot from heat, more damage from the electrode e that glows more and also a little powdery residue on it afterwards.

Not sure if I explain myself well or if anyone here has an idea of how to do this better but I am taking a chance and would be very grateful for any help. Or of course if anyone knows of a better place to find info on this that would be great.

Here is my latest sculpture and the small feet are what I am working toward soldering.

Thanks for you help.

[Patrice LeméeParticipant @patricelemee72098]

[Kiwi BlokeParticipant @kiwibloke62605]

Hi Patrice. Wow! That's impressive craftsmanship. Perhaps you could find time to describe some of your methods – I'm sure many of the forum members would be interested. I'm sure you'll receive a warm welcome here.

As to your problem: It seems that the 'larger piece' isn't going to be easy to heat from what is almost a point-source of high temperature, but not much heat energy. The piece will act as a heat-sink. I'd imagine that you will need to deliver considerable heat (rather than temperature) to it, possibly over a large enough area to avoid local damage, and this sounds like a job for a small blow-torch. If the 'larger piece' can be brought up to near-soldering temperature, the resistance soldering equipment may be able to complete the job. Sounds like it may be a three-handed job though…

[JasonBModerator @jasonb]

What size unit have you got? you really need one sized to heat the biggest component rather than use a small unit to try and get heat into big items

[Brian GParticipant @briang]

I was recently (and annoyingly) reminded that a mini toaster-oven reaches a high enough temperature to melt soft solder, and accidentally reflow soldered part of a model. Fortunately I was able to reheat the model in the oven and move them back to their original positions.

Could you use an oven to bring the whole of the work to a temperature below the melting point of the solder, remove it and quickly carry out the resistance soldering? Heating in an oven should produce much less oxidation than a flame, and by heating the whole model there would be enough heat stored to assist in the soldering process.

Brian

[Michael GilliganParticipant @michaelgilligan61133]

Welcome, Patrice

From my limited experience … Although resistance soldering is wonderful in the right situation, it is probably a “blunt instrument” for what you are trying to do; and I think you have correctly identified the problem.

What materials are you joining, and what are the sizes ?

MichaelG.

.

Edit: American Beauty has some helpful videos, but I’ve seen nothing comparable to your work.

https://www.youtube.com/user/SolderingGuru

Edit: I have only tried a microwelder very briefly … but was impressed !

https://www.lampert.info/en/faq#question18

Edited By Michael Gilligan on 06/10/2019 08:30:52

[Nicholas FarrParticipant @nicholasfarr14254]

Hi Patrice, I'm not familiar with resistance soldering or its techniques, but like Kiwi Bloke has said, maybe pre-heating could be an answer. If using a flame directly is not desirable, then maybe a hot plate of some description might in order, which could be heated in a few different ways. One way I used a hot plate instead of a soldering iron or a direct flame, is shown below where I soldered a thin piece of brass shim to a thicker brass ring and then turning it over to solder another one on the other side.

The heat source is a cheap camping stove type attachment for a gas blow lamp cylinder and the block on top is just to hold it down. Hope it can help or give you inspiration for some other technique.

Regards Nick.

Edited By Nicholas Farr on 06/10/2019 08:40:58

[I.M. OUTAHEREParticipant @i-m-outahere]

I have used a hot air gun to reflow electronic components so maybe you could use one to pre heat the bigger components ?

[IanTParticipant @iant]

I use the same thing as Nick.

My somewhat cruder set-up is a cleaned up lump of 3/8th 6" square mild steel on the gas hob (when the wife is watching telly!). You can then deliver 'spot' heat via a small gas torch if required… this for soft soldering smaller brass pieces to bigger ones, where the larger piece is acting as a heat sink and preventing more usual soldering approaches.

Don't think this will help Patrice though (lovely work by the way)

Regards,

IanT

[VidarParticipant @vidar]

I take everything back – must have been sleepy initially! That does indeed look like some weird soldering or brazing. Still, try resistance welding or oven brazing? I leave the comment though in case you want to try that approach or as some points might still be valid. And you might want to try a copper rather than graphite electrode.

Resistance soldering isn't actually soldering but basically welding by short circuiting. Most will know it from battery packs and metal grid shopping trolleys for instance. It is a very quick and precise, but does leave mark unless specifically adapted to avoid it. I can think of a few factors to help minimize this:

The reason you get marks is that the welding pin is also getting a bit stuck. Thus the resistance of that contact point is not electrically leading well enough compared to the area you actually want to weld. There are a few things you can do to improve on that difference:

• High pressure – make sure the welder and the pieces you want to weld are in tight contact.
• Little contact area for the actual weld. If the area of the weld is much larger than the contact point it will be a good electrical lead too. Try using a centre punch and make a ever so tiny dimple – the edges will stand up a bit and make much smaller inital contact areas. Your continued high pressure will flatten them down again when they melt as you weld. You might want more than one such dimple. (Try searching "projection welding" if you need inspiration – or just "spot welding" for the more general picture).
• Very clean contact area without any oxidation layer on top. Remove as much resistance as possible from the welder contact point.
• As the metal heats and melts it will then tend to cool and contract at different rates. The edges cool faster than the center, and you might get a tiny welding distortion. The only way I've seen to avoid this being visible is in the excellent Dan Gilbert – spot welding video. (Recommended!)

(As for discoloration that is a function of the heat generated and just a very thin layer on the surface. It can be removed by sanding or chemically). 

If you have welds in very hard to reach places could oven brazing be an alternative?

Edited By Vidar on 06/10/2019 10:52:00

Edited By Vidar on 06/10/2019 10:53:18

[Patrice LeméeParticipant @patricelemee72098]

First of all thanks a lot for all the good words, always very much appreciated. And of course for all the great info, that’s awesome. I should have come here a long time ago I think since what I am making is really making model too, just different subjects and use all the tools and techniques you guys do. If you don’t mind I’ll stick around and hopefully can contribute too. I’ll also make a proper introduction post later today since I think some of you might like to see my workshop, still a work in progress but getting there. (I have to subscribe to the Workshop magazine, wonder if they ship to Canada (Québec).

Ok let me try and address all your suggestions.

Gas welding is not possible because of insurance. My shop is part of my house and I can not have something like OA. That’s one reason I went with resistance soldering.

Heating up the whole sculpture is also not very practical. First because of the amount of cleanup needed afterwards because of the amount of heat needed (some place might not even be accessible anymore from other components). And then some of those other components are also soldered and would desolder. That’s why a more concentrated form of heat is perfect.

I have a 1800W unit which is a high powered one in their lineup. Throws in a lot of heat and should do the job, I did not want to buy an underpowered unit like you said Jason.

Never researched a MicroWelder but I will. From what I remember though those were very expensive, in the 8-10K$ range. That might be hard to get approved by “The One Who Must Be Obeyed”

Vidar, thanks for the video link to Mr. Gilbert, some very interesting stuff. I will probably watch the whole series. When I get into the shop later today I’ll do a few tests with your recommendations and take a few pics to show progress.

Again a very big thanks for all your help.

[Dave HalfordParticipant @davehalford22513]

Put a small sheet of copper between the work and electrode?

[VidarParticipant @vidar]

Posted by Patrice Lem�e on 06/10/2019 14:23:44:

Never researched a MicroWelder but I will. From what I remember though those were very expensive, in the 8-10K$ range. That might be hard to get approved by “The One Who Must Be Obeyed”

The professional resistance micro welders for repair are indeed expensive, but there didn't use to be much else that could weld away a tiny scratch in plastic mold for instance. These days I think they have fairly hard competition from laser micro welders. Not entirely sure what they are priced at, but jewelry suppliers likely have them.

I picked up my micro welder from an auction at a closing plastic manufacturer. It was dirt cheap as such speciality gear often is when laywers without a clue just want to get rid of stuff in a hurry.

The principle driving them is simple enough though, and a battery strip welder does pretty much the same. And they are much more reasonably priced – roughly US 100 and upwards I think.

The main benefit of resistance welding is the speed and the very small heat affected area. With a weld in a fraction of a second very little of the surrounding area gets heated at all.

I look forward to seeing your pictures

[Patrice LeméeParticipant @patricelemee72098]

Vidar, thanks for the info, definitely worth looking into

Here is what I did today in the shop.

First I cleaned up a piece of 304 stainless and put somewhat of a mirror finish on it as I would on a sculpture for example

Then flattened a pair on electrodes, these are the copper coated ones.

and cleaned up the flat on the carbon electrodes

I then applied some heat using the highest output my machine will do and about the amount of time needed to melt the solder. Here is the resulting marks. Carbon electrodes on the left and copper coated ones on the right.

I then cleaned up a bit with a small buff wheel and green chrome using a rotary tool like I would in tight spaces. Sorry, this time the carbon are on the right and copper clad on the left.

As you can see the carbon ones leaves much less of a mark. The copper even deposited a bit of copper on the surface. So I think the carbon electrodes are my best bet and what I need to try and improve.

Here is a pic to give an idea of size and other concerns like a curved surfaces and also to show how hard it is to get close keeping in mind that I also need to be able to stick a solder wire in there.

That’s why as much as I like the sacrificial plate idea I don’t see how to implement it.

Mind you the amount of scarring is not that bad. I might have to live with it or find a way to incorporate it in the design. But I would still like to see if I can’t minimize it some more first.

Thanks again for looking and all your help. I’ll post more as I find it and of course feel free if an idea no matter what jumps to mind.

[jann westParticipant @jannwest71382]

If your insurance won't allow oa welding (because of acetylene) you can always try oxy propane as a fuel … not quite as hot … but still pretty hot for soldering and brazing. Also you could try jewelers micro tig welding systems. Welding and soldering is about heat management (and the effects of entropy so fiddily jibs like yours may benefit from a hybrid solution … eg holding the body in a clamp, applying heat from a flame two or three at tactical points near the weld site to raise general temperatures in the vicinity, then using intense localised heat for the actual welding function. If you don't have 9 hands then tactical clamps can hold gas torches.

[VidarParticipant @vidar]

Well, this entire resistance soldering concept is new to me, so I've learned something here.

Resistance welding on the other hand is not about heating as such and doesn't use any solder at all. For that thickness though you will need quite a powerful source to do resistance welding. So that is likely out.

To my ignorant eye this resistance soldering concept seems to be heating by short circuit – and then real slow as compared to resistance welding. Thinking out lout ideally the solder contact point should be a bad enough resistor to heat up by itself and before the rest of the circuit. Then you could connect electricity over a wider area and or at a less visible place further away. Sadly solder is typically great at leading electricity. You might need bad solder…

If this is just about heating a spot locally, and quickly at that, the obvious thing would be to make contact on the thinner part. I assume that is impossible since you're doing this. Local and more powerful heat sources like TIG or gas welding sources might be an improvement but you run the risk of melting the material itself if not careful.

I'm running out of other ideas here but here are a few more:

1. Back to oven brazing but with strategic use of solders with different melting points to keep earlier solders from melting when adding new ones.
2. Pure mechanical connection – use a tiny third part to connect them.
3. Tiny welding gas torch with suitably thin needle to apply heat directly. (Oxygen/hydrogen, acetylene/oxygene, or even just propane). Bend needle if hard to reach?
4. Go utterly old school: Take a big chuck of copper with some pointy bit on it and heat the entire thing to some 600-900 degrees. Press against your ara to heat as some superheated old style soldering iron. If needed add heat sinks to reduce the heat reaching earlier solders.

[Michael GilliganParticipant @michaelgilligan61133]

Vidar,

I’m not sure if you followed my earlier link, but …

This video is well-worth a look: **LINK**

MichaelG.

[ still waiting for a nice win on the Lottery, or Premium Bonds ]

.

Edit: … also this one: https://youtu.be/5JaRY24fCWQ

Edit: …and this very informative blog:  http://www.silversmithing.com/puk.htm#Blog

Edited By Michael Gilligan on 07/10/2019 09:17:35

[VidarParticipant @vidar]

Michael,

Sorry, I somehow missed that. No idea why they would call it a micro TIG? It sure seems like resistance welding. That said if they have a tungsten, and use an inert gas, I guess it qualifies as Tungsten Inert Gas welding. Fair enough, but as you typically want to avoid contacting the material with the tungsten electrode I guess they do get a fair bit of tungsten inclusions in the weld.

The results though look a lot like what I get from my micro resistance welder. Mine is classic resistance though with copper electrodes and no cover gas. Mine got a foot pedal for activation instead of pressing down the tip. I guess that might give a bit more pressure control. (Or more realistically worse variation of the pressure). Neither does mine have presets – I have to make the settings manually.

Mine can do something theirs can't though as mine can use rolling copper electrodes. So you can roll along with a sharp edge and a make a seam, or roll over welding powder with a flat edge to fill in tiny scratches or add thickness.

That one looks specialized for jewelry though, and mine was made for a different purpose, so I'm sure they are each best suited for their respective tasks.

[Patrice LeméeParticipant @patricelemee72098]

Jann, I can not use Oxy-propane either, I am stuck with electricity. Only gas allowed is something inert like the argon for my TIG.

Vidar, heating the smaller part doesn't work cause solder flows towards heat and since you never get the large part up to temp this way the solder never wets to it. I do use mechanical bonds from time to time but I would like to have the solder option too. Thanks for all the good ideas. Would you happen to have a brand and model number of your micro resistance welder. I would like to learn about it some more.

Thanks Michael I'll take a look at those videos.

[VidarParticipant @vidar]

I'm not really a soldering person as you can likely tell, but heating principles should be universal physics. My idea wasn't really about heating the entire big part, but quickly dumping enough heat into to local area to be soldered.

All materials have some measure of heat conductivity. (This is often closely connected to their electric conductivity, so silver, copper, aluminium transfers heat fast and steel not so fast and so on). Thus if one has a heat source that manages to heat quicker than the material can distribute it away then the local area gets hotter than rest of the part. More powerful heat sources can dump in heat faster for greater potential temperature difference and so on.

It is a factor in minimizing affected welding areas, and I figured it might be similar with soldering – if you can't heat a big part then aim for a brutally quick local heating so what you need heated don't have the time to distribute away the heat. (Uses less energy too as you don't waste energy to heat material that doesn't need heating. Not really a factor at this scale though).

My micro welder is some old japanese machine. I'll try to take a look later, but chances are that particular one is not in sale anymore. That said those machines seem fairly similar – try searching for "micro resistance welder" "mold repair welder" or similar. A quick try by me found this one which seems fairly similar:

"Sunstone D-CD320" – for a tiny example:

**LINK**

Edited By Vidar on 08/10/2019 11:51:00

[Grindstone CowboyParticipant @grindstonecowboy]

Firstly, I am very impressed by your work.

Secondly, and I may be (probably am) talking absolute rubbish here, could you tin the larger piece first in the precise spot you are going to attach the smaller part, then only the solder has to melt and the piece is 'pre-wetted' for want of a better term? For that matter, could you tin both parts?

[Tim StevensParticipant @timstevens64731]

I wonder whether there is a source of confusion here ?

Could the term 'soldering' as used by the OP mean 'hard soldering' – or what we might call 'silver soldering' ?

Tim

[Neil WyattModerator @neilwyatt]

My approach would be to look for ways to do the jointing that allow any marks to be polished out afterwards.

Neil

[Patrice LeméeParticipant @patricelemee72098]

Vidar, thanks for the info and link.

Grindstone, yes tinning parts could be a solution in some instances but I still have to minimize scoring of the surface. I could tin the large part and then clean up the marks and then apply the small tinned part and fuse them with less heat but that means cleaning it very well in between not to have impurities especially from the buffing, that is hard to clean especially from a hole. Plus the way it's going now the scoring is happening very soon in the process, I am troubleshooting that with help from Virgil at American Beauty.

Tim,I am sorry as you can see this is not my area of expertise. How does calling it soldering versus hard soldering or silver soldering create confusion?

Neil, that is something I will have to do for sure but I am just trying to minimize the marks first to make it easier cause in some instances it could be very hard to reach those areas or impossible to change the design to make them accessible.

Thanks again for all the help.

[Roger WoollettParticipant @rogerwoollett53105]

Tim,I am sorry as you can see this is not my area of expertise. How does calling it soldering versus hard soldering or silver soldering create confusion?

The term "soldering" covers a range of filler alloys. "Soft soldering" usually means using a lead or tin based alloy with small quantities of other metals to change the melting point. Temperatures around 200 – 350 degrees Centigrade are common and heat can be applied by a flame or soldering iron.

Fillers that melt above 450 degrees C are strictly brazing alloys although the terms "hard" or "silver" sldering are often used. Model engineers tend to use silver solders thart melt from 630 degrees C and upwards. Silversmiths use a different range of silver based alloys described as "easy" ,"medium" or "hard" with melting points above 700 degrees C. These can be used on items that will be hallmarked. Most people will use a flame for these temperatures.

I hope this explains the confusion.

[Author]

Posts