CD wire butt welder - Page 1
Forum section: electronics / projects

author: richcj10
author_rank: Unknown
timestamp: September 19, 2012, 02:00:22 am
content: I am working on a system that gets up to a high operational temp (250+ C). I need to attach two wires to each other. I can't use solder because it would melt off. I used to use metal crimps but it was very hard to get a good crimp. I think using a wire butt welder would work. Any ideas on implementation? This is pretty fine wire. ( 24-28 Gauge) Some of the designs out there would seem to just blow the wire away instead of welding it together.Thanks,Rick

author: Paul Moir
author_rank: Frequent Contributor
timestamp: September 19, 2012, 02:17:16 am
content: I've done a bit with a capacitor, but nothing that big. Worked OK.You can TIG copper wire together (or strange stuff like thermocouple wire) if you have access to a rig. Otherwise, silver solder is another option. It liquifies around glowing hot so is good for high temperature service, and all you need is a propane, butane or MAPP torch to use it on something small. We use this for soldering heater wires together. Also there's some high temperature heat shrink out there for insulation. I think I can get a digikey link for you if you want.

author: notsob
author_rank: Frequent Contributor
timestamp: September 19, 2012, 02:24:57 am
content: This may be totally of no use to you - but have a look anyway ( cap discharge spot welder)http://www.pittnerovi.com/jiri/hobby/electronics/welder/index.html

author: richcj10
author_rank: Unknown
timestamp: September 19, 2012, 02:32:42 am
content: I did see this. I don't know what it will do to small wire...I was hoping to go simpler as well.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: September 19, 2012, 03:54:33 am
content: See now, you made me go into the shop.I got a pretty good weld with 63000uF @ 30v in some 26AWG solid core. The wire was twisted together and the end welded to form a ball. The energy was delivered via a pair of #14 solid core wire. I only got dross on DCEP but got good welding on DCEN. (Translation: attach the positive wire to the wire to be welded, then touch the negative to the tip to form an arc.)No shielding gas = no guarantees, but it's so brief I imagine contamination isn't a big deal. You'll need a lot more duration if you want to do resistive welding rather than arc.

author: richcj10
author_rank: Unknown
timestamp: September 19, 2012, 03:59:26 am
content: Sweet! This is a start!For clarification, did you attach the positive side of the cap to the wire. Then you connected the negative wire to the center of the twisted wire connection?Thanks,Rick

author: Paul Moir
author_rank: Frequent Contributor
timestamp: September 19, 2012, 04:16:53 am
content: Yes, that's what seems to work (and makes sense, it should put most of the heat of the arc into the work).It's tricky to get to work exactly right and I have doubts about how strong it is, but all you need to try is a capacitor & power supply. I'd feel a lot better about the silver solder, but you have to buy it by the troy ounce!PS - I assume you know the dangers, etc of this. To you and to your capacitors. Now if you don't mind, there's this green spot floating in front of me.

author: nanofrog
author_rank: Super Contributor
timestamp: September 19, 2012, 07:49:46 am
content: What was up with the crimps that they weren't sufficient?

author: richcj10
author_rank: Unknown
timestamp: September 19, 2012, 10:39:22 am
content: When you have 6 - 2pair (2 T/C, 2 heaters, 2 sensors) wires into a one inch area the crimping tool is too big to help. We had to crimp them by hand. When we did this to the very fragile wires we would sometimes break them in the process or not get a good crimp before the hermetical seal was added.I need to join stainless steel to platinum and stainless steel to nichrome.

author: nanofrog
author_rank: Super Contributor
timestamp: September 19, 2012, 07:29:46 pm
content: Quote from: richcj10 on September 19, 2012, 10:39:22 amAh, OK.I assume that assembling the wires (crimp, weld, silver solder) outside of the space limited setting isn't possible (pre-assemble then install into the enclosure).So given the dissimilar metals, I'd say resistance weld would give the best results in such a limited space (heat required for silver solder might not be acceptable; for example, 15% silver would melt @ ~800C).

author: aluck
author_rank: Regular Contributor
timestamp: September 19, 2012, 09:45:06 pm
content: Google for "DIY spot welder" - there are a plenty of homemade designs. Nothing fancy, just a big transformer and interrupter circuit.

author: G7PSK
author_rank: Super Contributor
timestamp: September 22, 2012, 09:34:40 am
content: For thin wire you would be better of with an ultrasonic welder.

author: richcj10
author_rank: Unknown
timestamp: September 23, 2012, 03:51:10 am
content: Thanks,I think I will try the resistance welder first just because it would be the easiest to build.Thanks,Rick

author: G7PSK
author_rank: Super Contributor
timestamp: September 23, 2012, 05:10:34 pm
content: I did not notice at first but I see that you want to join dissimilar metals, you may well find that this is not possible using a fusion process. This is where friction welding such as ultrasonic and rotary or friction stir welding techniques are useful.

author: IanB
author_rank: Super Contributor
timestamp: September 23, 2012, 06:26:12 pm
content: Going back to the top, I can't help thinking that some kind of crimped butt splice would be the right thing for the job. Something like once of these, perhaps?http://www.molex.com/molex/products/family?key=splice&channel=products&chanName=family&pageTitle=IntroductionIf you were having trouble before, it might have been a problem with your tools or crimping process rather than the method itself. Might be worth taking another look at crimping before getting into more exotic methods where getting a satisfactory result might be even harder?

author: richcj10
author_rank: Unknown
timestamp: September 23, 2012, 06:28:44 pm
content: They only have wire nuts for 24 gauge or less. Not a crimping device.

author: SeanB
author_rank: Super Contributor
timestamp: September 23, 2012, 08:12:30 pm
content: I think the problem is the wires are thin, most Pt100 bare probes are 48SWG, as thin as a hair. Resistance welding to a thick substrate ( almost any other wire will be thick by comparison) will probably be the best, with 100% post welding optical inspection under a microscope.

author: richcj10
author_rank: Unknown
timestamp: September 23, 2012, 09:29:11 pm
content: SeanB,Are you also suggesting a resistance weld?Thanks,Rick

author: SeanB
author_rank: Super Contributor
timestamp: September 24, 2012, 05:39:24 am
content: Resistance weld, either using a folded metal foil to protect the thin wire from burning through ( thin foil folded over the other wire and welded, then slide the thin one in and weld again over the wire so it bonds to both foils) or breaking from stress. You have a problem there, if you could get a small ceramic substrate with printed metal areas to act as a termination it would be better. Place wires then IR reflow with silver solder paste, I have some that I use to solder stainless steel mesh with.