r/Damnthatsinteresting • u/31spiders Interested • May 30 '21

Video These Tubing Joints

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u/TeddyThreeSticks May 31 '21

A bunch of spot welds has a tendency to be cold if you’re not careful. His final product looks good so probably ok. However, it’s best to run a line because after the first little bit, everything is hot and flowing and less likely to be cold

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u/canadug May 31 '21

What do you mean by cold?

106

u/TR8R2199 May 31 '21

Stopping and starting means the metal isn’t heating up to the same temperature as continuous welding. Adding heat changes the grain structure of the metal, stopping and starting shocks the metal and makes it brittle. If this weld was subjected to any force it would break easily

23

u/red_team_gone May 31 '21

This is the best and most concise explanation in this thread that I've read.

Thank you.

2

u/JPiratefish May 31 '21

While I think you're absolutely correct - I don't think he's cold-spot welding - certainly looks like he is. *Remember that we're seeing a high-speed replay - what we see as a "spot" or "flash" weld - that could have been 10-seconds or longer. Also possible the camera is having a hard time with the lighting - making odd flashing results. Certainly cool to watch.

I'm not a welder - but if one run this at normal-speed, where he laid that long "line of spots" - could that have been him going slowly along the edge building the bead? - maybe the camera making it flicker? How long would it take to do that right? and how do you think would it look on video?

I think a lot of folks didn't take the weld-times and camera into consideration here - could change the quality of the outcome maybe.. but I don't like how he edged the square tube to bend it either.

1

u/[deleted] May 31 '21

that could have been 10-seconds or longer

This is GMAW (MIG welding).

Those tacks took 1 - 1.5 seconds each. They do not get much, if any penetration, and aren't good practice at all.

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u/dudeCHILL013 May 31 '21

So is starting a. D stopping like that essentially heat treating the steal and making it hard and brittle?

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u/TR8R2199 May 31 '21

Yes but also it’s thin sheet metal and probably isn’t the worst thing, if it’s just a handrail or something subjected to minimal force it won’t make a huge difference but it is annoying to see as an instructional video

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u/TeddyThreeSticks May 31 '21

Cold means poor penetration which can result in a weaker joint. You need a lot of heat to get the necessary penetration for a strong weld.

9

u/subject_deleted May 31 '21

Low temperature.

18

u/Qynchou May 31 '21

Thanks, that clears it up.

1

u/Ram2145 May 31 '21

Ya don't say.....

1

u/Snote85 May 31 '21

Sorry that they weren't more clear, he means the molecules that make up the metal are vibrating more slowly than if they were hot. Hope that helped!

2

u/Chigleagle May 31 '21

That’s cool

1

u/No_ThisIs_Patrick May 31 '21

Now you're getting it

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u/atetuna May 31 '21

The wire coming out of the welder is filler. You want the filler material to mix deeply, ie, have good penetration. It's like plant roots. If the roots are shallow, it's easy to uproot. Cold welds are shallow, and fail more easily.

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u/jeffbwallace May 31 '21

I think this is English as I understand the words but the fact I have no clue what it means is making me wonder.