DIY Stress Relief?

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Um... not this kind -> I'm looking to weld up mild steel plates and tubes/channels, machine them, embed them in epoxy-granite (if you don't know what that is, there's a reaaaaallllly looooong thread about epoxy-granite over on CNC Zone - see below for links) and not have the weldment move during machining or later over time.Material thickness will vary from 0.120" to possibly 0.500" (if my hopped-up HF Dual-Mig 151 can handle it... it's still in pieces so we'll see just what it's capable of when I get it together). Given the equipment at hand, I figure that the thicker parts will need pre-heat and insulation in addition to possibly doing the welding in multiple passes... and if I have to scale down my ambitions, that's OK (the whole thing is experimental anyway, so....)So, I figure that I ought to be doing some sort of stress-relief on the weldment prior to machining it....I've read about people using needle-descalers on welds, as well as vibratory techniques; used both with and instead of heat treatment.Anybody here have any experience with any of these techniques? Does the needle-descaler actually do anything useful as far as stress relief is concerned? Anybody here ever DIY up a rig to do this kind of stuff?I was thinking of perhaps cooking up a DIY heat treating oven out of a fairly beefy barbecue sourced from Craigslist and modified with refractory insulation, extra burners (if needed - depends on how efficient the insulation makes it) and a thermocouple-controlled temperature management system (like one of those PID controllers available on eBay).Any Ideas? Opinions? Rotten fruit? ----------------------------------------------------------------------------------------Epoxy-granite subforum: http://www.cnczone.com/forums/epoxy-granite/Epoxy-granite thread: http://www.cnczone.com/forums/epoxy-...ete-frame.html
Reply:You may want to try eng-tips.com. I think you may be able to connect with a weld engineer or a metallurgist.
Reply:As for the needle gun, i understand this to actually impart stress into the area, which allows it to withstand cracking better.  Sometimes we shotpeen radii that we worry are in a heavily stressed area.  This helps avoid fatigue cracking.  Sort of a work hardening, but on the surface only. Stress relief is allowing stresses to decrease in the part by heating it up in furnace with no constraints.  Hopefully, the part has minimal stresses when the process is complete.  After you machine it, the part won't shift.  We usually heat treat at 50 degrees F below tempering temperature.  1 hour per inch of thickest cross section.  It'll probably fall in the 1050 F range.  I forget the rise and fall rates as I'm not a weld engineer.  Basic idea seems to be slow ramp up and slow down. Keep it in the furnace until some temp that isn't critical then air cool.Getting someone to heat treat for you might be cheap enough to avoid building your own.   They could also probably give you common heat treat methods since you're talking about mild steels. Just fyi, a lot of our mild steel wps's avoid heat treat since we are in the repair industry and no one wants to heat treat machined parts.  Maybe you don't need to heat treat.  Our parts get hot in operation.  Yours won't if I understand correctly. If it does need ht, it may also mean that you need to temper first to get consistent material properties. Sorry for the long response and also not knowing the answer, lol :-)Cheers,
Reply:thought I was going to need a jar of vasilene....lolOf all the things I lost I miss my mind the most...I know just enough about everything to be dangerous......You cant cure stupid..only kill it...
Reply:Last edited by MinnesotaDave; 08-22-2015 at 12:11 AM.Dave J.Beware of false knowledge; it is more dangerous than ignorance. ~George Bernard Shaw~ Syncro 350Invertec v250-sThermal Arc 161 and 300MM210DialarcTried being normal once, didn't take....I think it was a Tuesday.
Reply:BrittToo much data - and no info - start over.Opus
Reply:Sheesh.... I come here looking for advice from serious minded people who know what they are talking about, and all I get is a bunch of boobs! Weelllll... almost two weeks ago I ordered a couple of books from the James F. Lincoln Foundation that cover the subject (in particular "Metals and How to Weld Them" - for $10 + s&h it's hard to go wrong with that one) and have been reading them. I think I'm going to try the heat-treating approach, so I've also been looking at DIY forges and backyard metal casting stuff online... and as long as it's properly insulated on the inside, I think a decent sized propane BBQ (like, say, one with a 60,000 BTU burner on it) will do the trick. I've also ordered "Gas Burners for Forges, Furnaces, and Kilns" from Amazon, so I'll see what that says about the subject too...I might make it Arduino controlled instead of using an eBay controller, so that I can set up temperature profiles for various tasks...
Reply:Originally Posted by engineer1984As for the needle gun, i understand this to actually impart stress into the area, which allows it to withstand cracking better.  Sometimes we shotpeen radii that we worry are in a heavily stressed area.  This helps avoid fatigue cracking.  Sort of a work hardening, but on the surface only. Stress relief is allowing stresses to decrease in the part by heating it up in furnace with no constraints.  Hopefully, the part has minimal stresses when the process is complete.  After you machine it, the part won't shift.  We usually heat treat at 50 degrees F below tempering temperature.  1 hour per inch of thickest cross section.  It'll probably fall in the 1050 F range.  I forget the rise and fall rates as I'm not a weld engineer.  Basic idea seems to be slow ramp up and slow down. Keep it in the furnace until some temp that isn't critical then air cool.Getting someone to heat treat for you might be cheap enough to avoid building your own.   They could also probably give you common heat treat methods since you're talking about mild steels. Just fyi, a lot of our mild steel wps's avoid heat treat since we are in the repair industry and no one wants to heat treat machined parts.  Maybe you don't need to heat treat.  Our parts get hot in operation.  Yours won't if I understand correctly. If it does need ht, it may also mean that you need to temper first to get consistent material properties. Sorry for the long response and also not knowing the answer, lol :-)Cheers,
Reply:The specific application that I'm concerned with right this second doesn't have a fatigue issue - because if it's moving that much, something has gone horribly, horribly wrong...  but that doesn't mean that other situations I might be interested in won't... so, good to know.