Welding Tips and Tricks

I came across an aluminum welding project on the internet, which involved peening a "built up" aluminum TIG weld bead which was to repair a cast aluminum engine block.



There are also other pictures of the sequence before and after the peening on this page:
http://www.aftracingheads.com/project15.html

I'm guessing that this peening was likely done by holding a ball peen hammer over the bead, and smacking that with another hammer, is that right?

I've heard about peening a cast iron weld before, to reduce tension in the weld bead, and reduce the potential of the cast iron cracking. Would this aluminum peening be done also to reduce tension stresses in the weld bead? Could it be to work harden the metal to build strength? I'm just curious what this technique is for, when to use it, etc.

I dont know anthing about the process but, it gives a cool appearance..

Yeah, might be sort of like blasting really large steel shot...

I doubt appearance was the reason for them doing that step however, because if you look at the next pictures in their sequence, they machined it flat:

Lot of myth's out there about peening welds ....... seen a lot of guy's do it. It's kind of reminds me of guy's in the gym bench pressing with there feet up on the bench. Most do it because they saw somebody else do it and it looked cool, while there is little to no training science to back it up ( reduces your overall stability, and places your sacro at the wrong angle, and sinks your chest ). Weld peening is generally inefective and un-called for in all but a few cases. It is done by directly striking the weld with the peening hammer. What is effective and sometimes called for is a controlled reduction in the heat, in an oven, grill, etc. To slowly cool the material thereby reducing internal stresses.

Trackmaster,
you are right when you say a lot of people do it because they saw someone else do it and also that it is only called for in specific situations, but there is actual data to prove that it is effective "when done properly". That is the key, most , in fact almost all do it wrong therefore offering little in effect causing most to think it doesn't work. Most of the peening of welds is done on cast iron. As for the peening of aluminum, for me that is a first. If the peening on this aluminum was just done on the surface after the last bead was laid, it would have very little effect. If it was done from the very first bead and continued till the last then it would have much more of an effect of relieving tension in the welded area. I believe , and this is obviously a guess, the the reason behind the peening was 1. that it was a casting and 2. it was machined after welding. Anytime you do maching after heavy welding, especially on something this small, you want to relieve as much stress in the weld area as possible or you risk cracking again.

Jim, I do stand corrected in that i neglected to include mentioning Cast Iron. It is a different beast altogether, and somewhat unpredictable in results depending on the quality and service life that the part has experienced. I guess i was reffering to other metals, carbon steels, Chromoly 4130, 6061 Aluminum etc. where in my experience and training in the aerospace field as well as aircraft engine mounts, and racing frames, peening does not remove stresses from welding from a purely metallurgical stand point. These types are "normalized, tempered, stress relieved, or hardened, as you will by what is done with the part after it's welded. Ie, how it's allowed to cool, or be re-heated to a specific tempurature, time, and scheduled cool down, or sometimes simply precipitation hardening. Fortunately most do just fine without any of that if welded properly and/or pre-heated! Not to many folks have access to a large programable oven! Really depends on what the process spec's call for. Even on cast iron, peening is most often done when "pinning" cracks in engine blocks for instance. They are best repaired by furnace welding where the entire casting is raised at the same time to temperature and the entire casting cools at the same rate. It's really more about the surrounding heat affected zone cracking than the weld bead itself. But i say if it makes ya feel better, peen away! Of course it's only my opinion & background, and i still learn new things all the time ...... lot's of skilled folks out there for sure!
- Lou

Trackmaster,
Didn't mean to offend you by my comment. Was just saying that there is data to prove that peening,"when done properly" and I stress properly, can and does relieve stress in the weld zone. Not to the same degree that PHT does but enough to achieve favorable results. But the thing is, is that almost all who employ peening as a "mild" stress reliever do it wrong. And I am only talking about cast iron, not carbon steel, chromoly, aluminum or anything else.

I don't know how it translates to thicker material, but "peening" automotive sheetmetal repairs is an absolute must. on thin (18-22ga mild steel) when you weld in a patch panel, particularly on something like the bottom of a door skin where it's big and flat, where you stop your welds (skipping around to minimize heat input) it will put a 'dart' in the metal next to the weld. if you don't hammer the weld and stretch the metal back out, you'll never get the weld flat after you're done welding. it also helps to grind some/all of the weld off before you hammer it flat, unless you're fusing the panels together w/ no rod. the weld deposit can sometimes cause you to put a low spot on either side of the weld when peening. not the end of the world, but it saves time to grind them off first and not have to hammer it out later.

as far as that aluminum piece in the OP, I'd say it had the crap hammered out of it to move the aluminum around so when it was machined, there were no low spots.

Oh man, Jim plz, no offence taken at all! I learn everyday from guy's like yourself and others. Nothing wrong at all with covering all bases, and as well we don't always have access to the "ideal or perfect" way to do things. I am a firm believer in doing what it takes to make it work! Plus who can argue with success!! And btw, i have peened many a weld myself, - Lou