Chief Delphi - Massive Hit

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No matter how skilled a welder, there are material properties to consider.

In extruded form it would have been 6061-T651:
tensile strength of about 45ksi and yield of 40ksi.

After welding is in the -T0 condition:
tensile strength of about 18ksi and yield of 8ksi.

Eventually 6061 will age back to T4 or so, which is pretty close (70%), but it requires heat treat to get to T6/T651 strength levels.

Compared to the base (original) material, a welded area in aluminum can be a significant weakness that needs reinforcement.

Quote:

Originally Posted by animenerdjohn (Post 1271822)

At Hub City we had a pretty fun collision with 16 :rolleyes: . You can see the numerous places our frame split. We Covered the whole thing in tin foil and had it rewelded (This time without the faces being ground off). No issues. http://i.imgur.com/h1bglpH.jpg

Quote:

Originally Posted by Kevin Sevcik (Post 1272165)

I have to say, I have little sympathy for people who go to all the trouble of welding up a frame, only to grind all the reinforcement off. As you discovered there, unless you've done a proper bevel prep on the edge, a butt joint is quite likely to have low penetration and little fusion of the base metal. And so you can end up with fractures that follow the original seam quite impressively. Any time one of my mentors suggests we weld something up and grind it flush, I give them the evil eye and they usually decide that perhaps we don't actually need to grind it, actually...

This x 2.

I would prefer an open root weld in this situation over a bevel, less prep effort and virtually no chance of a LOF defect. I say having written WPSs and earned an AWS certification in TIG welding aluminum.

Quote:

Originally Posted by btslaser (Post 1274575)

A flush weld with the proper relief bevel and penetration would have been fine (it was 1/8" wall 1x2 6061 tubing). Had the welds not been ground flush it also would have been fine (as was the case for the NASA repair welds on one side only that lasted another regional and the championships). We told our sponsor NOT to grind these welds but after they were smooth and sexy the welder assured us that there was plenty of penetration. Lesson learned... we should have sent it back.

Unless the welder has (or had) a certification in the weld they did, they have no qualification to make such a statement. Welders are not generally structural engineers, "plenty of penetration" might not be strong enough even if the weld did have full penetration.

Also, as mentioned by three_d_dave, welded material is generally weaker and needs the extra material provided by the weld bead even with full penetration.

This is what a single-sided, single-pass aluminum weld should look like:

Quote:

Originally Posted by three_d_dave (Post 1274597)

No matter how skilled a welder, there are material properties to consider.
...
Compared to the base (original) material, a welded area in aluminum can be a significant weakness that needs reinforcement.

Agreed. I actually ran some FEA on the front portion of the frame and felt it was adequate (had it been properly welded) even with the reduced strength in this area. The front was actually lower on my list of concerns as there are fairly large cutouts and holes in a WCD frame that reduce the strength more than 70% in certain areas.

Quote:

Originally Posted by JamesCH95 (Post 1274601)

I should have inserted this in quotes or added an icon... I said this rather tongue in cheek. There was virtually no penetration.

For extra overkill points, the next time a welder says that, you can send the part off for ultrasonic inspection to see if it really does have plenty of penetration.

Quote:

Originally Posted by Kevin Sevcik (Post 1274912)

For extra overkill points, the next time a welder says that, you can send the part off for ultrasonic inspection to see if it really does have plenty of penetration.

Ha!

Heck, even a mirror to get a look at the back of the weld...