Question for judges and experienced builder connected with welding

[PatrykBindacz]

If such a poor fitting is acceptable? If not, what can be done to prevent disqualification?

Kind regards

joint.jpg

[Claude Rouelle]

Do you think that this is the best welding that you can do to prepare yourself for a mechanical engineering career? What is your definition of excellence and how far do you think you are from that definition?

Here is my take: The question is not whether this is acceptable by technical inspection or not but if you are proud of this welding. After all FSAE / FS competition is much more about offering you the chance to get better prepared for your engineering career than the pass / not pass technical inspection.

By The Way... who are you?

[Drew Price]

To more closely answer your question, there is a stipulation in the rules which requires that all tube joints be welded 360* degrees around their circumference, so you need to join that weld bead all the way around until it meets the weld on the other side of the joint.

This is true of any tube joint in the required structural portions of the frame, and should be followed for any other tube fabrication on the car.

[Jonny Rochester]

It looks like you are TIG welding. I am TIG welding our chassis also, but MIG can also be used if you like, which would be faster and easier. If the tubes fit together nice, a good TIG weld will be a bit lighter and more pro looking.

To get a better weld, it helps to have the tubes fitting together better before you start to weld. But with practice, you can learn to fill the gaps you end up with. We end up with lots of gaps also, but I do fill all the gaps with weld.

For the corners as in your picture, adjust your tungsten tip out a bit longer, maybe to 10mm, if you normally have it out 7mm. This helps get in the corners. Point the arc towards the full tube, as it can take the heat.

[Alumni]

Keep in mind that any welded joint is a major source of compliance in your chassis. The weld is always weaker than the surrounding tubes, and if you have huge gaps resulting in the tubes being made of weld you're going to end up with a floppy chassis. Which will in turn snowball into a cracked chassis.

[Charles Kaneb]

I'd fail that at a tech inspection at a kart track. It only takes a few hours at a grinding wheel to know how to fit tubes together properly.

Get an air-powered rotary tool with a carbide burr and the thinwall stuff used in FSAE cars will be easy to get right.

[Jonny Rochester]

Keep in mind that any welded joint is a major source of compliance in your chassis. The weld is always weaker than the surrounding tubes, and if you have huge gaps resulting in the tubes being made of weld you're going to end up with a floppy chassis. Which will in turn snowball into a cracked chassis.

Sorry I can't agree with this. A long unsupported tube is a source of compliance. The welded part is the strong bit (unless you are very very bad at welding).

If the gaps are properly welded up, it is still strong. The bad thing then is that you have extra weld and the chassis becomes heavier, (bad if you are worried about a 31kg chassis vs 30.5kg).

[Alumni]

Jonny, I think we're playing different games in different stadiums across town here. A long unsupported tube is obviously compliant because of poor triangulation.

A weld such as the above will be more flexible than one fit and welded and treated properly, which will still be more flexible than the same joint made of billet (if it were possible.)

If you could get a perfect weld and fitment around the entire tube, then the difference would probably be negligible. From the discussion on the UTAS thread, you probably have more experience than both myself and virtually all members of this forum so you are probably much closer, but will never reach that theoretical perfection.

If anyone doesn't believe me, it would not be that difficult to test different weld methods and post-treatments and bring the results to design with you!



Now - for some other random blatherings...

Did you know that weldments are not allowed in most anything that would be considered "life critical" in the aerospace industry? This is because even done to the best that modern metallurgy and science allows, they are still considered to be major stress concentrations and weak points, to the degree that it is standard to assume that your weldment has as much as 20% less strength than a similar stamping or casting etc. due to the fact that they are always considered to have internal cracks and low fatigue life.

[Jonny Rochester]

There is no post treatment. We are just talking about mild steel here. The tube is mild steel, the weld material is mild steel. No heat treatment can be done or is needed.

The tube is 1.6mm wall. The weld thickness varies, but maybe 2.5mm thick. If the weld material has 20% less strength, then which part is stiffer?

[Z]

Patryk,

As noted above, continue that weld all the way around the joint and it will be fine. Follow Jonny's tech-tips above.

I might grind off some the high points to the left of the arrow for a better look (use small angle-grinder, linisher, or 6 mm round-file for inside the "V"). If in doubt about the strength, then add more weld metal! Contrary to comments above, you should be able to make these sorts of welded joints much stronger than the surrounding tubes (ie. test to destruction, and the tubes should fail, NOT the weld).

Do NOT paint your frame until just before comp, or at most just give it a light undercoat. Chances are that during testing you will find that you have to add lots of little brackets, tabs, etc..., which is always frustrating when done after the final "bling" paint job.
~o0o~

FWIW, many, many lifetimes ago, in a universe far, far away, I worked as a "Welding Certification Assistant" (or some such...), on everything from off-shore oil-rigs to nuclear power stations.

Interestingly, all the super-critical weldments on these were done with good old-fashioned STICK-WELDERS (ie. "MMA", etc.)! Yep, all the high-pressure oil pipelines with internal pressures exceeding the yield strength of mild-steel (!), the nuclear containment vessels, etc. I always laugh when "real racers" suggest that "stick-welding is an abomination only suitable for farmers mending their front-gates".

The reason that welded components are not allowed on (some) critical aero components is primarily because those parts are small enough that they can be easily made from a single forging, or machined from billet, or otherwise made in one piece. There is no need to build-up the parts via welding. Secondly, the types of welds I mentioned in above paragraph took at least a couple of days to prepare (bevel joints, preheat, etc.), another full day to do the welding, another day or two for the stress-relief ("heated blanket" wrapped around weld), and then about a week or more for the Non-Destructive-Testing.

The NDT was mainly ultrasonic and X-ray, with the X-ray using a radioactive "bomb" (ie. a lump of "bad stuff" normally kept in a large lead box). This naturally required clearing of a large area of the worksite for a day or two while the "bomb" worked its magic. The ultrasonic testing was a lot quicker and cheaper (so always done first), but it relied on the skill of the operator and his "interpretation" of fuzzy lines on a CRO screen. The slower and more expensive X-rays produced a photographic record, so were preferred by the lawyers.

Any slag-inclusions, porosity, or cracking found near the root of the weld meant that the whole weld had to be cut out, and back to square one! Small defects near the surface were locally cut-out and repaired.

So, quite obviously a long and thorough procedure. And for the same reasons (ie. cost!) the finished welds were designed to be AT LEAST as strong as the surrounding (significantly cheaper) material.

Bottom line, I would have no qualms welding up an FSAE frame with a stick-welder. My NDT would be no more than a quick "visual inspection".

Z

(PS. Just saw Jonny's last post. AGREED!)