Welding or Bolting vs gluing panels on, a science project... - Hot Rod Forum : Hotrodders Bulletin Board
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Old 05-14-2007, 09:39 PM
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Brian Martin,Freelance adviser
 
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Welding or Bolting vs gluing panels on, a science project...

Well, we have talked about this a number of times, can "gluing" panels on a car possibly be as strong as welding it on. Well, my 10 year olds science project may have the answer!

He cut 12 pieces of 20 gauge steel. We then welded them together in pairs. We butt welded with the MIG, "plug welded" with the MIG, spot welded with a $20,000 ProSpot STRSW and drilled 1/4" holes and bolted two as well. HE (grinding and gluing them by himself) then bonded with Winzer Universal Panel bonding adhesive another piece of metal to each of the pairs of welded and bolted sets.

We put clamps on them and pulled them apart using the Chief frame rack at work (10 year old boys love destroying things, don't they?).

Here are the results, the glue won every single time! Pretty impressive I would say.

Brian


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Old 05-15-2007, 12:07 AM
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And how much force was needed to pull the welds apart?
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Old 05-15-2007, 03:47 AM
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Yep same question?
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Old 05-15-2007, 06:54 AM
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I'm guessing if he pulled with a frame jack, there wasn't measuring equipment involved.

The reason the glue wins is because a) there is more joined surface area involved and b) in the case of the welds, the heat creates a stress concentration... The heating and cooling makes the metal locally stronger, but at the edge of the heat effected zone what happens is that the non-heat treated metal is put under greater stress because it has to allow for greater displacement because on one side, metal is displacing normally and on the other side, the heat treated metal is displacing less. I'm not sure I explained that clearly or correctly though.

Where the glue will be more likely to fail first would be under a bending load, or where you're trying to peel the panels apart.

But I have to say, that's a pretty good science project, well done!
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Old 05-15-2007, 08:12 AM
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Force, let me put it this way, our trial test was with two pieces spot welded together. Now, I was setting up the spot welder and showing him how to use it and so forth so we put about six or seven spot welds across it. WAY more than you would on a car or what the factory does. In that test the metal at the clamp ripped before the welds failed.

We plan on doing the test again, this time with the Mythbusters "Make the glue fail be damned" sort of aditude. We will be adding more welds, butt welding it completely across and reducing the glue area. And yes, there will be a "peeling" sort of test as well. But that is not the sort of forces that the metal is up against.

Force? Don't know how much, the gauge was right in the way where we were forced to work behind a car that was on the rack. Next time we do it I'll be sure to have access to the gauge. I do know that the bolted panel appeared to have the most resistance. It held for a LONG time, I couldn't believe it.

The interesting thing here is, I have been welding for 30 years or more. I was using a $1500 220 volt MIG welder and a $20,000 spot welder (Though he basically did the spot welding by pushing the button ) . My son is 10 years old using the $30 glue for the first time. He used a HF $10 angle grinder and a 36 grit disc to clean up the metal, then using the free manual applicator applied glue.

The glue learning curve is a hell of a lot less than the welding!

Brian
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Old 05-15-2007, 08:23 AM
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Try bending flanges and then join them. For this trial, you should see the glue fail first.
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Old 05-15-2007, 08:59 AM
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I'm in the aerospace industry and we use adhesives quite a bit. As others have noted, bolts and welds result in point loads. This can require local reinforcements (adding weight) and actually result in a weaker part.

Bonding provides a much larger surface area and can be stronger. A bonded joint is almost always stiffer, which is why many new cars use adhesive bonded panels. The problem is that you need to be sensitive to how you bond. Adhesives are very good in pure shear, pretty good in pure tension, and completely horrible in peel. Design of the joint is therefore very important.

Workmanship is equally important. Any contamination (oil, grease, dirt) will cause bond failure. Surfaces need to be abraded. We actually use an epoxy primer on the surfaces prior to bonding. This allows a proper surface prep then protects the surface. You simply wipe it down with solvent prior to bonding.

Depending on the adhesive, you can get materials that are very strong but brittle or materials that are less brittle but also less strong. There's a range of products available, depending on the application. Finally, most adhesives have a relatively low allowable temperature range, which can be a problem.
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Old 05-15-2007, 10:31 AM
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My only concerne of adhesives is its lifespan.
I'm sure they're more than strong enough.
To many are super strong when new but weaken over time.
At some point in time most all adhesives crystalize and deteriorate.
(It may take 100 years but eventually.)
Hopefully it'll take a long time like that with panel adhesives to
where it'll outlast the car and is not a factor.
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Old 05-15-2007, 11:50 AM
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Great project!
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Old 05-15-2007, 12:23 PM
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Great test Brian.
My hat is off to you for having the balls to publish your
findings. (due to the chance of opposition and ridicule ).
I need to make you up a certificate for it
It will definetly read "Certifiable"
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Old 05-15-2007, 01:05 PM
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Thanks Guys. Jim, what this test "proves" is limited to the test, if that can't be understood and someone wants to give me a hard time, so be it.

I think it is pretty clear, as well as it's limits!

I was talking to my boy this morning about some of the things posted about the test by others and we will be doing it again with some different tests and I can't wait!

Brian
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Old 05-15-2007, 02:37 PM
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Quote:
Originally Posted by jcclark
My only concerne of adhesives is its lifespan.
I'm sure they're more than strong enough.
To many are super strong when new but weaken over time.
At some point in time most all adhesives crystalize and deteriorate.
(It may take 100 years but eventually.)
Hopefully it'll take a long time like that with panel adhesives to
where it'll outlast the car and is not a factor.
Jim, I got to thinking about this. First off, the metal near welds is the first to go when rusting....would the adhesive be better, even though in many decades there may be some integrety lost? Would the loss over many decades be any worse than the normal integrety loss from corrosion?

I honestly don't think it much matters. The car that is not cared for will deteriorate in whole, every single part, until it is not useable. The ones that are cared for well will probably hold up much better as a whole.

I mean, I have to wonder what THIS adhesive would look like if it had been used on some Model A back in 1931....would it still be solid after 75 years? I don't know. But any other Model A body still needs a lot of attention anyway.

I don't know, I do know that these adhesives are being used in everything from space travel to TV and radio antennas hundreds of feet in the air! I think it just isn't something we need to even think about. We will be dead and gone and so will our children before it fails, if it ever does.

Brian
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Old 05-17-2007, 07:38 PM
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Brian Martin,Freelance adviser
 
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Well, the projects were judged today by some out of town science guy and out of 60 kids he came in second! This was a BIG deal for him. He doesn't usually get very good grades and struggles a lot with school so this was a shot in the arm.

Brian

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Old 05-17-2007, 08:58 PM
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That's a cool test, nice job. Used in the right application the adhesives are definately better than welding, they each have their strong and weak points.
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Old 05-17-2007, 09:42 PM
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cool, him winning second place and all. Someones got to ask, what took first?
I always heard too that adhesives perform very when trying to pull apart from the ends, but not so good in peel.
I can say when removing glued on panels on fiberglass hoods at work most will require a bit of heating to get apart, but some older dryed out fiberglass it seems to come off pretty easy in spots. Not like you can exactly weld fiberglass, but something I've noticed.
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