okay here's what's going on...

I'm have an appointment to put on my SFCs tomorrow morning. They will be welded on, and they are MAC SFCs. I have a 92 Z28...

For some reason I went and told my dad I'm welding SFCs on my car tomorrow, and oh boy, here it comes, a lecture in metalergy.

He is telling me that when metal is heated, it loses its "crystaline" structure. He told me after a time that part of metal that was heated will lose all it's strength and cracks will appear. He is basically screaming at me telling me that I will ruin my car by welding these things on.

I told him that what he is telling me is complete and said I'm doing it anyway.

Anybody have any input on this case. He told me he took an engineering course in university and many metalergy classes and he knows what he's talking about. I would like to prove him wrong...

 

I've never heard that one.

Would you mind shrinking your sig just a tad, so that it will fit on the screen, b/c what happens is, it makes the text run over, and we have to scroll back and forth to read.
Just asking politely..

 

Ask him how all the rest of the car is held together...

When they weld them on, most likely they'll use some sort of a wire feed welder (MIG) which minimizes the heating of any parts other than right where they're welding. Kind of like all the frame welds that are already there and not failed yet.

 

ya. think about all the things that are welded.... what would be the purpose of welding it it made things weaker..

 

well he just gave me a whole lesson and told me that when they heated the metals to build the car, they heated them to a certain temperature, and the strength of the metal was based on what temperature they heated the metal to, and how long they let it cool.

If they cooled it fast, then the metal would be brittle. If they cooled it slow, then the metal would be flexible.

He says that if the mechanic applies heat to my frame he will ruin this "crystal-line" structure and the properties my metal has now and... lada da...

 

maybe with torch welding......... but not with a mig

 

Don't ask him like this...but have you ever seen them put a car in an oven at the factory...for welding purposes?

I know when you weld some types of aluminum and cast iron you need to pre heat it. And I would say that you car frame is neither aluminum or cast iron.

If it really weakened the car that much they wouldn't do it as a reenforcing strategy. I know any amount of logic won't help because my dad tells me the same kinda stuff when I walk around the house the N2O bottle.

 

O.K., I'll play Devil's Advocate. I'm also afraid I'll have to agree with him. Welding metals requires heating the base and added metal (and/or filler material) to a point of being molten, to alloy the pieces together. This process WILL affect the microcrystalline structure of the metals and weaken them. In that respect, he is 100% correct.

However, from a practical standpoint, welding is also often the most effective means of joining two pieces of metal. Despite the weakening of the surrounding material, the strongest attachments are typically through welding.

A trained or certified welder will understand this metallurgical "Catch 22" and adjust the heat settings accordingly. He/she also will not quench the area immediately to provide the best possible annealing and may even reheat the area overall, then quench to normalize the parts (preventing hard and soft spots). Of course, under your car this might not be practical, so cross your fingers and hope the welder uses the correct minimum heat settings and works quickly and in several areas at once instead of building a long, continuous bead.

The factory uses resistance (spot) welding to connect the sheet metal while creating the smallest possible weaknesses. They also have the advantage of welding bare metals and finishing it later to prevent corrosion. Learning something from them, make sure you finish the area after the welding to prevent corrosion.

To quote a certified welder I know, "Welding is one of the worst things you can do to metal. It is also the best way to stick metal together."

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Later,
Vader
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All my life I've been searching for something. Something never comes - never leads to nothing...

 

i'll have to agree with him and Mr. Vader. welding does indeed change the grain structue of the metal ,as does machineing, stamping and any other metal working process. welding is the worse thing you can do to a piece of metal from a metallurgical stand point. it also is one of the easiest and most cost effective ways to join two pieces of metal. usually the weak point is not the weld nor the unheated metal but what is know as the heat affected zone (HAZ). this is the area where internal cracking will occur frmo residual stress and hydrogen embrittlement. there are methods and process that greatly reduce the chance of cracking in the weld or base metal. most likely you have A36 mild steel SFCs and similar metal in the car and any metallurgical problems would be very remote. get them welded and don't worry about it. the only real problem you might encounter would be from a low quality weld and that's not very likely because the metal is so thin it's hard to not get good penetration and fusion.

 

Ye, hate to say it but technically your Dad is right. Many of a metal's properties are determined by the cooling process it goes through when it is formed. When you weld it you bring the surrounding material up to a temperature that will allow the molecular structures to disorganize and go back to a different lattice structure. But if it is allowed to cool at the same rate that it was meant to when it was made it will go back to the intended structure. However if the welder is not certified and does not know what material he is working with he may let it cool to quickly and the molecules will not mesh back together in the strong structure they where meant to be. This disjointed rearrangement leaves voids in the lattice stucture which easily form cracks.

But usually quenching is required to cool the metal to quickly. That is why bridges have such strict welding guidelines. There is water in the enviroment so quenching is almost unavoidable. So as long as your welder is not over there throwing buckets of water on the welds to cool them off you should be ok.

 

LOL.. I came home with my CO2/Argon bottle (for MIG welding), walked it in thru the kitchen, and said "Dad, look what i just bought!" "What the hell is that in the house for??? Where do you plan on putting it?!?!" "In the garage." "What?!?" (laughs) But as soon as I told him the thing couldn't explode (and that's why I didn't go with oxy/acetelyne welding- don't want Those bottles falling over!), he understood and calmed down. LOL... just remembering the look on his face...

Oh, but yeah, like was said, the SFC's will get welded on to the car with processes meant for similar metals... your car's already got tons of welds on it. As long as you go to someone who knows what they're doing, you'll be fine. My frame was welded back in '96, and it's holding strong. The suspension still aligns, the car isn't crabbing or cracking in half or anything else dangerous. The shop I went to knew their stuff. If your shop grabs a big old arc welder with the amperage at it's highest setting, yeah, they'll have a bitch of a time welding that on, never mind any metalurgical problems. And if nothing else, you could always talk to them about it, and have your dad talk to them when you bring the car in.

 

Have someone post the pic of the stress cracks that appear around the back corner of the side glass that are caused from too much flexing. I'd perfer rearanging the crystilyne structure in a small area of my frame as opposed to a big crack on top of my car. Oh well just my 2 cents, hopefully somone knows the type pic I'm talking about.

David

 

you mean these??

 

That's them!

 

Tell your dad, he should call the navy, and quick before the fleet cracks and sinks!!

Applying heat to a piece of metal is a good way to ruin it, your dad is theoretically right, but he is forgetting that welding is a highly developed process. It took many years to figure out how to properly weld metal. That is why a welding certification is worth more than a piece of paper. Unless you going to weld it with oxyacetylene ( and poorly at that) you'll be fine. MIG is the prefferred process for this job, and it works very well.