Re. Best finish and Stainless Rear subframes

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nite fire - 20 Jun 2004 21:37 GMT

Having spent 6 years working at a Stainlees Steel fabricators and seen many
wierd and wonderful machines, frames and pressure vessles made from
stainless I am convinced that structural integrity of the material from a
metallugical point of view would not be a problem
However, to ensure that the subframe itself did not fail, the original
design would have to be copied faithfully and not just the relevant mounting
and pivot points set up on a jig. All bends and pessings would need to
follow the originals and any welding carried out by a coded welder. Taking
into account minor tooling costs, labour and materials you should be able to
do this for about ?1750 or so ( I have priced it out!). Then again if you
spent lots of money on full tooling, jigs, presses etc you could put it into
production, get type approval etc and realy clean up!
I mean no offence by the above but please understand that
a Stainless Steel is in many cases an acceptable replacement for mild steel
b One off fabrication are difficult and expensive.
c Sometimes you may want the best but its not really what you need.

Dave

Steve68s wrote:

> Can you get stainless mig wire?

Yes.

> ... I was thinking of making a whole rear
> subframe out of stainless steel, of a slightly thicker gauge than

standard,

We've covered why stainless steel isn't a simple direct replacement for
mild steel several times in recent discussions about stainless
fasterners. I would think fatigue failures would be almost inevitable in
a stainless steel subframe.

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Graham W - 21 Jun 2004 15:05 GMT

> Having spent 6 years working at a Stainlees Steel fabricators and seen many
> wierd and wonderful machines, frames and pressure vessles made from
> stainless I am convinced that structural integrity of the material from a
> metallugical point of view would not be a problem

Having spent 5 years studying engineering, I can tell you that stainless
steel is a very fine material, a great asset to mankind, but it is most
certainly not a direct replacement without design changes for midl steel
in automotive applications.

> However, to ensure that the subframe itself did not fail, the original
> design would have to be copied faithfully and not just the relevant mounting
> and pivot points set up on a jig.

Quite the contrary, if the original design has any sort of fatigue issue
whatsoever, stainless will make it far worse. A stainless steel replica
would have to be designed with great care to ensure no stress
concentrations occur and would probably look quite different in many key
areas.

> I mean no offence by the above but please understand that
> a Stainless Steel is in many cases an acceptable replacement for mild steel

Yes, but it *is* different, and a design which works in mild steel may
need changes in a vibrating environment to avoid fatigue.

In a static environment, the strength and stiffness properties of
stainless are usually similar enough to mild steel to use the same
design, but in any sort of vibrating load environment, it's fatigue
properties are very different and will trap the unwary engineer.

> b One off fabrication are difficult and expensive.

Far more than is justified for most automotive applications!

> c Sometimes you may want the best but its not really what you need.

Sometimes you've just left $$ out of the equation when figuring out
what's best... When you do the calculation right, stainless sudenly
doesn't look so marvellous!

>>>Can you get stainless mig wire?
> Yes.

You should use a different MIG gas too, but I believe that a low oxygen
argon mix can often do both stainless and mild steel acceptably well.

I'm no welder, but I've (not) watched some very good welders working on
my projects.

I stand by my comment below:

>> We've covered why stainless steel isn't a simple direct replacement for
>> mild steel several times in recent discussions about stainless
>> fasterners. I would think fatigue failures would be almost inevitable in
>> a stainless steel subframe.

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nite fire - 22 Jun 2004 00:11 GMT

I agree with your comments about the design having to be correct. That is
what I was trying to say but now I re-read it I realise I didnt make the
point I wanted.

> > Having spent 6 years working at a Stainlees Steel fabricators and seen many
> > wierd and wonderful machines, frames and pressure vessles made from
[quoted text clipped - 52 lines]
> >> fasterners. I would think fatigue failures would be almost inevitable in
> >> a stainless steel subframe.

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