FWD rear suspension subframe - bolted vs welded?

[rationull]

This is just a random general question I've had for a while.

My car and my wife's are both FWD with independent rear suspension. Mine (a Honda Civic) has the rear control arms bolted to a subframe piece that's welded to the unibody in the middle of the car, while the wife's (Mazda3) has a separate subframe assembly that's bolted to the unibody, more like how the front subframes/engine cradles are attached on both cars.

What are the reasons for choosing one method of manufacture over the other? It seems to me like a bolt-on subframe would be easier to tweak from model to model and would be cheaper to manufacture as well. Unless I'm wrong and a welded one is cheaper, why would a manufacturer go with a welded subframe?


I can probably get some pictures if need be but I don't have any right now...

 

[mechanicx]

I think a bolted-in subframe is usually more expensive and stronger because the subframe is thicker steel sections, although if a heavier subframe is welded to the body rails there would be little difference and could be stronger.

 

[Hokiefyd]

I've owned a few FWD Toyota sedans, and both have bolted-in rear subframes. The subframes are isolated by rubber bushes. I don't recall how my FWD Cadillac sedans were...both had IRS ('97 Seville and '01 STS), but I believe they had direct mounting points for the suspension. I don't recall exactly.

Edit: I take it back; I know the '97 had a bolted-in subframe, isolated by four large rubber bushes.

A bolted subframe would offer more isolation from road noise (Hondas are known for road roar, aren't they?). I agree that a welded subframe would be cheaper to install, and probably lighter as well. A bolted subframe would have to be a structural member itself because it's only attached at four points, so it must be strong on its own. I imagine a welded subframe could be made thinner because it will become integral to the car once installed.

I think a bolted subframe would be easier to repair if the vehicle is in an accident.