Steel--there doesn't seem to be an advatage for weight using plasitc.

I remember an interview with one of the lead guys in charge for the 4th gen F-body---he said if they could do it over again--they'd go steel. Must know what hes talking about.

 

Plastic for light weight, durability and less prone to rust. However, i dont want this carbon fiber crap it has to be grade A stuff that is dent resistant as well, as guaranteed to las 1,000 years..so i can keep my car for ever
In all seriousness we will prob never see a fully steel car again..its too heavy, will hurt mpg, plus it wont have the desired crash test rateing, my GOD the car will be able to withstand a direct hit to the rear and not be totalled out. But that wont be what they want cause every car has to pretty much self destruct in order to pass the crumple zone test.

 

Lets at least make the inner door out of steel . My like new trans am has a nice long stress crack that goes from the upper front hindge to the lower . The door sags like early 80's Monte

 

Actually, the energy-absorbing features on a car are generally steel. The plastic is just cosmetic... a pretty "shell" if you will that covers up the business parts of a collision protection structure. As steel has a very defined yield point and then allows plastic deformation it tends to be a lot better at absorbing energy than the plastics used for body panels - they usually just shatter and aren't relied on for absorbing energy.

If you look at the bumper, door beam and subframe structure of an F4 carefully you'll see that the energy absorbing features are all there and not in the plastic panels. There are egg-crate features on the bumper systems that absorb energy, but they aren't appropriate for a "Class A" painted exterior panel.

In the rear of the car you have a steel unibody structure in which the rear quarters ARE part of the energy absorption system. That's why they remained steel - they were integral to the system and it would have been too costly to convert the car to a Corvette-type spaceframe back there.

Plastic technology is constantly evolving, but so is steel technology. The comparison between steel and plastics (or carbon fiber or aluminum) are not as simple as just weighing out the materials.

A properly designed steel structure utilizing the right steels can be as lightweight and cost effective as any other system if the assumptions utilized during the design process are correct and judicious attention is paid to the unique properties of the material. That generally means a unibody with stressed exterior panels.

Plastics start to get advantageous when a subframe structure or spaceframe structure is utilized, or when difficult to stamp styling features are specified (peaked fenders are a nightmare our of steel). The first Corvettes were fiberglass specifically due to styling.

An interesting sidelight that bodes well for plastics is hydroforming. By allowing steel frame structures to be made out of far fewer components (which require a weld or rivet or other fastening methodology at each joint - adding lots of cost), the business case got skewed back toward spaceframe or full frame structures and away from unibodies in certain applications. Solstice is a wonderful example of this fact - it's a relatively inexpensive car that got to use a spaceframe structure because hydroforming made it financially practicable. Think of it as a miniaturized Corvette.

 

But how much weight would you say the plastic parts actually save on the Camaro?

Actually, if my steel fender took a hit that hard, I would simply replace the whole fender (don't believe in putty... it's an east coast thing ). What's more, with steel I don't have to worry about wrenching the gaps, and it's significantly cheaper to boot.

 

Guessing here...

Something over 50 lbs., maybe up to 100 lbs. The big areas for saving are probably the hatch and the doors.


Finished prices are going to be close to the same and the plastic is easier to wrench into place (it'll deform a bit easier, especially on a bumper cover). The steel will tend to transmit more deformation to the underlying structure than the plastic (which will crack), so you'll have to budget for that with the steel too.