What are the drawbacks of composite/plastic body panels?

[Evman]

As everyone knows, weight is becoming a major problem with cars, and there are many ways manufacturers can go to reduce weight but for various reasons they dont... Plastic panels such as guards, bootlids, etc seems to be a good start in my opinion, but there must be negatives seeing as they're not being used...

From what I can come up with these are the pros compared to steel:
-Weight
-Elasticity
-Pedestrian safety
-Ease of manufacturing (?)
-Cost (?)

And the cons:
-Strength
-Heat deformation

Am I missing something big? Surelly the cost factor wouldn't be a big deal would it? There must be a lot of money that goes into getting presses and stuff setup for steel...

[SICK SS]

maybe it wont crumple so it wont handle a crash like steel part would with its crumple zones.

[bpm]

worked on a landrover freelander yesterday, front guards were plastic. older discoveries had alot of aluminium panels on them too.

[Big_Valven]

I have a feeling SICK SS is right about crumpling - I would think current plastics would crumple a little too easily, even if only used for outer panels each panel plays a part in overall rigidity and strength.

I don't think car makers are spending enough time on research into composites though, or we're not hearing enough about it. Fibre composite panels such as carbon fibre offer huge advantages over metals but are too expensive and specialised at this stage. I think they need to start working on a mainstream composite material suitable for automotive use, but I think the sticking point will still be cost. I think it'd be possible to build a commodore with composite panels well below 1500kg.

[Holden Man]

Chrysler came close to making one a little while ago >

http://en.wikipedia.org/wiki/Chrysler_CCV

http://aycu09.webshots.com/image/41088/2004092538924595428_rs.jpg (http://allyoucanupload.webshots.com/v/2004092538924595428)

[CSP]

Plastic panels such as guards, bootlids, etc seems to be a good start in my opinion, but there must be negatives seeing as they're not being used...

Metallic paint doesn't react with plastic like it doesn with metalic panels. Look at the colour difference on any VE car between panels and bumpers.

[Dug]

Metallic paint doesn't react with plastic like it doesn with metalic panels. Look at the colour difference on any VE car between panels and bumpers.

and THAT is exactly what I reccon the problem is. They want to be able to sell a pretty car, that doesn't have too many colour matching problems. Mind you, nissan were able to get the paint matching right on the X-Trail, which has plastic front guards.

[Evman]

Metallic paint doesn't react with plastic like it doesn with metalic panels. Look at the colour difference on any VE car between panels and bumpers.

I never realised that...Surely a better primer or prep would help though wouldn't it?

[GHZ28]

I never realised that...Surely a better primer or prep would help though wouldn't it?

That is the trick, almost in its entirety. The primer and base colour and paint composition.

My 94 Camaro has all GRP panels apart for the bonnet and rear quarters which are steel to provide fire resistance and a strong cantilever for the roof respectively. The roof panel itself is GRP though, just stuck on to the steel frame.

From the factory there was no discernable difference in paint colour from panel to panel, even the rear bumper which is plastic beside the metal rear quarter matched.

It has since had a partial respray here in Australia, and now there is some slight colour change between panels, but I think more the repainted vs original paint ones which have had nearly 15 years exposure to the environment.

Crash protection does not seem to have been an issue either, camaro and corvette meet all Australian crash requirements, and of course the US and European ones as well.

An up side is that minor impacts, which do not break the paint surface normally result in no residual damage, the panels just pop back out. One golf ball attack on mine left an area of slightly crazed paint, and was part of the reason for the partial respray.

Lifetime rust through warranty is pretty safe too. ;)

The base colour of my panels is a light yellow, and the primer metallic looking grey, and the paint is called purple pearl metallic. Sure looks better than the see through silver on my VZ ute.

Cheers,

garry