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crissdee
578686.  Sat Jul 04, 2009 7:21 am Reply with quote

Quote:
Faced with driving these ugly lumps of metal,


weren't they plastic/fibreglass?

 
Davini994
578696.  Sat Jul 04, 2009 7:43 am Reply with quote

Yes. Why are car outsides still made of metal? Bikes were fibreglass for a bit, are plastic now. Much better!

KTM X-Bow:



KTX RC8:



KTM are historically an Austrian off road motorbike company who have been expanding into a lot of different areas of late, like the superbike and roadster above. They are famous for their orange stuff.

 
PDR
578710.  Sat Jul 04, 2009 7:59 am Reply with quote

Davini994 wrote:
Yes. Why are car outsides still made of metal? Bikes were fibreglass for a bit, are plastic now. Much better!


Because composite construction is between one and two orders of magnitude more expensive for volume production, let alone for maintenance and repair.

Metals are also much more easily recycled - in fact use of metals is generally much more environmentally sound from pretty well all aspects, so promotion of the un-necessary use of non-metals should obviously be make a criminal offence...

:0)

PDR

 
tetsabb
578711.  Sat Jul 04, 2009 8:00 am Reply with quote

Oddly I saw a Bond Bug yesterday on my way to the shops. It was occupied only by a male driver, no passenger of either sex.

 
Davini994
578736.  Sat Jul 04, 2009 8:50 am Reply with quote

PDR wrote:
Davini994 wrote:
Yes. Why are car outsides still made of metal? Bikes were fibreglass for a bit, are plastic now. Much better!


Because composite construction is between one and two orders of magnitude more expensive for volume production, let alone for maintenance and repair.

Metals are also much more easily recycled - in fact use of metals is generally much more environmentally sound from pretty well all aspects, so promotion of the un-necessary use of non-metals should obviously be make a criminal offence...

That's surprising, I would have thought it would be cheaper. Surely the petrol saved with it being so much lighter would be much greater though?

Recycling is easy enough with a PET mark or whatever, and would be much easier with the volume and systemisation that using it on cars would bring. And the same point about the weight for environmental friendliness. No?

On the maintenance and repair, I feel what you say about that deeply, being part way through repairing about a metre of cracks in my nose cone. I've been putting stickers and laquer on this morning in fact!

 
PDR
578783.  Sat Jul 04, 2009 10:26 am Reply with quote

Davini994 wrote:
That's surprising, I would have thought it would be cheaper. Surely the petrol saved with it being so much lighter would be much greater though?


The starting materials (glass/carbon/kevlar cloth, various resins) are more expensive to start with, and these materials have a short shelf life (even with cryogenic storage). The manufacturing process involves producing pre-preg sheets, cutting multiple fragments to shape, and laying the fragments into a mould. The laying-up is a skilled, manpower-intensive process to preconsolidate the layers. The whole assembly is then bagged with perforated films, peel-plies and breather felts and the bag is evacuated to futher consolidate the laminates. The bagged mould is finally placed in an autoclave where a pressure of up to 6Bar is applied to the outside of the bag and the temperature is wound up to anythiong from 1000 to 900degC (depending on the particular materials and the application) for an hour or more. On removal from the autoclave the assembly is left too cool before removing the bag, films, felts etc and finally popping the part from the mould. The moulds themselves last between 30 and 200 uses before needing replacement though wear or damage.

Of course that's using high-volume prepreg techniques - wet layups take MUCH longer and far more operator skill.

Against this a metal part needs a single press tool which can be CNC or copy-machined. the input material is flat sheet and the production process involves placing the sheet into the press and pushing the "go" button. The tool lasts typically 10,000 impressions before needing replacement, and the parts are ready to use within seconds of pressing the button.

Whilst it is possible to produce lighter components in composites (hence the use in aviation), it rather depends which design cases dominate. For a car the usual dominant case is the crash-protection one. Metals have the distinct advantage that they plasticly deform, absorbing crash energy. Compsites don't, so a composite bodyshell has to be substantially stronger than a metal one to achieve the same crashworthiness. This tends to reduce the weight advantages. Then there's the minor point that only the very high-end cars can actually afford worthwwhile composite materials (carbon/kevlar etc). To do (say) a Ford Mundano bodyshell in carbon/epoxy would costs over 12k just for the material - never mind the manufacturing costs!

Quote:

Recycling is easy enough with a PET mark or whatever, and would be much easier with the volume and systemisation that using it on cars would bring. And the same point about the weight for environmental friendliness. No?


It's very easy to put a PET mark on a part, but I have a pile of plastic part with PET marks that I've been watching for months and they have yet to recycle themselves...

:0)

What I meant was the actual recycling processes. For metals it's generally a simple matter of melting down and refining the resulting melt (which is essentially the same aswas done to produce the material originally). For all but a few plasrtics the recycling processes involve chemical burns or other complex chemical reactions to extract usable materials for recycling. Some thermoplastics can be greground into fresh moulding powders, but few of these are "structural" materials. Glass/carbon composites aren't really recycleable.

Quote:

On the maintenance and repair, I feel what you say about that deeply, being part way through repairing about a metre of cracks in my nose cone. I've been putting stickers and laquer on this morning in fact!


If you want any glass cloth drop me a line - I have rolls of the stuff from 0.004" up to 0.040" 40g/m^2 up to 400g/m^2)...

PDR

 
austinallegro
578824.  Sat Jul 04, 2009 12:27 pm Reply with quote


Another plastic orange car.

 
Davini994
578839.  Sat Jul 04, 2009 12:46 pm Reply with quote

Hmm, I probably shouldn't question you on this, but... aren't you overengineering a bit there? I know you like to be a really great engineer, but still... ;)

Plastic farings for a motorbike are a few hundred quid new, manufactured, painted. They don't absorb anything, they are just there to deflect the wind and look pretty - they aren't load bearing, or crash absorbing. Are car body panels crash absorbing? I thought it was just the chassis and frame.

The stuff used for bikes is essentially the same sort of standard as would be used in say a dashboard - which are just liquid injection moulded, I'm pretty sure, having worked in a mould factory as a bairn. I've got an old bike from '86 which has glass fibre farings which exploded when I ran over a half brick and smashed it up into it. Some Corvettes have some poor quality plaggy body panels to Clarkson's annoyance.

All of which is a lot less interesting than the process you've described above, which presumably you know about because of it's use in aviation. Where is it used? When you say short shelf life, are you talking about on the vehicle or waiting for manufacture?

The layering of stranded sheets to get the strength is interesting. Is there a simple reason why turning sheets into a part is such a skilled unautomated job? How do you quality assure such parts? Is this why they aren't used more?

Quote:
If you want any glass cloth drop me a line - I have rolls of the stuff from 0.004" up to 0.040" 40g/m^2 up to 400g/m^2)...

Thanks for that. I haven't tried that way. I've used plastic weld (slightly bendy glue) with struts (cut cable ties), which you can see on the piccy if you peer really hard. And a bit of an experiment with a soldering iron and a plastic filing box which went well and is probably the way of the future.

 
Davini994
578841.  Sat Jul 04, 2009 12:46 pm Reply with quote

austinallegro wrote:
Another plastic orange car.

Not sure about the quality of the paint finish on that.

 
PDR
578911.  Sat Jul 04, 2009 2:20 pm Reply with quote

Davini994 wrote:
Hmm, I probably shouldn't question you on this, but... aren't you overengineering a bit there? I know you like to be a really great engineer, but still... ;)

Plastic farings for a motorbike are a few hundred quid new, manufactured, painted. They don't absorb anything, they are just there to deflect the wind and look pretty - they aren't load bearing, or crash absorbing. Are car body panels crash absorbing? I thought it was just the chassis and frame.

The stuff used for bikes is essentially the same sort of standard as would be used in say a dashboard - which are just liquid injection moulded, I'm pretty sure, having worked in a mould factory as a bairn. I've got an old bike from '86 which has glass fibre farings which exploded when I ran over a half brick and smashed it up into it. Some Corvettes have some poor quality plaggy body panels to Clarkson's annoyance.

All of which is a lot less interesting than the process you've described above, which presumably you know about because of it's use in aviation. Where is it used? When you say short shelf life, are you talking about on the vehicle or waiting for manufacture?

The layering of stranded sheets to get the strength is interesting. Is there a simple reason why turning sheets into a part is such a skilled unautomated job? How do you quality assure such parts? Is this why they aren't used more?

Quote:
If you want any glass cloth drop me a line - I have rolls of the stuff from 0.004" up to 0.040" 40g/m^2 up to 400g/m^2)...

Thanks for that. I haven't tried that way. I've used plastic weld (slightly bendy glue) with struts (cut cable ties), which you can see on the piccy if you peer really hard. And a bit of an experiment with a soldering iron and a plastic filing box which went well and is probably the way of the future.


Ah, I see what you're getting at. No - cars do not generally have a seperate chassis with cosmetic body panels. That approach went out in the 60s because it is too heavy and too expensive to build. Nowadays it wouldn't be acceptable because the weak external panels would not provide adequate protection to pedestrians in impacts.

Today's cars are unitary structures - pretty well every panel is load-carrying. Since the late 80s even the main glass panels are usually stressed as well (which is why they are glued on and take a couple of hours to replace). It's possible to use non-structural plastics for some panels - bonnets, boot-lids and the odd fairing or spoiler, but for everything else you need structural composites (glass/kevlar/carbon) or metals. Injection moulded plastics just don't have the strength.

Producing structural composites in large quantities isn't cheap. People have tried to simplify or automate it, but the bottom line is that it is just too sensitive to details. You ask how such structures are "QA'd", and that is indeed an excellent question. It's a combination of process controls, inspections and a few NDT techniques. The integrity of the laminate can be verified with ultrasonics and the integrity if the resin is assured by the autoclave records, hardness tests, conductivity tests and a few other things.

PDR

 
PDR
578914.  Sat Jul 04, 2009 2:21 pm Reply with quote

Davini994 wrote:
austinallegro wrote:
Another plastic orange car.

Not sure about the quality of the paint finish on that.


Yes, I notice that fisheye as well...

:0)

PDR

 
Ion Zone
578956.  Sat Jul 04, 2009 3:43 pm Reply with quote

Nobody ever remembers how gay the Pink Panther was.



 
Sadurian Mike
578962.  Sat Jul 04, 2009 3:48 pm Reply with quote

Oh some of us do....

 
Davini994
578991.  Sat Jul 04, 2009 4:16 pm Reply with quote

That is interesting PDR, I had no idea. Structural composites would be quite good at stabbing people too I'd imagine.

 
PDR
579002.  Sat Jul 04, 2009 4:45 pm Reply with quote

It's certainly not the kind of fibre they recommend in a balanced diet...

PDR

 

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