gridwalker wrote:Marcush, I note two uses of the magic words "for sure" in your last comment : now I am starting to suspect that you are actually an F1 Driver ...
gotcha.. for sure I´m the famous german f1 driver from southern germany ......maybe i should show you the famous finger...
lazy use of language ..my bad ..sorry.
as a modelmaker I know a few things about laminating and having earned my money for years fabricating /TIG welding I was just throwing in my 2 cents.
As a driver I´m useless I have to confess ....for sure i would be a constant scorer if they had contnued the RealBrawnGP forsure contest...
Thanks for the imput guys, had a family friend who works for a company called mastenbroek.....http://www.mastenbroek.com/....run sketch through a CAD program today. The preasures involved (2.5 to 4bar) would not really put alot of stress on the frame, although he did alter the outer frame work from box section to I beams, while also incorporating some triangle plates to increase weld contact area. He has also recomended a compressor with increased volume, rarther than preasure, as one i have that fills dive tanks may take upto an hour to come up to a worthy preassure.
Please make no mistake, this isnt some backyard construction. The people helping build it with me have over 80yrs of experience on metal fabrication between the pair of them.
The largest part i will need to produce has a maximum size of
Length :- 1600mm
Width :- 900mm
Height :- 800mm
If i were to use carbon i believe 8 layers of carbon twill (with every other layer at a 45o pitch), 1 layer of 15mm nomex, and another 7 layers of twill & 1 kevlar layer in the middle(wet layup) will be adequate enough to provide a safe monocoque to support the 2 subframes needed to be hung from it. 2 carbon bulkheads around the cockpit and pedals.
The whole idea of the project it to spend time with my son, not so much the end product. it'll be a joint learning project. I would love to try fiberglass infustion but in all honesty it looks a little hit and miss for a person with limited experience. At worst i will use fiberglass but increase the layers of glass to compensate for the loss of strength. Its not a MUST to use an autoclave obviously, all i was establishing was if my desire to own the biggest cooker on my street was a worthy one.
i'll carry on with the idea at the back of my head to a few months, although i should really be spending time on the ideas for the car itself. i'll open another thread at some point for my 2/3 scale f1 project for more great feedback from you all
Although I may agree with you in this specific case, keep in mind that sometimes the journey of building the car is more fond of a memory than driving (cough-maintaining-cough) it.
Richied76,
Another potential problem You may want to consider is that while more amatuer race organizers are becoming more educated on carbon chassis, they are also starting to require equivalency documentation - usually requiring a long process of approval (relative to steel spaceframes). The days of showing up to tech inspection and driving out 30mins later could very well turn into an all-day-event-of-rejection if the organizers are not comfortable with anything on the car. A single cosmetic defect could ratify Your car un-raceable and once denied, it's logged in Your car's logbook...
You may consider building a spaceframe prototype, dial in Your geometries & setups, and develop the carbon tub accordingly. The force/load data available from the spaceframe chassis will help You make better decisions during the carbon tub design.
The autoclaved carbon tub, while it is an immense challenge, it can be done. Just make sure You're 100% sure that the unique challenges You will face, are the challenges You want to face. Not to mention the risks, and failure modes...
It´s not up to me, to pass judgement on your project, I see where you are coming from and what you would like to achieve and I wish you the best.
It´s doable, but no easy feast, and will go hand in hand with some serious costs, especially when you just plan a "one off" built.
Just some thoughts.
Most race car monocoques and safetycells (such as in DTM) use aluminium honeycomp and not nomex honeycomp.
The reason is impact protection and energy absorbtion on impact.
This is maybe not a consideration for your project, as you may don´t want to race it, and don´t need homologation, but I wanted to mention it.
Mind about and plan for the location of hardpoints for your suspension pickup points, seatbelt attachment points !!!!, engine attachments and attachments of main components such as your pedalbox, suspension rockers, damper and anti roll bar brackets etc.
You can´t (or at least should not) just drill a hole throught your monocoque put a bolt through it and put a washer & nut onto the other side, as it will crush your honeycomp core.
So you need to keep a lot of things in mind, when designing and building your tub. You would need to fix the location of these hardpoints during the layup process and stop them from moving during the curing.
Then you need jigs to drill your holes and cut your threads into the hardpoints after you have cured the tub.
To achieve good bonding these hardpoints need good preparation and degreasing before layup (no touching with sweaty/greasy fingers etc.)
Delamination around these hardpoints, either during the built/curing process or during use, is a serious "problem/needs consideration" when using a carbon tub.
Delamination on suspension hardpoints is not uncommon in the event of an crash or impact.
This is not allways apparent by visual inspection, and normaly these points get inspected in regular intervals using NDT methods (mainly ultrasonic analysis). Repair in case of delamination is sometimes possible but not allways easy to achieve.
In the event of an big accident or an unlucky angle etc. there is a good chance that your tub is a write off.
Sure this risk exist with a spaceframe as well, but repair is much more easy in this case.
As Riff_Raff and others pointed out, the advent of out-of-autoclave (OoA) systems have made things easier and simpler to produce.
They become more and more common and offer some serious adventages.
They will replace autoclave systems more and more over the next years, mainly due to the shorter production time, and the cheaper/easier infastructure required.
In the first curing cylce diagram I posted you see a comparsion between an OoA system (Quickstep)and a autoclave production system.
As you can see, you don´t need any pressure (just a slightly higher vacuum), the same temperatures and save ~3hr in production/curing time (less energy used for heating).
I seriously doubt, with appologize, that you can achieve a good enough quality (even for a noncomercial project) with wet layup in this case, especially not when you use a honeycomp core material.
Please mind about it, in the end it´s up to you, but if you go to all this effort, go and use a prepreg cloth, it´s not that much more expensive if you consider all things, and will make life a lot easier for you. - IMHO
Good luck.
Last edited by 747heavy on 10 Dec 2010, 01:50, edited 1 time in total.
"Make the suspension adjustable and they will adjust it wrong ......
look what they can do to a carburetor in just a few moments of stupidity with a screwdriver." - Colin Chapman
“Simplicity is the ultimate sophistication.” - Leonardo da Vinci
Very interesting project. I have worked for a company who purchased several autoclaves and was around when they were commissioned.
The biggest part of this project will be keeping safe. An at the risk of really demoralising you, there are a few things which you absolutely must consider since they are legal requirements.
Think, 4bar acting on your door of say 1m x 1m is 40tons of force (if I have done the maths right) If your door happens to pop open at that pressure it will kill someone.
There are various pressure vessel directives you must follow when designing something to take that pressure. Basically these directives class a pressure vessel based on the fluid type (air in this case) and the value of Pmax x Volume. Basically the more PxV the more stringent the laws are and require coded welders to perform and certify the work. Also vessels containing air are classed as worse than those containing fluid since the energy density is hgher.
Being a pressure vessel it must be stamped and inspected to some sort of schedule. This is a legal requirement! More importantly (sice you have already started design it seems) I also believe its a requirement that it is designed by someone qualified/certified to.
Anyway, if you have the money a certified designer and coded welder is not difficult to find but this will really cost you.
So pressure related issues aside, the next biggest challenges are things you can design and test for in safety is the heat profile and vacuum system design. Its very important to make sure the fan and heating system is designed so that you achieve the required ramp rates EVENLY throught the whole clave. This will likely require lots of tests using it as an oven only (no pressure) and with variation of fan speeds and heating power. Once this is sorted you are well on the way to a good system. Some resin types are extremely sentivive to the ramp rates. In fact I have worked with the 8552 system posted by 747H using the Quickstep process. We realised this needed a very slow ramp rate to let all the gases escape from the resin otherwise you end up with a part which looks like swiss chees under a microscope.
Next up is the vacuum system. There is nothing complicated in setting up this but to have a good reliable system will take some patience in selecting and designing the detail (fittings, valves etc). You will need multiple ports for vacuum and sensing (typically 1 vac port per 1.5sqm of part to cure) which doesn't leak and is able to be vented to atmosphere (some pre-pregs require this)
If you get the last two trick right (heat profile and vacuum system) you will already be able to cure high quality parts from pre-preg. There are some vacuum consolidation only prepregs from Toray (using resin 2510) which are even certified for aviation use.
Anyway, I hope you still have the will to push on with this. Though my gut instinct is to make a good quality oven with a vacuum system rather than a full autoclave. I'm a qualified engineer whos worked for a couple of years in composites and I would not have the balls to design an autoclave.
Wouldn't try making an autoclave ever...far too dangerous!
I'd suggest you research "vacuum assisted resin transfer molding" as an alternative to autoclave/prepreg for composites. VARTM uses dry fabrics, rather than prepreg, doesn't require high temperature tooling, and the equipment can be accumulated for a couple hundred bucks. Strength to weight isn't quite on par with autoclave parts, but is probably the best of the rest, so to speak.
And as a bonus, you'll actually be able to spend some time with your son, rather than be working 2 jobs trying to pay for it all!
I'd be happy to tell you more if you're interested. Cheers!
Your original post seems to suggest wetlay resin systems not prepreg which if thats the case you dont need a clave,with wetlay vac you have to run a controlled leak an only pull -20 on the vac gauge or you will be pulling all the resin out of the part
Unless you have LOTS of time an LOTS of money dont even think about resin transfer !!! people will tell you its the future an is simple an easy to use (thats normally by the people selling it) it takes a LONG time to learn an is only easy on simple parts.When Mclaren did the SLR they were on 95% scrap rate for the 1st year an wasnt below 50% after 3 yrs
If you want to go for a clave the easiest way is to book time at someones clave i can give you details of several who rent out time
If you want to build your own the quickest an easiest way is cut the end of a gas tank,they are rated to 200psi so as long as everything is done by a coded welder an you have the interlock for the door designed corectly your half way there
There are lots of other things to think off,heaters,fan,vac an temp control to name a few.If you are serious i can give you details of a company that has some vessels avalible an another company that can help with all the other parts but be aware a 4ft by 6ft clave will be 15k home built but thats not too bad as one from Autoclaves LTD would be over 100k
To use prepreg your going to need 2 cooks at the least thou its a lot better doing 3 as you tend to do a lot of work on your core once its cooked.genral cook on a 125deg material (cycom919,mtm28 or mtm57 to name a few) would be ramp to 80 at 2 deg a min,dwell for half hour then 2 deg to 135 for 1.5 hrs all at 90psi.you will need a 30 psi cook for your core an third cook if you went that route
Well worth talking to ACG for materials an also Amber composites an CML for core Vac innovations are best for consumables
Lots of techniques an tricks to learn that you wont find in any book an LOTS of the stuff you will find in books is rubbish
Lots of stuff you need but off the top of my head vac pump,lines,bag an sealing tape,vac points,release film,bleed blanket,release agent
seek the serices of a composite engineer,you dont want to do a tub an just put x amount of layers all over thats not the way composites work
want any help just ask
I'm not clear on why you need an autoclave at all. I have a co-worker who's brother build wings and noses and other parts for NHRA drag teams and ALMS..no autoclave at all.
I have seen C.F. laid up on the Internet in a manner most resembling laying up fiberglass. Why do these parts NOT need an autoclave and a tub does...I thought it was for the pristine atmosphere.?.?
To achieve anything, you must be prepared to dabble on the boundary of disaster.”
Sir Stirling Moss
