Is the BMW i3 the most advanced production car?

[Lycoming]

Perhaps you have noticed that BMW uses practically unidirectional fabric for the preforms. They use very small sections in order to align the fibre direction with the predominant direction of the stresses.

Forgive, but what is so special about this? Isn't most carbon cloth unidirectional?

It's not even uni cloth; they're getting the carbon as tows on a spool, which is pretty much as it comes off the production line. They're stitchingg it into preforms themselves. Somewhat unusual in automotive industry, where it seems everybody is most used to prepreg cloth, but this isn't unusual in aerospace.

Though, if you think uni cloth/prepreg is unusual, you clearly don't know much about fibre composites.

The BMW look is very different when you inspect the naked crash cell.
http://www.bmwblog.com/wp-content/uploa ... 55x491.jpg

If you follow the pattern all around the huge side frame around the two door cut outs you realise that they have at least 15-20 3D-layup sections of predominantly unidirectional fabric used only for this part.

You could do that with prepreg too. For small volume, it's faster overall with prepreg since it takes a lot of time and money to set up the machine to stitch the preforms, but obviously this isn't small volume.

I should also add that the nylon thread they use to stitch the preforms add basically nothing to the mechanical performance of the part, but do contribute 1-2% of the final part weight.

Not everything on an airplane goes through an autoclave. There has been a big push in recent years to go out of autoclave.

HUGE push. Hear much more about it then prepreg work these days. Autoclaves are usually your bottleneck, but installing more is extremely expensive, especially for aerospace sized 'claves. The really big ones need to be designed into the building itself.

I am curious what the void content is with this fast of the shot. They must be using some monster vacuum pumps.

As am I.

I'm not going to split hairs with you. So this point is done for me. BMW uses renewables. Other brands don't. I can't even see a claim that another manufacturer tries to generate the energy for making his body shell material by renewables. Because BMW does it is irrelevant for the carbon foot print and the eco balance how much energy they use. It is green energy.

Ok.

But would it be more green if they used a less energy intensive process to produce their cars and allowed the hydro energy they save to go into offsetting energy production from a coal plant? Obviously that's not easy to answer, but it's just something to think about.

[Tim.Wright]

Using green electricity is just a question of money though. You pay your utility company a bit more and they tell you that your energy is clean.

Even though BMW might be using clean energy, I still suspect its significantly more energy than a steel body.

[WhiteBlue]

Prepreg and Preform is a different thing. I don't want to go into detail, but prepregs are pre-impregnated which the BMW 3D-Preform isn't. The BMW Preform is dust impregnated on the surface and 3D formed in a press. It is also not entirely unidirectional. It is 85% unidirectional approximately. I'm pretty sure the whole process is quite unique when you study it in all its detail. One aspect of the preform fabrication is the robotic manufacture including the trimming of the 3D preforms by robots. People who think this is trivial should better investigate with some other manufacturers how close to mass fabrication they are. I know for sure Toyota tried very hard to license the technology from BMW in return for their fuel cell technology where they are advanced much further. They were turned down.

[WhiteBlue]

My inexperienced eyes found unidrectional carbon fiber cloth for sale at prices as low as $12.46/yard.
This stuff has been around forever.

[...] The issue was achieving reinforcement in variable directions with unidirectional or near unidirectional fabric. It is not the fabric that is the break through but the robot based 3D-Prepreg technology which makes it possible to use such matching reinforcement and align forces and reinforcement in a near automatic process with short cycle time.

[flynfrog]

Prepreg and Preform is a different thing. I don't want to go into detail, but prepregs are pre-impregnated which the BMW 3D-Preform isn't. The BMW Preform is dust impregnated on the surface and 3D formed in a press. It is also not entirely unidirectional. It is 85% unidirectional approximately. I'm pretty sure the whole process is quite unique when you study it in all its detail. One aspect of the preform fabrication is the robotic manufacture including the trimming of the 3D preforms by robots. People who think this is trivial should better investigate with some other manufacturers how close to mass fabrication they are. I know for sure Toyota tried very hard to license the technology from BMW in return for their fuel cell technology where they are advanced much further. They were turned down.

Its really not unique at all this is pretty much the process for any RTM part. Like I said in an earlier post the only thing new with this is the resin. You dont have the level of automation in aviation because you don't need the cycle time and usually cant justify the tooling cost vs hand lay.

Pretty cool 3d preforming going on now

http://www.compositesworld.com/articles ... production

[Powerslide]

carbon fiber is entirely recyclable except it loses a lot of its strength thats it. There is a small sports car manufacture (name escapes me), just new, who are building carbon fiber chassis two seaters completely based on used and cut outs of carbon fiber.

[flynfrog]

carbon fiber is entirely recyclable except it loses a lot of its strength thats it. There is a small sports car manufacture (name escapes me), just new, who are building carbon fiber chassis two seaters completely based on used and cut outs of carbon fiber.

ehh not really. You have to do something with the resin then they just grind up the fiber. You cant recycle it in the same was as say steel where you get the same product back. You get ok filler material that takes a rather large amount of processing. I know boeing was feeding the uncured drops from ply cutting and doing some compression molding with it.

[Just_a_fan]

I'm not going to split hairs with you. So this point is done for me. BMW uses renewables. Other brands don't. I can't even see a claim that another manufacturer tries to generate the energy for making his body shell material by renewables. Because BMW does it is irrelevant for the carbon foot print and the eco balance how much energy they use. It is green energy.

Ok.

But would it be more green if they used a less energy intensive process to produce their cars and allowed the hydro energy they save to go into offsetting energy production from a coal plant? Obviously that's not easy to answer, but it's just something to think about.

At least you understood my point. If the total amount of electricity a country uses comes from a mix of sources then all users of that electricity contribute to emissions because the "green" energy any one of them uses could have been used elsewhere instead of "dirty" energy. That's why it's actually "greener" to use less energy rather than paying a "green" supplier who just puts their energy in to the overall energy pool.

[Just_a_fan]

Prepreg and Preform is a different thing. I don't want to go into detail,

Why not? This is a technical forum where we love detail.

[flynfrog]

Prepreg and Preform is a different thing. I don't want to go into detail,

Why not? This is a technical forum where we love detail.

Preform usually refers to dry fabric that has been cut formed and tackified together. The preform can take shape if set on a form and heated. The tackifiers I prefer are solid at room temp then get sticky at temp. There are others that are always sticky depending on what you are doing. There are such things as prepreg preforms depending on process

Prepreg is usually fabric or tow that has been pre impregnated with resin. This is the back bone of most composite work. It comes on rolls or spools. If its fabric you cut it out place it in a mold vacuum bag and cure. Tow is usually wound. You can also buy tape and use an automated Tape layer.

If you click the link I posted above you can see some pictures of preforms before molding.

[idfx]

It's really cool, the information on the manufacture of carbon fiber.
type of cloth is a new subject
bmw gina was another interesting car.

[Steven]

Related to the OP, BMW announced they target expansion of their carbon fibre use to its entire range of cars
http://www.autoblog.com/2014/05/13/bmw- ... nvestment/

[Gaetan7TB4]

Hi all,

I was wondering if you could tell me more about the preform system.

There are several points I would like to know :
-what kind of binder do they use to keep in shape the preform ?
-what kind of system do they use to make the preform ? Heating + vacuum ? Press ?
-how is the taping performed ? by hand on the mould ? automated system ?

I am currently looking for possibilities to create preforms in order to achieve fast cycles in my RTM process, that's why I am wondering all of this.

And excuse my english, I am french !

Cheers,

Gaetan

[flynfrog]

Hi all,

I was wondering if you could tell me more about the preform system.

There are several points I would like to know :
-what kind of binder do they use to keep in shape the preform ?
-what kind of system do they use to make the preform ? Heating + vacuum ? Press ?
-how is the taping performed ? by hand on the mould ? automated system ?

I am currently looking for possibilities to create preforms in order to achieve fast cycles in my RTM process, that's why I am wondering all of this.

And excuse my english, I am french !

Cheers,

Gaetan

There are many commercially available tackier systems from aerosol sprays to heat set powders.

I have used all of the above to do preforming.

No sure what you mean exactly by taping?

[Gaetan7TB4]

Hi,

and Thanks flynfrog for your answer !

I meant by taping the positionning of the different layers of UD. Is it done by a robot or by hand ? Because you would need to put precisely and with the right angle all the reinforcements !?

About the binding powders, I am currently looking into their effect on the final part : does the binder affect the mechanical properties of the part ? Does the binder affect the flow, during the rtm process ? How can we measure/see the wash-out phenomenon where the binder gets pushed by the resin during the injection ?

Are you working in a composite part making company ?

Cheers

Gaetan