Go Back   BMW i3 Forum: A BMW i3 Forum > BMW i3: News > News, Rumors, and Updates

LinkBack Thread Tools Search this Thread Display Modes
Old 06-17-2014, 02:35 AM   #1
Mike's Avatar
Join Date: Dec 2012
Posts: 552
Post BMW i3 & i8 repairs and safety (carbon fiber 101)

BMW i3 & i8 repairs and safety (carbon fiber 101)

BMW’s use of carbon fiber in a mass-production car has raised questions – serious questions concerning safety, sustainability, and, of course, any additional costs that may arise during ownership on top of what is already an expensive machine.

We’ve not heard of any BMW i3 crashes (and certainly not i8 crashes, at least not in the hands of the public), but with thousands already on the road incidents will surely happen. As such, BMW’s blueprint for managing carbon fiber production, recycling, and repair has not yet been put to the test.

In the meantime, here are the answers to some questions you might have.

How does BMW even repair carbon fiber?

The simple answer is that it doesn’t. If a small winglet snaps off the front of a Formula 1 car during a race, it gets a whole new nose during the next pit-stop. Should there be reasonable damage then the entire part goes in the bin, no questions asked.

A BMW i3 owner is not in a race, however, nor is he or she backed by millions of dollars-worth of new parts. As such, the German automaker has devised a process of ‘repairing’ damage carbon fiber reinforced plastic (CFRP) bodywork by selectively replacing it.

BMW-i3-repair-03 Yes, that’s a contradiction, but it makes sense in that the entire panel needn’t be replaced, only the section that’s damaged. A specifically designed carbon milling tool (complete with vacuum, to suck up carbon dust) slices through the bodywork impossibly cleanly. This means that a made-to-measure replacement panel can be glued into place, resulting in an almost seamless fix.

The i3′s frame also has a number of predetermined ‘cut-points’, making life easier for service personnel and expediting the repair process.

And how much does it all cost?

BMW says that the accident repair costs of its new electric i3 are similar to those of the 1 Series. However, the latter of those cars is a traditional mass-market hatchback while the former is hugely advanced both in terms of drivetrain technology and materials science. How is coast parity possible, then?

Small bumps are by far the most common form of ‘accident’ in cars, and the vulnerable bodywork on the BMW i3 is made of thermoplastic. This means that most of the time energy from the impact is absorbed without the panels permanently deforming. Should the driver prang something unusually hard, however, replacing this plastic plating is neither difficult or costly, requiring only the new part and the removal of screws and clips. The process is also quick.

Likewise, the i3′s aluminum chassis – known as the ‘Drive’ module – is repaired by bonding and riveting, something BMW has been doing on its other production cars for more than a decade, so costs are broadly the same across the board.

BMW-i3-repair-02 And what about the carbon fiber? It is undoubtedly expensive in comparison to other materials used in the construction of the BMW i3, but this increased cost, BMW says, is offset by the speed of repairs and the plastic bodywork.

BMW says that replacing a damaged section of carbon fiber reinforced plastic on the i3 is so quick and easy that owners/insurance companies will pay less in labor costs, and that replacing damaged plastic panels is considerably cheaper than finding new steel or aluminum ones.

One potential spanner in the works is that, when replacing sections of carbon fiber, BMW only supplies an entire side of the car’s carbon fiber frame. That’s a big piece of composite, so won’t come cheap (we won’t know just how much until somebody needs one).

But I heard the BMW i3 wasn’t that safe?

BMW must have been a little embarrassed when the i3 scored only four out of five stars in Euro NCAP safety tests, particularly as only a couple of weeks beforehand some company executives had boasted that the hatch was so strong one example had been used in more than one crash test.

Four stars in the European test is respectable, but it puts the i3 behind the Nissan LEAF, Chevrolet Volt, and even the smaller Renault ZOE. To put it another way, the tiny Mitsubishi i-MiEV also achieved four stars.

It must be noted, though, that the BMW scored very highly for adult and child occupant safety, falling down only on driver’s left-leg and rear-impact whiplash protection. The only reason it scored four stars instead of five, in fact, is that pedestrian safety was deemed to be poor.

BMW-i3-repair-01 Another worry for prospective buyers is that of carbon splinters and dust in the event of heavy crash, leading to irritation of the eyes and lungs. BMW told ecomento.com, however, that the carbon fiber reinforced plastic modules in the i8 and i3 are treated to multiple coats of lacquer to prevent this.

Also worth mentioning is that the BMW i3′s lithium-ion battery disconnects from the car’s high-voltage system the moment the passenger restraint systems are triggered in a crash. This is to prevent any short-circuiting that could lead to a fire.

Doesn’t CFRP contradict the car’s sustainability?

Strictly speaking, yes it does. Carbon fiber is one of the hardest materials to recycle, being neither biodegradable or photodegradable. BMW has, however, tried to limit materials and energy reduce wastage as much as possible.

For a start, the carbon fiber itself comes from a plant at Moses Lake, Washington. The plant is a joint venture between BMW AG and SGL Carbon, and the entire facility is powered by locally-sourced hydroelectric power.

At the other end of the production process, the carbon fiber reinforced plastic components, along with the rest of the car, are assembled using wind-power alone at BMW’s plant in Leipzig.

BMW-i8-carbon-fiber-repair Of course, the carbon fiber has to be cut into the appropriate shapes before it’s injected with resin, which leads to a huge amount of offcuts. These offcuts can be ‘repurposed’, BMW says, and fed back into the manufacturing process. The result of this is that every BMW i3 features around 10 percent recycled carbon fiber.

BMW takes carbon fiber recycling a step further, however, by recycling mouldings that have already been resinated. These parts now require thermochemical decomposition at high temperatures, which inevitably uses a lot of energy, but ultimately allows the carbon fiber to be reused. The rear seat mount in the i3 is made in this way, as is the roof.

Article Found At: BMW i3 & i8 repairs and safety (carbon fiber 101) | ecomento.com
Mike is offline   Reply With Quote

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are On
Pingbacks are On
Refbacks are On

All times are GMT. The time now is 06:30 AM.

Powered by vBulletin® Version 3.8.7
Copyright ©2000 - 2018, vBulletin Solutions, Inc.
Search Engine Friendly URLs by vBSEO 3.6.1