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BMW i3 repair highlights

Inside the BMW i3 body….

By Andrew Marsh, 26.10.15
Posted in: In-depth | Public | Technology Trends

The i3 has been on sale around the world for more than 1 year, and still represents a step change in automotive engineering, especially from a collision repair point of view. The headline is of course the carbon fibre reinforced plastic (CFRP) body shell, but as we shall see the shell is a good deal more sophisticated than that. Let’s start with the exterior:

All of the exterior skin panels are made from a wide variety of thermoplastics, with the exception of the lower tailgate skin which is glass and the roof skin which is painted CFRP. The removal, preparation and bonding of these parts is important and must follow the BMW repair method process. © BMW AG

Unusual features include the front seat belt integrated into the rear door (as seen before on Mazda RX-8, Mini Clubman R55 and most ‘King cab’ pickups) and removal of the front door to remove the fixed or moving glass. Indeed body side rebuild involves adjusting the gapping and flush fit for the front door, front door glasses, rear door and rear door glass. Super.

The front and rear door skins are held in place on the aluminium door carrier frame with single use clips. In addition the front and rear door skins, rear door glass and tailgate spoiler have the facility to adjust the panel flush fit with the surrounding panels via the adjuster integrated into the mounting clip shown above right. © BMW AG

Carriers are used for both the front as well as rear wings which are important for panel location, and so must be replaced in the event of damage. The front right wing can have access to the fuel filler neck if the range extender engine option has been specified, whilst the rear right wing has the high voltage charge port access. © BMW AG

There are sacrificial bolt on elements to the core body shell covering the front upper and lower aluminium bumper beams, the front subframe (which is emphatically never to be used as a lifting point), the rear frame aluminium braces and the rear bumper beam. The high voltage battery pack sits between the central members, on the underside of the passenger compartment floor. © BMW AG

The front frame can be sectioned in situ for either a chassis leg section or indeed a chassis leg / front strut tower section. The process is intricate, involves bonding as well as riveting and uses brace inserts (supplied by BMW) inside the sectioned joint.

The front and rear aluminium frames are linked in the centre and then bonded and screwed to the CFRP shell. This is done in-plant – BMW can supply either the front or rear frame, but not the entire assembly unless as a complete body module. © BMW AG

There are a large number of CRPP structural repair methods available, which include precise instructions about how to:

  • Prepare new CFRP panel to existing CFRP panel joints.
  • Prepare CFRP to aluminium panel joints.
  • How to soften the original bonded joint (maximum permitted temperature 120 degrees C to avoid damaging the CFRP resin matrix).

Scary? Well for those used only to welding steel, perhaps. We can see directly from this that it is essential to have the right training in place to cope with bonding, riveting and handling of CFRP. In addition the methods must be followed closely. Overall the whole process is ‘M.E.T’ centric, and once the principles are understood there are no outstanding issues.




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