JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013 - 20

E.V.

The first series production vehicle
with a carbon fibre passenger cell
The BMW Group’s specialists along the BMW
body-in-white process chain have steadily
refined and automated the CFRP production
process at the Landshut and Leipzig plants
so that, for the first time, it is now possible to mass-produce CFRP body components
cost-efficiently and to a high quality standard by introducing an ultra-modern new-generation CFRP series production system with
very short cycle times.
BMW i3 CFRP Life Module

A highly innovative
approach

By
Dr. Jochen Kopp,
Head of Technology
Development CFRP,
BMW Group

he BMW Group sees
carbon-fibrereinforced
plastics (CFRP) not
simply as a niche application,
but as a pioneering technology
for automotive design in general.
Through systematic development of processes, production
equipment and workforce with
the sustainable goal of series
production, the group’s CFRP
production and technology team
has achieved a unique level of
technical expertise.

The starting point for CFRP production is the so-called precursor, a polyacrylonitrile fibre that
is also found in fleece textiles. In
a complex, multi-stage process
conducted under varying temperature and pressure conditions, the constituent elements
of the fibre are removed one by
one by gasification, eventually
leaving a fibre just seven micron
thick and consisting of virtually pure carbon with a stable
graphite structure. At 0.007
millimetres, the diameter of the
fibre is about a tenth that of a
human hair. For automotive applications, approximately 50,000
of these individual filaments are
bundled into rovings or heavy
tows, which are also used in large
rotor blades for wind turbines.
The fibre bundles are subsequently processed into special
non-woven fabrics.
Weaving would kink the fibres
and detract from their special

properties. The specific
alignment of the fibres in the
same plane is crucial to achieving the optimum attributes of a
CFRP component.
With more than ten years of research and production expertise,
BMW, together with
SGL Automotive Carbon Fibers,
now develops and produces
carbon fibres and carbon fibre
sheets. An ultra-modern, renewably powered carbon fibre production plant was built at Moses
Lake, Washington, USA.
After a three-month testing
period, the production of carbon
fibres for processing at the BMW
joint venture plant in Wackersdorf, Germany, started in 2011.
During the so-called “preforming” stage in the BMW plants
at Landshut and Leipzig, the
custom-cut but still flat fabric
begins to acquire a three-dimensional shape. Several of
these preformed stacks can
eventuallybe joined to form a
larger component. In this way,

20 jec composites magazine / No83 August - September 2013

CFRP can be used, for example,
to produce highly integrated
components with a large surface
area, which would be extremely
cumbersome to manufacture
from aluminium or sheet steel.
The BMW Group has acquired
valuable expertise over
the years to render the still flexible fabric sufficiently manageable so that the preforms
maintain a stable shape and
can be joined with maximum
precision. The preformed stacks
are then ready for the next stage
in the process: resin injection,
or impregnation. Only through
bonding the fibres with the resin,
and the subsequent hardening process, does the material
achieve its rigidity, which is key
to its outstanding qualities. The
resin transfer moulding (RTM)
process involves high-pressure
injection of resin into the
preforms. The impregnation
of the fibres by the resin is a
highly complex process full of
conflicting requirements. For
example, on the one hand the

JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013

Table of Contents for the Digital Edition of JEC COMPOSITES MAGAZINE - Issue #83 - August/September 2013