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BMW Media information 04/2014 Page 1
1. The BMW i production concept. ....................................................................... 2
2. Life module: full integration of CFRP production in the
manufacturing process. ......................................................................................... 3
3. Lightweight and robust: the thermoplastic outer skin. ....................... 5
4. Drive module: lightweight construction for the chassis structure
parts, electric motor and high-voltage battery. ....................................... 6
5. Parallel processes: assembly. ............................................................................ 8
The BMW i8 Production.
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BMW Medien- information 04/2014 Seite 2
Innovative manufacturing technologies and the application of new materials
characterize the production process for BMW i cars. Their production stands
at the beginning of a value chain that is completely aligned with sustainability
criteria. From the raw materials production to the energy-efficient vehicle
operations and the recycling as the last step, the chosen approach makes a
considerable contribution to the favorable overall life cycle assessment of the
plug-in hybrid sports car BMW i8. In both the development and the
production of the BMW i8, the outstanding technological expertise of the
BMW Group comes to the fore.
The BMW Group’s global lead in automotive engineering is demonstrated,
among other things, in the industrial production of components made of
carbon fiber reinforced plastics (CFRP). The development and production of
both the combustion engine and the electric motor of the hybrid sports car
are also carried out completely by the BMW Group.
The innovative vehicle architecture of the BMW i8 comprises two elements:
the Life module, the passenger cell made of carbon fiber reinforced plastic
(CFRP), and the aluminum Drive module, which incorporates the entire
drivetrain and chassis technology. The LifeDrive concept and use of CFRP
allows production times to be cut by half compared to those required for an
equivalent car built along conventional lines. The process is less investment
intensive as the high costs required for a conventional press shop and paint
shop are no longer an issue and the Life and Drive modules can be
manufactured alongside one another.
The BMW i production network comprises a plant in Moses Lake, Washington
State, for the carbon fiber production and a plant in Wackersdorf for the
processing into carbon fiber laminates. Both these facilities are operated by
SGL Automotive Carbon Fibers (ACF), a joint venture set up by the
BMW Group and the SGL Group. They are joined by the BMW Group’s own
plants in Dingolfing, Landshut and Leipzig.
1. The BMW i production concept.
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When it comes to the BMW i8, the BMW Group can draw on many years of
experience in working with carbon fiber reinforced plastics (CKRP). The
production of the CFRP passenger cell for the plug-in hybrid sports car is
completely integrated in the BMW i car manufacturing process.
Carbon fiber production using hydroelectric power / Moses Lake,
The carbon fiber plant in Moses Lake (USA) produces carbon fibers from a
polyacrylonitrile-based thermoplastic textile fiber precursor. A complex multi-
stage process eventually leaves a fiber that consists of virtually pure carbon
with a stable graphite structure. This fiber is just seven microns
(0.007 millimeters) thick. A human hair, by comparison, has a diameter of
50 microns. For automotive application, approximately 50,000 of these
individual filaments are bundled and wound on reels, prior to further
processing. Even in this first step, the production of carbon fibers at the plant
in Moses Lake, WA, the power needed in production is solely sourced from
fully renewable energy sources.
Processing into carbon fiber laminates in Wackersdorf.
The fiber rovings produced in Moses Lake are sent to the Wackersdorf
Innovation Park, for industrial processing into lightweight carbon fiber
laminates. Carbon laminates with different fiber alignments are arranged into
stacks made up of several layers and following various lines, before being cut
Production of CFRP components in Landshut and Leipzig.
The stacks supplied by Wackersdorf are turned into CFRP body components
at the innovation and production facilities at BMW’s Landshut and Leipzig
plants. The body parts for the BMW i8 are made in Landshut while Leipzig
produces the components for the BMW i3.
A preform mold is used to give the preformed carbon fiber stacks a stable,
three-dimensional form. Several of these preformed blanks can then be joined
to form a larger component. In this way CFRP can be used, for example, to
produce body components with a large surface area that would be difficult –
or significantly more expensive – to manufacture from aluminum or sheet
steel. Preforming and preform joining are followed by the next stage in the
2. Life module: full integration of CFRP
production in the manufacturing
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process: high-pressure resin injection using Resin Transfer Molding (RTM). Here,
liquid resin is injected into the preforms under high pressure. As the fibers and
the resin bond, and in the subsequent hardening process, the material
acquires the rigidity that is key to its outstanding qualities.
The CFRP presses work to precisely defined, specially developed time,
pressure and temperature parameters until the resin and hardener are fully
cross-linked and the resin is hard. This automated manufacturing process
eliminates the need for the time-consuming hardening process in an oven,
which would normally be required in manual CFRP production processes.
The CFRP process is no longer comparable with conventional sheet steel
manufacturing. This industrialized manufacture of CFRP is extremely
economical and makes the production of large CFRP composite components
for the automotive industry a feasible proposition for the first time.
Even complex assemblies with many structural elements already integrated,
such as an entire side frame for the BMW i8 Life module, are produced at the
facility with a high level of automation. Additional processing stages include
the finishing work, such as precise contour cutting and the insertion of
remaining openings. This work is performed using a special waterjet cutting
system and the bonding surfaces are then sandblasted before further
processing. A conventional sheet steel side frame, by contrast, would have to
be built up successively from several different inner and outer components.
Joining of the CFRP components at the body shop in Leipzig.
The CFRP composite components are bonded together in the new body
shop in Leipzig. This is where the basic structure of the Life module for the
BMW i3 and the BMW i8 takes shape. There is no noise from bolting or
riveting and no sparks from welding in the manufacturing process for a CFRP
body. Instead, only the latest bonding technology is used, which is
100 per cent automated. In this unique, BMW-developed assembly process,
the individual components are positioned at a precisely defined bond line gap
in order to ensure the resulting joint is as strong as possible.
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The outer skin of the BMW i8 is made entirely of thermoplastic; it is produced
at the BMW site in Landshut. The weight of the plastic parts is around half
that of sheet steel parts. Plastic also provides corrosion-free outer protection
and requires less energy to manufacture, as well as being resistant to minor
The futuristic shape of the BMW i8 prompted the specialists in the production
area of Plastics Exterior to align the production technology accordingly. The
size of the components and the complex design language, combined with the
car’s gap size requirements, led to the model-specific development of the
synthetic granules as well as to an alignment of the production, which is
specifically geared toward meeting the BMW i8 requirements. The bumpers,
for instance, are given in their multi-tone paint coat in a highly specialized
facility. This way a bi-color look can be achieved; at the same time, the weight
is optimized significantly. Contrary to conventional models, not the complete
body of the BMW i models is pained in a multi-stage process. Instead, the
bumpers, front, rear and side parts are painted individually, which conserves
resources. In the first step of the painting procedure, the entire bumpers are
painted in black. Subsequently, the paint specialists at the Landshut site cover
parts of the component with masking tape to ensure the separation of the
different paint coats. In meticulous, delicate manual work, they cover the areas
that are supposed to stay black. Then, the bumper goes through the paint
facility again, this time for the second color, which is applied to all areas that
are not masked. This paint process is handled by an innovative, automated
robot facility. At the rear bumper, a tri-color design is achieved thanks to the
additional mounting of a separately painted component; this additional color
imparts a striking visual effect. While the conventional paint process coats the
entire body-in-white in one piece, the assembly of separately painted
attachment parts offers the possibility to create very special visual effects.
3. Lightweight and robust:
the thermoplastic outer skin.