How a BMW i is created: The LifeDrive concept in four steps.
The BMW i3 is an electrically powered vehicle produced from modern lightweight materials and stands for a new, sustainable mobility. Its innovative architecture consists of two elements: The aluminum Drive-module with drive systems, chassis and energy storage, as well as the Life-module of carbon fiber reinforced plastic (CFRP), which constitutes the passenger compartment. Thanks to the LifeDrive concept and the use of CFRP the production time is also reduced to the half compared to the conventional automobile and is more economical.
Life module from CFRP: An innovative cabin.
The BMW i3 The Life-module primarily consists of carbon fiber-reinforced plastic, in short: CFRP. The creation of this innovative material takes place in the joint venture, SGL Automotive Carbon Fibers (SGL ACF) CF in the American Moses Lake and the Wackersdorf Innovation Park.
Carbon fiber production.
The carbon fiber is produced from a thermoplastic textile fibers made from polyacrylonitrile. This is to be split into a complex process until only an seven microns thin fiber consisting of pure hydrocarbons remains. A human hair measures about 50 microns in comparison. Subsequently, approximately 50,000 of these individual filaments to so-called "roving", ie combined and wound fiber bundles. The energy is produced exclusively from locally available renewable hydropower and is therefore 100 percent CO2-free.
Further processing into textile scrims.
In the second step, the fiber bundles are processed into lightweight textile scrims. Nest with different fiber orientations are superimposed to form stacks, arranged and designed in several layers and different orientations. The CFRP waste is recycled and is used again in the production. Around ten percent of the amount of carbon fiber used in the BMW i3 are recycled material already.
Production of CFRP components.
The stacks are further processed in the BMW plants in Landshut and Leipzig to body parts for the BMW i3 and BMW i8. A heating tool gives the cut carbon fiber scrims initially a stable, three-dimensional shape. Several of these preformed parison blanks can then be assembled into a larger component. So also large-area body parts can be produced, which could be realized only with difficulty or with significantly higher costs of aluminum or steel sheet. After making up preforms and the next process step follows: the resins under high pressure after the RTM (Resin Transfer Moulding). In this case, liquid resin is injected into the preform blank at high pressure. Only by combining the fibers with the resin, and then curing the material gets its stiffness and thus its excellent properties.
The carbon fiber composite components are joined together to the basic structure of the Life-module. Due to the high geometric integration the BMW i3 Life-module needs only one third of the components in comparison with a conventional steel body - 150 CFRP components. In CFRP body an exclusively modern, 100 percent automated bonding technique is used instead of screws, rivets and welding. The individual components are assembled to contactless up to a precisely defined adhesive gap in the unique, joining process developed by BMW. This guarantees the optimum strength to the bond.
Outer skin of the BMW i: Lightweight and durable.
The BMW i3 is the first BMW ever, in which the entire outer skin is made of plastic. Only the roof is made of recycled CFRP. The parts are by half lighter than steel and at the same time a corrosion-free surface protection, which can be produced energy-saving. The material is also insensitive to minor damage. 25 percent of the materials used for the thermoplastic outer parts are either recycled or made from renewable resources.
When painting the outer skin panels shine and resistance to environmental influences. The paint passes through dry separation without the waste of water and with only a quarter of the usual energy expenditure. In addition, 70 percent less water is needed because the body no longer needs to be protected against corrosion in several steps, painted and dried. The elimination of the conventional cathodic painting 10 kg weight can be saved in addition.
Drive-Module: structural support, high-voltage battery and electric motor.
The Drive-structure carrier of the BMW i3 consists of coated aluminum carriers and aluminum castings. The complex frame construction of approximately 160 individual parts provides an ideal housing for the battery and allows for optimal weight distribution with a very low center of gravity in the vehicle - with consequent benefits for driving dynamics.
In the production of the battery extensive BMW expertise is used. First, high-performance lithium-ion cells are processed into solar modules of 400 assembly steps together. Then the modules are lifted into a storage sump aluminum and manually interconnected in series. At the end of the assembly of storage lid and base takes place. The memory is designed so that individual battery modules can be easily replaced for repair.
In the interior of the electric motor is a housing with stator and rotor. The stator is the inner core of the engine and is wound around two kilometers of copper wire. The special feature: Compared to other electric machines it is very small and compact by a special winding the copper wires. That saves weight and space. Before the rotor is in the inner housing, it is covered with a thin resin layer. The 125 kW engine E and the drive electronics has been developed by the BMW Group.
BMW i installation: Parallel processes.
When assembling the drive module 230 kilogram battery is built into the chassis and placed the engine-transmission unit.
An optional Range Extender (two-cylinder gasoline engine) is available, which raises the car's range to 300 kilometers. After mounting the preassembled front axle and other structural parts of the BMW i3, the Drive-module is ready for final assembly.
From the body shop the CFRP passenger cell enters the assembly hall. On the so-called "life-belt" it receives the custom features. This is followed by the "marriage" with the aluminum Drive-module. Cabin and chassis are thereby glued together and screwed in addition for optimum stability. After that the BMW i3 receives its final outer plastic dress.
The lead time in body construction and installation is 20 hours, only half the conventional production time. The reason: operations take place in parallel and fewer body parts in the CFRP structure need to be installed. Together with other BMW vehicles the BMW i3 then goes through the finish area with comprehensive quality controls.