We have the first pictures of the BMW i3 production line in Leipzig. With full production starting in August and BMW has already been running a few i3 test chassis through the production process.
BMW will launch the electrically powered i3 this summer, arriving in European dealerships in October. US customers will have wait till early 2014 to get their hands on an i3. The i3 represents a new form of sustainable mobility in urban areas. As the first premium electric vehicle, the BMW i3 rises to the social, ecological and economic challenges of our time. With its groundbreaking new vehicle architecture, the concept calls for the use of modern lightweight construction materials as well as innovative production processes. Take a tour of the production process used to build the BMW i3.
Industrialization of CFRP production
In order to compensate for the extra weight of the electrical components, BMW i consistently uses lightweight construction and innovative materials in its vehicles. The concept and production of the car were also completely redefined at the outset. The Life module – the passenger cell of the future BMW i3 – is made primarily of carbon fiber-reinforced plastic, i.e. CFRP. The use of this light and crash-resistant high-tech material on such a scale is unique in the mass production of a vehicle, as the large-scale use of CFRP was previously deemed too expensive, and the processing and manufacture too complex and insufficiently flexible. But BMW recognized the potential of the material early on, and after over ten years of intensive research and process optimization, materials, systems and tools, the BMW Group is the only automobile manufacturer to possess the necessary expertise for industrialized CFRP mass production. The advanced level of the production process today is discernible above all in the process safety achieved, the fast cycle times, and the high standard of quality in the CFRP components produced.
Lightweight construction materials such as aluminum or carbon fiber nevertheless require greater energy expenditure for their manufacture than steel, for example. This is why BMW attaches maximum importance to sparing resources and extensively CO2-free power supply in manufacturing and processing. Energy and water consumption, process waste water, solvent emissions and waste are the main focus here, with the savings a direct result of the new production concept. Together with the affiliated joint venture SGL Automotive Carbon Fibers (ACF), the BMW Group holds a unique position in the industry as the "owner" of all process steps, from fiber through to the recycling of fibers and composites.
Moses Lake: carbon fiber manufacture with hydroelectric power
A precursor, a thermoplastic textile fiber made of polyacrylonitrile, is used to create the carbon fibre at SGL ACF in Moses Lake, U.S.A. All elements of the fiber are split off in gaseous form in a complex, multi-stage process until only one fiber is left consisting of virtually pure carbon with a stable graphite structure. This is only seven micrometers (0.007 millimeters) thick, compared to a human hair, which measures around 50 micrometers. For use in the automotive sector, around 50,000 of these individual filaments are combined into "rovings" or "heavy tows" and wound for further processing. In addition to the automotive applications, fiber composites of this thickness are also used in large turbine blades of wind power systems, for example.
To manufacture the carbon fibers in Moses Lake, all of the energy for production is obtained renewable from locally available hydroelectric power, making it 100 per cent CO2-free. The ultramodern works in Washington State also sets standards in energy efficiency. In comparison to conventional CFRP production, the CO2e (global warming potential) saving is around 50 per cent. In order for the BMW i3 to roll off the assembly line in Leipzig on schedule at the end of 2013, the ultralight high-tech fibers have been in production since the end of 2011. Two production lines each with a current capacity of 1,500 tonnes per year ensure the necessary supply. This constitutes a supply of around ten per cent of global CFRP production today.
The two parent companies BMW Group and SGL Group have invested around US $100 million in the production facility in Moses Lake to date and have created 80 new jobs.
Wackersdorf: processing into textile fabrics
At the second site of the joint venture, in Wackersdorf Innovation Park, the fiber bundles produced in Moses Lake are further processed into light textile fabrics on an industrial scale. Unlike woven fabrics, the fibers are arranged side by side on one level rather than interlaced or interwoven with each other. A woven structure would bend the fibres and reduce the excellent properties somewhat, because it is the fiber alignment itself in the fabric that guarantees the optimal characteristics of the eventually produced component.
After an investment of EUR 20 million and the creation of around 100 new jobs, today several thousand tonnes of carbon fiber fabrics can be manufactured per year at the Wackersdorf site. These form the starting material for the manufacture of CFRP parts and components in the BMW works in Landshut and Leipzig.
Landshut: further processing into CFRP components
The carbon fiber fabrics supplied from Wackersdorf are further processed into CFRP body parts at the pressing plants in Landshut and Leipzig. In Landshut, the BMW Group specialists have succeeded in further developing and automating the manufacturing process for CFRP components in the last ten years to such a point that today, economical and high-quality mass production with high process safety is possible. The roofs for the BMW M3 and M6 models and the bumper supports for the M6 have already been in industrialized CFRP production in Landshut for some time.
After an investment of EUR 40 million and the start of carbon production with around 100 employees in March 2012, the Landshut site is considered the definitive innovation and production center for CFRP components. Landshut relies on its own junior staff to secure the high level of technical expertise needed for processing innovative lightweight construction materials, increasing the number of trainees to 40 young employees per year.
Leipzig: proprietary material manufacturing with variable formulation
The newly established pressing plant in Leipzig is equipped with state-of-the-art technology for CFRP in automotive manufacture. BMW now manufactures its own carbon fibre composite materials at this facility designed for industrial mass production. The formulation, i.e. the composition, strength and geometry of the CFRP parts, can be individually modified or adapted in the pressing plant at any time during the manufacturing process depending on the design specifications. The tailor-made carbon fiber fabric supplied from Wackersdorf is first formed into its eventual shape in the preforming process. A heating tool gives the laminate a stable, three-dimensional form. Several of these preformed workpieces can then be assembled into a larger component. This makes it possible to manufacture large body components, which are difficult to produce in aluminum or sheet steel. After finishing and preforming, the next process step is resignation under high pressure using the RTM process (Resin Transfer Molding). The RTM resin injection procedure used in the aerospace industry and in boat and wind turbine construction involves injecting liquid resin into preformed workpieces under high pressure. The bonding of the fibers with the resin and the subsequent hardening lends the material its stiffness and thereby its excellent properties.
CFRP industrialization has begun
With a closing force of up to 4,500 tonnes, the pressing plant works in accordance with precisely defined time, pressure and temperature parameters developed in-house until the resin has bonded with the hardening agent completely and is cured. This special proprietary BMW manufacturing process eliminates the need for an additional time-consuming curing process in a separate oven, which usually follows a CFRP pressing step. This new pressing plant specially designed for CFRP does not resemble a conventional sheet steel manufacturing facility. The production-specific investments have a much more streamlined investment structure, significantly reducing construction costs through the elimination of a classic paintshop and cathodic immersion bath coating, for example. The production process is trend setting, saves a huge amount of time and makes the industrialization of large CFRP composite components realistic for the first time. This is the only way to obtain preformed parts from the pressing plant in a matter of single-digit minutes.
Even complex assemblies such as an entire side door frame of the BMW i3 Life module leave the facility with many structural elements already integrated, optimal product quality, flawless functionality and very high fitting accuracy. The only remaining tasks are refinements such as precision cutting of the component contour and the insertion of any missing openings. For this, the parts are processed with a special water jet cutting system, sandblasted, and the adhesive surfaces roughened for further processing. Unlike the CFRP preformed part, it would be necessary to assemble several internal and external components in succession for a traditional sheet steel side frame. A normal sheet steel architecture requires significantly more body parts overall and so would be heavier than the LifeDrive module of the BMW i3 because of its design.
Revolution in car body construction with new precision tools
The newly produced CFRP composite components from the new Leipzig pressing plant and supplied CFRP parts from the Landshut pressing plant are assembled in the new car body construction hall. Around 150 parts, one third fewer than in the conventional sheet steel construction, make up the basic form of the Life module of a BMW i3. There is no noise pollution from screwing or riveting, no sparks flying during welding, and only the latest adhesive technology is used, which is 100 per cent automated. A technology mastered by BMW alone. In the unique joining process developed by BMW, the individual components are assembled without touching to an adhesive gap of 1/16 of an inch in order to ensure optimal strength after the adhesive procedure. In the newly developed manufacturing process, all connecting components in the Life module are always separated by the same gap and so receive the same amount of adhesive. Only this precision guarantees perfect power transmission between the individual CFRP components and therefore the highest standard of quality in the mass production series. In total, there is a precisely defined bonded range per car of 525 feet in length and 3/4 of an inch in width.
Time saved with instant adhesive
CFRP car body compartments are generally only manufactured for special vehicles, in racing and for extravagant individual sports cars. The production costs are of comparatively minor importance for these small production quantities. The curing time for the adhesive bonds can be more than one day. To minimize this time for mass production of the BMW i3, BMW has greatly accelerated this curing process.
A newly developed adhesive can now be processed for only 90 seconds before developing adhesion following application to a component. Half an hour later it is hard. This property represents a ten-fold acceleration of a traditional bonding process. In order to further reduce the curing time to the single-digit minute range, BMW has developed an additional thermal process. This involves additional heating of specific adhesion points on the CFRP parts to be bonded to further accelerate the curing process by a factor of 32.
Body color can be chosen up to six days before final assembly
The high-strength CFRP passenger cell (Life module) manufactured in Leipzig passes from body construction to the new assembly hall where it is bonded with the aluminum Drive module. The basic Drive module supplied from Dingolfing is completed in Leipzig before being screwed and glued inseparably to the Life module. Only then does the internal CFRP Life module cell receive its final external plastic housing. For the painted multi-part outer skin, thermoplastic injection molded plastics are primarily used, as is also the case in traditional vehicle construction (front/rear apron, side sill etc.). The colored plastic preformed parts are screwed inconspicuously to the interior Life module cell during final assembly using special mounts.
CFRP recycling and the BMW i: a closed loop
In the course of developing the BMW i, the BMW Group devised the first recycling concept of its kind worldwide for CFRP components, body components and sorted production waste which was suitable for series production. In different procedures, the valuable recyclable materials from production and even from damaged/scrapped vehicles are reused in automotive construction and channeled back to the production process or used in other applications.
In the recycling process, carbon fiber recycling with "dry", unresinated material is differentiated from composite material recycling (CFRP), in which "wet", resinated plastics are used. The dry carbon offcuts created during production can be reprocessed into valuable non-woven textiles and reused in the manufacturing cycle. Around ten per cent of the carbon fiber used in the BMW i3 now is recycled material, a process unique in the automotive industry worldwide.
In composite material recycling – the processing of resinated carbon fibers – CFRP is first separated industrially from the mixture with other plastics and, for example, processed in a pyrolysis facility. The heat from the resin breakdown process is used to separate the undamaged carbon fibers. These fibers can then be used to manufacture components and reduce the new fiber requirement. For example, the rear seat pan is made from this recycled carbon fiber. It meets the BMW quality standard 100 per cent and weights 30 per cent less than the conventional glass fiber matt construction. Ground or cut into short fibers, the recycled CFRP or carbon fibers are also used in many areas outside the automotive industry, for example, in the textile and electronics industries (housing material for control units). The use of "secondary CFRP fibers" is part of a sustainable material cycle that spares resources and secures raw materials for future uses.
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