A driver or passenger seat can be compared to a good piece of
clothing: It must be very well finished, suit well, fit perfectly and must
neither pinch nor scratch. Due to in-house development and production it was
possible to exclusively produce the 7 Series model’s seats featuring innovative
elements in accordance with the customer requests and to follow the aim of "offering
maximum comfort at maximum functionality". Thanks to pathbreaking production
methods and the BMW specialists’ long-standing know-how these comfortable seats
with their different production variants currently amounting to 6,000 became a
reality. The use of virtual tools helped at an early stage to considerably
reduce by up to 30 percent the time needed for the development of features such
as seat covers through the quick and accurate creation of prototypes. Production
methods have been redeveloped and innovative technologies have been used to pay
tribute to the demands of flexibility, a wide range of options, sustained
production and, last but not least, profitability.
The vast array of high-tech features of the new 7 Series model’s
seats, whose full equipment includes up to 34 electromotors and 6 electronic
control units, made necessary the integration of new methods of testing. The
electrically adjustable backrest width, a feature never seen before in
automobile construction, and the climate seat featuring active ventilation,
could only be realized through the use of revolutionary sewing methods and
innovative materials (climate-controlled leather).
At the BMW Plant in Dingolfing around 700 employees are
currently working on the production of seats, being responsible for the
manufacture of complete seats for 5 and 7 Series cars as well as for sewing
high-quality leather for small-lot and individual production.
Robots perform three-dimensional sewing operations – an industry first.
Three-dimensional sewing operations made possible by
state-of-theart control technology has become a reality. A robot-controlled
sewing system, a BMW in-house development, produces the components for the 7 Series model’s exclusive leather upholstery.
When the BMW product and process engineers designed the system they were, for example, initially faced with the apparently easy
task of joining the varicoloured threads necessary for the different
leather colours to a filament yarn that automatically goes through a
needle’s eye in case of a colour change. It was not possible to simply knot
the two ends of the threads together in case of a colour change as even
the world’s smallest knot does not go through a needle’s eye that is
only 0.5–0.7 mm wide. Another method had to be found to tie the
threads together. The answer was "splicing", which is a method and a
technical term better known from sailing. What does "splicing" mean in
this respect? In an air chamber the ends of the threads are
disentangled into individual threads and twisted together at the same time. The
spliced joint has a tensile strength of about 90 percent, which is
enough for the old thread to pull the new thread through the needle’s eye, the advantage being that the spliced joint is not thicker than the
thread itself, which allows an all-automatic change of colours.
The method of "splicing" forms an important yet small part of
the complex robotized sewing system that was launched in the middle
The system is a closed, square conveyor system that is
masterminded by two interbus systems. It is currently made up of six and in
future of eight workpiece carriers, two all-automatic colour yarn changers for
15 colours, a colour recognition sensor and pleating tool, three
docking stations that connect the travelling workpiece carriers with the
bus lines and a robot, which is the actual highlight, that, in addition to
two- and three-dimensional sewing operations, is responsible for changing
the upper thread and the under-thread in case of a colour change.
The following is to give you an example of the sewing operations
that have to be performed on the centre section of the BMW 7 Series
model’s backrest’s rear side: The required leather components are put on
the appropriate workpiece carrier – three leather pieces are placed
in the middle and two leather strips respectively to the left and to
the right of them. The colour of the leather is determined by means of
sensors. The respective information is transmitted to the workpiece carrier’s
data storage medium, the former advancing to and stopping at the
first docking station. The data are read out from the storage medium,
evaluated and passed on. The changer of the upper- and under-thread is told
which colour is to be used. The pleating tool receives information on
the position of the transverse seams and the robot is told which
program must be selected for two-dimensional and three-dimensional seams.
Then the actual production process starts. In case of a colour
change a transport slide takes the bobbin out of the magazine. After that,
the old bobbin is replaced by the new one by a robot. A grappler grips
the upperthread spool and takes it out of the changer system equipped with 16 different colour variants and threads the yarn through the
needle eye of the sewing arm. The following commands are received by the
workpiece carrier via the bus system: Raise middle part, press side parts
to the middle parts, sew transverse seams. After that, the middle piece
is stretched by means of air intake in order to ensure precise
longitudinal seams (three-dimensional seams). The enormous advantage of this high-precision system lies in its flexibility and high degree of automation, allowing the processing of different pieces of
leather and the repositioning of seams. The system can even be used for the processing of other parts. A second robot that will be
responsible for the production of the front and rear seats of other models is
planned to be commissioned in 2003.
The use of the vacuum foaming method in the production of seats. Back in 1995 the BMW Plant in Dingolfing launched the
conventional production of foam parts for front seats, rear seats and center
armrests. Three years later the vacuum foaming technology was developed
within the company, which was further advanced since then and finally
made ready for use in series production. With this technology the
engineers achieved a weight reduction by 20 percent while maintaining the
quality standard and realizing a high level of fatigue strength and
superior comfort at the same time. A further effect of this technology is
a reduction of costs exceeding 1 million Euros each year as less
material is needed.
Hidden perfection: the reaction process.
Fine mist – a separating agent – is sprayed by a robot on the
aluminium tool heated up to a temperature of 55° Celsius, this process
being necessary for the later removal of the finished formed parts.
Then various foam-in parts like wire, fleece etc. are fixed in the
form, these later serving as fastening points when upholstering. Two huge
mixing heads are moved by a so-called gantry robot along a programmed
and type-specific travel way above the tool, relasing the fluid PUR
system with a pressure of up to 200 bar. The two components polyhydric
alcohol and isocyanate are mixed in the mixing head, flow into the
aluminium tool and moisten the bottom of the lower part, which is the part
of the upholstery that will be visible in the end. After the tool has
been closed, the hardening process is started, whereby millions of small
cells are stabilized and consolidated at a temperature of more than 100°
Innovation: Vacuum hardening process.
During the conventional non-vacuum hardening process millions of foam cells "battle with" the atmospheric pressure when rising up
within the tool and are thus prevented from adopting their ideal form.
Due to the pressure exerted on them the cell structure becomes more compact
and therefore heavier.
During the new production process the tool’s top side and bottom
side are tightly pressed together by air cushions after the mould
carrier has been closed. The air in the tool is sucked out at the annular
gap via a closed-circuit pipeline. Thanks to the vacuum state the foam
develops an ideal cell structure, even though 20 percent less material is
used in the process. During the hardening process the vacuum is removed,
the tool is automatically opened and the finished foam part is taken
out of the tool. To open the cell walls that are still closed and to make
the seat component elastic, the former is subsequently processed by a
vacuum press. Finally, the component is made available to the
upholsterers after it has cooled down and undergone examination.
The new vacuum process is consistent with the environment and complies with the high BMW safety and quality standards. At the moment the technology is exclusively used at the Dingolfing
Plant. Plans to extend it to the Munich Plant’s production are currently