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Each day as many as 1,200 tons of sheet metal are
processed in the various press lines. Being the biggest press shop
within the production network, the Dingolfing Plant has twelve press
lines with 65 individual presses, nine multi-stage presses and five
so-called coil plants. With the latter blanks of different sizes can
be cut out from the sheet metal coils. More than 300,000 body
components made of sheet metal such as roofs, doors, side panels or
floor pans are produced for all BMW model series in the Dingolfing
press shop every day.
Steel and aluminum sheet rolls are the base
material
The steel and aluminum sheet is delivered in
coils that weigh up to 35 tons. The width, thickness and form of
galvanizing depend on the part to be pressed. The thickness is between
0.65 mm and 3 mm. 82 percent of the new 7 Series model’s sheet metal
components are made of high strength steel and approximately 95 percent
of the sheet metals are already galvanized on both sides upon
delivery. They are used for those parts of the body where protection
against corrosion is of particular importance. The external sheet
metal of the underbody, for example, is galvanized on both sides.
After the blanks have been cut out from the coils
– without wasting too much material – they are processed by press
plants which are up to 90 meters long. Depending on how complex the
desired pressed part is, three to seven steps have to be completed.
The material has to be drawn, that is to be shaped, cut, edged
(whereby a narrow brink on the edge of the sheet metal is bent) or
reshaped. The entire waste material produced during these processes is
collected and returned to the steel or aluminum supplier’s production
cycle.
In the press shop the utmost cleanliness has to be
observed during operation and it goes without saying that we fulfil
this standard. A human being’s hair, for example, lost during the
forming process would leave its mark on the sheet steel part and lead
to an undesirable asperity, as the slightest impurities and deviations
in dimension have an adverse and enduring effect on the quality of the
product.
Vacuum transfer press – highly flexible and
powerful
One of the biggest vacuum transfer press in the
automotive industry the world over was put into operation at the
Dingolfing Plant in autumn 1999. The press with a length of 90 meters,
which costs more than 45 million Euros, has a maximum press force of
9,500 t and is able to produce 13 parts a minute. Blanks with a size
of 4.5 x 2 meters can be processed with this press. Amongst other
things, this press makes possible the production of a complex side
panel from one single piece of sheet steel. The all-automatic tool
change does not even take eight minutes.
Formed with high pressure
Since spring 2000 the internal high-pressure
forming method is applied at the Dingolfing stamping shop. To put it
in simple terms: When applying this method, a water-oil emulsion is
pressed into tubes, these then being formed into body parts by the
closed tool with a locking pressure of up to 5,000 t. Inside the tubes
a pressure of up to 400 bar is built up. This trendsetting method,
which makes possible the production of complex and high-strength
components, allows the reduction of the number of body parts. BMW is
the only manufacturer to produce parts by means of the internal
high-pressure forming method in this complex form. Because of these
achievements the steel innovation prize was awarded to BMW in 2000.
Surface quality lies in the hands of the production
workers
At the end of the production process our
production workers finally inspect with a practised eye each steel and
aluminum part. There is no other system that can replace the
scrutinizing quality of the human eye as there is an infinite number
of different types and forms of asperities and cracks. Under the
prerequisite of appropriate response times there are no computer-aided
systems nowadays that can be used for carrying out this task as there
is an almost infinite number of representations of problematic
conditions of surfaces. Should there actually be some deviation from
the projected state, the affected production line will be
stopped. The production workers employed at the facility where the
irregularities were noticed localize the source of error and are also
responsible for correcting the failure as quickly as possible.
Visual and measurement tools equipped quality checking of the painted
surface
Metrology
Metrology – recognizing trends, taking preventive
measures. Dimensional inspection, that is checking the predefined
dimensions of a sheet steel part, is done most accurately by means of
robots. Man particularly uses technology when it comes to measuring
complex three-dimensional objects. Thus for example man is not in a
position to produce feasible results when taking the accurate
measurement of a cone’s height or a point on a tight surface such as a
fender. Measurement robots are used for this task that work with an
accuracy of a hundredth of a millimeter.
State of the art measurement technology in use with the BMW 7 Series
The parts are measured by means of random sampling
in separate rooms for measuring. The measurement conditions in these
rooms are always the same, that is the temperature is kept to a
constant value and there are specially supported measuring tables that
help to prevent measurement errors attributable to vibrations caused
by the production process. Random sampling is sufficient as changes in
measurement only occur during the production of several umpteen
thousand pressed parts. Thus deviations can be recognized in time long
before the tolerance limit is reached and, if necessary, preventive
action can be taken by adjusting, for example, the presses’ tools
which weigh up to 50 tons.
Measurement of the 7 Series side frame
The press and stamping shop in Dingolfing
| |
Press shop |
Stamping shop |
|
Employees |
ca. 1,200 |
ca. 325 |
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Volume |
40,600 qm |
11,600 qm |
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Range of components |
More than 800 serial parts; Range of components extends from small
add-on pieces up to side panels with a length of four meters |
Approximately 4,100 serial parts; Range of components encompasses
add-on pieces, structural parts and parts produced by means of the
Internal High-pressure Forming method |
|
Consumption of material |
1,200 tons / day |
325 tons / day |
|
Production volume |
more than 300,000 / day |
up to 1,250,000 Teile parts / day |
|
Number of presses |
79 - Press forces between 300 up to 9,500 tons |
25 - Press force from 100 to 5,000 tons |
|
Tool weight |
up to 50 tons |
up to 40 tons |
|
Retooling process - depending on the facility |
up to 40 retooling processes/day, Retooling times: 7 up to 50
minutes |
up to 130 retooling processes/day, Retooling times: 20 up to 120
minutes |
The body assembly shop – Bonding, welding, bolting
done to perfection
While in the pressing plant it is quite hard to
imagine that the stacked sheet steel will take the shape of an
automobile, but it is much easier to get an idea of the end product in the
body assembly shop. At BMW the construction of the body-in-white
incorporates the gradual joining of several hundred individual steel
and aluminum parts of many different sizes and thicknesses. In the
body assembly shop the foundations are laid for the car’s final
characteristics such as its crash behavior. The main objective in the
construction of the body -in-white is in simple terms the production
of a high-accuracy body ready to be passed on to the experts in the
paint shop.
Fully automated robot station doing adhesive and welding operations to
connect the side frame with the body shell
An intelligent mixture of materials – large-scale
use of high-strength steel and aluminum where it is feasible.
Lightness, stiffness, paintability and corrosion resistance are just
some of the ever-increasing demands modern bodies have to fulfill
today. This is why the use of a specific, intelligent mixture of
materials has long been a tradition at BMW, most obviously and
consistently realized in the production of the new 7 Series model’s
body-in-white.
Light metals such as aluminum are used for this
trendsetting automobile particularly where they entail true advantages
for the customer, so for example in the production of side panels and
the hood. The basic material used is steel of a higher strength. The
intelligent mixed construction leads to a desirable reduction of
weight resulting in a lower fuel consumption as well as an optimum
distribution of weight on the axles, which has a positive effect on
the dynamic performance as everybody knows.
82 percent of the BMW 7 Series model’s
body-in-white consists of high-strength steel which offers advantages
in terms of crash behavior and weight. The rest is made up of
aluminum. About 480 steel sheet and aluminum parts with a thickness
ranging from 1 mm to 2.25 mm are welded, bonded and bolted in the body
assembly shop. Almost 5,800 welding spots, the application of adhesive
on more than 150 running meters, weld seams of an overall length of
more than four meters, bolted joints on lids and fenders as well as
further conventional inert gas weld seams make the new BMW 7 Series
model’s body-in-white an integrated whole.
In order to limit the great variety of variants
before assembly in order to comply with the customer-oriented sales
and production process KOVP, only four different bodies-in-white are
produced for the new 7 Series model: a left-hand drive version, a
right-hand drive version, one variant with and one variant without
sunroof. Bolts and fasteners are positioned in such a way as to permit
the construction of all variants at a later date. With the
introduction of the stretched version in 2002 the number of variants
will increase to eight. For comparison: At the moment there are more
than 100 body variants for the 5 Series models.
Body structure – driving pleasure and safety
The outstanding body stiffness of the new 7 Series
model decisively contributes to driving pleasure. Thus the initial
flexural resonance is at 26 Hz, and the initial torsional resonance at
29 Hz. This means in plain language that the body is extremely
insensitive to bumpy road surfaces or vibrations caused by the
drivetrain.
This advancement was made possible by the use of
state-of-the-art CAD systems for the computation and design of the
structure and, amongst other things, the use of highly advanced body
adhesives for additional reinforcement of the body joints. Compared
with an unbonded body, flexural and torsional stiffness is up by up to
15 percent.
In addition to that, adhesive bonding results in
an increase in the absorption of energy by approximately 15 percent,
which is of great benefit to passive safety.
Safety – basic concept for a high standard of
passenger safety:
• an extremely stiff passenger cell 82
percent of which is made of high-tensile steel,
• bonded body joints result in a 15 percent
increase in the absorption of energy,
• increased load-carrying ability of the
stress-bearing structures in case of frontal and and rear collisions
as well as roll-over accidents,
• optimum use of the deformation zones,
• optimum protection against side impacts
with the risk of intrusion reduced by 20 percent,
• compatible design of the front end
structure.
Large-scale use of spot-welding adhesive bonding
technology
In 1999 BMW specialists began to use a new joining
technology, the socalled spot-welding adhesive bonding technology,
which is meanwhile well-advanced and used in series production. Before
spot welding is done, an adhesive is applied to join the steel plates,
which increases stability, acts as a seala nt and has a
noise-dampening effect. With the start of production of the new 7
Series models in 2001, this technology was realized and used in
industrial-scale manufacture for the first time.
Due to adhesion plus spot-welding technology
large-surface flanged joints are created. This helps to increase the
body stiffness resulting in an improved crash behaviour. At the same
time this technology makes it possible to reduce the steel plates’
thickness and to do without reinforcing materials, the use of which
has been necessary up to now. Adhesive bonding is a joining technology
which has not long been used in the automobile industry’s construction
of bodies-in-white but it shows an enormous potential. Through the use
of special adhesives it is possible to join materials of the same type
and of different types (synthetic materials and steel) to form a
bonded and non-positive joint. The adhesives’ double action is taken
advantage of in this process. The parts to be joined are bonded by
adhesion (adhesion of the glue to the component) and cohesion
(internal strength of the glue) at a low temperature.
Whereas in the past adhesive was applied to a
flange length of about eight meters, adhesive on the new 7 Series
model is applied to a flange length of 150 meters. The application of
the adhesive is performed most accurately by robots on a large-scale
basis.
Flexible inline metrology
When the production of the new BMW 7 Series model
started, the world’s first inline measuring units were installed at
the Dingolfing body shop, which consistently monitor the serial
production processes and carry out a 100 percent check of the
dimensions by means of temperature compensated measuring robots.
The new measuring units are directly integrated
into the production line (that is why they are called "inline") and
are able to take threedimensional measurements. They help to ensure
the accurate operation of the welding robots and are in a position to
intervene where it is necessary. The sensor system has been fully
integrated into the robots’ control system. The sensors can be
programmed directly via the robots’ "teach panel". There is a cyclic
alignment mechanism operating between the inline facility and the
measuring rooms.
State of the art inline measurement technic with infrared and laser
tools
The technology is most flexible, as it is
robotized and can be reprogrammed within a few hours. If the body’s
measuring points have to be changed, for example, the reprogramming
only takes about 2 hours, whereas conventional stationary
installations require much more time to be reprogrammed. In the
production process of the BMW 7 Series model’s body the four flexible
inline measuring units check at 100 percent the front end, the rear
end and the underbody at 62 measuring points each as well as the body
carcass at 105 measuring points. A central data base for all future
inline measuring units is in the planning stage in order to ensure a
more efficient documentation in addition to process monitoring and
control.
180° flanging (edging of the shell) of the
body-in-white’s rear lid
The all-new striking design structure of the new
BMW 7 Series model’s rear end called for adjustments in the production
process. Whilst on the previous 7 Series model edging and the 90°
flanging of the rear lid’s shell were done in the press shop, this is
no longer possible on the new BMW 7 Series model. The inner panel of
the "supported boot lid" can no longer be precisely fitted into the
already edged shell. The solution is that the press shop now delivers
the shell without flanging. This step has been integrated into the
body assembly process. An additional tool device allows 180° flanging
resulting in an harmonic joint of the rear lid and the side panel in
the interest of good looks and a high degree of functionality.
Specialists working in the BMW laboratories carry out endurance tests
to check the rear lid’s functionality. During such a test the boot lid
is opened and closed 12, 000 times at predefined speeds and different
temperatures and must pass this test undamaged. The range
oftemperatures extends from minus 30° up to plus 80° Celsius.
Simulation tool ROBCAD
ROBCAD, a graphic three-dimensional software
simulation tool is used for the most realistic planning of optimum
processes, workstations and assembly operations prior to the start of
series production. This system generates virtual solutions as to
production which help to plan, check, simulate and program offline the
production and engineering process. This tool is used to achieve a
quicker and much smoother transition from design to actual production.
Aluminum: A highly sensitive material
The 7 Series is the first model series on which
BMW uses aluminum shell parts (front lid and fenders) on a
large-scale basis. For many years the BMW specialists have built up
their know-how necessary for dealing with this lightweight material.
The BMW Z8, for example, has an all-aluminum body, which is nearly
fully hand-finished in the BMW Group’s aluminum competence center in Dingolfing.
Aluminum was also used by BMW several times in the past
for different components, so for example for the aluminum engine
block of the legendary BMW 507 in the fifties, or in 1973 for the
BMW
3.0 CSL, whose front and rear lids and doors were already made of
aluminum.
As far as the new BMW 7 Series model is concerned,
automation and mechanization instead of manufacture are given top
priority when dealing with aluminum. Aluminum is a very sensitive
material to deal with. The tolerances are very tight when processing
this material.
The body shop in Dingolfing
|
Number of employees |
approximately 2,800 |
|
Area |
about 166,000 square meters |
|
Main points of the production program |
5 Series and 7 Series body-in-white; Z8 body-in-white |
|
Characteristics of the new BMW 7 |
|
| Series body-in-white |
around 95% |
| Robots |
250 |
| Welding points |
5,749 |
| Application of adhesives to |
a 150 meter length of flange |
| Welding seams |
7.40 meters |
|
Weight |
around 430 kg |
All-aluminum chassis
Within the BMW Group’s production network
Dingolfing is also the center of production for BMW chassis components
and systems. Work is done by about 2,400 employees on an area of
approximately 80,000 square meters. At the Dingolfing plant the BMW
engine and chassis division mainly produces front and rear axles,
front wheel and rear wheel drives for all BMW model series as well as
wheelsets for motorbikes. The new BMW 7 Series model’s all-aluminum
chassis is the result of a consistent extension and optimization of
the employees’ know-how gained in lightweight construction and
processing aluminum when constructing the 5 Series models. Back in
1995 BMW was the first automobile manufacturer to build a welded
aluminum chassis on a large-scale basis. Not only does the aluminum
chassis help to reduce weight, it also enhances traction, increases
the car’s dynamic performance and lowers fuel consumption. When
producing the allaluminum chassis of the new BMW 7 Series model
advanced and all-new production technologies are used.
High-performance welding process – tandem welding
This technology provides for the use of two wire
electrodes instead of one wire electrode when setting the weld seam at
the front axle cross-member. Thanks to this technology more material
can be melted on and the process speed for weld seams is two to three
times higher than before.
High-speed processing of aluminum axles
The so-called High Speed Cutting (HSC) technology
is used in this process. A high-speed milling technology for the
mechanical processing of up to 140 surfaces, edges and bores. The
processing time for the front and rear axle is reduced by
approximately one third.
Geometric simulation for the virtual determination
of processes
On the new 7 Series model all welding and handling
tasks the construction of the suspension involves have for the first
time been predetermined virtually. In the planning stage prior to the
start of series production it was thus possible for the engineers to
determine by means of computer simulation the optimum position of the
installations and robots even before the hardware design. Thus the
engineers had the opportunity to check the installations for
accessibility and ergonomic layout well in advance.
Internal high-pressure forming
BMW is the world’s first automobile manufacturer
to use the internal high-pressure forming technology in the
construction of rear axles. The use of this technology incorporates
the bending of tubes, which are later inserted into a forming tool.
After that, hydraulic fluid is pressed into both ends of the tube in a
high-pressure process, so that the tubes adopt the contours of the
tool. Thanks to this innovative production method components can be
formed that are so favorable in their geometry that they make optimum
use of the area available in the underbody in the interest of the
axles’ stiffness and stability and have considerable advantages in
terms of weight over shell-type constructions.
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The
inside story of how BMW's are made...
