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The fascinating power of production.
Production of the BMW 7series in Dingolfing (Germany)

The fascinating power of production

The BMW Plant in Dingolfing: Flexible manufacture of automobiles at its finest.

From the steel roll to the body-in-white.

Throwing a glance at colours.

Customized for the customer.

Making available superior comfort – The production of seats exemplified.

Quick processes: Punctual, prompt, appropriate.

The BMW Plant in Dingolfing: A survey – Milestones on the way to success.

General conspectus: Pictures from the BMW Plant in Dingolfing

 

Formed with a press force of up to 9,500 tons.

At the Dingolfing press shop components of many different sizes, which are made of sheet metal, are elaborately formed by huge presses. At a later stage these parts are joined together to form a BMW body-in-white.

The parts are produced six days a week and 24 hours a day. Work is done in three and four shifts from Sunday 7.30 pm to Saturday 3.30 am. The remaining idle times are mainly used for maintenance work.

Each day as many as 1,200 t 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 aluminium sheet rolls are the base material.

The steel and aluminium 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 highstrength 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 metres 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 aluminium 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 metres, 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 metres 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 hand of the production workers.

At the end of the production process our production workers finally inspect with a practised eye each steel and aluminium 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.

Quality checking of the painted surface in the BMW plant Dingolfing / Germany
Visual and measurement tools equipped quality checking of the painted surface

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 millimetre.

measurement technology in use wiht the BMW 7series (E65)
State of the art measurement technology in use with the BMW 7series

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 7series (E65) side frame
Measurement of the 7series side frame

The press and stamping shop in Dingolfing – a short survey.

  Press shop Stamping shop
Employees ca. 1,200 ca. 325
Fertigungsfläche 40,600 qm 11,600 qm
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 metres 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 t / day 325 t / 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 t 25 - Press force from 100 to 5,000t
Tool weight up to 50 t up to 40 t
Retooling process - dependent 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.

Whilst in the pressing plant it is quite hard to imagine that the stacked sheet steel will take the shape of an automobile, 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 aluminium 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 behaviour. 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.

robot station doing adhesive and welding operations in the BMW plant Dingolfing / Germany
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 aluminium where it is feasible. Lightness, stiffness, paintability and corrosion resistance are just some of the ever-increasing demands modern bodies have to fulfil nowadays. 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 aluminium 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 highstrength steel which offers advantages in terms of crash behaviour and weight. The rest is made up of aluminium. About 480 steel sheet and aluminium 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 metres, weld seams of an overall length of more than four metres, 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.

 

New: 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 metres, adhesive on the new 7 Series model is applied to a flange length of 150 metres. The application of the adhesive is performed most accurately by robots on a large-scale basis.

New: 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.

inline measurement technic with infrared and laser tools in the BMW plant Dingolfing / Germany
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.
 

New: 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.

Aluminium: A highly sensitive material.

The 7 Series is the first model series on which BMW uses aluminium 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 allaluminium body, which is nearly fully hand-finished in the BMW Group’s aluminium competence centre in Dingolfing. Aluminium was also used by BMW several times in the past for different components, so for example for the aluminium 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 aluminium.

As far as the new BMW 7 Series model is concerned, automation and mechanization instead of manufacture are given top priority when dealing with aluminium. Aluminium is a very sensitive material to deal with. The tolerances are very tight when processing this material.

The body shop in Dingolfing – a short survey.

Number of employees approximately 2,800
Area about 166,000 square metres
Main points of the production programme 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 metre length of flange
  Welding seams 7.40 metres
  Weight arround 430 kg

 

All-aluminium chassis.

Within the BMW Group’s production network Dingolfing is also the centre of production for BMW chassis components and systems. Work is done by about 2,400 employees on an area of approximately 80,000 square metres. 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-aluminium chassis is the result of a consistent extension and optimization of the employees’ know-how gained in lightweight construction and processing aluminium when constructing the 5 Series models. Back in 1995 BMW was the first automobile manufacturer to build a welded aluminium chassis on a large-scale basis. Not only does the aluminium chassis help to reduce weight, it also enhances traction, increases the car’s dynamic performance and lowers fuel consumption. When producing the allaluminium chassis of the new BMW 7 Series model advanced and all-new production technologies are used.

Example: 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 crossmember. 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.

Example: High-speed processing of aluminium 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.

Example: 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.

Example: 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 favourable 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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Source: BMW Group. March 2002.



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