Fascination Production of the BMW Group. An insight in the BMW 3 Series car manufacturing in Munich Plant.
Please see here the 2D production process.
Materials and processes. The press shop marks the beginning of the production process. Here, powerful presses shape chassis parts from precisely cut metal blanks. The corresponding tool sets create automobile parts such as side frames, doors, hoods and roofs from various thicknesses of metal.
The die-cut raw material is between 0.7 and 2 mm thick; in addition to steel blanks, so-called tailored blanks are also used. These consist of welded metal plates of various thicknesses and differing degrees of surface finishing.
Press performance. A chassis press has an overall pressing performance of 8,100 tons and processes up to 150,000 kg of metal into ca. 13,000 parts daily. To keep production interruptions as short as possible, tools are changed fully automatically in around eight minutes.
Every stroke of the pressing tool in its 54-meter-long housing results in four outer door shells – 48 per minute! This enables even very large parts, such as side frames, to be made in one piece. Manufacturing large metal components from one blank is highly advantageous for vehicle quality: the fewer the individual pieces, the greater the overall precision in terms of fit and the greater the reduction of welding spots and danger of corrosion.
High degree of automation. Industrial robots are an integral part of chassis construction. With a degree of mechanization exceeding 95%, this is the most highly automated production area. A chassis consists of many units that have been previously assembled into complete modules on individual welding lines.
The underbody, consisting of the front end, rear end and floor pan, is assembled together with the side framing and roof into a body-in-white. Doors, engine cover, sidewalls and tailgate complete the chassis.
Quality and precision. A complete chassis requires up to 4,700 welding spots. Also protective gas seams must be soldered and welded; numerous stud bolts affix aggregates and components during assembly as well.
BMW's diverse car models can be manufactured in arbitrary order during the chassis construction process. Particularly powerful and advanced control mechanisms are needed to ensure the agile production system within the BMW Group. A key role in this complex process is played by a data storage medium that accompanies all vehicles through every step of the process. This transponder contains all necessary information and transmits it wirelessly to the appropriate manufacturing station. Welding robots thus find out which chassis variant must be handled.
Pre-treatment. To ensure that a customer’s very personal favourite colour actually adorns the car over its entire lifespan, the paint process comprises many working processes and several coats of paint. Before the first of a total of four layers of paint can be applied, the body in white has to be pre-treated in order to obtain a clinically clean surface.
After that, a zinc phosphate coating is applied to the body shells on freely moving conveyor units in immersion curves that vary according to vehicle type. This offers the basis for the secure adherence of the following corrosion protection layers, which are applied using the cathodic dip painting method. This coating is then baked in dryers, after which the second coating, the so-called “primer”, is applied. This serves to a certain extent as an undercoat to even out the smallest of surface imperfections.
Colour. After the primer has been baked, the topcoat (base coat) in the colour ordered by the customer is then applied. Primer and topcoat (base coat and clear lacquer) are then applied by robots using high-speed rotary atomizers. These rotate up to 60,000 times a minute and ensure the even distribution of the electro-statically charged paint particles over the earthed body shell and the interior of the vehicle. This guarantees optimum use of material. Furthermore, a new paint supply system reduces loss of paint when changing colours.
As soon as the body shells have left the interdeck dryer, the transparent clear lacquer is applied. This last coat of paint increases the chemical and mechanical stability of the surface and gives the paintwork its brilliant shine.
After yet a further drying procedure, the painted body shells finally pass through specially illuminated testing stations in which experienced paint specialists and fully automatic measuring cells examine the entire body surface (colour, gloss, effect, depth of layer). Finally, the body shells are then sent to the assembly department.
In the first process, the chassis assembly, painted chassis are mounted with all the features and fittings ordered by the customer. Individual assembly units and components such as motors, transmissions, axles, doors or fenders are pre-mounted in separate areas. Heavy components like seats or pre-mounted doors are moved with handling equipment to optimise ergonomic activity at the workplace. Swinging assembly apparatuses turn the vehicles on the assembly line so that employees do not have to work with their hands above their heads.
Motor assembly. This is where crankcases, camshafts and cylinder heads are processed using computer-controlled machine tools. Employees are largely responsible for monitoring and adjustment tasks.
Motor assembly, however, still requires great mechanical skill. Pistons and bearings are installed and pre-assembled cylinder heads, aggregates, belt drives and wiring harnesses mounted.
After the motor is complete and running, it's time for technology again. The motors are electrically driven on so-called cold testing benches and monitored by numerous sensors that ferret out possible errors.
Infinite diversity. One of the strengths of the BMW Group's vehicles is individuality. Every vehicle that rolls off the belt is unique. The number of possible automobile variations is astronomically high: considering only the BMW 7 Series, there are 10 to the 17th power, or 100,000,000,000,000,000 variants.
To manage this enormous complexity, reliable coordination of parts production processes is vital. Above all, pre-assembled model-specific components and component groups such as engines, seats or cockpits are sent to the main assembly line in the precise order needed – specialists call this "just-in-sequence".
Wedding. The pre-mounted car body is delivered to the end-assembly area "just in sequence", i.e. at the right time and place on the assembly line. The actual climax of the assembly process, the so-called wedding – when the engine, drive and chassis first meet – can now take place. As soon as the wheels are mounted, the vehicle rolls into the testing area, either under its own power or on a belt.
Quality Assurance. Aided by sophisticated inspection technology, all vehicle functionalities undergoe last testings here. In the finishing area, highly qualified employees give the new vehicle any necessary last-minute touches. The new automobile can finally be delivered to the sales department.
