Folding systems:
Hänchen hydraulic cylinder as a plug-and-play unit
It happens in 20 seconds: The outer and the inner section of a vehicle door are positioned precisely to one another in the folding system; the components are in their original positions. In the initial stage, the so-called preliminary folding stage, the folding flange of the outer part is adjusted by approximately 45 degrees. In order to achieve this, the folding cylinder moves the folding bed into the preliminary folding position, so that the component moves against the preliminary folding jaws. After withdrawing the preliminary folding ram, the folding cylinder continues to press the folding bed against the final folding jaws. The edge of the fold is continuously sealed; the outer and inner part are interlocked with one another. The fact that this joint satisfies Audi's high standards for quality and appearance, and additional technical requirements, is, of course, taken as read. The door is completed during the remaining production process in the bodywork plant, and makes its way through production to the finished vehicle. At present, the folding systems for year 2001 models, i.e. for the VW Polo and the successor model for the SEAT Ibiza, are being erected in AUDI AG's tooling division.
Core component hydaulic cylinder
The main players in this procedure are 13 Hänchen hydraulic cylinders from the catalogue range. Since 1991, Audi's tooling division in Ingolstadt has been using products manufactured by the hydraulic specialist from Ostfildern near Stuttgart in its folding systems. Throughout the entire VW group of companies and elsewhere, these folding systems join the outer and inner sections and the welded assemblies of doors, bonnets and boot lids, and side wall frames without welding. "The hydraulic cylinders are core components which are subjected to maximum requirements", says Dipl.-Ing. (technical college) Ernst Beringer from the Audi tooling division of the requirements. "As a drive with a high level of force and precision, they have to operate non-stop for up to 15 to 17 shifts per week. We initially used tension rods for this task, but these failed to fulfil our requirements as regards stability. We have now been using Hänchen hydraulic cylinders for nine years, and are very satisfied with them." This is expressed, for example, in the fact that no spare parts are stored for hydraulic cylinders. Even an inventory of gaskets is dispensed with, as Hänchen guarantees a world-wide service with 24-hour delivery time for these components. Despite tough competition, the Audi AG tooling division supplies VW companies both at home and abroad, and also produces folding systems for other body construction system suppliers. With the understanding of a system supplier, according to Beringer, these folding systems are used to satisfy customers' high quality standards.
Plug-and-Play unit from the E-kat
In this case, the hydraulic cylinder is a plug-and-play unit for the system engineers; as a standard Hänchen cylinder, its dimensional accuracy is such that replacement can be carried out at any time, and throughout the world, within the Sunday maintenance shift. For the sake of simplicity, only three models are used; each of these is selected and ordered by Beringer and his team with the aid of Hänchen's electronic catalogue, E-Kat. The cylinders can therefore be adapted to the relevant installation situation in the optimum manner. In addition, the E-Kat enables cost-effective purchasing and guarantees the shortest possible delivery times. For the future, the Audi engineers have integrated important features into version 2.0: Interfaces permitting the integration of design data directly into Audi's CATIA CAD system will be generated. "This is the start of quality and cost-effectiveness in procurement", says the engineer.
Folding has many advantages
In standard production, folding has diverse advantages in comparison with welding: It is a joining technique which can be used at visible points without reworking. As a result of the joining technology alone, it enables sealing and corresponding corrosion protection. Any type of metal can be folded, including aluminium body elements, for which welding involves enormous additional effort. In addition, modern, third generation folding systems enable very high yield due to short cycle times. Finally, this processing technique enables a high degree of dimensional accuracy of a mere ±0.2 mm, as a result of which door and lid gaps can be kept extremely small, a characteristic displayed by all VW and Audi models.
The use of hydraulics
In this case, the quality of folding is especially determined by the folding radius: The smaller the better. In order to achieve this, the Audi engineers proceed as follows: The outer part, whose flange is approximately 90 degrees open, is inserted into the folding system and positioned precisely. A robot adds the welded assembly which is to be joined as the inner part. Hydraulic cylinders close the C-hoops with the folding jaws and position the preliminary folding jaws for the first folding step. A further cylinder moves the folding bed vertically upwards, and subsequently generates the necessary pressure in order to close the fold to an aperture angle of 45°. The preliminary folding jaws are now hydraulically withdrawn again. The folding bed moves against the final folding jaws and closes the fold with a correspondingly high pressure of 100 bar with 80 N/mm calculated along the length of the fold. The system therefore achieves the low bending radius which is required. Finally, the C-hoops are opened again, the folded part is removed from the folding system and further processed in the corresponding production process.
Third generation folding systems
The idea of actuating the preliminary folding jaws via a ram function has made the folding system considerably more compact and inexpensive. In the first generation, preliminary pressing was carried out in a 5-metre high press; final folding was carried out in a further, equally large, unit. In the second generation, the folding jaws were assembled above one another in two separate assemblies. The process was then completed in a 2.2-metre high system. The new systems of the third generation, with the C-hoops, have been in use since 1998, and are now only 1.6 metres high. The low folding time of 20 seconds is achieved as a result of this movement procedure optimisation.
Hydraulics - a significant basis for high precision in folding systems
High-quality hydraulic components create a considerable prerequisite for the fulfilment of customers' requirements for a folding system. These folding systems generate the necessary force and enable a high degree of movement and positioning precision; this is the experience of the Audi tooling division. "In Hänchen, we at Audi have a tried-and-tested partner. In this manner, we are able to achieve gap dimensions which satisfy the world's most stringent requirements with precise, extremely reliable cylinders in compact folding systems", Behringer is convinced.(end)
