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Development of a production technology for tubes with a collapsible zone to be used in modern car design concepts

To improve the future safety standard of cars with rear-wheel drive, tubes with a collapsible zone will be used as a design element in their power trains. For this purpose, a high-volume production method will be developed.

An important development goal of all design departments in the automotive industry is to create new power-train solutions of reduced weight and higher safety standard. For all vehicles with rear-wheel drive, the designers are focused on the cardan-shaft. The cardan-shaft is the transmission element between the engine and the rear-axle. It consists of several mechanical components like hinges and muffs, which are welded on the ends of the so called 'cardan-tube'. This cardan-tube itself has a diameter between 50 and 70 mm and a wall thickness of between 1.5 and 2.5 mm. The tubes on both ends are reduced in their diameter and machined, in order to meet the welding requirements of the connection components. To meet the above mentioned requirements of the future power-trains this cardan-tube has to fulfil the following key demands: - The tube shall be as light as possible (thin-walled). - It shall transmit high torque. - In an axial crash, the tube shall collapse in a predetermined manner. - It shall work with low vibrations. - It shall have a long life cycle. The actual design of cardan-tubes is plane tubes with reduced endings. At these tube-ends the connection-components are welded on. These conventional cardan-tubes are evaluated as not 'crash able', because they are too stiff in the axial direction. The state-of-the-art production method of a conventional cardan-tube is the diameter reduction on a draw bench by means of an inner mandrel with a matrix (punching tools). Goals of the planned R&D project are: * To create a production-method for high volume-production with which a predefined collapsible zone can be formed. * To design a modified draw bench with a suitable tool-set, with which the collapsible zone can be formed parallel to the forming process of the reduced welding-ends. * To build a prototype of the new draw bench. * To produce sample parts with the new draw bench according to the new production-method and demonstrate in adequate test cycles that the above mentioned key demands are fulfilled. * To develop a range of tube-diameters and wall thicknesses within which the new production method will work. * To develop standards for the steel tubes as a preliminary product for the new cardan-tubes with collapsible zone. The above mentioned properties of a cardan-tube with reduced ends and a collapsible zone need new production technologies. Both cooperation partners are aware that they will have to solve new problems. According to their experience, they know that unforeseeable technical problems can include high risks including the risk to fail. In this case the method of resolution is creating an automatic forming process with which the collapsible zone can be formed parallel to the forming of the reduced ends of the tube. In this process, the problem will occur where the collapsible zone can not be formed by closed dies, instead it has to be formed by the free flow of the steel. Both partners are convinced about finding a set of process parameters of forming speed, forming force and tool shape to keep the demanded collapsible zone within narrow tolerances. But we are aware that unexpected external troubles can result in the process of free material flow not being controlled as exactly required. Possible external influences are: - Inhomogeneities of the tube material; - Geometric varieties of the tube's shape; - Abrasion or friction varieties of the tool surface. If one or more of these possible influences means that the shape of the collapsible zone will vary too much, a much more complex and a much more expensive machine tool solution must be created. In this case, it is an open question whether the automotive industry will accept a design proposal which leads to higher costs. Keywords: tube forming process.
Acronym: 
CRASHTUBE
Project ID: 
4 126
Start date: 
06-08-2007
Project Duration: 
25months
Project costs: 
2 450 000.00€
Technological Area: 
Road Vehicles technology
Market Area: 
Other industrial equipment and machinery

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