Design for manufacturing in THF of Fe320 welded tubes

Tube hydroforming (THF) is a valid alternative process to obtain shaped tubes. Automotive industry uses THF process to produce structural parts (rear axel, engine cradle), safety devices (roll bars) and exhaust systems. Also in bicycle and motorbike industries THF is widely used to obtain light framed parts and exhaust systems. The well-known THF advantages (weight reduction, enhancing of the part resistance, better tolerances) are often available only as the results of Design for Manufacturing (DFM) rules applied to the existing parts, produced by using conventional techniques, that need to be redesigned in order to be actually realized with this technique. In last years Technologies and Manufacturing Systems (TMS) Research Group of Brescia and Bergamo Universities (Italy), focused its researches on tube hydroforming designing and realizing an experimental equipment for running THF experiments and, at the same time, implementing several FE models by using the commercial explicit code PAM-STAMP 2G 2003®. This allowed the acquisition of basic knowledge and rules for the design of THF products. The present research shows the results of the cooperation between TMS Research Group and one of the most important motorbike producer in the re-engineering of the engine cradle of a scooter. The actual part is produced through the welding of two stamped sheets (deep drawn and blanked) forming a hollow component. Maintaining the same stiffness requirements (moment of inertia) of the actual part, a new engine cradle has been designed starting from a Fe320 welded and pre-bended tube (2 mm thickness) in order to obtain an equivalent part using THF process so reducing the number of components and the assembly time. The investigated process parameters (internal fluid pressure and axial feeding vs time) have shown to be dramatically material dependent. The knowledge about THF process collected by TMS Research Group made it possible to set-up a FE model implemented in PAM STAMP 2G 2003®. This model allowed the identification of the simplest way of producing the part verifying its feasibility and its final characteristics, especially the thickness distribution. Experimental THF tests on this re-engineered component could be done in the Brescia University Lab using the above mentioned experimental equipment for THF. The present research shows how coupling new technologies and DFM rules it is possible to improve objects characteristics both in terms of mechanical resistance, product quality and production time.