FRICTION IN ASYMMETRIC FEEDING TUBE HYDROFORMING

Tube hydroforming (THF) technology is receiving much interests in automotive and pipe industry thanks to its advantages in terms of final part quality and manufacturing costs. In THF a tube is placed in a die and is expanded by means of high pressure filled-in media. The sealing and the material feeding are guaranteed by two punches that plastically deform and then push the tube edges. To obtain sound parts, the tube expansion zones still represent a criticalness in THF, in fact the severe thinning the tube can undergo in those areas leads to bursting before the die is completely filled. Consequently, the high friction acting on the tube prevents the material flow towards the expansion zones. In this work, an experimental test campaign will show how unbalanced friction conditions can influence the material flow and the geometry of the expanded material in Y-Joint pipes hydroforming. In fact, studying a semi-free expansion of the tubes using different feeding zones length, the tube expansion will follow its free evolution that depends on the imposed unbalanced conditions at the tube edges.