Analysis of wall thickness variation in the hydro-bending of a double-layered tube

The hydro-bending process of a double-layered tube is an effective approach for the manufacture of large-diameter, ultra thin-walled curved tubes. The hydro-bending of a mild/stainless steel double-layered tube is investigated here using numerical simulation and experiments. The thickness distribution of the inner tube is investigated in depth through a combination of numerical simulation and theoretical analysis. We found that maximum thinning occurred not at the center of the outer arc but at a nearby point and the maximum thinning ratio of the outer arc was 14.3 %. The reason the maximum thickness reduction occurred at a nearby point rather than the center point of the outer arc was well illustrated and was that the point with the biggest axial stress moved towards the tube ends. The analysis provides further theoretical foundation for the hydro-bending process of ultra thin-walled components.