Is the tube wall thinned in the area of cross section corner?
A- There is much concern, and rightfully so over the issue of material thinning in the cross section corners during hydroforming. Material thinning during hydroforming stems from Traditional High Pressure Hydroform (HPH) processes that utilize an undersized tube to prevent pinching when the die is closed. Once the die is closed high internal pressure is used to blow or stretch the tube to form the cross section corners. Unfortunately the high internal pressure creates high friction between the tube and cavity. As the tube expands to fill the cavity, wherever it makes contact the material tends to freeze in place due to the high friction. As the material expands into the corners the stretching is distributed over a smaller and smaller area resulting in local thinning of the tube. Typically the thinnest area will be found at the tangent point of the corner, this is where the tube is most likely to fail. To counteract the effect of friction most High Pressure Hydroform processes coat the
