INNER SURFACE ROUGHNESS EVOLUTION AND SLIP DEFORMATION OF MICRO METAL TUBE DURING HOLLOW SINKING

This study aimed to clarify the effect of the activity of the multiple slip systems on the height change of each grain of the inner surface of tube during the hollow sinking. A stainless steel tube with an outer diameter of 1.50 mm, and a wall thickness of 0.045 mm, which had only one grain across the wall thickness, was used as a starting material. The starting material was drawn without an inner tool in a single pass. The height unevenness and crystal orientation of the inner surface of the drawn tube were examined in the same measurement area using a laser microscope and an electron back scattered diffraction, respectively. The Schmid factor was calculated for each grain using the crystal orientation and the stress state which is the tensile and compressive in the drawing and transversal directions, respectively. The grains were generally convex when the calculated strain was positive, vice versa. The calculated strain is the sum of the deformations of the multiple slip systems with large Schmid factors where slip strain γ was replaced with the Schmid factor. It was suggested that the height unevenness of the inner surface of the grains are caused by the multiple slip deformation in the drawing of micro metal tubes with a small number of grains across the wall thickness. Therefore, it is expected that the unevenness of the grains can be simply predicted.