Outer diameter and surface quality of micro metal tubes in hollow sinking

To clarify deformation behavior of tubes in hollow sinking, the outer diameter and surface quality of the final drawn tubes were evaluated. Copper tubes were drawn for one pass under various drawing conditions (e.g., die reduction, drawing speed ratio, and die half angle) without an inner tool. The result of the experiment indicates the deformation behavior of tubes during hollow sinking. The outer diameter of the drawn tube on the die entrance became less than that of the starting material. Free surface roughening seems to develop on the outer surface of the drawn tube on the die entrance side due to the outer diameter reduction. Therefore, the height deviation in the outer uneven surface of the drawn tube on the die entrance became greater than that of the starting material. The height deviation on the die exit side was less than that on the die entrance side because of the tube deformations subjected by the die. The outer diameter decreased from the die approach end as either the drawing speed ratio or the die half angle increased. The height deviation in the outer uneven surface of the drawn tube on the die exit side became larger as the outer diameter decreased from the die approach end due to free surface roughening.