Investigation of the bright and dark line on the inner wall of a thin-walled copper tube by drawing with a floating plug

Abstract

Abstract In this paper, it was investigated that the defects of the bright and dark lines on the inner wall of a thin-walled copper tube by drawing with a floating plug based on analyzing the stress distribution. The experiments were conducted by employing a stereomicroscope, metallographic microscope and scanning electron microscope, respectively, meanwhile the three-dimensional finite element was applied to study the defect. It was demonstrated by the research results that the large gap between the sizing section of the plug and the outer die caused the inner wall bright and dark lines. The wall thickness was increased when the tube passed by the area without inner support which gave rise to local material uplift along the radial direction. The raised material became folds due to the effect of “leveling” when the tube pass by the conical section and the sizing sections. The fold was the essence of the bright and dark line by macroscopic scale observation. The bright and dark line was ultimately eliminated by adopting the drawing die with reasonable geometrical parameters according to experimental and simulated results.