Surface Flattening Mechanism of Extruded Aluminum Pipes by Inside-Ironing Process

A surface flattening test by inside-ironing was carried out for hot-extruded aluminum pipes. The pipes have many scratches with a depth of about 1 μm formed by extrusion on their outer surface. A simulation test was also conducted using pipes with V-shaped grooves of about 14 μm depth which were preformed by a diamond tracer. There exists a difference in flattening process between the scratches and the grooves due to the difference of their initial configuration. The cross-sectional curve of the scratches consists in low-frequency waviness and high-frequency roughness, and the waviness is almost flattened at an earlier stage, followed by the roughness. The scratches thus disappear. The effects of the relative slip between metal and tool surface on the flattening of the scratches should be further clarified.