Formability Improvement by Die-bearing Grooves in Tube Extrusion with Spiral Inner Projections

Abstract

Extruded tubes are used in many industrial fields. Many of these tubes have a same cross-sectional shape in axial direction. However, non-uniformity has recently begun to be required for these components in particular usage. For example, circular cupper tubes with spiral inner projections are used for the improvement of heat exchange in air conditioners. Roll forming is a suitable method for the manufacturing of cupper tubes. However, roll forming is applicable only for cupper and its productivity is not high, resulting in high cost. In the present paper, additional small grooves were newly carved on the surface of bearing for the acceleration of spiral movement of the tube during extrusion. While relatively small projections were formed on the outer surface by the die-bearing grooves, large ones were formed on the inner surface by the mandrel grooves. With increase of bearing length, the more the spirality was improved. Sufficient and stable spiral angles were achieved under appropriate conditions, compared to those extruded without die-bearing grooves.