An investigation into the forming of integral fins

Abstract

Integral fins occupy a significant place in the design and construction of various types of heat exchangers because of their improved fin-effectiveness. Moreover, when they are produced by forming — as opposed to cutting — processes, they involve minimum wastage of material and lead to a high production rate. Although integral fins have been in use for the past few years, however, little published material is available concerning study of the related forming processes and their governing parameters. In the present paper, the authors have attempted to analyse the forming process employed — somewhat similar to thread forming — using existing slip-line fields for rough-wedge indentation into a semi-infinite rigid-plastic mass. Theoretical values of the torque exerted on the workpiece compare well with experimental results obtained in the forming of circular transverse fins on commercially-pure aluminium tubes and rods. However, the applicability of the analysis is restricted to the range of short fins (up to a height of 4mm for rod stock of 25.5-mm diameter, in the present work). Experimental results also suggest that the torque is highly dependent on the forward tension applied to the workpiece. Some optimal value of tension seems to exist, beyond which the torque tends to increase, and the present paper suggests some physical explanations justifying this phenomenon.