A finite element model to analyse forming defects in rolling-extrusion of finned tubes

Abstract

Finned tubes improve the efficiency of air-cooled heat exchangers by increasing the transmission surface area. The rolling-extrusion process can be employed to their manufacturing by plastic deforming single- or multi- material tubes. The forming steps are usually performed by rotating specific heads composed of a series of disks, whose dimensions are customised to achieve the desired fins’ sizes in terms of height, thickness and pitch. Process parameters, such as the temperature of the disks and of the processed material or the lubricant conditions mainly affect the quality of the obtained products in terms of performance, but also in terms of integrity of both manufactured parts and employed equipment. Numerical simulations resulted to be important in understanding the stress and strain distribution during the forming phase of the tubes. Anyway, the process dynamics and the geometries to be produced require 3D simulations that usually are complex to be set and really time consuming. In the proposed research, empirical industrial expertise on rolling extrusion of finned tubes was exploited to propose a 2D numerical approach able to provide manufacturing directions at changing of the pointed-out process conditions. Specifically, the numerical model was set for manufacturing a bimetallic finned tube for oil & gas applications. The model was set to achieve conditions in terms of shape and size of the fins comparable to the experiments. The model was subsequently employed at changing of the process parameters highlighting their influences on the conditions that can result on products non-conformities and/or in rupture of the rotating heads impacting significantly on both product quality and production capacity.