During the expansion forming of aluminum tube, the efficiency of heat exchanger diminishes due to the adhesion of groove and expansion ball inside the tube. Despite its importance, a limited number of researches on the adhesion problems in aluminum tube expansion have been published. This study aims to analyze the adhesion occurring during the expansion forming of aluminum tube for heat exchanger and to identify its location. For this, the method of using the statistical analysis of geometry by image processing and the slope of force measured from expansion forming was suggested. The new method discovers the adhesion location from the standard deviation of groove height measured before and after expansion of tube and the differentiation of force measured from expansion forming. To prove this method, the area with deviation of groove height above average was discovered, and it was confirmed that from the actual expansion of tube cross-sectional images, the height of some grooves was abnormally shorter due to adhesion. Also, from this method, it was confirmed that the changes in differentiation of force occurring from the expansion of the tube also include the information on adhesion location.

Abstract:In the expansion process of a fin-tube heat exchanger, the process variables and shape of the expansion ball affect the deformation of the tube's inner grooves, the adhesion, and the expansion force. These factors influence the efficiency of heat transfer and the lifetime of the expansion equipment. Therefore, this study analyzed the influential variables of the tube expansion process as well as the expansion ball design through experiments and simulations. A new method was proposed to determine the severity of adhesion in the tube's inner grooves using the expansion force rate. Expansion experiments with Al tubes show that the expansion force decreases when using a lubricant with high viscosity and when the lubricant remains on the expansion ball for a longer duration. Finite element analysis was also performed to examine the expansion of Cu tubes, which showed that the expansion force was higher when using expansion ball shapes that have higher contact area between the ball and tube surface. The radius of curvature of the expansion ball also influenced the expansion force. However, increasing the ratio of the radial force to the expansion force increased the deformation of the tube's inner grooves.