An experimental and numerical study of the expansion forming of a thick-walled microgroove tube

Abstract

CO2 refrigerant-based air conditioning and refrigeration (ACR) is an increasing concern in many industrial sectors for its zero ozone depletion potential. One of the major requirements in its application is the forming technology of thick-walled tube according to the extremely high pressure working conditions of the ACR system. This article presents a study on the expansion process joining the thick-walled microgroove copper tube to aluminium fins. Experiments of the forming process have been carried out. Finite-element models are developed to investigate the deformation of overall and local structures. Evaluation of the joining quality along the longitude axis of the tube is first attempted. The agreement of the results on the contact surface profile confirms that the joint is far away from full contact in the axial section. Formation mechanism of the unexpected contact status lies in displacement of the contact points along the section of the fin collar, which is mainly related to the expanding ratio. To improve the forming quality, discussion on processing parameters and die geometry is conducted. Results show that the expanding ratio is the major factor influencing the thermal—mechanical performance of the joint and 2–6 per cent can be the comprehensively beneficial range for a thick-walled ACR tube; average contact pressure can reach 1.76 Mpa under proper set. The results are helpful for improving the energy efficiency ratio performance of the natural refrigerant-based system.