Connection strength analysis and prediction of external swaging based on tube deformation measurement

Abstract

Fittings have extensive use in the aerospace, automotive, and other industries as they serve as sealing and connecting components for tube systems. External Swaging (ES) forming creates a permanent joint through plastic deformation of the metal. This technique is not dependent on the tube's wall thickness and offers benefits such as high-pressure resistance and effective sealing. Using the forming process of a 10 mm Ti-3Al-2.5 V tube with an adapted 21-6-9 fitting as an illustration, a three-dimensional finite element model for the entire assembly was developed. The model consists of the tube, fitting, elastic clamp, and crimping tool. The formation mechanism and joint strength of external swaging are analyzed by numerical simulation and experimental testing. The results show that during the extrusion process, the tangential contact between the extrusion tool and the elastic clamps converts external radial loads into circumferential loads, resulting in circumferential strains in the tube. Circumferential strain creates an arched sealing area between the tube and fitting contact surfaces, providing sealing and joint strength. The joint strength of 10.60 kN was determined through finite element simulation. The load required for forming is determined by analysis to be 80.13 kN. and the relationship between squeeze load, crimp volume and joint strength is clarified. The study revealed that the height of the arch area aligns with the connection strength's change rule concerning extrusion load, fitting the two found that when the external extrusion load changes, the two are linear rule of changing. Based on this, a method is suggested for forecasting the strength of a joint by measuring the height of the arch in the tube after forming.