Investigation On The Formability Of A Tube In Hydroforming With Radial Crushing Under The Simple Loading Paths

Tube hydroforming with radial crushing (THFRC) process is particularly applicableto the tube which is difficult to shape due to lack of axial feeding. And the formability isaffected markedly by loading path and forming condition when the tube bulged inTHFRC process. But the fundamental studies about the compacting mechanism are soscattered due to the younger of this technology. In this paper, the formability of the tubewhich was formed in THFRC process under the simple loading path and various formingconditions was investigation by experimental research, numerical simulation andtheoretical analysis.The formability of the1Cr13Mn9Ni1N tube expanded into a square cross-sectionunder the simple loading paths was explored by a self-developed THFRC device.Meanwhile, the numerical simulation was carried out by commercial softwareDYNAFORM. The simulation results were validated by comparison with theexperimental results.A new and practical method of determining the friction coefficient in expansionzone of THFRC was proposed on the basis of the exclusive friction characteristics ofTHFRC process. Futhermore, according to a poor asymmetry of the bugled profile incross-section obtained by THFRC process, the effect of friction on the forming accuracywas investigated under four simple loading paths. The result shown that, when thefriction condition was assumed to be identical (or various), the highest forming accuracyof the bulged tube can be obtained with the decreasing of the internal pressure (or frictioncoefficient).The effect of the forming conditions and the loading paths on the material fillingability, wall-thickness distribution and the potential fracture location of the bulged tubewere analyzed. The results shown that constraint conditions at tube ends had a largeeffect on the wall thickness distribution under the linear or constant loading path, it alsohad a large influence on the filling ability under the linear loading path. Moreover, thebest filling ability and worst wall thickness distribution can be obtained under theconstant loading path in THFRC process, the second one can be got under the linearloading path. However, the worst one can be gained under the linearly loading path infree hydro-bulging process.At last, ultimate pressure of the THFRC tube under various forming conditions wereacquired by numerical simulation. And the accurate relational expression about theultimate pressure and the fill ability or the wall thickness distribution was obtained by regression analysis method. The potential burst position of THFRC tube was forecast, theresult shown that it was located in the centre of the round corner and the transition of theround corner.The results achievements could pave the way for reasonable evaluation of theformability and improve the forming accuracy of the THFRC part. The frictioncoefficient method proposed has obtained the inventive patent (patent number: ZL201010183838.0). The self-developed device has practical guidance significance todevelop the new device.