Experimental Research And Numerical Simulation Of Elliptical Heads By Integral Hydro-bulging

To cut down the high expense of manufacturing small-lot elliptical heads, a new technology of integral hydro-bulging elliptical heads was designed in this paper.The new technology was studied by experimental method and numerical simulation. Firstly, the stress of the head under the internal pressure was analyzed, and the critical pressure formula of integral hydro-bulging elliptical heads was obtained. Then , the integral hydro-bulging experiments were carried out using two Q235 samples of different geometries with initial size ofΦ360×3mm. The round flat state sample cracked in the hydro-bulging process. A elliptical head with axial ratio of 2.6 was obtained by loading the pre-bended sample to 7 MPa and then unloaded. The axial ratio was very close to that of the standard elliptical head (the axial ratio is 2). These experiments provided basic data and showed the feasibility of integral hydro-bulging elliptical heads. Based on the experiments, the numerical simulations of integral hydro-bulging elliptical heads have been proceeded. The results of the simulations were compared with that of the experiments. Some parameters were analyzed, such as stress concentration, the value and the distribution of the equivalent stress,etc. The results showed that the initial geometry of the sample had great effect on the results of the hydro-bulging. The welded seam was the weak spot in the hydro-bulging process. When the initial round flat state sample was on hydro-bulging, the stress concentration on welded seam was serious. The plastic strain of the testing material was bigger. The equivalent stress was 507MPa and the equivalent strain was as high as 42.5% under 3MPa internal pressure, leading to cracking sample. Pre-bended sample could obviously reduce the stress concentration in the hydro-bulging process. When the internal pressure was 7MPa, the equivalent stress of the welded seam was 460.8MPa, the equivalent strain was 10.5%, just 24.7% of that of the round flat state sample under 3MPa internal pressure. Comparing experiments with numerical simulations, the radius of pre-bended zone to round flat plate beening 1/9 would be appropriate. It effectively reduced the value of equivalent stress and the equivalent strain of welded seam in the hydro-bulging process.By analysing the stress field, strain field in the hydro-bulging process and the sample geometry after hydro-bulging, it revealed the regularity of integral hydro-bulging elliptical heads. The hydro-bulging sample structure and the technology also have been optimized. On this basis, the integral hydro-bulging experiment was carried out using Q235 sample, with initial size ofΦ3600×30mm. The results showed that under 10 MPa pressure, the sample axial ratio was 1.89, less than that of the standard elliptical head; the max equivalent strain on the welded seam was 12.9%, less than the limit of the material elongation 27%; the thickness on the top of the sample was reduced 7.7% at most, less than the value of GBT4746-2002 13%. There did not exist local high strain and local thinning, and other phenomenons in the hydro-bulging process. All of these approve that the technology of integral hydro-bulging elliptical heads is feasible.