Buckling behavior modeling and prevention in hydro-pressing forming process of high strength metal tubes

Tube hydro-pressing is an advanced hydroforming process with less-loading requirements suitable for manufacturing tubular components of high strength metals such as dual-phase steels and titanium alloys. However, the thin-walled tube blank is prone to be buckling under bending moment and circumferential compressive stress during the hydro-pressing process. To prevent this defect, an analytical model of critical supporting pressure was firstly established based on energy theory during the corner filling process. The factors influencing critical supporting pressure were analyzed to understand the characteristics in hydro-pressing for different tube materials. Subsequently, hydro-pressing experiments were conducted on two typical high strength metal tubes: DP590 dual-phase steel and TA18 titanium alloy. The experimental results verified the accuracy of the analytical model and revealed the influence of the material on the critical supporting pressure. It is shown that the critical supporting pressure required for forming is positively related to strength coefficient (K) and negatively related to strain hardening exponent (n) and diameter-thickness ratio (d₀/t) of the tube, but has little dependence on height-to-width ratio (h/w) of cross-section. For the two typical tubes, the critical supporting pressure required for forming was 4.11 MPa and 1.36 MPa, respectively. Stable corner filling can proceed without any buckling instability defects when the supporting pressure in the forming process is higher than the critical value mentioned above. These results provide theoretical support for the development and application of the tube hydro-pressing process.