Experimental investigation into the electropulsing assisted pulsating gas forming of CP-Ti tubes

A novel electropulsing assisted pulsating gas forming (EAPGF) process of commercial pure titanium (CP-Ti) tubes by using pressurized argon filled into a sealed tube was developed to optimize the process scheme and reduce the cost of die heating. The formability of CP-Ti tubes was tested on the self-designed innovative gas forming platform by applying three different frequencies of electropulsing. Based on the uniaxial tensile tests assisted by the electropulsing, the principle of EAPGF was modeled and interpreted by the generalized Johnson-Cook model. At first, the temperature variation of the experimental tubes assisted by electropulsing of three frequencies was measured and analyzed. High-frequency electropulsing will make the temperature rise steadily. Low-frequency electropulsing will cause a serration-shaped growth of the temperature. Moreover, the influences of the pulse duration and frequency on the forming pressure, the relative load, the expansion ratio, the shape deviation and the thickness distribution in the middle section were investigated. The relative load fluctuates periodically with an oscillation of temperature as well as internal pressure induced by electropulsing. In terms of the three frequencies, the higher bulging limit and more uniform deformation were observed in the condition of low frequency. From the result of microstructure analysis through EBSD, the low-angle grain boundaries (LAGBs) exhibit a strenuous increase attributed to the deformation assisted by electropulsing, with the higher increment at a lower frequency. Obvious dynamic recrystallization was observed at the electropulsing frequency of 1/20 Hz from the KAM distribution in the specimens. Finally, a modified EAPGF was suggested by adjusting pulsating hydroforming parameters by regulating the parameters of electropulsing. The relative load was adjusted to pulsate around 0.0577, and a typical adjustable CP-Ti tube with 60 % expansion ratio was successfully fabricated.