Rapid Hot Forming Technology Of Titanium Alloy Bellows

Metal bellows is an important industrial part,which can compensate displacement of pipes or tubular parts caused by thermal and mechanical deformation through its telescopic ability, and can reduce vibration and noise. With low density, high strength, strong corrosion resistance and good high-temperature stability, titanium alloy has been gradually used in the production of high-performance metal bellows. However, what makes a manufacturing problem is titanium alloy’s characteristic of hard deformation. Although superplastic forming can realize the forming of titanium alloy bellows, the disadvantages of high cost and low productivity greatly limit the industrial application of this process. In this paper, current auxiliary thermoforming process was used to achieve the rapid hot forming of titanium alloy bellows, and current auxiliary thermoforming process was conducted thorough research to expand its practical application.Firstly, current auxiliary bending test of TC4 titanium alloy was conducted to study bending behavior of titanium alloy under the effect of current. The mold based on two kinds of insulating material, mica plate and PTFE plastics, can achieve sheet bending forming under the condition of ohmic heating. The results show that bending parts have a greater tendency to crack with lower current intensity(temperature) and smaller bending radius. With no crack, bending parts appear springback under low current strength(temperature), and the lower the current intensity, the greater the springback. But bending parts appear inward shrinkage under high current intensity(temperature) due to the uneven distribution of temperature.Then, numerical simulation of titanium alloy bellows’ forming process based on MSC.MARC software was conducted to analyze the effect of process parameters on forming results. The simulation results show that wall thickness reduction of bellows become less with larger feeding height, and clamping too fast will lead to wrinkling defects which usually occur at the lowermost ripple. Meanwhile, the test parameters were initially identified by numerical simulation.Finally, current auxiliary thermoforming test of bellows using Ti31 and TC4 titanium alloy was conducted. The forming apparatus based on ceramic mold can achieve bulging with ohmic heating. The results show that tube blank manufactured by automatic TIG is much better than that manufactured by manual argon arc welding. The efficiency of titanium alloy bellows’ current auxiliary thermoforming is high, and the whole forming process can be controlled within 6 min. After pickling, the surface of bellows is in good state with no pits, scratches and other surface defects. The proper axial feeding makes the wall thickness of titanium alloy bellows become more uniform, with Ti31 titanium alloy bellows’ largest thinning rate of 18% and TC4 titanium alloy bellows’ largest thinning rate of 16%.