Current Auxiliary Forming Of Titanium Bellows And Quality Control

Corrugated expansion joint has the function of displacement compensation,anti-vibration，noise reduction and sealing. It is one of the key component ofproduction equipment and pipeline in modern industry, bellows is the basic element ofexpansion joint. Titanium alloy has the excellent property of heat resistant, corrosionresistant, and high specific strength, it has been gradually applied to manufacturebellows. But the cold forming performance of titanium alloy is poor, titanium alloybelongs to the difficult deformation materials, and the rebound is serious. The rejectionrate is high, the equipment is complex, the cost is high when using the traditional coldforming method, such as hydraulic forming, rolling, and spinning, to manufacturecorrugated pipe. Superplastic forming bellows belongs to hot forming process, Thebellows which are produced in this method have accurate size and there is no residualstress, but the production cycle is long, and the energy consumption is large. Titaniumand titanium alloy have high electrical resistivity and low thermal conductivity, so thispaper uses the method of current auxiliary to form titanium bellows, applys bigcurrent, low voltage to the tube, and it can be heated to the forming temperature in avery short time，and the energy consumption can be reduced, then uses the flatulenceand axial loading to form titanium corrugated pipes, with short cycle, high efficiency.Firstly, this paper manufactures quartz ceramic die that is used for formingcorrugated pipes with the gelcasting process. This paper analyzes the influence ofdifferent composition and preparation methods in order to make high solid fraction,good surface quality and high density ceramic die, and finally determines theparameters as follows：slurry completely curing time is90min, vibration time ofinjection molding is25min, slurry vacuum degassing treatment time is25min, feedingmaterials appropriately after casting to improve the surface quality of the die.Conducting a current auxiliary bulging experiment at four current550A,600A,650A and700A in order to determine the current parameters of bellows forming. Thispaper finally chooses current of650A, current density of8.09A/mm~2as formingparameters by comparing the bulging height and bulging pressure. Using finite elementsimulation software Marc to simulate the bellows forming, compare and analyze the condition of bellows sticking mold and wall thickness distribution under differentparameters, preliminarily determine the process parameters: the primary wave pressureof1.5MPa, bulging time of150s, pressure of2.5MPa, hold time of200s.Forming one wave and double wave bellows and optimizing process parameters,finally determine the parameters of bellow forming: current of650A, current density of8.09A/mm~2, the pump pressure of0.1MPa for axial load, the primary wave pressure of1.0MPa, bulging time of250s, pressure of2.0MPa, hold time of400s. The wallthickness distribution of Bellows is uniformity, thickness reduction radio is25%; thechange of structure is: the grain of largest deformation wave and the highest formingtemperature trough grow up obviously.