Optimization Of High Temperature Alloy GH4169 Bellows Hydroforming Process

Metal bellows is a type of elastic compensation parts,with good damping and noise reduction effect and imperviousness,widely applied in oil pipelines,aviation engines and other fields.The hydraulic forming process is one of the major methods for producing metal bellows.Since the conventional hydraulic forming process of bellows is prone to significant wave thinning that causes the rigidness and fatigue lifetime of bellows to decline.Moreover,because of their excellent strength,hardness and corrosion resistance,refractory alloys are increasingly used for producing bellows.However,these materials have poor plastic flexibility and are less likely to withstand excessive thinning at wave crest,resulting in low yield rate of finished products.To address the significant thinning at wave crest of hydraulic forming process of bellows,a movable die sheet is added between the forming dies of the conventional process.So the hydraulic forming process of bellows encompasses three steps from two steps.The finite element software Abaqus was used to simulate the two methods before and after the optimization of hydraulic forming process of refractory alloy GH4169 bellows by building an axisymmetric finite element model with an outer diameter of 37.1 mm,a wall thickness of 0.3mm and a forming die spacing of 13 mm to analyze the distribution patterns of the equivalent stress and equivalent plastic strain of the two forming methods and to study of influence of the internal pressure on thinning rate and wave height of the conventional process.With unchanged process parameters of the conventional hydraulic forming method of bellows,the influences of the first expansion pressure,thickness and corner radius of the movable die on the wall thinning rate of bellows produced by the optimized process were studied.The results showed that the thinning rate was 18.08% and the crest height was 5.514 mm at a pressure of 20 MPa in the conventional process;the optimal process parameters for the optimized process were: the first expansion pressure was 40 MPa,the thickness of movable die was 6 mm,and the corner radius of movable die was 0.8 mm,with which the wall thinning rate was 16.68%,and the crest height was 5.509 mm.Through the comparison of the two processes,it can be found that the crest height was almost unchanged and the thinning rate was reduced by 1.4%,with the decline range of 7.7%.An experimental scheme of the two processes was developed using the hydroforming bellows mold designed with the optimal process parameters derived from the simulation to carry out the experiment of hydraulic forming bellows.The wall thickness of the experimentally formed bellows was measured to calculate and compare the wall thinning rate with the simulation results.The comparison showed that the distribution pattern of thinning rate was consistent at large,with a value less than 1%,demonstrating the rationality and accuracy of the finite element analysis of the hydraulic forming process of bellows.The secondary development of Abaqus was conducted in Python language by establishing a modeling optimization system of bellows hydraulic forming,in which the Abaqus modeling process was parametrized and presented on interface.The modeling is completed by entering pertinent parameters in the interface of the system,which facilitates users to easily and quickly carrying out studies of hydraulic forming process optimization of bellows.