Prediction And Control Of Forming Accuracy Of H96 Double-ridged Rectangular Waveguide Tube Considering Variable Elastic Modulus In H-type Rotary Draw Bending

With the characteristics of wide working frequency band,low equivalent characteristic impedance and small size,the H96 brass double-ridged rectangular waveguide has a wide application prospect in the fields of aviation,aerospace,radar and satellite communication as the microwave transmission channel and connector.With the rapid development of communication field,it is urgent to form the bent tube with high forming accuracy,that is the bent tube should meet the requirements of cross-sectional dimensional accuracy and compact structure.However,due to the special ridge structure of double-ridge rectangular waveguide and constraint of multiple dies,severe cross-sectional deformation will inevitably occur in the H-typed rotary draw bending.Serious cross-sectional deformation would affect the microwave transmission characteristics and mechanical properties such as the strength and rigidity of bent bend.In addition,after unloading the bending dies,the springbak is also inescapable.Springback will not only change the cross-sectional deformation,but also reduce the bending angle and increase the bending radius.Cross-sectional deformation and springback both make it difficult to meet the requirements of forming accuracy of bent tube.In order to realize the precise forming of H-typed double-ridged rectangular bent tube,using the method of finite element simulation and experiment,the prediction and control of forming accuracy of the H96 double-ridged rectangular tube during the H-bending process are systematically and thoroughly studied.It has important guiding significance for advancing the development of precise plastic forming technology of complex communication bent tube in the fields of aerospace and radar.The main research contents and results are as follows:Through the repeated loading and unloading test,the quantitative relationship between elastic modulus and plastic strain of H96 brass double-ridged rectangular tube is obtained and described by segmental linear function.Based on the function,the elastic-plastic constitutive models in the bending and springback process which considering variable elastic modulus of H96 tube,are established and embedded into ABAQUS software.It is found that the establishment of the constitutive model with variable elastic modulus can improve the prediction accuracy of these models,in which the prediction accuracy of cross-sectional deformation and springback angle can be increased by about 5%and 22.89%,respectively.After solving the key technology of modeling,the H-typed bending and springback models of H96 double-ridged rectangular tube considering variable elastic modulus with flexible-cores rigid mandrel,cuneate rigid mandrel and deformable PVC mandrel are established.The reliability of these models are verified by experiments.Based on these models,the variation of forming accuracy of double-ridged rectangular bent tube with the bending angle and bending radius under those three mandrels is compared.it is found that,under different bending conditions,when using the cuneate rigid mandrel and PVC mandrel,the cross-sectional deformation,springback angle and springback radius of bent tube are significantly smaller than that with the flexible-cores rigid mandrel.When the relative bending radius R/H is less than 2.5,the PVC mandrel has the best inhibition effect on the cross-sectional deformation.When R/H is greater than 2.5,the PVC mandrel can reduce the spacing deformation of ridge grooves more effectively,but the cuneate mandrel matching the bending radius has a better restraining effect on the deformation in height direction,and it can control the springback angle and springback radius of bent tube with different bending angles under large bending radius more effectively than PVC mandrel.Considering the cost of mandrel and bending efficiency,the cuneate mandrel matching the bending radius is the more suitable mandrel for forming bent tubes with different bending angles under large bending radius.It is also found that no matter what kind of mandrel is used,the shrinkage deformation of ridge groove can not be restrained effectively.Therefore,considering the ridge groove can be constrained by filler,and the reliable H-typed bending and twice-springback models of double-ridged rectangular tube with ridge groove fillers are established.It is found that only filling fillers into ridge grooves can reduce the cross-sectional deformation,especially the height deformation of ridge groove,but it has a poorer effect on the height,width deformation of section and spacing deformation of ridge grooves.By using the ridge groove fillers and mandrel simultaneously,the deformation of section can be effectively reduced,and the distribution of cross-sectional deformation in the mandrel-support area and the non-mandrel-support is more uniform.Therefore,filling fillers into the ridge grooves is an effective method to improve the forming accuracy of double-ridged rectangular bent tube.The influences of the size of filler on the forming accuracy are studied.Compared with the width of filler,the influence of height of filler on the cross-sectional deformation and springback radius is more significant.In order to avoid excessive springback angle,at least the height or width of filler should be consistent with the size of ridge groove.Therefore,when determining the size of filler,only keeping the height size of filler consistent with the height of ridge groove can effectively control the cross-sectional deformation and springback of bent tube.Using single factor and sensitivity analysis method,it is obtained that when selecting the material of filler to improve the forming accuracy of bent tube,the strength coefficient K and elastic modulus E should be considered firstly,the larger K can reduce the deformation more effectively,and the larger E can reduce the springback angle and radius more effectively.The filler with higher yield strengthσ_sor smaller hardening exponent n,which is more conducive to the reduction of height deformation of ridge groove,can be selected as far as possible.The reliability of this selection criterion is verified by using 65Mn spring steel filler.On the premise that the ridge grooves are constrained by fillers,the influences of different process parameters on the forming accuracy of bent tube are revealed.Then based on the comprehensive evaluation index method,the optimal combination of process parameters,which can reduce cross-sectional deformation of bent tube after springback,is determined:Vp=30mm/s,μ_m=0.02,μ_b=0.25,μ_p=0.1,μ_w=0.1,c_m=0.15,c_b=0.25,c_p=0.1,c_w=0.1.Based on the combination,the springback angle and springback radius of bent tube under different bending conditions are obtained by simulation,then the prediction and control models of springback angle and springback radius are established.The reliability of these models are verified by an example,which also shows that these models have very high prediction and control accuracy for springback.It incidates that based on these models,the appropriate initial bending angle and radius of bent tube can be obtained and used in the over bending and die compensation methods.The above research not only enriches the research on the prediction and control of the bending accuracy of double-ridged rectangular waveguide,but also has an important guiding significance for improving the manufacturing level of complex communication waveguide bends in the fields of aviation,aerospace and radar.