| Fluid pipes are widely used in petroleum,chemical industry,natural gas and other industries.Due to the requirement to be used in harsh areas such as extreme cold and extreme heat,the production of modern fluid pipes is developing towards the trend of "large caliber,high pressure transportation,high steel grade pipes".Cold-drawn fluid tubes are used more and more,and the quality requirements are higher and higher.The traditional method of producing fluid pipe usually adopts the drawing die with fixed short core head.The drawing precision of single pass drawing is as follows: the dimension deviation of outer diameter is D2 grade and the deviation of wall thickness dimension is S2 grade.In order to further improve its cold drawing accuracy,multi-pass drawing is adopted,which will affect production efficiency and cold drawing cost.In order to solve this problem,a double-diameter cold-drawing die is designed in this paper,taking cold drawing fluid tube as an example.The purpose of this die is to achieve high cold drawing precision in one drawing process.In this paper,the drawing process is simulated and analyzed by using the finite element software ABAQUS.The forming precision,drawing force and equivalent residual stress of cold drawn steel pipe with fixed short core die and double diameter die are analyzed and compared.In order to verify the feasibility of the double-diameter die,the structural parameters of the double-diameter die are optimized and analyzed.Under the same conditions(the same batch of billets,the same pretreatment process,the same cold drawing die structure parameters,etc.)the finite element simulation analysis of the cold drawing process of fixed short core die and double diameter die is carried out by using the finite element software ABAQUS,.The results show that:(1)for the two kinds of dies,the drawing deformation law is the same: the larger the size of billet outer diameter,the larger the deformation amount of outer diameter and the larger the deviation of outer diameter dimension;The larger the blank wall thickness size,the smaller the inner wall deformation,and the smaller the finished product wall thickness dimension deviation.(2)drawing precision: the fixed short core head single diameter die outer diameter deviation grade can reach D2 grade,the wall thickness deviation.The outer diameter deviation grade of double-diameter die drawing die can reach D3 grade,and the wall thickness deviation grade can reach S3 C grade,which can reach S3 A grade and double-diameter die drawing die product outer diameter deviation grade can reach D3 grade and S3 C grade.The results show that the outer diameter precision of double-diameter die can be improved by one grade and the wall thickness deviation can be reduced by about 50%.(3)the drawing force of single-diameter short-core die and double-diameter die can be verified,and the precision of outer diameter of single-diameter and double-diameter dies can be improved by one grade compared with that of fixed short core die.The simulation results are basically consistent with the formulas used in the calculation of draft force in China.The drawing force of the double-diameter die is about 20% higher than that of the single-diameter short core die.(4)the analysis of the equivalent residual stress shows that the maximum residual stress of the two kinds of dies occurs at the interface of the internal die inlet angle and the sizing band.At the same time,there is little difference between the two values.The results of this analysis are in agreement with the maximum position of die wear in practice.The main technological parameters(entrance angle ?,length h and relative position L)of the double-diameter die were simulated and optimized by orthogonal experiment,and processed by the method of extreme difference analysis.The results show that:(1)the order of the influence of process parameters on the forming accuracy and equivalent residual stress of cold drawing outer diameter of double-diameter die is as follows: the entrance angle ? > the relative position of the front and rear pass sizing band L > the length h of the front and back pass sizing band;The influence order of wall thickness forming precision is as follows: the length of front and rear pass sizing band h > the relative position of front and rear pass sizing band L > the entrance angle ?.(2)the forming accuracy and equivalent residual are considered comprehensively.Under the influence of residual stress,the optimum parameters obtained by simulation optimization are as follows: entrance angle ? = 11 °,length of pre-and post-pass sizing band h = 22 mm,relative distance of front-to-back pass sizing band L = 19 mm.Under the optimized die structure condition,the outer diameter deviation grade of drawing precision is D3 grade,the wall thickness deviation is S4 A grade,and the equivalent residual stress and drawing force can be improved by one grade,which can meet the quality requirements of finished products. |
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