The Deformation Law And Control Methods Of Titanium Alloy Wire During Semi-dieless Drawing

Semi-dieless drawing technology is an advanced material processing technology,which has the advantages of short flow and near net-shape.Using this technology can solve the problems of products with large size fluctuation by dieless drawing and low deformation amount with large drawing force by traditional die drawing for producing difficult-to-form metal materials.However,the semi-dieless drawing technology has characteristics of multivariable,non-linear and strong-coupling,which leads to the complexity of its deformation law and difficulty of precision forming control.The deformation instability such as fracture,accumulation and leakage in the forming process restricts the development and application of semi-dieless drawing technology.In this thesis,TC4 titanium alloy wires are used as raw materials.The deformation rules of wire semi-dieless drawing are studied by means of finite element simulation,experiments and theoretical analysis.The deformation instability mechanism of semi-dieless drawing is analyzed.Then the corresponding control model is proposed and the control system is developed.These works lay a foundation for continuous and stable semi-dieless drawing technology.The main results are listed as follows:The deformation law of the TC4 titanium alloy wire during the initial stage of semi-dieless drawing is revealed.In the initial stage,the diameter of the entering wire increases,which causes the accumulation of the metal wire at the entrance of the die or broken at the exit of the die.As the heating temperature increases from 650℃ to 1050℃,the diameter fluctuation of the entering wire decreases from 0.15 mm to 0.04 mm and then increases to 0.08 mm.When the drawing speed increases from 0.32 mm/s to 0.36 mm/s,the diameter fluctuation of the entering wire is less than 0.04 mm,and the number of transition sections increases from 2 to 4.When the deformation increases from 33%to 51%,the diameter fluctuation of the entering wire increases from 0.04 mm to 0.08 mm,and the maximum diameter of the entering wire decreases from 3.0 mm to 2.6 mm.The mechanism of drawing interruption in the initial stage of semi-dieless drawing is studied.In the initial stage,the dieless drawn wire diameter increases by lowering the drawing speed,and the above process leads to formation of transition section.When the transition section enters the drawing die,the velocity of the metal wire reduces gradually and the drawing speed of dieless drawing section reduces gradually at the same time.When the feeding speed of dieless drawing section keeps constant,the speed ratio of dieless drawing will reduce gradually which results in interruption of semi-dieless drawing.When the drawing speed decreases from 0.38 mm/s to 0.34 mm/s,the diameter of the entering wire increases gradually from 2.43 mm to 3.0 mm,the speed of the entering wire decreases gradually from 0.34 mm/s to 0.249 mm/s and the speed ratio of the dieless drawing section decrease gradually from 1.36 to 1.The feeding speed control model during the initial stage of semi-dieless drawing is proposed.According to maintaining the speed ratio of the dieless drawing section constant during the deformation process,and the volume constancy law,the equation of the feeding speed was deduced.When the deformation amount of the semi-dieless drawing is 33%,44%and 51%,the feeding speed control model is adopted in the initial stage,and the speed ratio of dieless drawing section is stable at 1.28,1.52 and 1.8,respectively.The feeding speed control model can keep the speed ratio of the dieless drawing section constant during the initial stage of the semi-dieless drawing,and then keep the entering wire diameter constant,thus avoiding the interruption of semi-dieless drawing.The deformation law of TC4 titanium alloy wires during the quasi-steady stage of semi-dieless drawing is illustrated.In the quasi-steady stage of semi-dieless drawing,the entering wire diameter and its size fluctuation increase,which results in the metal wire fracture at the die exit.With increasing drawing speed or decreasing die diameter,the semi-dieless drawing process easily becomes unstable.The semi-dieless drawing was conducted under the condition of heating temperature of 950℃,distance between die and heating coil of 30 mm,feeding speed of 0.25 mm/s,drawing speed of 0.53 mm/s,and die diameter of 2.0 mm.The drawing speed of the dieless drawing section decreases from 0.53 mm/s to 0.21 mm/s and then to 0 during the semi-dieless drawing,which shows a fluctuating decreasing trend.The speed ratio of dieless drawing section decreases from 2.12 to 0.84 and then to 0,which also shows a fluctuating decreasing trend.The diameter of the entering wire shows a fluctuating increasing trend owing to the variation in the drawing speed,which results in the instability during the semi-dieless drawing.Based on the Matlab software,a kind of fuzzy control system is established,which is used to control the accuracy of the entering wire diameter during the quasi-steady stage.The maximum membership function method is used to solve ambiguity,and the offline fuzzy control rule table is obtained.When fuzzy control is adopted,the diameter of the entering wire maintain basically constant,and the maximum diameter fluctuation is 0.06 mm.When fuzzy control is not adopted,the diameter of the entering wire fluctuates continuously,and the maximum diameter fluctuation is 0.8 mm.Fuzzy control can be used to control the diameter of the entering wire effectively,and the quasi-steady stage of semi-dieless drawing is stable.The control system of the semi-dieless drawing is developed and the TC4 titanium alloy wire is prepared.This control system was used to control the entering wire diameter.The semi-dieless drawing was conducted under the condition of feeding speed of 0.25 mm/s,drawing speed of 0.34 mm/s,initial wire diameter of 3.0 mm and die diameter of 2.45 mm.The entering wire diameter is basically stable at 2.6 mm,and the diameter fluctuation is less than 0.06 mm.The difficult-to-form TC4 titanium alloy wire is prepared,and continuous and stable semi-dieless drawing is realized.When the deformation amount of TC4 titanium alloy wire is 30%,the drawing force of semi-dieless drawing and die drawing is 1700 N and 3800 N,respectively.The deformation amount of TC4 titanium alloy wire can be up to 60%by semi-dieless drawing and less than 40%by die drawing.Compared with die drawing,semi-dieless drawing has the advantages of low drawing force and large deformation amount in a single pass.