Study On Deformation Behavior Of Pure Titanium Foils During Elevated Temperature Micro Pneumatic Deep Drawing Process

In recent years,with the increasing demand for micro parts in communication,electronics,medical and other fields,the rapid development of micro parts forming technology has been greatly promoted.The micro deep drawing process was developed on the basis of traditional deep drawing process,which is mainly used in the manufacture of micro cups.In order to obtain larger drawing height,uniform wall thickness distribution and better surface quality,the high temperature micro deep drawing process,the micro hydraulic deep drawing process and other processes have been successfully developed.Although the drawing height of the micro cup can be improved in the high temperature micro deep drawing process,the surface quality of the micro cup is poor.Due to the low ignition point of the hydraulic medium,the micro hydraulic deep drawing process can only be carried out at room temperature.Although better surface quality of micro cup can be obtained,the drawing height of the micro cup is small.In order to obtain the micro cup with higher drawing height,better surface quality and relatively uniform wall thickness distribution,the elevated temperature pneumatic micro deep drawing process is proposed in the current study.In this process,the high temperature and high pressure air is used as the forming medium to realize the high-temperature forming of metal foil.The better surface quality and relatively uniform wall thickness distribution of the micro cup can be obtained by the elevated temperature pneumatic micro deep drawing process.In order to obtain the influence of process parameters on the deformation behavior of pure titanium foil in the micro pneumatic deep drawing process,the micro pneumatic deep drawing processes of the with different deformation conditions were carried out using the pure titanium foils with different thicknesses.In order to obtain accurate FE simulation results,the constitutive equation with size effect of pure titanium foil was established.The FE model of the micro pneumatic deep drawing process of pure titanium foil is established by the secondary development of the FE simulation software combined with the constitutive equation of pure titanium foil with considering the size effect.The reliability of the FE model is verified by the experiment.By analyzing the experimental and FE simulation results,the effects of different process parameters on the deformation behavior of pure titanium foils in micro pneumatic deep drawing process were obtained.The micro cup with high forming height,relatively uniform wall thickness distribution and good surface quality was obtained by optimizing the process parameters.The main research contents of this study are as follows:(1)Due to the current facility of the micro pneumatic deep drawing process can not be conducted for the high temperature forming,the necessary modification of the facility is needed.Firstly,the facility modification scheme is proposed.The feasibility of the modification scheme is confirmed by using the FE simulation method.The analysis results of temperature distribution of the modified mold showed that the modified scheme is feasible and can meet the experimental requirements.(2)In order to obtain the influence of different forming parameters on the deformation behavior of pure titanium foils in micro pneumatic deep drawing process,the experiments with different forming parameters were carried out.In order to reduce the workload of the experiment without reducing the reliability of the experimental results,the experimental scheme was optimized through orthogonal design in this study.The effects of thickness of foil,forming medium pressure,punch speed and punch stroke on the deformation behavior of pure titanium foils were studied.With the increase of foil thickness,the higher the forming height,the smaller the thickness change and the lower the thinning rate.(3)The power hardening constitutive equation of pure titanium foil is established with considering the size effect and strain gradient theory.Based on the experimental and FE numerical study of the nanoindentation experiment of the pure titanium foil,the material constants in the power hardening constitutive equation of the pure titanium foil were determined by using the one section gradient descent method.The intrinsic length of pure titanium foil used in this study is 6.89 μm.The equivalent strain gradient is 0.0268μm.(4)In order to obtain the stress-strain distribution and deformation behavior of pure titanium foils in micro pneumatic deep drawing process,the deformation processes were studied with FE simulation.The FE model of the micro pneumatic deep drawing process of pure titanium foil is established by the secondary development of the FE simulation software by combining with the constitutive equation of pure titanium foil with considering the size effect.The reliability of the FE model is verified by the experiment.Compared with the simulation results of the FE model with the traditional power hardening constitutive equation,the simulation results of the FE model with considering the size effect are in good agreement with the experimental results.(5)The deformation behavior of pure titanium foil in the elevated temperature micro pneumatic deep drawing processes with different process parameters was studied by using the FE model considering size effect.The effects of forming temperature,foil thickness,the gap between punch and die,forming medium pressure,friction coefficient,punch speed,punch stroke and other process parameters on the wall thickness distribution,drawing height and forming force in the elevated temperature micro pneumatic deep drawing processes of pure titanium foil were obtained.By the analyzing the simulation results,the optimal combination of process parameters was obtained:deformation temperature is 160℃,the forming medium pressure is 1 MPa,the punch speed is 4 mm/s,the punch stroke is 2 mm,the friction coefficient is 0.04,and the clearance between punch and die is 0.11 mm.The numerical simulation results of the elevated temperature micro pneumatic deep drawing processes under the best technological parameters are obtained.