Investigation On A Micro-rolling&Incremental Sheet Forming Process For Thin-walled Metal Components With Microgroove Arrays

Thin-walled sheet components are widely used in the fields of aerospace,automotive,ships and energy equipment,etc.The rapid development of these fields has placed increasingly high demands on component performance and delivery time.Traditional structural solutions are difficult to meet the increasing performance requirements of thin-walled curved components,and surface microfeatures with special functions such as drag and noise reduction,wear resistance,and super hydrophobic provide an effective solution.However,it lacks a process method that integrates macroscopic forming and functional surface microfeatures fabrication.Traditional sheet forming processes rely on dies with long design and manufacturing development cycles and high costs.Therefore,this paper proposes and investigates a novel micro-rolling&incremental sheet forming hybrid process to fabricate thin-walled metal components with microgroove arrays.Firstly,an experimental platform for microgroove micro-rolling based on self-designed micro-rolling tool was built,and the influence of key process parameters on the morphology of flat sheet microgrooves was investigated.The results showed that the depth of microgrooves decreased while the width and rolling force increased as the diameter of the rolling ring increased.The depth of microgrooves decreased by 7.7 μm and the width increased by 55.8 μm when the diameter of the rolling ring increased from 300 μm to 500 μm.As the rolling depth increased,the depth,width of the microgrooves and rolling force all increased.The average depth of microgroove was 25.01μm and the average width of microgroove was 290.46 μm at a rolling depth of 0.15 mm.The feed rate had little effect on the microgroove size and rolling force.A microgroove depth prediction model was established with an average error and maximum error of less than 5%and 15%,respectively.Secondly,the influence law of macroscopic incremental forming on the inner and outer surface morphology of micro-grooved sheets was investigated.On the one hand,due to the stretching and thinning of the side walls during incremental forming,the depth of both transverse and longitudinal grooves on the formed part was significantly reduced compared to micro-grooved sheets,by between 21%and 60%.On the other hand,due to the influence of the maximum strain direction on the microgrooves during incremental sheet forming,the width of transverse grooves decreased by about 10%on average,while the width of longitudinal grooves increased by more than 30%on average.In general,the depth reduction rate and width increase rate of transverse grooves were both less than those of the longitudinal grooves.A model of the relationship between the spacing of longitudinal microgrooves before and after incremental forming was established based on the geometric position relationship before and after sheet deformation,with a maximum error of 3.15%.In addition,the quality of the inner surface of the formed part increased as the forming angle increased and decreased as the step-down size and tool head diameter increased.Thirdly,the sheet properties and microstructure changes after micro-rolling&incremental sheet forming hybrid process were experimentally investigated.After micro-rolling,the hardness of the microgroove edges and the strength of the microgroove sheet increased as the rolling depth increased.This is due to the presence of {10-12} tensile twins and an increase in the proportion of {11-22} compression twins on the microgroove sheet after micro-rolling,which increases the hardness of the microgroove sheet.Meanwhile,the presence of twin boundaries hinders the dislocation movement and thus improves the strength of the sheet.After incremental forming,the change in hardness of the formed parts with different rolling depths was not significant,while the strength increased slightly with the increase of the rolling depth.The grain morphology of the formed parts with different rolling depths is approximately the same,thus the change in hardness is not significant.The formed parts fabricated by microgrooved sheets had a higher dislocation density and thus the strength of the formed parts increased.Finally,a study on the optimization of incremental forming process parameters for geometric accuracy was carried out.The effects of opening size,forming times,forming strategy and the addition of a backing die on the geometric accuracy of the formed parts were explored,and the distribution pattern and formation reasons of geometric errors on the formed parts were analyzed.The results showed that the geometric errors on the formed parts were generally axially symmetrically distributed and mainly composed of five parts.Increasing the forming opening size and forming times can respectively reduce the geometric errors at the upper end of the forming opening and at the sidewall.The adoption of multi-pass forming strategy can to some extent reduce the geometric errors in the side wall,while the use of single pass forming strategy can reduce the geometric errors in the middle of the formed part.Additionally,the addition of a backing die can significantly reduce the geometric errors in these areas simultaneously.