Study Of Multi-stage Micro Deep Drawing And Size Effect Of TA1 Pure Titanium Foil

Metal plasticity microforming technology outperforms other microfabrication technologies due to its high processing efficiency,low production cost,high strength of formed parts,etc.Therefore,it has become a key technology for the manufacturing of micro parts.On the other hand,micro deep drawing technology,as an important plastic microforming process,has been widely adopted in the forming and manufacturing of hollow,thin-walled and cup-shaped micro-metal parts.However,during the micro-drawing forming process,with reduced feature size of the part,the deformation and the forming mechanism perform differently in macro-forming,showing obvious wrinkling and earing forming defects.Multi-stage and small-deformation forming technology is important to improve part forming quality by reducing the deformation of single forming.Therefore,in this paper,TA1 pure titanium(Ti)foil with the thickness of 50 μm was used for the in-depth investigation of the size effect and deformation mechanism of microtensile mechanical properties.The multi-stage micro blanking-deep drawing forming system was developed to systematically investigate the size effect on material deformation,dimensional accuracy and surface quality of forming cups during single-pass and multi-stage micro deep drawing forming process.The conclusions of this paper will provide some reference value for the development of plastic microforming technology for ultrathin materials.The as-received TA1 pure Ti foil was annealed at different temperatures to obtain pure Ti foil specimens with different grain sizes.By investigating the dimensional effects of microtensile mechanical properties of annealed pure Ti foil with different temperature,it was found that the plasticity and flow stress of the material gradually decreased with the decrease of T/D(specimen thickness/grain size).Based on the surface layer model and grain size model,the constitutive models of TA1 pure Ti foil micro-stretch material with T/D > 1 and T/D < 1 were established,which revealed the mechanism of the size effect of flow stress on TA1 pure Ti foil.Based on EBSD,SPM and DIC techniques,the fracture mechanism during micro-tensile deformation was investigated,and the results showed that the local micro-orientation at the grain boundaries and within the grains increased with the increase of grain size.The degree of strain localization increases early in the plastic deformation process,inducing an increase in the surface roughness of the deformed specimen.As the deformation proceeds,the uneven deformation increases,leading to premature fracture failure.TA1 pure Ti foil with a thickness of 50 μm was subjected to single stage micro blanking–deep drawing experiments,and it was found that there were two kinds of textures,i.e.,{10(?)0} and {11(?)0},in the plane direction of the as-received pure titanium foil,which caused wrinkles and earing effects during the micro deep drawing process,leading to poor forming results.After annealing at 600°C/60 min,the {10(?)0} and {11(?)0} textures gradually faded out,new {0001} textures were generated,and the anisotropy of the material was greatly reduced,which improved the surface quality of the formed parts,but a small amount of deformation wrinkles still remained.When the annealing temperature of the blank increased to 650°C–700°C,the coarse grain inhomogeneous plastic deformation led to poor forming effect of the material,appearing strong wrinkling effect or deep drawing fracture.Although the forming quality of single-stage micro drawn parts can be effectively improved through microstructure control of the blank,there are still forming defects,such as wrinkling and cracking.To manufacture micro-drawn cups featuring high CH/CD(cup height/cup diameter ratios)and high quality,a multi-stage micro deep drawing system was designed and studied.Based on the finite element assisted and theoretical calculations,the design of the number of drawing stages,the drawing ratio and the drawing depth of each stage were determined.Through the three-stages micro deep drawing experiments on pure titanium foil specimens with a thickness of 50 μm,micro drawn parts with a diameter of 0.6 mm and a CH/CD of 1.6 were successfully prepared with good forming quality and almost no wrinkles on the surface.With multi-stage micro-drawing,the "ironing effect" generated by the unilateral clearance can effectively alleviate the wrinkling of the final micro-drawn parts,and improve the surface finish of the parts.To further explore the effects of material microstructure and process parameters on the forming quality of multi-stage micro drawn parts,the effects of grain size,deformation speed and punch radius on the forming performance were systematically investigated.The results show that the material grain size has a significant effect on the micro drawn cup forming.At the blank annealing temperature of 600°C,the uniformly recrystallized grains were distributed inside the blank with reduced material anisotropy,and the optimal effect of final micro parts forming can be achieved.The deformation velocity can be utilized to improve the forming quality of the deep drawn parts.Compared with grain size,the deformation velocity has less effect on the forming quality of the deep drawn cup.In addition,for pure Ti foil specimens with small grain size,the punch radius has less effect on the thickness thinning of multi-stage drawn parts.However,for specimens with coarse grains,small punch radius will significantly intensify the thickness thinning effect of the drawing cup and the phenomenon of deep drawing fracture.Therefore,in the multi-stage micro deep drawing of pure Ti foil,uniform small grains blank and large punch radius can be used to obtain the micro parts with excellent forming quality.