Micro deep drawing experimental and numerical simulation study of pure titanium

<p dir="ltr">In recent years, the demand for micro parts in various industries is increasing. Microforming has been widely used in aerospace, medical, electronic communications, and other fields because of its superior conductivity, thermal conductivity, and plasticity. The rapid rise of micro electromechanical system (MEMS) has also promoted the development of miniaturisation of parts. With the development of miniaturisation and lightweight, microforming has a very broad development prospects because of its high efficiency, low cost, short duration, and less pollution. Titanium is an enormously useful metal, and frequently employed for a wide range of applications in recent years, across a broad range of different fields, including chemical plants, aerospace, military, and medical industry. The combination of microforming and titanium will have a promising application in future advanced manufacturing. Therefore, it is logical to study the performance of titanium in the microforming. The effects of grain sizes on the mechanical properties of pure titanium foil are studied through annealing process. The effects of grain sizes on the deformation behaviour of micro parts in micro deep drawing (MDD) were studied by both experimental and simulation methods. Finally, the micro cup with the average height of 0.69 mm and the average radius of 0.49 mm was successfully produced.</p><p dir="ltr">In this study, the grain size increases from 33 to 54 μm with the increase of heat treatment temperature, while the tensile strength and hardness of pure titanium foil decrease. The wrinkles increase with the increase of grain sizes. The rule of earing is not significant due to the grain heterogeneity. As the grain size increases, the number of pits on the surface increases. The surface roughness Ra is 0.24 μm when the grain size is 38 μm, which is the smallest. The highest one is 0.84 μm as the grain size is 54 μm. The peak drawing force decreases from 48 to 37 N as the grain size increases. For the final drawing force, it is 11.8 N as the grain size is 54 μm, this is relevant to poor forming quality of the material.</p><p dir="ltr">Finite Element Method (FEM) was utilised in this study. A Voronoi polycrystalline model considering size effects was used to simulate the MDD process with Ti foil, and the simulation results exhibit a good agreement with the experimental results in term of drawing forces. The simulation results show the wrinkle increases with the increase of the grain size from 33 to 54μm, the thickness of inhomogeneous deformation area of the cup mouth increases from 0.042 to 0.071 mm, the standard deviation of the thickness distribution increases from 1.206 to 1.77 mm, the maximum drawing force decreases from 33.34 to 21.54 N and the distributions of stress and strain are more inhomogeneity.</p><p dir="ltr">In this study, novel water-based TiO2 nanolubricants with excellent dispersion stability and lubrication performance were developed and applied in MDD with a 40 μm-thick pure titanium foils. The lubricants consisting of TiO2 nanoparticles (NPs), 10 wt% glycerol, 0.1 wt% sodium dodecyl-benzene sulfonate (SDBS) and balanced water were synthesised in a facile process. The MDD tests were then carried out using the lubricants with varying concentrations of 0.5, 1.0 and 2.0 wt%. The results show that the formability of micro cups could be significantly improved when the nanolubricants are applied. Especially, 1.0 wt% TiO2 nanolubricant demonstrates the best lubrication performance by significantly reducing the final drawing forces, and surface roughness, and improving the shape accuracy. The lubrication mechanisms including the ball bearing and mending effects of TiO2 NPs on open lubricant pockets (OLPs) and close lubricant pockets (CLPs) areas were then revealed through microstructural observation.</p>