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To improve the quality of products produced from microforming, various nanolubricants have been applied in the field of micromanufacturing in recent years. In this paper, the effects of glycerol-based lubricant containing TiO2 NPs (NPs) on micro deep drawing (MDD) of austenitic stainless steel (ASS) SUS301 were studied, and the lubrication mechanism involved was discussed. The MDD experiments were conducted with the SUS301 foils under dry, 1, 2, and 4 wt% TiO2 NP lubrication conditions. The results show that the use of the TiO2 nanolubricants can significantly improve the quality of the drawn cups in terms of decreased wrinkling and surface roughness. Besides, the concentration of TiO2 NPs influences lubricity by reducing friction during the MDD process. The peak drawing force is the lowest when 2 wt% nanolubricant is applied, which drops to 72.54 N from 77.38 N under dry conditions. The micro cup drawn under 2 wt% TiO2 nanolubricant has the best quality among those obtained under all the lubrication conditions. The lubrication mechanisms are derived from the mending effects of TiO2 NPs and the formation of thin lubricant films associated with the open lubricant pockets (OLPs) and close lubricant pocket (CLPs) theory in the MDD. The CLPs function as reservoirs that retain lubricants to counteract the load pressure, whereas the OLPs lead to lubricant leakage due to the higher flow resistance. It was found that the lubricant film and NPs are insufficient at a low concentration (1 wt%), while the lubrication performance can be enhanced with increased NP concentration. However, there exist apparent agglomerations on the surface of the produced micro cup when using 4 wt% nanolubricant, which greatly deteriorates the lubricant performance in the MDD process. It is concluded that the lubricant containing 2 wt% TiO2 NPs demonstrates the best lubrication performance during the MDD of ASS SUS301. [ABSTRACT FROM AUTHOR]

Micro deep drawing (MDD) is a fundamental process in microforming which has wide applications in micro electromechanical system (MEMS) and biological engineering. Titanium possesses excellent mechanical properties and biocompatibility, which makes it a preferred material in micromanufacturing. In this study, eco-friendly and low-cost water-based TiO2 nanolubricants were developed and applied in the MDD with 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 with 40 μm-thick pure titanium was 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, the use of 1.0 wt% TiO2 nanolubricant demonstrates the best lubrication performance by significantly reducing the final drawing forces, and surface roughness, and the wrinkles by up to 24.2%, 12.55% and 4.82%, respectively. The lubrication mechanisms including the ball bearing and mending effects of NPs on open lubricant pockets (OLPs) and close lubricant pockets (CLPs) areas were then revealed through microstructure observation. [ABSTRACT FROM AUTHOR]

Effects of various lubrication conditions on macroscale deep drawing have been investigated extensively while in microscale due to the open and closed lubrication pocket theory and friction coefficient escalation, proper lubricant concern becomes severe. Microforming is used to produce lighter and more energy-effective products accordingly; in this study, magnesium-lithium (Mg-Li) alloy is chosen to form a superior micro-cup due to its ultralight weight with outstanding ductility. Mg-Li is a new material in microscale; consequently, to study the mechanical properties, a heat treatment process is performed. The dry and oil lubrication conditions are chosen as benchmarks to investigate effects of TiO2 oil-based nano-additive lubricant. Finite element (FE) modelling has been conducted and the simulated results are agreed well with the experimental results where the drawing force is significantly affected by the nano-particle. The formed cup quality regarding the surface roughness has been evaluated extensively by consideration of various parameters and the quality improvement is substantial. [ABSTRACT FROM AUTHOR]

In this study, the micro deep drawing (MDD) experiments of an austenitic stainless steel with 40 μm in thickness were conducted using the lubricants containing different mass fractions of graphene nanosheets (GNS) in ethanol. Prior to the MDD tests, the lubricants with GNS concentrations of 5, 10, and 15 mg/ml were synthesised by mixing different amounts of GNS with pure ethanol, and then sprayed uniformly on the blank surface. The friction-reduction mechanisms of the GNS in the MDD were discussed by analysing the profile and surface roughness of the microcups. The results indicated that the GNS could reduce the friction and improve the surface quality of the micro products during the MDD process. In particular, the lubricant with 10 mg/ml GNS enabled the lowest drawing force, wrinkling, and surface roughness of the drawn microcup. These findings contribute to a better understanding of the friction-reduction mechanisms of using GNS in the MDD of materials. • The coating behaviour of the graphene lubricants are compared. • The role of graphene lubricant in micro deep drawing is shown to be important in reducing the friction. • The effect of utilising graphene lubricants for improving the quality of the micro cups is demonstrated. [ABSTRACT FROM AUTHOR]

Micro-hydromechanical deep drawing (MHDD) is a promising micro-manufacturing technology to fabricate micro-metallic products in batch scale. Size effects significantly affect MHDD regarding both material properties and friction. Hydraulic pressure on the blank and its development differ from that in conventional hydromechanical deep drawing. Combined influence of fluid pressure, surface roughness and material inhomogeneity of the blank was investigated in this study via MHDD experiments and advanced FE simulation considering strong fluid-solid interaction (FSI) and size effects. The MHDD experiments under different hydraulic pressures were conducted using the annealed foil followed by the advanced FE simulation. The foil can be successfully drawn into micro-cups, however, wrinkles occurred under high hydraulic pressures. Wrinkle height and number are affected by hydraulic pressure and size effects. Average hydraulic pressure on the blank is lower than the inlet pressure, and pressure development on the blank depends on location and is complex, due to transition of sealing between the blank and die. The maximum drawing force increases, while the contact forces and pressures on the blank holder and die decrease with an increase of hydraulic pressure. Optimal hydraulic pressure for MHDD should be determined with consideration of size effects and MHDD tool geometry. • Micro-hydromechanical deep drawing experiments and advanced simulation with consideration of FSI, material surface morphology and inhomogeneity were conducted. • Change of the sealing between the blank and die significantly affects mean and local hydraulic pressure development on the blank, which further impacts MHDD. • Hydraulic pressure reduces contact forces and maximum contact pressures on both blank holder and die, which benefits wear behaviour of MHDD tools. • Integrated effect of hydraulic pressure and size effects influences wrinkling. • Optimal hydraulic pressure should be determined with consideration of foil's properties and MHDD tool geometry. [ABSTRACT FROM AUTHOR]

To comprehend the role of water-based nanolubricant in micro flexible rolling, corresponding characterisation with respect to different concentrations of nanolubricants, surface roughness variation subjected to each micro flexible rolling phase and dispersion of nanoparticles (NPs) were studied systematically. The results reveal that increasing NPs get trapped into the surfaces from the thicker zone to the thinner zone. Downward transition zone with favourable deformation features leads to the smoother surface roughness. Nanolubricants can effectively decrease rolling traces due to the beneficial nanolubrication mechanisms. Notably, the maximum reduction for rolling force is around 18% for the case under 2.0 wt% nanolubricant rolling condition. The current study provides great potential insights in how nanolubrication takes effect in microforming areas. • Water-based nanolubricants distinctly reduce the rolling forces during micro flexible rolling. • Increasing NPs get trapped into the surfaces from the thicker zone to the thinner zone. • Downward transition zone with favourable deformation features leads to the smoother surface roughness. • More remained NPs are detected near the middle area along the transverse direction of the specimen. • Water-based nanolubricants can effectively decrease rolling traces due to the beneficial nanolubrication mechanisms. [ABSTRACT FROM AUTHOR]