Increase in ironing limit of aluminium alloy cups with lubricants containing nanoparticles

The seizure resistance in the ironing process of aluminium alloy cups was improved with lubricants containing SiO2 nanoparticles, and the ironing limit of the cups was increased. The effects of suspending different concentrations of SiO2 particles in sulfur based mineral oils at three viscosity levels on increasing the ironing limit of Al 3003-O cylindrical cups before seizure were investigated using a lapped TiCN cermet die under a near production rate of 100 mm/s. By suspending a mere 1.0 wt% of SiO2 in oil with a kinematic viscosity of 170 mm2/s, the ironing limit of the cup was increased from 24.8% to 35.2%. The ironing limit was slightly reduced to 34.8% when the viscosity level was excessive i.e., 500 mm2/s with 1.0 wt% of SiO2. When the viscosity level was too high, the ironing load increased and the seizure resistance was slightly reduced. However, the amount of increase for the low viscosity oil was only 27.5% with 5.0 wt% of SiO2. When the viscosity was too low, the film thickness at the contact surface was less than the average surface roughness, leading to direct contact between the asperities. Hence, a large amount of SiO2 was required to prevent seizure. The surface roughness of the ironed cups remained unchanged with the presence of the nanoparticles in the lubricant. By increasing the ironing limit, lightweight cups with a smooth surface, thin wall thickness and elongated height were successfully formed in the experiment. The seizure resistance of the ironing die was also improved with the medium and high viscosity oils containing nanoparticles for obtaining high ironing ratios.