the effect of micropits and bio-lubricants on aluminum cold work extrusion performances

Abstract

Many attempts have been made to replace mineral oil-based with biodegradable lubricant such as vegetable oil in order to reduce environmental impacts. Palm oil based is available in abundance in Malaysia at cheaper price compared to mineral based lubricant but reports on using this oil as an alternative lubricant is hardly found especially in cold metal forming applications. This study aims to evaluate and compare the tribological performances between two different types of palm oil-based and mineral oil-based lubricants using modified die surface geometry (with and without micropits at top and bottom positions, sharp T45 and radius R45 taper angle) during cold extrusion process. All extrusion process parameters were fixed during experiments, i.e. deformation ratio (3:1), speed range (8.1-8.3 mm/s), piston displacement stroke (40 mm), micropit depth (30 µm), diameter (600 µm), distance (1 mm) and 27 percent of area density. Top position of micropit exhibits the lowest friction and extrusion load with finer billet surface in all trials. It is also found that palm stearin (PS) performs better than palm kernel (PK) in terms of extrusion load and billet surface roughness. Similar results also obtained in paraffinic mineral oils experiments where VG460 outperforms VG95. Higher viscosity in both type of lubricants is the main reason that contributes to this performance. Comparing between PS and VG460, the performance of mineral oilbased is still superior than palm oil-based but the difference is very marginal in terms of extrusion load and billet surface roughness. The achievable extrusion load and billet surface finish under PS lubricant are 48.9 kN and 0.11µm respectively. The optimum tribological performance of mineral oil-based VG460 over palm oil-based PS is attributed to the large viscosity difference between VG460 (1347.60 mm2/s) and the PS (48.29 mm2/s). Since there is only marginal difference in tribological performance, it can be concluded that palm oil-based has a great potential to be developed further as an environmental friendly lubricant for replacing mineral oilbased type.