Effects of die geometry and extrusion speed on the cold extrusion of aluminium and lead alloys

An experimental investigation is made on the effects of die reduction in area, die angle, loading rate on the quality of the extrusion products, extrusion pressures and flow pattern of cold extruded aluminium and lead alloys shapes of inner circular sections with four symmetrical projections. The radii of curvature for both extruded lead and aluminium alloys and the average hardness values of the extruded products along the projections and along the circumferential solid positions are found to increase with increase in die reduction in area, and slightly with increase of the loading rates. It shows that the non-dimensionalised values of the specific coring pressures, Pc/ϕ, and maximum extrusion pressures, Pmax/ϕ, depend primarily on the die angle, loading rate and total reduction in area of the cross-section of the complex-shaped section. These are found to be minimum at a die angle of 90°, which is recommended for die design so as to minimise extrusion pressure and hence increase die life. Empirical formulae, relating the specific maximum extrusion pressure and coring pressure to the reduction in area, R, can be expressed in the form P/ϕ=a+b ln(1/(1−R)), where a and b are constants for a given material. Similarly, empirical formulae of the form P/ϕ=a′+b′ ln(V) are used to express the extrusion pressures (maximum or coring) P/ϕ, to the extrusion speed. Extrusion defects and the flow patterns of the extruded complex-shaped section are highlighted and discussed.