An aluminium billet is extruded through a steel die by a piston 150mm diameter. If the piston stroke is 1.2 m and the average pressure on the face of the piston is 100MN/m2.

The force exerted by the piston can be calculated using the formula:

Force = Pressure x Area

First, let's calculate the area of the piston:

Radius of piston = 150 mm / 2 = 75 mm = 0.075 m
Area of piston = π * (0.075)^2 = 0.01767 m^2

Now, we can calculate the force:

Force = 100 MN/m^2 * 0.01767 m^2 = 1.767 MN

Since the piston stroke is 1.2 m, the work done by the piston can be calculated using the formula:

Work = Force x Distance

Work = 1.767 MN x 1.2 m = 2.12 MN.m or 2.12 MJ

Therefore, the work done by the piston in extruding the aluminium billet through the steel die is 2.12 MJ.