Complex sentence: When a piston is cast the alloy is heated until liquid, then poured into a mould to create the basic alloy cools and solidifies it is removed from the mould and the rough casting is machined to its final shape.
Split into simpler sentences: When a piston is cast the alloy is heated until liquid, then poured into a mould to create the basic shape. After the alloy cools and solidifies it is removed from the mould and the rough casting is machined to its final shape.