The piston is one of the most important components of internal combustion engines (rotary’s excluded). It’s a solid disk that cycles back and forth throughout the hollow cylinder of the engine block. The piston connects to the crankshaft via a connecting rod and as fuel is ignited hot gasses formed by the combustion push the piston along the cylinder causing the crankshaft to turn.
Typically, pistons are made by either casting which involves pouring molten metal into a mould or forging which utilizes high temperature and pressure to force the metal into shape. This video outlines the forge process and starts from an aluminum bar stock which is processed via metal presses and automated lathes/mills.