Alternative Manufacturing Technology of Torsion Bars with Hexagonal Ends for Front Suspension of Trucks

The front suspension of four-wheel-drive trucks is usually designed with torsion bars with hexagonal anchoring ends, a shape that is adapted to forging. Currently made in spring steel, a full-hardening heat treatment is required after forging the ends.

An alternative manufacturing technology has been derived from the mass production of splined end bars used in rear suspension of passengers cars and cabin tilt devices of medium and heavy duty trucks. The main differences are the steel grade and the forming method of the heads. Head forming is the combination of open die upsetting and machining. This method allows to achieve an extremely smooth and defect free transition shape between the hexagonal anchor and the body, where stress concentration occurs. The steel chosen is a carbon steel that must undergo a superficial hardening. This type of steel is not prone to cracks either during the upsetting or the water quenching operations. Engineering advantages are explained.