How automotive tailgate springs are manufactured

An automotive tailgate spring, also known as a car trunk or boot spring, is an extension spring fitted to the tailgate linkage. When the lid is released by the trunk-unlock key, the spring lifts it to a preset angle and holds it open, acting as a support. Because the part must survive many open-close cycles, its manufacture is controlled at every step.

Manufacturing steps

The spring is produced on a multi-axis CNC spring coiling machine, which winds stainless steel wire into the finished dimensional shape of the electric tailgate spring. The wire is a high-residual-stress spring steel with a compressive strength of 200 MPa.

The formed spring is held at 430-460 °C for 40 minutes to soak and set the material, then immediately air-quenched. Quenching the wire after the heat soak and cooling it quickly preserves strength and improves the spring's resistance to load relaxation, which extends its working capability.

Working characteristics

A spring produces large elastic deformation under an external force and returns to its original shape when the force is removed, which is why springs are used as elastic elements throughout mechanical equipment.

Functions of a spring

In a mechanism a spring can control the movement of the mechanism or the position of parts, cushion shock and absorb vibration (as in vehicle suspension and shock absorbers), store energy (as in the springs of horological instruments), measure force (as in a spring scale), and change the natural resonant frequency of a system.

Common spring types

Springs are classified by construction: coil springs (cylindrical or tapered in shape, and tension, compression or torsion in loading), ring springs, disc (Belleville) springs, flat spiral (scroll) springs and leaf springs.