Manufacturing Process of Automotive Leaf Spring Products

Automotive leaf springs (also known as leaf springs) are key load-bearing and vibration-damping components in traditional vehicle suspension systems. Their manufacturing process is complex and demanding, with the core objective of achieving high strength, high fatigue life, and good elastic performance.

Generally, high-strength hot-rolled spring steel strip coils or fixed-length straight bars are selected, such as 60Si2MnA, 50CrVA, 55Cr3, SUP series, etc. The material must meet strict chemical composition and mechanical property standards.

The inspected spring steel raw material is cut using a circular saw or band saw. Laser cutting or water jet cutting can also be used, but the cost is higher. The cutting step must ensure length accuracy and end face quality (perpendicularity, flatness) and reduce burrs.

Heat the cut steel strip to the austenitizing temperature range to prepare for hot forming. This process requires strict control of heating temperature and time (usually around 900°C - 950°C, depending on the material) to avoid overheating, burning, or decarburization.

Place the heated steel strip into a roll forging machine to roll it into leaf spring plates with a preset curvature (spring eye) and variable cross-section (main leaf) or equal cross-section (helper leaf) shape. This is a crucial step in obtaining the required stiffness and stress distribution.

Quickly transfer the formed leaf spring plate, still in the austenite state, to a quenching oil tank for immersion cooling to obtain a high-hardness martensitic structure, laying the foundation for subsequent tempering to achieve high strength and high elasticity.

Heat the quenched leaf spring plate to a specific temperature (usually around 400°C - 500°C, depending on the material and requirements), hold it for a sufficient time, and then cool it (usually air-cooled). This eliminates quenching stress, improves toughness and plasticity, and obtains the comprehensive mechanical properties required for the leaf spring.

Send the tempered leaf spring plate to a pass-through or hanging shot peening machine. The surface of the leaf spring is bombarded with a high-speed stream of shot, introducing a beneficial residual compressive stress layer and improving the surface microstructure. This is one of the most critical processes for improving the fatigue life of the leaf spring.

Drill or ream the spring eye of the main leaf to ensure the dimensional accuracy and surface roughness of the pin hole. The non-spring eye end can be chamfered, ground, or otherwise processed to remove burrs and improve assembly.

Use a pre-stressing machine (hydraulic or mechanical) to place a single leaf spring (or sometimes a multi-leaf combination) into a fixture and apply a load several times (e.g., 2-3 times) exceeding the design full load to cause plastic deformation. After unloading, the required positive camber height is obtained, improving the stress distribution and inter-leaf friction during the operation of the automotive leaf spring and increasing fatigue life.

Stack multiple leaf springs (main leaf, helper leaf) in order and fix them together with a center bolt or clamp (rebound clip). Apply grease or install anti-friction shims/sliders between the leaves to reduce inter-leaf friction, wear, and noise.

To ensure the durability of the leaf spring under harsh conditions, painting, baking varnish, plastic spraying, or zinc-chromium coating is usually applied to the surface of the leaf spring.

Before delivery, the leaf springs also need to undergo finished product sampling inspection to ensure that the dimensions and quality of the products meet customer requirements.

The manufacturing of automotive leaf springs is a complex process that integrates materials science, plastic processing, heat treatment, surface engineering, and precision testing. Each process is closely linked and collectively determines the strength, elasticity, fatigue life, and durability of the final product. As the automotive industrys requirements for safety, comfort, lightweighting, and long life continue to increase, the processing technology of leaf springs is also constantly evolving and optimizing. Strict quality control and continuous innovation are key to ensuring that leaf springs meet the stringent usage requirements of modern automobiles.