Leaf spring is a suspension system for vehicles that has been used as far back as medieval times. They were originally called carriage or laminated springs. Its system has been tried and true, primarily used on almost all vehicles up to the 1970’s and still today on trucks and vans that haul heavy loads.
The spring leaf is made up of an arc-shape, slender piece of steel that is stacked with the same material in smaller sizes and bolted together creating a reinforced bow-like item. It is then attached to the rear axle and the chassis providing support to any additional weight that is added to a vehicle, preventing the axle from buckling in and snapping from the pressure of an extreme amount of weight that it was not originally designed to carry.
What is the Purpose of a Leaf Spring?
The overall purpose of a leaf spring is to provide support for a vehicle. It also provides for a smoother ride absorbing any bumps or potholes in the road. Leaf springs are also used to locate the axle and control the height at which the vehicle rides and helps keep the tires aligned on the road.
Because of its benefits, leaf springs are in high demand. Casual transportation is just one of the ways leaf springs have contributed to our transportation industry. These days, leaf springs are more popular with heavy commercial vehicles like trucks, SUVs, and vans.
Leaf Spring Manufacture
Manufacturing of leaf springs can be divided in to three broad areas:
– Preparing leaves
– Bending
– heat treatment
– shot peening
– Assembling
– presetting
– surface treatment
Leaves for multi-leaf springs are prepared by cutting and stamping whilst parabolic leaves are hot rolled in a purpose-made rolling machine. The ends of the main leaf are heated and the eyes are then hot rolled. The leaves are heated and individually bent to the correct arc radius and, whilst still clamped between the bending tool, each leaf is quenched in oil to receive high strength and the correct shape. Parabolic leaves also have an arc radius but are however normally straight in the thicker central section. The leaves are finally tempered for high material toughness and strength.
After cooling, the shot peening process is necessary for all parabolic leaves. For multi-leaf springs however, it is normally only the two safety-critical leaves that require shot peening. The bushes are pressed into the eyes and the stack of leaves assembled. Positive stresses are then introduced into the spring by a pre-stressing process.
The multi leaf surfaces are protected against corrosion by painting of the outer surfaces and by lubrication between each leaf. Parabolic leaves are individually painted on all surfaces.