Case Study: Piston Brake Spring-Return Assembly

Process: Conventional Press & Sinter (PM)

Material: FN-0208 Nickel Steel

Density: 6.9 g/cm³

Leak Test: Withstands 300 psi of Hydraulic Pressure

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End Use and Function

Used in a hydraulic power take off system in work truck applications, this innovative designed piston brake spring-return assembly engages the clutch-pack under pressure while the taper feature acts as a brake when disengaged. This design replaced a design that was fully machined from bar stock, resulting in high cost and scrap loss.  

Fabrication

The piston is compacted with two lower punches and one upper punch, achieving the spline geometry and appropriate density distribution. Used in the as-sintered condition, the piston requires a vibratory de-burring operation that is performed prior to finish machining. The piston cup, also used in the as-sintered condition, has complex geometry that is achieved using tooling with three lower and two upper punches. This mating part is also machined to achieve the tight tolerance, surface finish, and geometric dimensioning of the inner diameter and sealing surfaces.     

Results

Although other metal forming processes were considered, PM became the design of choice because of robust materials and shape forming capabilities. The ability to form the tone ring feature on the inner hub of the piston allowed for an optional hall effect that was not available on the prior design that was machined from bar stock. This allowed the supplier to be the first to market with this unique hydraulic power take off system used in work truck applications.