Case study of PM hydraulic valve actuator mechanism
February 15, 2021Conventional powder metallurgy (PM), also known as press-and-sinter, is a net-shape processing technology that yields components with little or no secondary machining operations. Utilizing this metal-forming technology was pivotal in reducing the cost of this component while enhancing the reliability and durability.
In the PM process, custom-blended metal powders are fed into a die, compacted into the desired shape, ejected from the die and then sintered (solid-state diffused) at a temperature below the melting point of the base material in a controlled atmosphere furnace.
The compaction step requires the part to be removable from the die in the vertical direction with no cross movements of the tool members. The sintering step creates metallurgical bonds between the powder particles, impacting the necessary mechanical and physical properties to the part.
Hydraulic valve actuator mechanism
This award-winning component acts as the spring seat of a hydraulic valve actuator mechanism. It was originally designed as a plastic injection molded part. However, the plastic softened in the operating environment causing the part to fail.
Fabrication
The tooling concept for this two-level part consists of a straight-walled die, a flat lower punch, a formed upper punch, and a core rod. The part is made from SS-316H-20 and is compacted to a green density of 6.5 g/cm3 prior to sintering at 1,150º C (2,100º F) in a purehydrogen atmosphere. The sintered parts have a density of 6.6 g/cm3 and the nitrogen content is kept below 0.03 wt.% to ensure good ductility for the part and the durability required for the cyclical loading of the hydraulic actuator. The five blades of the component are 6 mm (0.25 in) long and too thin (0.66 mm [0.025 in]) to be compacted to net shape directly, so extra material is added in the region of the blades. A low-cost turning operation is needed to achieve the final part geometry. Post machining includes a specialized deburr and careful handling to prevent any part-to-part contact.
Results
Because the part is small, the amount of material removed by the turning operation is a small percentage. The waste associated with traditional CNC-type machining would have been much larger. The particularly unique aspect of this was that, while the plastic injection molded component had a metal injection molded-type geometry, the price of using conventional PM over MIM was 50% less even with the secondary turning operation.