Influence of surface pores on selective laser melted parts under lubricated contacts: a case study of a hydraulic spool valve

Abstract

ABSTRACT Hydraulic valve spools can be produced with hollow structures using SLM to increase dynamic response. The contact between the valve spool and body is crucial and relates to the performance of a hydraulic valve, which has not been studied. This paper investigates the reciprocating contact of an SLM-fabricated spool valve from a tribological aspect. By varying the process parameters, porous and standard spool samples (18Ni-300 steel) were produced using SLM. The lubricating behaviours of 18Ni-300 samples under various contact pressures and reciprocating frequencies were investigated in comparison to a real spool sample (hardened 38CrMoAl steel) using conventional manufacturing. The results indicate that the standard SLM 18Ni-300 spool sample has comparable tribological performance compared to the conventional manufactured 38CrMoAl sample. The SLM fabricated sample, with a number of large pores, has the highest friction coefficient under a wide range of contact conditions due to rough surfaces and cracks. Compared to the standard sample, the presence of a few small pores positively affects lubrication by providing local extra lubrication and serving as debris containers. Such an effect becomes very notable under low pressure, reducing the friction coefficients by half.