Experimental comparison of the flow rate and cooling performance of internal cooling channels fabricated via selective laser melting and conventional drilling process

Injection molds with conformal cooling channels have been deemed increasingly important in the mold manufacturing industry. Selective laser melting (SLM) has proven to be an effective process to fabricate conformal cooling molds. However, the surface quality and morphologies of SLM-fabricated cooling channels are different from that of conventional drilled channels. To investigate the differences in the coolant flow rate and cooling performance between SLM-fabricated and drilled cooling channels, test molds with cooling channel diameters of phi 2 mm, phi 3 mm, and phi 4 mm were fabricated via SLM and the computer numerical control (CNC) process. A test system was designed and set up to investigate the flow rate and cooling performance of two types of test molds. The geometrical shape, dimensional accuracy, and surface morphologies of the SLM-fabricated cooling channels were characterized using optical microscopy and laser microscopy. The results indicated that the SLM-fabricated cooling channel exhibited an elliptic shape due to the lack of support along the building direction. The flow rate of the SLM-fabricated cooling channels was smaller than that of the drilled channels due to the low dimensional accuracy and roughness surface. The cooling performance of the SLM-fabricated cooling channels was also poorer than that of the drilled channels due to the presence of unmolten particles and a loose layer on the SLM-fabricated surface. Theoretical analysis was conducted on the influence of surface roughness on the flow rate and cooling performance of two types of channels and the friction factor; Nusselt number and heat transfer coefficient were obtained.