Investigation of the cooling performance of chemically etched millimeter-scale channels made by selective laser melting

In the fields of plastic injection molding and die metal casting, drilling cooling channels into the molds had, until recently, been the only way to form a cooling channel within these molds. With the advent of selective laser melting (SLM), conformal cooling channels have been designed and manufactured to follow the shape of the mold. However, it is challenging to fabricate millimeter-scale channels by SLM due to manufacturing limitations. Unmelt powders and unsupported surfaces result in high roughness and clog of channels, especially when the diameter is less than 2 mm. This work aims to show how the diameters and roughness of 1- to 4-mm-scale cooling channels made by SLM affect their cooling performance. A chemical etching process was used to polish the internal surface of the cooling channels. The etching results in this research show that low-concentration (6% by mass) hydrochloric acid can effectively reduce the roughness of aluminum channels manufactured using a selective laser melting printer. Temperature data was collected and analyzed to show how the diameter roughness of the channel affects heat transfer. It was found that reduced roughness can improve the heat transfer performance for the 2-mm cooling channel. However, with the increase of the pressure and diameter, the heat transfer improvement by etching was reduced. The untreated cooling channels outperformed the etched ones for the 3-mm cooling channels under a high inlet pressure.