Removable Fillers for VPS Fabrication of Closed Channels

An improved process has been devised for making closed channels (e.g., coolant channels) in a heat-exchanger liner or a similar metal object. The process involves the following steps: First, grooves destined to become closed channels are machined into the object from one surface. Next, a ceramic filler material is troweled into the grooves, made flush with the surface, and allowed to harden by evaporation of water. Next, vacuum plasma spraying (VPS) is used to deposit metal on the exposed metal and filler surface areas to cover the grooves and thereby form closed channels (see figure). Finally, the filler material is removed from the channels. This process satisfies a need for making the channels at lower cost and in less time than is possible by an older process in which the grooves are filled with wax, then a thin layer of copper is electroplated on the exposed metal and wax surface areas, then a thick nickel structural jacket is deposited on the copper.