Additive manufacturing structures and methods that enable the facile release of 3D printed parts are described. In one implementation, an additive manufacturing structure includes: a body; and a recessed section formed through a surface of the body, the recessed section comprising: a pour hole for filling the recessed section with a liquid metal or metal alloy that solidifies into an insert having a surface for forming a 3D object in a 3D printing device; and one or more air holes configured to release air displaced by the liquid metal or metal alloy.