In one example in accordance with the present disclosure, an additive manufacturing system is described. The additive manufacturing system includes a build material distributor to deposit metal powder build material on abed. The additive manufacturing system also includes at least a first electrode below the bed and a second electrode above the bed to generate a non-uniform electric field to compact deposited the metal powder build material. A hardening system of the additive manufacturing system selectively hardens metal powder build material in a pattern of a layer of a three-dimensional object to be printed.