Selective laser sintering of precoated sands is a process utilized to produce molds and cores for rapid casting by adding sand layer by layer and heating it using a laser beam. During the process, the resin flows and binds the grains; subsequently, an oven is used for the postcuring treatment to complete the curing of the resin. The aim of this paper was to study the laser-material interaction using a diode laser to directly obtain the material consolidation. It was the first step in the definition of a new approach for process investigation and innovation. Two main aspects were investigated with the laser source in a standstill position: first, the influence of the laser power, the location of the focal spot, and the exposure time on sand consolidation; second, the shape and dimension of cured samples depending on the process parameters. The experimental data, in terms of weight and size of the hardened sands, were analyzed, and a master curve was found. In Part II of this paper the selective laser sintering process will be implemented to produce shells.