Coaxial double-beam laser preheating forming slow cooling stress sustained-release device and method

The invention discloses a coaxial double-beam laser preheating forming slow cooling stress sustained-release device and method. The device comprises beam expanding lenses, collimation convex lenses and focusing convex lenses, wherein the beam expanding lenses, the collimation convex lenses and the focusing convex lenses are sequentially arranged in the emergent direction of laser beams, the beam expanding lenses are used for conducting beam expanding on the laser beams, the collimation convex lenses are used for outputting the laser beams subjected to beam expanding in parallel, and the focusing convex lenses are used for receiving the parallel laser beams and outputting coaxial double beams. Planes A used for outputting the laser beams in parallel so as to form large light spots A are arranged at the convex face central positions of the focusing convex lenses, the convex face portions of the focusing convex lenses enable the laser beams to be focused so as to form small light spots B, and the light spots A and the light spots B are coaxial. By the adoption of the device and method, the convex lenses and concave lenses are combined for use, so that the coaxial double beams with the sizes of the light spots capable of being adjusted are generated, the large light spots are used for preheating and slowly cooling metal powder, the laser absorptivity of materials is improved, stress is released, the temperature gradient is lowered, and the tissue defects such as segregation, cracks and holes are reduced; the small light spots are used for forming, the focusing performance is good, energy is stable, and the forming efficiency, precision and quality are improved.