Research on laser solid forming of TC4 alloy based on fractal scanning

The application of fractal scanning pattern in laser solid forming (LSF) of TC4 alloy was investigated through experiments. The forming characteristics of the fractal scanning path were discussed and the influence of process parameters (laser power, overlap rate etc) on the forming quality of TC4 alloy was studied. A method of eliminating the formation defects under fractal scanning pattern was proposed. Study shows that under fractal scanning pattern, the main defects of TC4 alloy formed by the LSF process are ill bonding and porosity, because the height of deposition at the corner of the fractal path is larger than that under linear scanning pattern resulting in the concave on the formation surface. The defects including ill bonding and porosity are relieved to some extent with the increase of the laser power and overlap rate, but still obvious. According to the obtained conclusion and formation characteristics of fractal scanning pattern, a ″semi-spot vibration″ strategy is proposed. The strategy means that the beginning scanning position of each layer offset by half a laser spot along x and y direction to make the concave; therefore the convex formed by two adjacent deposition layers respectively overlap each other and thus the deterioration of surface quality is restricted effectively.