Numerical Simulation Of Shape Evolution Of Tubular Preform In Spray Forming Process

A prediction model of the shape of preform was established based on a fixed multi-nozzle test and development equipment of spray forming. The movement parameters of substrate was optimized according to the deposition behaviour of the droplets, and the growth process of deposit and the shapes of preform were simulated. Finally, the effecting mechanism of the atomizers with a tilt angle to the shape of preforms was studied by analyzing the simulation results.Firstly, the modeling was simplified according to the relative motion between the atomizer and substrate, and the spray distance h and radius r of each deposition point was calculated, by introducing a visibility algorithm called"BFC+shape function"and tracing the coordinates of each deposition node, a mathematical model was established. And then by analyzing the helical trajectory and deposition behaviour of the droplets on the deposition surface, a basic condition for optimizing the movement parameters (u,ω) of the substrate was acquired. Namely, when the translatory velocity u and the rotational speedωof the substrate satisfy u/ω≤d_max/2π, a continuous mass distribution on the surface, and further a continuous surface can be formed, in which the d_max presents utmost screw pitch that can form a successive and uniform mass flux distribution on the deposition surface and should be calculated under the minimum tilt angle of the atomizers (if the working atomizer is more than one) and the deposition endpoint. Ultimately, the shape and growth process of 7075-aluminum alloy were simulated.The simulated results show that when the atomizer with a tilt angle (β≠0) was used, due to the asymmetry of the mass flux distribution on the deposition surface, the thickness of each deposition layer is un-uniform, and the transition region of the fabricated tubular preform became longer obviously while the length of the stationary growth region decreased, all of which caused a decrease of the yield. In addition, the simulation results also indicate that the un-uniform distribution of the thickness of each deposition layer has no relation with the movement parameters of the substrate (u,ω) and the spray distance h0. Therefore, when the equipment is used to fabricate tubular preforms, it should choose the atomizer with a tilt angle of 0o to get a preform with an ideal shape.