Laser Solid Forming (LSF) is an advanced manufacturing technology based on rapid prototyping and laser cladding technologies. The deposited layer is formed from the interaction of laser beam, powder flow and the substrate; consequently, the geometry and size of the deposited layer are very sensitive to the process conditions. In fact, the deposition is not always carried out on an ideal flat surface. Therefore, an understanding of the deposited characteristics on fluctuant substrate is important for process control. In this research, multi-layer deposition experiments were carried out on a fluctuant substrate that was prefabricated with different amplitude and frequency. The morphology evolution of multi-layer deposition on a fluctuant surface was investigated, and the effects of powder defocus position on the evolution behavior were discussed. The results showed that good deposition characteristics and self-healing effect can be obtained with appropriate negative defocus. Under the condition of negative defocus, when the thickness of the layer at the trough of wave is less than the fixed-step of the Z-axis lifting, the powder concentration will increase with the deposition, leading the thick ness of the single layer to increase, until it equals the fixed-step. As the frequency increases, the slope of the substrate increases as well. Due to the gravitational effects, the molten pool at the peak of the wave has a tendency to spread out, which leads to decreased thickness. Molten pool at the trough of the wave has a tendency to get together which leads to increased thick ness, so during the following deposition, the fluctuant amplitude decreases gradually and the flat surface will be obtained.

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