| Laser cladding rapid prototyping is a new and advanced manufacturing technology that has been developed on the basis of combining laser cladding technology with rapid prototyping technology, and has become an important researching direction in the advanced manufacturing technology. At present, the solid focused laser spot is commonly used in this technology, and the type of powder feeding is the coaxial powder outside the laser. The method has some defects, normally the powder spot is bigger than laser spot, so the coupling performance of the laser spot and the cladding powder is poor, and the formed parts have rough surface. Meanwhile the technology is mainly applied to the direct forming of the simple components, the internal structure of formed parts is more onefold, for example of solid of revolution, no support cantilever beam and thin walled parts, etc. This paper uses a new forming process of coaxial powder feeding inside-laser beam based on the hollow annular focusing system, the emphasis of this paper are the research on the effect of variable powder spot on the cladding forming and the accumulation of complex components containing intersected structures inside.According to the insufficient of detection methods to the laser beam centring, a detection device of the light beam centring is designed. The device is not only applicable to strong light beam, but also suitable for weak light beam.Using image processing technology, get the boundary discrete points of the powder beam, and using the least squares for powder beam boundary line fitting, eventually get the functional expression of powder spot size and the distance from the powder exports on Z axis, all these based on C# language program. Utilizing special structure of the coaxial inside-laser beam powder feeding nozzle, we finished several single-channel experimental studies on the variable powder spot, and the result of the experiments show that powder spot between inside and outside round of the annular laser spot, more conducive to obtain smooth cladding layer.The effect of the main laser processing parameters such as laser power, off-focus distance, scan velocity and powder feed rate on the qualities of cladding layer is also studied by an orthogonal test. The scanning direction test is taken with the optimal case of the orthogonal test, and the test demonstrates that the method of coaxial powder feeding inside-laser beam can reduce the influence of scanning direction on the quality of the cladding layer.Aim at cross cladding layers generate of overlapping problem, this paper proposes them a cladding layers reserved clearance, and test the feasibility of the scheme. And a formed part is designed with China Bank standard for model. Put forward three solutions, this paper determines the optimal scheme is reserved clearance through experiments. And through the test for optimizing the reserved clearance and the scan route, finally get a part without apparent ridgy phenomenon and the gap at the surface level off cross parts. |
