| In coaxial powder-feeding laser cladding process, laser beam, powder flow and shielding gas are injected simultaneously by flowing through the runner of nozzle. Laser beam is focused from the nozzle axis; powder is emitted along the feeding channel by gas and heated quickly when meeting with laser beam then becomes molten droplet in shielding gas to spray to the surface of work piece.Coaxial synchronous powder-feeding laser cladding can effectively improve cladding quality, reduce dilution rate and implement automation easily. Therefore, the current research on equipment for materials supply is focused on coaxial powder-feeding nozzle. In this paper, two kinds of coaxial nozzles, Hole nozzle and Ring nozzle, were designed and manufactures in view of existing problems under large tilt angle, such as uneven powder gathering, unsatisfied cooling and low utilization, etc. Some experiments were then conducted to test the nozzles.The Hole nozzle has not only the general characteristics of ordinary coaxial powder-feeding nozzle, but also the following advantages: (1) even powder gathering in the case of large tilt angle; (2) good cooling effect since the cooling runner was designed to cool nozzle core directly; (3) high utilization of powder since the nozzle structure was designed reasonably; (4) the position of focal point of powder flow can be easily adjusted vertically or radially relative to that of laser beam; (5) improved uniformity of powder since it is easy to form"powder curtain"by powder flow and shielding gas in the cladding zone; (6) the conical face at lower edge of nozzle can improve gathering and utilization of powder.The Ring nozzle has the following advantages: (1) the gap size of the ring tapered channel can be fine adapted to different sizes of powder; (2) good cooling effect since the cooling runner was designed to cool nozzle core directly; (3) improved uniformity of powder since it is easy to form"powder curtain"by powder flow and shielding gas in the cladding zone and three tangential powder-feeding holes with long enough channel were designed; (4) the position of focal point of powder flow can be easily adjusted vertically relative to that of laser beam.Experiments were conducted to test the reliability of the nozzles by means of calculations of dilution rate and utilization and tests of powder gathering, process, micro hardness, etc. the variation of focus size of powder flow was also explored under different conditions. Results showed that the two coaxial powder-feeding nozzles designed satisfied requirements of nozzle in laser cladding process and could be used for laser cladding 3-D manufacturing.
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