Plasma Spray Forming

In the course of plasma spray, the plasma jet is comprehensively functioned by such effects as thermal pinch, magnetic pinch and mechanical compression and the flow is jetting at a high speed, the energy is concentrated and its center temperature is so high as to reach upwards of 15 000 ℃ which is capable of melting various kinds of materials inclusive of ceramic, it has a broad applied prospects in the fields of automobile, electronics, telecommunications, medical treatment, air navigation & space navigation and light industries etc because of being able to rapid fabricate thin-walled metals, ceramics and alloy parts thereof, metal moulds, functionally gradient material moulds and so on, and it has become a research spotlight for the scholars. The technology of plasma spray forming (PSF) is introduced, and the two different kinds of technique presented in this paper are studied. Some typical links in the course of technical process is also analyzed, including original prototype fabrication and surface treatment, post-treatment of formed workpiece and demoulding methods. When spraying, it should select the appropriate making methods of prototype according to the dimensions, shapes and forming accuracy as required by the formed parts. At the same time, it should be paid to the characteristic of the material for the prototype. The main purpose of surface treatment of the prototype is to raise the quality of formed parts and ensure the integrity demoulding of the coating. The method of the prototype’s surface treatment is closely related to the demoulding method, which is mainly comprised of destructive demoulding, non-destructive demoulding and composite demoulding, and is key technology in PSF. In order to eliminate these intrinsic defects and improve its performance, the fabricated parts can be given the necessary post-treatment so as to further raise the mechanical strength and surface quality. There are many methods for the post-treatment such as chemical reinforcment, metal melt-infiltration, laser-melting and self-propagating high-temperature synthesis, etc., all these methods can decrease the porosity and raise the quality of coating and service performance; whereas the finishing machining can improve the surface roughness of spray formed parts. In the course of spray forming, affected by such complex and complicated factors as electric field, the entangled ambient gas and introduced powder, as a result, it shall induce the instability of the spray condition and affect the forming quality. This paper has, on the basis of large quantity of experiments, analyzed every links in the course of PSF, summarized and evaluated the main factors affecting on the quality of formed parts, such as prototype characteristic, characteristic of plasma jet, powder characteristic, spray gun and spray parameters. The experiments prove that the process of PSF is simple and the cost is lower in rapid tooling with complex and complicated fine patterns, and PSF is apt to form special-shape and thin-walled parts made of some protective materials so as to protect those fragile workpieces. Therefore PSF is a new technology with broad and brilliant prospects of development.