Research On Magnetically Constricted Plasma Arc Cutting Process

Plasma arc cutting(PAC) is one of the most popular thermal cutting technologies because of its high efficiency, smooth cutting section and tiny thermal deformation, but it still exists process problems on the thick plate cutting, such as large groove bevel, much hang slag and other quality problems. Magnetically constricted PAC enhances the cutting process by adding external magnetic field to alter physical characteristics of cutting plasma arc. The external magnetic field affects qualities of kerf by changing the energy and momentum exchanging process between arc and work pieces. Current researches, however, merely take deeper account of the mechanism of magnetically constricted PAC technology.With the support of National Natural Science Foundation of China and other projects, this dissertation studies on air plasma arc cutting technology based on numerical simulations and processing experiments in order to improve cutting quality. In details, influencing rules of cutting parameters and external longitudinal magnetic field on process and cutting section quality are studied, and the mechanism of magnetically constricted PAC technology is explored. The dissertation firstly introduces background of the project, in which state-of-the-art and trends of PAC technology is shown. Current research results of magnetically constricted PAC are analyzed specifically so as to find out shortcomings and solutions of magnetically constricted PAC. Secondly, a unified computing model for cutting arc and work pieces based on magnetohydrodynamics is formulated in the Fluent Package of ANSYS. Furthermore, temperature field and flow field of arc plasma, melting zone of work pieces are calculated using SIMPLE algorithm in order to figure out how they are influenced by cutting parameters and external longitudinal magnetic field. Finally, high-speed photography experiment and plasma arc cutting experiment are carried out. According to the results of these experiments, quality of cutting section(groove angle, surface roughness, kerf width and so on) is analyzed, and effects of basic process parameters(cutting current, gas flow, cutting speed) and excitation current of magnetic field generator on this factor are concluded.The numerical model and the experimental process support each other, which helps to understand process principles of PAC and provides some guidance for studies of the plasma arc cutting with magnetic constraints. Several conclusion can be drawn through numerical simulation and experimental results: cutting current and gas flow have significant effects on energy and momentum significantly, which affect qualities of kerf by changing the energy and momentum exchanging process; nozzle height and cutting speed caused a certain impact on the cutting quality; as magnetic field intensity changes, temperature and axial velocity of plasma arc change little, but the magnetic will lead rotation of arc and change heating balance of work piece, thus groove angle of product side can be controlled.