The Equipment Of Negative Polarity Weak Plasma Arc Overlaying Welding And The Researching Of Arc Character

The thesis had researched and designed the negative polarity weak plasma arc overlaying welding, overlaying welding gun and the control system of PLC. The negative polarity weak plasma arc overlaying welding composes top gun, under gun and isolator in the middle. The double metal electrode replaces full core tungsten electrode as the top gun of straight polarity plasma arc overlaying welding gun and sphere constricting nozzle replaces taper constricting nozzle are the key points of the negative polarity weak plasma arc overlaying welding gun. The two characters of gun are decided by the condition of negative polarity weak plasma arc's burning. It has been found that the gun was fine in the experiment and the welding piece achieved the request of technology. The overburning of electrode and welding gun reduce obviously.There are some problems in negative polarity weak plasma arc overlaying welding equipment, such as low robotization, imprecision and low efficiency. Aiming at the trend of automatic welding development, one kind of PLC automatic control technology has been developed for specialized use of the negative polarity weak plasma arc overlaying welding in this paper. Automatic welding process was realized through PLC control of the welding torch movement. It was proved by systems operation that the welder has advantages of high control precision, high reliability, fast response speed, high automatic level. Consequently, it brings merits of reduced labor intensity, increased welding quality and productivity, lower rejection rate, convenient operation and maintenance.Analyzed the influence of protection air current and content to energy density, the distribution graph of negative polarity weak plasma arc radial pressure, the heat distribution of plasma arc, the combustion stability and static characteristic graph of negative polarity plasma arc. The result indicate: negative polarity weak plasma arc has the same distribution of homogeneity arc pressure, the distribution graph of arc voltage, the distribution graph of arc current and distribution area of cathode spot, they all have saucer shape, cathode spot takes up 50% of the effective energy, 90% of the current distributes in an area of annulus that the internal is 10mm, energy density can be controlled by protection air current.