Research On The Heat Dissipation Conditions In Micro-plasma Arc Welding Of Ultra-thin Plate

The most important problem in the welding of thin plate is the burning and deformation, especially in the ultra-thin plate. The sheet metal with thickness less than 0.2 mm, is more widely applied in the fields of electronics industry, medical equipment, aerospace, precision instrument and daily life. Therefore, the precision welding technology of ultra-thin and super fine product has got an increasing attention and been widely studied. During the welding process of micro-plasma arc welding(MPAW) of ultra-thin plates, the requirement of welding heat input is very strict, and the welding process is difficult to control. The forming quality of welding of the ultra-thin plates is related not only to the heat input, but also to the heat dissipation rate of welding plates after welding. Due to the complexity of the heat dissipation in the welding process, many theories have not yet been clearly studied, and the scientific research cost can be greatly improved by a large number of experimental methods, which need to spend a lot of money, time and manpower. With the development of modern science and technology, the finite element method has been widely studied and applied used to analyze the numerical simulation of the welding process. The research status of MPAW and the reasons and solutions of the special problems in the welding of thin plates were detailed discussed in this paper. Also, through the finite element simulation software, the heat radiation conditions of the thin plate MPAW process were analyzed, and the optimization of the thin plate MPAW process was carried out in this paper.The transient numerical analysis model of the ultra-thin plates welding with the assembly fixture was established based on the actual working condition of 0.1 mm thin plate MPAW. A modified Gauss heat source model was adopted in the arc heat source model, and the face to face contact model was established in the contact surface of fixture and welding plates. The heat dissipation of fixture with backing and clamping had strong effect on temperature distribution of ultra-thin plates MPAW. It was suitable for the analysis of the temperature distribution on the weldments by using the combination model of fixture and welding board. Also the finite element analysis results agreed highly with the experimental results,And then the effect of heat dissipation on the temperature field and the stress field of the ultra-thin plate welding was researched. The results showed that the heating and cooling process of MPAW of ultra-thin plates were greatly influenced by the heat dissipation of the fixture, which could obviously reduce the high temperature range and high temperature residence time in the welds and the welded area and decrease the degree of grain coarsening, which had great significance on the performance of the welded joint and the forming quality of the welded joint. Fixture and fixture free heat dissipation are quite different in ultra-thin welding stress and deformation. It will decrease residual stress and plastic deformation of ultra-thin sheet, and narrow the deformation range, when in the condition of fixture heat dissipation.Then the effect of different parameters on the heat dissipation of the ultra-thin plate is analyzed according to the welding heat dissipation model. The research shows that, when the other welding parameters are constant, increasing the contact pressure can improve the heat dissipation capability of the welding process, and the effect of the heat dissipation of the ultra-thin plate is decreased when the pressure increases to 0.7 MPa; When the contact pressure unchanged, changing the pressure distribution fixture distance constraint, fixture constraint distance are closer, fixture for thin plate welding heat dissipation capability is stronger, in the assembly position allows, plate spacing closer is better.Then according to the influence of the parameters of welding assembly and processes on the welding process of heat dissipation, the experiments in MPAW using nickel alloy sheet with thickness of 0.1 mm were carried out and the processes were optimized. The research showed that during the process with direct current welding ultra-thin plates in MPAW, the quality of the joints would be better when the welding current and welding velocity were set to be 3.5 A and 5 mm/s, respectively.