Research On Heat Insulated Friction Stir Welding Tools

Friction stir welding is a solid phase welding technology in which melting doesn't occur during welding process.It has high energy efficiency,does not produce harmful gases and waste,at the same time,it solves the problem that the weld is prone to have defects and low joint strength in traditional fusion welding technology.FSW is particularly suitable for welding low hardness and low melting point metals such as aluminum and magnesium alloy.Currently,the study of FSW is focused on optimization of welding parameters,tool design,material flow,heat generation mechanism,and their effect on microstructure and properties.In this paper,experiments and numerical simulation were used to investigate the heat transfer from the tool to the spindle during FSW process,a heat insulated FSW tool was designed to reduce heat transfer to spindle,and the heat loss during welding,so as to improve the welding thermal efficiency.With the help of finite element numerical simulation,a new structure of FSW tool was designed.Plasma spraying method was used to spray Y2O3 stabilized ZrO2 thermal barrier coating on the handle surface of FSW tool to reduce heat transfer to spindle direction.Welding experiments on 5mm thick 6061-T6 aluminum alloy plate using conventional FSW tool and the heat insulated tool was carried out,and the temperature field of tool,spindle,and the welding plate during welding period was measured,to study the thermal insulation effect of heat insulated tool and the welding thermal efficiency.It was found out that in the case of tool rotation speed 800 r/min,welding speed 30 mm/min,the steady temperature of the outer surface of the spindle was up to 82.8? using conventional FSW tool,when using heat insulated tool,the max temperature was 43.1?,temperature decreased significantly.Finite element numerical simulation results show that under the above conditions,the heat power transferred to the spindle was 88.4W with conventional tool,in contrast to 42.2W with heat insulated tool,more than 50% heat transfer was reduced.In the case of tool rotation speed 800 r/min,welding speed 200 mm/min,the maximum temperature of welding nugget zone was about 430 ? with conventional FSW tool,and 460 ? with heat insulated tool,the temperature was increased by 30 ?,the heat power to spindle was 84.8W with conventional tool,and 43.3W with heat insulated tool,the welding thermal efficiency were 92.2% and 96.0% respectively,the thermal efficiency was increased by 3.8%.In this paper,a preliminary study on possible effect of the thermal insulated FSW tool for steel welding was also implemented with the finite element simulation.The heat insulated FSW tool was found to significantly reduce spindle temperature and improve the welding thermal efficiency in steel friction stir welding process.