Experiments On The CNC Milling Of Bent Pipe Surface And Equipment Design For Internal Surface

As transport tools of oil, gas and liquid bent pipes play an important role in nuclear power station, oil and gas industry, chemical industry and other fields. Such as the main pipe of nuclear power station, it is large pipe with thick wall, connecting the steam generator and reactor pressure vessel. Its quality affects the safety of nuclear power station. Its surface quality is important factor to its overall quality. The difficulties to machine its surface are interference, poor quality consistency and inefficiency. Multi-axis CNC technology in the machining of complex surface has huge advantage, which can solve interference, increase cutting stability and improve the machining quality. So it has high theoretical significance and application value to carry out the study on the machining of the bent pipe surface using multi-axis CNC technology and the study on the development of special equipment.Using nuclear power station main pipe as prototype, this paper analyses its geometrical characteristics and presents new methods for the machining of bent pipe surface, including the methods of3-axis and5-axis machining the external surface of the main pipe sample piece, the methods of4-axis and5-axis machining the internal surface of the main pipe sample piece and the method of machining the internal surface of main pipe for nuclear power station with special equipment inside the pipe.Based on theoretical analysis, milling experiments are carried out on the internal and external surface of main pipe sample piece using3-axis machining center and5-axis machining center.The results show that, with the improvement of speed, the reduction of feed rate, cutting depth and the row space, quality of external surface becomes better. Compared with5-axis machining, the surface quality consistency of3-axis machining is poorer, the surface roughness range from Ra3.07um-Ra3.14um, but efficiency increases by5%; compared with4-axis machining, the surface quality consistency of5-axis machining is better, the surface roughness range from Ra3.05um-Ra3.10um, efficiency decreases6%. So it is right choice to machining the external surface by3-axis machine tools and machining the internal surface by5-axis machine tool.The main pipe is long and full bore. According to it special equipment which machining the internal surface of main pipe inside the pipe is designed. With the modern design methods of CAD and modular design, function module partition is finished, each specific module is detailedly designed, including the power system design, the transmission system design and the structure design for all parts of the mechanical module, the milling force is calculated and according to it the motor power is determined, finally the stiffness and strength of base for arc guide are checked. The results show that, auxiliary support effectively reduce the deformation of guide base (the deformation is1.82mm without support and0.38mm with support), the stress in the most dangerous section of arc guide base is94.84MPa, far less than the allowable stress, which meets the design requirements.The results show that it is a good way to machining the external surface of bent pipe with3-axis machining technology and to machining the internal surface of bent pipe with5-axis machining technology.At the same time, it is a good method to machining the internal surface of main pipe inside the pipe with special equipment.The research results support the machining of main pipe surfaces for nuclear power station and other bent pipes of its kind in theory and practice.