Deep-Hole Drilling Experiment On Nuclear Tube Sheet And Analysis Of Machining Quality

In the new energy,nuclear energy is considered to be the most efficient and most mature technology.AP1000 nuclear power technology is the most advanced nuclear power technology,becoming the main direction of China’s nuclear power development in the next period of time.Steam generator tube sheet is a key component of nuclear power equipment,there are as many as 20050 precise deep holes(φ17.73×800 mm).How to machine deep hole efficiently and reliably has become the bottleneck of China-made products.This study combines the development of deep-hole drilling on the nuclear tube sheet,and carries out the experimental research on drilling performance of BTA deep-hole drill and analysis of hole machining quality,which has important practical significance to promote the localization process of China’s nuclear power products.Based on the quality requirements of deep-hole drilling,this paper described the main forms of deep-hole drilling error,analyzed the main source of deep-hole machining error,proposed the methods of error control and the improvement of machining accuracy and surface quality.Based on the structural characteristics and material properties of nuclear power tube plate parts,analyzed the difficulty of deep-hole drilling on the nuclear tube sheet,and determined the deep-hole drilling system and tool type.The way to start research work are designing and developing deep-hole drill,carrying out drilling experiments,analyzing and improving deep-hole drill.Based on the drilling experiment with the designed deep-hole drill,the cutter teeth wear,chip shape and drilling force in deep-hole drilling were observed and measured,as well as the hole dimension precision,the verticality and the surface roughness of the drilling hole,studying the drilling performance of the deep-hole drill.And on this basis,through several design improvements,the deep-hole drill basically can meet the requirements of deep-hole drilling on the nuclear tube sheet.The experiment results show that the machining quality of the drill(including the dimension precision,the radial pulsation error,the surface roughness,etc)has great influence on aperture size and the surface roughness.The drill wear not only affects the aperture size and the surface roughness,but also influences the perpendicularity of the hole.The cutter tooth structure of the drill,especially the chip breaking structure has great influence on chip formation and chip removal condition.Mating clearance between guiding bush and drill,concentricity error between guiding bush,drill pipe bracket and power head spindle have great impact on the aperture size and the perpendicularity of the hole.When the guiding bush due to wear and the mating clearance increases to a certain extent,there is obvious horn shaped orifice,and during the initial drilling,vibration and noise are large,so the drilling process is not stable.Furthermore,the results showed that the cutting fluid has great influence on the drill wear and the quality of hole machining,especially for nickel-based surfacing layer drilling.When the cutting fluid is used inappropriately,the adhesive wear of the cutting edge and the guiding pad are serious and fast,and the hole machining quality is very poor.Sometimes even only after a nickel-based surfacing layer hole(depth of only about 10 mm)is drilled,it is unable to continue to use.According to the experiment results,through several design and improvements,the designed specialized deep-hole drill for the nuclear tube sheet,its working life can be comparable with foreign similar deep-hole drill.Further research work is to improve the machining quality of the drill,optimize the coating process,improve the machining quality of deep-hole drilling accessories(such as the guiding bush,etc),and develop suitable cutting fluid,so as to improve deep-hole machining quality and reliability of the nuclear tube sheet,promoting the localization of nuclear power products in China as soon as possible.