| In the manufacture of equipment and components for nuclear power steam generator tube sheets,hollow axles,heat exchangers,separators,boiler tube sheets,it is often necessary to drill deep-holes with small diameters,large quantities,and high quality requirements.The present thesis focused on the AP1000 nuclear power steam generator tube plate needing to drill 20050 high-quality deep-holes with a hole diameter of about 17.73mm.The hole depth is 800mm and the aspect ratio is as high as 45:1.The deep-hole drilling force can reflect the stability of the drilling process,the surface quality of the deep-hole,and the life of the drill,while the deep-hole drilling force is affected by the complex machining environment and tool structure,making it difficult to study;Drilling parameters(speed n,feed rate f)have a greater impact on the surface integrity of deep-holes,chip morphology,and dill wear,and it is of great significance to choose appropriate drilling parameters for deep-hole machining.This thesis attempts to study the deep-hole drilling mechanics and processing parameters on the surface integrity of deep-holes,chip morphology,tool wear,and optimizes the drilling parameters to provide selection of processing parameters.The mechanical model of the staggered tooth BTA drill was established,and the drilling process of the deep-hole BTA drill was simulated.The results show that the main factors affecting the torque,axial force and tangential force are the feed rate,the width of the flank wear band and the radius of the tip arc.The main factors affecting the radial force are the width of the flank wear band and the knife sharp arc radius;both axial force and torque increase with an increase in drilling speed and feed.The surface integrity and chip morphology of deep-holes were studied.Through the experiment of 13MnNiMoR drilling with staggered BTA drill,the effect of drilling speed and feed rate on the surface integrity of deep-hole and chip morphology was revealed.The change law of macro and micro morphology of deep-hole drilling surface was studied.The results show that increasing the rotation speed can improve the surface quality of deep-hole,but increasing the feed rate can decrease the surface quality of deep-hole;the main macro defects include grooves and workpiece material shedding,and the micro defects include adhesions,chip scratches,and pits.The effects of drilling speed and feed rate on the surface roughness and microhardness of deep-hole were studied.The results show that the surface roughness of deep-hole increases with an increase in the feed rate,and decreases with an increase in the speed;the microhardness of the surface of the deep-hole changes similarly,showing an increasing trend;as the feed rate and speed increase,the depth of the work hardened layer gradually increases,which indicates that deep-hole drilling has better extrusion strengthening on the surface of the deep-hole effect.The influence of drilling speed and feed rate on chip shape was studied.The results show that as the feed rate increases,the chip bending degree of different cutter tooth decreases and the chip length decreases.As the speed increases,the chip length decreases and the degree of curl decreases.The wear patterns and wear mechanisms of the tooth of the staggered tooth BTA drill were studied,and an optimized model of drilling speed and feed was established.The results show that the damage of the drill mainly occurs in the guide block,the middle teeth are relatively few,and the center teeth are the least;the external tooth have the greatest degree of wear,and the wear zone is more uniform.The middle teeth have less wear than the external teeth.The wear zone is uneven.There are more built-up edges.The center teeth have the least degree of wear,mainly at the edge of the cutter tooth.The wear mechanism of teeth is bond wear,oxidation wear and diffusion wear;the optimal processing parameter is that the speed n is 912r/min,and the feed amount f is 0.092mm/r. |
PDF Full Text Request