Chip Morphology And Tool Wear In Deep-hole Drilling For The EA4T Railway Axle

EA4T is of a material, widely used in high speed hollow railway axle due to thefact that it has higher strength, toughness and fatigue strength. At present, with highdevelopment of High-speed Rail, subway and EMU high-speed trains in China, thedemand for high-quality hollow axle is increasing. The quality and efficiency of thedeep hole processing of hollow axle largely determine the production efficiency andprocessing cost of the axle. EA4T efficient drilling deep hole drilling technology andthe related theory research has received a widespread attention. In this paper, the TiNcoating cemented carbide BTA deep-hole drill EA4T axle technology is used as theresearch object. The deep-hole drilling model and cutting force, deep-hole chipmorphology and tool wear, etc. are studied. The main research contents are asfollows:(1) Research on deep-hole drilling model and cutting force model. BTA deephole drilling model is established. The orthogonal cutting model is studied byconsidering cutting bending moment the knife blunt round radius and tool wear etc.,the cutting force and the relevant parameters of theory are calculated. Studied theoverall stress of staggering teeth BTA drill, according to the principle of static balance,combined with micro mechanics analysis model of cutting blade, the basic equationsof drilling force and torque affected by multi-parameters is established consideringthe work-piece material coupling cutting tool structure and cutting parameter and toolwear, and the simulation and experimental are researched.(2) Research on deep-hole chip morphology. In order to build the basicevaluation system of deep cuttings morphology, the morphological characteristics ofdeep chips, deformation features and breaker’s characteristics have been reflected. ByEA4T,40CrMoA deep hole drilling test, a lot of cuttings samples have been got, and the article researches on the law that drilling conditions influence cuttingsmorphology; The chip source can be accurately distinguished by the followingindexes, cutting width and length and radius of curvature; the basic rules of chipmorphology and drilling conditions are quantitatively evaluated by the chipcompression ratio CCR, chip breaking rate CBR, chip capacity coefficient R and chipradius of curvature K, the basic evaluation index of deep hole chip morphology ispreliminary established. Finally, the optimum drilling conditions of EA4T deep holeprocessing is proposed according to the chip breaking rate CBR index. On the basis ofmaximum strain theory, the chip breaking conditions are studied, when the bendingfracture strain is larger than the critical value, the chip will reverse break, a chipbreakage condition based on deep-hole chip morphology evaluation index isestablished. Influential factors of chip breaking are analyzed, and the control methodof deep-hole drilling cutting chip is proposed. In the case of the work-piece materialand tool parameters is under certain matching, cutting speed and feed reasonably is akey factor to ensure the ideal chip morphology. Finally the relationship between chipcompression ratio, chip breaker rate, chip the chip coefficient, radius of curvature ofthe chip and the amount of cutting have been derived, and theoretical formula and testdata Conclusion also have been identical.(3) Research on BTA bit wear characteristics and wear mechanism. Based onthe theory of diffusion and theory of layer peeling, through the cutting tool wearexperiment of deep hole drilling EA4T, the wear characteristics of wrong tooth BTAdrill and single tooth BTA drill are analyzed, and wear morphology and wearmechanism of three knife tooth of the wrong tooth BTA drill is studied. Wearcharacteristics of the side tooth, middle tooth and center tooth are: to the edge toothback flank, belt wear and boundary wear are the main features and to the front flank,Kenwa wear is the main feature, in which the failure of the cutting tool dues to thecoating peeling on the pointed cutter as well as chipping; typical wear characteristicof middle tooth is built-up edge, and bond wear is prominent; the boundary wear isthe main feature of the center gear, especially severe boundary wear occurs on the pointed cutter due to the presence of the zero speed cutting, and even cracks,chipping and fracture of tool failure characteristics will occur.The rake, flank wear parts are analyzed by the energy spectrum and scanningelectron microscopy. Kenwa wear form appears on rake teeth, edge tooth and themiddle teeth; on the site of Kenwa, element diffusion is active. wear mechanismmainly dues to diffusion, which owes to adhesive and abrasive wears playing a roleand wear is serious, the middle part,which is located on both sides of Kenwa,isadhesion wear; flank wear mainly includes adhesive wear, abrasive wear and microchipping; edge wear on the pointed cutter is serious. Three tool edge tooth tips haveserious damage, resulting in the tool failure.(4) Segment wear research on TiN coating BTA drills. When TiN coating ispresent, the first wear stage of BTA starts. It is also the main working stage of cuttingtool. The reason is the diffusion loss of Ti and N elements; after the disappearance ofTiN coating is second wear stage of BTA bit. Tool wear is intense, which will causetool failure in the short term. The main reason of wear is that Diffusion wear andadhesive wear occur between the substrate and the work piece of cemented carbidecutting tool. In different cutting conditions, results of tool wear experimentsare:①cutting speed has more effect feed rate to the cutting tool wear;②single toothBTA drilling tool wear is more serious than the staggering teeth BTA drilling toolwear, and the cutting stability is poorer;③TiN coating can significantly improve thetool’s durability.