Investigations On The Macro-micro Effect Of BTA Deep Hole Drilling Mechanism And Surface Integrity

According to the urgent need for deep hole drilling technology on the key manufacturing technology of aerospace,high-speed trains,national defense industry,automobile manufacturing and engineering machinery industries,as well as the national strategic industry development demand and the rapid ascension of strategic position for manufacturing,deep hole machining technology with intelligence,precision and high efficiency,is gradually becoming a product upgrading and the important basis for the development of new industries.But the deep hole machining technology theory and in-depth study of drilling mechanism is still insufficient,which is limited by the nature problems with the “Process dependency” of deep hole drilling system and the “status mutability” about machining process.There are decisive and leading effects for promoting the development of deep hole machining technology to make adjustment in intelligent manufacturing pattern through the fundamental research.The systematical theoretical and experimental research for deep hole drilling mechanism and surface integrity are carried out from the macroscopic and microscopic scales.Combining with the results of the study,further explore the deep hole processing optimization and control of surface integrity,so that to provide reliable scientific basis and technical support for promoting the technology level of deep hole equipment manufacturing industry in our country and independent innovation capacity.Deeply analyzed the deep hole drilling mechanism through the stop-quickly experiment in deep hole drilling.The result reveals the different cutting zone and burnishing zone with stepped distribution characteristics.Meanwhile,study the surface layer formation mechanism and influencing factors under drilling and burnishing coupling effect.The elastic-plastic contact model about the burnishing process of guide pads is established based on Hertz contact theory.In addition,the thin shear plane model of drilling tool is established according to the unit cutting tools linear synthesis,and a solution method of the cutting force and torque in deep hole drilling is presented.After researching the dislocation theory,the deep hole drilling mechanism,microcosmic surface profile and formation mechanism of work hardening are systematically studied from the microscopic scale.As a result,the deformation areas of deep hole drilling are defined for the first time.A part of the major research contents focus on the guide pads which affect the quality of machining hole directly.The transverse cutting plane contact model of deep hole drilling is established by introducing a contact angle(k)on the transverse section,and then,developing research on the influence of the guide pad geometric parameters and the distribution regularity on machining quality.Besides that,the stability criterions of drilling tools are discussed respectively under the conditions of the unstable state,the critical stable state and the steady state based on the stability theory.And the dynamic responses of the cutting tool-boring bar system under three different conditions are studied systematically through building the cutting tool-boring bar system models and the vibration mode equations.The research results show that the simply-supported contact between tool and workpiece is closer to the actual.Furthermore,the system dynamics models of drilling tool with two guide pads and three pads are established respectively.The comparative experiments include the boring bar vibration and the hole cylindricity verify that the designed tool with three guide pads has obvious advantages in the dynamic stiffness,damping and vibration suppression performance.Qualitative and quantitative mechanical characterization of the surface and subsurface region is undertaken from macroscale and micro-scale by using tracing stylus instruments,nanoindentation,X-ray scattering techniques,backscatter electron microscopy and electron backscatter diffraction microscopy.The microstructure,nanohardness and grain structure of cutting zone and a burnishing zone are comparatively analyzed,so that they reverse reasoning the combined deep hole drilling mechanisms with drilling and burnishing.The variation regularity of the surface microhardness and residual stress are studied under different machining parameters.The deep hole drilling surface roughness prediction model is established based on the inner surface detection test and roughness test.Moreover,the microstructure and mechanical properties with the variation of the depth distances from the surface are analyzed used BED,Nanoindentation and EBSD.The analysis revealed that the dislocation density,grain size and shape of different surface layers cause a gradient variation characteristic of the deep hole surface.As well,that verified the deep hole drilling mechanism,strain hardening and surface characteristics based on the dislocation theory.Finally,through integrating the theory and experimental research and basing on the Euler beam model,establish the deep hole machining surface morphology trajectory.Furthermore,a control method of the assistant supporting mechanism moving automatically to best supporting position is presented combining with the deep hole drilling in practical.And design an intelligent assistant supporting mechanism based on the magnetorheological fluid and mechanical damping.A series of experiments about the cutting tool-boring bar vibration characteristics,machined surface roughness and chip macro morphology,are carried out,and the results show that the method can suppress chatter efficiently and surface quality of machined holes can be improved significantly.