Investigation On Machining Stability During Turning And Grinding Operation

In every metal cutting process,dynamic stability is a crucial problem due to its noticeable role in the performance and other process outcomes.The process parameters,the cutting tool condition,and the dynamics of the machine tool influence greatly the dynamic stability of the process.Whatever method used to predict the process stability condition,accurate results are obtained when the machine tool dynamics and the cutting process parameters are perfectly included in the method.Turning and grinding operations are the most effective machining methods to produce round and flat metal and nonmetal parts for various industrial applications.Chatter vibrations are major constraints encountered by machinists limiting them to achieve the part quality demand during turning and grinding operation.Some of the consequences of cutting vibrations and chatter are shorter tool life span,cutting tool damage,inaccurate dimensions of the workpiece,poor quality of the surface finish,and harmful noise.A reliable dynamic model of the turning and grinding operations should include a workpiece excited by the dynamic cutting forces.Dynamic interfaces between the workpiece and moving tool generate cutting forces which can excite chatter vibration under certain conditions.Chatter vibrations are a very complicated dynamic problem in the machining area.In this dissertation,some sources of dynamic instability during turning and grinding operations have been reviewed to get a proper understanding of the current contribution in this research direction.Various methods available in the literature of stability control by chatter detection and suppression have been studied.After a deep review,the scope of this dissertation has been pointed out as identifying a new source of regenerative chatter in turning operation and analyzing the vibration conditions in the cylindrical and the flat surface grinding operations to develop the mathematical models establishing the modes of turning and grinding vibration instability excitation.In the turning operation,the thesis focuses on the stability analysis for a single-point cutting tool deflection in turning operation by considering a single-degree of freedom model of the cutting tool oscillations.Cutting under stable and chatter process parameter conditions were identified and analytically studied by simulation and experimental approaches.A numerical model of the cutting tool deflection is established by the use of a cantilever beam model.The magnitude of the permissible cutting tool deflection under the applied cutting load is estimated by theuse of the three-dimensional finite element method.MATLAB is used to compute the system time series from the initial value using fourth-order Runge–Kutta numerical integration.The cutting forces under stable and chatter cutting conditions are obtained by the use of a straight hard turning with minimal fluid application experimental setup.A single-point cutting tool made from high-speed steel(HSS)is used for cutting.A lot of research efforts were made in the last decades to understand,identify and suppress regenerative chatter vibrations in turning operation,but the study on regenerative vibrations due to single-point cutting tool deflection in turning operation has not been focused on.Recent studies reported chatter vibrations as a result of cutting a wavy surface of the previous cut,and the chatter vibration resulting from the tool deflection in turning operation was not reported.In this dissertation,a new model is developed to analyze and predict chatter vibrations under a single-point cutting tool deflection in turning operation.A turning operation dynamic model is developed to investigate the effect of tool deflection on the dynamic stability condition of the process.This new model indicates that the tool deflection induces the process vibrations which transit from periodic,quasi-periodic,and chaotic type.For the flat surface grinding operation,the dissertation presents a new dynamic model to analyze a particular instability condition in the normal and tangential components of the process.Analytical comparison between the influence of the normal and tangential components of grinding forces on the vibration conditions of the process is established.The vibration response of the process is obtained through the bifurcation diagrams,for the depth of cut and the cutting speed as the bifurcation parameters.The workpiece is assumed to be rigid and the grinding wheel is modeled as a nonlinear two degrees of freedom mass-spring-damper oscillator.The results of the process dynamic model simulation revealed that the vibration condition is more affected by the normal component than the tangential component of the grinding forces.Besides,for the increase of the depth of cut and cutting speed,the results show a nonlinear dynamic behavior of the process in the normal direction and increase of the amplitude of vibration in the tangential direction.In the cylindrical grinding process,the dissertation develops a new model of the traverse cylindrical grinding process vibrations to analyze a particular type of dynamic instability induced by the in-feed rate.The grinding wheel is modeled as a constant speed moving oscillator excited by the grinding forces to provide a time-varying excitation load to induce the workpiece deflection.The workpiece is regarded as a simply supported non-uniform Euler-Bernoulli beam.The numericalanalysis is used to obtain the governing equations of the process dynamics.MATLAB is used to obtain the dynamic response of the process.The experiment is used to validate the model simulation results.The results of the tested grinding mode show that the dynamic stability of the process can be benefited at the in-feed rate 0.01mm/sec while reducing the grinding time.For each cutting operation,the results of the developed dynamic model have been validated by the experiment.An agreement between the analytical model simulation results and the real cutting experimental results were noticed.