Topic :An Investigation into Cutting Process Dynamics in End Milling using Tool Condition Monitoring
Place of Research:
Dr. Babasaheb Ambedkar Technological University, Lonere, Dist: Raigad
In the modern context of manufacturing environment, and especially in the area of machining; tool condition monitoring has gained a tremendous importance nowadays. In the present research, the major aim is to develop a tool condition monitoring system in end milling for machining of hardened steel. Today the area of research is also focused on machining of hardened steel because of demand from small die shop to aerospace industries. The major advantage of this material is retention of its high strength and good wear resistant property at elevated temperatures. Thus, in this research, solid carbide flat end mill of 12 mm diameter with 4-flute is selected for machining of hardened steel, as we are mainly concern with finishing operation only using end milling cutter.
The major challenge posed in this research is to justify effect of different machining parameters on the tool wear and surface finish of the workpiece. It has been observed that the cutting forces generated during the cutting process play a vital role as far as the tool wear and surface roughness are concerned, it also provides rich information about the status of the tool. For the selected tool and work combination, the cutting forces generated during machining along three mutually perpendicular axes are measured using a Kistler make table dynamometer on Hass CNC milling machine along with the DynoWare software interface. Simultaneously during machining, the values of tool wear using Nikon’s Tool Maker’s microscope and surface roughness using Mitutoyo make surface roughness tester are recorded for the designed experiments. After the detailed analysis using the principal components analysis method, the optimum values of the machining parameters are obtained. The threshold value of resultant cutting forces is then determined, and it is the major decision variable in the tool condition monitoring system that decides the current status of the tool.
Furthermore, considering the results of the experiments that have been conducted, electronic circuit for tool condition monitoring is designed and fabricated using a microcontroller accordingly. By using C-Sharp programming, the resultant cutting forces during machining are displayed graphically after interfacing the TCM system with the machine tool. If the values of cutting forces during machining go beyond the threshold value set in the TCM system, it is apparently an indication of excessive wear on the cutting tool. Hence, a warning signal for replacement of the tool will be given by the TCM system.
Thus, it may be concluded that while performing end milling operation on the hardened steel material, an excessive wear that occurs on the end mill, will promptly be detected by the proposed tool condition monitoring system. This will aid the machine tool operator for timely replacement of the tool to obtain the required surface finish on the product as per the given specifications. Another advantage is that, fatal damage of the machine tool can be avoided leading towards safety. From the studies, it is found that downtime on an average machine tool due to cutter breakage is of the order of 6.8% to 20% in industry. By adopting the tool condition monitoring system, the down time of machine tool can be reduced to some extent, thus fulfilling the necessary goal. But besides this, the industrial viability of the tool condition monitoring system is yet to be justified for cost effectiveness and its implementation in the industries.
Prof (Dr) Milind P Ray
Topic : A Numerical Simulation of Shockwave – Cylindrical Inhomogeneity Interface Interaction
A comprehensive numerical investigation of the interaction of a planar shock with an isolated cylindrical gas inhomogeneity (termed as `shock-bubble interaction') is performed in this work. A large range of the governing parameters is included in the matrix of simulations, with an objective to understand the flow physics of this complex problem. These parameters include the Atwood number, ranging from -0.7 to 0.7, and the Mach number of the shock, ranging from 1.2 to 6. Two-dimensional geometry is considered, and the Euler equations of gas dynamics are used as the basic flow model in view of the fact that the viscosity effects are negligible for most of the time of interest. A finite volume reconstruction-evolution methodology is used for the simulations. Several high-resolution multi-fluid solvers are developed, using a fifth order weighted essentially non-oscillatory approach for spatial reconstruction and a third order Runge-Kutta scheme for temporal integration. Nine different inter-cell face flux evaluation schemes, comprising of exact and approximate Riemann solvers available in the literature are incorporated. Multi-fluid simulation capability is achieved using the Ghost Fluid Method (GFM) that uses a level set approach for identification of the interface between the two fluids. A thorough benchmarking for the shock-bubble interaction, performed using experimental and numerical simulation results available in the literature, shows that approximate Riemann solvers predict flow features such as shocks more sharply than the flux vector splitting schemes and the HLLC inter-cell flux evaluation scheme is the most robust for the present high-resolution methodology.
Following the benchmarking of the codes, a parametric study with the chosen values of the governing parameters is performed. The results of the parametric study are presented qualitatively using schlieren images of the developing flow field, and quantitatively by providing time-sequence data of the evolution of the integral features of the gas bubble such as axial and lateral dimensions, translational velocity of the bubble, calculation of the circulation in the flow-field and of stretching rates experienced by the bubble. The behavior of these integral features is found to be consistent with the vorticity characteristics, which in turn, are determined by the baroclinic source term for the vorticity. The translational velocities and the maximum circulation within the flow-field compare fairly well with analytical models available in the literature. An investigation of the effect of superimposing sinusoidal perturbations on the bubble surface shows that such features influence the deformation behavior of the bubble, with an increase in the shock Mach number reducing the stretching rates. Finally, a preliminary investigation of high-temperature effects associated with the high Mach numbers of the incident shock is carried out by incorporating a temperature-dependent specific heats model for high-temperature air. In order to incorporate this feature, the basic calculation procedure is appropriately modified. The simulations performed for an incident shock of Mach number 6 indicate that the effect due to temperature-dependent specific heats seems to be of significance only in the case of smaller Atwood numbers.
Research Centre: Indian Institute of Technology Bombay, Powai, Mumbai