Prediction of cutting forces in five-axis micro-ball end milling

Five axis micro-ball end milling has been shown as a viable option for machining complex free form surfaces with high aspect ratios and provide micron-scale tolerances. Unfortunately, due to the high fragility of the cutting tool, premature tool failure has been a major challenge in micro-scale machining. Tool strength of a micro-ball end mill can be easily exceeded by the strain induced by cutting force, thus cutting force is desired to be accurately predicted. Traditionally, researchers have used the mechanistic relationship between experimental force and chipload to develop empirical cutting force models for end mill operation. However, these models suffer the drawbacks including the need for extensive experimental calibration, and the limitation to in-plane tool movements. Therefore a comprehensive cutting force model that is suitable for micro-ball end milling operation is desired. The work in this thesis presents a five-axis ball end milling force model that is specifically tailored to micro-scale machining. A composite cutting force is generated by combining two force contributions from a shearing/ploughing slip-line field model and a quasi-static indentation model. To fully capture the features of micro-scale five-axis machining, a unique chip thickness algorithm based on the velocity kinematics of a ball end mill is proposed. This formulation captures intricate tool trajectories as well as readily allows the integration of runout and elastic recovery effects. A workpiece updating algorithm has also been developed to identify tool-workpiece engagement. As a dual purpose, historical elastic recovery is stored locally on the meshed workpiece surface in vector form so that the directionality of elastic recovery is preserved for future time increments. The model has been calibrated and validated through a comparison with experiment data gain by five axis micro-ball end mill testing. Simulation results show reasonably accurate prediction of end milling cutting forces with minimal experimental data fitting. A potential model application for machining process planning is also presented

Smooth Trajectory Generation for Machine Tools and Industrial Robots

This thesis presents accurate and time-optimal smooth reference trajectory generation techniques for manufacturing equipment such as high-speed machine tools (MT) and industrial robots (IR). Typical machining tool-paths for MTs and IRs are defined as a series of discrete linear moves. Although Point-to-Point (P2P) feed motion can be generated by interpolating each linear segment with high-order velocity profiles, the continuous and accurate transition between consecutive segments is necessary to realize a non-stop contouring motion for efficient manufacturing. To generate continuous feed motion along sharp cornered tool-paths, most numerical control (NC) systems blend (smooth) corners locally using various curves and splines. The feed (speed) is reduced around the blend sections so that the motion system’s kinematic limits are respected. This thesis proposes 2 novel techniques to enable modern MT and IR to generate non-stop rapid motion along discrete tool-paths. Firstly, a Kinematic Corner Smoothing (KCS) technique has been proposed to generate time-optimal (minimum time) motion trajectories in a real-time within axis kinematic limits. A novel real-time interpolation technique based on Finite Impulse Response (FIR) filtering has also been proposed to suppress residual vibrations for high positioning accuracy of machine tools and motion systems as well. These two techniques are tailored for Cartesian structured motion systems such as 2-3 axis machine tools. Finally, a decoupled FIR filtering technique has been developed to synchronously interpolate tool position and orientation for accurate motion generation for 5-axis MTs and IRs. These techniques are computationally lightweight and suitable for real-time implementation on modern NC systems. Simulation and experimental validation on Cartesian and 5-axis machine tools are presented to validate the effectiveness of the developed algorithms to interpolate along with discrete commands for high-speed and high-accuracy motion

Proceedings of the 4th International Conference on Innovations in Automation and Mechatronics Engineering (ICIAME2018)

The Mechatronics Department (Accredited by National Board of Accreditation, New Delhi, India) of the G H Patel College of Engineering and Technology, Gujarat, India arranged the 4th International Conference on Innovations in Automation and Mechatronics Engineering 2018, (ICIAME 2018) on 2-3 February 2018. The papers presented during the conference were based on Automation, Optimization, Computer Aided Design and Manufacturing, Nanotechnology, Solar Energy etc and are featured in this book

Model-based Tool Condition Monitoring for Ball-nose End Milling

Ph.DDOCTOR OF PHILOSOPH

In conversation with simulation: The application of numerical simulation to the design of structural nodal connections

The thesis explores methods for integration of structural analysis, design and production in a digital design environment. The somewhat ambiguous title implies the ambition to make such integration in relation to the explorative phase of the design process which is described by Donald Sch\uf6n as having a conversational character. A conversation between the designer and the representation by the means of the tool. The tool is in this context a simulation and instead of exploring the potential of automatic optimisation, the simulation is used for designer driven exploration. The aim of the thesis is to give an overview of how this type of integration is currently being approached and to contribute with new tools and methods in that pursuit. The motivation behind the work is to lower the threshold for the application of structural analysis in early-stage design, with an ambition of architectural qualities and resource efficiency in mind. An overview of the historical context is portrayed with broad brush strokes, followed by a more precise account of the mathematical and physical context, which is complemented by an attempt to describe how our tools and roles tend to interplay in the composition of the design process. Methods such as the finite element method, isogeometric analysis, smoothed particle hydrodynamics and peridynamics, including their related geometrical representations are introduced in relation to this context. A variety of production techniques are also discussed in relation to material mechanical properties for conventional building materials such as steel, concrete and wood.The method development is approached through the use of numerical and physical experiments which are applied for design of material-efficient structural components, with a particular design process perspective. The nodal connection is chosen as an application because it combines geometrical and structural complexity in an element that is of crucial importance for a holistic spatial setting, while often being produced in a material inefficient way, with poor attention to detail.The three articles that are included follow a trajectory from large to small, from the holistic to the particular. The first article is a description of the computational design work with the roof for the new international airport of Mexico City. The second article aims to address one of the challenges that were faced in that project with material inefficiency for nodal connections, with a critical perspective on optimisation. The final article presents an extension/modification for the peridynamics theory enabling variable particle sizes and an irregular particle distribution through the introduction of a concept called force flux density. The development is motivated by limitations found in the present theory through numerical experiments. The method enables simulation of phenomena such as brittle fracture, for which correlation with Griffith\u27s theory of fracture is shown. Further work includes an extension of the force flux method from 2D to 3D, including calibration of material a model for 3D printed steel. Other possibilities involve the exploration of how such a method can adapt to the various stages of the design process, where requirements of accuracy, speed and interactivity will vary

Automated Process Planning for Five-Axis Point Milling of Sculptured Surfaces

Ph.DDOCTOR OF PHILOSOPH

Investigation of cutting mechanics in single point diamond turning of silicon

As a kind of brittle material, silicon will undergo brittle fracture at atmospheric pressure in conventional scale machining. Studies in the last two decades on hard and brittle materials including silicon, germanium, silicon nitride and silicon carbide have demonstrated ductile regime machining using single point diamond turning (SPDT) process. The mirror-like surface finish can be achieved in SPDT provided appropriate tool geometry and cutting parameters including feed rate, depth of cut and cutting speed are adopted.The research work in this thesis is based on combined experimental and numerical smoothed particle hydrodynamics (SPH) studies to provide an inclusive understanding of SPDT of silicon. A global perspective of tool and workpiece condition using experimental studies along with localized chip formation and stress distribution analysis using distinctive SPH approach offer a comprehensive insight of cutting mechanics of silicon and diamond tool wear. In SPH modelling of SPDT of silicon, the distribution of von Mises and hydrostatic stress at incipient and steady-state was found to provide the conditions pertinent to material failure, phase transformation, and ductile mode machining. The pressure-sensitive Drucker Prager (DP) material constitutive model was adopted to predict the machining response behaviour of silicon during SPDT. Inverse parametric analysis based on indentation test was carried out to determine the unknown DP parameters of silicon by analysing the loading-unloading curve for different DP parameters. A very first experimental study was conducted to determine Johnson-Cook (J-C) model constants for silicon. High strain rate compression tests using split Hopkinson pressure bar (SHPB) test as well as quasi-static tests using Instron fatigue testing machine were conducted to determine J-C model constants.The capability of diamond tools to maintain expedient conditions for high-pressure phase transformation (HPPT) as a function of rake angle and tool wear were investigated experimentally as well as using SPH approach. The proportional relationship of cutting forces magnitude and tool wear was found to differ owing to wear contour with different rake angles that influence the distribution of stresses and uniform hydrostatic pressure under the tool cutting edge. A new quantitative evaluation parameter for the tool wear resistance performance based on the cutting distance was also proposed. It was also found that the machinability of silicon could be improved by adopting novel surface defect machining (SDM) method.The ductile to brittle transition (DBT) with the progressive tool wear was found to initiate with the formation of lateral cracks at low tool wear volume which transform into brittle pitting damage at higher tool edge degradation. A significant variation in resistance to shear deformation as well as position shift of the maximum stress values was observed with the progressive tool wear. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of the new and worn diamond tools.As a kind of brittle material, silicon will undergo brittle fracture at atmospheric pressure in conventional scale machining. Studies in the last two decades on hard and brittle materials including silicon, germanium, silicon nitride and silicon carbide have demonstrated ductile regime machining using single point diamond turning (SPDT) process. The mirror-like surface finish can be achieved in SPDT provided appropriate tool geometry and cutting parameters including feed rate, depth of cut and cutting speed are adopted.The research work in this thesis is based on combined experimental and numerical smoothed particle hydrodynamics (SPH) studies to provide an inclusive understanding of SPDT of silicon. A global perspective of tool and workpiece condition using experimental studies along with localized chip formation and stress distribution analysis using distinctive SPH approach offer a comprehensive insight of cutting mechanics of silicon and diamond tool wear. In SPH modelling of SPDT of silicon, the distribution of von Mises and hydrostatic stress at incipient and steady-state was found to provide the conditions pertinent to material failure, phase transformation, and ductile mode machining. The pressure-sensitive Drucker Prager (DP) material constitutive model was adopted to predict the machining response behaviour of silicon during SPDT. Inverse parametric analysis based on indentation test was carried out to determine the unknown DP parameters of silicon by analysing the loading-unloading curve for different DP parameters. A very first experimental study was conducted to determine Johnson-Cook (J-C) model constants for silicon. High strain rate compression tests using split Hopkinson pressure bar (SHPB) test as well as quasi-static tests using Instron fatigue testing machine were conducted to determine J-C model constants.The capability of diamond tools to maintain expedient conditions for high-pressure phase transformation (HPPT) as a function of rake angle and tool wear were investigated experimentally as well as using SPH approach. The proportional relationship of cutting forces magnitude and tool wear was found to differ owing to wear contour with different rake angles that influence the distribution of stresses and uniform hydrostatic pressure under the tool cutting edge. A new quantitative evaluation parameter for the tool wear resistance performance based on the cutting distance was also proposed. It was also found that the machinability of silicon could be improved by adopting novel surface defect machining (SDM) method.The ductile to brittle transition (DBT) with the progressive tool wear was found to initiate with the formation of lateral cracks at low tool wear volume which transform into brittle pitting damage at higher tool edge degradation. A significant variation in resistance to shear deformation as well as position shift of the maximum stress values was observed with the progressive tool wear. The magnitude and distribution of hydrostatic stress were also found to change significantly along the cutting edge of the new and worn diamond tools