Metal cutting is a widely used method of producing manufactured products. The technology of metal cutting has advanced considerably along with new materials, computers, and sensors. This new edition treats the scientific principles of metal cutting and their practical application to manufacturing problems. It begins with metal cutting mechanics, principles of vibration, and experimental modal analysis applied to solving shop floor problems. Notable is the in-depth coverage of chatter vibrations, a problem experienced daily by manufacturing engineers. The essential topics of programming, design, and automation of CNC (computer numerical control) machine tools, NC (numerical control) programming, and CAD/CAM technology are discussed. The text also covers the selection of drive actuators, feedback sensors, modeling and control of feed drives, the design of real time trajectory generation and interpolation algorithms, and CNC-oriented error analysis in detail. Each chapter includes examples drawn from industry, design projects, and homework problems. This book is ideal for advanced undergraduate and graduate students, as well as practicing engineers.

Manufacturing Automation: Metal Cutting Mechanics, Machine Tool Vibrations, and CNC Design

Computer Controlled Systems: Theory and Design

Machine tool feed drives

Chatter suppression techniques in metal cutting

Virtual machine tool

Reference trajectory generation plays a key role in the computer control of machine tools. Generated trajectories must not only describe the desired tool path accurately, but must also have smooth kinematic profiles in order to maintain high tracking accuracy, and avoid exciting the natural modes of the mechanical structure or servo control system. Spline trajectory generation techniques have become widely adopted in machining aerospace parts, dies, and molds for this reason; they provide a more continuous feed motion compared to multiple linear or circular segments and result in shorter machining time, as well as better surface geometry. This paper presents a quintic spline trajectory generation algorithm that produces continuous position, velocity, and acceleration profiles. The spline interpolation is realized with a novel approach that eliminates feedrate fluctuations due to parametrization errors. Smooth accelerations and decelerations are obtained by imposing limits on the first and second time derivatives of feedrate, resulting in trapezoidal acceleration profiles along the toolpath. Finally, the reference trajectory generated with varying interpolation period is re-sampled at the servo loop closure period using fifth order polynomials, which enable the original kinematic profiles to be preserved. The proposed trajectory generation algorithm has been tested in machining a wing surface on a three axis milling machine, controlled with an in house developed open architecture CNC.

High speed CNC system design. Part I: jerk limited trajectory generation and quintic spline interpolation

Accurate modeling and identification of the feed drives' dynamics is an important step in designing a high performance CNC. This paper presents a method for identifying the dynamic parameters, as well as the friction characteristics of machine tool drives. The inertia and viscous friction are estimated through an unbiased least squares scheme. The friction model is developed by observing the disturbance torque through a Kalman filter, while jogging the axes under closed loop control at various speeds. The overall axis model is used in designing a high speed feed drive control system, which has been presented in Part III of this paper. As verification of the identified friction model, contouring test results without and with friction compensation are also presented.

High Speed CNC System Design. Part II : Modeling and Identification of Feed Drives

Sliding Mode Controller Design for High Speed Feed Drives

A servo control system capable of delivering rapid and accurate feed motion is a necessity for high speed machine tools The control law must be designed to provide a high tracking bandwidth as well as adequate disturbance rejection and parameter variation robustness, in order minimize the following errors in each axis This also contributes to the minimization of the contour errors in the machined part This paper provides a systematic approach for designing such a control law Position, velocity, and disturbance estimates are obtained using a Kalman filter The feedback loop is closed using a pole placement controller with disturbance cancellation, in order to counteract the detrimental effects of friction, cutting forces, and drive parameter variations The overall tracking bandwidth is widened by compensating for the closed loop dynamics in a feedforward manner Also, the tracking errors due to friction transients at the corners and arc quadrants are reduced by precompensating for the expected friction forces The contribution of each component in the control scheme to the contouring accuracy has been experimentally verified, and the overall contouring performance has been demonstrated in high speed machining tests The experimental results were obtained using the smooth trajectory generation algorithm and identified axis and friction models which have been presented in Parts I and II respectively, of this paper

High speed CNC system design. Part III: high speed tracking and contouring control of feed drives

This paper presents a trajectory planning strategy for maintaining the tool positioning accuracy in high speed cornering applications. A 3D contour error estimation algorithm is presented for determining the geometric deviation from arbitrarily shaped toolpaths. Two spline fitting strategies are developed for smoothening sharp corners. The under-corner approach reduces the toolpath length, and therefore the cornering time. This technique yields successful results when used with a high bandwidth servo controller (such as sliding mode control), capable of accurately tracking the commanded toolpath. The over-corner approach is based on stretching out the sharp corner with a smooth curve, which counteracts the ‘undercut’ caused by the large phase lag in low bandwidth servo controllers (such as P–PI control). The cornering feedrate is adjusted in the Virtual CNC platform, developed in the first part of this article, to ensure that contour error violation does not occur. The achieved cornering accuracy is verified in experiments, which are in close agreement with predictions obtained with the Virtual CNC.

Kaan Erkorkmaz

Papers

High speed CNC system design. Part I: jerk limited trajectory generation and quintic spline interpolation

High Speed CNC System Design. Part II : Modeling and Identification of Feed Drives

Sliding Mode Controller Design for High Speed Feed Drives

High speed CNC system design. Part III: high speed tracking and contouring control of feed drives

Virtual CNC system. Part II. High speed contouring application