THE UNIFIED-GENERALIZED MECHANICS OF CUTTING APPROACH—A STEP TOWARDS A HOUSE OF PREDICTIVE PERFORMANCE MODELS FOR MACHINING OPERATIONS

Abstract

This paper presents the series of on-going investigations, which led to the development of the ‘Unified-Generalized Mechanics of Cutting Approach’ to predictive modelling of various technological performance measures for the wide spectrum of machining operations used in practice. It is shown that this approach involved the development of generalized mechanics of cutting analyses of the cutting processes for machining with single edge and multi-edge (form) tools and the establishment of a generic database of basic cutting quantities and edge force coefficients. This was followed by the development of a methodology for modelling each machining operation used in practice, based on the generalized cutting analyses and database. The models developed for turning, drilling and milling operations as well as machining with form tools and the novel rotary tool turning operations are briefly described together with recent research on predictive modelling of ball end-milling and machine tapping operations. It is shown that the models for the different machining operations could be ‘unified’ into a modular computer application structure, drawing on the generic cutting analyses and database. This ‘unified’ approach could represent a step towards the development of a ‘House of Predictive Models’ sought by the CIRP Working Group on modelling of machining operations. The considerable scope for further research is discussed in this paper.     

Optimal machining cycles for numerically controlled metal-cutting machines

The design of optimal automatic machining cycles for numerically controlled metal-cutting machines is considered, in theoretical terms. Dynamic programming permits the optimization of an unlimited number of control parameters for all the machining operations in numerically controlled metal-cutting machines.     

The problem resolution of designing of cycles in the conditions of modern automated production

The design of machining cycles in automated production entails the development of a theory regarding the selection of optimal automatic cycles for numerically controlled metal-cutting machines. This theory is based on dynamic programming and permits optimization of an unlimited number of control parameters for all types of machining operations.     

A GENERIC MECHANICS OF CUTTING APPROACH TO PREDICTIVE TECHNOLOGICAL PERFORMANCE MODELING OF THE WIDE SPECTRUM OF MACHINING OPERATIONS

ABSTRACT

The need for quantitatively reliable predictive models for the many technological machining performance measures to optimize the economic performance of machining operations, and to design machine tools and cutting tools that enhance this economic performance, has been highlighted. Also highlighted is the formidable task of establishing the required quantitative technological performance data and equations, and the gap between theory and practice. The development and generic nature of the “unified or generalized mechanics of cutting approach” to technological performance prediction for the wide spectrum of machining operations is presented and discussed in this paper. Suggestions for overcoming some practical difficulties and extending the scope of this predictive modeling approach are also considered.     

在钢料薄切削层车削下的加工表面光洁度

在半精加工及精加工钢料时切削厚度常小于0.05毫米以至接近于5微米（μ）,其时加工光洁度一般要求较高。由于此时切削厚度较薄,加工光洁度与刀刃参数如刀刃不平度、楔角及刀刃圆半径等有着较密切的关系,而所用冷却润滑液及切削过程中所产生的积屑瘤也对加工光洁度起着一定的影响。鉴于这一问题在过去文献中尚缺乏系统的参考资料,本文报导了我们在车床上进行的比较系统的试验,目的在于使所得的结果可供生产上用点接触刀具加工中碳钢料时的参考与比较。     

An experimental evaluation of the capabilities of a fluidised-bed fixturing system

A phase-change fixture is a single adaptive device which can hold parts of various shapes and sizes while they are subjected to a wide variety of manufacturing operations. In this paper, a fundamental experimental investigation of adaptable fluidised-bed phase-change fixturing systems is presented. The results of this experimental investigation, which focuses on evaluating the ability of these fixtures to resist complex combinations of axial, bending and torsional loads, have provided estimates of the fixturing capability of this class of fixtures. This work has precipitated the development of a semi-automated hydraulically-operated prototype fixturing system, which is currently being employed to fixture parts of various shapes and sizes for several diverse manufacturing tasks, including metal-cutting operations, on a horizontal-axis LeBlond-Makino MC65-A60 machining centre.     

Selection of metal-cutting machines in operational design by means of PLM systems

A method is proposed for the selection of metal-cutting machines in the design of technological operations using Teamcenter and UNIGRAPHICS NX software.     

A STUDY ON CHIP BREAKING LIMITS IN MACHINING

Abstract

Prediction of chip breaking in machining is an important task for automated manufacturing. This paper presents a study on chip breaking limits. Based on the chip breaking curve, the critical feed-rate is modeled through an analysis of up-curl chip formation, and the critical depth-of-cut is formulated through a discussion of side-curl dominant chip formation processes. Factors affecting chip-breaking limits are also discussed.

In order to predict the chip breaking limits, semi-empirical models are established. Although the coefficients that occur in the model are estimated through machining tests, the models are applicable to a broad range of machining conditions. The model parameters include machining conditions, tool geometry, and workpiece material properties.     

Influence of manufacturing errors in a metal-cutting machine with parallel kinematic structure on its machining precision

Possible manufacturing and assembly errors in a metal-cutting machine with parallel kinematic structure that affect its kinematic model are analyzed. On the basis of the manufacturing tolerances for the metal-cutting machine, the equations of the direct and inverse kinematic transformations are refined. An algorithm is derived for simulating the influence of geometric errors on the positioning precision of the actuator in the metal-cutting machine.     

Evolution of methods of assessing the accuracy of metal-cutting machines. 2. Evolution of concepts and models used in assessing the accuracy of metal-cutting machines

The evolution of methods used in assessing and monitoring the accuracy of metal-cutting machines is considered. Changes in terminology and in the concept of accuracy are discussed. Relations between the evolution of accuracy and the methods used for its determination are presented, in the context of the most important developments responsible for machine-tool accuracy. The development of models of machine-tool accuracy is reviewed, and the corresponding mathematical apparatus for the accuracy assessment is presented. The applicability of the various approaches is determined.     

Identifying the primary rigidity axes in the elastic system of a metal-cutting machine

A computer experiment based on CAE systems may be used to determine the primary rigidity axes in the supporting systems of metal-cutting machines. The formulation of the models, the experimental method, and the applicability of the method are considered.     

On implementation of the finite difference lattice boltzmann method with internal degree of freedom to edgetone

The lattice Boltzman method (LBM) and the finite difference-based lattice Boltzmann method (FDLBM) are quite recent approaches for simulating fluid flow, which have been proven as valid and efficient tools in a variety of complex flow problems. They are considered attractive alternatives to conventional finite-difference schemes because they recover the Navier-Stokes equations and are computationally more stable, and easily parallelizable. However, most models of theLBM orFDLBM are for incompressible fluids because of the simplicity of the structure of the model. Although some models for compressible thermal fluids have been introduced, these models are for monatomic gases, and suffer from the instability in calculations. A lattice BGK model based on a finite difference scheme with an internal degree of freedom is employed and it is shown that a diatomic gas such as air is successfully simulated. In this research we present a 2-dimensional edge tone to predict the frequency characteristics of discrete oscillations of a jet-edge feedback cycle by theFDLBM in which any specific heat ratio γ can be chosen freely. The jet is chosen long enough in order to guarantee the parabolic velocity profile of a jet at the outlet, and the edge is of an angle of α=23°. At a stand-off distancew, the edge is inserted along the centerline of the jet, and a sinuous instability wave with real frequency is assumed to be created in the vicinity of the nozzle exit and to propagate towards the downstream. We have succeeded in capturing very small pressure fluctuations resulting from periodic oscillation of the jet around the edge.     

An Enhanced Force Model for Sculptured Surface Machining

Abstract

The ball-end milling process is used extensively in machining of sculpture surfaces in automotive, die/mold, and aerospace industries. In planning machining operations, the process planner has to be conservative when selecting machining conditions with respect to metal removal rate in order to avoid cutter chipping and breakage, or over-cut due to excessive cutter deflection. These problems are particularly important for machining of sculptured surfaces where axial and radial depths of cut are abruptly changing. This article presents a mathematical model that is developed to predict the cutting forces during ball-end milling of sculpture surfaces. The model has the ability to calculate the workpiece/cutter intersection domain automatically for a given cutter path, cutter, and workpiece geometries. In addition to predicting the cutting forces, the model determines the surface topography that can be visualized in solid form. Extensive experiments are performed to validate the theoretical model with measured forces. For complex part geometries, the mathematical model predictions were compared with experimental measurements.     

Investigations on exit burr formation mechanisms based on digital image correlation and numerical modeling

Abstract

Requirements on burr height and burr amount on machined parts are getting stricter. This leads to method development from manufacturing companies to predict burr distribution and its size along part edges. A deeper understanding of burr formation mechanisms will assist to more accurate model development. This study aims to analyze the exit burr formation, which is formed during orthogonal cutting of a brittle cast aluminum alloy. A customized digital image correlation (DIC) system with the help of a high-speed camera was used to measure the displacements fields. It calculates strain fields during burr initiation and development in orthogonal cutting of T7 heat-treated cast aluminum alloy ENAC-AlSi7Mg0.3 as well. Those results are then qualitatively compared with a numerical model of the burr with chamfer formation developed and simulated using a finite element method, to ensure a good correspondence between experiments and simulation. This model is used to complete the DIC study of burr with chamfer formation mechanisms during crack propagation leading to chamfer formation. The analysis of numerically obtained stress triaxiality fields and of DIC observations from experiments are compared to the assumptions made from analytical models. Finally, necessary improvements of an existing burr formation analytical model are proposed.     

Evaluation of elastic modulus for unidirectionally aligned short fiber composites

An analytical approach of to reinforcement for of short fiber reinforced composites has been extended to include the estimation of elastic modulus. The model is based on the theoretical development of shear lag theory developed by Cox for unidirectionally Aligned aligned Short short Fiber fiber Compositescomposites. Thus, the evolution of conventional models is described in detail along with the effect on the modulus of various parameters. Results are shown with experimental data as well as the comparison of other theories. It is found that the present model agrees well with experimental data and resolves some of the discrepancies among the previous models. It is also found that the present model is very accurate yet relatively simple to predict Young’s modulus of discontinuous composites and has the capability to correctly predict the effects of fiber aspect ratio, fiber volume fraction, and fiber/matrix modulus ratio. This paper was recommended for publication in revised form by Associate Editor Chongdu Cho Hong Gun Kim received a B.S. and M.S. degree in Mechanical Engineering from Hanyang University in 1979 and 1984. He then went on to receive his Ph.D. degrees from University of Massachusetts in 1992, respectively. Dr. Kim is currently a Professor at the Department of Mechanical & Automotive Engineering at Jeonju University in jeonju, Korea. He is currently serving as an Editor of the KSAE and KSMTE. Dr. Kim’s research interests are in the area of fuel cell, FEM analysis, mechanical design, and composite mechanics. Lee Ku Kwac received a B.S. degree in Precision Mechanical Engineering from Chosun University in 1999. He then went on to receive his M.S. and Ph.D. degrees from Chosun University in 2001 and 2005, respectively. Dr. Kwac currently a Professor at the Department of Mechanical & Automotive Engineering at Jeonju University in jeonju, Korea. Dr. Kwac’s research interests are in the area of fuel cell, nano-mechanism, and micro-machining.     

ASSESSMENT OF MACHINING MODELS: PROGRESS REPORT

Abstract

Progress in developing and assessing predictive modeling of machining processes has been hindered by the extremely localized nonlinear physical phenomena that occur in machining and the many different types of models ranging from theoretical to empirical. The difficulty in assessing models has been cited by industry as the major barrier to use of modern machining models. Current practice in industry is to machine and change tools conservatively, or to conduct costly empirical studies for a limited selection of tools and coolants. The Assessment of Machining Models project will assess the ability of modern machining models to predict the outputs of machining processes based upon a consistent, well measured calibration data set. The data set is nearly complete and is to be used in benchmarking the predictive capability of machining models in blind tests. This paper presents the project motivation, goals, and representative calibration data set results. The next steps in the effort include release of the calibration data, solicitation and collection of predictions, and evaluation and reporting of results.     

Temperature Measurement in the Metal-Cutting Zone of a Lathe

A method is proposed for industrial measurement of the temperature in the metal-cutting zone. The method employs the thermal-equilibrium equation to determine the amount by which the local temperature exceeds the ambient value. The concept of a heated body is introduced: the part of the workpiece that is converted to chip and is deformable in the course of cutting. A method of determining the mass of the heated body is formulated and experimentally verified.

     

MANUFACTURING PROCESSES AND EQUIPMENT

ABSTRACT

For the past fifty years researchers have developed various machining models to improve cutting performance. Several approaches have been taken including analytical techniques, slipline field solutions, empirical approaches and finite element techniques. Of these, the finite element approach provides the most detailed information on chip formation and chip interaction with the cutting tool. Finite element models have been developed for calculating the stress, strain, strain-rate, and temperature distributions in both the chip and the workpiece. In addition, tool temperatures, machining forces and cutting power requirements can be determined. This information is extremely, useful for developing more fundamental understanding of complex machining problems. This paper presents a critique of finite element approaches used for simulating machining processes. Several applications of the finite element technique for simulating various machining problems are also reviewed. A new application for determining diffusion wear rates in cutting tools is described, and future directions for finite element modeling of machining processes are discussed.     

Numerical analysis of welding residual stress using heat source models for the multi-pass weldment

Numerical prediction of welding-induced residual stresses using the finite element method has been a common practice in the development or refinement of welded product designs. Various researchers have studied several thermal models associated with the welding process. Among these thermal models, ramp heat input and double-ellipsoid moving source have been investigated. These heat-source models predict the temperature fields and history with or without accuracy. However, these models can predict the thermal characteristics of the welding process that influence the formation of the inherent plastic strains, which ultimately determines the final state of residual stresses in the weldment. The magnitude and distribution of residual stresses are compared. Although the two models predict similar magnitude of the longitudinal stress, the double-ellipsoid moving source model predicts wider tensile stress zones than the other one. And, both the ramp heating and moving source models predict the stress results in reasonable agreement with the experimental data.     

Control System Design for a Neutralization Process using Block Oriented Models

Abstract

This paper focuses on the development of a non‐linear controller for a neutralization process. Block oriented models, namely the Wiener and Hammerstein model structures, are used for the controller design. A neural network architecture that has the capability to model the steady state behavior of a complex non‐linear process is developed. The dynamic behavior is modeled with a linear model. The pH process considered in this study exhibits drastic changes in the gain, even over a small operating range. In this study, the performance of controllers designed using Weiner and Hammerstein models are compared with a PI controller for servo and regulatory changes. The comparison results based on integral square error (ISE) values shows that the Weiner model based controller is suitable for a pH process.