PREDICTIVE MODELING OF MACHINING PERFORMANCE IN TURNING OPERATIONS

Recent definitions of machining performance have been based on technological machining performance measures such as cutting forces, tool-life/tool-wear, chip-form/chip breakability, surface roughness, etc. However, modeling work on these performance measures has so far been characterized by isolated treatment of each of these measures. The modeling approach followed by the machining research group at the University of Kentucky aims for an integrated predictive modeling methodology for the major technological machining performance measures. Extensive use of analytical, experimental, numerical, and Al-based approaches is made in the development of these predictive models. This paper presents the outline of this modeling effort and reports the progress made to date in implementing it.     

基于遗传算法的超精密切削表面粗糙度预测模型参数辨识及切削用量优化

建立易于分析各切削用量对粗糙度影响关系的表面粗糙度预测模型和最优的切削用量组合,是超精密切削加工技术的不断发展的需要。针对最小二乘法和传统优化方法的不足,提出了将遗传算法用于超精密切削表面粗糙度预测模型的参数辨识,并用于求解最优切削用量,给出了金刚石刀具超精密切削铝合金的表面粗糙度预测数学模型和切削用量优化结果,进行了遗传算法和常规优化算法的比较,结果表明遗传算法较最小二乘法和传统的优化方法更适合于粗糙度预测模型的参数辨识及保证切削用量的最优。     

FINITE ELEMENT ANALYSIS OF CHIP FORMATION IN GROOVED TOOL METAL CUTTING

Abstract

This paper presents the simulation of chip formation in grooved tool cutting using DYNA3D, 3D FEM software for dynamic nonlinear analysis that was used to simulate the orthogonal cutting problem. First, a flat-face cutting tool was employed in the simulation to verify the validity of the FEM model. Next, the same simulation techniques were used to study the effects of different groove geometries on the chip formation process in grooved tool cutting. In the first set of grooved tool simulations, the depth of the groove was constant while the width was decreased. In the second set, the width was constant and the depth was increased. By analyzing the chip flow, chip curl, chip thickness, stress and strain in the chip, the effects of different groove widths and depths on the chip formation process were then discussed.     

FINITE ELEMENT ANALYSIS OF CHIP FORMATION IN GROOVED TOOL METAL CUTTING

This paper presents the simulation of chip formation in grooved tool cutting using DYNA3D, 3D FEM software for dynamic nonlinear analysis that was used to simulate the orthogonal cutting problem. First, a flat-face cutting tool was employed in the simulation to verify the validity of the FEM model. Next, the same simulation techniques were used to study the effects of different groove geometries on the chip formation process in grooved tool cutting. In the first set of grooved tool simulations, the depth of the groove was constant while the width was decreased. In the second set, the width was constant and the depth was increased. By analyzing the chip flow, chip curl, chip thickness, stress and strain in the chip, the effects of different groove widths and depths on the chip formation process were then discussed.     

A MACHINING PERFORMANCE STUDY IN DRY CONTOUR TURNING OF ALUMINUM ALLOYS WITH FLAT-FACED AND GROOVED DIAMOND TOOLS

This paper presents the results from an experimental study of dry contour turning operations on aluminum alloys (6061B and 2011-T3) using PCD flat-faced and diamond coated grooved tools. The machining performance is assessed on the basis of cutting forces, chip flow, chip-form and surface roughness observed during contour turning operations. The constantly varying cutting conditions (especially effective depth of cut due to varying geometry of the contour surface) and effective tool geometry cause a wide fluctuation in cutting forces and the ensuing chip flow. The chip flow angle is measured along the contour geometry using high-speed filming techniques and these results are compared with predicted chip flow values from the measured experimental cutting forces (which are measured along the entire contour geometry). The resultant surface roughness at different locations along the contour profile is measured and correlated with the chip flow and chip-form variations. Machining performance issues specifically relevant to dry contour turning of aluminum (such as problems due to poor chip flow and the resultant poor surface roughness) are studied and the effectiveness of selective work-tool (both tool material and tool geometry) pairs is illustrated.     

FINITE ELEMENT ANALYSIS FOR CHIP FORMATION IN HIGH SPEED TURNING OPERATIONS BY ARBITRARY LAGRANGIAN EULERIAN METHOD

A two-dimensional finite element (FE) model for the high speed turning operations when orthogonally machining AISI H13 tool steel at 49HRC using poly crystalline cubic boron nitride (PCBN) is described. An arbitrary Lagrangian Eulerian (ALE) method has been adopted which does not need any chip separation criteria as opposed to the traditional Lagrangian approach. Through FE simulations temperature and stresses distributions are presented that could be helpful in predicting tool life and improving process parameters. The results show that high temperatures are generated along the tool rake face as compared to the shear zone temperatures due to high thermal conductivity of PCBN tools.     

A NEW CONCEPT FOR DECOUPLING THE CUTTING FORCES DUE TO TOOL FLANK WEAR AND CHIP FORMATION IN HARD TURNING

Determining the temperature field in metal cutting when the tool flank is progressively worn requires the knowledge of the forces due to tool flank wear and that due to chip formation. In the past, these forces have been computed from data experimentally measured with a dynamometer, under the assumption that the chip formation configuration remained unaltered when the tool flank is progressively worn. This approach has been used in the literature even though there has been evidence that it is not correct. The error introduced by this doubtful assumption in computing the maximum surface temperature in the work-piece can be significant.

Of late there has been considerable interest in employing hard turning as the final finishing process in place of grinding and superfinishing. Consequently, the ability to accurately predict the maximum surface temperature and its distribution in the workpiece is now most desirable, for avoiding thermal damage to the machined surface. This paper discusses a new method based on the thickness of the microstructural change in chips to decouple the tool-flank forces for predicting the maximum surface temperature and its distribution in the workpiece.     

EFFECTS OF CUTTING SPEED WHEN TURNING AGE HARDENED INCONEL 718 WITH PCBN TOOLS OF BINDERLESS AND LOW-CBN GRADES

Application of polycrystalline cubic boron nitride (PCBN) tools as an alternative for ceramic and cemented carbide tools in machining superalloys has been frequently identified as a solution for enhancing process efficiency but only a limited number of studies has been done in this area. The current study explores the effect of the cutting speed, which was varied in a wide range (2–14 m/s), on machinability of age hardened Inconel 718 with PCBN tools. Performance of binderless PCBN grade and grade with low-cBN content was evaluated in terms of tool life, tool wear, cutting forces and surface quality. Chip formation and process dynamics were analyzed as well. It was found that low-cBN grade provided 70–90% better surface finish and tool life than the binderless at moderate speeds (5–8 m/s). Performance of both grades at low and high speed ranges was non-satisfactory due to notching and flaking respectively. At low cutting speed adhesive wear plays a major role while as the speed increases a chemical wear becomes dominant.     

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

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.     

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.     

OPTIMIZATION OF CUTTING CONDITIONS IN DRILLING OPERATIONS WITH PLANE RAKE FACED TWIST DRILLS

Optimization analyses and strategies for drilling operations on CNC machine tools with plane rake faced (PRF) twist drills are presented using a deterministic optimization approach. The optimization is based on criteria typified by maximum production rate while allowing for a range of practical constraints. The optimization analyses result in a deeper understanding of the effect of the constraints and a clearly defined optimization strategy that guarantees the global optimum solution. A numerical study is finally carried out to assess the optimization model and demonstrate the economic benefits of using this model over handbook recommendations in selecting the drilling parameters.     

FEM INVESTIGATION FOR ORTHOGONAL CUTTING PROCESS WITH GROOVED TOOLS-TECHNICAL COMMUNICATION

Rigid-visco-plastic finite element models are used to simulate the chip formation and cracking in the turning processes with grooved tools. The Johnson-Cook constitutive equation and Johnson-Cook damage model, which are appropriate for high-speed machining, are assumed for the workpiece material properties. Thermal effects in cutting are considered. The tool material is considered as rigid, but heat-conducting, with the properties of tool material H11. The calculated chip back-flow angle, curling radius and thickness are analyzed as three typical chip shape parameters. The effects of land length and second rake angle of the grooved tool on chip formation, cracking and temperature are discussed. Some simulation results are compared with other published analytical and experimental results.     

OPTIMIZATION OF THE CUTTING EDGE GEOMETRY OF COATED CARBIDE TOOLS IN DRY TURNING OF STEELS USING A FINITE ELEMENT ANALYSIS

This paper investigates the effects of edge radius of a round-edge coated carbide tool on chip formation, cutting forces, and tool stresses in orthogonal cutting of an alloy steel 42CrMo₄ (AISI 4142H). A comprehensive experimental study by end turning of thin-walled tubes is conducted, using advanced coated tools with well-defined cutting edge radii ranging from 5 to 68 microns. In parallel, 2-D finite element cutting simulations based on Lagrangian thermo-viscoplastic formulation are used to predict the cutting temperatures and tool-stress distributions within the tool coating and substrate. The results obtained from this study provide a fundamental understanding of the cutting mechanics for the coated carbide tool used, and can assist in the optimization of tool edge design for more complex geometries, such as chamfered edge. Specifically, the results obtained from the experiments and simulations of this study demonstrated that finite element analysis can significantly help in optimizing the design of coated cutting tools through the prediction of tool stresses and temperatures, especially within the coating layer.     

EFFECT OF CUTTING SPEED AND SURFACE CHEMISTRY OF CUTTING TOOLS ON THE FORMATION OF BUL OR BUE AND SURFACE QUALITY OF THE GENERATED SURFACE IN DRY TURNING OF AA6005 ALUMINIUM ALLOY

In the present investigation, AA6005 (ISO: AlSiMg) alloy was machined in turning operation with different cutting tools, such as uncoated cemented carbide insert, PVD TiN coated, CVD diamond coated and PCD insert, under dry environment. Effect of cutting speed was studied for each of the cutting tools with regard to the formation of built-up layer (BUL) or built-up edge (BUE). The rake surface of the tools was characterized by optical microscopy, scanning electron microscopy (SEM) and energy dispersive X-ray (EDX) spectroscopic microanalysis. Particular emphasis was given on wear mechanism of PVD TiN coated insert, conventionally used in machining ferrous alloys, during dry turning of AA6005 alloy. It has been observed that increase of cutting speed from 200 m/min to as high as 1000 m/min could not substantially reduce formation of BUL over tool rake surface during dry machining of AA6005 alloy with uncoated or PVD TiN coated cemented carbide inserts. The potential of diamond-based tools in dry machining of aluminium alloy was also studied. Finally, the effect of cutting speed on surface finish of the workpiece machined with different cutting tools was studied during dry turning of AA6005 alloy.     

OPTIMIZATION STUDIES ON HOLE-MAKING TOOLS FOR HIGH-PERFORMANCE CUTTING AUSTENITIC STAINLESS STEEL

Austenitic stainless steel is a kind of difficult-to-cut material utilized widely in various industry fields. Hole-making tools are the uppermost obstacle of high performance cutting, so the optimizations of tools are imperative. This paper presents respectively the optimal geometrical characteristics and corresponding coating for high performance cutting austenitic stainless steel. The appreciated cutting performance of optimized tools with optimized cutting parameters has also been evaluated completely through experiments. Optimized special drills with point angle 138° and helix angle 38° was decided and TiCN coating was selected as the best coating. However optimized taps had different geometry structures for tapping through holes and blind holes. The former adopted the spiral pointed tap with inclination angle 15 °. The latter was spiral fluted tap with helix angle 34°. In high-performance cutting austenitic stainless steel, the optimized cutting parameters of special drills are 16 m/min and 0.13 mm/rev. The research results will be of great benefit for the development and application of high efficient and precise drills and taps of high performance cutting austenitic stainless steel.     

OPTIMIZATION STUDIES ON HOLE-MAKING TOOLS FOR HIGH-PERFORMANCE CUTTING AUSTENITIC STAINLESS STEEL

Austenitic stainless steel is a kind of difficult-to-cut material utilized widely in various industry fields. Hole-making tools are the uppermost obstacle of high performance cutting, so the optimizations of tools are imperative. This paper presents respectively the optimal geometrical characteristics and corresponding coating for high performance cutting austenitic stainless steel. The appreciated cutting performance of optimized tools with optimized cutting parameters has also been evaluated completely through experiments. Optimized special drills with point angle 138° and helix angle 38° was decided and TiCN coating was selected as the best coating. However optimized taps had different geometry structures for tapping through holes and blind holes. The former adopted the spiral pointed tap with inclination angle 15 °. The latter was spiral fluted tap with helix angle 34°. In high-performance cutting austenitic stainless steel, the optimized cutting parameters of special drills are 16 m/min and 0.13 mm/rev. The research results will be of great benefit for the development and application of high efficient and precise drills and taps of high performance cutting austenitic stainless steel.     

EFFECT OF CUTTING CONDITIONS ON THE SERRATED CHIP FORMATION IN HIGH-SPEED CUTTING

Titanium alloy Ti6A14V has been widely used in many engineering fields due to its attractive specific strength and corrosion resistance. A deep understanding of the material's machinability is of primary importance. This article investigates the serrated chip formation mechanism of Ti6Al4V alloy under high-speed cutting by finite element analysis. The effect of the cutting conditions on the serrated chip formation is analyzed comprehensively. The study found that when the initial chip thickness becomes small or when the rake angle becomes large, the size of sawtooth decreases and the number of sawtooth increases. The serrated chip morphology is more sensitive to the initial chip thickness. The severe fluctuation of cutting forces is caused by the formation of sawtooth in chipping. To minimize the serrated chipping in high-speed machining, the initial chip thickness is the most important factor to consider.     

复杂冲压件成形过程的截面分析技术

基于有限变形虚功率增量型原理的弹塑性大变形有限元理论,建立了高精度的八节点四边形单元平面应变状态下的截面分析模型,并应用非均匀有理B样条曲线描述模具截面线进行接触判断。旨在用很短的计算时间,获得较理想的板料冲压成形的模拟结果。方模具圆坯料胀形和深拉延成形过程以及发动机油底壳深拉延的模拟与试验结果,表明了该截面分析技术的正确性、可行性和高效性。     

MACHINING PARAMETERS OPTIMIZATION FOR ALUMINA BASED CERAMIC CUTTING TOOLS USING GENETIC ALGORITHM

Alumina-based ceramic cutting tools can be operated at higher cutting speeds than carbide and cermet tools. This results in increased metal removal rates and productivity. While the initial cost of alumina based ceramic inserts is generally higher than carbide or cermet inserts, the cost per part machined is often lower. Production cost is the main concern of the industry and it has to be optimised to fully utilize the advantages of ceramic cutting tools. In this study, optimization of machining parameters on machining S.G. iron (ASTM A536 60-40-18) using alumina based ceramic cutting tools is presented. Before doing the optimization work, experimental machining study is carried out using Ti [C,N] mixed alumina ceramic cutting tool (CC 650) and Zirconia toughened alumina ceramic cutting tool (Widialox G) to get actual input values to the optimization problem, so that the optimized results will be realistic. The optimum machining parameters are found out using Genetic algorithm and it is found that Widialox G tool is able to machine at lower unit production cost than CC 650 tool. The various costs affecting the unit production cost are also discussed.     

球头刀具刃形建模与过渡刃设计

针对回转刀具的几何特性,提出了广义螺旋运动概念,并应用这一概念建立了球头刀具典型刀刃曲线的通用数学模型。针对某些刀刃曲线的特殊性质和球队刀具的刃形分布要求,提出了过渡刃的概念及其设计方法。