Small Depth Of Cut Research Articles

Mathematical model of micro turning process

In recent years, significant advances in turning process have been achieved greatly due to the emergent technologies for precision machining. Turning operations are common in the automotive and aerospace industries where large metal workpieces are reduced to a fraction of their original weight when creating complex thin structures. The analysis of forces plays an important role in characterizing the cutting process, as the tool wear and surface texture, depending on the forces. In this paper, the objective is to show how our understanding of the micro turning process can be utilized to predict turning behavior such as the real feed rate and the real cutting depth, as well as the cutting and feed forces. The machine cutting processes are studied with a different model compared to that recently introduced for grinding process by Malkin and Guo (2006). The developed two-degrees-of-freedom model includes the effects of the process kinematics and tool edge serration. In this model, the input feed is changing because of current forces during the turning process, and the feed rate will be reduced by elastic deflection of the work tool in the opposite direction to the feed. Besides this, using the forces and material removal during turning, we calculate the effective cross-sectional area of cut to model material removal. With this model, it is possible for a machine operator, using the aforementioned turning process parameters, to obtain a cutting model at very small depths of cut. Finally, the simulated and experimental results prove that the developed mathematical model predicts the real position of the tool tip and the cutting and feed forces of the micro turning process accurately enough for design and implementation of a cutting strategy for a real task.

Predictive Tool Life Model of CBN in Ti6Al4V High Speed Turning and Cutting Parameter Optimization

Ti6Al4V is a difficult to machine alloy with low cutting efficiency and server tool wear. A series of orthogonal turning tests with CBN (Cubic Boron Nitride) in higher speed scale was carried out on a CA6140 lathe. The experiential functions of tool life based on orthogonal experiment were developed. The tool wear morphologies were examined by scanning electron microscope (SEM) and energy disperse spectroscopy (EDS), adhesion, diffusion and micro-chipping were the major wear mechanisms of CBN tool. Finally, the cutting parameters of CBN tool in Ti6Al4V dry turning were optimized based on tool life-efficiency contour analysis, in same cutting efficiency, the higher cutting speed and small depth of cut are the better selection, it means that utilization of CBN tool enables the high cutting speed turning of Ti6Al4V.

Effect of Different Coating Materials on Cutting Performance in High-Speed Machining of Mold Steels

Different materials coated on milling tools (tungsten carbide) such as TiCN, TiAlN, TiN and DLC are integrated in this study for the analysis of cutting performance such as tool wear, surface roughness and noise induced in high-speed machining of mold steels such as NAK80 and SKD61 under different combinations of cutting conditions. The study attempts to find out the advantages and adaptabilities in various coating materials being suitable for which cutting circumferences with specific performance request. High-speed milling experiments of NAK80 and SKD61 mold steels with four materials coating tools were carried out in the laboratory. The tool wear was measured through the toolmaker’s microscope and the roughness of the machined surface was measured by the roughness measuring instruments after each surface layer was removed from the workpiece in the experiment. Besides, the noise-mediator was used to detect cutting noise during each surface layer workpiece removing of high-speed milling process, and the curl chips removed from the workpiece were also collected for the result verifications. Good surface quality and small amount of tool wear can be achieved under the cutting conditions of high-speed revolutions, small feed rate and small depth of cut for four materials coating tools. From the observations of the annealing temperature from the removed chips and the analysis of the cutting noise levels, TiAlN material coating tool has the better tool life and it is suitable for rougher high-speed machining, while DLC material coating tool only has a good surface roughness in shallow cut and hence it is not suitable for high-speed machining of mold steel with excellent cutting performance request.

Experimental validation of numerical thermal models for dry grinding

The purpose of this work was to experimentally validate numerical thermal models of the dry grinding manufacturing processes. Two models were developed: one for low depths of cut that ignored the effects of the contact angle, referred to as the shallow grinding model, and one for large depths of cut that included the effects of the contact angle, referred to as the deep grinding model. Both of the models were developed using the commercial finite element package ANSYS and were then compared to in-process temperatures acquired with a full-field infrared video camera. The comparison showed that the numerical models were capable of accurately predicting the shape and intensity of the temperature contours of the infrared images as well as temperature profiles extracted form the images within a margin of error of approximately 9–17%. The results also showed that the shallow grinding model was more precise at small depths of cut while the deep grinding model was more precise at larger depths of cut and that there was a clear transition region where both models performed equally well. The thermal partition ratios used in the numerical models were initially calculated using existing analytical models and refined using a temperature matching technique between the temperature measurements and the numerical models. It was found that during shallow grinding the analytical models were able to predict the actual thermal partition ratios within an average error of 5.7%, while during deep grinding the average error increased to approximately 13.4%.

Comparison of numerically and analytically predicted contact temperatures in shallow and deep dry grinding with infrared measurements

Contact zone thermal models of the grinding process are an important tool for the proper selection of process parameters to minimize workpiece damage while improving process efficiency. Validating contact zone thermal models with experimental measurements is difficult due to the high-speed and stochastic nature of the grinding process. In this work an infrared imaging system is used to validate two numerical thermal models, which are then compared to an established analytical contact zone thermal model. The two numerical thermal models consist of a shallow grinding model and a deep grinding model, where the deep grinding model takes the contact angle into account while the shallow grinding model does not. The results show that at small depths of cut both the numerical models and the analytical model perform well; however, as the depth of cut is increased the numerical models’ accuracy increases as compared to the analytical model. The increase in accuracy may be a result of the 2D solution of the numerical models as compared to the 1D solution of the analytical model. Additionally, it was found that the contact angle has very little effect on the contact temperatures. This work also reinforces Rowe's analytical work, using experimental and numerical results, which indicated that the workpiece temperatures are reduced by grinding at higher Peclet numbers for a given material removal rate.

The role of crystallographic orientation on the forces generated in ultra-precision grinding of anisotropic materials such as monocrystalline silicon

Monitoring forces when grinding crystalline materials is advantageous for optimising process conditions, improving process control and producing high quality parts. Yet, this is challenging in precision applications where aerostatic spindles and small depths of cut are common. This work presents a system of measuring grinding forces in precision applications. Several experiments demonstrate the performance in monitoring diamond wheel dressing, detecting workpiece contact and process monitoring. The system appears promise for monitoring precision wafer.

Toughness and the transition between cutting and rubbing in abrasive contacts

The transition between rubbing and cutting when a facet-first pyramid is slid along the surface of a ductile material is investigated with new experiments under both constant depth of groove and constant load, and with a new ductile fracture mechanics analysis for the cutting regime. The critical attack angle at which the transition occurs is shown to be controlled by the toughness/strength ( R/ τ y ) ratio of the material, the depth of groove, friction and the face angle of the tool. The new analysis is contrasted with the Bowden and Tabor approach in Sedriks and Mulhearn [A.J. Sedriks, T.O. Mulhearn, Mechanics of cutting and rubbing in simulated abrasive processes, Wear 6 (1963) 457–466; A.J. Sedriks, T.O. Mulhearn, The effect of work-hardening on the mechanics of cutting in simulated abrasive processes, Wear 7 (1964) 451–459] and with other approaches for the same events, and it explains why certain assumptions in Sedriks and Mulhearn can be justified. The analysis shows that the vertical load during sliding is different from that required for indentation to the same depth below the surface. Consequently the depth of the groove during sliding under deadweight loading is different from the depth resulting from initial indentation. At very small attack angles, the depth can be smaller than the static indentation depth, but as the attack angle increases, so does the depth of groove formed by cutting. The relevance of the model to abrasive wear and polishing is discussed, along with implications for Krushschov–Babichev wear resistance diagrams and the Archard equation. The analysis explains why the specific energy in grinding increases at small depths of cut. Measurement of the critical attack angle in scratching with a facet-first indenter may possibly be a way to estimate the fracture toughness of small samples when other, more conventional, methods are difficult to carry out.

Finite element modeling of 3D turning of titanium

The finite element modeling and experimental validation of 3D turning of grade two commercially pure titanium are presented. The Third Wave AdvantEdge machining simulation software is applied for the finite element modeling. Machining experiments are conducted. The measured cutting forces and chip thickness are compared to finite element modeling results with good agreement. The effects of cutting speed, a limiting factor for productivity in titanium machining, depth of cut, and tool cutting edge radius on the peak tool temperature are investigated. This study explores the use of 3D finite element modeling to study the chip curl. Reasonable agreement is observed under turning with small depth of cut. The chip segmentation with shear band formation during the Ti machining process is investigated. The spacing between shear bands in the Ti chip is comparable with experimental measurements. Results of this research help to guide the design of new cutting tool materials and coatings and the studies of chip formation to further advance the productivity of titanium machining.

Modeling of Cutting Forces Under Hard Turning Conditions Considering Tool Wear Effect

Quantitative understanding of cutting forces under hard turning conditions is important for thermal modeling, tool life estimation, chatter prediction, and tool condition monitoring purposes. Although significant research has been documented on the modeling of forces in the turning operation in general, turning of hardened materials involves several distinctive process conditions, including negative tool rake angle, large tool nose radius, and rapid tool wear. These process conditions warrant specific treatment in the analysis of cutting forces. This paper first addresses these issues by formulating an oblique chip formation force model through the extension of a two-dimensional (2D) mechanistic force model while considering the effect of tool geometry complexities. The coefficients of the mechanistic force model are estimated by applying a genetic algorithm in overcoming the lack of explicit normal equations. Then the forces occurring due to flank wear are modeled by extending a 2D worn tool force modeling approach into a three-dimensional analysis to accommodate the effect of low feed rate, small depth of cut, and relatively large tool nose radius in hard turning. The total cutting forces are the linear summation of forces due to chip formation and forces due to flank wear. The model-predicted forces match well with experimental results in the turning of hardened 52100 bearing steel under practical cutting conditions (low feed rate, small depth of cut, and gentle cutting speed) using cubic boron nitride (CBN) tools under the progressive tool flank wear conditions.

Monitoring force in precision cylindrical grinding

Abstract Aerostatic spindles are used in precision grinding applications requiring high stiffness and very low error motions (5–25 nm). Forces generated during precision grinding are small and present challenges for accurate and reliable process monitoring. These challenges are met by incorporating non-contact displacement sensors into an aerostatic spindle that are calibrated to measure grinding forces from changes in the gap between the rotor and stator. Four experiments demonstrate the results of the force-sensing approach in detecting workpiece contact, process monitoring with small depths of cut, detecting workpiece defects, and evaluating abrasive wheel wear/loading. Results indicate that force measurements are capable of providing useful feedback in precision grinding with excellent contact sensitivity, resolution, and detection of events occurring within a single revolution of the grinding wheel.

2608 高硬度微細形状部品の精密切削に関する研究(S71-2 高速・高精度加工とエコマシニング(2),S71 高速・高精度加工とエコマシニング)

This paper describes a basic machinability of hardened steel in precision cutting. High accuracy and high efficiency machining of micro parts such as a contact probe for a current inspection of semiconductor has been demanded. For its realization, it is essential to understand the micro cutting phenomenon such as the surface texture, the tool wear with small depth of cut and low cutting speed. In this study, the precision cutting experiments of a carbon tool steel (SK105) by cermet and ultra-fine grained carbide tools were carried out with an ultra-precision cutting machine. It was found that the feed rate, the cutting speed and the edge sharpness of tool significantly influence the surface finish.

In-process force monitoring for precision grinding semiconductor silicon wafers

Forces generated during precision wafer grinding are small and present challenges for accurate and reliable process monitoring. In this work, these challenges are met by incorporating noncontact displacement sensors into an aerostatic spindle that is calibrated to measure grinding forces from the relative motion between the spindle rotor and stator. This arrangement allows the calculation of grinding forces without introducing compliance into the structural loop of the grinding machine. Aerostatic spindles are used in precision wafer grinding requiring high stiffness and very low error motions (5-25 nm). Several experiments evaluate this force sensing approach in detecting workpiece contact, process monitoring with small depths of cut, and detecting workpiece defects. The results indicate that force measurements offer good performance for monitoring precision wafer grinding since this approach provides excellent contact sensitivity, high signal resolution, and has sufficient bandwidth to detect events occurring within a single revolution of the grinding wheel.

A general algorithm for profiling and dressing grinding wheels when using a grinding spindle on a CNC lathe

Remarkable progress is being made in the technology for grinding complicated geometrical parts. Today, some factories are considering adding a grinding spindle to a turning lathe to save buying an additional expensive new grinding machine. The grinding spindle will be interchangeable with a turning boring bar and it will need two types of software. First is a program and subroutine to control the machine movement during the grinding profile of the work-piece. Second a program and a subroutine are needed to profile the new grinding wheels according to the grinding profiles of the work-piece, as well as dressing the grinding wheels after usage. In the case of a very small depth of cut, a long program will be required. Each different shape of grinding wheel will require different software. There are no detailed descriptions for this problem in the literature or machine manuals. This paper presents a general algorithm to make the profiling and dressing programs for grinding wheels easier. The programmer will use this algorithm for creating a subroutine suitable for the machine dressing system. This algorithm can be used on grinding machines as well as on an additional grinding spindle on a hollow spindle lathe. This subroutine will be used for profiling and dressing the most common shape of grinding wheels. The programmer will then only need to fill in the parameters which describe the contour of the grinding wheels. This algorithm has been applied on a hollow spindle lathe equipped with a numerical Sinumeric 840C control. Several grinding wheels have been profiled and dressed using the proposed approaches, and satisfactory results were obtained.

Microstructural and reliability in grinding of silicon nitride

Abstract A sintered Si 3 N 4 matrix has been characterized by TEM. The film thickness distribution of Si 3 N 4 was measured by high resolution transmission electron microscopy (HREM). Surface grinding is performed on two table speeds of 0.08 and 0.25 m s −1 with different depth of cut. The ground surfaces were observed with scanning electron microscopy (SEM). The surface texture was found to have greater dependence on depth of cut and table speed. The surface roughness is improved after smaller depth of cut. The flexural strength of ground specimens were measured by four-point flexure tests. The effect of depth of cut during grinding on the flexural strength and reliability of silicon nitride is investigated. The large depth of cut of 30 μm/pass resulted in a further decreased in strength of 540 MPa and a Weibull modulus of 7.5. When the depth of cut of 5 μm/pass were subjected to the ground specimens, the average strength was increased to 670 MPa and Weibull modulus to 9.1.

Brittle-ductile transition in monocrystalline silicon analysed by molecular dynamics simulation

For a better understanding of essential mechanisms of material removal at extremely small depth of cut and of the brittle-ductile transition in the material removal process of monocrystalline silicon, nonometric deformation behaviour in three-point bending of defect-free monocrystalline silicon is analysed by molecular dynamics (MD) computer simulation. MD simulations show that plastic deformation takes place through a phase transformation from diamond to amorphous structures. The critical octahedral shearing stress for phase transformation is estimated to be 12–14 GPa. In the deformed region, a crack nucleus on atomic scale can be generated owing to thermally activated vibration of atoms. After the crack nucleus, the crack extension takes place under a certain stress field. The crack initition takes place when a tensile stress reaches a certain critical value of about 30 GPa at the crack nucleus. The critical values for plastic deformation and crack initiation depend on crystal orientation and hydrostatic pressure. It is shown that there can also be critical criteria of the stress field to determine whether plastic deformation or crack initiation would predomiantly take place. When the plastic deformation proceeds to a crack initiation, ductile mode machining can be realized.

Residual stress and surface roughness when facing age hardened Inconel 718 with CBN and ceramic cutting tools

The demand for increasing productivity when machining heat resistant super alloys has resulted in the use of advanced cutting tools such as ceramics and cubic boron nitride (CBN). However, the effects of these tools on the surface integrity, especially the residual stresses created, in the high speed facing operation of Inconel 718 has not been dealt with. In this paper, the residual stresses and the surface roughness when facing age hardened Inconel 718 using CBN and mixed ceramic cutting tools at their respective optimum performance based on productivity has been investigated. The residual stress and surface finish generated during facing with CBN cutting tools have been investigated as a function of speed, depth of cut, coolant, tool geometry and nature of the tool coating. In addition, mixed ceramic cutting tools have been investigated for comparison. The results show that mixed ceramic cutting tools induce tensile residual stresses with a much higher magnitude than CBN cutting tools. The residual stresses and the surface roughness generated by CBN cutting tools are more sensitive to cutting speeds than depth of cut. The use of coolant results in either compressive residual stresses or lowers the magnitude of the tensile residual stresses, whereas dry cutting always resulted in tensile residual stresses. From this investigation, it is suggested that round CBN cutting tools should be used at slow cutting speeds (150 m/min) and small depths of cut (0.05 mm) and with the use of coolant to achieve compressive or minimal tensile residual stresses and good surface finish.

Cutting Force Prediction in End Milling with Small Depth of Cut in Consideration of Cutting Situation Change

The study deals with an accurate cutting error prediction of end milling in the finishing operation. As it was indicated that the consideration of cutting edge roundness improves the accuracy of cutting force simulation, a new estimation method of cutting force has been proposed for end milling with the straight flute tools, based on the calculation of the actual depth of cut. The influence of cutting edge roundness was not considered in the conventional cutting error prediction. Then, the study proposes an extended estimation method of cutting error for the helical flute end mill. It is necessary to calculate the actual depth of cut with an accurate description method of workpiece surface since the amount of cutting error on workpiece surface usually changes with the height of a cutting flute. As a change in workpiece surface in machining is correctly estimated by the calculation of the actual depth of cut, the estimation of cutting error is attained by referring to the form of machined workpiece surface, which is left behind after the end mill passed. A prototype of simulation system is developed, based on the proposed method. The effectiveness of the proposed estimation method is demonstrated by making cutting experiments with helical flute end mill under the cutting condition of finishing operation. The predicted cutting error shows a good qualitative agreement with the measured one, thus the more accurate prediction of cutting error is realized by the proposed method.

102 マイクロボールエンドミルによるガラスの高能率切削(OS12 最新切削加工)

A very small depth of cut has achieved the crack-free removal of brittle materials, known as ductile mode machining. Because a ball end mill has complex shape of cutting edge, cutting situations vary widely according to the change of tool-workpiece interference region. It hasn't been, clarified how the change of cutting situations of a ball end mill affects brittle-ductile transition. This report investigates inclination and tilt of a micro ball end mill affects to the brittle-ductile transition in machining of the borosilicate glass. As a result, it is found that inclination and tilt of a micro ball end mill have a significant effect on the brittle-ductile transition. Deep depth of cut with good finished surface by ductile mode cutting is obtained using a ball end mill vertically to the workpiece surface at a tool feed rate 0.078mm/s.

Finite element analysis of the structural dynamics of a vertical milling machine

The structural stiffness of a machine tool is one of the main criteria that establishes its ability to produce accurate precision components. High stiffness is required both statically and dynamically each affecting different aspects of the machming process. The need for high static stiffness arises from the requirement to produce parts to a desired size and shape [l] and although finish machining often takes place with small depths of cut and correspondingly light cutting forces, the resulting deflections can still be excessively large if the machme has inadequate static stiffness. The resulting deflection can thus produce out of tolerance work-pieces. The need for high dynamic stiffness results from two separate aspects of the machining process. In the first case inadequate dynamic stifhess will result in poor quality surface finish of the machined parts due to relatively low levels of vibration occurring during finish machining operations. In the second case low dynamic stiffness can have more serious consequences when under heavy machining conditions the resulting vibration might be sufficiently high to cause the process to be terminated in-order prevent possible damage to the machine. Traditionally machme tool structures were designed from experience with limited aid from manually carried out calculations using classical theory for such as beam bending, twist and shear. With the advent of powerful desktop computers and the associated Finite Element Software, at costs that are within the grasp of the typical machine tool manufacturer, it is now possible to determine the structural stiffness values for maclvne tools to a hgh order of accuracy and in a relatively short time scale. This paper outlines the static and dynamic structural analyses of a vertical milling machine that were to be subsequently validated against measured results [2, 31.

単結晶シリコンの超精密加工におけるクラック発生に及ぼす結晶方位の影響

The crack-free removal of material, known as ductile mode machining, has been achieved by a very small depth of cut. In this study, the nano-scale layers of single-crystal silicon surface are machined by micro-Vickers hardness indenter witch is assumed to be a single abrasive grain. The subsurface crack as well as the surface crack are observed by a scanning prove microscope and a scanning laser microscope. When surface cracks are not observed by decreasing the depth of cut, the machining has been commonly considered to be in ductile mode. Although crack-free machining seems to be accomplished, the subsurface crack progress under the groove. The transition point determined by the subsurface crack is found to be a more shallow depth of groove than the point by the surface crack. Therefore the evaluation of the subsurface crack is significant especially in finish machining. The dependency of the depth of the subsurface crack on crystallographic direction is revealed. This dependency is due to the fact that mechanical properties of single-crystal silicon are affected by the crystallographic direction.