Further Development of Oxley’s Predictive Force Model for Orthogonal Cutting

An analytical modelling approach based on Oxley's predictive machining theory is presented to evaluate the cutting forces, chip thickness and temperature distributions in the orthogonal cutting process. In this approach, the work material properties are modelled using the Johnson–Cook constitutive material law, which represents the flow stress of the material as a function of strain, strain rate, and temperature. For the determination of the tool-chip interface temperature, an evenly distributed rectangular heat source near the cutting edge is used instead of a plane heat source. The tool thermal model is simplified by neglecting the temperature variations along the tool-chip interface to avoid the high cost of computation time. Finite difference method is applied for solution of the thermal model. The performance of the developed model is validated with the experimental data in machining of steel 1045. A comparison of the outputs from Oxley's original model and the modified model is provided. The model is further assessed by using two other materials, Al 6086-T6 and Ti6Al4V. Close agreements with experimental results have been shown.     

Failure mechanisms of a PCD tool in high-speed face milling of Ti–6Al–4V alloy

High-speed milling tests were carried out on Ti–6Al–4V titanium alloy with a polycrystalline diamond (PCD) tool. Tool wear morphologies were observed and examined with a digital microscope. The main tool failure mechanisms were discussed and analyzed utilizing scanning electron microscope, and the element distribution of the failed tool surface was detected using energy dispersive spectroscopy. Results showed that tool flank wear rate increased with the increase in cutting speed. The PCD tool is suitable for machining of Ti–6Al–4V titanium alloy with a cutting speed around 250 m/min. The PCD tool exhibited relatively serious chipping and spalling at cutting speed higher than 375 m/min, within further increasing of the cutting speed the flank wear and breakage increased greatly as a result of the enhanced thermal–mechanical impacts. In addition, the PCD tool could hardly work at cutting speed of 1,000 m/min due to the catastrophic fracture of the cutting edge and intense flank wear. There was evidence of workpiece material adhesion on the tool rake face and flank face in very close proximity to the cutting edge rather than on the chipped or flaked surface, which thereby leads to the accelerating flank wear. The failure mechanisms of PCD tool in high-speed wet milling of Ti–6Al–4V titanium alloy were mainly premature breakage and synergistic interaction among adhesive wear and abrasive wear.     

Investigation of Tool Wear and Surface Finish by Analyzing Vibration Signals in Turning Assab-705 Steel

Various occurrences in machining influence the machining dynamics and thus produce vibration in the cutting tool-workpiece arrangement. In this investigation, with tri-axial accelerometer mounted on the tool-holder in turning ASSAB-705 steel, vibration signals have been captured with and without cutting. The nature of vibrations arising in the cutting tool at different cutting conditions has been investigated. It has been observed that the RMS amplitude of vibration along all three axes for the increasing cutting speed was mixed in nature; however, an increasing trend was noticed in the vibrations along the feed, V_x and radial, V_y directions. The vibration along the main cutting direction, V_z was mixed, initiated by large vibration and then decreased until a particular cutting speed was reached and finally increased steadily. The feed vibration component, V_x has a similar response to the change of the workpiece surface roughness, while the other two components, V_y and V_z have the more coherent response to the rate of flank wear progression throughout the tool life. The natural frequency of different machine parts vibration has been found to be within the band of 0 Hz – 4.2 kHz, whereas the frequencies of different occurrences in turning varied between 98 Hz and 42 kHz.     

Thermal modeling of drilling process in titanium alloy (Ti-6Al-4V)

Abstract

In drilling in titanium alloys, heat trapped in a hole adversely affects tool life, hole surface quality and integrity. Therefore, modeling temperature distribution in drilling is vital for effective heat dissipation and improving quality of drilled surfaces. The existing numerical and finite element models consider only frictional heat, whereas the effect of shear heat generation and tertiary heat generation is neglected. In the present work, a comprehensive thermal model of the drilling process is developed by considering all heat generated in shear, friction and tertiary zones. The drill cutting edges are divided into a series of independent elementary cutting tools (ECT). The calculated heat flux loads are applied on an individual ECT in the finite element model to determine the temperature distribution and the maximum temperature around the cutting edge. The temperature in the drill was also measured experimentally with the help of an Infrared (IR) camera. The results of numerical simulations lie within the error of ～8.75% when compared to the prior studies, and ～5.41% when compared to our experimental work. The thermal model gives the temperature distribution, and the maximum temperature observed at the corner of cutting edge was 604.2°C at a cutting speed of 35?m/min.     

Finite element modeling of micro-milling: Numerical simulation and experimental validation

In this study, micro-milling of Inconel 718 was investigated. For this purpose, cutting tests were conducted by using uncoated tools and taking four different feed rates (1.25, 2.5, 3.75, and 5 µm/flute) and a constant cutting velocity (48 m/min) into account. In numerical modeling, thermomechanical behavior was modeled using the modified Johnson–Cook material model. Analyses were also conducted for different cutting tool edge angles (+8°, 0, and ?8°). In the numerical analyses, cutting force, tool stress, and cutting temperature values were estimated depending on tool rotation and cutting tool edge type and compared with experimental results. When the results obtained from the study are considered, it is seen that the experimental cutting force and temperature values are in harmony with the numerical results. Moreover, it is seen that there is an increase in cutting force, cutting temperature, and stress values depending on the feed rate. In addition, in the numerical analyses for different cutting tool edge geometries it was observed that cutting force temperature and tool stress values varied depending on the edge geometries.     

Effects of Cutting Parameters on Tool Insert Wear in End Milling of Titanium Alloy Ti6A14V

Titanium alloy is a kind of typical hard-to-cut material due to its low thermal conductivity and high strength at elevated temperatures, this contributes to the fast tool wear in the milling of titanium alloys. The influence of cutting conditions on tool wear has been focused on the turning process, and their influence on tool wear in milling process as well as the influence of tool wear on cutting force coefficients has not been investigated comprehensively. To fully understand the tool wear behavior in milling process with inserts, the influence of cutting parameters on tool wear in the milling of titanium alloys Ti6Al4 V by using indexable cutters is investigated. The tool wear rate and trends under different feed per tooth, cutting speed, axial depth of cut and radial depth of cut are analyzed. The results show that the feed rate per tooth and the radial depth of cut have a large influence on tool wear in milling Ti6Al4 V with coated insert. To reduce tool wear, cutting parameters for coated inserts under experimental cutting conditions are set as: feed rate per tooth less than 0.07 mm, radial depth of cut less than 1.0 mm, and cutting speed sets between 60 and 150 m/min. Investigation on the relationship between tool wear and cutting force coefficients shows that tangential edge constant increases with tool wear and cutter edge chipping can lead to a great variety of tangential cutting force coefficient. The proposed research provides the basic data for evaluating the machinability of milling Ti6Al4 V alloy with coated inserts, and the recommend cutting parameters can be immediately applied in practical production.     

Effects of cutting parameters on tool insert wear in end milling of titanium alloy Ti6Al4V

Titanium alloy is a kind of typical hard-to-cut material due to its low thermal conductivity and high strength at elevated temperatures, this contributes to the fast tool wear in the milling of titanium alloys. The influence of cutting conditions on tool wear has been focused on the turning process, and their influence on tool wear in milling process as well as the influence of tool wear on cutting force coefficients has not been investigated comprehensively. To fully understand the tool wear behavior in milling process with inserts, the influence of cutting parameters on tool wear in the milling of titanium alloys Ti6Al4V by using indexable cutters is investigated. The tool wear rate and trends under different feed per tooth, cutting speed, axial depth of cut and radial depth of cut are analyzed. The results show that the feed rate per tooth and the radial depth of cut have a large influence on tool wear in milling Ti6Al4V with coated insert. To reduce tool wear, cutting parameters for coated inserts under experimental cutting conditions are set as: feed rate per tooth less than 0.07 mm, radial depth of cut less than 1.0 mm, and cutting speed sets between 60 and 150 m/min. Investigation on the relationship between tool wear and cutting force coefficients shows that tangential edge constant increases with tool wear and cutter edge chipping can lead to a great variety of tangential cutting force coefficient. The proposed research provides the basic data for evaluating the machinability of milling Ti6Al4V alloy with coated inserts, and the recommend cutting parameters can be immediately applied in practical production.     

Tool edge radius effect on cutting temperature in micro-end-milling process

The cutting temperature plays an important role in micro-scale cutting process due to the fact that the dimension of the micro-cutter is small and the value of micro-cutter wear is sensitive to temperature. In this paper, the temperature distribution of the micro-cutter in the micro-end-milling process has been investigated by numerical simulations and experimental approach. Micro-end-milling processes are modeled by the three-dimensional finite element method coupling thermal?Cmechanical effects. The micro-cutter cutting temperature distribution, the effect of various tool edge radii on cutting force, and the effective stress during micro-end-milling of aluminum alloy Al2024-T6 using a tungsten-carbide micro-cutter are investigated on. The simulation results show that with increase of tool edge radius the cutting force increases, while the effective stress and mean cutting temperature decreases slightly. In increasing the tool edge radius, the maximum effective stress and cutting temperature region of the micro-cutter occur from the rake face to the corner on the tool edge and the flank face. The tool edge radius has been found to be the major factor affecting micro-cutter temperature distribution. The experimental verification of the simulation model is carried out on a micro-end-milling process of aluminum alloy 2024-T6 with a high-precision infrared camera. The influence of tool edge radius on cutting temperature distribution was verified in experiments.     

Finite element analysis of the influence of tool edge radius on size effect in orthogonal micro-cutting process

The size effect in metal cutting is evident in the nonlinear scaling phenomenon observed in the specific cutting energy with decrease in uncut chip thickness. It has been argued by many researchers that this scaling phenomenon is caused mainly by the cutting tool edge radius, which purportedly affects the micro-cutting process by altering the effective rake angle, enhancing the plowing effect or introducing an indenting force component. However, the phenomenological reasons why the tool edge radius causes size effect and the relationship between the tool edge radius and the characteristic length scale associated with the size effect in micro-cutting has not been sufficiently clarified. In this paper, a strain gradient plasticity-based finite element model of orthogonal micro-cutting of Al5083-H116 alloy developed recently is used to examine fundamentally the influence of tool edge radius on size effect. The applicability of two length scales—tool edge radius and the material length scale l in strain gradient plasticity—are also examined via analysis of data available in the literature.     

FUZZY EXPERT SYSTEM FOR PREDICTION OF KERF QUALITIES IN PULSED LASER CUTTING OF TITANIUM ALLOY SHEET

Laser cutting is an advanced thermal cutting process of complex nature. It's process behavior drastically changes with slight variation in processing conditions. The prediction of process performance becomes more difficult if cutting materials have non-favorable optical and thermal properties. Titanium (Ti) alloys are characterized by their low thermal conductivity and high chemical reactivity at elevated temperature and hence difficult to cut by laser. It has been found that complex and nonlinear behavior of manufacturing process can better be dealt with the application of artificial intelligence (AI) tools. The aim of present research is to develop a fuzzy expert system for prediction of the laser cutting process behavior of Ti alloy (Ti-6Al-4 V) sheet. A hybrid approach of neural network and fuzzy logic theory has been applied to develop the fuzzy expert system to predict the kerf widths and kerf deviation. The predicted results have been compared with the experimental data and found appropriate. The effects of significant process parameters on the different quality characteristics such as kerf widths and kerf deviation have been discussed.     

A comparative study of multilayer and functionally graded coated tools in high-speed machining

Multilayer-coated tool systems have been effective in controlling mechanical and thermal loads, especially in high-speed cutting regime. In this study, cutting performance of tungsten carbide tools with restricted contact length and multilayer chemical vapour deposition deposited coatings, TiCN/Al₂O₃/TiN (in series) and TiCN/Al₂O₃–TiN (functionally graded), was investigated in dry turning. Cutting tests were conducted on low carbon alloy steel AISI/SAE 4140 over a wide range of cutting speeds between 200 and 879?m/min. Results including cutting forces, chip compression ratio, shear angle, contact area inclusive of sticking and sliding phenomena and tool flank wear are presented. In particular, prediction of heat partition into the cutting tool inserts was carried out using a combination of experimental tests and the finite element method. The results show that coating layouts and cutting tool edge geometry can significantly affect heat distribution into the cutting tool. The paper clearly shows the role and potential benefits of applying different top coats on the rake and flank faces with regards contact phenomenon, impact on thermal shielding and tool wear. An appropriate coating layout selection is crucial in controlling tool wear, especially in high-speed machining.     

WEAR PERFORMANCE OF MULTILAYER-COATED CARBIDE TOOLS

Three multilayer-coated carbides [two trigon-shaped inserts: Ti(C,N)/TiC/Al₂O₃ (T1), Ti(C,N)/ Al₂O₃/TiN (T2) and one 80°-rhomboid shaped insert: TiC/Al₂O₃/TiN (T3)] were used to machine a martensitic stainless steel at various combinations of cutting speed and feed rate without coolant to assess their wear performance. Significant nose wear and chipping/fracture of the cutting edge were the predominant failure modes affecting tool performance at higher speed conditions. Plucking of tool materials was the main rake face wear phenomenon observed on T1 grade insert with alumina as the top-layer coating when machining at the lower speed conditions. Attrition and plastic flow were the main wear mechanisms observed on the ceramic coating layers, with dissolution-diffusion being the probable wear mechanism of the tool grades where tungsten carbide substrate had direct contact with the flowing chip. The fitted statistical wear models revealed T3 grade insert with 80°-rhomboid shape as having the highest speed-feed capability, resulting in the highest material removal rate relative to T1 and T2 grade inserts with trigon shapes.     

用数值仿真优选Al2O3/ZrO2(Y2O3)陶瓷刀具的切削参数

用数值仿真分析Al2O3/ZrO2(Y2O3)陶瓷刀具切削刃表面的温度场、应力场变化。采用瞬态和稳态有限元法确定模拟的初始变量,基于Deform2D和Johnson-Cook流变模型构建仿真切削模型,并对Al2O3/ZrO2(Y2O3)陶瓷刀具加工1045淬火钢进行仿真切削,实际切削和仿真切削的结果对比具有等同的一致性。结果表明,用Lagrange和任意拉格朗日欧拉方法获得稳态切削时刀刃接触表面的温度场和应力场,当改变切削速度和进给量参数时,将引起温度场和应力场的梯度变化,由此优选出最佳切削加工条件(切削速度vc、进给量f),为诊断陶瓷刀具的切削寿命和可靠性提供了理论数据。     

Studies on high-efficiency and high-precision orthogonal turn-milling-The effects of relative cutting speed and tool axis offset on tool flank temperature

The cutting-edge temperature on the flank face in dry turn-milling of medium carbon steel (ISO C45) is measured using a two-color pyrometer with an optical fiber. In turn-milling, undeformed chip geometry is complex due to its dependence on several factors including diameter of the cutting tool, number of tooth, diameter of the workpiece, tool-work revolution speed ratio, depth of cut, feed per tooth, tool axis offset, and the cutting distance. In this study, the undeformed chip is analyzed and visualized by the 3D-CAD system, and the effects of the cutting parameters in turn-milling, especially relative cutting speed and tool axis offset on tool flank temperature, are investigated. It is interesting that the relative cutting speed does not significantly affect the tool flank temperature, where it increases by approximately 20 °C at most when relative cutting speed increases from 124 m/min to 217 m/min. In addition, tool flank temperature varies by approximately 40 °C when the tool axis offset is changed from 0 mm to 9.2 mm due to the change in the undeformed chip geometry.     

不同涂层刀具切削淬硬H13钢加工性能研究

为了研究不同涂层刀具切削淬硬H13钢的切削性能,进行了多层Ti化合物涂层、TiAlN涂层以及MTTiCN厚Al_2O_3TiN涂层材料刀具车削加工淬硬H13钢试验,分析了不同的涂层材料刀具与切削力、切削温度、涂层刀具磨损以及刀具寿命的关系。研究得出:多层Ti化合物涂层刀具受到三个方向的力都大于其它两种涂层的刀具,而且切削温度最高;用TiAlN涂层刀具切削时温度最低;切削过程中三种刀具后刀面磨损程度不同,发现多层Ti化合物涂层刀具磨损最为严重,寿命最短;MT-TiCN厚Al_2O_3Ti N涂层材料刀具比多层Ti化合物涂层刀具寿命长30%;TiAlN涂层刀具的切削寿命最长比多层Ti化合物涂层刀具寿命长45%。     

A comparative study of the tool–chip contact length in turning of two engineering alloys for a wide range of cutting speeds

Tool chip contact length is an important parameter in machining, as it provides an indication of the size of area of interaction between the hot chip and the tool surface and hence the interface heat transfer zone. Heat transfer and thermally activated wear modes usually dominate tool wear in the high speed machining of steels and machining of titanium alloys at most cutting speeds. In this study, existing models for the prediction of tool–chip contact length are reviewed and examined for their suitability in high speed machining of two widely used engineering alloys. Orthogonal turning tests for AISI 1045 steel and Ti6Al4V titanium alloy are conducted for a range of cutting speeds from conventional to high speeds. New contact length models are presented for both materials covering a wide range of cutting speeds. More significantly, these contact length models are appropriate for high speed machining where thermal loads significantly influence process performance. Additionally, the work discusses how the machinability of engineering materials influences the ability to predict contact length.     

In-service behaviour of (Ti,Si,Al)Nx nanocomposite films

This paper reports on the optimization of (Ti,Si_,Al)N_x coatings to improve the performance of coated tools in dry cutting applications. The performance and the wear mechanisms of (Ti,Si_,Al)N_x tungsten carbide coated tools were investigated. Tool life and tool failure modes were thoroughly examined by scanning electron microscopy (SEM) complemented with energy dispersive spectroscopy (EDS) in order to study the wear mechanisms. After 15 min at high cutting speed (200 m/min), the cutting edges of almost all the coatings still remained in good conditions. The results presented on this paper confirmed that nc-(Ti_1?xAl_x)/a-SiN_x nanocomposite coatings offer a significant potential to operate in extreme environments, since this coating outperformed one of the best solutions actually available in the market for high speed turning. An improvement on the tribological behaviour of (Ti,Si_,Al)N_x films was also observed with thermal annealing before the turning tests, due to a self hardening effect as consequence of the spinodal segregation of the (Ti,Al,Si)N metastable phase. On the other hand, no significative increase on the performance of the coated tools was observed with depositing an amorphous Al₂O₃ interlayer.     

Comparative evaluation of machinability characteristics of Nimonic C-263 using CVD and PVD coated tools

Machining of Nimonic C-263 has always been a challenging task owing to its hot strength, low thermal conductivity, tendency to work harden and affinity towards tool materials. Although coated tools have been used to overcome some of these challenges, selection of coated tool with appropriate deposition technique is of immense significance. The current study attempts to comparatively evaluate various performance measures in machining of Nimonic C-263 such as surface roughness, cutting force, cutting temperature, chip characteristics, and tool wear with particular emphasis on different modes of tool failure for commercially available inserts with multi-component coating deposited using chemical vapour deposition (CVD) and physical vapour deposition (PVD) techniques. Influence of cutting speed (V_c) and machining duration (t) has also been investigated using both coated tools. The study demonstrated remarkable decrease in surface roughness (74.3%), cutting force (6.3%), temperature (13.4%) and chip reduction coefficient (22%) with PVD coated tool consisting of alternate layers of TiN and TiAlN over its CVD coated counterpart with TiCN/Al₂O₃ coating in bilayer configuration. Severe plastic deformation and chipping of cutting edge and nose, abrasive nose and flank wear along with formation of built-up-layer (BUL) were identified as possible mechanisms of tool failure. PVD coated tool successfully restricted different modes of tool wear for the entire range of cutting speed. Superior performance can be attributed to the hardness and wear resistance properties, thermal stability due to presence of TiAlN phase and excellent toughness owing to PVD technique and multilayer architecture.     

Calculation of negative-pressure chip in suction-type internal chip removal system and analysis of influencing factors

Compacted graphite iron (CGI) is considered as the ideal material to make modern fuel-efficient diesel engine. Due to the vermicular or worm-like graphite distributed among the ferrite/pearlite matrix, CGI behaves better physical and mechanical properties in comparison with gray cast iron (GCI) and spherical graphite spheroidal cast iron (SGI). However, these good properties bring about the machining challenges. So it is important to appropriately select cutting parameters to machine this material with economy and efficiency. The present study investigated the influence of cutting parameters, such as cutting speed V, feed rate f, and exit angle Ψ, on workpiece material removal volume Q and cutting burr height on the entrance side H₁ and on the exit side H₂ during high-speed milling of CGI by the coated carbide tools_. On this basis, the relatively optimum high-speed cutting parameters were selected under the research condition. Cutting tool failure mechanism was also investigated with the aid of scanning electronic microscope (SEM) and energy-dispersive system (EDS) (SUPRA55, Germany) analysis. The results showed that Q, H₁, H₂, and the type of cutting burr on the exit side of the machined surface could be influenced by the cutting parameters. And the relatively optimum cutting parameters are V = 800 m/min, f = 0.25 mm/rev, and Ψ = 60°. Adhesive wear and thermal cracks which were perpendicular to the cutting edge were common wear mechanisms during the cutting process. However, with an increase in feed rate, mechanical cracks which were parallel to the cutting edge could be found on the flank face of the cutting tool.     

Temperature measurement and machining damage in slotting of multidirectional CFRP laminate

Compared to metallic materials, carbon fiber-reinforced plastics (CFRPs) have lower thermal conductivity and minor thermal expansion coefficient. Despite this, their machining can generate accuracy errors if the cutting temperature is not controlled. In this paper, an experimental study of slotting of multidirectional CFRP laminate (G803/914) with three micrograin carbide burr tools with different geometries is considered in order to investigate tool-workpiece contact point temperature, chip temperature, machined surface damage, subsurface defects and tool degradation. The experiment is made on a computer numerical control (CNC) machine with cutting speed ranging from 80 to 200 m/min and feed per tooth from 0.008 to 0.060 mm/rev/tooth. The data were analyzed in order to establish empirical models showing the dependence of cutting temperature on tool geometry and cutting conditions. Based on the results, it is concluded that cutting speed is the factor influencing cutting temperature the most, the heat generated during slotting is removed mainly by chips and the chip temperature is greater than the tool-workpiece contact temperature of about 18.5°C on average for the three burr tools.