Investigation of the effect of rake angle and approaching angle on main cutting force and tool tip temperature

This paper deals with the comparison of measured and calculated results of cutting force components and temperature variation generated on the tool tip in turning for different cutting parameters and different tools having various tool geometries while machining AISI 1040 steel hardened at HRc 40. The geometric variables (approaching angle and rake angle) of the tool were changed using selected cutting parameters; thus, the cutting force components and temperature variations on tool face (in secondary shear zone) were determined. The selected cutting variables and the tools in different geometries were tested practically under workshop conditions. In this way, the essential information about the validity of selected values was obtained. During the tests, the depth of cut and cutting speed were kept constant and each test was conducted with a sharp uncoated tool insert. For making a comparison, the main cutting force/tangential force component for different cutting parameters and tool geometries were calculated by Kienzle approach and the temperature values were calculated based on orthogonal cutting mechanism. Finally, the effects of cutting parameters and tool geometry on cutting forces and tool tip temperature were analysed. The average deviation between measured and calculated force results were found as 0.37%. The cutting force signals and temperature values provided extensive data to analyse the orthogonal cutting process.     

Statistical analysis of surface roughness and cutting forces using response surface methodology in hard turning of AISI 52100 bearing steel with CBN tool

The present work concerns an experimental study of hard turning with CBN tool of AISI 52100 bearing steel, hardened at 64 HRC. The main objectives are firstly focused on delimiting the hard turning domain and investigating tool wear and forces behaviour evolution versus variations of workpiece hardness and cutting speed. Secondly, the relationship between cutting parameters (cutting speed, feed rate and depth of cut) and machining output variables (surface roughness, cutting forces) through the response surface methodology (RSM) are analysed and modeled. The combined effects of the cutting parameters on machining output variables are investigated while employing the analysis of variance (ANOVA). The quadratic model of RSM associated with response optimization technique and composite desirability was used to find optimum values of machining parameters with respect to objectives (surface roughness and cutting force values). Results show how much surface roughness is mainly influenced by feed rate and cutting speed. Also, it is underlined that the thrust force is the highest of cutting force components, and it is highly sensitive to workpiece hardness, negative rake angle and tool wear evolution. Finally, the depth of cut exhibits maximum influence on cutting forces as compared to the feed rate and cutting speed.     

Tool wear measurement in turning using force ratio

The aim of this work was to develop a reliable method to predict flank wear during the turning process. The present work developed a mathematical model for on-line monitoring of tool wear in a turning process. Force signals are highly sensitive carriers of information about the machining process and, hence, they are the best alternatives for monitoring tool wear. In the present work, determination of tool wear has been achieved by using force signals. The relationship between flank wear and the ratio of force components was established on the basis of data obtained from a series of experiments. Measurement of the ratio between the feed force and the cutting force components (F_f/F_c) has been found to provide a practical method for an in-process approach to the quantification of tool wear. A series of experiments was conducted to study the effects of tool wear as well as other cutting parameters on the cutting force signals, and to establish a relationship between the force signals, tool wear and other cutting parameters. The flank wear and the ratio of forces at different working conditions were collected experimentally to develop a mathematical model for predicting flank wear. The model was verified by comparing the experimental values with the predicted values. The relationship was then used for determination of tool flank wear.     

Performance of carbide tools with textured rake-face filled with solid lubricants in dry cutting processes

Surface texturing with different geometrical characteristics was made on the rake face of the WC/Co carbide tools, molybdenum disulfide (MoS₂) solid lubricants were filled into the textured rake-face. Dry cutting tests were carried out with these rake-face textured tools and a conventional tool. The effect of the texture shape on the cutting performance of these rake-face textured tools was investigated. Results show that the cutting forces, cutting temperature, and the friction coefficient at the tool-chip interface of the rake-face textured tools were significantly reduced compared with that of the conventional one. The rake-face textured tool with elliptical grooves on its rake face had the most improved cutting performance. Two mechanisms responsible were found, the first one is explained as the formation of a lubricating film with low shear strength at the tool-chip interface, which was released from the texturing and smeared on the rake face, and served as lubricating additive during dry cutting processes; the other one was explained by the reduced contact length at the tool-chip interface of the rake-face textured tools, which contributes to the decrease of the direct contact area between the chip and rake face.     

An innovative experimental study of corner radius effect on cutting forces

The cutting forces are often modelled using edge discretisation methodology. In finish turning, due to the smaller corner radii, the use of a local cutting force model identified from orthogonal cutting tests poses a significant challenge. In this paper, the local effect of the corner radius r_? on the forces is investigated using a new experimental configuration: corner cutting tests involving the tool nose. The results are compared with inverse identifications based on cylindrical turning tests and elementary cutting tests on tubes. The results obtained from these methods consistently show the significant influence of the corner radius r_? on the cutting forces.     

Cutting temperature of ceramic tools in high speed machining of difficult-to-cut materials

This paper deals with an experimental and analytical investigation into the different factors which influence the temperature distribution on Al₂O₃---TiC ceramic tool rake face during machining of difficult-to-cut materials, such as case hardened AISI 1552 steel (60–65 Rc) and nickel-based superalloys (e.g. Inconel 718). The temperature distribution was predicted first using the finite element analysis. Temperature measurements on the tool rake face using a thermocouple based technique were performed and the results were verified using the finite element analysis. Experiments were then performed to study the effect of cutting parameters, different tool geometries, tool conditions, and workpiece materials on the cutting edge temperatures. Results presented in this paper indicate that for turning case hardened steel, increasing the cutting speed, feted, and depth of cut will increase the cutting edge temperature. On the other hand, increasing the tool nose radius, and angle of approach reduces the cutting edge temperature, while increasing the width of the tool chamfer will slightly increase the cutting ege temperature. As for the negative rake angle, it was found that there is an optimum value of rake angle where the cutting edge temperature was minimum. For the Inconel 718 material, it was found that the cutting edge temperature reached a minimum at a speed of 510 m/min, and feed of 1.25 mm/rev. However, the effect of the depth of cut and tool nose radius was almost the same as that determined in the turning of case hardened steel. It was also observed in turning Inconel 718 with ceramic tools that, cutting forces and different types of tool wear were reduced with increasing the feed.     

Extracting cutting force coefficients from drilling experiments

Determining cutting force equations and the associated specific cutting pressures require a relatively large number of orthogonal cutting tests. These tests need to cover wide ranges of cutting speeds, feeds, and rake angles. Given the inherent variation of the rake angle and the tangential velocity over the drill's cutting lip, this work introduces a methodology for extracting these cutting force coefficients by performing a few drilling experiments on pre-drilled pilot holes.First, the contributions of the ploughing forces acting on the lip and margin are determined. Subtracting these edge forces from the measured total values, torque and thrust cutting forces and the corresponding cutting pressure distributions along the lip are derived. These distributions are then used to produce equations that estimate cutting force coefficients over a wide range of cutting parameters. The coefficients determined in this work from drilling experiments in Aluminium 6061-T6 compare favorably with others generated from orthogonal cutting experiments reported in the literature.     

Effects of micro-milling conditions on the cutting forces and process stability

Determining stable cutting conditions for corresponding cutting tools with specific geometries is essential for achieving precision micro-milling with high surface quality. Therefore, this paper investigates the influence of the tool rake angle, tool wear and workpiece preheating on the cutting forces and process stability. An advanced micro-milling cutting force model considering the tool wear is proposed. The micro-milling cutting forces are predicted and compared with experimentally obtained results for two cutting conditions and four edge radii measured at different stages of the tool wear. It is found that the cutting forces increase by increasing the edge radius. It is also observed that the cutting forces are higher at a rake angle of 0° compared with a rake angle of 8°. The increase of the cutting forces is mainly associated with the change of the friction conditions between the tool and workpiece contact. Stability lobes are obtained for different edge radii, rake angles of 0° and 8°, initial workpiece temperature and different measured static run-outs. The predicted stability lobes are compared with the micro-milling force signals transformed into the frequency domain. It is observed that the predicted stability limits result in good correlation with the experimentally obtained chatter free conditions. Also, the stability limits are higher at smaller edge radii, higher preheating workpiece temperature and positive rake angles.     

Simulation of the main cutting force in Crankshaft turn broaching

The measurement of the cutting forces of a turn-broaching machine is very complex due to the relative movement between workpiece and tool. In this work the cutting forces were simulated through the modeling of the process kinematics and by applying the Kienzle equation. A new experimental approach was proposed to determine the cutting forces using a conventional CNC turning machine tool. Through a series of experiments, the model has been calibrated. A comparison between the numerical and experimental results showed a similar trend. The effect of maximum cutting depth, workpiece diameter, cutting edge inclination angle, and feed rate on the main cutting force has been studied.     

Analysis of an equivalent tool face for the cutting speed range prediction of complex grooved tools

Manufacturers need to obtain optimal operating parameters with a minimum set of experiments as well as minimizing the simulations in order to reduce machining set up costs. The cutting speed, V_c, is one of the most important cutting parameter to evaluate; it clearly most influences, on one hand, tool life, tool stability, and cutting process quality, and on the other hand controls production flow. In addition, in today's applications, complex groove geometries have made more difficult the assessment of cutting models for the prediction of tool-material–work-material combination behaviour. In this paper, an original approach based on the experimental estimation of the friction coefficient and enabling to simplify the complex groove geometry in a flat rake face is presented. A model for cutting force prediction is also proposed. Four different complex grooved inserts and three different cutting tool material grades for each insert are studied for the modelling approach. Orthogonal cutting simulations using the Thirdwave Systems’ AdvantEdge code package are compared with experimental measurement. Results show good agreement and that this approach may reduce both number of experiments and simulation times to determine the cutting speed range. Finally, the paper ends with discussions and concluding remarks.     

Performances of micro-textured WC-10Ni3Al cemented carbides cutting tool in turning of Ti6Al4V

Cutting performances of micro-textured WC-10Ni₃Al cutting tools compared with micro-textured WC-8Co cutting tools in turning of Ti6Al4V was investigated in this study. Cutting forces, cutting temperature, and tool life based on the criterion of a 300 μm flank wear were measured. The wear tracks of the rake face and flank face for micro-textured WC-10Ni₃Al cutting tools were analyzed. It is found that WC-10Ni₃Al cutting tools had smaller heat damages during LST compared with WC-8Co cutting tools, which was benefit for avoiding premature tool failure during Ti6Al4V machining process. Micro-textures on the rake face could effectively reduce cutting forces, cutting temperature, adhesion on the rake face, and hence increase tool life, especially at higher cutting speed.     

Modeling of velocity-dependent chip flow angle and experimental analysis when machining 304L austenitic stainless steel with groove coated-carbide tools

This paper presents an analysis of experimental cutting forces and the study of the chip flow angle when machining 304L austenitic steel with a groove coated tool under dry condition. Experiments were conducted on a wide range of cutting conditions with a particular attention to ensure a great confidence in the obtained results. A detailed analysis of experimental cutting forces and the identification of empirical cutting force equations similar to that usually used for flat tools are proposed. The main focus of this work is on the study of chip flow angle deduced here from experimental cutting forces, considering that the chip flow direction is collinear to the friction force. From a comparison between experiments and two often used approaches, it appears that the experimental chip flow angle estimation, based on neglecting the complex tool geometry and adopting a zero rake angle, is bounded by the two considered modelings that renders useful for the proposed study. From experiments it is also observed an increase of the chip flow angle as the cutting velocity is increased. A velocity-dependent modeling with two distinct strategies of identification is then proposed in order to capture the cutting velocity effect on the chip flow angle.     

Accurate 3-D cutting force prediction using cutting condition independent coefficients in end milling

The instantaneous uncut chip thickness and specific cutting forces have a significant effect on predictions of cutting force. This paper presents a systematic method for determining the coefficients in a three-dimensional mechanistic cutting force model—the cutting force coefficients (two specific cutting forces, chip flow angle) and runout parameters. Some existing models have taken the approach that the cutting force coefficients vary as a function of cutting conditions or cutter rotation angle. This paper, however, considers that the coefficients are affected only by the uncut chip thickness. The instantaneous uncut chip thickness is estimated by following the movement of the position of the center of a cutter. To consider the size effect, the present method derives the relationship between the re-scaled uncut chip thickness and the normal specific cutting force, K_n with respect to the cutter rotation angle, while the other two coefficients—frictional specific cutting force, K_f and chip flow angle, θ_c—remain constant. Subsequently, all the coefficients can be obtained, irrespective of cutting conditions. The proposed method was verified experimentally for a wide range of cutting conditions, and gave significantly better predictions of cutting forces.     

Radial immersion angle estimation using cutting force and predetermined cutting force ratio in face milling

Radial immersion ratio is an important factor to determine the threshold for tool conditioning monitoring and automatic force regulation in face milling. In this paper, a method of on-line estimation of the radial immersion angle using cutting force is presented. When a tooth finishes sweeping, a sudden drop of cutting force occurs. This force drop is equal to the cutting force that acts on a single tooth at the swept angle of cut and can be obtained from the cutting force signal in feed and cross-feed directions. The ratio of cutting forces in feed and cross-feed directions acting on the single tooth at the immersion angle is a function of the immersion angle and the ratio of radial-to-tangential cutting force. In this study, it is found that the ratio of radial-to-tangential cutting force is not affected by cutting conditions and axial rake angle. Therefore, the ratio of radial-to-tangential cutting force determined by just one preliminary experiment can be used regardless of the cutting conditions for a given tool and workpiece material. Using the measured cutting force during machining and a predetermined ratio, the radial immersion ratio is estimated in the process. Various experiments show that the radial immersion ratio and instantaneous ratio of the radial to tangential direction cutting force can be estimated very well by the proposed method.     

A model for cutting forces generated during machining with self-propelled rotary tools

In this paper, a force model for self-propelled rotary tool is presented. Conventional oblique cutting force predictions were reviewed and extended to predict the cutting forces generated during machining with the self-propelled rotary tools. The model presented is based on Oxley's analysis and was verified by cutting tests using a typical self-propelled tool. Good agreement was obtained between the predicted and the experimentally measured forces under a wide range of cutting conditions. The effect of different cutting conditions on the friction coefficient along the chip/tool interface and tool rake face normal force were also presented and discussed.     

A study of micropool lubricated cutting tool in machining of mild steel

This paper presents an experimental study of the performance of micropool lubricated cutting tool in machining mild steel. Microholes are made using femtosecond laser on the rake face of uncoated tungsten carbide (WC) cutting inserts. Finite element analysis is conducted to assess the effect of microholes on the mechanical integrity of the cutting inserts. Liquid (oil) and solid (tungsten disulfide) lubricants are used to fill the microholes to form micropools. A comparative study is conducted between micropool lubricated (surface-textured) cutting tools and dry/flood-cooled conventional (untextured) cutting tools. Three cutting force components are measured and compared. Tool–chip contact length and chip morphology are examined using optical microscope. It is found that the mean cutting forces (F_f, F_t, and F_c) are reduced by 10–30% with micropool lubrication. The chip–tool contact length is reduced by about 30%. Coiling chips are produced with micropool lubricated cutting tool while long and straight chips are formed with the conventional cutting tool. Liquid and solid lubricants are found to be equally effective in reducing the contact length and coefficient of friction at the chip–tool interface. There is no adverse effect on the performance of the insert with microholes on the rake face.     

Generalized dynamic model of metal cutting operations

This paper presents a unified mathematical model which allows the prediction of chatter stability for multiple machining operations with defined cutting edges. The normal and friction forces on the rake face are transformed to edge coordinates of the tool. The dynamic forces that contain vibrations between the tool and workpiece are transformed to machine tool coordinates with parameters that are set differently for each cutting operation and tool geometry. It is shown that the chatter stability can be predicted simultaneously for multiple cutting operations. The application of the model to single-point turning and multi-point milling is demonstrated with experimental results.     

A new thermomechanical model of cutting applied to turning operations. Part I. Theory

In this paper, an analytical approach is used to model the thermomechanical process of chip formation in a turning operation. In order to study the effects of the cutting edge geometry, it is important to analyse its global and local effects such as the chip flow direction, the cutting forces and the temperature distribution at the rake face. To take into account the real cutting edge geometry, the engaged part in cutting of the rounded nose is decomposed into a set of cutting edge elements. Thus each elementary chip produced by a straight cutting edge element, is obtained from an oblique cutting process. The fact that the local chip flow is imposed by the global chip movement is accounted for by considering appropriate interactions between adjacent chip elements. Consequently, a modified version of the oblique cutting model of Moufki et al. [Int. J. Mech. Sci. 42 (2000) 1205; Int. J. Mach. Tools Manufact. 44 (9) (2004) 971] is developed and applied to each cutting edge element in order to obtain the cutting forces and the temperature distributions along the rake face. The material characteristics such as strain rate sensitivity, strain hardening and thermal softening, the thermomechanical coupling and the inertia effects are taken into account in the modelling. The model can be used to predict the cutting forces, the global chip flow direction, the surface contact between chip and tool and the temperature distribution at the rake face which affects strongly the tool wear. Part II of this work consists in a parametric study where the effects of cutting conditions, cutting edge geometry, and friction at the tool–chip interface are investigated. The tendencies predicted by the model are also compared qualitatively with the experimental trends founded in the literature.     

工艺参数对单晶硅超精密加工切削力的影响

为了了解单晶硅超精密车削过程中不同切削参数及刀具前角对切削力的影响,利用单晶金刚石车刀对单晶硅进行单因素变量超精密车削试验。试验结果表明:进给量f和切削深度a_p对X、Y、Z方向的切削力F均有增大的趋势;而在切削速度v_c增加时,各方向的F逐渐减小;切削前角减小时,切削力反而增大。通过各因素对切削力F的变化幅值可以得到,对F影响较大的参数为a_p及f。选取最佳组合参数对单晶硅进行超精密切削试验,得到极为光滑的表面。     

The significance of normal rake in oblique machining

3D molecular dynamics (MD) simulations of oblique machining of an aluminum workmaterial with a single straight cutting edge were conducted over a wide range of normal rake angles (−45° to +45°) and inclination angles (0° to 45°). Three distinct rake angles, namely, the normal rake angle, α_n, the velocity rake angle, α_v, and the so-called effective rake angle, α_e, associated with oblique machining were considered. Variation of the three components of force (cutting, thrust, and oblique), force ratio (thrust force/cutting force), and specific energy (energy required for unit volume of material removed) with rake angle and inclination angle were determined. Based on the analysis of the simulation results, it is shown that normal rake angle is the angle of significance influencing the mechanics of oblique machining, especially from the point of view of cutting force and specific energy in machining, as reported at the macro scale by many in the literature.