Tool Rake Face Research Articles

Chip formation and its effects on cutting force, tool temperature, tool stress, and cutting edge wear in high- and ultra-high-speed milling

In the present study, experimental tests and finite element simulation were conducted in order to investigate chip formation and its effects on cutting force, tool temperature, tool stress, and cutting edge wear in high- and ultra-high-speed (v = 200∼2000 m/min) milling. It was found that the serration of chip became more and more obvious as the cutting speed increased. Most of the saw-tooth chip was separated at the cutting speed of 2000 m/min. During the formation process of the separated saw-tooth, the high temperature in the shear band had substantial effect on the initiation of the crack in the chip. When the cutting speed increased, the formation frequency of the saw-tooth increased with decreasing growth rate and the tool-chip contact length exhibited a decreasing trend. At each cutting speed used in the present work, the fluctuation frequency of cutting force, tool temperature, and tool stress was consistent with that of the saw-tooth formation. The saw-tooth formation which led to periodically changing cutting thickness had great effects on the cyclical fluctuations of the cutting force, tool temperature, and tool stress. When the cutting speed increased from 650 to 2000 m/min, the amplitude of the cutting force and tool temperature grew 116 and 93 %, respectively. The higher degree of chip serration at higher cutting speed resulted in the substantial change of the cutting thickness, leading to greater mechanical and thermal impact. The tool temperature had greater effect on the tool stress than the cutting force did when the cutting speed was relatively high. Due to the small tool-chip contact length at cutting speeds of 1550 and 2000 m/min, no obvious wear appeared on the tool rake face. Because of the higher average value and the higher amplitude of tool stress at the cutting speed of 2000 m/min, chipping emerged on the tool cutting edge. This phenomenon was not found on the cutting edge when the cutting speed was 1550 m/min.

Surface textures on cemented carbide cutting tools by micro EDM assisted with high-frequency vibration

This paper demonstrates the process of micro electro-discharge machining (micro EDM) assisted with high-frequency vibration machining micro holes and linear grooves which are straight or inclined on WC/8 % Co (MA) and WC/15 % TiC/6 %Co (MB) cemented carbide cutting tool rake face or scrap reeling slot. Low-voltage sensing contact is introduced to determine the exact position of holes and grooves. Morphology of textured regions is examined and the elemental chemical composition of close proximity region to a straight hole is identified. Results show that micro holes and linear grooves with high dimension accuracy and exact position are machined as expected by micro EDM assisted with high-frequency vibration. There is no debris accumulating around the cavities. Materials of MA cutting tool adhere on the micro tool electrode slightly, while the dimension of adhesion position becomes constant after 3 μ holes are finished. However, the adhesion does not occur during machining MB cutting tools. The distance of edges of grain refinement regions and areas where elemental chemical composition varies to the contour of the hole is no more than 15 μm.

Wear patterns and wear mechanisms of cutting tools used during the manufacturing of chopped carbon fiber

Chopping carbon fiber is an efficient way to manufacture short carbon fiber reinforced plastic (SCFRP). Drastic wear of cutting tools during this process has been observed because of the highly abrasive nature of carbon fiber. Wear patterns and wear mechanisms need to be investigated to reduce tool wear and prolong tool life. This paper presents the formation and transition of wear patterns during the chopping process. The chopped rate is less than 95% after 21k cuts; thus, tool specimens and data are collected from the initial 21k cuts. Overall, the wear forms a crescent shape along the tool edge at one cutting position. This wear pattern is due to an uneven wear volume caused by the uneven distribution of filaments in the fibers, which forms an oval profile of the chopped carbon fiber. The oval profile results in more crescent shaped wear, which causes a more uneven filaments distribution, leading to a high wear rate. Conical structures at the ends of the chopped carbon fiber and micro scratches on the tool edge are observed. Thus, the abrasive wear mechanism during chopping is verified. The wear pattern on the tool profile is a combination of cutting edge rounding (CER) and rake face wear. Two wear stages divided by 8k cuts are introduced: the CER wear stage (before) and rake face wear stage (after). In the CER wear stage, the wear rate is basically stable at 32μm/2k cuts and the wear pattern is an increasing CER up to 20μm. The rake angle is approximately stable at 79°. In the rake face wear stage, the wear rate begins to increase and the wear pattern transitions from the CER wear to massive rake face wear in which the CER decreases and leans towards the flank face and the rake angle rapidly decreases. The CER decreases to 4μm, and the rake angle decreases to 14° at the end. The wear pattern includes a groove that appears on the tool rake face in this stage, which is similar to crater wear on the rake face of a traditional turning tool because of the low hardness of the tool interior. Moreover, analytical models based on 3-body abrasive wear theory are developed to explain these wear patterns and wear mechanisms.

Evolution of residual stress in Ti–Al–Ta–N coatings on hard metal milling inserts

Coated WC–Co hard metal milling inserts applied in milling application show thermal fatigue induced by interrupted tool-workpiece contact and wear as the two main damage mechanisms. Depending on the magnitudes of thermal and mechanical loads, either wear or thermal fatigue in form of combcracks may be dominant and determine the insert's lifetime. The present work illustrates the evolution of residual stress in an arc-evaporated Ti–Al–Ta–N coating for two different milling test setups, in one of which wear acted as the dominant damage mechanism. In the other test setup thermal fatigue fostered the formation of combcracks. Earlier work revealed a location on the tool's rake face, referred to as region of interest, with a significant buildup of tensile residual stresses in the WC phase of the substrate using synchrotron facilities. The residual stress state in the coating was determined in this region of interest by a cover method on the tools' rake faces after a defined number of cuts by X-ray diffraction using in-house facilities. In the wear dominated test setup, compressive residual stresses remained present until the end of tool life in coatings. Tensile residual stresses were found in coatings on inserts in which thermal fatigue was dominant.

Precision prediction of cutting force in oblique cutting operation

This paper presented a general model for predicting the cutting forces in oblique cutting operation with respect to vector transformation derived from orthogonal cutting process. The developed model is based on that the fundamental mechanics of the friction relationship between tool and material (chip) at the primary and secondary shear zones are the same when the flowing relationship between tool and chip is the same for the cutting processes with different inclination angles, including the orthogonal cutting process, in which inclination angle is 0. The cutting force loading on tool rake face in oblique cutting process with any inclination angle can be determined by the orthogonal cutting force data with the same tool-chip flowing relationship. To achieve precision orthogonal cutting force data, a mechanics model for orthogonal cutting process considering cutting speed, rake angle, and depth of cut is proposed and the predicting coefficients are calibrated by a set of turning tests. At last, a series of experiments under different cutting conditions are conducted to confirm the validity of the developed model. There is a good agreement between the experimental and simulative results, which shows the model is effective for cutting force prediction in orthogonal and oblique cutting operations.

Finite element modeling of hard turning process via a micro-textured tool

Literature survey showed that the micro-textures on the tool rake face can help in reduction in friction at chip-tool interface and therefore, reduction in the cutting forces. Consequently, the current work is based on FE simulation of hard turning of bearing steel (AISI52100). Four types of micro-textures have been considered on the tool rake face: non-texture, perpendicular, parallel, and rectangle. Johnson-Cook (J-C) material constitutive law has been considered for the workpiece with temperature-dependent material properties. Experimental work has been performed at cutting conditions: type, parallel; edge distance, 0.195 mm; pitch size, 0.110 mm; and height of the texture, 0.049 mm to validate the current machining model. Parametric study of effect of tool feature parameters on the cutting forces has been performed. Based on the current model, it is observed that the perpendicular shape showed the minimum cutting force. The maximum reduction of 28 % was predicted in the effective coefficient of friction compared to the non-textured surface. Additionally, effect of size of the texture (edge distance, pitch size, texture height) and the friction factor at tool-chip interface on the process responses is predicted. The perpendicular texture at an edge distance of 100 μm, pitch size of 100 μm, and texture height of 50 μm showed the most effective shape and size for the minimum cutting forces and effective friction. It is simulated that the chip flow angle can be governed by the shape/size of the texture on the tool rake face. It is expected that the current model can further be helpful in the characterization of other hard materials and complex texture shape/size.

Modelling and prediction of tool-chip interface temperature in hard machining of H13 steel with PVD coated tools

Cutting tool temperature determines the tool life and workpiece machined surface integrity, which mainly refers to the tool-chip interface temperature at the secondary deformation zone. PVD coating on cutting tools can greatly reduce cutting temperature through changing the heat partition into tool rake face at the tool-chip interface. Therefore, the tool-chip interface temperature has a decisive role on the cutting tool temperature. This paper presents the tool-chip interface temperature based on mathematical model using moving heat source method. FEM was set up to simulate the cutting process and validate the mathematical model predictions. Results show that the tool-chip interface temperature of TiAlN coating is higher than that of TiN coating. For both coated tools, the tool-chip interface temperature increases with the cutting speed. Under the same cutting parameters, the cutting temperature increases with the distance from the tool tip along the tool-chip contact surface.

アルミニウム合金に対するＤＬＣコーテッド工具のドライ切削性能

The purpose of this study was to clear the conditions for good performance in dry cutting of aluminum alloys with non-hydrogenated diamond-like carbon (DLC) coated tool. The intermittent and continuous cutting tests were conducted under dry condition to 4 types of aluminum alloys. Consequently, it was found out that DLC coated tool showed good performance in intermittent cutting of A5052 and A7075 (Wrought aluminum alloys), but it didn't show good performance in intermittent cutting of AC2A and AC8A (Aluminum castings) and in continuous cutting of A5052 and AC2A. It was thought that the disappearance of DLC coating on the tool rake face caused adhesion in cutting of aluminum castings and continuous cutting of wrought aluminum alloys.

High Speed Machining of Inconel 718 Focusing on Tool Surface Topography of CBN Tool

Nickel-based superalloys such as Inconel 718 provide several advantages, including a high-temperature strength and high corrosion resistance. Therefore the demand for such materials has rapidly increased, particularly in the aviation and gas turbine applications. On the other hand, they are known as one of the most difficult-to-cut materials due to their mechanical and chemical properties and the tool life is extremely short. Recently, Cubic-Boron-Nitride (CBN) has received a considerable attention as a material for cutting tools and has already established itself in many areas of machining. However, the performance of CBN tools is still insufficient in practical use, especially in the high speed machining of Inconel 718. To overcome this problem, we first conducted orthogonal cutting experiments on Inconel 718 in a wide range of cutting speeds (20 m/min - 300 m/min) in order to clarify the wear mechanisms of the CBN tool in high speed machining. As a result, it was found that the micro tool surface topography, such as grinding marks on the tool rake face, has a significant impact on the progression of the crater wear of the CBN tool when the cutting speed was increased to over 100 m/min. Based on these results, we prepared several cutting tools with different surface topography and evaluated their cutting performances. The experimental results showed that the polished rake face reduced the initial crater wear by approximately 40% compared to the non-polished tool.

Experimental Study and Modeling of Steady State Temperature Distributions in Coated Cemented Carbide Tools in Turning

Plastic deformation of the tool is one of the most important wear modes in metal cutting, especially in continuous cutting operations. Since the strength of the tool material depends strongly on the temperature, a correct temperature distribution in the cutting edge is of key importance for the prediction of plastic deformation of the cutting edge.The temperature distribution in coated cemented carbide cutting tools is investigated using experimental techniques (IR-CCD) and finite element analysis. CVD-coated cemented carbide inserts are tested in continuous turning of quenched and tempered steel (AISI 4340). Cutting forces and edge temperature distributions are measured in 2D orthogonal turning. Finite element simulations of orthogonal turning of AISI 4340 steel with CVD coated cemented carbide inserts are performed. The simulation results are used to predict steady state temperature distribution in tool by performing further coupled thermo-mechanical finite element simulations. Different methods of heat source on tool rake face are used.It is observed that steady state temperature distribution from simulation matcheswell with experimental result.

Cutting Tool Crater Wear Measurement in Turning Using Chip Geometry and Genetic Programming

Tool wear prediction plays an important role in industry automation for higher productivity and acceptable product quality. Therefore, in order to increase the productivity of turning process, various researches have been made recently for tool wear estimation and classification in turning process. Chip form is one of the most important factors commonly considered in evaluating the performance of machining process. On account of the effect of the progressive tool wear on the shape and geometrical features of produced chip, it is possible to predict some measurable machining outputs such as crater wear. According to experimentally performed researches, cutting speed and cutting time are two extremely effective parameters which contribute to the development of the crater wear on the tool rake face. As a result, these parameters will change the chip radius and geometry. This paper presents the development of the genetic equation for the tool wear using occurred changes in chip radius in turning process. The development of the equation combines different methods and technologies like evolutionary methods, manufacturing technology, measuring and control technology with the adequate hardware and software support. The results obtained from genetic equation and experiments showed that obtained genetic equations are correlated well with the experimental data. Furthermore, it can be used for tool wear estimation during cutting process and because of its parametric form, genetic equation enables us to analyze the effect of input parameters on the crater wear parameters.

Characterization and Modelling of the Rough Turning Process of Large-scale Parts: Tribological Behaviour and Tool Wear Analyses

Machining large-scale parts in several industries (nuclear, naval, energy…) is a challenge for machine tools operators. Various problems are encountered, like respecting specified dimensions, deformation of the workpiece during machining, limit of the cutting speed, excessive tool wear, etc. All these difficulties are related to the large size of the machined part, which may have several meters and weigh several hundred kilograms. This study focuses on analysis of the rough turning process of a shell component, having few meters, as a part of steam generators of nuclear power plants. During the rough turning step, a high material removal rate (moderate cutting speed, but high depth-of-cut and feed rate) is necessary to achieve the workpiece in reasonable time. Experimental and theoretical analyses are conducted to highlight the intense thermomechanical loading at the tool–workmaterial interface. Revealed physical phenomena at the tool rake face, like adhesion and abrasive wear types, using various characterization techniques, are reproduced by a numerical model developed to simulate the cutting process. As an interest result, contact discontinuities at the tool–chip interface as well as where the wear is highly localized are well predicted as observed on scanning electron microscope. These contact discontinuities are attributed to the grooved rake face of the insert, designed with a chip breaker to reduce the tool–chip contact area and to promote the chip fragmentation. This study can be helpful for the design of rough turning inserts, by analysing the effectiveness of the rake face geometry (contact area, chip breaker…).

Numerical investigation of effects of cutting conditions and cooling schemes on tool performance in up milling of Ti-6AL-4V alloy

Ti-6Al-4V is widely used in industry because of its high strength-to-weight ratio at elevated temperatures, its excellent resistance to fracture and corrosion, and biological properties. However, Ti-6Al-4V is classified as hard-to-cut material because of its high chemical reactivity with most tool materials and its low thermal conductivity that causes high temperature on the tool face. Consequently, prediction of the tool temperature distribution has great significance in predicting tool wear pattern. In this research, finite element method (FEM) is employed to conduct numerical investigation of the effects of cutting conditions (cutting speed, feed rate, and axial depth of cut) in corner up milling on temperature of the tool rake face. The tool material used is general carbide, and the behavior of the workpiece Ti-6Al-4V is described by using Johnson-Cook plastic model. Because of the computational expense, a separate heat transfer model is built to analyze the heat transfer process after the tooth disengages the workpiece and before it engages the workpiece again to predict change of temperature distribution during this cooling process while subjected to different cooling schemes. This research provides helpful guidance for selecting optimal cutting conditions and tool cooling strategies in up milling Ti-6Al-4V alloy.

Performance of mixed ceramics and CBN tools during hard turning of martensitic stainless steel

This paper describes the wear behavior of a ceramic and a PcBN cutting tool during the turning of AISI 440B stainless steels at different machining conditions. Experimental results showed that the wear mechanism for ceramic cutting tool is predominantly abrasive wear and for cBN tools was adhesive wear and abrasive wear. The abrasive wear is as a result of hard carbide particles in the workpiece material resulting in grooves formed on the flank face. There was formation of transferred layer followed by plastic deformation on the rake face of PcBN tool when cutting at low speed and feed rate. Better surface finish (Ra) was recorded for ceramics but with deteriorating surface topography. The results also show that good dimensional accuracy can be achieved with cBN tools using CNC machine with high static and dimensional stiffness coupled with high-precision hard turning.

Study on serrated chip formation and tool wear of cermet tools for milling stainless steel 3Cr13Cu

Cermet tools are used to mill stainless steel 3Cr13Cu (44HRC) for studying tool failure modes and the influence of the serrated chip formation on tool wear. Crack and peeling are identified to be the main failure modes of the cermet tool as they form mechanical fatigue cracks and thermal cracks in a cutting process. At lower cutting speeds, the mechanical fatigue crack is produced earlier than the thermal crack at the tool rake face, while at higher cutting speeds, it is the thermal crack that was generated earlier at the tool rake face. The experiments demonstrate that the boundary wear and the serrated chip formation of cermet tools are closely related with the mechanical fatigue crack formation.

Material Response at Tool–Chip Interface and Its Effects on Tool Wear in Turning Inconel718

Because nickel-based alloy Inconel718 has poor thermal conductivity and serious work hardening, it is identified as a difficult-to-process material. The serious tool wear leads to short tool life. In this study, physical vapor deposition-coated carbide tools were used to machine Inconel718. The material response for different cutting speeds at the tool–chip interface and its effect on tool wear were studied. The results showed that at low cutting speed (v c = 20 m/min), cold welding and adhesion occurred at the tool–chip interface under high stress, and then the built-up edge (BUE) formed. The peeling off of BUE led to chipping. When the cutting speed (v c) was 45 m/min, diffusion and oxidation occurred at the tool–chip interface. The new generated material reduced tool hardness and bond strength of Co. The wear debris was generated in tool rake face. Flakes of wear debris fell from the tool substrate, which increased tool wear. When the cutting speed was 32 m/min, the softer oxides generated at the tool–chip interface served as a boundary lubrication layer. They can effectively weaken the adhesion between tool and chip, which made the chemical wear and adhesive wear reach equilibrium. Furthermore, the friction coefficient is reduced. Tool wear is reduced under this cutting condition.

Direct observation of fluid action at the chip-tool interface in machining

The present study seeks to realize an improved understanding of the action of cutting fluid through direct observation of the chip-tool interface. That is, using transparent tools made of sapphire in conjunction with a high-speed, CCD-based imaging system, the chip-tool contact condition and its evolution in the presence of cutting fluid are directly observed during 2-D orthogonal machining of pure lead and Al6061-T6. Then, spatial and temporal analysis of the images of the chip-tool interface is made for measuring the contact length and velocity profile along the tool rake face, and the contact conditions are correlated with the cutting forces measured. The results are compared with those made when cutting dry to clarify the effects of cutting fluid action, and a picture of the action of cutting fluid at the chip-tool interface is presented finally.

Experimental and numerical study of laser-assisted machining of Ti6Al4V titanium alloy

Laser-assisted machining combines several experimental parameters such as cutting speed, feed rate, depth of cut, laser power and distance between tool rake face and the laser beam axis. The optimization of these parameters is necessary to ensure the efficiency of assistance and to increase productivity. This paper focuses on the understanding of the physical phenomena during laser-assisted machining, and on optimising this process. This contribution is based on an experimental and a numerical study. The experimentalpart highlights the effects of the laser power as well as the distance between the tool rake face and the axis of the laser beam. As for the numerical part, it was performed on the ABAQUS/Explicit software.The proposed model improves the understanding of the physical phenomena of chip formation and the cutting force reduction when machining with laser assistance. In addition, this model allows a better optimization of laser and cutting parameters.Numerical findings generally corroborate experimental results and can lead to some other information difficult to catch experimentally.The main contention in the paper is that the distance between the axis of the laser beam and the tool rake face is the most important parameter that controls the reduction of the cutting force. This cutting force reduction can exceed 50%.

Cutting force–based analysis and correlative observations on the tool wear in diamond turning of single-crystal silicon

The condition of a cutting tool is an important factor to ultraprecision machining processes. Tool wear has a strong influence on the cutting forces, resulting in poor surface roughness and dimensional tolerance of the workpiece, particularly in ultraprecision machining hard brittle materials. This article presents a cutting force–based analysis and correlative observations on diamond tool wear in machining of single-crystal silicon. The Daubechies wavelet (dB3, level 4) was employed to correlate standard deviation of magnitude on the decomposed cutting and radial forces with initial diamond tool wear. Moreover, the flank wear and the micro-fracture were observed using scanning electron microscopy on the respective flank face and rake face of the diamond cutting tool used. No crater wear was detected on the rake face of the diamond tool until cutting distance of up to 9 km.

Diffusion Wear Mechanism of Single Crystal Diamond Tool in Machining Die Steels

Ultra-precision diamond cutting of ferrous metals has not been successful in application due to significant tool wear. In this work, numerical simulations and experimental investigations are presented in order to study the interface diffusion between diamond tool and workpiece materials. A diffusion model with respect to carbon atoms from diamond tool penetrating into chips and machined surface was established. The numerical simulation results of the diffusion process reveal that the distribution laws of carbon atoms concentration have a close relationship with diffusion distance, diffusion time and the original carbon concentration of the work material. In addition, diamond face cutting tests of die steels with different carbon content are conducted at different depth of cuts and feed rates to verify the previous simulation results. The wear morphology of rake face and flank face of diamond tool were detected by scanning electron microscopy. Energy dispersive X-ray analysis was proposed to investigate the change in chemical composition of the chips and machined surface. The results of this work benefit for a better understanding on the diffusion wear mechanism in single crystal diamond cutting of ferrous metals.