Negative Rake Angle Research Articles

A machinability evaluation based on the thermal and mechanical properties of two engine valve steels

Iron-based superalloys are difficult to machine because of their thermal and mechanical properties provided by alloying elements as nickel, chromium, titanium, and aluminum. However, parts made with this kind of material has to be machined during their production processes. In this work, two different automotive engine valve steel grades, VAT 30® and VAT 36®, were compared in terms of machinability, considering cutting power consumption, roughness of the machined surface, and tool life, besides the identification of the main tool wear mechanisms that have led to the end of tool life. The main goal of this work is to understand the difference in these machining outputs based on the thermal and mechanical properties of these two materials. In order to reach this goal, turning tests were held using two different cooling conditions, conventional and high-pressure coolant. Also, two PVD-coated carbide inserts were applied, one with negative rake angle and another neutral. Finally, cutting speed was tested in two levels, providing a full 24 factorial planning. Results show that VAT 30® has shown higher machinability in terms of tool life in almost every condition, although this steel presents higher hardness, mechanical strength, and strain hardening coefficient, besides lower thermal conductivity. However, it also presents lower ductility and abrasiveness, features that retarded abrasion and attrition as tool wear mechanisms, in such a way that tool life could have been lengthened.

Numerical and experimental investigation of tool geometry effect on residual stresses in orthogonal machining of Inconel 718

Residual stress has become more important than ever with the increasing performance requirement of components especially for those applied in safety-critical areas. As the machining process is fundamentally correlated with the acquired component properties, it is essential to fully understand the formation mechanism of residual stresses in the cutting process and its influence on the performance of the component. This paper presents results based on numerical and experimental analysis on the effect of tool geometry on thermal-mechanical load and residual stresses in orthogonal machining Inconel718 alloy. The Coupled Eulerian-Lagrangian (CEL) method is used to simulate the effect of tool geometry on temperatures, forces, equivalent plastic strains, and residual stresses. The local normal/tangential stress is introduced to determine the degree of the tensile plastic deformation induced by the tool. It is observed that a negative rake angle and a sharp edge radius tool tend to generate more compressive stress on the machined surface than the ones generated with positive rake angle tools and/or lager edge radius. Besides, an increase in flank wear produces less magnitude of compressive stress in subsurface due to a decreased local normal stress caused by increased flank contact length.

Investigation of the Subsurface Temperature Effects on Nanocutting Processes via Molecular Dynamics Simulations

In this investigation, three-dimensional molecular dynamics simulations have been performed in order to investigate the effects of the workpiece subsurface temperature on various nanocutting process parameters including cutting forces, friction coefficient, as well as the distribution of temperature and equivalent Von Mises stress at the subsurface. The simulation domain consists of a tool with a negative rake angle made of diamond and a workpiece made of copper. The grinding speed was considered equal to 100 m/s, while the depth of cut was set to 2 nm. The obtained results suggest that the subsurface temperature significantly affects all of the aforementioned nanocutting process parameters. More specifically, it has been numerically validated that, for high subsurface temperature values, thermal softening becomes dominant and this results in the reduction of the cutting forces. Finally, the dependency of local properties of the workpiece material, such as thermal conductivity and residual stresses on the subsurface temperature has been captured using numerical simulations for the first time to the authors’ best knowledge.

On the machinability of the Ni-30 high-temperature iron-based superalloy

Superalloys are high-performance materials which combine high tensile, creep and fatigue strength, besides good ductility, toughness and resistance to corrosion, properties that are also responsible for their low machinability. The VAT 30® alloy contains an austenitic stainless steel base with additions of chromium, nickel, titanium and aluminum, and it is mainly applied on the manufacture of valves of combustion engines, due to its advantageous characteristics. This alloy exhibits both high ductility and abrasiveness, features that may promote both attrition and abrasion wear mechanisms on the tool used to cut it. This work contains some investigations about the effect of cooling condition, tool rake angle and cutting speed on the machinability of Ni-30 alloy in terms of cutting power consumption, surface roughness and tool life, besides the tool wear mechanisms. Conventional and high-pressure coolant injected toward the tool rake face was compared, as well as negative rake angle and neutral tooling, besides two different cutting speeds. Results show that high-pressure coolant may reduce cutting power consumption and even increase the volume of material removed during tool life up to 45% in some cases, but this same influence has not been verified regarding the workpiece arithmetical mean roughness value. Negative and neutral rake angle tools did not present very different results in terms of power and roughness, but negative tools provided considerably higher volume of material removed per tool life (up to 75% in one condition). Cutting speed showed strong effect on the cutting power, as expected, but no reasonable effect on workpiece surface roughness; regarding tool life, the cutting speed increase typically reduced the volume of material removed per tool life with conventional cooling, but when high-pressure coolant was used, this effect was attenuated. Abrasion and attrition were the main tool wear mechanisms in any tested condition.

Optimization of Cutting Process Parameters in Inclined Drilling of Inconel 718 Using Finite Element Method and Taguchi Analysis.

Nickel-based superalloys are famous in the demanding applications. Inconel 718 is one of the most commonly used nickel-based superalloys due to its extraordinary inherent properties. Inconel 718 is a suitable material for high temperature applications due to the properties such as anti-oxidization, high hot hardness, high creep, and fatigue strength. Drilling operation is one of the most widely used manufacturing operations in almost all industrial sectors. However, drilling operation is very complex in nature due to the presence of intricate geometry of the drill bit. In conventional drilling, cutting is performed by the combined action of the chisel edge and the two or more cutting lips. In depth analysis of the cutting process shows that chisel edge starts with an indentation at the center of the twist drill. Then away from the center, chisel edge performs orthogonal cutting with negative rake angle. Whereas, cutting action at the cutting lip is oblique in nature, and force analysis involves the use of element formulation due to involvement of radius. It is rarely found in the literature where drilling operation at different inclination angles is conducted and analyzed. The presented study numerically investigates the cutting performance of drilling operation, when operated at different inclination angles. The study revealed cutting force variation at different inclination angles due to the different tool workpiece engagement for each inclination. The magnitude of thrust force increased when inclination angle is changed from 30° to 60°. It can be linked with the higher chip load initially in this case as compared to the 30° inclination angle. The cutting temperature was affected by spindle speed (53.7%), followed by feed rate (33.31%) and inclination angle (3.44%).

An experimental study on the effect of tool geometry on tool wear and surface roughness in hard turning

The main purpose of this study is to investigate the influence of tool geometry (cutting edge angle, rake angle, and inclination angle) and to optimize tool wear and surface roughness in hard turning of AISI 1055 (52HRC) hardened steel by using TiN coated mixed ceramic inserts. The results show that the inclination angle is the major factor affecting the tool wear and the surface roughness in hard turning. With the increase in negative rake and inclination angles, the tool wear decreases, and the surface roughness increases. However, the surface roughness will decrease when the inclination angle increases to overpass a certain limit. This is a new and significant point in the research of the hard turning process. From this result, the large negative inclination angle (λ = −10°) should be applied to reduce the surface roughness and the tool wear simultaneously. With the optimal cutting tool angles in the research, the hard machining process is improved remarkably with decreases of surface roughness and tool wear 8.3% and 41.3%, respectively in comparison with the standard tool angles. And the proposed tool-post design approach brings an effective method to change the tool insert angles using standard tool-holders to improve hard or other difficult-to-cut materials turning quality.

Applicability of cutting theory to nanocutting of metallic glasses: Atomistic simulation

Using molecular dynamics simulation, we perform simulations of cutting a CuZr metallic glass at a wide range of rake angles. Plasticity in the metallic glass is governed by the formation of parallel shear bands in the chip. The chip is clearly separated from the uncut workpiece by a primary shear zone, from which the shear angle can be easily determined. The dependence of the shear angle on the rake angle and the friction angle follows closely Merchant’s theory of cutting. This agreement is particularly pronounced in the case that the force exerted on the workpiece is far from the cutting direction; this occurs for negative rake angles.

Cutting Forces, Chips Formation and Surface Roughness in Rock Cutting Using Negative Rake Angle

This research pertains to rock cutting used negative rake angle. The parameters used are negative rake angles of 0o, -5o, -10o, -15o, -25o, -30o, and -40o. Negative rake angle is known to play an important role in rock machining. Negative rake angle produces more chips powder in front of the tool surface. The interaction between these particles affects the thrust force that suppresses the rock surface. A large thrust force generates hydrostatic pressure around the tooltip. According to the findings of this research, negative rake angle -25o leads to the largest thrust force and smallest surface roughness for 15.17 N and 1.21 ?m, respectively with smooth and uniform chips. The rock surface and the resulting chips powder was observed by scanning electron microscope (SEM) in order to prove the effect of hydrostatic pressure working on the tooltip. Meanwhile the hydrostatic pressure changed the brittle cutting mode into a brittle-ductile cutting mode.

Prediction of critical undeformed chip thickness for ductile mode to brittle transition in the cutting of single-crystal silicon

In order to achieve the ductile mode cutting of silicon and avoid the generation of subsurface crack damage, the undeformed chip thickness in the diamond cutting process must be controlled below the critical value. Therefore, the critical undeformed chip thickness (CUCT) for the ductile mode cutting of silicon is studied in this paper for guiding the selection of cutting parameters in the diamond cutting of silicon. Considering the anisotropy of single-crystal silicon, the prediction method of the CUCT in the ductile cutting of silicon is proposed on the basis of calculating the anisotropic fracture strength of silicon and subsurface stress distribution induced by the cutting force. Moreover, the influence of the anisotropy of single-crystal silicon, cutting tool parameters and friction coefficient in the cutting process on the CUCT are discussed, respectively. The results show that the anisotropic CUCT depends on the cutting surfaces and cutting directions. In addition, the diamond cutting tool with a negative rake angle of −40° is generally suitable for ductile cutting on the silicon (001), (110) and (111) surface when the friction coefficient in the cutting process is in the range of 0.05–0.30. Under this cutting condition, the minimum CUCT on the silicon (001), (110) and (111) surface is in the range of 150 ∼ 250 nm, 160 ∼ 290 nm and 150 ∼ 250 nm, respectively. The lower limit of the minimum CUCT on the three surfaces corresponds to the friction coefficient of 0.30 in the cutting process, and the upper limit corresponds to the friction coefficient of 0.05. Furthermore, a sharp-nosed cutting tool is also beneficial to improve the CUCT in the cutting process.

Molecular Dynamics Study of the Effect of Abrasive Grains Orientation and Spacing during Nanogrinding.

Grinding at the nanometric level can be efficiently employed for the creation of surfaces with ultrahigh precision by removing a few atomic layers from the substrate. However, since measurements at this level are rather difficult, numerical investigation can be conducted in order to reveal the mechanisms of material removal during nanogrinding. In the present study, a Molecular Dynamics model with multiple abrasive grains is developed in order to determine the effect of spacing between the adjacent rows of abrasive grains and the effect of the rake angle of the abrasive grains on the grinding forces and temperatures, ground surface, and chip formation and also, subsurface damage of the substrate. Findings indicate that nanogrinding with abrasive grains situated in adjacent rows with spacing of 1 Å leads directly to a flat surface and the amount of material remaining between the rows of grains remains minimal for spacing values up to 5 Å. Moreover, higher negative rake angle of the grains leads to higher grinding forces and friction coefficient values over 1.0 for angles larger than −40°. At the same time, chip formation is suppressed and plastic deformation increases with larger negative rake angles, due to higher compressive action of the abrasive grains.

BASICS OF AUTOMATION OF PROFILING OF HIGH-EFFICIENT INSERTS OF THE TOOL FOR THREAD MACHINING

Many modern threaded joints especially in the oil and gas industry, must satisfy high requirements for steel mechanical properties of which they are made. To ensure efficient threading of such hard-to-machine materials (ultimate strength is more than 1250 MPa), it is necessary to use carbide cutting inserts with the negative rake angle at its corner. However, modern manufacturers of such inserts make them only with a zero value of the rake angle. This is due to the difficulty of profiling of the insert cutting edge. This article proposes the basics of such inserts automatic profiling which is based on the algorithm developed by the authors. It includes two corrective calculations of the insert cutting edge profile, namely: the radial displacement of the corner and the tangential displacement of the area forming the crest of the thread. As a result, the computer application with the input parameter of the rake angle and output parameter of the upgraded profile of the insert cutting edge is received.

Influence of the Rake Angle on Nanocutting of Fe Single Crystals: A Molecular-Dynamics Study

Using molecular dynamics simulation, we study the cutting of an Fe single crystal using tools with various rake angles α . We focus on the (110)[001] cut system, since here, the crystal plasticity is governed by a simple mechanism for not too strongly negative rake angles. In this case, the evolution of the chip is driven by the generation of edge dislocations with the Burgers vector b = 1 2 [ 111 ] , such that a fixed shear angle of ϕ = 54.7 ∘ is established. It is independent of the rake angle of the tool. The chip form is rectangular, and the chip thickness agrees with the theoretical result calculated for this shear angle from the law of mass conservation. We find that the force angle χ between the direction of the force and the cutting direction is independent of the rake angle; however, it does not obey the predictions of macroscopic cutting theories, nor the correlations observed in experiments of (polycrystalline) cutting of mild steel. Only for (strongly) negative rake angles, the mechanism of plasticity changes, leading to a complex chip shape or even suppressing the formation of a chip. In these cases, the force angle strongly increases while the friction angle tends to zero.

Ultraprecision laser-assisted diamond machining of single crystal Ge

In this paper we present an experimental study on ultraprecision machining (UPM) of single crystal Ge using the μ-LAM process. The material is oriented with the cutting plane normal to the <111> direction. It is shown that increased hydrostatic pressures on the surface during cutting by increasing the tool radius and negative rake angle can aid in enhancing ductile material removal from the surface. It is shown that the cutting performance can be increased by approximately 400% using the optimal tool geometry. It is also shown that the optimal tooling geometry with a steep negative rake angle, i.e. −65°, is capable of producing repeatable surface form and finish over long cutting distances. Finally, it will be shown that the laser beam used for μ-LAM, with the right amount of power, produces surfaces that are under less post machining residual stresses.

Research on Workability of Tool Cutters Working under Conditions of Shockless Loads and Friction

The paper deals with hard cutters of drill bits for drilling rocks. The research on geometry of hard alloy and steel cutters of bits that work either under conditions of shockless loads was carried out in this work. The rationale of tungsten carbide and cobalt composition according to their hardness and robustness is provided. Different alloys were suggested to be used for tools working either under conditions of shockless loads or under shock loads for drilling rocks of high hardness. The rock deformation process was identified to occur by cutting and shearing forces. The highest influence on the cutting process is exerted by the acuity angle and back rake angle. Peculiarities of work of cutters with positive, negative and neutral back rake angles were determined as part of the main research. The dependence of penetration depth on the back rake angle of the cutter was obtained. Indicators of wearing identified in the research are including the type and properties of interacting surfaces characterized by the roughness of cutting bit surface, the hardness of materials in contact zone, friction mode that depends on unit pressure, movement rate, the nature of load application, and the rate of interaction of working parts of bit.

An analytical grinding force model based on individual grit interaction

Abstract Grinding force is an important parameter that affects the productivity and quality of industrial products. The very high negative rake angles of the grits play an important role in the material removal mechanism resulting in the formation of a stagnant area ahead of the grits called the dead metal zone (DMZ). Ploughing force also comes into effect when the undeformed chip thickness is comparable with the cutting edge radius of the active grits. Based on these facts, in this study, a new model is proposed to predict the grinding forces and understand the material removal mechanism. This is achieved by modeling the grit-workpiece micro-interaction and geometry of the grinding wheel, enabling the engaged grits and undeformed chip thickness to be defined. An analytical kinematic-geometrical force model considering dead metal zone and ploughing, as well as practical conditions such as run out and wheel wear has been developed. The input parameters of the model are grinding conditions, workpiece material and wheel properties, and sliding coefficient of friction between wheel-workpiece pair. The grinding force is composed of three portions including ploughing, cutting and formation of DMZ. The influential parameters on each force portion are analyzed. Considering the physical mechanisms involved in the grinding process, the model provides more in-depth knowledge about the grinding forces which can be used for finding the optimum conditions. This model is able to explain some inherent characteristics of grinding forces such as the high ratio of normal to tangential force and high specific grinding energy in low feed rates and depth of cuts. A series of experiments were carried out to evaluate the model accuracy and the contribution of each force portion is discussed in detail. The model predicts the grinding force and its fluctuations accurately without the need for performing grinding calibration tests which is a clear advantage compared to the current models.

Osseodensification in Implant Dentistry for Ridge Expansion and Transcrestal Maxillary Sinus Augmentation: Case Report

Osseodensification has been a subject of interest in the research arena. It employs densah bur, with negative rake angle and counterclockwise motion, to perform nonsubtractive drilling. In the presence of copious irrigation, it can push the bone trabeculae into the osteotomy instead of leaving it. This compaction can increase bone density, bone volume and subsequently enhance implant stability. The aim of this study is to report a case using densah bur successfully for osseous densification and crestal maxillary sinus augmentation. Further clinical trials are required to validate these findings and confirm whether it can be used for ridge expansion.

Effect of Tool Rake Angle and Crystal Orientation on Ductile Mode Cutting of Hard/Brittle Materials

The effects of negative rake angles on the ductile mode cutting of soda glass and sapphire were studied. In addition, the machining mechanism was studied using a groove-cutting model based on the orthogonal cutting theory. It was found that the specific cutting forces in ductile mode cutting increase on both the soda glass specimen and on the sapphire specimen when the rake angle of the tool becomes negative. The difference between the experimental data and theoretical data of the specific cutting forces becomes large when the tool has a high rake angle on the negative side. This is attributed to effects of the roundness of the edge, the effects of the roundness of the nose, and the plowing mechanism, which causes plastic flow of the work material to both sides of the groove. The specific cutting force of sapphire depends on the cutting direction against the crystal orientation. The specific cutting force of sapphire depends on the cutting direction in terms of the crystal orientation. The anisotropy of the cutting force of sapphire also depends on the rake angle of the tool.

Study on the critical negative rake angle of the negative rake angle tool based on the stagnant characteristics in micro-cutting

The critical negative rake angle of negative rake angle tool is the critical criterion for the state of cutting and plowing in micro-cutting. It affects the flow characteristics of cutting material, the deformation state of chip, the quality of the machined surface, and the amount of tool wear. Meanwhile, a stagnant region often appears in front of the tool surface when a negative rake tool is used to cut the plastic metal material, which would increase the actual negative rake angle. Therefore, based on the stagnant characteristics and the infinite shear strain approach, this paper constructs a critical negative rake angle model, and the orthogonal cutting experiment and the finite element model are used to verify the correctness of the model. By analyzing the deviation of the effective critical negative rake angle (theoretical value) and critical negative rake angle (experimental value), it can be known that the theoretical value is 0.36–4.15% larger than the experimental value, which indicates that the model considering the existence of stagnant region is closer to the actual critical negative rake angle. In addition, the relationship between the stagnant region (the deviation) and the multi-cutting factors can provide experimental basis of angle for solving the effective critical negative rake angle when the critical negative rake angle is known.

Study on chip removal mechanism of PCD ball-end milling (1st report) cutting simulation by orthogonal cutting

ABSTRACT A polycrystalline diamond (PCD) ball-end mill is effective for processing molds made of hard and brittle materials, such as cemented carbide and ceramics and having fine and complex shapes with a high aspect ratio. The PCD ball-end mill has a distinctive feature of its cutting edge, which it has a simple spherical shape without sharp cutting edge found on conventional cemented carbide and cubic boron nitride (cBN) ball-end mills. The rake angle varies depending on the depth of cut. In cutting using the PCD ball-end mills, flow type chips are observed and mirror finish surface without micro fracture can be realized by adopting the ductile-cutting mode. However, the mechanism of chip generation in this cutting with the PCD ball-end mills has not been fully clarified. In this study, to simulate the cutting mechanism of the PCD ball-end mill, an orthogonal cutting experiment was conducted using an ultrafine PCD cutting insert having nose radius similar to that of the PCD ball-end mill, for basically understanding the chip formation mechanism of the PCD ball-end mill. Consequently, we designed an experimental setup with a spring constant force for applying simulation of thrust force of the PCD ball-end mill. As a result, the chips could be generated at down to −75° of rake angles and the relationship between the negative rake angles and the chip generation mechanisms were clarified.

Optimization of cutting parameters of residual stresses in simultaneous turning technique

The simultaneous turning technique is used to increase the rotary component’s fatigue life by increasing the surface compressive residual stresses. Cutting velocity, cutting tool rake angle, nose radius, feed and tool separation distances are the major cutting parameters in simultaneous turning. Computer simulation was performed by finite element analysis software ABAQUS 6.14. It was used to predict the surface residual stresses and optimization of the cutting parameters was carried out using Taguchi method. MINITAB software was employed for this purpose. The study revealed that the optimal combination of cutting parameters are 150 m/min cutting speed, 0.1 mm/rev feed, 4° negative rake angle, 0.1 mm tool nose radius and 0.4 mm tool separation distance. These optimal values yielded a highest circumferential and axial surface residual stresses of −817.59 and −928.04 MPa for the surface turned by first tool whereas for surface machined by other tool it was −875.89 and −1010.44 MPa.