Effect Of Cutting Edge Radius Research Articles

Effects of Cutting Edge Radius on the Surface Integrity of Milled Ti6Al4V Alloy

Effects of Cutting Edge Radius on the Surface Integrity of Milled Ti6Al4V Alloy

Effects of Cutting Edge Radius on Surface Integrity in Machining of Nickel-Based Cast Superalloy: An In Situ Imaging Approach

Abstract Cutting edge radius is a crucial factor affecting surface integrity during metal machining, which determines product performance. However, the exact mechanism of how the cutting edge radius affects machined surface has not yet been understood, especially lacking in situ evidence during the material removal process. In this article, effects of cutting edge radius on surface roughness, subsurface deformation, and work hardening of nickel-based cast superalloy are studied through an in situ imaging approach. Based on continuous high-speed filming and digital imaging correlation (DIC) techniques, detailed chip formation and quantitative subsurface plastic deformation under various cutting edge radii are analyzed, and the formation of built-up edge (BUE) is observed when using a large edge radius. Furthermore, when the cutting edge radius is greater than the uncut chip thickness (h), the thickness of plastic deformation increases dramatically. On the other hand, the machined surface roughness can be improved when the cutting edge radius is between 30% and 60% of h. The sharp cutting tools or the cutting edge radius higher than 60% of h result in a poor surface quality on the machined surface during nickel-based cast superalloy machining. The effects of cutting edge radius on machined surface generation are systematically categorized as cutting with chipping, cutting with significant plowing, and cutting with plowing accompanied by BUE formation.

Numerical predictions of orthogonal cutting–induced residual stress of super alloy Inconel 718 considering dynamic recrystallization

Manufacturing processes, such as machining, can produce residual stresses in products. Residual stress and its distribution can be the main factor influencing the fatigue life of machined components and has already been the subject of many experimental and numerical studies. The high-temperature condition, as a result of machining, makes a change in the microstructural properties of the material and consequently affect the mechanical properties of the workpiece. A major metal component of aircraft structure and engine components is nickel-based alloys due to their resistance to heat, corrosion, thermal fatigue, thermal shock, creep, and erosion. When these critical structural components in the aerospace industry are manufactured with the objective to reach high-reliability levels, surface integrity is one of the most relevant parameters used for evaluating the quality of finish-machined surfaces. The residual stresses and surface alterations including white layer, depth of work hardening, micro-cracks, and oxidation induced by machining of nickel-based alloys are extremely critical due to safety and sustainability concerns. Integrated Computational Materials Engineering (ICME) links physics-based models to predict the performance of materials based on their processing history. The Johnson–Mehl–Avrami-Kolmogrov (JMAK) model is used to develop a microstructure-based modeling approach that takes into account dynamic recrystallization (DRX) that causes grain size changes. Allied with that, a grain size parameter on the flow stress behavior of the material is considered by adding a grain size-dependent term to the traditional Johnson–Cook (JC) model as a novel framework. The impact of the simulation of the orthogonal cutting process is implemented in a finite element method (FEM) model–based commercial software, ABAQUS-explicit, with a coupled Euler-Lagrangian (CEL) approach. By relying on the VUHARD user subroutine capabilities with Fortran language, ABAQUS-explicit can be steered to model the material behavior considering the term of DRX. The forecast capability of the developed model is assessed by comparison of the results by changing the depth of cut and cutting edge radius effect on the residual stress. Then, the correlation between the grain size evolution and temperature distribution by changing the cutting velocity is investigated.

Cutting edge radius effect on the surface integrity of orthogonal turned aluminium alloy Al6082 with different initial microstructure

In the present study, the combined effect of initial microstructure and relative tool sharpness (RTS) on the surface integrity of aluminium(Al6082) alloy has been investigated. Orthogonal turning is carried out on as-received and heat-treated specimen with group of edge radiused tools. Surface roughness and micro hardness have been evaluated with respect to number of turns for varying RTS value. Results indicate that the workpiece material adhesion on the tool has significantly influenced the surface roughness. In addition, below the critical RTS, the surface integrity is greatly influenced by the grain size of the material.

Analytical prediction of cutting tool temperature distribution in orthogonal cutting including third deformation zone

The present study introduces a novel model for the prediction of temperature in a cutting tool while the effects of all three deformation zones are considered. The model considers the effect of cutting-edge radius and the third deformation zone for the first time in the literature in terms of temperature prediction using thermo-mechanical approach with dual-zone friction model. The material behavior is defined by the Johnson-Cook constitutive model. For the calculation of heat flux on the rake and flank faces, a dual-zone model was used. The temperature distributions at the tool-chip and tool-workpiece boundaries were determined analytically, and the temperature distribution inside the tool was calculated using the Finite Difference Method. In order to verify the model, experiments were performed with AISI1050 steel and Al7075 workpiece materials using tungsten-carbide cutting tools. A good agreement is observed between the model predictions and the test results. This study also examined the effects of cutting-edge geometry and cutting conditions on cutting temperature, which can be used in optimized selection of cutting parameters and tool geometry.

Effect of tool edge radius on material removal mechanism in atomic and close-to-atomic scale cutting

For mechanical cutting, when cutting depth is decreased to atomic and close-to-atomic scale(ACS), the material removal mechanism would be dominated by dislocation motion, different from conventional cutting and nanocutting. It is is greatly influenced by cutting edge radius effect in the aspects of chip formation, cutting forces, and stress distribution, etc. There appear three deformation zones in ACS cutting, including dislocation slip zone, chip formation zone and elastic deformation zone. As cutting-edge radius increases, both of dislocation slip zone and chip formation zone are suppressed while the elastic deformation zone tends to continually grow. When cutting edge radius is increased to be larger than a threshold, the elastic deformation zone is further transformed into one elastic and plastic deformation zone, while a very small chip formation zone, and dislocation zone is remained ahead of rounded cutting edge. Consequently, though the minimum cutting depth is decreased to single atomic layer, the material removal behaviour is also dominated by extrusion action of cutting tool, following the mechanism of nanocutting. The research findings would provide theoretical guidelines to the cutting tool design for atomic and close-to-atomic scale cutting.

Mechanism of atomic and close-to-atomic scale cutting of monocrystalline copper

Mechanical cutting is one of promising subtractive machining processes to enable the atomic and close-to-atomic scale (ACS) manufacturing of the processed surface with atomic scale form accuracy or functional feature size. When cutting depth is decreased to ACS, minimum chip thickness could be decreased to several atomic layers and even single atomic layer. Consequently, there arises one disruptive cutting technology towards atomic and close-to-atomic scale manufacturing, i.e. ACS cutting, the next-generation cutting technology different from conventional cutting, microcutting and nanocutting. In this paper, one ACS cutting model is proposed to study the material removal mechanism at close-to-atomic scale and even atomic scale. It is postulated that chip formation in ACS cutting is conducted by shear stress-driven dislocation movement, significantly different from the shearing-dominated chip formation in conventional cutting and the extrusion-dominated chip formation in micro/nano cutting. Moreover, two kinds of sizing effects, namely, cutting edge radius effect and atomic sizing effect, would greatly influence the surface generation and material removal in ACS cutting.

Effect of cutting edge radius on micro end milling: force analysis, surface roughness, and chip formation

Producing miniaturized components from a wide variety of engineering materials is one of the most important fields of interest in manufacturing industry. Micro end milling is considered to be one of the efficient methods to produce complex 3D micro components. In micro machining, undeformed chip thickness is comparable to the tool edge radius, which introduces a critical undeformed chip thickness. Below the regime of critical undeformed chip thickness material is not removed but plowed. Ti-6Al-4V is one of the most popular titanium alloy because of its superior properties such as resistance to heavy loads, corrosion resistance, lightness, and bio-compatibility. This paper investigates micro end milling characteristics of the Ti-6Al-4V titanium alloy through a series of cutting experiments. Here the size effect in micro end milling was observed by studying the effect of the cutting edge radius on process performance. In order to understand the effect of the cutting edge radius on machining performance, range of feed per tooth was selected in such a way that it includes both within and outside the size effect region. This paper explores how cutting edge radius affects the cutting force, coefficient of friction, surface roughness, and chip formation during the micro end milling process. A size effect region was obtained from the variation of cutting force with feed per tooth. It was found that feed per tooth in the vicinity of 1-μm range is critical feed per tooth value, which is approximately one third of the cutting edge radius. Below this value, the cutting edge radius effect is predominant which would result in more ploughing mechanism. This was evident from the deviation of cutting force from the linear trend, increase in coefficient of friction, and surface roughness value at lower feed per tooth. In addition, a cutting force model was proposed considering the cutting edge radius effect and has been validated with experimental results.

Influence of relative tool sharpness (RTS) on different ultra-precision machining regimes of Mg alloy

Opportunities for new applications of lightweight Mg alloys are emerging in bio-medical fields, especially in medical devices and implants. The biodegradable Mg-based alloys wield advantages over their counterparts of SS 316 L, Co-Cr, and Ti-based alloys due to good biocompatibility observed during in-vivo and in-vitro assessments. However, in such aqueous environments, biodegradable magnesium alloys experience the limitation of higher corrosion rates, which causes loosening of the fixation implant. More importantly, it causes an undesirable chemical imbalance in the human body. This undesirable side effect of the promising Mg alloys can be subdued by improving the quality of the implant’s surface which interacts with the human biology. One way to do it is by imparting compressive stress via mechanical processing such as tool-based machining process. Mechanical micro-machining, especially the ultra-precision turning, could be a viable method to fabricate Mg alloy implants and components with the high surface finish necessary for superior corrosion resistance. However, the cutting mechanics of Mg alloy is poorly understood due to the scarcity of processing data and cutting parameters at ultra-precision level. In this paper, with ultra-precise cutting of Mg alloy (AZ91D), a novel “burnishing-like” surface finishing phenomena has been established. Additionally, some of the critical machining results are identified that are crucial for the comprehension of the cutting mechanics. These entities are cutting edge radius effect on the chip formation, material flow angle, machining-induced stress, surface burn marks, chip-tool contact surface, and the fallacy of “no chip formation” phenomenon. Therefore, knowledge derived from this study will enhance the understanding of cutting mechanics at ultra-precision level, and consequently improve the machining results of Mg alloy for bio-medical, electro-mechanical, and space-telecommunication applications.

Effect of cutting edge radius on 'burnishing-like' mechanism in micromachining

In micro-machining, when undeformed chip thickness (a) becomes smaller than the size of tool edge radius (r), the cutting edge radius effect arises by transforming the cutting mechanism from concentrated shear deformation into an extrusion-like behaviour. To analyse the edge radius effect, the governing process parameter is identified as the ratio of a/r. With variation of a/r, 'extrusion-like' finishing zone was identified for Brass and Mg alloy by considering the machined surface integrity, µ-chip morphology and machined surface finishing (Ra). Moreover, 'dirt-like' chip formation could be misleading as "no chip formation" at extreme small a/r value due to the inability of human eye to clearly observe such chips. Finally, 'burnishing-like' finishing is identified in the 'narrow a/r zone' by considering the surface integrity and improvement of machined surface roughness profile. This novel study will help to produce superior quality finishing without requiring post processing of the machined surface.

Effect of cutting edge radius on 'burnishing-like' mechanism in micromachining

In micro-machining, when undeformed chip thickness (a) becomes smaller than the size of tool edge radius (r), the cutting edge radius effect arises by transforming the cutting mechanism from concentrated shear deformation into an extrusion-like behaviour. To analyse the edge radius effect, the governing process parameter is identified as the ratio of a/r. With variation of a/r, 'extrusion-like' finishing zone was identified for Brass and Mg alloy by considering the machined surface integrity, µ-chip morphology and machined surface finishing (Ra). Moreover, 'dirt-like' chip could be misleading as no chip formation at extreme small a/r value due to the inability of human eye to clearly observe such chips. Finally, 'burnishing-like' finishing is identified in the 'narrow a/r zone' by considering the surface integrity and improvement of machined surface roughness profile. This novel study will help to produce superior quality finishing without requiring post processing of the machined surface.

Modelling of flow stress by correlating the material grain size and chip thickness in ultra-precision machining

Abstract Inducing compressive stress on the machined surface is a desirable practice in ultra-precision metal cutting to improve the part quality. An important parameter to analyse the machining performance is the material flow stress, which plays a crucial role in the material deformation characteristics in machining. As the dimensions of the workpiece descend from macro to micro scale in metal forming, the flow stress reduces accordingly. Hence, based on the ‘surface model’ analogy developed for metal forming coupled with the crystal plasticity effect, an attempt has been made in this study to construct a flow stress model for ultra-precision machining process. While developing the model, for the first time, the size factor (η, d/ho) is introduced to incorporate the material ‘grain size effect’ in ultra-precision machining. The proposed model is validated with experimental results of Al6082 alloy of different grain sizes. Orthogonal turning experiments were conducted on an ultra-precision machine by utilizing the concept of ‘cutting edge radius effect’, which is identified as the relative tool sharpness (RTS) and quantified as the ratio of undeformed chip thickness (hc) to edge radius (rn). In this paper, the investigation on the material flow stress is carried out by considering the phenomenon of the shifting material flow separation (cutting) from primary deformation zone to material deformation (ploughing and rubbing) at tertiary deformation zone. The distribution of contact stresses along the tool rake and flank faces at the minimum value of RTS (hc/rn) of 0.01 substantiates the ploughing effect (compressive stresses are induced into the machined layer) rather than chip separation. Moreover, the distinct variation of the machined surface quality and μ-chip morphology at the extreme low and high RTS conditions distinguishes the material ploughing effect from the cutting effect. Additionally, for the same RTS value, it is found that different grain materials (Cu and Mg alloy) exhibited variations in flow stress, chip morphology and surface quality. Therefore, material grain size is an influential factor for analysing machining performance with material flow stress at ultra-precision level.

Influence of Cutting Edge Radius in Micromachining AISI D2

Chip formation is a dynamic process that is often non linear in nature. A chip may not form when the depth of cut is less than a minimum chip thickness. This paper presents an investigation of cutting edge radius effect on micromachining AISI D2 tool steel via simulation. The chip growth, chip formation and material deformation mechanism was investigated using commercial finite element analysis software. A model is developed with consideration of the arbitrary LagrangianEulerian (ALE) method. The chip growth, chip formation and material deformation was investigate under three criteria such as a/r<1, a/r>1 and a/r=1. The model showed that the chip is formed at a/r >1 while material extrusion performed under a/r<1.

A study on the effect of tool-edge radius on critical machining characteristics in ultra-precision milling of tungsten carbide

A crack-free surface can be finished on brittle materials by a specialized but traditional machining technique known as ductile-mode machining. In ductile-mode machining of brittle material, crack propagation is suppressed by selecting a suitable combination of tool and machining parameters leading to the removal of material through plastic deformation enabled by dislocation motion. In ductile-mode machining, the tool–workpiece interaction is of critical significance for the capability of the cutting process to finish a crack-free surface on a brittle material. This interaction is largely dictated by the cutting-edge radius of the tool when the undeformed chip thickness is comparable to the edge radius as is the case of ductile-mode machining. This paper presents the experimental results of ductile-mode milling of tungsten carbide to investigate the effect of cutting-edge radius on certain critical machining characteristics associated with the ductile–brittle transition specific to milling process of brittle material. The experimental results have established that an increase in the cutting-edge radius within a certain range increases the critical feed per edge leading to the improvement of material removal rate in ductile-mode milling. An increasingly negative effective rake angle is desired during milling with larger edge-radiused tool to suppress the crack propagation in the cutting zone to achieve ductile-mode machining. The results also identify the effect of the edge radius on certain other parameters such as critical specific cutting energy, plowing effect and subsurface damage depth to comprehend the ductile–brittle transition phenomenon in ductile-mode milling.