Simulation of chip-formation by a single grain of pyramid shape (original) (raw)

Machining simulation of Ti6Al4V using coupled Eulerian-Lagrangian approach and a constitutive model considering the state of stress

Simulation Modelling Practice and Theory, 2021

The accuracy of a machining model depends on the capability of this model to describe the physical phenomena associated to the real machining system. This includes the material constitutive model and the approach used to describe the field flow of the material in cutting. In this paper, a model of high speed machining (HSM) of Ti6Al4V titanium alloy is developed. This cutting model includes the proposed constitutive model considering the influence of strain hardening, strain-rate, temperature, and state of stress (e.g., stress triaxiality and Lode parameter) in the material plasticity and damage. Finite Element Method (FEM) using Coupled Eulerian-Lagrangian (CEL) approach is used to simulate the cutting model. A sensitivity analysis of the influence of the mesh topography on the chip geometry and cutting force is performed resulting in the determination of the optimal element size and element orientation. Simulation results obtained using the CEL approach are compared with those obtained using the Lagrangian one. Moreover, simulated cutting force and chip geometry obtained using the proposed constitutive model are compared with those obtained using the Johnson-Cook (J-C) model, and experimental data. Both chip geometry and cutting force predicted by the proposed constitutive model is closer to the experimental one than the J-C constitutive model. The CEL approach combined with the proposed constitutive model can simulate material side flow, which results in a larger width of chip compared to the width of cut, and in the formation of lateral burr on the workpiece. It also permits simulating the cyclic variation of the plastic strain and topography of the machined surface along the cutting direction, observed experimentally.

Influences of Cutting Speed and Material Constitutive Models on Chip Formation and their Effects on the Results of Ti6Al4V Orthogonal Cutting Simulation

ESAFORM 2021, 2021

The highly used Ti6Al4V alloy is a well know hard-to-machine material. The modelling of orthogonal cutting process of Ti6Al4V attract the interest of many researchers as it often generates serrated chips. The purpose of this paper is to show the significant influence of cutting speed on chip formation during orthogonal cutting of Ti6Al4V along with different material constitutive models. Finite element analyses for chip formation are conducted for different cutting speeds and are investigated with well-known Johnson-Cook constitutive model, a modified Johnson–Cook model known as Hyperbolic Tangent (TANH) model that emphasizes the strain softening behavior and modified Johnson-Cook constitutive model that consider temperature dependent strain hardening factor. A 2D Lagrangian finite element model is adopted for the simulation of the orthogonal cutting process and the results from the simulations such as calculated forces, chip morphologies are analyzed and are compared with the exper...

A new material model for 2D numerical simulation of serrated chip formation when machining titanium alloy Ti–6Al–4V

International Journal of Machine Tools and Manufacture, 2008

A new material constitutive law is implemented in a 2D finite element model to analyse the chip formation and shear localisation when machining titanium alloys. The numerical simulations use a commercial finite element software (FORGE 2005 s ) able to solve complex thermo-mechanical problems. One of the main machining characteristics of titanium alloys is to produce segmented chips for a wide range of cutting speeds and feeds. The present study assumes that the chip segmentation is only induced by adiabatic shear banding, without material failure in the primary shear zone. The new developed model takes into account the influence of strain, strain rate and temperature on the flow stress and also introduces a strain softening effect. The tool chip friction is managed by a combined Coulomb-Tresca friction law. The influence of two different strain softening levels and machining parameters on the cutting forces and chip morphology has been studied. Chip morphology, cutting and feed forces predicted by numerical simulations are compared with experimental results. r

Analysis and Modeling of the Micro-Cutting Process of Ti-6Al-4V Titanium Alloy with Single Abrasive Grain

Materials

Modeling of material displacements in the microcutting zone is complex due to the number and interdependence of factors affecting the results of the process. An important problem in the modeling process is the selection of the constitutive model and its parameters, which will correctly describe the properties of the material under the conditions of triaxial compression, which is characteristic for the areas of the contact zone of the blade and the processed material in abrasive machining processes. The aim of the work was to develop computer models (with the use of the finite element method) of the microcutting process with a single abrasive grain, which were verified with the results of experimental tests. The paper presents the methodology of modeling the processes of microcutting with abrasive grains, whose geometrical models were created based on optical scanning methods. Observations of the microcutting process were carried out with the use of a high-speed camera and an optical...

Simulation of serrated chip formation in micro-milling of titanium alloy Ti-6Al-4V using 2D elasto-viscoplastic finite element modeling

Production Engineering, 2016

Finite element simulations have been utilized in analyses of machining process for several decades. In mechanical micromachining, finite element simulation can also be used for predicting cutting forces, minimal chip thickness, temperatures, and tool wear. The accuracy of results and the computational cost are highly dependent upon the assumptions which govern that particular chip formation problem. This study presents a comparison of two different material assumptions in finite element simulation of micro-milling titanium alloy Ti-6Al-4V. The same simulation was conducted by using the elasto-viscoplastic and the viscoplastic material assumptions. The predicted results are compared against the experimental observations. The results have shown that the material assumption has a major effect on the mechanism of chip formation and heat generation but a minor effect on the cutting force and tool wear prediction. In terms of computational cost, it was found that the simulation with the viscoplastic material assumption can reduce simulation time up to eight times that of required for a simulation with elasto-viscoplastic assumption.

Computational Materials Science and Surface Engineering Effect of the cutting speed on the chip morphology and the cutting forces

Purpose: The aim of this research is to make a first experimental analysis of the effect of the cutting speed on the chip morphology, and of the cutting forces in the orthogonal turning process of the titanium alloys Ti-6Al-4V. Design/methodology/approach: The methodology has consisted of proving a series of parameters combinations: f, feed rate, Vc, cutting speeds are explored in a range from 50 to 250 m/min, and is analyzing the different types of chips and the evolution cutting forces appeared during each one them, and determined the analytical model of plastic deformation ratio. Findings: Tests achieved have shown three main types of chips: Continuous chip at 50 m/min, Flow chip for speeds ranging around 100 m/min, and Shear localized chip starting from the transition speed of 125 m/min and above. The modification of the mechanism of chip formation is associated with the appearance of shearing instability. Chip segmentation by shear localisation is an important process which is ...

Modelling of material cutting with a material microstructure-level (MML) model

In this research work a material microstructure-level cutting model (MML cutting model) is presented. The crystal plasticity theory is adopted for modeling the cutting of the titanium alloy Ti-6Al-4V in orthogonal case. In this model, the grains of the studied material are explicitly presented, and their orientation angles and slip system strength anisotropy are considered as the main source of the microstructure heterogeneity in the cutting material. To obtain the material degradation process, the continuum self-consistent intragranular damage model and discrete cohesive zone inter-granular damage model, were developed, wherein the zero thickness cohesive element is implemented to simulate the bond between grain interfaces. This model was validated by a comparison with compression tests from literature. Results demonstrate the possibility to capture the influence of the microstructure on the material removal in terms of chip formation. Particularly, it is demonstrated that the grain orientation angle plays an important role for the chip segmentation and its periodicity during the cutting process.

Analytical modeling of machining forces of ultra-fine-grained titanium

The International Journal of Advanced Manufacturing Technology, 2018

In this work, the machining of ultra-fine-grained pure titanium (UFG Ti) in an integrated manufacturing process combining severe plastic deformation (SPD) process and machining process is investigated through analytical modeling with experimental validation. UFG Ti is increasing finding usefulness in lightweight engineering applications and biomedical applications because of its sufficient mechanical strength, manufacturability, and biocompatibility. The UFG Ti is prepared by a SPD process, namely equal channel angular extrusion (ECAE) from commercial pure grade 4 titanium. However, the machining process in the integrated manufacturing process has not been fully understood in the context of machining forces and temperatures. The machining forces are predicted in this work using extended chip formation model. In this model, the average temperature at the primary shear zone is calculated based on the equilibrium between generated heat and plastic work. Orthogonal cutting tests were conducted under various cutting conditions with experimental force measurements using a piezoelectric dynamometer. Good agreements are observed between predicted forces and experimental forces. In addition, sensitivity analyses were performed to investigate the influence of input J-C constants and cutting condition parameters on the accuracy of the predicted machining forces. The predicted machining forces were compared to machining forces of Ti-6Al-4V alloy under various cutting conditions, which are widely used in engineering and biomedical applications. This work extends the applicability of analytical models in machining to a broader class of materials. It will promote the use of UFG Ti and the integrated manufacturing process in engineering and biomedical applications.

Detailed modeling of cutting forces in grinding process considering variable stages of grain-workpiece micro interactions

A B S T R A C T Grinding forces are a key parameter in the grinding process, most previous studies on grinding forces, however, (i) were regardless of grain-workpiece micro interaction statuses and (ii) could only predict average/maximal grinding forces based on average/maximal cutting depths or chip thicknesses. In this study, a novel detailed modeling methodology of grinding forces has been analytically established, experimentally validated and utilised to study a specific issue that previous methods can not address. Based on the proposed method, grinding forces with detailed information (e.g. three components including rubbing, plowing and cutting forces) could be accurately predicted. Except for grinding forces, the proposed methodology also enable the availability of other grinding process details at the grain scale (e.g. the ratios of grains that are experiencing rubbing, plowing and cutting stages to the total engaging grain number). Validation experiment results have proved that, the proposed method could, to a large extent, describe the realistic grinding forces. Based on the proposed method, the effects of grinding conditions (including depths of cut, wheel speeds, workpiece feed speeds and grinding wheel abrasive sizes) on each component of grinding forces (rubbing, plowing, and cutting forces) have been analyzed. Some new findings, which could enhance the existing understandings of grinding forces and guide industrial manufacture, have been gained. The proposed method therefore is anticipated to be not only meaningful to provide a new way to model grinding forces in detail, but also promising to study other grinding issues (e.g. grinding heat, machined surface topography, grinding chatter), especially under the trend of miniaturization and microfabrication where grinding details at the grain scale are highly needed to optimise the micro grinding tool efficiency and micro-grinding accuracy.

Influence of material models on serrated chip formation in simulation of machining Ti-6Al-4V titanium alloy

2009

Titanium and its alloys are today used in aerospace, automotive and medical device industries. Ti-6AL-4V alloy is the most suitable Ti alloy used because it offers great mechanical characteristics such as high strength-to-weight ratio, toughness, superb corrosion resistance and bio-compatibility. However, Ti alloys are difficult-to-machine materials with considerable manufacturing problems. Due to the low thermal conductivity, temperatures rapidly reach high values affecting phase-transformation and causing severe tool wear. In this study, the feasibility of using finite element analysis to investigate the cutting tool micro-geometry effects in machining of Ti6Al4V titanium alloy is exploited. 2-D finite element modeling of machining has been considered to investigate the influence of material models for Ti-6AL-4V titanium alloy on tool forces, chip formation and temperatures and stresses using PcBN tools with a distinct edge radius. Serrated and cyclical chip formation has been simulated using damage models in processes simulations and compared with experimental results from literature.