Microhardness Prediction Based on a Microstructure-Sensitive Flow Stress Model During High Speed Machining Ti-6Al-4V

2018 ◽  
Vol 140 (9) ◽  
Author(s):  
Qingqing Wang ◽  
Zhanqiang Liu
Keyword(s):  
Flow Stress ◽  
Grain Refinement ◽  
High Speed ◽  
Direct Consequence ◽  
Deformation Twinning ◽  
Machining Process ◽  
High Speed Machining ◽  
Stress Model ◽  
Machined Surface ◽  
Flow Stress Model

Exploring the hardening mechanisms during high speed machining (HSM) is an effective approach to improve the fatigue strength and the wear resistance of machined surface and to control the fragmentation of chips in a certain range of hardness. In this paper, the microhardness variation is explored from the perspective of microstructural evolutions, as a direct consequence of the severe deformation during HSM Ti-6Al-4V alloy. A microstructure-sensitive flow stress model coupled the phenomena of grain refinement, deformation twinning, and phase transformations is first proposed. Then the microstructure-sensitive flow stress model is implemented into the cutting simulation model via a user-defined subroutine to analyze the flow stress variation induced by the microstructure evolutions during HSM Ti-6Al-4V. Finally, the relationship between the microhardness and flow stress is developed and modified based on the classical theory that the hardness is directly proportional to the flow stress. The study shows that the deformation twinning (generated at higher cutting speeds) plays a more important role in the hardening of Ti-6Al-4V compared with the grain refinement and phase transformation. The predicted microhardness distributions align well with the measured values. It provides a novel thinking that it is plausible to obtain a high microhardness material via controlling the microstructure alterations during machining process.

A New Microstructure-Sensitive Flow Stress Model for the High-Speed Machining of Titanium Alloy Ti–6Al–4V

2016 ◽  
Vol 139 (5) ◽  
Author(s):  
X. P. Zhang ◽  
R. Shivpuri ◽  
A. K. Srivastava
Keyword(s):  
Flow Stress ◽  
Titanium Alloys ◽  
High Speed ◽  
Flow Behavior ◽  
Stress Sensitivity ◽  
Machining Process ◽  
High Speed Machining ◽  
Stress Model ◽  
Mechanical State ◽  
Flow Stress Model

The flow stress in the high-speed machining of titanium alloys depends strongly on the microstructural state of the material which is defined by the composition of the material, its starting microstructure, and the thermomechanical loads imposed during the machining process. In the past, researchers have determined the flow stress empirically as a function of mechanical state parameters, such as strain, strain rate, and temperature while ignoring the changes in the microstructural state such as phase transformations. This paper presents a microstructure-sensitive flow stress model based on the self-consistent method (SCM) that includes the effects of chemical composition, α phase and β phase, as well mechanical state imposed. This flow stress is developed to model the flow behavior of titanium alloys in machining at speed of higher than 5 m/s, characterized by extremely high strains (2–10 or higher), high strain rates (104–106 s−1 or higher), and high temperatures (600–1300 °C). The flow stress sensitivity to mechanical and material parameters is analyzed. A new SCM-based Johnson–Cook (JC) flow stress model is proposed whose constants and ranges are determined using experimental data from literature and the physical basis for SCM approach. This new flow stress is successfully implemented in the finite-element (FE) framework to simulate machining. The predicted results confirm that the new model is much more effective and reliable than the original JC model in predicting chip segmentation in the high-speed machining of titanium Ti–6Al–4V alloy.

Microstructure Sensitive Flow Stress Based on Self Consistent Method

2016 ◽  
Author(s):  
Xueping Zhang ◽  
Rajiv Shivpuri ◽  
Anil K. Srivastava
Keyword(s):  
Flow Stress ◽  
Titanium Alloys ◽  
High Speed ◽  
Machining Process ◽  
High Speed Machining ◽  
Stress Model ◽  
Mechanical State ◽  
Self Consistent ◽  
Consistent Method ◽  
Flow Stress Model

Flow stress in the high speed machining of titanium alloys depends strongly on the microstructural state of the material which is defined by the composition of the material, its starting microstructure and the thermo-mechanical loads imposed during the machining process. Previous researchers have determined the flow stress empirically as a function of mechanical state parameters such as strain, strain rate and temperature while ignoring the changes in the microstructural state such as alpha-beta phase transformations. This paper presents a new microstructure sensitive flow stress model based on the self-consistent method (SCM) that includes the effects of chemical composition, α phase and β phase, as well mechanical state imposed. This flow stress is developed to model the flow behavior of titanium alloys in machining, at speed of higher than 5m/s, characterized by extremely high strains (2∼10 or higher), high strain rates (104∼106s−1 or higher) and high temperatures (600∼1300°C). The flow stress sensitivity to mechanical and material parameters is analyzed. A new SCM-based Johnson-Cook (JC) flow stress model is proposed whose constants and ranges are determined using experimental data and the physical basis for SCM approach from literature. This new flow stress is successfully implemented in the finite element framework to simulate high speed machining process and compared with other types of flow stress models in terms of chip morphology. The predicted results confirm that the new model is much more effective and reliable than the original JC model in predicting chip segmentation in the high speed machining of titanium Ti-6Al-4V alloy.

On the Flow Stress Model Selection for Finite Element Simulations of Machining of Ti6Al4V

2014 ◽  
Vol 611-612 ◽  
pp. 1274-1281 ◽  
Author(s):  
Stano Imbrogno ◽  
Giovanna Rotella ◽  
Domenico Umbrello
Keyword(s):  
Finite Element ◽  
Flow Stress ◽  
Chip Morphology ◽  
Experimental Tests ◽  
Finite Element Method Simulation ◽  
Machining Process ◽  
Stress Model ◽  
Machining Processes ◽  
Flow Stress Model ◽  
Materials Flow

Numerical simulation of machining processes represents a promising tool able to reproduce the cutting conditions without the need to perform a large number of experimental tests. In order to obtain reliable results from the finite element method simulation, is then necessary to properly set up the simulation conditions and to implement the most suitable materials behavior according to the real workpiece characteristics. These data are available in commercial softwares libraries but often they have difficulties to properly represent the machined workpiece behavior. Thus, advanced model are implemented in the software to improve the simulations performance and to obtain realistic results. In this work, the more suitable materials flow stress, within those proposed in literature, is sought to simulate the machining process of Ti6Al4V. The results of the simulations have been compared with those obtained experimentally in terms of temperature, chip morphology and cutting force. The results confirm the need to properly select the materials flow stress model according to the physical sample.

scholarly journals Simulation of Grain Refinement Induced by High-Speed Machining of OFHC Copper Using Cellular Automata Method

2020 ◽  
Vol 142 (9) ◽  
Author(s):  
Jun Zhang ◽  
Xiang Xu ◽  
José Outeiro ◽  
Hongguang Liu ◽  
Wanhua Zhao
Keyword(s):  
High Temperature ◽  
Cellular Automata ◽  
High Strain Rate ◽  
Strain Rate ◽  
Grain Refinement ◽  
High Speed ◽  
High Strain ◽  
Machining Process ◽  
Ofhc Copper ◽  
High Speed Machining

Abstract During high-speed machining (HSM), the microstructure of materials evolves with significant plastic deformation process under high strain rate and high temperature, which affects chip formation and material fracture mechanisms, as well as surface integrity. The development of models and simulation methods for grain refinement in machining process is of great importance. There are few models which are developed to predict the evolution of the grain refinement of HSM in mesoscale with sufficient accuracy. In this work, a cellular automata (CA) method with discontinuous (dDRX) and continuous (cDRX) dynamic recrystallization (DRX) mechanisms is applied to simulate the grain refinement and to predict the microstructure morphology during machining oxygen-free high-conductivity (OFHC) copper. The process of grain evolution is simulated with the initial conditions of strain, strain rate, and temperature obtained by finite element (FE) simulation. The evolution of dislocation density, grain deformation, grain refinement, and growth are also simulated. Moreover, cutting tests under high cutting speeds (from 750 m/min to 3000 m/min) are carried out and the microstructure of chips is observed by electron backscatter diffraction (EBSD). The results show a grain refinement during HSM, which could be due to the occurrence of dDRX and cDRX. High temperature will promote grain recovery and growth, while high strain rate will significantly cause a high density of dislocations and grain refinement. Therefore, HSM contributes to the fine equiaxed grain structure in deformed chips and the grain morphology after HSM can be simulated successfully by the CA model developed in this work.

Influence of Material Flow Stress on Surface Roughness in High-Speed Machining

2012 ◽  
Vol 723 ◽  
pp. 219-224
Author(s):  
Su Yu Wang ◽  
Wen Jie Yang ◽  
Wen Chao Wang
Keyword(s):  
Surface Roughness ◽  
Flow Stress ◽  
Material Flow ◽  
High Speed ◽  
Vertical Direction ◽  
Contact Theory ◽  
High Speed Machining ◽  
Machined Surface ◽  
Simulation Based ◽  
Side Flow

A mechanical model of surface roughness is established based on the Kragelskii-Drujanov theory of friction and wear and Hertz elastic contact theory. Effect of material flow stress on remnant height of the machined surface was investigated. Test showed that the machined surface morphology provides the phenomena of the side flow in the vertical direction of ploughing in high-speed machining. The remnant height values on the machined surface of the high-speed machining are obtained by DEFORM-3D simulation. Based on the results it can be concluded that the surface roughness values of the workpiece increase with material flow stress.

Prediction of the Surface Roughness in High-Speed Machining Based on Molecular-Mechanical Theory of Friction

2011 ◽  
Vol 308-310 ◽  
pp. 1134-1138 ◽  
Author(s):  
Su Yu Wang ◽  
Wen Chao Wang ◽  
Tao Yu ◽  
Bin Jiang
Keyword(s):  
Surface Roughness ◽  
Flow Stress ◽  
Mechanical Model ◽  
High Speed ◽  
High Speed Machining ◽  
Mechanical Theory ◽  
Machined Surface ◽  
Aisi 1045 Steel ◽  
Aisi 1045 ◽  
1045 Steel

Surface roughness is an important parameter to evaluate the quality of high-speed machining (HSM). This paper establishes a mechanical model based on the molecular-mechanical theory of friction to study factors that influence the surface roughness in HSM. The relationship between flow stress and the remnant height on the machined surface is obtained. The HSM process of AISI-1045 steel is simulated by using finite element method (FEM) based on DEFORM-2D and the flow stress is obtained. The surface roughness of workpiece machined by HSM is calculated based on the value of flow stress and the mechanical model. The result shows that the surface roughness of workpiece in HSM is acceptable, and the mechanical model supplies a method to study the surface roughness in HSM.

Research on High-Speed Cutting of Cr12MoV Hardened Steel - A Review

2020 ◽  
Vol 15 ◽  
Author(s):  
Fei Sun ◽  
Guohe Li ◽  
Qi Zhang ◽  
Meng Liu
Keyword(s):  
High Speed ◽  
Cutting Temperature ◽  
High Hardness ◽  
High Strength ◽  
Hardened Steel ◽  
Parameters Optimization ◽  
Future Research ◽  
High Speed Machining ◽  
Machined Surface ◽  
Stamping Die

: Cr12MoV hardened steel is widely used in the manufacturing of stamping die because of its high strength, high hardness, and good wear resistance. As a kind of mainstream cutting technology, high-speed machining has been applied in the machining of Cr12MoV hardened steel. Based on the review of a large number of literature, the development of high-speed machining of Cr12MoV hardened steel was summarized, including the research status of the saw-tooth chip, cutting force, cutting temperature, tool wear, machined surface quality, and parameters optimization. The problems that exist in the current research were discussed and the directions of future research were pointed out. It can promote the development of high-speed machining of Cr12MoV hardened steel.

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