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.

Conditions for Consistent Implementation of Flow Stress Models Incorporating Dynamic Recrystallization into Finite Element Simulation Codes

2013 ◽  
Vol 762 ◽  
pp. 325-330 ◽  
Author(s):  
Markus Bambach
Keyword(s):  
Finite Element ◽  
Flow Stress ◽  
Dynamic Recrystallization ◽  
Type Model ◽  
Stress Model ◽  
Fe Method ◽  
Analysis And Design ◽  
Evolution Of Microstructure ◽  
Stress Models ◽  
Flow Stress Model

Dynamic recrystallization (DRX) is widely used in industrial hot working processes to control the microstructure and properties of the workpiece and to keep the forming forces low. For the analysis and design of metal forming processes powerful simulation methods, must notably the Finite Element (FE) method, have been developed. Various models are available that consider the coupled evolution of microstructure and flow stress during hot deformation processes. Some of these models have been implemented into FE codes and are widely available now. However, for the implementation of flow stress models incorporating DRX into an FE formulation, special smoothness requirements exist that are not automatically fulfilled by the available flow stress models. This work reviews some conditions that a flow stress model incorporating DRX has to fulfill in order to be consistently embedded into an FE code for large plastic deformation. A specific Sellars-type model is analyzed for consistency with these conditions. It is shown that the use of a classical JMAK equation for the DRX kinetics within these models is problematic for Avrami exponents smaller than or equal to 3, for which the flow stress model is not sufficiently smooth. DRX kinetics based on the work of Cahn are proposed to remedy the differentiability issues.

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.

Comparison of Different Extrapolation Models for Materials in the Closed-Extruding Fine Blanking Simulation

2018 ◽  
Vol 1145 ◽  
pp. 123-128
Author(s):  
Ming Deng ◽  
Jiang Po Niu ◽  
Yi Long Ma ◽  
Lin Lv
Keyword(s):  
Finite Element ◽  
Flow Stress ◽  
Finite Element Simulation ◽  
Great Influence ◽  
Stress Model ◽  
Forming Process ◽  
Fine Blanking ◽  
Finite Element Software ◽  
Element Simulation ◽  
Flow Stress Model

The selection of the flow stress model of materials has a great influence on the plastic forming simulation of metal. For closed extrusion fine blanking, selecting the accurate and appropriate material flow stress model can make the finite element simulation closer to the real situation, and the simulation data is more reliable. In order to solve the accuracy problem of finite element simulation closed-extruding fine blanking, 5 types of flow stress fitting curve equations were obtained based on the data of sheet metal tensile test. With the secondary development of finite element software Deform-2D, the circular piece of closed-extruding fine blanking forming process was simulated, whose diameter is 14 mm and thickness is 30 mm. The simulation results of different rheological models were compared after physical experiment being carried out.The results show that Ludwik extrapolation rheological model is suitable for finite element simulation of closed-extruding fine blanking technology, which effectively improves closed-extruding fine blanking simulation accuracy. Lay the foundation for the application of closed-extrusion fine blanking in industry.

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.

Rapid Finite Element Prediction on Machining Process

2013 ◽  
Author(s):  
Long Meng ◽  
Xueping Zhang ◽  
Anil K. Srivastava
Keyword(s):  
Finite Element ◽  
Programming Model ◽  
Cutting Speed ◽  
Chip Morphology ◽  
Machining Process ◽  
Fe Model ◽  
Machining Processes ◽  
Machined Surface ◽  
Element Analysis ◽  
Python Language

Finite Element Analysis (FEA) is widely used to simulate machining processes. However, in general, it is time consuming, error-prone, and requires repeated efforts to establish a verified successful Finite Element (FE) model. To rapidly investigate the effects of parameters such as tool angle, feed rate, cutting speed, and temperatures generated during the machining process, an efficient approach is proposed in this paper. The technique has been used to achieve rapid FF simulation during turning and milling processes using Python language programming of Abaqus. Sub-model 1 is programmed to simulate the chip formation process in Abaqus/Explicit. Sub-model 2 is programmed to simulate the cooling spring-back process by importing the machined surface into Abaqus/Implicit. The proposed method is capable of simulating the chip morphology, stress, strain and temperature of the machining process with different parameters immediately. The established FE models are automatically solved in batch by programming script. Post-processing is programmed by Abaqus script to easily achieve and evaluate the simulation results. The Programmed FE models are validated in terms of the predicted chip morphology, cutting forces and residual stresses. This method is extraordinarily efficient saving more than 33% simulation time in comparison to existing FEA approach used for machining processes. Moreover, the script is concise, easy to debug, and effectively avoiding interactive mistakes. The rapid programming model provides a novel, efficiency and convenient approach to thoroughly investigate the effects of a large number of parameters on machining processes.

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.

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