Metallo-Thermo-Mechanical Coupled Process Modeling

During machining processes, steels often behave in a complicated manner involving severe plastic deformation, fracture, phase change, grain size change, etc.  Metallurgical transformation occurs in the chip or on the workpiece machined surface due to intense, localized and rapid thermal mechanical working during machining. This is especially evident in high-speed machining, thermally enhanced machining, grinding and hard turning with severe tool wear.  As the heat generated in the cutting process raises the workpiece material temperature above its critical phase transformation temperature, a metallurgical transformation will occur, and the latent heat and plasticity due to the transformation will affect the machining process.  Mechanical deformation, heat transfer, and microstructure are all strongly coupled together, each affecting the others, and these effects has been termed metallo-thermo-mechanical coupling.  

The purpose of this study is to quantitatively disseminate the underlying mechanisms through prediction of the microstructure change using a multi-physics model, which considers both phase transformation and grain refinement. two-dimensional (2D) or three-dimensional (3D) cutting simulations are undertaken via ABAQUS or AdvantEdge FEM software incorporating these two mechanisms as user-defined subroutines to investigate the surface microstructure alteration for AISI 1045 steel, AISI 52100 steel, and AISI 1060 steel.

 


 

Hard Drilling of AISI 1060 Steel

 

Hole surface microstructures are very critical to the mechanical performance and fatigue life of metallic products from drilling processes. When steel material is drilled at a fully hardened condition, hole surface microstructures are often subject to transition because of the intense thermo-mechanical loading in the drilling process. A white layer can be formed on the surface of a drilled hole of carbon steels with high matrix hardness.

In this study, a multi-step numerical analysis is conducted to investigate the potential mechanism of surface microstructure alterations in the drilling process of hardened steels. 

Multi-step numerical models

1. 3D simulation of steady state drilling using AdvantEdge.

2. Extract steady-state temperature and stress fields from 3D simulation.

3. Define the initial conditions of 2D CEL simulation in ABAQUS with the imported temperature and stress fields, and conduct the coupled modeling simulation.

Subsurface Microstructure

The comparison of simulated profiles of shear strain, total dislocation density, grain size along the penetration with the SEM and TEM micrograph near surface of a hole. 

Hardness

Simulated transformed phase composition and microhardness profile near the hole surface.

The increase of microhardness was predicted in the top nanocrystalline white layer due to the severe plastic deformation.

A 10-60 µm of tempered martensitic structure was predicted to have a decrease in microhardness due to the tempering effect. 

White Layer

Effects of drilling parameters: (a) cutting speed; (b) feed.

Although the thickness of the nanocrystalline white layer varies with different drilling process parameters, such as the cutting speed and feed, it mainly depends on the thermally driven phase transformation.

   

 

Hard Turning of AISI 52100 Steel

 

The formation of white layer in hard turning can be attributed to two main factors: thermally driven phase transformation and mechanical grain refinement due to severe plastic deformation. 

The purpose of this study is to quantitatively disseminate the underlying mechanisms through prediction of the microstructure change using a multi-physics model, which considers both phase transformation and grain refinement. 

3D hard turning simulations are undertaken via AdvantEdge FEM software incorporating these two mechanisms as user-defined subroutines to investigate the surface microstructure alteration for AISI 52100 steel.  Comparisons with the experimental data at various cutting conditions prove that the proposed model can accurately predict the critical surface microstructural attributes such as phase compositions, grain size, microhardness, and residual stress during hard turning of AISI 52100 steel.

 

3D FE modeling

3D hard turning FE simulation via AdvantEdge FEM and the flow chart of the user subroutione.

Simulation results

The 3D simulated fields of cutting temperature, phase change, dislocation density, and grain size.

Refined microstructure produced at low-to-moderate cutting speeds are mainly caused by severe plastic deformation, whereas white layer formation at high cutting speeds is caused by both thermally driven phase transformation and grain refinement due to SPD

Hardness

At a cutting speed of 91.4 m/min, an increase of surface hardness of 0.83 GPa was predicted to be caused by SPD. 

At a cutting speed of 274.3 m/min, an increase of surface hardness of 1.43 GPa was predicted to be caused by a combination of martensitic transformation and SPD.

   

 

Metallo-thermo-mechanical coupled analysis of orthogonal cutting of AISI 1045 steel

 

This work is concerned with prediction of the phase change effect on orthogonal cutting of AISI 1045 steel based on a true metallo-thermo-mechanical coupled analysis.  A metallo-thermo-mechanical coupled material model is developed, and a finite element model is used to solve the evolution of phase constituents, cutting temperature, chip morphology, and cutting force simultaneously using ABAQUS. 

The model validity is assessed using the experimental data for orthogonal cutting of AISI 1045 steel under various conditions, with cutting speeds ranging from 198 to 879 m/min, feeds from 0.1 to 0.3 mm, and tool rake angles from -7° to 5°.  A good agreement is achieved in chip formation, cutting force and cutting temperature between the model predictions and the experimental data.

 

 

Coupled Analysis

Metallo-thermo-mechanical coupling in cutting of steels.  

 

FE Modeling

Predictions of temperature, von Mises stress and phase field  

 

 

Phase Change Prediction

Prediction of phase fraction of austenite in the chip and comparison of the predicted maximum tool-chip interface temperature (Tint) with experimental data.