Chapter 11home.iitk.ac.in/~jrkumar/download/Chapter 11 - Multiscale Modelling.pdf · Chapter 11...
Transcript of Chapter 11home.iitk.ac.in/~jrkumar/download/Chapter 11 - Multiscale Modelling.pdf · Chapter 11...
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Chapter 11
Multiscale Modelling of Hybrid Machining Processes
Dr. J. Ramkumar1 and Ishan Srivastava2
1Professor and 2Research Student
Department of Mechanical Engineering
Micromanufacturing Lab, I.I.T. KanpurMicromanufacturing Lab, I.I.T. Kanpur
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Organization of the presentation
• Introduction
• Multiscale Modelling Fundamentals
- Basics of Multiscale Modelling Technologies
- Multiscale Modelling Methodologies and Strategies
- Modelling & Simulation Approaches for Machining Processes
• Multiscale Modelling For Laser-Assisted Hybrid Machining Processes
- Process Work Principle and features.
- Multiscale Modelling Considerations
- Pre- and Postprocessing
• Case Study
• Conclusions
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Introduction
Multiscale modelling refers to the analysis of systems which involves
- wide range of physical/chemical/mechanical/thermal/fluid phenomenon's
- Nano-meso-micro-macro scale coupling
- Different spatial and temporal scales
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Different techniques used for modelling phenomenon of
different length domain.
IntroductionDensity Functional
Theory (DFT)
Molecular Dynamic Simulation (MDS)
Dissipative Particle Dynamics (DPD)
Finite Element Method (FEM)
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Multiscale Modelling Fundamentals
Basics of Multiscale Modelling Technology
• To determine the response of a process chain to specific inputs and boundary conditions.
• Earlier, usually restricted to a specific spatial/temporal scale.
• Now replaced with multiscale-modelling (Spanning over multiple level of space and time)
Multiscale Problems
Type-A
Problems involving local defects and singularities.A macroscale model is sufficient for most physical domain.
Ex- chemical reactions at specific locations, crack defects during machining process, dislocations or boundary layers in deformed materials.
Type-B
Some information is missing from macroscale model, so microscale model is either used everywhere or is coupled with macroscale model.
Ex- heat flow in heat exchangers, mass transport in chemical reactions, swirl formation in fluid flow.
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Basics of Multiscale Modelling Technology
Coupling Methods
Coupling implies to combining results of different part models into a single, comprehensive solution.
Manual Coupling
• Inputs to a code at one scale are influenced by study of the outputs of a previously run code at another scale.
• Ex- Coupling timescale: Hours to weeks
Loose Coupling b/w codes
• Typically performed using workflow tools
• Often in different memory spaces
• Ex- Coupling timescale: minutes
Tight Coupling b/w codes
• Typically performed using coupling methods (e.g. CCA)
• Maybe in same memory spaces
• Hard to develop changes
• Ex- Coupling timescale: Seconds
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Multiscale Modelling Fundamentals
Multiscale Modelling Strategies and Methodologies
Methods
Analytical
Numerical
1. Matched Asymptotics
2. Averaging Methods
3. The WKB Method
4. The Mori-Zwanzig
Formalism
1. Linear Scaling Algorithms
2. Sublinear Scaling Algorithms
3. Type A & B problems
4. Concurrent and Sequential
coupling
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Multiscale Modelling Strategies and Methodologies
Sequential Multiscale Modelling
• Establish the macroscale model with some details
of the constitutive relations that are
precomputed from micro or nanoscale models.
• Macroscopic model is determined first.
• Only suitable when the number of parameters
passed between the models are few.
• Very effective when simulation of specific
materials and application is involved in multiscale.
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Multiscale Modelling Strategies and Methodologies
Concurrent Multiscale Modelling
• In this, a series of processes which combine
information available from distinct length and
time scales into a single coherent, coupled
simulation.
• The quantities needed in macroscopic model are
computed on-the-fly from microscopic model as
the computation proceeds.
• Different scales of material behaviour are
considered concurrently.
• Different scaled algorithm are combined together
with matching procedures invoked in some
overlapping domain to resolve Multiphysics.Micromanufacturing Lab, I.I.T. Kanpur
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Modelling and Simulation Approaches for Machining Processes
• In the manufacturing field, metal material machining processes are essential to produce designed products that
are worth many billions of dollars.
• For manufacturing of advanced materials and products, the underlying phenomenon in processes span a wide and
hierarchically organised sequence of time and length scales.
• Multiscale modelling is effectively used to predict and test the capability of the designed product so as to optimise
the production process.
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Multiscale Modelling of Laser-Assisted Hybrid Machining Process
• Hybrid machining is based on the
simultaneous and controlled
interaction of process mechanism
and/or energy sources having a
significant effect on performance
parameters.
• Ex- Laser-assisted milling, vibration-
assisted grinding.
• For the assisted hybrid machining, the
main mechanical cutting is coupled
with one or several other types of
energy inputs such as ultrasonic
vibration, thermal, fluid, magnetic field
etc.
Laser-assisted Milling
Laser-assisted turning
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Process work Principles and Features
• The laser beam is focused directly in front of the cutting tool,
softens the material so machining becomes easier.
• An increase in the temperature offers an increase in the surface
roughness.
• In comparison to conventional cutting, the plastically deformed
layer within the workpiece’s subsurface is deeper and more
uniform which indicates the existence of favourable compressive
residual stress.
• Due to heat the deformation shifts from brittle to ductile. Hence,
difficult-to-machine materials can be easily machined using
Laser-Assisted-Machining (LAM).
• Only a narrow location is heated so as to have minimum Heat-
affected Zone (HAZ).
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Multiscale Modelling Considerations for Laser -Assisted Hybrid Machining
• Laser beam energy is absorbed by the w/p surface and converted to thermal energy causing the temperature to rise.
For thermal response, in a cylindrical coordinate system is expressed as,
Schematic Diagram for turning
The Heat generated due to the plastic deformation could be calculated as:
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Pre- and Postprocessing
Material Parameters
• Tensile Strength• Yield Strength• Reduction of Area• Elongation• Modulus of Elasticity• Density• Specific Heat
Cutting Parameters
• Cutting Speed• Feed Rate• Depth of Cut• Cutting Width• Workpiece Speed
Tool Related Parameters
• Rake Angle• Relief Angle• Radius of Tip• Sand wheel Diameter• Hardness
Laser-Related Parameters
• Laser Power• Laser Beam Diameter• Laser Head Velocity• Pyrometer Laser Head
Output
• Component Geometry• Surface Residual Stress• Overall Temp. Distribution• Cutting force• Stress Variation
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Case Study: Laser-Assisted Machining of Mold Steel
• A 2D numerical Model of the laser assisted cutting of
NAK80 is done.
• Combination of two process:
• Simulation of moving laser heat source applied on
the local surface of workpiece which causes the
corresponding temperature field to rise and
material to soften.
• Simulation of cutting process with stress leading to
plastic deformation and finally shear.
• Chemical composition of NAK80 is:
C, 0.15%; Si, 0.3%; Mn, 1.5%; Ni, 3.0%; Al, 1.0%; Cu,
1.0%; Fe, 93.05%
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Case Study: Laser-Assisted Machining of Mold Steel
Boundary Conditions and Assumptions
• Tool is rigid.
• Workpiece is assumed to be isotropic and follows
Johnson-Cook Plastic criterion.
• No material phase transformation is assumed
under machined surface is considered.
• Rake angle = 10
• Clearance angle = 6
• Tool nose angle = 0.02 mm
• Cutting Speed = 25 mm/s
• Depth of Cut = 0.1 mm
• Laser power = 2000 W
• Laser Head Velocity = 25 mm/s
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Case Study: Laser-Assisted Machining of Mold Steel
Results and Conclusion
• The temperature distribution as a result of laser radiation was simulated. The corresponding laser heat
flux follows Gaussian distribution.
• The final temperature is 1270 C at the local position near the laser spot; the maximum thickness of HAZ is
around 7.5 mm.
• The max. cutting forces and stresses caused by LAM are 1290 MPa and 2290 MPa which are obviously
lower than their conventional contemporaries.Micromanufacturing Lab, I.I.T. Kanpur
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Thank You
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