- 1. Presentation on A Bond Graph Approach to Model Gas Metal Arc Welding(GMAW) Presented by: Abhay Singh Rana M.E. CAD/CAM Engineering Roll No: 851281001 1 Under The Guidance of Dr. Tarun Kumar Bera Associate Professor Department of Mechanical Engineering Thapar University, Patiala
- 2. Introduction • Estimation and control of droplet sizes in Gas Metal Arc Welding (GMAW) is an application of Magneto hydrodynamic systems. • Two approaches being used are SFBM (Static Force Balance Model) and MFBM (Modified Force Balance Model). • SFBM quite accurately [1] predicts the radius of globular mass transfer drop with the force equilibrium equations. Where surface tension is to be equal to gravitational and electromagnetic forces.
- 3. Literature Survey Sl No. Author Publication Publisher Key Points 1 Nabeel Arif, Jae Hak Lee and Choong Don Yoo Modeling of globular transfer considering momentum flux in GMAW IOP Publishing Journal of Physics D: Applied Physics Basic Introduction of the equilibrium models. Characteristic Curves of forces, with current and arc angle. 2 L A Jones, T W Eagar and J H Lang Magnetic Forces acting on molten drops in gas metal arc welding J. Phys. D: Appl. Phys. Derivation of the expression for the electromagnetic force, Film of Droplet formation.
- 4. Literature Survey 3 C . Sozou and W. M. Pickering The development of magnetohydrody namic flow due to an electric current discharge Journal of fluid mechanics Modeling in magnetohydrodynamic domain Problem Formulation with numerical methods (Introduction to Magnetic Diffusion) 4 W J Greene An Analysis of Transfer in Gas- Shielded Welding Arcs AIEE Basic derivation of Electromagnetic Force
- 5. Literature Survey 5 J.F. Lancaster The physics of fusion welding Part 1: The electric arc in welding IEE REVIEW Basics of Welding 6 J. C. Amson Lorentz force in the molten tip of an arc electrode Brit. Journal of Applied Physics (IOP Publishing) Complete derivation of Lorentz force and proof of assumptions. 7 P. M. Heertzes, L. H. de Nie and H. J. de Vries Drop formation in liquid- liquid systems - I Prediction of drop volumes at moderate speed of formation Chemical Engineering Science, Pergamon Press Basic equations for water drop detachment.
- 7. SFBM Model • Drop is detached when Surface tension force is equal to sum of forces due to gravity, drag and electromagnetism. • (1) • The problem with SFBM is that when at large currents the error starts to get large, hence the necking phenomenon is also considered through Pinch Instability Theory (PIT). • Model is valid in case for arc lengths greater then the diameter of the radius of electrodes. • It fails when short circuiting is involved.
- 8. • When momentum flux forces increase on higher currents, SFBM does not give accurate results, so MFBM is used. • (2) • For very accurate results numerical techniques are used[3][4]. Results are far more accurate then any analytic technique
- 9. Legend 1) Rw =Radius of Wire 2) I=Supplied Current 3) P1=Plane 1 4) Ra=Droplet Radius 5) U=Flow Velocity 6) J0=Current Density in zero current emission density region 7) J2=Current Density on plane p2 8) J=Constant current density in truncated sphere Figure.3 Globular Droplet, With pressure, currents and Planes [1]
- 10. • (4) • α=Ratio of diameter of droplet and diameter of wire. • α is an useful parameter to vary in order to recognize mode of transfer i.e. Globular/Spray. Force due to Mass Transfer(Fmf)
- 12. • Resulting electromagnetic force: (3) • In Figure. X Lorentz force of the cone A is independent of apex angle, hence that cone is depicted as plane 1 in the figure. X1 and the zero current emission density zone is considered to be below plane P2, having X-sectional area of electrode wire.[1][3]
- 13. Magnetohydrodrodynamics • In MHD Maxwell equations are coupled with Navier Stoke’s Equations to find out the variance of 9 variables i.e. 3 components of Velocity(V),3 components of Magnetic field(B) and thermodynamic properties ( density, pressure and internal energy) • Final Equilibrium equation gives the relation between the 9 variables in ideal MHD. • Causal difference between Electrical engineering Approach and MHD approach.
- 14. Equilibrium Equations • Equilibrium equation for Numerical Analysis
- 15. Legend for Characteristic curves • Fd= Drag Force • Fg= Gravity Force • Fem=Electromagnetic Force • Fmf= Force due to Momentum Flux • Ft= Detaching Force • Fγ= Surface tension force • Figure. 4 show the behavior of Fem and Fmf against arc covered angle.Figure.5 shows the current at which detaching force equals Surface tension force
- 16. Characteristic Curves for MFBM Models[1] Fig. 4 Plot of EM force with arc angle[1] Fig.5 Detaching Force with Current[1]
- 17. Photographs of Melting Drop[4] Fig. 6 Process of Droplet detachment at 260 Amp and 29 V in 1.6 mm φ electrode[2]
- 18. Analogy to hydraulic System • Carefully looking at Fig.6 and not considering the electromagnetic force. Droplet detachment can be seen as water drop detachment with low velocity and uniform acceleration This dictates the basic premise of modeling, where scheme is to model the hydraulic circuit and pass it on to magnetic domain by use of a suitable Gyrator.
- 19. Figure.7 Detaching Water Droplet[Google Images]
- 20. • If we look closely in that figure we can approximate upper part of the fluid in drop growth stage, as a truncated cone and the lower part as an truncated sphere. The hydraulic bond graph model is prepared, with these simplifications, we can say that the necking phenomenon is taken into account as the top part is truncated cone, but it is far from ideal as rn is not changing
- 21. Nomenclature Used in Bond graph • Radius at necking • Radius of the drop • Volume flow rate • Magnetic Permeability • Magnetic field Intensity H • Surface tension Co-efficient γ • X-sectional Area A(x) • Shoulder Angle θ
- 22. Hydraulic Bond Graph Modeling • Fluid Inertance: It is defined as “The pressure difference required for a unit flow rate change”. • (4) • (5) (6)
- 23. Fluid Capacitances • The capacitance reflects storage capacity and is given as the ratio of the volume flow rate and the rate of pressure variation. • (7) • In the same way • (8)
- 24. Fluid Resistances • Basic model is taken as inviscid, so viscous resistances are neglected. • Bernoulli’s Resistance which represent the pressure variations with varying X- sectional area is used. These are Modulated Resistances. • (9)
- 25. Bond graph Fig.8 Bond graph of drop detachment model
- 26. Input Radius Plot.1 Input radius (drop)
- 27. Theoretical Volume Plot.2 Desired Volume Curve.
- 28. Model Volume output Model Volume output is within 50 percent error with respect to theoretical volume Plot.3 Actual Volume Curve