5.3 (a) Top view of the velocity vector and (b) cross-sectional view at the central axis of the vehicle. The cross-sectional view shows RS with -Y while, AS with -Y of the material.
Introduction
- Preamble
- Motivation
- History
- Terminology
- Microstructural features
- Process parameters
- Research objectives
- Thesis structure
- Target applications
A downward force is required to maintain the tool position at or below the material surface. The effect of process parameters on the real-time material flow behavior of the FSW process is part of this study.
Literature Review
- Introduction
- Material selection
- Process parameters
- Tool geometries
- Microstructure
- Defects
- Material flow behaviour
- Dissimilar friction stir welding
- Analytical and numerical methods
- Summary
- Gaps in literature
- The scope of the thesis
The optimal parameter provided by the different researchers is shown in Table 2.1. The parameters such as tool torque, temperature and friction force depend significantly on the rotation. The effect of tool geometries on the material flow behavior of the material is lacking in the literature.
Model Methodology
Introduction
Heat generation in FSW tool
- Heat generation due to flat cylindrical shoulder with cylindrical probe
- Heat generation due to sliding in the shoulder There are two components of heat generation in shoulder i.e
- Heat generation in flat cylindrical shoulder with conical probe
- Heat generation in shoulder
- Heat generation in conical probe
There are two components of heat generation in the shoulder namely i) Heat generation due to vertical pressure (ii) Heat generation due to shoulder movement Heat generation due to vertical pressure is explained below. There are two major parts of the probe that are responsible for heat generation, namely i) the probe tip surface and ii) the side surface of the probe. The details of the heat generation on both the probe tip and side surface are described below. Heat generation due to vertical pressure on the probe tip.
Only half of the curved surface is responsible for generating heat during probe travel. 𝑄𝑝 = 23𝜋𝑓𝜔𝑃𝑟𝑝3 + 2𝑓𝜋𝑆𝑦𝑠∗ 𝜔𝑟𝑝2𝑙 + 𝑓𝑆𝑦𝑠∗ 𝜋𝑟𝑝𝑙 𝑣 (3.15) Therefore, the total heat production due to friction in a flat cylindrical probe with a cylindrical shoulder is As explained in Article 3.2.1, the total heat production in the shoulder is given by Eq.
The details of heat generation both on the probe tip and side surface are described below Heat generation due to base. In this heat generation, we only take into account half of the curved surface area, which is responsible for the heat generation during the travel of the workpiece.
Heat generation due to plastic deformation
- Heat generation in flat cylindrical shoulder and cylindrical probe
- Heat generation in shoulder
- Heat generation in probe
- Heat generation in flat cylindrical shoulder with conical probe
- Heat generation in shoulder
- Heat generation in conical probe
The details of heat generation both on probe tip and side surface are described below. Heat generation due to the rotational movement of the probe Force acting on the probe on its surface. Sticking angular velocity 𝜔 and 𝜏∗ is considered to be the shear strength of the material at 80% of its melting point temperature, due to this shear stress between the layers the total heat generation is calculated as follows.
Takes elementary ring on the curved surface area of the probe at a distance r from the center and thickness δr and slant thickness δs.
- Three-dimensional finite element model
- Meshing details
- Material flow models for similar material
- Governing equations
- Solver and discretization schemes
- Material properties
- Dissimilar material VOF Model
- Boundary conditions
- Experimental details
- Summary
The analysis is carried out on a temperature profile basis for the four different mesh sizes. The heat generation is divided by the total tool surface area of the tool to give heat flux. The schematic diagram of the material flow model used in the current analysis is shown in Figure 3.13.
Heat loss due to radiation is negligible. f) The effect of gravity on the material flow is negligible. 𝐾𝐴(∇𝑇) (3.79) where, c is the specific heat of the material, K is the thermal conductivity of the material, and T is the temperature of the fluid. The schematic diagram of the model used in the present analysis of the flow of different material is shown in Figure 3.15.
For measuring the temperature of the workpieces, 1 mm diameter K-type thermocouples (chromel and alumel wires) are used. The schematic diagram of the experimental setup for recording the thermal profile is shown in Figure 3.19.
![Table 3.1: Temperature-dependent material properties of Aluminium used in FE analysis[142], [143]](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10448832.0/69.892.218.700.164.433/table-temperature-dependent-material-properties-aluminium-used-analysis.webp)
Transient Thermal Analysis
- Introduction
- Effect of rotational speed
- Effect of traverse speed
- Effect of tool diameter
- Results of sticking and sliding conditons
- Temperature distribution along the thickness
- Experimental details
- Summary
The temperature values reached in the weld line and 14 mm away from the weld line are shown in Figure 4.3. While the temperature values according to the perpendicular distance from the weld line are shown in Figure 4.5. To study the effect of tool diameter, the tool rotation speed is taken as constant at 1400 rpm and the feed rate is 2 mm/s.
The analysis is carried out at a rotational speed of 1400 rpm, 2 mm/s in welding or travel speed for a tool diameter of 27 mm. The contour of the temperature along the weld line and on the cross-section is shown in Figure 4.9. A thermocouple used in the center of the plate is used to confirm the simulation results shown in Figure 4.10.
In this chapter, the analysis of the thermal transition is carried out and the effect of the rotation speed, the speed of movement and the diameter of the tool shoulders is studied. It was found that the dominant heat generation in bonding increases at high tool rotation and travel speed.
Material Flow Behaviour
- Introduction
- Modelling details
- Results and discussion
- Validation of model
- Summary
Similarly, the thermal conductivity and viscosity of the material are considered to be 220 W/m-K and 1.3 kg/m-s, respectively. The material flow is assumed to be laminar and therefore the model used in the analysis is a laminar model. The maximum velocity obtained in the material is 1.46 m/s towards the outer edge of the tool and on the top surface of the material.
Figure 5.3 (b) also shows that a rotation is formed by the movement of the material around the threaded tool pin. The advancing side has this spin at the top while on the receding side the spin is at the bottom end of the material. The rotation speed is very low compared to the material adjacent to the tool wall.
Also, the viscosity of the material is again taken as constant (1.3 kg/m-s) for this analysis. The velocity vector maps at three sections of the material are shown in Figure 5.7.
Material Flow Behaviour for Different Pin Profiles
Introduction
Modelling details
Results and discussion
- Effect of rotational speed on material flow
- Effect of translational velocity on material flow
The material velocity is higher at the outer edges of the shoulder compared to the remaining surface of the tool shoulder surface except for the probe base area. Whereas the back side of the tool has more deformation as the viscosity of the material is much lower due to high temperature. The shape and size of the pin of different tool geometries causes the material to behave differently.
Shown here is the material movement caused at the front and back of the tool by all pin geometries along the weld line. The flow contour of the material flow of the conical plug geometry on plane 2 is shown in Figure 6.12. The flow separation region is shown in the box located on the advancing side just next to the edge of the tool shoulder, as shown in Figure 6.12.
The vector representation on a plane 3 mm below the upper surface of the material is shown in Figure 6.16. It is observed that as the number of revolutions of the pin increases, the velocity of the particles in the vicinity of the tool pin also increases.
Summary
The width of the material flow decreases as the tool speed increases, so less material is mixed as shown in Figure 6.17. Near the top surface, mixing of the agitated material on the draw side is found to be good at 2 mm/s, but not at the other two tool speeds, so the optimum feed rate should be used to avoid defects of the vehicle. A volume of fluid (VOF) approach is used to study the liquid mixing of aluminum and copper alloys.
Material Flow Behaviour of Dissimilar FSW
- Introduction
- Modelling details
- Results and discussion
- Experimental procedure
- Experimental results
- Summary
Coupled thermo-material flow model provides temperature and material velocity distribution of Al-Cu FSW. The top view of the welding plate for the welding temperature distribution performed at 1100 rpm, welding speed 2 mm/s with 1 mm eccentricity towards the aluminum side is shown in Figure 7.3. The maximum value of Vx is reached right at the edge of the tool shoulder for a tool rotation of 1300 rpm.
Higher values of the X-velocity component directly affect the surface finish of the weld zone. The higher values of Vy are obtained on the RS compared to the AS of the weld. The maximum and minimum velocity (Vy) of the materials remain constant for all three cases.
The microstructure of the base material and the welded lump zone are studied to understand the quality of the weld. Temperature data is recorded 20 mm apart on both sides of the plates.
Material Flow Behaviour for Defected Geometry
- Introduction
- Modelling details
- Results and discussion
- Summary
The velocity response is studied in a defective and undamaged plate with the help of velocity-time graphs. When moving from point A to B, i.e. away from the tool pin, the magnitude of the velocity in the mid-thickness of the undamaged plate increases from 0.29 to 0.36 m/s. However, it is found that Vx changes significantly when moving away from the tool pin, which is observed from Figure 8.5 (b) and Figure 8.6 (b).
This suggests that the unaffected plate geometry has a smoother velocity profile when moving away from the tool's axis of rotation. The Vz velocity component is responsible for material movement along the thickness of the plate. But a huge difference in the speed of the two geometries is achieved near the edge of the shoulder.
Therefore no material circulation movement is achieved along the thickness of the material in case of defective geometry. In this chapter, the material flow rate response of defective and undamaged plate is studied while keeping the same parameters of the welding process.
Conclusions and Future Scope
Conclusions
The size of the vortex zone becomes more compact close to the pin in case threaded pin geometry is desirable. In the case of a cylindrical pin profile, the heating and deformation areas are more uniform, thus achieving a uniform viscosity profile throughout the height of the tool pin. The probability of defect formation like worm or tunnel defect is more in advancing side due to presence of flow separation zone in advancing side.
In the material flow analysis, the peak magnitude of each velocity component is greater in the case of a defective weld compared to an intact weld. The defect-free geometry provided much smoother changes in the material flow velocity component compared to the defect geometry. When moving away from the axis of rotation of the tool along the weld line, a sharp increase and decrease in the magnitude of the velocity of the X component is observed.
Good material circulation is observed for healthy weld geometry across the thickness of the plate. However, no circulation of material is observed along the thickness of the weld plate due to defective geometry.
Future scope
McClure, "Dynamic recrystallization in friction-stir welding of aluminum alloy Journal of materials science letters, vol. McClure, "Dynamic recrystallization in friction-stir welding of aluminum alloy Journal of Materials Science Letters, vol. Ma, “Effect of friction and stir welding parameters on the microstructure and mechanical properties of a variety of Al–.
Sommers, "En termisk model af friktionsrørsvejsning i aluminiumlegeringer," International journal of machine tools and production, vol. Williamson, "A thermomechanical hot channel approach for friction stir welding," Journal of materials processing technology, vol. Huber, "Thermal models for bobbin tool friction stir welding," Journal of Materials Processing Technology, vol.
Desrayaud, "A simple Eulerian thermomechanical modeling of friction tube welding," Journal of Materials Processing Technology, vol. Allehaux, "Mechanical and thermal modeling of friction tube welding," Journal of Materials Processing Technology, vol.
International Journals
![Table 2.2: Optimized FSW process parameters which provided defect-free weld [36].](https://thumb-ap.123doks.com/thumbv2/azpdfnet/10448832.0/40.892.92.776.144.253/table-optimized-fsw-process-parameters-provided-defect-free.webp)
