Mahanta, present and former heads of the department, to expand all necessary facilities in the department. The purpose of the present work is to evaluate the optimal conditions for friction pipe welding for joining both similar and dissimilar materials.
Introduction
- Background of welding
- Classification of welding techniques
- Introduction to Friction Stir welding
- Industrial applications of FSW
- Research objectives
- Thesis structure
- Target application
Based on the research gaps found in the previously published literature, the objectives of the present work were decided. The applications of the outcomes produced from the current study can be implemented in the industries mentioned in Section 1.4.1.
Literature review
Introduction
Operating parameters and their effect on weld quality
- Summary
Dawes & Thomas [11] described the tool development approach taken at The Welding Institute (TWI) and described the tool design aspects of the roll shoulder concept. They analyzed the effect of welding speed on the microstructure and mechanical properties of the stir zone (SZ).
Mechanical and Microstructural properties study
- Summary
Due to the tremendous plastic deformation of the material at nugget zone experiences very high temperature which leads to the development of texture and recrystallization [51, 52]. However, some researchers have reported that the small recrystallized grains of the nugget zone contain high density of sub-boundary sub-grains and dislocations.
FSW of dissimilar materials
- FSW of dissimilar alluminium alloys
- FSW of alluminium to other alloys
- Summary
Small compressive residual stresses were detected in the parent metal adjacent to the heat-affected zone and the nugget zone. The minimum hardness value of the samples was found in the HAZ on the withdrawn side.
Numerical and analytical study
- Summary
132] used a temperature-dependent elastic viscoplastic model to simulate the friction stir welding process. Sinclair et al [141] tested the feasibility and final quality of the FSW weld by introducing an additional heating source before the FSW tool.
Introduction
Transient thermal analysis
- Heat generation at cylindrical tool shoulder and cylindrical tool pin
- Heat generation at cylindrical shoulder
- Heat generation in cylindrical probe
- Heat generation at cylindrical tool shoulder with conical tool pin
- Heat source model
- Heat source model for similar material
- Heat source model for dissimilar material
- Three-dimensional finite element model
- First boundary condition
- Second boundary condition
- FE model
Transient thermal analysis and experimental studies of FSW on similar and dissimilar materials b) Heat generation due to tool shoulder movement. Only half of the curved surface area is responsible for heat generation during the travel of the probe. Heat development due to vertical pressure at the probe tip is shown in equation (3.10), which corresponds to equation (3.5), .. b) Heat development due to the rotational movement of the probe.
Transient thermal analysis and experimental investigation of FSW on similar and dissimilar materials. Only half of the curved surface is responsible for heat generation as the probe travels. Therefore, the total heat generation in a flat cylindrical shoulder with conical probe is given in equation (3.32).
Experimental setup and procedures
- Design of Experiments
Here, a K-type thermocouple with a diameter of 1mm was used to measure the temperature of the working parts. These thermocouples were fixed 14 mm and 16 mm apart on the center of the weld line on the top side of the plate in both specimens. The clamping of the test pieces was done so that the movement of the plates was totally limited to both the plunging and translational forces of the FSW tool.
The tool speed and the translation speed of the bearing were set before each weld. After lowering the rotary tool into the plate thrust and visually ensuring full contact between the tool shoulder and the plate surface, the bearing movement was activated.
Mechanical and microstructural properties study
- Tensile test
- Microstructural study
- Compositional and fractograph analysis
The two diagonal lines of the indenter make an indentation on the sample surface by the load removal. The welded samples were cut along the specific areas of different welding zones using the precision cutter as shown in Figure 3.17a. The sample mounting was done by encapsulating the sample in compression mounting compound (phenolic resin) in a hydraulically operated press shown in Figure 3.17b.
Polishing was performed with a single disc automated polishing machine with five specimen holders shown in Figure 3.17c. After etching the sample with the appropriate reagents, the sample was thoroughly examined using the optical microscope shown in Figure 3.18.
Summary
The composition estimations and elemental mapping were performed to understand the material flow and mixing of Cu-Al dissimilar compounds. The fractograph examination was carried out to understand the nature of the fractured surface of the tensile test specimens.
Transient thermal analysis
Introduction
- Effect of tool pin geometries on FSW
- Summary
The temperature distribution from the center of the weld line away from the weld line for the cylindrical probe diameter of 6 mm and shoulder diameter of 25 mm, flat circular shoulder friction surface is shown in Figure 4.2 where the rotational and transverse speed of the tool were 1400 rpm and 112 mm/min respectively. From Figure 4.16, the maximum temperature obtained with the tool with a shoulder diameter of 20mm is 5400C; therefore it is highly preferable to choose the tool shoulder diameter within the range of 18-20 mm. From Figure 4.17 it was observed that shoulder diameter and pin ratio tools up to about 3.3, the peak temperature rise is high.
Experimental and numerical temperature data for flat shoulder with 6 mm diameter cylindrical needle as shown in Figure 4.18. The maximum centerline temperatures range from 440-5400C for different immersion strengths as shown in Figure 4.21.
Numerical studies on thermal history of FSW on dissimilar alloys
- Summary
The results of the FE thermal analysis results for different metals are shown in Figure 4.26 to 4.33. The cross-sectional temperature contour for traverse speed (ts) of 120 mm/min, rotation speed (rs) of 1000 rpm and plunging force of 4000 N is shown in Figure 4.28. It is seen that the peak temperature varies non-uniformly around the center of the weld line.
In Figures 4.30 and 4.31, the graphs show that the maximum temperature increases rapidly for the Prs / ts ratio up to 3x105 and beyond, that the maximum temperature rise is slow. It was found that the peak temperature varies unevenly around the center of the weld line on two different metal plates.
FSW of similar materials
Introduction
Effect of tool pin geometries and operating parameters on weld quality of aluminum alloy
- Metallographic examination
- Tensile strength
- Summary
Metallographic tests on transverse cross-sections of various welded specimens were performed to study the microstructures in different zones of the welded specimens. The hardness measured in different zones of the welded specimens was plotted as shown in Figure 5.7. The effect of varying the tool pin geometry on the stress-deflection/stress-strain characteristics of tensile test specimens welded at 80 mm/min speed with 1400 rpm is shown in Figure 5.9.
With the variation in tool rpm and traverse speed, a definite amount of variation in tensile strength and elongation of the test specimens occurred. As expected, the plots clearly indicate a clear dependence of the mechanical properties on the rpm-traverse speed ratio.
Friction stir Welding of thick aluminum alloy plates
- Tensile Properties
- Effect of dwell time on mechanical properties
- Microstructure
- Micro-hardness
- Summary
The FSW welds were cut according to ASTM specifications for tensile testing as shown in Figure 5.15. The effect of dwell time on the tensile properties of FSW specimens welded by the conical probe FSW tool is shown in Figure 5.23. From Figure 5.23 it can be observed that the residence time has a significant effect on the draw property.
While high dwell times caused higher temperature increases, wormhole defects were observed in the weld zone as shown in Figure 5.23. The microhardness of the FSW samples was measured using a computerized microhardness tester shown in Figure 3.15 in Chapter 3.
FSW of dissimilar materials
Introduction
FSW of alluminium and copper alloy plates
- Microhardness
- Tensile strength
- Metallographic study
- Elemental scanning
- Summary
Therefore, the screw tools shown in Figure 6.2 were used in this work for performing the FSW experiments. Hardness variations at horizontal distance from the weld centerline are shown in Figure 6.3 and Figure 6.4. The effects of process parameters for the two tool pin profiles on FSW of Cu-Al joints are shown in Figures 6.6 and 6.7.
Transient thermal analysis and experimental investigations of FSW in similar and different materials with unaffected base Aluminum material and Figure 6.8b shows the intact copper base material. Transient thermal analysis and experimental investigations of FSW in similar and dissimilar materials.
Investigation of FSW on dissimilar alluminium alloys .1 Introduction .1 Introduction
- Optimisation of FSW on AA1100-AA5083
- Summary
Transient thermal analysis and experimental investigations of FSW on similar and different materials Table 6.7 Normalization of output data (Grey relational generation). The average of all the gray relational coefficients corresponding to the selected answers gives the gray relational score. The maximum value in the gray relational stage represents the optimal experiment containing the optimal output data.
Transient thermal analysis and experimental studies of FSW on similar and dissimilar materials. Therefore, the optimum process parameters obtained for the maximum gray relational grade are TRS: 815 rpm, WS: 63mm/min, TD: 24mm, TP: TC. Therefore, the optimal process parameters obtained for the maximum gray relational grade are TRS: 815 rpm, WS: 63 mm/min, TD: 24 mm, TP: TC.
Summary and Conclusions
Summary
Conclusions
It was also found that tools with a trapezoidal plug and a tapered cylindrical plug profile produced acceptable welds for welding thick aluminum alloys, and the same result was observed for less thick plates. For welding different materials, especially high-strength, low-strength alloys, the above-mentioned tools do not produce good welds. It has been found that when welding various Cu-Al combinations, right hand helix threading tools with clockwise rotation of the tool produce good welds.
The material mixture was homogeneous and this was revealed by the study of mechanical properties, microstructural studies and EDX analysis of welded joints. It was noted that for welding different material combinations, (ie AA1100-AA5083 and Cu-Al) clamping the harder material on the advancing side with slight tool offset towards the softer material side lead to homogeneous material mixing and produced good welds.
Scope for future work
The numerical and experimental methodology developed in this work can be profitably applied in the similar and dissimilar FSW in practical application. This process can be extended to hybrid FSW process such as plasma arc assisted FSW or Laser assisted welding, especially for high melting point materials (e.g. low carbon steel, stainless steel).
Barcellona A, Buffa G, Fratini L, Palmeri D (2006) On microstructural phenomena occurring in friction stir welding of aluminum alloys. Song M, Kovacevic R (2003) Thermal modeling of friction stir welding in a moving coordinate system and its validation. Buffa G, Fratini L, Shivpuri R (2007) CDRX modeling in friction stir welding of AA7075-T6 aluminum alloy: Analytical approach.
Chao YJ, Qi, X (1998) Thermal and thermomechanical modeling of friction tube welding of aluminum alloy 6061-T6. Anil Kumar Deepati, Pankaj Biswas (2013) A study on friction tube welding of 12 mm thick aluminum alloy plates.
