Technology Guwahati for the award of the degree of Doctor of Philosophy has been conducted under the min. Biswajit Parida to the Indian Institute of Technology Guwahati for the award of the degree of Doctor of Philosophy has been supervision in the Department of Mechanical Engineering, Indian Technology Guwahati.
Nomenclature
Wi The weight is assigned to the first quality characteristic wi The firing force of the ith rule. WUTS Weight assigned to UTS WWBT Weight assigned to WBT WYS Weight assigned to YS.
MSE of training and testing datasets 170 Figure 6.6 Variation of MSE with learning rate for different outputs 171 Figure 6.7 Variation of MSE with bootstrap for different outputs 172 Figure 6.8 Number of hidden neurons versus training and testing MSE 174 Figure 6.9 Variation of MSE with learning rate 1 (weight) for different outputs 175 Figure 6.10 Change of MSE with learning level 2 (middle) for different outputs 176 Figure 6.11 Change of MSE with learning level 3 ((Expansion of Gaussian function)).
List of Tables
Contents
Experimental Investigation and Characterization of Welds 83
Finding Appropriate Starting Position and
Introduction
- Background and Motivation
- Objectives of the Research
- Contribution of the Thesis
- Organization of the Thesis
Detailed experimental investigations have been carried out on most of the process parameters to find out their influence on the bond properties. Finally, in this chapter the detailed effect of the significant parameters on the joint properties has been discussed.
Literature Review
- Introduction
- Literature-1: Experimental Set
- Literature-2: Experimental Investigation
- Process Parameters
- Microstructural studies
- Mechanical Properties
- Techniques for Finding the Significant Process Parameters
- Literature-3: Start and End Limitations
- Literature-4: Modeling of FSW Process
- Statistical Models
- Thermo Mechanical Models
- Soft Computational Models
- Others
- Literature-5: Optimization of FSW Process Parameters
- Literature-6: Process Defects and Testing
- Literature-7: Condition Monitoring
- Major Gaps from the Literatures
The hardness of the softened zone decreased with decreasing welding speed [Aydin et al., 2012]. Average hardness and UTS NZ increased with increasing displacement speed [El-Rayesa and El-Danaf, 2012]. 2008] studied the influence of welding speed on the microstructure and mechanical properties of friction stir welded Al alloys.
They concluded that there was an increase in the homogeneity of the joint's mechanical properties. Wei et al. [2007] investigated the effect of welding parameters on the quality of the Al-Li FSW joints. The tensile strength and hardness of NZ of AA7020-O Al alloy joints increased with increased welding speed [Gaafer et al., 2010].
The tensile strength of the joints increased with the increase in welding speed, while the fatigue performance decreased. Sample welded at lower rotational speeds showed superior mechanical properties compared to UTS [Kumbhar et al., 2011]. The tensile strength of the FSW assembly with water cooling [Xu et al., 2012] was almost the same as that of the BM.
Sundaram and Murugan [2010] developed regression models to predict the ultimate tensile strength (UTS) and tensile elongation (TE) of the aluminum alloy dissimilar friction tube welded joints.
Experimental Setup
- Introduction
- L-Clamps
- S-Clamps
- Development of a
- Top Plate
- Clamp
The extent of tool movement along the joint line is difficult on both upper parts, due to which the set-up time is also longer. To improve the grip, new types of S-shaped clamps have been produced. When using S-clamps, the movement of the workpiece along the direction of the tool movement is eliminated. But the lateral movement perpendicular to the movement of the tool, of the working parts during immersion still remained.
Even in some cases it was not there initially, but after a small vehicle the gap traveled. Keeping in mind all possible problems, it has been designed, developed and manufactured within a special type of equipment, the details of which are. Even in some cases it wasn't there initially, but after a small vehicle trip the gap was created.
The developed fixture is very useful for performing FSW operations in a vertical milling machine. Two M16 screws for the vertical tig of the clamp are provided on each clamp, and the protruding part of dimensions 20×20 mm ensures the movement of the workpiece along the welding direction.
Development of a Special Fixture
- Backing Plate
- Support Plate
- Fixture Assembly
- Workpiece and Tool Material
After fabricating the two separate parts on different machines, it is joined together to form a single part as shown. It also provides safety to the top plate in case the tip of the tool goes beyond the thickness of the workpiece.
It is a mild, flat piece of steel, as shown in the clamping force on the workpiece. It also provides safety to the top plate in case the tip of the tool goes over. Its main purpose is to forge plasticized material that will ensure that the plasticized material is kept within the weld zone.
It is designed in such a way that all the functions required to perform FSW operation.
Workpiece and Tool Material
Tool Fabrication
The different tool geometries considered in this paper are straight cylindrical (SC), tapered cylindrical (TC), square (SQ) and threaded tool (THRD). Initially all 8 numbers of straight cylindrical tools and 8 numbers of narrow cylindrical tools were prepared using machine lathe. For the preparation of square and threaded tools, initially the tool pins were made into a straight cylindrical shape using a lathe.
Then with a milling cutter, squares with suitable diagonals were prepared and with a lathe, straight threads with 1mm opening were prepared.
Temperature Measurement During Welding
Temperature Measurement During Welding
Observations
The developed fixture is stiff enough to hold the workpieces securely without creating gaps between the interfaces during tightening and during FSW use. It prevents the workpiece from moving in the direction of tool movement due to horizontal force. Because support plates are used above the workpiece, a uniform tension force is applied to the entire workpiece to be joined.
Once the tool movement is aligned with the assembly line, the next job will take much less time, which will reduce overall setup time.
Major Findings
Experimental Investigation and Characterization of Welds
- Introduction
- Experimental Methods
- Observations from Preliminary Experiments
- Design of Experiments
- Specimen Preparation and Testing
- Identification of Significant Process Parameters
- Evaluation of Signal to Noise Ratio
- Analysis of Variance
- Grey Relational Analysis
- The Utility Concept
- Desirability Function Approach
- Fuzzy Assisted Grey Relational Analysis
- Results and Discussions
- From Taguchi’s Single Response Analysis Technique
- From Different Multi Response Analysis Techniques
- From Full Factorial Design of Experiments to Significant Process Parameters
- Observations
- Major Findings
The choice of the parameter to be varied in two levels is important. From the initial trials (discussed in Section 4.2.2), the scope of work of PD was found to be less, as it was varied in two levels. The output of the fuzzification process is given by µSj(xi), where the symbol µS(x) is the membership function.
The percentage influence of the considered process parameters on the measured outputs is shown in Fig. Finally, the utility values for each trial condition of the experiment were calculated by eq. The prediction of the corresponding GRG, UV, DV and MPCI values () can be obtained from Eq.
The macro photographs of the connection cross-sections for all connections are shown in Figure. This leaves smaller gaps that need to be filled at the base of the joints. From the images it can be seen that both the face and the root are of the joint.
The macrographs of the joint diameter for all the welds are shown in Fig.
Finding Appropriate Starting Position and
Elimination of the End Hole in FSW
- Introduction
- Methodology
- Results and Discussions
- Being the usual practice there was no outward mater
It occurs when welding begins and ends precisely by aligning the shoulder of the tool with the starting and ending edges of the workpiece material, as shown in 5.2(a). In this case, some offset distance was provided at both the beginning and end of the connection. In this case, welding was started and stopped precisely by aligning the tool shoulder with the start and end edges of the workpiece.
The weld was started and stopped precisely by aligning the circumference of the tool pin with the starting and ending edges of the workpiece material. No restraint was provided either at the beginning or at the end of welding as shown in Fig. Again the tool shoulder was aligned with the leading and trailing edges of the workpiece material, as shown in Fig.
Thus, welding was started and stopped at a distance of 1 mm away from the starting and ending edges of the workpiece material as shown in the figure. In this case, solid pieces of aluminum were available at the beginning and end of the panels.
Observations
The experimental results showed that both Cases 5, 9, 10 and 11 can be implemented to solve the initial position problem. Among all the cases, Case-9 proved to be the better approach to overcome the end-hole limitations in FSW. Because although it is insignificant, but the tab size and welding time can be reduced in Case-9 compared to Case-10 and 11.
Thermal history in the middle of the connections showed a similar trend, except in case 6, where there was a failed connection. The suitable distance from which welding can be started was found to be 1 mm to 5 mm, after which the joint strength decreases. It has been found that the starting problem can only be solved by providing a good restriction without adding extra material.
The end hole can be eliminated by providing a small rectangular piece with a size larger than the shoulder diameter and by moving the tool pin some distance away from the end edges of the workpiece.
Major Findings
Modeling of FSW Process
- Introduction
- Artificial Neural Network
- Back Propagation Neural Network
- Structure of BPNN
- BPNN Model Development Steps
- Radial Basis Function Network
- Structure of RBFN
- RBFN Model Development Steps
- Results and Discussions
These two passes are repeated until a desired level of training of the network is achieved. The basic structure of the multilayer neural network and the back-propagation learning algorithms used in this work are explained in the following subsections. Then values of the learning rate (η), the momentum coefficient (α) and an activation function (logistic sigmoid in the present work) are assigned.
The area of each input scales linearly to the area of the activation function. The problem of overfitting or overlearning of the network is often observed, which may be due to the presence of noise in the training dataset. The output layer is generally linear but can be non-linear [Taghi, 2004] and provides the network's response to the activation pattern.
The number of basic functions, ie. the number of hidden neurons was varied in the range from 5 to 30 in steps of one. 2#L6# (6.12) where, 26# is the output of the kth output neuron with the ith input pattern in the nth iteration, 236 # is the weighted sum of the kth output neuron with the ith input pattern in the nth iteration, Vjk(n ) is the connection weight between the jth hidden neuron and the kth output neuron at the nth iteration.
