PARAMETRIC OPTIMIZATION IN FRICTION WELDING OF ALUMINUM ALLOY 6351 AND STEEL 304 A PROJECT REPORT Submitted by
PARTH NAGADIA ARUN PATEL RUCHIT PATEL In fulfillment for the award of the degree Of
Bachelor of Engineering In
Mechanical Engineering
NARNARAYAN SHASHTRI INSTITUTE OF TECHNOLOGY JETALPUR GUJARAT TECHNOLOGICAL UNIVERSITY, AHMADABAD MAY 2014
i
NARNARAYAN SHASTRI INSTITUTE OF TECHNOLOGY, JETALPUR MECHANICAL ENGINEERING
CERTIFICATE This is to certify that the project work entitled “PARAMETRIC OPTIMIZATION IN FRICTION WELDING OF ALUMINUM ALLOY AND STEEL 304 ” by PARH NAGADIA [100340119014] , ARUN PATEL [100340119100], RUCHIT PATEL [100340119029] has been carried out under my guidance in fulfillment of the Bachelor of
Engineering in Mechanical Engineering- 8th semester of Gujarat Technological University, Ahmadabad during the academic year 2014.
INTERNAL GUIDE
H.O.D MECHANICAL
Mr. BIREN DESAI
Mr. MANISH PATEL
Dr. SARDADEVI MANDALAPU Principal, NSIT-JETALPUR
ii
ACKNOWLEDGMENT
A dissertation like this would not have been emerge without considerable debts to various people for their help with specialist information, concepts for debate and valuable assistance in the preparation and completion of this study. First of all we are humbly expressing thanks to our respected guide Prof. Biren Desai who has always been prepared to offer me help at any time, in spite of having busy schedule. We heartedly thank for their inspiration, devoted attention, ingenious suggestions and unconstrained availability which were of great help in giving this work the present form. We are also thankful to Our Head of Department Prof. Manish Patel for his valuable time and constant help given to me during this dissertation work. We are also thankful to all the faculty members of Mechanical Engineering Department and all my friends who have directly or indirectly helped me during this dissertation work. Finally, we would like to render my heartiest thanks to my family for their great support during this dissertation work.
Sincerely, Nagadia Parth R. Patel Arun B. Patel Ruchit A.
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TABLE OF CONTENT SR. NO.
CONTENT
PAGE NO.
Chapter 1
Title
i
Certificate
ii
Acknowledgement
iii
Table of content
iv
List of figure
vi
List of tables
vii
Abstract
viii
Introduction
1
1.1Introduction
1
1.2 Friction welding 1.2.1 Types of friction welding
Chapter 2
1.3 Principal of friction welding
6
1.4 Stage of process
7
1.5 Taguchi method
8
1.6 Eight step in Taguchi methodology
9
1.7 Non distractive test
11
1.8 Advantage
12
1.9 Disadvantage
13
1.10 Application friction welding
13
1.10.1 Commercial
14
1.10.2 Aerospace
14
1.10.3 Hydraulic
15
1.10.4 Bimetallic
15
Literature review
16
2.1Literature review Chapter 3
2
16
Design of experiments
20
3.1 Introduction
20 iv
3.2 Material Selection
21
3.3 Selection of friction welding parameters & their level
23
3.3.1 Constant process parameters during experiment
23
3.3.2 Variable parameters during experiment
23
3.3.3 Output parameter of experiment
23
3.4 Experiment set up procedure
24
3.4.1 Machine Specification
24
3.4.2 Geometry of specimen
25
3.4.3 Material properties
25
3.5 Hydraulic equipment
Chapter 4
Chapter 5
26
3.5.1 Hydraulic device
26
3.5.2 Hydraulic power pack
27
3.6 Experiment set up
27
3.7 Selection of orthogonal array
29
3.8 Tested work piece
30
3.7 Experimental result table
31
Results and validation
32
4.1 Results and discussion
32
4.2 Tensile test
33
4.3 Analysis of experiment data
34
4.4 Analysis of variance
37
4.5 Radiography test results
39
4.6 Validation
40
Conclusion
43
5.1 Conclusion
43
References
45
v
LIST OF FIGURE
FIG. NO 1.1
FIGURE
PAGE NO. 4
1.2
RFW Process Layout continuous drive friction welding
1.3
The basic steps in friction welding
8
1.4
Aeronautics part
13
1.5
14
1.6
Gas turbine impeller and shaft Friction welded piston clutch and impeller casting
1.7
Bimetallic Electric Plug
15
3.1
26
3.2
Hydraulic devices Hydraulic Power Pack
3.3
Schematic Diagram Experiment Set Up
28
3.4
Experiment set up
29
3.5
Before tested part after tested part
31
4.1
Universal Testing machine
34
4.2
Graphical analysis tensile strength with different parameter
39
7
14
27
vi
LIST OF TABLES
TABLE NO.
PARTICULAR
PAGE NO
3.1
Friction stir welding parameters and their levels
24
3.2
chemical properties of material used in present study
25
3.3
Mechanical properties of material used in present study
25
3.4
Orthogonal Array [L9]
30
3.5
Experiment result table with different parameter
31
4.1
S/N Ratio of experiment Reading
36
4.2
Optimum Parameter
37
4.3
NDT test report
40
4.4
Chemical properties of AA 6082 and AA 6351 with steel 304
40
4.5
Obtained tensile strength results AA 6082 and steel 304
41
4.6
Obtained tensile strength results AA 6351 and steel 304
41
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PARAMETRIC OPTIMIZATION IN FRICTION WELDING OF ALUMINUM ALLOY 6351 AND STEEL 304 Submitted By
NAGADIA PARTH RANJITBHAI PATEL ARUN BHARATBHAI PATEL RUCHIT ASHWINBHAI
Supervised By Prof. BIREN DESAI Narnarayan Shastri Institute of Technology, Jetalpur
ABSTRACT
In friction welding, the joints are formed in the solid state by utilizing the heat generated by friction. The objectives of this study are obtaining friction weld element of Aluminum 6351, steel 304 and optimizing the friction welding parameters in order to establish the weld quality. This paper discusses use Taguchi experiment design technique for maximizing tensile strength of friction welding Al (6351) and steel 304. An orthogonal array of L9 was; Using ANOVA and signal to noise ratio of robust design, effect of tensile strength of friction welding process parameter (Rotational speed, forging force, time) is evaluated and optimum welding condition for maximizing tensile strength is determined and also NDT (Radiography test) testing to measure continuity of weld joint.
Keywords—
Friction Welding, Stainless Steel,
Optimization by Taguchi methodology
viii
Aluminum,
Tensile Strength,
CHAPTER 1
INTRODUCTION
1 INTRODUCTION 1.1 Introduction This thesis is a contribution to research work with the final ambition of friction welding steel to aluminum material. The friction welding process was selected for joining steel to an aluminum material after a literature study showed that this is a possible feasible technology. The goal of this thesis is to help in the assembly of this machine and to gain some experience in welding this particular material combination because not a lot of experimental research can be found on this topic. The principles of welding steel to aluminum material can also be applied to other dissimilar material combinations.[2] Energy savings and environmental preservation are important issues for us to resolve. Since reducing the weight of vehicles is one of the efficient measures, the use of the combination of steel and aluminum alloy has been increasing in fabricating vehicles. Under this situation, many trials to weld steel to aluminum alloy have been conducted. However, present structures made of stainless steels cannot be entirely replaced with aluminum alloy structures, taking into account strength, weld ability, and economics, although it is possible to replace part of a structure with aluminum alloy components.[2]
1.2 Friction welding Friction welding is a solid-state joining process that can produce high-quality welds between two components with either similar or dissimilar chemical compositions. The friction welding components are forced to rub against each other, thereby generating heat at the interface. This softens the material on either side of the rubbing interface. The softened materials starts to flow together to initiate a weld. Once enough heat has been generated, the rubbing action is terminated and the contact pressure is maintained or increased for a period of time, to promote the solid-phase bond. Therefore, the friction 1
CHAPTER 1
INTRODUCTION
welding process requires a machine which is designed to convert mechanical energy into heat at the joint interface using relative movement between work pieces. [1-5] Friction welding is the welding process in which the heat required for welding is obtained by friction between the ends of the two parts to be joined .One of the parts to be joined is rotated at a high speed near and the other part is axially aligned with the second one and pressed tightly against it. The friction between the two parts raises the temperature of both the ends. Then the rotation of the part is stopped abruptly and the pressure on the fixed part is increased so that the joining takes place. This is also called as Friction Welding. As it is known, friction welding is used extensively in various industries nowadays. Heat in friction welding is generated by conversion of mechanical energy into thermal energy at the interface of the work pieces during rotation under pressure. Various ferrous and non-ferrous alloys, which have circular or non-circular cross sections, having different thermal and mechanical properties can easily are joined by the friction welding method. Friction welding is classified as a solid-state welding process where metallic bonding is produced at temperatures lower than the melting point of the base metals. Friction time, friction pressure, forging time, forging pressure and rotation speed are the most interesting parameters in the friction welding method [3]
1.2.1 Types of friction welding Linear Friction Welding (LFT) Linear Friction Welding is one type of friction welding that is mainly used for the aerospace industry as it allows the welder to weld different materials; it is used for repairing of machinery parts and to build state of the art gas turbine parts that are difficult to build using conventional welding methods. Basically, it involves non-melting plastic deformation process to produce high integrity weld parts with lesser or no prior surface preparation. In linear friction welding as the relative motion between the work pieces is linear. It is used in joining turbine blades to the rotor in the aerospace industry. Now-a-days 2
CHAPTER 1
INTRODUCTION
researchers are working on low-price linear friction welding machines for automotive industry where it may be used for manufacturing brake discs, wheel rims piston heads etc. In LFW process the parts to be welded are forced to come in direct contact of each other and then they are subjected to an overturned motion .This results in frictional heating of work pieces at the weld plane, thereby raising its temperature near to its Melting point. As time passes this thermo-plastic layer is extruded at the periphery of the weld-layer as undulated sheets of metal termed as flash. The formation of flash conforms the fact that any interfacial has been thrown out during the friction between the parts. The heat affected zone (HAZ) in LFW is small because the joining of parts takes place at a faster rate and the direct heat input to the weld-pool is just enough to create a small HAZ. So with proper selection of material and weld parameters, the material deformation at the weld surface can be controlled.[7] Till today a lot of research has been done on LFW. It has been commonly accepted that friction welding can be differentiated into 3 stages such as (i) A dry friction stage, followed by (ii)
An increased rigorous contact, and
(iii) Some kind of steady phase once the required high weld temperature is acquired. It is not known how the surface dirt is thrown out – specifically from the mid-point of the weld surface. The problems that lie with LFE are the tribology of the job, heat flow in the weld pool and more specifically the representation of the thermo-plastic material flow during steady state LFW. It is a necessity that these facts have to be systematically addressed so that an appropriate material extrusion model can be formulated accurately. This will ensure in reduction of computational cost found in doing FEA of the processes be kept within acceptable limits.
Spin Welding This is mainly used for welding polymers. It includes four stages such as (i) The dry friction stage (ii) The transition stage 3
CHAPTER 1
INTRODUCTION
(iii) The steady state stage (iv) The cool down phase. In the solid friction stage, frictional heat is generated due to the interaction between the work pieces between the two surfaces. This stimulates the polymer material to get heated up until the melting point is attained. The generation of heat depends on the applied tangential velocity and the pressure. In the transition stage, a thin molten polymer layer gets formed which appears as a result of the frictional heat generation. A thin molten layer exists at the starting and accordingly the shear rate and viscous heating contributions are large. As the process goes on this layer grows thicker and temperature raises to that required for welding. The steady stage involves the outward melting of the polymer and it achieves a steady rate. In this stage the thickness of the layer remains constant. This stage is kept until a certain "melt down depth" has been attained at which the rotation is stopped. At the final stage the polymer is allowed to cool and during cooling it solidifies to form a strong joint.[6]
Rotary Friction Welding (RFW) In RFW, one work piece is rotated against the other. It is the most commonly used friction welding process in automobile industry. The process has been used to manufacture suspension rods, steering columns, gear box forks and drive shafts and engine valves, in which there is requirement of welding of unalike materials of valve stem and head.
Fig. 1.1 RFW Process
4
CHAPTER 1
INTRODUCTION
Inertia Friction Welding In this friction welding, the energy required to make the weld is harnessed from the rotational KE stored in a fly wheel of the welding set up. In Inertia Friction Welding, one part is connected to a flywheel and the other is constrained from rotating. The flywheel is accelerated to a specific rotational speed to store the required energy. Then the driving motor is withdrawn and the work pieces are forced together to interact directly. This drives the surfaces to rub against each other under pressure. The kinetic energy stored in the rotating flywheel forces the part attached to t to rotate and this rotation is opposed by the other constrained part which results in generation of heat. Due to the opposition by the constrained work piece the fly wheel get slowed down and its KE gets converted into heat. An increment axial force is applied before rotation stops. The axial force is kept for a specific time even after rotation stops.
Friction Stud Welding It was developed by the USA Navy in 1998 and was first commercially performed at a depth of 1300 feet and involved the friction welding of anode continuity tails to riser base piles using a work-class ROV. The instrument used for the welding process was a Circle Technologies HMS 3000, which is hydraulically-driven, electronically-controlled, and rated to a depth of 3,000 feet (910m). Based on this concept, the Naval Sea Systems Command (NAVSEA) initiated another program to evaluate underwater friction stud welding for use in submarine rescue. Oceaneering developed the application for commercial offshore submarine repairs at the same time when Navy tried to use the method to for underwater friction stud welding for rescue missions in case of underwater accidents in sea. But there was a little public information on the mechanical properties of underwater friction stud welding. The usability of this process for any offshore repairing without a complete knowledge of mechanical, corrosion, and fatigue would not be acceptable.
5
CHAPTER 1
INTRODUCTION
Friction Stir Welding Friction Stir Welding (FSW) is a recently developed friction welding process which was developed at The Welding Institute (TWI), Cambridge, UK [19].This method uses a rotating non-consumable welding tool. This technique uses a non- consumable rotating tool to create frictional heat and distortion at the welding position, thereby upsetting the development of a joint, while the material is in the solid state. The main benefits of FSW, being a solid-state procedure, are low alteration, absenteeism of melt-related flaws and great joint strong point, even in those alloys that are considered non-joinable by conventional practices (e.g.,5xxx and 6xxx series aluminum alloys). In addition, friction stir welded joints are regarded as the absence of filler-induced glitches or defects, since the method necessitates no filler. Also the hydrogen damage that occurs during welding of steel and other iron alloys has to be avoided by decreasing the hydrogen contents of the friction stir welded joints.[7]
1.3 PRINCIPLE OF FRICTION WELDING: Friction welding is carried out by translating or rotating one component comparative to another along a mutual boundary, whereas smearing a compressive force through the joint. The frictional heat gets spawned at the boundary softens both components and when they got altered the border material gets extruded out of the ends of the combined so that fresh material from each module is gone along the new interface. The relative cue is then stopped, and a advanced closing compressive power is applied earlier to the joint is permitted to cool. The main aspect of friction welding is that no liquefied solid is generated as the weld gets created in the solid state itself.[7] The definition of friction welding in the American Welding Society (AWS) C6.1-89 standard is as follows: „Friction welding is a solid-state joining process that produces coalescence of materials under compressive force contact of work pieces rotating or moving relative to one another to produce heat and plastically displace material from the faying surfaces. Under normal conditions, the faying surfaces do not melt. Filler metal, flux, and shielding gas are not required with this process‟. [7] 6
CHAPTER 1
INTRODUCTION
Fig: 1.2 Layout continuous drive friction welding [3] The principle of this method is the changing of kinetic energy (it may be rotational or translational) energy into heat energy through friction. One piece is obsessed and revolved about its axis while the other part to be joined to it is engrossed and is not revolved but can be relocated axially to create interaction with the spinning component. When fusion temperature is reached, then gyration is clogged and forging pressure is smeared. Heat is produced due to friction and is focused and contained at the edge, grain structure is polished by scorching exertion. Then the joint gets formed but there is no melting of material.
1.4 Stages of the process: Generally, friction welding involves three basic stages. During the first stage, sometimes called the heat-up stage, the two components, which have a relative motion with respect to each other, are brought into contact and an axial compressive force is applied. Heat generated by friction increases the temperature of the components at the rubbing interface, which decreases the materials‟ flow stress. Eventually, the material is unable to withstand the applied axial compressive force and plastically flows outwards to form the flash, carrying oxides and contaminations. Flash formation takes place during this stage, which is denoted as the burn-off stage. Finally, during the forging stage, the welding process is completed by stopping the relative motion and applying a high compressive force. [1] Show in figure 1.3 First one work piece is rotated and other is held stationary as shown in the Figure A. When the appropriate rotational speed is reached, the two work 7
CHAPTER 1
INTRODUCTION
pieces are brought together the axial force is applied, as shown in the Figure B. Rubbing at the interface heats the work piece locally and upsetting starts, as shown in the Figure C. Finally, the rotation of one of the work pieces stops and the upsetting is completed, as shown in the Figure D.
Figure 1.3 The basic steps in friction welding [2] The weld produced is characterized by the narrow heat affected zone, the presence of plastically deformed material around the weld (flash), and the absence of fusion zone.[2]
1.5 Taguchi method After the Second World War, the allied forces found that the quality of the Japanese telephone system was extremely poor and totally unsuitable for long-term communication purposes. To improve the system the allied command recommended establishing research facilities in order to develop a state-of-the-art communication system. The Japanese founded the Electrical Communication Laboratories (ECL) with Dr. Genichi Taguchi in charge of improving the R&D productivity and enhancing product quality. He observed that a great deal of time and money was expended on engineering experimentation and testing. Little emphasis was given to the process of creative brainstorming to minimize the expenditure of resources. He noticed that poor quality cannot be improved by the process of inspection, screening and salvaging. No 8
CHAPTER 1
INTRODUCTION
amount of inspection can put quality back into the product. Therefore, he believed that quality concepts should be based upon, and developed around, the philosophy of prevention.[10] Taguchi started to develop new methods to optimize the process of engineering experimentation. He believed that the best way to improve quality was to design and build it into the product. He developed the techniques which are now known as Taguchi Methods. His main contribution lies not in the mathematical formulation of the design of experiments, but rather in the accompanying philosophy. His concepts produced a unique and powerful quality improvement technique that differs from traditional practices. He developed manufacturing systems that were “robust” or insensitive to daily and seasonal variations of environment, machine wear and other external factors. [10] To achieve desirable product quality by design, Taguchi suggests a three-stage process: system design, parameter design, and tolerance design. System design is the conceptualization and synthesis of a product or process to be used. The system design stage is where new ideas, concepts and knowledge in the areas of science and technology are utilized by the design team to determine the right combination of materials, parts, processes and design factors that will satisfy functional and economical specifications. To achieve an increase in quality at this level requires innovation, and therefore improvements are not always made. In parameter design the system variables are experimentally analyzed to determine how the product or process reacts to uncontrollable “noise” in the system; parameter design is the main thrust of Taguchi‟s approach. Parameter design is related to finding the appropriate design factor levels to make the system less sensitive to variations in uncontrollable noise factors, i.e., to make the system robust. In this way the product performs better, reducing the loss to the customer.
1.6 Eight-steps in Taguchi methodology Step1: Identify the main function, side effects, and failure mode Step2: Identify the noise factors, testing conditions, and quality characteristics Step3: Identify the objective function to be optimized Step4: Identify the control factors and their levels 9
CHAPTER 1
INTRODUCTION
Step5: Select the orthogonal array matrix experiment Step6: Conduct the matrix experiment Step7: Analyze the data; predict the optimum levels and performance Step8: Perform the verification experiment and plan the future action[10] The final step in Taguchi‟s robust design approach is tolerance design; tolerance design occurs when the tolerances for the products or process are established to minimize the sum of the manufacturing and lifetime costs of the product or process. In the tolerance design stage, tolerances of factors that have the largest influence on variation are adjusted only if after the parameter design stage, the target values of quality have not yet been achieved. Most engineers tend to associate quality with better tolerances, but tightening the tolerances increases the cost of the product or process because it requires better materials, components, or machinery to achieve the tighter tolerances as we discussed in earlier chapters. In contrast, taguchi approach is based on executing one large comprehensive experiment. This approach is not based on the principal of sequential experiment. More specifically a comprehensive experiment is planned assuming that the comprehensive experiment is planned assuming that the objective and all the data analyzed by analysis of variance in term of measure devised by Taguchi know as signal –to-ratio‘s. Finally, based on this calculation, taguchi shows how to choose the “optimum “condition. [6] The steps included in the Taguchi parameter design are: selecting the proper orthogonal array (OA) according to the numbers of controllable factors (parameters); running experiments based on the OA; analyzing data; identifying the optimum condition; and conducting confirmation runs with the optimal levels of all the parameters. Basically, the degrees of freedom for the orthogonal array should be greater than or at least equal to those for the process parameters. In this study, an L9 orthogonal array was used. This array has twenty six degrees of freedom and it can handle three-level process parameters. Each FS welding parameter is assigned to a column and twenty seven welding parameter combinations are available.
10
CHAPTER 1
INTRODUCTION
The main effects indicate the general trend of influence of each parameter. Knowledge of the contribution of individual parameters is the key to deciding the nature of the control to be established on a production process. Analysis of variance (ANOVA) is the statistical treatment most commonly applied to the results of the experiments to determine the percentage contribution of each parameter against a stated level of confidence. Taguchi suggests two different routes for carrying out the complete analysis. In the standard approach the results of a single run or the average of repetitive runs are processed through the main effect and ANOVA (raw data analysis). The second approach, which Taguchi strongly recommends for multiple runs, is to use the signal-tonoise (S/N) ratio for the same steps in the analysis.[9] The preferred parameter settings are then determined through analysis of the “signal-to-noise” (SN) ratio where factor levels that maximize the appropriate SN ratio are optimal. There are three standard types of SN ratios depending on the desired performance response. Smaller the better (for making the system response as small as possible):
SNS= -10 log
1 4
𝑛 2 𝑖=0 𝑌𝑖
Larger the better (for making the system response as large as possible):
SNL= -10 log
1 4
1 𝑛 𝑖=0 𝑌𝑖 2
1.7 Non destructive test Nondestructive testing (NDT) is the process of inspecting, testing, or evaluating materials, components or assemblies for discontinuities, or differences in characteristics without destroying the serviceability of the part or system. In other words, when the inspection or test is completed the part can still be used. In contrast to NDT, other tests are destructive in nature and are therefore done on a limited number of samples ("lot sampling"), rather than on the materials, components or assemblies actually being put into service. These destructive tests are often used to determine the physical properties of materials such as impact resistance, ductility, yield and ultimate tensile strength, fracture 11
CHAPTER 1
INTRODUCTION
toughness and fatigue strength, but discontinuities and differences in material characteristics are more effectively found by NDT. Today modern nondestructive tests are used in manufacturing, fabrication and in service inspections to ensure product integrity and reliability, to control manufacturing processes, lower production costs and to maintain a uniform quality level. During construction, NDT is used to ensure the quality of materials and joining processes during the fabrication and erection phases, and in-service NDT inspections are used to ensure that the products in use continue to have the integrity necessary to ensure their usefulness and the safety of the public.
1.8 Advantages Friction welding is cost-effective since it badges joining together dissimilar materials, one of them may be cheap and its quality controller cost may be minimal with an assurance of high strength welds. Furthermore, the weld cycle is very short, so that output is very eye-catching. Friction welding process may fit for mass manufacture. The friction welding route is right for non-homogeneous joints linking things having quite altered mechanical, chemical and thermal properties. The procedure is appropriate for automation and adoptable for robotic application. Other advantages are: - Material and machining charge savings is more - Full cross section gets bounded perfectly - High manufacture rates - Weld heat affected zone (HAZ) has a reasonable grain hot-worked construction -
Like and unlike materials can be welded with no extra fluxes or filler metals
- Superb mechanical properties are proven by fatigue, tensile, bend experiments - No hazardous gas is produced - No sponginess - No scatter - No need of recruiting certified welders for performing FSW -
It is more energy effective than other welding skills
- FSW joint strong point is similar or even greater than that of parent material -
It can weld cheap, less heavy or cylindrical material to expensive material.
12
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INTRODUCTION
1.9 Disadvantages Friction welding has some disadvantages such as friction welding of all structure is not practicable, a machine of adequate power is required and short run of the welding process may not be economical. Other disadvantages are cost of instruments required which must be right for the proposed joins, the cost of the tools to be used and the set up cost. These costs per weld may become very high for welding dissimilar materials such as Titanium, Magnesium etc. Close-fitting among parts and maintaining close concentricity that are required for FSW may become difficult in some cases. Likewise there may be rise in total cost when finishing procedures are required. 1.10 Applications of Friction Welding As time passes friction welding has found many applications in Commercial, Aerospace, Hydraulic, Automotive industries etc
1.10.1 Commercial Inertia Friction Welding is mainly used for commercial purpose because the weld is skillful rapidly and with smallest clean-up. Since the weld has high strength, it delivers a solider quantity than customary welds. Tool additions, tool spaces, baseball bats, air cylinders, ammunitions, fasteners, oil cylinders and water tube fittings, bicycle parts, medical equipment, marine equipment, electrical tools, photographic and sound apparatus are made using inertia friction welding.
Figure 1.4 Aeronautics part 13
CHAPTER 1
INTRODUCTION
1.10.2 Aerospace Inertia Friction welding and friction stir welding are mainly used in aerospace industry. These are used to manufacture aero-plane parts such as gas turbine wheels and shafts, pressure containers, landing stage gear struts, ball screw assemblies, actuator modules and gear assemblages. Many friction welded parts have been cast-off in satellites, space shuttles etc.
Figure 1.5 Gas turbine impeller and shaft
1.10.3 Hydraulic: Hydraulic cylinders and valves are manufactured and repaired through inertia welding. The cylinders are entirely machined and the caps are welded on later for cost reductions and nominal inventory necessities. For manufacturing irregular profiles, the cylinder is welded to a bigger part of material to decrease cost and machine time. This method is also used for piston manufacturing.
Figure 1.6 Friction welded piston clutch and impeller casting 14
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INTRODUCTION
1.10.4 Bimetallic application Aerospace and aircraft components, cutting tools, agriculture machinery, automotive parts, oil filled cylinders, waste canisters, military equipment, spindle blanks and bimetallic components used in electrical machines are manufactured using different friction welding techniques.
Figure 1.7 Bimetallic Electric Plug
15
CHAPTER 2
LITERATURE REVIEW
2 LITERATURE REVIEW 2.1 Literature Review 1.
It is a fact that the essential force to originate sliding a material is better than that to continue motion so the coefficient of static friction becomes greater than coefficient of dynamic friction. It is detected that the choice of standards of frictional forces varies by orders of scale dependent on the span of the tenders, macroscopic or microscopic. Mathematically,
Friction force = coefficient of friction X normal weight 2.
A.R.D. Industries manufactures friction welded parts and has performed sub-contract friction welding of costumer goods for a large number of companies that include agricultural, automotive, electrical, forestry, mining, transportation and other correlated industries. A.R.D. Industries is one of the biggest frictions welding subcontract manufacturer in Canada.
3.
Whitley Eder Paduan Alves* Institute of Aeronautics and Space São José dos Campos – Brazil The purpose of this work was to assess the development of solid state joints of dissimilar material AA1050 aluminum and AISI 304 stainless steel, which can be used in pipes of tanks of liquid propellants and other components of the Satellite Launch Vehicle. Tests were conducted with different welding process parameters and the results were analyzed by means of tensile tests, Vickers micro hardness, metallographic tests and SEM-EDX. The strength of the joints varied with increasing friction time and the use of different pressure values.[14]
4.
Emel Taban a,*, Jerry E. Gould b, John C. Lippold. Dissimilar friction welding of 6061-T6 aluminum and AISI 1018 steel. Specifically, the introduction of aluminum alloy parts into a steel car body requires the development of reliable, efficient and 16
CHAPTER 2
LITERATURE REVIEW
economic joining processes. Since aluminum and steel demonstrate different physical, mechanical and metallurgical properties, identification of proper welding processes and practices can be problematic. In this work, inertia friction welding has been used to create joints between a 6061-T6 aluminum alloy and a AISI 1018 steel using various parameters. Optimum speed rpm related to bending strength (Mpa).[12]
5.
Calvin Blignault study about Friction welding established empirical formula that determines the relationship between welding speed, material thickness, tool geometry and material type. The following formula indicates the relationship between these parameters.[18]
V = feed rate mm/min = material facto = tool factor t = material thickness (mm)
6.
J. Adamowski et al. analyzed the mechanical properties and micro structural variations in Friction Stir Welds in the AA 6082-T6 with varying process parameters. Tensile test of the welds was done and relation among the process parameter was judged. Microstructure of the weld interface was observed under optical microscope. Also micro hardness of the resulting joint was measured. It was observed that test welds show resistance to increment of welding speed, Hardness reduction was observed in weld nugget and heat affected zone (HAZ). The reason for this occurrence was the kinetic and thermal asymmetry of the FSW process.. The hardness was inferior to that of fusion welding. Tunnel defects were found in the nugget zone.[15]
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CHAPTER 2
7.
LITERATURE REVIEW
M.Vural scrutinized the friction stir welding competency of the EN AW 2024-0 and EN AW 5754-H22 Al alloys. These two Aluminum alloys are extensively used in the industry. The experiment presented that the hardness value of EN AW 2024-0 at the weld area is increased about 10-40 Hv. This may be the result of recrystallization and compact grain structure formation. But hardness of EN AW 5754-H22 got decreased due recrystallization and loose grain structure formation. Welding performance of EN AW 2024-0 is 96.6 and for EN AW 5754-H22 it is 57%. Welding performance of dissimilar Aluminum alloys EN AW 2024-0 and EN AW 5754-H22 is reached a value of 66.39%. Analysis of Welding zone using scanning electron microscope showed no change in the microstructure in the welding zone. Hardness distribution at the weld zones didn’t show any significant change in hardness.
8.
Yong-Jai Kwon et al. investigated the friction stir welding between 5052 aluminum alloy plates with a thickness of 2 mm. The tool rotation speeds were ranging from 500 to 3000 rpm under a constant traverse speed of 100 mm/min. Welded joints were obtained at tool rotation speed 1 000, 2000 and 3000 rpm. At 500, 1000, and 2 000 rpm onion ring structure was clearly observed in the friction-stir-welded zone (SZ). The effect of tool rotation speed on the onion rings was observed. Gain size in the SZ is smaller than that in the base metal and is decreased with a decrease of the tool rotation speed. The study showed that the strength, tensile strength of the joint is more than that of the parent metal. The investigation also demonstrated that the joint is less ductile than the parent alloy.[20]
9.
Yeung, M.N. Ahmad Fauzi,M.B. Uday, H. Zuhailawati, A.B. Ismail are investigated Microstructure and mechanical properties of alumina-6061 aluminum alloy joined by friction welding alumina-6061 aluminum alloy joints were welded successfully by friction welding. Some interesting developments of microstructure and properties were observed in the welding area. The HAZ is very narrow, if not non-existent, in the case of 1250 rpm and the bending strength values obtained were greater in joint using rotational speed of 2500 rpm than with 1250 rpm. The use of higher rotational speed with constant friction time and pressure increases the bending strength of 18
CHAPTER 2
LITERATURE REVIEW
friction welded as a result of heat input, high plastic deformation and shearing of grains at the interface.[16]
10. Wang, SHUBHAVARDHAN R.N & SURENDRAN S in investigated friction welding to join stainless steel 304 and aluminum 6082 materials via continuous drive friction welding process and study about austenitic stainless steel (AISI 304) and aluminum materials were welded successfully. The welding process was investigated by tensile testing, impact testing, Vickers micro hardness testing, fatigue testing, micro structural observation, and EDS measurements with the following results. The weld joint with optimum upset pressure and upset time absorbed valuable amount of energy representing the complete bonding and good weld strength at the interface, compared with the other two, lesser upset pressure and upset time, and higher upset pressure and upset time weld joint specimens.[2]
11. Friction stir welding of different materials was done by D.Muruganandam for four different tool rotation speeds namely 600, 800, 1000 and1200 rpm. Radiology was done to study the defects in the weld joint. The analysis indicated that defect concentration was maximum for the 600 rpm tool rotation. It was a little reduced for 800 rpm and even lesser for the 1000 rpm speed rotation. Least defects were found at the highest rpm (1200). [23] 12. Shyam Kumar Karna1, Dr. Ran Vijay Singh2, Dr. Rajeshwar Sahai was carried out Application of Taguchi Method in Indian Industry and he investigate Taguchi Parameter Design is a powerful and efficient method for optimizing the process, quality and performance output of manufacturing processes, thus a powerful tool for meeting this challenge. Off-line quality control is considered to be an effective approach to improve product quality at a relatively low cost. [22]
19
CHAPTER 3
DESIGN OF EXPERIMENT
3 DESIGN OF EXPERIMENT 3.1 Introduction Design of Experiment (DOE) is a powerful technique used for exploring new processes, gaining increased knowledge of existing process and optimizing these processes for achieving world class performance. DOE is an experimental strategy in which effects of multiple factors are studied simultaneously by running tests at various levels of the factors. What levels should we take, how to combine them, and how many experiments should we run, are subjects of discussions in DOE. The Design of experiment is used to develop a layout of the different conditions to be studied. An experimental design must satisfy two objectives: first, the number of trials must be determined; second, the conditions for each trial must be specified. Before designing an experiment, the knowledge of the product/process under investigation is of prime importance for identifying the factors likely to influence the outcome. Design of experiments, DOE, is used in many industrial sectors, for instance, in the Development and optimization of manufacturing processes. Typical examples are the Production of wafers in the electronics industry, the manufacturing of engines in the car industry, and the synthesis of compounds in the pharmaceutical industry. Another main type of DOE-application is the optimization of analytical instruments. Many applications are found in the scientific literature describing the optimization of spectrophotometers and Chromatographic equipment. Usually, however, an experimenter does not jump directly into an optimization problem rather initial screening experimental designs are used in order to locate the most fruitful part of the experimental region in question. Other main types of application where DOE is useful is robustness testing and mixture design. The key feature of the latter application type is that all factors sum to 100%. Areas where DOE is used are in industrial research, development and production, Optimization of 20
CHAPTER 3
DESIGN OF EXPERIMENT
manufacturing processes, Optimization of analytical instruments screening and identification of important factors robustness testing of methods Robustness testing of products Formulation experiments. [16] In this investigation of friction welding, dissimilar material Aluminum alloy 6351 and stainless steel 304 is fixed to a fixture for the experiment and the fixture in turn is held with the help of chuck of a center lathe and the tool is attached to the drill chalk with hydraulic power pack system.
3.2 Material selection: Genetic Dissimilar metal joining offers the potential to utilize the advantages of different materials often providing unique solutions to engineering requirements. The main reasons for dissimilar joining are due to the combination of good mechanical properties of one material and either low specific weight or good corrosion resistance or good electrical properties of second material. Consequently, joining processes for dissimilar materials have received considerable attention in the recent years. The need to expand the use of lightweight structures in the automotive industry has increase interest in the use of both aluminum and magnesium as structural materials. However, the cost of aluminum compared to steel restricts its application for automobile parts. [1] Solid-state bonding of aluminum alloys to steels has been investigated by many authors for more than 50 years, probably because these are structural materials most widely used in a variety of industries, and possess mechanical and chemical properties quite different from each other. Recently, it attracts even more attention to meet the demands for weight reduction and enhancement of the energy efficiency of vehicles from an ecological point of view. Aluminum Alloy AA6351: Aluminum alloy AA6351 is a medium Strength alloy with excellent corrosion Resistance. It has the highest strength of the 64430 series alloys. Alloy AA6351 is known as a structural alloy. In plate form, AA6351 is the alloy most commonly used for machining.The addition of a large amount of manganese controls the
21
CHAPTER 3
DESIGN OF EXPERIMENT
Grain structure which in turn results in a stronger alloy. Alloy AA6351 machines well and produce tight coils of swarf when chip breakers are used. However, joining of aluminum to steel is not easy for the following reasons:
Much higher melting point of steel compared to aluminum,
Difference of the thermal expansion coefficients between steel and aluminum, the very tenacious superficial oxide film on aluminum alloys, which interferes with the Achievement of a metal-to-metal contact at the interface,
Formation of brittle intermetallic compounds (IMC). [3]
The most serious problem is the formation of brittle intermetallic compounds resulting from the reaction of Al with Fe. In particular, fusion welding involves the formation of large amounts of intermetallic compounds in the weld metal because steel and aluminum are mixed in the liquid state and thus has been considered to be unsuitable for fusion welding. [3] In contrast, formation of the intermetallic compound in solid-state welding can be
controlled by selecting suitable bonding parameters, since the creation of the IMC is controlled by diffusion of reacting elements in the solid state. For this, many investigations have been reported of solid-state bonding of aluminum alloy to steel. Friction welding is a process most widely used for joining of dissimilar metals because of its high productivity and reliability of the joint performance, in addition to the controllability of the formation of the IMC layer.[3] However, several authors have reported cases were friction welds of aluminum to steel fractured at the interface showing lower strength than the base metal, even when the IMC layer was less than 1 μm thick. In this regard, no clear explanation has been given for the controlling factor of the joint strength. In particular, aluminum alloys with a high Mg content have a lower joint efficiency and a narrower Pieter Rombaut 18 Academic Year 2010-2011 parameter window to obtain a high joint efficiency. Magnesium is therefore a very important element added to a variety of industrial Al alloys. [3].
22
CHAPTER 3
DESIGN OF EXPERIMENT
3.3 Selection of friction welding parameters and their levels The main variables in direct drive friction welding are the rotational speed, the axial forces and the welding time. These variables determine the amount of energy introduced in the weld zone and the rate of heat generation at the interface. It is to be noted that the heat generation rate is not constant across the weld interface and that it also varies during the different stages of the welding cycle.
3.3.1 Constant process parameters during experiment
Work-piece material- aluminum 6351 and steel 304 Diameter of work piece- 16 mm
3.3.2 Variables parameter during experiments:
Rotation speed Forging pressure (MPa) Friction time
Rotation Speed: Fiction welding is a process in which rotating speed due to heat for welding is produced by direct conversion of mechanical energy to thermal energy at the interface of the work pieces.
Forging pressure American Welding Society (AWS) as a solid state welding process that produces a weld under compressive force (forging pressure) contact of work pieces rotating or moving relative to one another to produce heat and plastically displays material from the faying surfaces. The joint strength increased and then decreased after reaching a maximum value, with increasing upset pressure and upset time.
Friction time: A longer upset time caused the excess piercing into a smooth aluminum material forming an intermetallic layer. However, some of the welds showed poor strength depending on some accumulation of alloying elements at the interface, which are the result of a 23
CHAPTER 3
DESIGN OF EXPERIMENT
temperature rise and the existence of intermetallic layers such as FeAl. The steps included in the Taguchi parameter design are: selecting the proper orthogonal array (OA) according to the numbers of controllable factors (parameters); running experiments based on the OA; analyzing data; identifying the optimum condition; and conducting confirmation runs with the optimal levels of all the parameters as per review paper
[12].
Table 3.1 Friction stir welding parameters and their levels Parameter Rotational speed (rpm) Forging pressure(MPa) Friction time (sec)
Level
Factor 1 965 200 8
A B C
2 1200 210 9
3 1500 230 10
Show the table 1 In order to investigate the effect of friction welding process parameters, most researchers follow the experimental techniques wherein three parameter has been varied over a period of time keeping other parameters constant. This kind of conventional parameter based design of experiment approach is time consuming and consumes enormous amount of resources.
3.3.3 Output parameters of experiments:
Tensile strength
Non Destructive Testing(radiography)
3.4 Experimental set-up and procedure. 3.4.1 Machine Specification: All gear lathe machine and machine specification below: All critical components like shafts, gears, pins, lead screw are made out EN-8/EN-9 alloy steel; force lubrication system in head stock; rigid and box section type bed; accuracy conforms to Indian standard IS: 1878 (Part-1) – 1993 Centre height – 175 mm
Admit between centre – 650 mm, 1000 mm
Swing over bed – 350 mm 24
CHAPTER 3
DESIGN OF EXPERIMENT
Over cross side – 215 mm
In gap – 540 mm
Speed – 965,1200,1500 rpm
Motor – 1440 RPM, 50 cycles, 3-phase, AC power, 2.25 kW/3 HP
3.4.2 Geometry of the Specimens:
Specimens were machined from materials according to the required dimensions[2].Specimen dimensions are as follows: AISI 304 Stainless steel and AA 6351 aluminum alloy Bars of length 100mm, Diameter Ǿ16 mm and steel 304 length 76mm and Ǿ16 with total quantity 27 piece.
3.4.3 Material properties: For present study reference ASTM (American standard testing of material) to mechanical and chemical properties take below: Table 3.2 chemical properties of material used in present study AA 6351
Si Zn Mg Mn Fe Cu Ti Sn Ni 0.907 0.89 0.586 0.65 0.65 0.086 0.015 0.003 0.002
Steel 304
Si 0.38
S 0.024
P 0.036
Mn 1.67
C 0.65
Al balance
Cr 0.054
Ni 18.2
Table 3.3 Mechanical properties of material used in present study Base material AA 6351 AISI steel 304
Tensile strength(MPA) 150 515
Elongation (%)
Yield strength(MPa)
16 48
85 205
After the orthogonal array has been selected, the second step in Taguchi parameter design is running the experiment. The aluminum alloy and steel was used in this investigation for being one of the most popular materials in aeronautic applications. All the welds were aluminum bar Ǿ16 mm and steel 304 also Ǿ16 mm. For experimental set-up and design, continuous friction welding method was used. This method required a machine resembling to a lathe equipped with a means of applying and 25
CHAPTER 3
DESIGN OF EXPERIMENT
controlling axial pressure. This all gear Lathe of having power 3Hp is made to function as a friction welding machine by fitting the following additional components. • Hydraulic system equipped with manual pressure indicator used to measure forge load and forging pressure. • One part hold in lathe chuck and other part to hold in grill chuck the given work piece • In experiment run on all gear lathe machine with different rotation speed, different forging pressure with time variation.
3.5 Hydraulic equipments 3.5.1 Hydraulic device The axial force needed to deliver the friction and forging pressures is produced by a hydraulic cylinder which is located at the right side of the machine.
1. Tube 63 x 10 mm
Figure: 3.1 Hydraulic devices 5. Bush
2. Rod Ǿ25 x 290 mm
6. Plate 120 x 120 x 22
3. Piston 63 x 50
7. supporting jaw
4. Seal 63 x 63
8. 4 Nos. Stud
3.5.2 Hydraulic power pack
26
CHAPTER 3
DESIGN OF EXPERIMENT
The function of the hydraulic power pack is to collect all the important hydraulic components into one freestanding module. The unit consists of a tank which acts as a storage space for the hydraulic system fluid and electric motor driven hydraulic pumps which pressurize the fluid and transmit power via the reducing and directional valves. A vane type pump supplies pressures at 4000kg/cm2 for all machine operations, except the forge pressure which is supplied by a mechanical or manual valve. When changing oil, the tank is drained and the interior should be examined through the inspection panel and all residue and sediment removed. The tank is filled with oil to a level indicated by the oil level and it is important that the level is maintained. Under normal conditions for continuous operation the fluid temperature should not exceed 65°C.
Figure: 3.2 Hydraulic Power Pack
3.6 Experiment set up : The setup used for the present work was designed and constructed according to the principals of continuous-drive welding machine. The spindle is driven by electric motor. Axial forces are controlled by a hydraulic mechanical valve. In this machine up to 20 Ton capacity a load cell is used to measure the axial force and controlled on a closed loop. An industrial PC stores and displays all important parameters – Axial Force, Spindle speed, Displacement and Spindle torque.
27
CHAPTER 3
DESIGN OF EXPERIMENT
A drive motor capacity with 3hp and to the 1400 rpm speed with adequate torque capacity was used for the friction welding of steel and aluminum bars of 16mm diameters taking into account the friction and the upset pressures. Usually the structure is fairly rigid to provide stability to the equipment working at high speeds and is driven by high pressure forging. Modern equipment is automatic and allows all the parameters be adjusted, controlled and monitored directly on the control panel. Figure 5 shows the continuous drive friction welding setup.
Figure 3.3 Schematic Diagram Experiment Set Up
Figure 3.4(a)
28
CHAPTER 3
DESIGN OF EXPERIMENT
Figure 3.4(b)
Figure 3.4(c) Figure 3.4 Experiment set up
3.7 Selection of Orthogonal Array To select an appropriate orthogonal array for experiments, the total degrees of freedom need to be computed. The degrees of freedom are defined as the number of comparisons between process parameters that need to be made to determine which level is better and specifically how much better it is. For example, a three-level process parameter counts for two degrees of freedom. The degrees of freedom associated with interaction between three process parameters are given by the product of the degrees of freedom for the three process parameters. Basically, the degrees of freedom for the orthogonal array should be greater than or at least equal to those for the process parameters. In this study, an L9 orthogonal array was used. A total of nine experimental runs must be conducted, using the combination of levels for each control factor as indicated in Table 2. Therefore, there are six degrees of freedom owing to the three welding parameters. Once the degrees of freedom required are known, the next step is to select an appropriate orthogonal array to fit the specific task. Basically, the degrees of freedom for the orthogonal array should be greater than or at least equal to those for the process parameters. In this study, an L9 orthogonal array was used. This array has twenty six degrees of freedom and it can handle three-level process parameters. Each Friction welding parameter is assigned to a column and twenty seven welding parameter
29
CHAPTER 3
DESIGN OF EXPERIMENT
combinations are available. A total of nine experimental runs must be conducted, using the combination of levels for each control factor (A–C) as indicated in Table 2. Table 3.4 Orthogonal Array [L9] Run 01 02 03 04 05 06 07 08 09
Level B 1 2 3 1 2 3 1 2 3
A 1 1 1 2 2 2 3 3 3
C 1 2 3 2 3 1 3 1 2
The selected parameters are listed in Table 4 along with their applicable codes and values for use in the Taguchi parameter design study.
3.8 TESTED WORK PIECE Figure shows the specimens number 9A, 9B, 9C after they were tested and removed from the tensile test machine. Effects of upset time and upset pressure on the strength of joints were examined in welding of equal diameter parts. Friction time was kept constant. The strength of joints was determined by tensile tests, and the results were compared to those of fully machined specimens. The fracture occurred at the interface of the dissimilar metal weld joint, strength of the weld joint was lesser than tensile strength of AL6351 aluminum alloy and steel 304 at 230 MPa there was an unbounded region around the centre of the fracture surface, although the aluminum alloy was partially bonded to the stainless steel. The welded specimens were machined according to ASTM section IX (200), and subjected to tensile tests on a machine Fie Make universal testing machine ,UTS-40,at DIVINE METALLURGICAL SERVICES PVT.LTD.
30
CHAPTER 3
DESIGN OF EXPERIMENT
Figure: 3.5 Before tested part after tested part
3.9 Experimental result tables: The experiment that was performed is meant to investigate the feasibility of welding between Stainless Steel and Aluminum. With taguchi optimizing methodology, enough frictional heat is generated to create the weld joints. Inappropriate RPM, improper feed (axial force to create proper friction) and inapt welding time may be the other drawbacks. With the facility that I had for performing the experiment the only parameters that was at my disposal to alter is the Rotational speed. Axial pressure and time variable depend on process parameter level. Table 3.5 Experiment result table with different parameter Run
Level
Tensile strength (MPa)
A
B
C
Trial 1
Trial 2
Trial 3
Mean
01 02 03 04 05
950 950 950 1200 1200
200 210 230 200 210
8 9 10 9 10
65 84 86 59 85
91 91 93 50 59
52 96 63 123 109
69.33 90.33 80.66 77.33 84.33
06 07 08 09
1200 1500 1500 1500
230 200 210 230
8 10 8 9
85 64 111 137
87 96 122 124
107 107 108 99
93 89 117.33 120
31
CHAPTER 4
RESULTS AND VALIDATION
4 RESULT AND VALIDATION 4.1 RESULT AND DICUSSIONS After conducting all the twenty seven experiments it is found that the welded joints in different cases have different strength. In case of Aluminum bar 6351 and steel 304 diameter 16mm, there is no formation of any joint as the material got deformed even before any joint get formed. This may be due to the fact that the surface velocity at the interface of each work pieces may be too high which results in high deformation and due the deformation, enough frictional heat cannot be generated and thus there is no welded joint formation. The drill chuck has no role in friction welding. Its sole role is to give mechanical support to the stainless bar and to protect it from any deformation. This experiment shows some promise as there is formation of welded joint. But the strength of the joint is not sufficient which is eminent from the fact that with a slight pressure it gets broken. The poor strength of the joint may be a result of the high strain on the work pieces during the experiment. The only reassuring fact in this case is that the set-up is able to generate enough surface velocity, hence enough frictional heat to create a joint between the two dissimilar materials Aluminum and stainless steel. In the case of aluminum bar rotational speed should be high than experiment demonstrated that deformation is very high. This may be happened due to the high stress generated at the tool-work piece interface because same cross section area. In the Taguchi method the results of the experiments are analyzed to achieve the following objectives: (1) to establish the best or optimal condition for the product or process, (2) to establish the contribution of individual factors, and (3) to estimate the response under optimal conditions.
32
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RESULTS AND VALIDATION
4.2 TENSILE TESTS After welding was performed, tensile tests were carried out to evaluate the tensile strength of joints, besides parameter settings, optimization and qualification of welding procedures and processes. The welded specimens were machined according to ASTM A370, and subjected to tensile tests on a machine with a load cell capacity of 100 KN at room temperature of 25°C, and a test speed of 1 mm/minute. The effect of friction time and friction pressure on the strength of joints was examined in welding of equal diameter parts. Upset time was kept constant. The strength of joints was determined by tensile tests, and the results were compared to those of fully machined specimens. Obtained tensile strength for all the three corresponding trials is given in the table 4.Tensile strength of the joints was estimated dividing the ultimate load by area of the specimen. The fracture occurred at the interface of the dissimilar metal weld joint, strength of the weld joint was lesser than tensile strength of AA6351 aluminum alloy 230Mpa, there was an unbounded region around the centre of the fracture surface, although the aluminum alloy was partially bonded to the stainless steel. As friction time and friction pressure for the joints are increased, tensile strength of the joints also increases Table 6, but, strength of the joints passes through a maximum, then, when friction time and friction pressure for the joints are further increased, tensile strength of the joints decreases. Thus, it is shown that friction time and friction pressure have a direct effect on joint y time and friction pressure affect cue of the metals the weld reduces the joint quality, but it was slightly softened. The fracture mechanism of joints with a shorter time may be different from that of joints with a longer friction time. After welding was performed, tensile tests were carried out to evaluate the mechanical properties of joints, besides parameter settings, optimization and qualification of welding procedures and processes.
33
CHAPTER 4
RESULTS AND VALIDATION
Figure: 4.1 Universal Testing machine The welded specimens were machined according to ASTM section IX (200), and subjected to tensile tests on a machine Fie Make universal testing machine ,UTS-40, at DIVINE METALLURGICAL SERVICES PVT.LTD.
4.3
Analysis experimental data:
This array is designated by the symbol L9, and is used to design experiments with up to twenty two Level factors. The array has 9 rows and 4 columns; each row represents a trial condition with factor levels indicated by the numbers in the row. Standard deviation:
σ=
1 4
𝑁 𝑖=1 (𝑥𝑖
− 𝑥𝑙)
2
The signal to noise ratio (S/N ratio) was used to measure the sensitivity of the quality characteristic being investigated in a controlled manner. In Taguchi method, the term „signal' represents the desirable effect (mean) for the output characteristic and the term 34
CHAPTER 4
RESULTS AND VALIDATION
„noise' represents the undesirable effect (signal disturbance, S.D) for the output characteristic which influence the outcome due to external factors namely noise factors. The preferred parameter settings are then determined through analysis of the “signal-tonoise” (SN) ratio where factor levels that maximize the appropriate SN ratio are optimal. There are three standard types of SN ratios depending on the desired performance response. In this array, it can be seen that any number of repeated observations (trials) may be used. Ti, j represents the different trials with i = experiment number and j = trial number. It should be noted that the Taguchi method allows for the use of a noise matrix including external factors affecting the process outcome rather than repeated trials, but this is outside of the scope of this article. To determine the effect each variable has on the output, the signal-to-noise ratio, or the SN number, needs to be calculated for each experiment conducted. The calculation of the SN for the first experiment in the array above is shown below for the case of a specific target value of the performance characteristic. In the equations below, yi is the mean value and si is the variance. yi is the value of the performance characteristic for a given experiment.
For the case of minimizing the performance characteristic, the following definition of the SN ratio should be calculated:
For the case of maximizing the performance characteristic, the following definition of the SN ratio should be calculated:
35
CHAPTER 4
RESULTS AND VALIDATION
Table 4.1 S/N Ratio of experiment Reading Level
Tensile strength (MPa) Trial Trial Trial 1 2 3 65 91 52
Mean
Standard deviation
S/N Ratio
69.33
10.65
17.36
96
90.33
4.92
25.27
93
63
80.66
12.81
15.92
59
50
123
77.33
8.44
18.37
10
85
59
109
84.33
20.41
12.32
230
8
85
87
107
93
9084
19.45
1500
200
10
64
96
107
89
18.23
13.37
08
1500
210
8
111
122
108
117.33
12.20
19.66
09
1500
230
9
137
124
99
120
15.74
17.69
Run A
B
C
01
950
200
8
02
950
210
9
84
91
03
950
230
10
86
04
1200
200
9
05
1200
210
06
1200
07
After calculating the SN ratio for each experiment, the average SN value is calculated for each factor and level. This is done as shown below for Parameter 1 (T1) in the array:
SN1 =
SN2 =
SN3 =
17.36+25.27+15.92 3 18.37+23.32+19.45 3 13.77+19.66+17.64 3
= 19.51 = 16.71 = 16.89
Once these SN ratio values are calculated for each factor and level, they are tabulated as shown below and the range R (R = high SN - low SN) of the SN for each parameter is calculated and entered into the table. The larger the R value for a parameter, the larger the effect the variable has on the process. This is because the same change in signal causes a larger effect on the output variable being measured.
36
CHAPTER 4
RESULTS AND VALIDATION
Once these SN ratio values are calculated for each factor and level, they are tabulated as shown below and the range R (R = high SN - low SN) of the SN for each parameter is calculated and entered into the table. The larger the R value for a parameter, the larger the effect the variable has on the process. This is because the same change in signal causes a larger effect on the output variable being measured. Table 4.2 Optimum Parameter Sr. no 01 02 03 ∆ (Range) RANK
RPM 19.51 16.75 16.89 2.8 2
PRESSURE 16.5 19.08 17.67 2.58 3
TIME 18.82 20.42 14.00 6.42 1
Please refer to the Worked out Example for a numeric example of how the data analysis procedure described here is applied. It can be seen that deposition rate has the largest effect on the friction time and that forging pressure has the smallest effect on the processor yield. It is noticed that optimum parameters with sufficient friction pressure and friction time results in a strong bonding at the interface of the dissimilar metal joints which provides greater weld strength.
4.4
Analysis of variance:
In design of experiment the results are analyzed due to one or more of the following three objectives. 1. To establish the best or the optimum condition for a product or a process. 2. To estimate the contribution of individual factors. 3. To estimate the response under the optimum condition. The optimum condition is identified by studying the main effects of each of the factors. The main effects indicate the general trends of the influence of the factors. Knowing the characteristics, i.e. whether a higher or lower value produces the preferred results, the level of the factors which are expected to produce the best results can be predicted. 37
CHAPTER 4
RESULTS AND VALIDATION
The analysis of variance (ANOVA) is the statistical treatment most commonly applied to the results of the experiments to determine the percentage contribution of each factors. Study of ANOVA table for a given analysis helps to determine which of the factors need control and which do not. Once the optimum condition is determined, it is usually good practice to run a confirmation experiments. In case of fractional factorial some of the tests of full factorial are conducted. The analysis of the partial experiment must include an analysis of confidence that can be placed in the results. So analysis of variance is used to provide a measure of confidence. Analysis provides the variance of controllable and noise factors. By understanding the source and magnitude of variance, robust operating condition can be predicted.
MINITAB SOFTWARE: Minitab is a statistics package. It was developed at the Pennsylvania State University by researchers Barbara F. Ryan, Thomas A. Ryan, Jr., and Brian L. Joiner in 1972. Minitab began as a light version of OMNITAB, a statistical analysis program by IITE. Minitab is distributed by Minitab Inc, a privately owned company headquartered in State College, Pennsylvania, with subsidiaries in Coventry, England (Minitab Ltd.) France. Today, Minitab is often used in conjunction with the implementation of Six Sigma, CMMI and other statistics-based process improvement methods. Minitab 16 is the latest version of the software.
Uses of Minitab: Data and File Management- spreadsheet for better data analysis. Regression Analysis Power and Sample Size Tables and Graphs Multivariate Analysis- includes factor analysis, cluster analysis, correspondence
analysis Nonparametric- various tests including sing test, runs test, Friedman test, etc. Statistical Process Control Measurement System Analysis
Analysis of Variance- to determine the difference between data points.[29] 38
CHAPTER 4
RESULTS AND VALIDATION
Figure 4.2 Graphical analysis tensile strength with different parameter From the above experimental work‟s results and study revealed that Rotational speed, forging pressure, friction time how much affected tensile strength. 1. With the increase of Rotation speed than increases tensile strength of joint. 2. With the increase forging pressure after some limit tensile strength remain constant.
4.5 Radiography test results: After welding was performed, non distractive tests were carried out to evaluate the discontinuity of joints and density of the film measured and confirmed to be between 1.5 to 4.0. Besides parameter settings, optimization and qualification of welding procedures and processes. The welded specimens were machined according to ASME SEC-V, ARTICLE 2 & 22, and subjected to radiography tests of SWSI technique, at Sigma Inspection & Testing Pvt. Ltd. (An ISO 9001- 2008 certified company).
39
CHAPTER 4
RESULTS AND VALIDATION
Industrial radiography involves exposing a test object to penetrating radiation so that the radiation passes through the object being inspected and a recording medium placed against the opposite side of that object. For thinner or less dense materials such as aluminum, electrically generated x-radiation (X-rays) is commonly used, and for thicker or denser materials, gamma radiation is generally used. The results of radiography test which were observed during the experiment were tabulated which are shown in below: Table 4.3 NDT TEST REPORT Sr. No
Test parameter
Result
01
Radiography test
No significant defect Indications are noticed. Hence acceptable.
4.6 Validation Validation of friction welding to aluminum 6351 and steel 304 to compare with friction welding 6082 and steel 304. Table 4.4 chemical properties of AA 6082 and AA 6351 with steel 304 [13] Zn
Element AA 6082 Element AA 6351
AISI 304 STAINLESS STEEL
Si
Zn
Mg
Mn
Fe
Cu
Cr
Al
0.75
0.080
0.718
0.536
<0.100
0.052
<0.001
0.080
Balance
Si
Zn
Mg
Mn
Fe
Cu
Ti
Sn
Ni
Pb
0.9 07
0.89
0.586
0.65
0.65
0.086
0.015
0.003
0.002
0.001
Si
S
P
Mn
C
Cr
Ni
0.38
0.024
0.036
1.67
0.054
18.2
8.0
To investigated friction wielding on dissimilar material 6351 and stainless steel 304 by taguchi methodology. For this purpose to validated other material 6058 and steel 304. 40
CHAPTER 4
RESULTS AND VALIDATION
Majorly different both material AA 6351 and 6058 chemical composition and mechanical properties. We are investigates and validated to tensile strength of dissimilar material AA 6351 and steel 304 to AA6082 and steel 304. We are validated value of tensile strength of dissimilar friction welding 6351 to 6082. SHUBHAVARDHAN R.N & SURENDRAN S are study about friction welding to join stainless steel and aluminum materials with The welded specimens were machined according to ASTM E 8M (2004), and subjected to tensile tests on a machine with a load cell capacity of 100 KN at room temperature of 25°C, and a test speed of 1 mm/minute. The initial step was to examine fracture surfaces for any noticeable difference in fracture mechanism between unsound joints with shorter and longer friction times. Obtained tensile strength results were given in Table. Table 4.5 Obtained tensile strength results AA 6082 and steel 304
Trials
Rotating speed
Friction time (s)
Upset pressure MPa
Tensile Strength
1 2 3
1400 1400 1400
3 5 7
210 210 210
136.43 188.40 149.6
Table 4.6 Obtained tensile strength results AA 6351 and steel 304 Trials
Rotating speed
Friction time (s)
Upset pressure MPa
Tensile Strength
1 2 3
1400 1400 1400
8 9 10
210 230 200
107 108 99
REMARK Finally we validated of friction welding strength of dissimilar material AA 6082 and AA6351 with steel 304. We compare friction welding parameter like rotation speed, friction time, forging pressure and tensile strength of material show table 1 and table 2. We are conclude that some variation of strength of joining material in this some reason direct effect to strength of joining. 41
CHAPTER 4
RESULTS AND VALIDATION
1. Different Chemical composition and mechanical properties of AA6082 aluminum alloy and AA 6351. 2. The results of this study have fundamental importance for the understanding and comprehension of the main characteristics of friction welding process, in this some error in experiment set up. 3. Error between experimental readings.
42
CHAPTER 5
CONCLUSION
5 CONCLUSION 5.1 Conclusion In the present study, stainless steel (AISI 304) and aluminum 6351 materials were welded successfully. The welding process was investigated by tensile testing and Non distractive test (radiography) measurements with the following results: 1. Optimum welding parameters should be properly selected in the friction welding of dissimilar material parts. 2. Tensile strengths for stainless steel 304 and aluminum 6351 parts yielded a positive result when compared to those of base metals. The joint strength increased and then decreased after reaching a maximum value, with increasing friction time. Sufficient heat to obtain a strong joint could not be generated with a shorter friction time. A longer friction time caused the excess formation of an intermetallic layer. However, some of the welds showed poor strength depending on some accumulation of alloying elements at the interface, which are the result of a temperature rise and the existence of intermetallic layers such as FeAl. 3. It is showed by the results of tension mechanical tests that presented mechanical properties which are not possible to achieve by means of fusion welding processes. 4. This presented an application of the parameter design of the Taguchi method in the optimization of Friction welding parameters. The following conclusions can be drawn based on the experimental results of this study:
Taguchi’s robust
orthogonal array design method is suitable to analyze this problem.
43
CHAPTER 5
CONCLUSION
5. It is found that the parameter design of Taguchi method provides a simple, systematic, and efficient methodology for the optimization of the Friction welding parameters.
6. Finally I have also performed NDT test in radiography and measure no signification discontinuity of friction welding with dissimilar material.
44
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