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Material Science and Engineering Faculty German University in Cairo

Automatic welding table

(Bachelor Thesis)

Author: Sherif Mohamed Rozza Supervisor: Dr. Yasser Fouad Submission Date: 15 January 2012

This is to certify that:

(i)

The thesis comprises only my original work towards the bachelor degree. (ii) Due acknowledgment has been made in the text to all other material used.

Sherif mohamed Abdel Hamed Rozza 15 January 2012

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Acknowledgments: I would like to show my gratitude and grateful to my supervisor , Prof Dr eng. Yasser Fouad for his great help, support , advice and that this thesis and all these results wouldn’t have been achieved without his hard work with me. Thank you Dr Yasser.

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Abstract
Automatic Welding is considered one of the most important ways of welding. Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. Welding has many processes as manual process, automatic process, Machine process and robotic process. Welding may be performed in many different environments, including open air, under water and in outer space. It used to build projects such as tanks, satellites, weapons, railroads, shopping malls etc. Welding is a potentially hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation. Therefore this project is carried out to produce the automatic welding table which improves the mechanical properties of the sheet. It improves the hardness of the sheet. Automatic welding table allow greater weld control, Improved and faster. Then the tensile test is done to analyze the strength after the welding process.

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Contents

Chapter 1 Introduction………………………………….……………..………………….….…....

………...................1 1.1 Motivation ………………………………………..…………….…………….…………...…. ………...4 1.2 Aim of the project ……………………………..……………….…………….………………. ………..4 Chapter 2 Literature Review 2.1 types of joining processes…………………………………………………………….…... ……............5 2.1.1 Manual joining processes……………………………………………………….…. ………..5 2.1.2 Semi automatic joining processes……………………………….……………….. …………6 .2.1.3 Automatic joining processes ………………………………..………………….…. ……….7 2.1.4 Automated joining processes…………………………………………………….. …………7 2.1.5 Machine joining process…………………………………………………………... ………..8 2.1.6 Industrial robots welding ………………………………………………………….. ……….9 2.2 ARC WELDING…………………………………………………………………………….......... ….11 2.2.1Arc welding processes……………………………………………………………………... …….….11 2.2.1.1 Shielded metal arc welding ………………………………………………... …………….11 2.2.1.2Tungsten Inert Gas Welding …………………………………………... …………………12 2.2.1.3 Submerged arc welding ……………………………………..……. ………………..…….14 2.2.1.4 Flux cored arc welding ………………………………………..…………..………. ……..15

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2.2.1.5 Plasma welding………………………………………………….. ……………………….17 2.3 Electric resistance welding……………………………………………………... ……………….....….19 2.3.1 Resistance welding processes…………………………………………………. ………………........19 2.3.1.1 Spot welding ……………………………………………………….……………..…. …..19 2.3.1.2 Seam welding……………………………………………………….……………….. …...20 2.3.1.3 Flash Welding…………………………………………………....…. ………………........20 2.3.1.4 Projection welding……………………………………………. ……………………...…..21 2.3.1.5 Resistance butt welding………………………………………………………….....…….21 2.4 BRAZING………………………………………………………………………………………. …….22 2.4.1 Brazing process……………………………………...……………………………………..…. ….…22 2.4.1.1 Torch brazing ………………………………………………………………......…..….…22 2.5 SOLDERING………………………………………………………………………………........…. …23 2.6 Thermit welding……………………………………………………………………………………. …24 2.6.1Thermit welding processes…….………………………………………...……………….. …….....…24 2.6.1.1 Laser beam …………………………...…………………….………….. ……………...…24 2.6.1.2 Electron beam welding ……………………………………………………..…. ….......…26 2.7 Gas welding…………………………………………………………………………….…….…….. …27 2.7.1 Gas welding process……………………………………………………………….……….. …….…27 2.7.1.1 Oxyacetylene welding……………………………………………….….. ……………..…27 2.7.1.2 Pressure gas welding……………………………………………….……. ………….……29 2.8 Solid state welding…………………………………………………………….……. …………...........29 2.8.1 Solid state welding process………………………………………………………………………….29 2.8.1.1 Forge welding ……………………………………………….…………... ………………31 2.8.1.2 Ultrasonic welding ………………………………………. ………………………………31 2.8.1.3 Cold working welding……………………………………………………………………32

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2.8.1.4 Friction welding…………………………………….…………………….……….... ……32 2.8.1.5 Electroslag welding …….………………………….………………………. …………….34 2.9 Metals ………………………………………………………..……………………..……...………. …35 2.10 Filler Metals…………………………………………………………...…………………. ………....36 2.11Protecting metal from atmospheric contamination………………………. ……………….……….....37 2.12 Control of weld metallurgy……………………………………………………………………. ….....37 2.13 Expansion and contraction of metals………………………………………. ……………………..…38 2.14 Butt welds……………...…………………………………………………………………………. …39 Chapter 3 Experimental setup……………………………………………………………………………40 3.1The body and frame……………………………………………………………………….. ………..…41 3.1.1 The table…………………………………………………………………………………….41 3.1.2 Upper part of the table……………………………………………………………... ………41 3.1.3 Wheels of the table………………………………………………………………………….43 3.1.4 Holder of the table………………………………………………………………... ………..44 3.1.5 Parts of the table section…………………………………………………………... ……….46 3.1.6 The motor with gearbox seating…………………………………………………... ……….48 3.1.7 The shaft ……………………………………………………………………………………49 3.1.8 Gears………………………………………………………………………………... ……...49 3.1.9 Rack………………………………………………………………………………...……… 50 3.1.10 Pulley……………………………………………………………………………... ………51 3.1.11 Safety electronic box………………………………………………………………………52 3.2 Motor………………………………………………………………………………..………………… 53 3.3 Gear box …………………………………………………………………………..……………….. …55 3.4 Inverter………………………………………………………………………………..……………. …56

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3.5 Wire remote control………………………………………………………………….………. …….…57 3.6 Assembly and Finishing………………………………………………………………..….. ……….…58 3.7 Testing ………………………………………………………………………………..……………. …62 3.8 Experiment Results ……………………………………………………………………. ………….….64 3.8.1 The tensile test.1…………………………………………………………….. …………..…64 3.8.2 The tensile test.2…………………………………………………………….. …………..…66 Chapter 4 Conclusion…………….…………………………………………………………………. …....68

Contents of figures
Figure (2.1) manual joining processes……………………………………………………………………...5 Figure (2.2) Semi automatic joining processes …………………...…………………... …………………...6 Figure (2.3) Automated or automatic joining processes …………………... …………………...…………7 Figure (2.4) Machine joining process…………………...…………………...…………………... ………...8

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Figure (2.5) Industrial robots welding …………………...…………………... …………………................9 Figure (2.6) Shielded metal arc welding…………………...…………………... …………………............12 Figure ( 2.7) Tungsten Inert Gas Welding…………………...…………………... ………………….........13 Figure (2.8) Submerged arc welding…………………...…………………...…………………... ………...15 Figure (2.9) Flux cored arc welding ………………………………………………………………………17 Figure (2.10) Plasma welding …………………...…………………...…………………... ………………18 Figure (2.11) Spot welding …………………...…………………...…………………... …………………20 Figure (2.12) Seam welding…………………...…………………...…………………... …………………20 Figure (2.13) Resistance butt welding …………………...…………………... …………………...……...21 Figure (2.14) Torch brazing …………………...…………………...…………………... ……………...…23 Figure (2.15) Laser beam welding …………………...…………………...…………………... …….……25 Figure (2.16) Electron beam welding …………………...…………………...…………………... ………26 Figure (2.17) oxyacetylene welding …………………...…………………...…………………... …….… 28 Figure (2.18) Forge welding…………………...…………………...…………………... …………….…. 30 Figure (2.19) Ultrasonic welding …………………...…………………... ……………………………......31 Figure (2.20) Friction welding …………………...…………………...…………………... ………...……33

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Figure (2.21) Electroslag welding …………………...…………………...…………………... ………… 34 Figure (2.22) EXPANSION AND CONTRACTION of metals …………………... ………………...…...38 Figure (2.23) direction of welding …………………...…………………... ………………………….…...39 Figure (3.1) the manufacturing table…………………...…………………... ……………………...……...41 Figure (3.2) Upper part of the table …………………...…………………...…………………... ………...42 Figure (3.3) Machine that is used to do these holes on the upper part …………………...……….………42 Figure (3.4) Wheels of the table …………………...…………………...…………………………. ……...43 Figure (3.5) this shape for connecting the wheels to it …………………... …………………....…………43 Figure (3.6) part of the holder………………………………………………………………………..…....44 Figure (3.7) part of the holder …………………...…………………...………………………... ………...44 Figure (3.8) part of the holder …………………...…………………...…………..………... ……………45 Figure (3.9) c-clamp…………………...…………………...…………………... ………………………...45 Figure (3.10) this part let the bearing hub wheel to move on it …………………... …………………...…46 Figure (3.11) this part to prevent the bearing hub to move away ……………….…... …………………...46 Figure (3.12) bearing hub wheel while moving …………………...……………………... ………………47 Figure (3.13) eight bearing hub wheel …………………...…………………... ………………………......47

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Figure (3.14) the motor with gearbox seating from the top view …………………... ……….…………...48 Figure (3.15) the motor with gearbox seating from the side view…………………... ………….………...48 Figure (3.16) the motor shaft …………………...……………………………….…... …………………...49 Figure (3.17) Gears …………………...…………………...……………….………... …………………...49 Figure (3.18) Gears when it is connected to the shaft …………………...... …………………...…………49 Figure (3.19) Rack…………………...…………………...………………...………... …………………...50 Figure (3.20) Rack with the gear …………………...…………………...…..…………. ………………...50 Figure (3.21) Pulley with open key hole …………………...………………………... …………………...51 Figure (3.22) Pulley with small hole …………………...…………………...…………….. ……………...51 Figure (3.23) Safety inverter box with an open and close door …………………..... …………………...52 Figure (3.24) Motor …………………...…………………...…………………...……………. …………...54 Figure (3.25) Gear box side view …………………...…………………...…………………... …………...55 Figure (3.26) Gear box upper view………………………….. ……………………………………………55 Figure (3.27) Inverter …………………...…………………….....…………………... …………………...56 Figure (3.28) Wire remote control …………………...……………….……………... …………………...57 Figure (3.29) first the design of the table …………………...…………………... …………………...…...58

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Figure (3.30) Grinding some parts and the edges of the table for finishing …………………...…………58 Figure (3.31) screws to attach some parts with others……...…………………... ………………………...59 Figure (3.32) Welding the small parts on the table to install the upper parts of table that will move.........59 Figure (3.33) the seating of the motor with the gearbox is done and ready to work……………………...60 Figure (3.34) Assembling and installing all the system different parts altogether (motor, gearbox, control unit, gears, pulleys, wheels) …………………...……………... …………………...…………………...... 60 Figure (3.35) Holding the torch of the welding and can do the operation…………………...……………61 Figure (3.36) Universal testing machine…………………...…………………... ………………………....63 Figure (3.37) Normal sample before testing…………………...…………………... …………….……...64 Figure (3.38) Normal sample after testing …………………...…………………... ………………….…...65 Figure (3.39) the two samples which are welded before testing…………………... ……………………...66 Figure (3.40) the two samples which are welded after testing…………………... …………………...…...66

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CHAPTER 1
Welding is widely used by metalworkers in the fabrication, maintenance, and repair of parts and structures. While there are many methods for joining metals, welding is one of the most convenient and rapid methods available. The term welding refers to the process of joining metals by heating them to their melting temperature and causing the molten metal to flow together. These range from simple steel brackets to nuclear reactors. Welding is a fabrication or sculptural process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the work pieces and adding a filler material to form a pool of molten material that cools to become a strong joint, with pressure sometimes used in conjunction with heat, or by itself, to produce the weld. Welding may be performed in many different environments, including open air, under water and in outer space. Welding is a potentially hazardous undertaking and precautions are required to avoid burns, electric shock, vision damage, inhalation of poisonous gases and fumes, and exposure to intense ultraviolet radiation. Welding, like any skilled trade, is broad in scope and you cannot become a welder simply by reading a book. You need practice and experience as well as patience; however, much can be gained through study. For instance, by learning the correct method or procedure for accomplishing a job from a book, you may eliminate many mistakes that otherwise would occur through trial and error. This chapter is designed to equip you with a background of basic information applicable to welding in general. If you take time to study this material carefully, it will provide you with the foundation needed to become a skilled welder.
Until the end of the 19th century, the only welding process was forge welding which blacksmiths had used for centuries to join iron and steel by heating and hammering. Arc welding and oxyfuel welding were among the first processes to develop late in the century, and electric resistance welding followed soon after. Welding technology advanced quickly during the early 20th century as World War I and World War II drove the demand for reliable and inexpensive joining methods. Following the wars,

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several modern welding techniques were developed, including manual methods like shielded metal arc welding, now one of the most popular welding methods,

as well as semi-automatic and automatic processes such as gas metal arc welding, submerged arc welding, flux-cored arc welding and electro slag welding. Developments continued with the invention of laser beam welding, electron beam welding, electromagnetic pulse welding and friction stir welding in the latter half of the century. Today, the science continues to advance. Robot welding is commonplace in industrial settings, and researchers continue to develop new welding methods and gain greater understanding of weld quality and properties.

Welding is one of the principle activities in modern fabrication, ship building and offshore industry. The performance of these industries regarding product quality, delivery schedule and productivity depends upon structural design, production planning, welding technology adopted and distortion control measures implemented during fabrication. The quality of welding depends on the following parameters: • • • • • • Skill of welder Welding parameters Shielding medium Work layout Plate edge preparation Fit-up and alignment

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Correct process and procedures Suitable distortion control.

Welding is basically a joining process. Ideally a weld should achieve a complete continuity between the parts being joined such that the joint is indistinguishable from the metal in which the joint is made. Such an ideal situation is unachievable but welds giving satisfactory service can be made in several ways. The choice of a particular welding process will depend on the following factors:
• • • • • • • • • • • •

Types of metal and its metallurgical characteristics; Types of joint, its location and welding position; End use of the joint; Cost of production; Structural size; Desired performance; Experience and abilities of manpower; Joint accessibility ; Joint design; Welding equipment available; Work sequence; Welder skill.

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1.1 Motivation
Observing any welding process can make any materials to be welded This project is done because it allow greater weld control, Improved and faster. The motivation behind this study was raised first from the need for such an automatic welding table in the workshop here at the GUC. The workshop has a manual welding but the automatic welding table lacks is enormously required in the presence of many students in welding classes. Thus, it was decided to design and manufacture this automatic welding table to form the materials that will be weld faster than the manual also to have an accurate final work.

1.2 Aim of the project
The objectives of this bachelor work are: 1) Surveying the automatic welding table system that can adapt to the workshop environment. 2) Designing of an automatic welding table with all its related components. 3) Manufacturing of all parts individually and assembling the whole device. 4) Installing the part at the workshop. 5) Testing the part for consistent performance.

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CHAPTER 2
Literature Review
Today, there are many welding processes available, provides a list of processes used in modern metal fabrication and repair. The classes are classified into subclasses which is the most popular welding processes

2.1 Types of joining processes 2.1.1 Manual joining processes A manual joining process is one that is completely performed by hand. The welder controls all of the manipulation, rate of travel, joint tracking and in some cases, the rate at which filler metal is added to the weld. The manipulation of the electrode or torch in a straight line or oscillating pattern affects the size and the shape of the weld. The manipulation pattern may also be used to control the size of the weld pool during out of position welding. The rate of travel or speed AT WHICH THE WELD progresses along the joint affects the width, reinforcement of the weld. The placement or location of the weld bead within the weld joint affects the strength, appearance and possible acceptance of the joint. The rate at which filler metal is added to the weld affects the reinforcement, width of the weld. The most commonly used manual arc welding process is shielded metal arc welding (SMAW) .the flexibility the welder has in performing the weld makes this process one of the most versatile. By changing the manipulation, rate of the travel or joint tracking, the welder can make an acceptable weld on a variety of material thicknesses

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The most commonly used manual arc welding, gas welding and brazing process.

Figure (2.1) Manual joining processes

2.1.2 Semi automatic joining processes Semi automatic joining processes is one in which the filler metal is fed into the weld automatically. All other functions are controlled manually by the welder. The additions of the filler metal to the weld by an automatic wirefeeder system enables the welder to increase the uniformity of the welds , productivity and the weld quality , the distance of the welding gun or torch from the work remains constant . This gives the welder better manipulative control; as compared to , for example shielded metal arc welding , in which the electrode holder starts at a distance of 14 in from the work . This distance exaggerates the slightest accidental movement made during the first part of the weld .in the SMAW process , The electrode holder must be lowered steadily as the weld progresses to feed the electrode and maintain the correct arc length .This constant changing of the distance above the work causes the welder to shift body position frequently. Because the filler metal is being fed from a large spool, the welder does not have to stop welding to change filler electrodes or filler metal. SMA electrodes cannot be used completely as they have a waste sub of approximately 2 in. This waste stub represents approximately 15 % of the filler metal that must be discarded.

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The frequent stopping for rod and electrode changes, followed by restarting, wastes time and increase the number of the weld craters. These craters are often a source of cracks and other discontinuous. In some welding procedures each weld crater must be chipped and ground before the weld can be restarted. Examples: gas metal arc welding, flux cored arc welding, submerged arc welding, gas tungsten arc welding, cold-hot wire feed.

Figure (2.2) Semi automatic joining processes

2.1.3 Automatic joining processes An automatic joining process is a dedicated process that does not require adjustments to be made by the operator during the actual welding cycle, all operating guidelines are preset, and parts may or may not be loaded or unloaded by the operator. Automatic equipment is often dedicated to one type of product or part; a large investment is usually required in jigs and fixtures used to hold the parts to be joined in the proper alignment. The operational cycle can be controlled mechanically or numerically (computer). The cycle may be as simple as starting and stopping points, or it may be more complex. A more complex cycle may include such steps as prep urge time, hot start, and initial current, pulse power, down slope, final current and post purge time. Automatic welding or brazing is best suited to large volume production runs because of the expense involved in specially jigs and fixtures. Some examples: typical GTAW automatic welding program.

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2.1.4 Automated joining processes Are similar to automatic joining except it is more flexible and easily adjusted or changed. Unlike automatic welding, there is no dedicated machine for each product. The industrial robot is rapidly becoming the main component in automated welding or joining stations. The welding are often controlled by microprocessors or computers , the equipment is controlled by programs or some commands expressed in codes that direct in welding also the programs can be stored and changed.

Figure (2.3) Automated or automatic joining processes

2.1.5 Machine joining process A machine joining processes is one in which the joining is performed by the equipment requiring the welding operator to observe the progress of the weld and make adjustments as required. The parts being joined may or not be loaded or unloaded automatic. The operator may monitor the joining progress by watching it directly, observing instruments only, or using a combination of both methods. Adjustments in travel speed, joint-tracking,

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work to gun or work to torch distance may be needed to ensure that the joint is made according to specifications The work may move past a stationary welding or it may be held stationary and the welding machine moves on a beam or track along the joint .on some large machine welds, the operator may ride with the welding head along the path of the weld to minimize adjustments during machine welds, a test weld is often performed just before the actual weld is produced. This practice weld helps increase the already high reliability of machine welds.

Figure (2.4) Machine joining process

2.1.6 Industrial robots welding

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An industrial robots is a reprogrammable design to move materials .industrial robots are powered by electric stepping motors , hydraulics or pneumatics and are controlled by a program , Robots can perform movements in x and y and z directions . Robots can be used with other components to increase production and the flexibility of the system. A computer or microprocessor can synchronize the robot’s operation to postioners, conveyors, automatic fixtures and other production machines parallel or multiple work stations increase the duty cycle and reduce the cycle time parts can be loaded and unloaded by the operator at one station while the robot welds at another station.

Figure (2.5) Industrial robots welding

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2.2 ARC WELDING Arc welding is a process that uses an electric arc to join the metals being welded. A distinct advantage of arc welding over gas welding is the concentration of heat. In gas welding the flame spreads over a large area, sometimes causing heat distortion. The concentration of heat, characteristic of arc welding, is an advantage because less heat spread reduces buckling and warping. This heat concentration also increases the depth of penetration and speeds up the welding operation; therefore, you will find that arc welding is often more practical and economical than gas welding. All arcwelding processes have three things in common: a heat source, filler metal, and shielding. The source of heat in arc welding is produced by the arcing of an electrical current between two contacts.

2.2.1 Arc welding processes
2.2.1.1 Shielded metal arc welding Shielded Metal Arc Welding (SMAW) also called Stick welding or manual welding is a process, which melts and joins metals by heating them with an arc between a coated metal electrode and the work piece. The electrode outer coating, called flux, assists in creating the arc and provides the shielding gas and slag covering to protect the weld from contamination and coming in contact with air. The electrode core provides most of the weld filler metal. The SMAW welding power source provides constant current power slope (CC) and may be alternating current (AC) or direct current (DC), depending many factors such as the electrode being used, the material being welded. The power in a welding circuit is measured in voltage and current. The voltage (Volts) is governed by the arc length between the electrode and the work piece and is influenced by electrode diameter. Current is a more practical measure of the power in a weld circuit and is measured in amperes (Amps). The amperage needed to weld depends on electrode diameter, the size and thickness of the pieces to be welded, and the position of the welding. Thin metals require less current than thick metals, and a small electrode requires less amperage than a large one. Advantages of Shielded Metal Arc Welding:


Simple, portable and inexpensive equipment.

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Wide variety of metals, welding positions and electrodes are applicable. Suitable for outdoor applications.



Disadvantages of Shielded Metal Arc Welding: • • • The process is discontinuous due to limited length of the electrodes; Weld may contain slag inclusions; Fumes make difficult the process control

Figure (2.6) Shielded metal arc welding

2.2.1.2 Tungsten Inert Gas Welding Tungsten inert gas (TIG) welding process, also known as (GTAW) is an arc welding process where a non-consumable tungsten electrode is employed to initiate the arc increases the arc emissivity. The weld area is protected from atmospheric contamination by a shielding gas, usually an inert gas such as

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argon or Helium or Mixtures of both, and a filler metal may or may not be used depending on the thicknesses being welded. Constant current welding power supply produces energy, which is conducted across the arc through a column of highly ionized gas. TIG is used to weld stainless steel, nickel alloys, titanium, aluminum, and magnesium, copper, brass, bronze and even gold. TIG can also join dissimilar metals to one another such as copper to brass and stainless to mild steel.
Some Applications as It is used extensively in the manufacture of space

vehicles, and is also frequently employed to weld small-diameter, thin-wall tubing such as those used in the bicycle industry ,GTAW is often used to make root or first pass welds for piping of various sizes. In maintenance and repair work, the process is commonly used to repair tools and dies, especially components made of aluminum and magnesium.

Advantages of Tungsten Inert Gas Arc Welding: •


Weld composition is close to that of the parent metal; High quality weld structure Slag removal is not required (no slag); Thermal distortions of work pieces are minimal due to concentration of heat in small zone.

• •

Disadvantages of Tungsten Inert Gas Arc Welding: • •


Low welding rate; Relatively expensive; Requires high level of operator’s skill.

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Figure ( 2.7) Tungsten Inert Gas Welding

2.2.1.3 Submerged arc welding Submerged arc welding (SAW) is a common arc welding process. It requires a continuously fed consumable solid or tubular electrode. The molten weld and the arc zone are protected from atmospheric contamination by being “submerged” under a blanket of granular fusible flux consisting of lime, silica, manganese oxide, calcium fluoride, and other compounds. When molten, the flux becomes conductive and provides a current path between the electrode and the work. This thick layer of flux completely covers the molten metal thus preventing spatter and sparks. SAW is normally operated in the automatic or mechanized mode, however, semi-automatic (SAW) guns with pressurized or gravity flux feed delivery are available. The process is normally limited to the flat or horizontal-fillet welding positions. Single or multiple (2 to 5) electrode wire variations of the process exist. SAW strip-cladding utilizes a flat strip electrode (e.g. 60 mm wide x 0.5 mm thick). DC or AC power can be used, and combinations of DC and AC are common on multiple electrode systems.

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Constant voltage welding power supplies are most commonly used; however, constant current systems in combination with a voltage sensing wire-feeder are available. Advantages of Submerged Arc Welding: • • • • • • • • • • • High deposition rates. High operating factors in mechanized applications. Deep weld penetration. Sound welds are readily made (with good process design and control). High speed welding of thin sheet steels up to 5 m/min (16 ft/min) is possible. Minimal welding fume or arc light is emitted. Practically no edge preparation is necessary. The process is suitable for both indoor and outdoor works. Distortion is much less. Welds produced are sound, uniform, ductile, and corrosion resistant and have good impact value. Single pass welds can be made in thick plates with normal equipment

Disadvantages of Submerged Arc Welding: • • Weld may contain slag inclusions; Limited applications of the process - mostly for welding horizontally located plates.

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Figure (2.8) Submerged arc welding

2.2.1.4 Flux cored arc welding Flux-cored arc welding is a semi-automatic or automatic arc welding process. FCAW requires a continuously-fed consumable tubular electrode containing a flux and a constant-voltage or, less commonly, a constant-current welding power supply. An externally supplied shielding gas is sometimes used, but often the flux itself is relied upon to generate the necessary protection from the atmosphere. The process is widely used in construction because of its high welding speed and portability. The advantage of FCAW over SMAW is that the use of the stick electrodes used in SMAW is unnecessary. This helped FCAW to overcome many of the restrictions associated with SMAW. There is two types of flux cored arc welding. One type of FCAW requires no shielding gas. This is made possible by the flux core in the tubular consumable electrode. However, this core contains more than just flux; it also contains various ingredients that when exposed to the high temperatures of welding generate a shielding gas for protecting the arc. This type of FCAW is attractive

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because it is portable and generally has good penetration into the base metal. Some disadvantages are that this process can produce excessive, noxious, under some conditions it can produce welds with inferior mechanical properties; the slag is often difficult and time-consuming to remove; and operator skill can be a major factor. Another type of FCAW uses a shielding gas that must be supplied by an external supply. This is known informally as "dual shield" welding. This type of FCAW was developed primarily for welding structural steels. In fact, since it uses both a flux-cored electrode and an external shielding gas, one might say that it is a combination of gas metal (GMAW) and flux-cored arc welding (FCAW). This particular style of FCAW is preferable for welding thicker and out-of-position metals. The slag created by the flux is also easy to remove. The main advantages of this process is that in a closed shop environment, it generally produces welds of better and more consistent mechanical properties, with fewer weld defects than either the SMAW or GMAW processes. it also allows a higher production rate. Advantages of Flux cored arc welding: • • • • • • FCAW may be an "all-position" process with the right filler metals. No shielding gas needed making it suitable for outdoor welding and/or windy conditions A high-deposition rate process. Some "high-speed" (e.g., automotive applications) Less precleaning of metal required Metallurgical benefits from the flux such as the weld metal being protected initially from external factors until the flux is chipped away Melted Contact Tip – happens when the electrode actually contacts the base metal. Irregular wire feed – typically a mechanical problem Porosity More costly filler material/wire.

Disadvantages of Flux cored arc welding: • • •


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Figure (2.9) Flux cored arc welding

2.2.1.5 Plasma welding

The plasma welding is one type of arc welding process by which single body is produced by heat is obtained from plasma between the work piece and tungsten or tungsten alloy electrode. There are two types of inert gas is employed for plasma welding process, one formed the plasma and other is shielding the plasma. Plasma is the ionized state of gas atoms. When an ionized gas passes through the electric current, it becomes mixture of ions, electron and highly excited atoms. Thus the energy of plasma and the temperature is dependent on the amount of the electrical power employed. A tremendous amount of temperature is obtained from plasma torch is about 500000F. There are two types of plasma arc torch is used, 1.Transferred arc torch, 2. Non-transferred torch. In the non transfer arc process the arc is produced between the tungsten electrode (-) and water cooled nozzle (+). Plasma is produced as a flame. The arc is totally independent of the work piece and it does not help to completion of electrical circuit. In the transferred arc process is also an arc is produced between the work piece (+) and electrode (-). In this process the produced arc is transferred electrode to work piece. It has extraordinary power of plasma arc, which posses high jet velocity and high plasma density. By this facility, it is used to cut and weld the metals. Which metals we cannot cut by means oxyacetylene process, there plasma arc can do very effectively due to its high arc travel speed. A pilot arc is established in between the electrode and nozzle for initial ignition. As the pilot arc touches the job, then immediately the main current start to flow between the work and electrode. Thus the arc is produced. Some Applications as Nuclear submarine pipe welding ,

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Cryogenic and aerospace component welding ,Nickel and high nickel alloy welding ,Melting the high melting point temperature metals ,Titanium plate welding up to 8 mm thickness ,Welding the stainless tubes up to 1/4” thickness. Advantages of plasma welding: • • • • • • It has excellent type weld quality. Arc is stabilized. It needs very simple type’s fixture. Root welding does not required. Penetration is uniformed. It produces radio-graphic quality welding.

Disadvantages of Plasma Welding: •


Expensive equipment; High distortions and wide welds as a result of high heat input.

Figure (2.10) Plasma welding

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2.3 Electric resistance welding Electric resistance welding refers to a group of welding processes such as spot and seam welding that produce coalescence of faying surfaces where heat to form the weld is generated by the electrical resistance of material is the time and the force used to hold the materials together during welding. Some factors influencing heat or welding temperatures are the proportions of the work pieces, the coating or the lack of coating, the electrode materials, electrode geometry, electrode pressing force, weld current and weld time. Small pools of molten metal are formed at the point of most electrical resistance (the connecting surfaces) as a high current (100–100,000 A) is passed through the metal. In general, resistance welding methods are efficient and cause little pollution, but their applications are limited to relatively thin materials and the equipment cost can be high. Advantages of Resistance Welding: • • • • • • •


High welding rates; Low fumes; Cost effectiveness; Easy automation; No filler materials are required; Low distortions. High equipment cost; Low strength of discontinuous welds; Thickness of welded sheets is limited - up to 1/4” (6 mm);

Disadvantages of Resistance Welding:



2.3.1 Electric Resistance welding processes:

2.3.1.1 Spot welding

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Spot welding is a resistance welding method used to join two to three overlapping metal sheets, studs, projections, electrical wiring hangers, some heat exchanger fins, and some tubing. Usually power sources and welding equipment are sized to the specific thickness and material being welded together.

Figure (2.11) Spot welding

2.3.1.2 Seam welding Seam welding is a Resistance seam welding is a process that produces a weld at the faying surfaces of two similar metals. The seam may be a butt joint or an overlap joint and is usually an automated process.

Figure (2.12) Seam welding

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2.3.1.3 Flash Welding Flash Welding is a Resistance Welding (RW) process, in which ends of rods (tubes, sheets) are heated and fused by an arc struck between them and then forged (brought into a contact under a pressure) producing a weld. The welded parts are held in electrode clamps, one of which is stationary and the second is movable.

2.3.1.4 Projection welding Projection welding is in group of resistance welding. In this welding process where weld joint is produced by heating is obtained from electrical resistance flow through the work, which held under electrode pressure. The localized welding joint is made by this welding method. The two surfaces of weld metal are held together in under pressure by the electrodes. When an electrical current flown through the weld electrode, it causes the projecting metals are melts and fuse the both material which is contacted. Thus the weld joint is made. In single operation a number of joint is made. The joint strength is depending on nature of projection. Some Applications are a very common use of projection welding is the use of special nuts that have projections on the portion of the part to be welded to the assembly. Also, used for welding parts of refrigerator, condensers, refrigerator racks, grills etc

2.3.1.5 Resistance butt welding Butt welding is another type of electric resistant welding. The two weld metals are placed in a machine in face to face matching and both are clamped separately. These clamps are act as a electrode. These clamps are carry the current. The weld metals are matched correctly same axes and same line touching each other. Both weld metals are holding under pressure. The source current is given through the electrode to the weld metal and supply is continuing until its reaching melting temperature. Previously load is applied to the metal and sufficient melting temperature, both are play master role for completed the butt weld. Some Applications as Pipes, tubing, bars, rods, light and medium weight structural shapes may be welded by butt weld ,Little thickness of ferrous and non-ferrous can be weld ,It has large application in wire drawing industries.

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Figure (2.13) Resistance butt welding

2.6 BRAZING Advantages of brazing: • • • • • • • Low thermal distortions and residual stresses in the joint parts; Microstructure is not affected by heat; Easily automated process; Dissimilar materials may be joined; High variety of materials may be joined; Thin wall parts may be joined; Moderate skill of the operator is required.

Disadvantages of brazing:
• •

Careful removal of the flux residuals is required in order to prevent corrosion; No gas shielding may cause porosity of the joint; Large sections cannot be joined; Fluxes and filler materials may contain toxic components; Relatively expensive filler materials.

• • •

2.4 Brazing process

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2.4.1.1 Torch brazing Torch brazing is by far the most common method of mechanized brazing in use. It is best used in small production volumes or in specialized operations, and in some countries, it accounts for a majority of the brazing taking place. There are three main categories of torch brazing in use manual, machine, and automatic torch brazing. Manual torch brazing is a procedure where the heat is applied using a gas flame placed on or near the joint being brazed. The torch can either be hand held or held in a fixed position depending on if the operation is completely manual or has some level of automation. Manual brazing is most commonly used on small production volumes or in applications where the part size or configuration makes other brazing methods impossible. The main drawback is the high labor cost associated with the method as well as the operator skill required to obtain quality brazed joints. The use of flux or self-fluxing material is required to prevent oxidation. Machine torch brazing is commonly used where a repetitive braze operation is being carried out. This method is a mix of both automated and manual operations with an operator often placing brazes material, flux and jigging parts while the machine mechanism carries out the actual braze. The advantage of this method is that it reduces the high labor and skill requirement of manual brazing. The use of flux is also required for this method as there is no protective atmosphere, and it is best suited to small to medium production volumes. Automatic torch brazing is a method that almost eliminates the need for manual labor in the brazing operation, except for loading and unloading of the machine. The main advantages of this method are: a high production rate, uniform brazes quality, and reduced operating cost. The equipment used is essentially the same as that used for Machine torch brazing, with the main difference being that the machinery replaces the operator in the part preparation.

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Figure (2.14) Torch brazing

2.5 Soldering
Advantages of soldering: • • • • • • • • • Low power is required; Low process temperature; No thermal distortions and residual stresses in the joint parts; Microstructure is not affected by heat; Easily automated process; Dissimilar materials may be joined; High variety of materials may be joined; Thin wall parts may be joined; Moderate skill of the operator is required.

Disadvantages of soldering: • • •


Careful removal of the flux residuals is required in order to prevent corrosion; Large sections cannot be joined; Fluxes may contain toxic components; Soldering joints cannot be used in high temperature applications; Low strength of joints.



2.6 Thermit welding Thermit Welding is a welding process utilizing heat generated by exothermic chemical reaction between the components of the Thermit (a mixture of a metal oxide and aluminum powder). Advantages of Thermit Welding: • • No external power source is required (heat of chemical reaction is utilized); Very large heavy section parts may be joined.

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Disadvantages of Resistance Welding: • •
• •

Only ferrous (steel, chromium, nickel) parts may be welded; Slow welding rate; High temperature process may cause distortions and changes in Grain structure in the weld region. Weld may contain gas (Hydrogen) and slag contaminations.

2.6.1Thermit welding processes
2.6.1.1 Laser beam welding Laser beam welding is a welding technique used to join multiple pieces of metal through the use of a laser. The beam provides a concentrated heat source, allowing for narrow, deep welds and high welding rates. The process is frequently used in high volume applications, such as in the automotive industry. Laser beam welding has high power density (on the order of 1 MW/cm2) resulting in small heat-affected zones and high heating and cooling rates. The spot size of the laser can vary between 0.2 mm and 13 mm, though only smaller sizes are used for welding. The depth of penetration is proportional to the amount of power supplied. A continuous or pulsed laser beam may be used depending upon the application. Milliseconds long pulses are used to weld thin materials such as razor blades while continuous laser systems are employed for deep welds. The LBW weld quality is high, similar to that of electron beam welding. The speed of welding is proportional to the amount of power supplied but also depends on the type and thickness of the work pieces. The high power capability of gas lasers make them especially suitable for high volume applications. LBW is particularly dominant in the automotive industry. Advantages of Laser Welding: • •
• •

Easily automated process; Controllable process parameters; Very narrow weld may be obtained; High quality of the weld structure;

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• •

Very small heat affected zone; Dissimilar materials may be welded. Very small delicate work pieces may be welded; Vacuum is not required; Low distortion of work piece. High cost equipment; Weld depth is limited.

• • • •

Disadvantages of laser Arc Welding:

Figure (2.15) Laser beam welding

2.6.1.2 Electron beam welding Electron beam welding (EBW) is a fusion welding process in which a beam of high-velocity electrons is applied to the materials being joined. The work pieces melt as the kinetic energy of the electrons is transformed into heat upon impact, and the filler metal, if used, also melts to form part of the weld. The welding is often done in conditions of a vacuum to prevent dispersion of the electron beam. When electrons of the beam impact the surface of a solid, some of them may be reflected (as "backscattered" electrons), and others penetrate under the surface, where they collide with the particles of the solid. In non-elastic collisions they loose their kinetic energy.

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It has been proved, both theoretically and experimentally, that they can "travel" only a very small distance under the surface before they transfer all their kinetic energy into heat. This distance is proportional to their initial energy and inversely proportional to the density of the solid. Under conditions usual in welding practice the "travel distance" is of the order hundreds of a millimeter. Just this fact enables, under certain conditions, the fast penetration of the beam. Some Applications as, this process is used in
joining of reactor components, It has large use in spaceship building, It is used in automobile engine component welding.

Advantages of Electron Beam Welding: • •


Tight continuous weld; Low distortion; Narrow weld and narrow heat affected zone; Filler metal is not required. Expensive equipment; High production expenses; X-ray irradiation.

• • • •

Disadvantages of Electron Beam Welding:

Figure (2.16) Electron beam welding

2.7 Gas welding One of the most popular welding methods uses a gas flame as a source of heat. In the oxyfuel gas welding process heat is produced by burning a combustible gas, such as MAPP (methylacetylene-propadiene) or acetylene, mixed with oxygen. Gas welding is widely used in maintenance and repair work because of the ease in transporting oxygen and fuel cylinders. Once

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you learn the basics of gas welding, you will find the oxyfuel process adaptable to brazing, cutting, and heat treating all types of metals.

2.7.1 Gas welding process
2.7.1.1 Oxyacetylene welding Oxyacetylene welding (commonly called oxyfuel welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. Pure oxygen, instead of air (20% oxygen/80% nitrogen), is used to increase the flame temperature to allow localized melting of the work piece material (e.g. steel) in a room environment. Oxy-fuel or oxyacetylene is one of the oldest welding processes. However, it is still widely used for welding pipes and tubes, as well as repair work. It is also frequently well-suited, and favored, for fabricating some types of metalbased artwork. In oxy-fuel or oxyacetylene welding, a welding torch is used to weld metals. Welding metal results when two pieces are heated to a temperature that produces a shared pool of molten metal. The molten pool is generally supplied with additional metal called filler. Filler material depends upon the metals to be welded. Oxy-fuel processes may use a variety of fuel gases, the most common being acetylene. The acetylene is obtained by the action of oxygen and calcium carbide. CaC2 + 2H2O = Ca (OH) 2 + C2H2 (Acetylene)

Acetylene is the primary fuel for oxy-fuel welding and is the fuel of choice for repair work and general cutting and welding. Acetylene gas is shipped in special cylinders designed to keep the gas dissolved. The cylinders are packed with porous materials then filled to around 50% capacity with acetone, as acetylene is acetone soluble. Acetylene is unstable and has high cost
Advantages of oxyacetylene welding:



In gas welding the heating and cooling rate is slow.

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• • • •

The flame can be controlled easily where need low and high temperature for welding or brazing or soldering. Filler metal deposit rate can be controlled easily, because source of heat and filler metals are separate. Preheating facility is in welder’s hand. So where required it can be applied. it is low cost and low maintenance.

Figure (2.17) oxyacetylene welding

2.7.1.2 Pressure gas welding The pressure gas welding is defined as, the coalescence body is produced by the heating of weld metal and heat source is some gas of mixture. Then apply the pressure on weld metal to complete the pressure gas welding. Any

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kind of filler metal is not used in this welding process. Its Application is commonly used in sheet metal welding, pipe welding, railroad joining etc.

2.8 Solid state welding Advantages of Solid State Welding:
• •

Weld (bonding) is free from microstructure defects (pores, non-metallic inclusions, segregation of alloying elements) Mechanical properties of the weld are similar to those of the parent metals No consumable materials (filler material, fluxes, shielding gases) are required Dissimilar metals may be joined (steel - aluminum alloy steel - copper alloy).




Disadvantages of Solid State Welding: • • Thorough surface preparation is required (degreasing, oxides removal, brushing/sanding) Expensive equipment.

2.8.1 Solid state welding process
2.8.1.1 Forge welding Forge welding is the oldest welding process. It has an application of the blacksmith’s method of metals joining. The metals which to be joint are heated in furnace or some other source of heat to the plastic stage or just below the molten stage of metals (looks like very bright). Then heated metals are bring on anvil from heat source and superimposed the both metals where to be joint. Apply the hammering or pressed together until a joint has been created. The applying of heat must be uniformed. Otherwise the joint is made weak or spongy rough appearance. So heat should not be too high or too little. To avoidance of oxidation a little amount of flux may be used in weld joint. There are mainly three types of forge welding method is used:

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• • • • • • • • • •
• •

Hammer welding. Roll welding. Die welding. In sheet metal welding. In ship building works. In automobile workshop. In refrigeration works. Good quality weld may be obtained; Parts of intricate shape may be welded; No filler material is required. Only low carbon steel may be welded; High level of the operators skill is required; Slow welding process; Weld may be contaminated by the coke used in heating furnace.

Some Applications as

Advantages of Forge Welding:

Disadvantages of Forge Welding:

• •

Figure (2.18) Forge welding 2.8.1.2Ultrasonic welding

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Ultrasonic welding is an industrial technique whereby high-frequency ultrasonic acoustic vibrations are locally applied to work pieces being held together under pressure to create a solid-state weld. It is commonly used for plastics, and especially for joining dissimilar materials. In ultrasonic welding, there are no connective bolts, nails, soldering materials, or adhesives necessary to bind the materials together. The applications of ultrasonic welding are extensive and are found in many industries including electrical and computer, automotive and aerospace, medical, and packaging. Whether two items can be ultrasonically welded is determined by their thickness. If they are too thick this process will not join them. This is the main obstacle in the welding of metals. However, wires, microcircuit connections, sheet metal, foils, ribbons and meshes are often joined using ultrasonic welding. Ultrasonic welding is a very popular technique for bonding thermoplastics. It is fast and easily automated with weld times often below one second and there is no ventilation system required to remove heat or exhaust. This type of welding is often used to build assemblies that are too small, too complex, or too delicate for more common welding techniques. Advantages of Ultrasonic Welding: • • • • • • •


Dissimilar metals may be joined; Very low deformation of the work pieces surfaces; High quality weld is obtained; The process may be integrated into automated production lines; Moderate operator skill level is enough. Only small and thin parts may be welded; Work pieces and equipment components may fatigue at the reciprocating loads provided by ultrasonic vibration; Work pieces may bond to the anvil.

Disadvantages of Ultrasonic Welding:

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Figure (2.19) Ultrasonic welding

2.8.1.3 Cold working welding

The cold welding process is performed in solid state, where metal joint is produced in the room temperature and also under of mechanical pressure. The joint is made without of filler rod. The main characteristic of this welding process is total absence of heat and flux. A specially designed die is used for restricting or controlling the deformation of weld parts. The pressure is applied by manually or with power driven. The amount of pressure is applied on three factors: 1. Nature of surface area of die. 2. Thickness of the metal. 3. Characteristic of material.
Some Applications as it is used in electronics industries for joining of small

transistors, also It has specific use in welding metals in explosive areas.

2.8.1.4 Friction welding

The friction welding is one of the solid state welding process, where weld joint is made by heating is created from mechanically induced sliding motion between rubbing surface in under pressure. The heat is generated by co-

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efficient of friction of the material. To get a quick heat from surface area, when the rotational speed is high. In this welding process the fusion is produced by rotating one of the weld parts to be joined against the fixed surface of the other part. Until fusion temperature is obtained in weld parts the rotation of rotating parts will be in high speed and under low pressure. Large amount of pressure will be applied in until both weld parts are welded. Different types of material can be welding by this process. The materials are: Carbon steel, alloy steel, copper to carbon steel, copper to aluminum, aluminum and its alloy, brass to bronze, tool steel, stainless steel, stainless steel to aluminum, tungsten, etc. Some Applications as Drill, tap, reamer etc. joining with shank, To joining of steering shaft and worm gear, engine valves, power transmission shaft etc, To production of bimetallic shaft joining ,To produce a bimetallic fastener which is used in nuclear plant. Advantages of Friction welding • • • • • • • It requires less time operation. Operational hazardous is less. The characteristic changing of granular structure is less. The weld joint may have not heat treated again. It has no need of flux, filler. So it is free of smoke, spatter and slag. Simplicity of operation. Power requirement is less.

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Figure (2.20) Friction welding

2. 8.1.5 Electroslag welding Electroslag welding is a highly productive, single pass welding process for thick in a vertical or close to vertical position. An electric arc is initially struck by wire that is fed into the desired weld location and then flux is added. Additional flux is added until the molten slag, reaching the tip of the electrode, extinguishes the arc. The wire is then continually fed through a consumable guide tube into the surfaces of the metal work pieces and the filler metal are then melted using the electrical resistance of the molten slag to cause coalescence. The wire and tube then move up along the work piece while a copper retaining shoe that was put into place before starting is used to keep the weld between the plates that are being welded. This process uses a direct current (DC) voltage usually ranging from about 600A and 40-50V , higher currents are needed for thicker materials. Because the arc is extinguished, this is not an arc process.
Some Applications as Electroslag welding is used mainly to join low carbon

steel plates and/or sections that are very thick, It can also be used on structural steel if certain precautions are observed Advantages • Benefits of the process include its high metal deposition rates—it can lay metal at a rate between 15 and 20 kg per hour (35 and 45 lb/h) per electrode Its ability to weld thick materials. The process is also very efficient, since joint preparation and materials handling are minimized while filler metal utilization is high

• •

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• •

The process is also safe and clean, with no arc flash and low weld splatter or distortion. Electroslag welding easily lends itself to mechanization, thus reducing the requirement for skilled manual welders. Coarse grain structure of the weld; Low toughness of the weld;

Disadvantages of Electroslag welding: • •

Figure (2.21) Electroslag welding

2.9 Metals
Properties of metals • • • • • Hardness Brittleness Ductility Toughness Strength

Metals that can be used in welding Carbon and alloy steels These steels classified into low carbon, medium carbon, high carbon depending on the percentage of the carbon in the materials Common name Low carbon Medium carbon High carbon Carbon content 0.15% max 0.30%-0.50% 0.50%-1.00% weldability excellent fair poor

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High manganese steel High manganese steel are used for such items as a power shovels, rock crushers, mine equipment, switch frogs. Stainless steel Stainless steel consists of alloys: austenitic, ferritic, martensitic, precipitation hardening. They are used such as chemical equipment, cooking materials, food processing equipment, and furnace parts. Chromium –molybdenum Chromium –molybdenum is used for high temperature service and aircrafts parts Copper and copper alloys There are different types of copper alloys. Copper is often alloyed with other metals such as zinc, nickel, iron, aluminum .Welding copper results in economy, speed, strength, ductility. Aluminum weldability Their characteristic is that has a great affinity for oxygen. Titanium It is silvery grey metal most important properties of the titanium are high strength to weight ration and excellent corrosion resistance. Magnesium It is an extremely light metal have a silver white color; it has considerable resistance to corrosion. Cast iron Cast iron is important to guard against cracks due to expanding and contractions during the welding process.

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2.10 Filler Metals When welding two pieces of metal together, you often have to leave a space between the joint. The material that you add to fill this space during the welding process is known as the filler metal, or material. Two types of filler metals commonly used in welding are welding rods and welding electrodes. The term welding rod refers to a form of filler metal that does not conduct an electric current during the welding process. The only purpose of a welding rod is to supply filler metal to the joint. This type of filler metal is often used for gas welding. In electric-arc welding, the term electrode refers to the component that conducts the current from the electrode holder to the metal being welded. Electrodes are classified into two groups: consumable and non consumable. Consumable electrodes not only provide a path for the current but they also supply fuller metal to the joint. An example is the electrode used in shielded metal-arc welding. No consumable electrodes are only used as a conductor for the electrical current, such as in gas tungsten arc welding.

2.11Protecting metal from atmospheric contamination Before performing any welding process, you must the base metal is clean. No matter how much the base metal is physically cleaned, it still contains impurities. These impurities, called oxides, result from oxygen combining with the metal and other contaminants in the base metal. Unless these oxides are removed by using a proper flux, a faulty weld may result. The term flux refers to a material used to dissolve oxides and release trapped gases and slag (impurities) from the base metal Advantages of fluxes for welding
• • •

It remains stable and does not change to a vapor rapidly within the temperature range of the welding procedure. It dissolves all oxides and removes them from the joint surfaces. It adheres to the metal surfaces while they are being heated and does not ball up or blow away.

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• •

It does not cause a glare that makes it difficult to see the progress of welding or brazing. It is easy to remove after the joint is welded. It is available in an easily applied form.

2.12 Control of weld metallurgy When the weld metal sodifies, the microstructures formed in the weld and the heat affected zone region determines the mechanical properties of the joint produced. Preheating and post welding heattreatment can be used to control the cooling rates in the weld and the heat affected zone regions and thus control the microstructures and properties of the welds produced. De oxidants and alloying elements are added as in foundry to control the weld metal properties. The foregoing discussion clearly shows that the status of welding has now changed from skill to science. A scientific understanding of the material and service requirements of the joints is necessary to produce successful welds which will meet the challenge of hostile service requirements.

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Figure (2.22) EXPANSION AND CONTRACTION of metals 2.13 Expansion and contraction of metals

When a piece of metal is heated, the metal expands. Upon cooling, the metal contracts and tries to resume its original shape. The effects of this expansion and contraction are shown in this figure. View a shows a bar that is not restricted in any way. When the bar is heated, it is free to expand in all directions. If the bar is allowed to cool without restraint, it contracts to its original dimensions. When the bar is clamped in a vise (view B) and heated, expansion is limited to the unrestricted sides of the bar. As the bar begins to cool, it still contracts uniformly in all directions. As a result, the bar is now deformed. It has become narrower and thicker, as shown in (view C). These same expansion and contraction forces act on the weld metal and base metal of a welded joint; however, when two pieces of metal are welded together, Expansion and contraction may not be uniform throughout all parts of the metal. This is due to the difference in the temperature from the actual weld joint out to the edges of the joint. This difference in temperature leads to internal stresses. All metals, when exposed to heat buildup during welding, expand in the direction of least resistance. Conversely, when the metal cools, it contracts by the same amount; therefore, if you want to prevent or reduce the distortion of the weldment, you have to use some method to overcome the effects of heating and cooling.

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Figure (2.23) direction of welding

2.14 Butt welds Butt welds are welds where two pieces of metal are joined at surfaces that are at 90 degree angles to the surface of at least one of the other pieces. The types of welds require only some preparation and are used with thin sheet metals that can be welded with a single pass. Common issues that can weaken a butt weld are the entrapment of slag, excessive porosity, or cracking. For strong welds, the goal is to use the least amount of welding material possible. Butt welds are prevalent in automated welding processes, such as submerged-arc welding, due to their relative ease of preparation. When metals are welded without human guidance; there is no operator to make adjustments for non-ideal joint preparation. Because of this necessity, butt welds can be utilized for their simplistic design to be fed through automated welding machines efficiently.

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Chapter 3
Experimental Setup
In this chapter the steps of manufacturing and selecting each component of the automatic welding table will be discussed and explained with the aid of pictures and figures. Every part was manufactured separately and later is being assembled to form the automatic welding table. Components of the automatic welding table are: 1- Body and frame. 2- Motor. 3- Gearbox. 4- Inverter. 5- Wire remote control.

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3.1The body and frame
3.1.1 The table The table is a basic piece that is generally consists of a flat top that is supported by either a set of legs. The table is made from metal; the table is a mechanical table, and made from iron. The table was designed by a length and width (100cm x 70cm) and the length of the legs are 80cm.

Figure (3.1) the manufacturing table

3.1.2 Upper part of the table This metal sheet with holes is the upper part of the table for holding the samples on it by screws while welding, and it is moving freely

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Dimension: 100cmx70cm and thickness 2mm

Figure (3.2) Upper part of the table

Figure (3.3) Machine that is used to do these holes on the upper part

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3.1.3 Wheels of the table Common inexpensive casters may include a brake feature, which prevents the wheel from turning. This is commonly achieved using a lever that presses a brake cam against the wheel. These institutional casters are ideal for any light duty application where the caster must be totally immobile when the caster brake is applied. Caster has a unique brake which locks both the wheel and the swivel bearing at the same time. This "Total-Lock" brake insures that the caster will not turn when the wheel is locked. This combination wheel brake is essential for safety in some applications such as on worktables, welding table, and medical equipment.

Figure (3.4) Wheels of the table

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Figure (3.5) this shape for connecting the wheels to it

3.1.4 Holder of the table The holder is made from iron and installed in one side of the table and contains three parts:


One part which can moving up and down depending on the length we need for the welding while holding the torch and then Installing this part by the screw

Dimension: length 75cm

Figure(3.6) part of the holder

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Second part which can moving right and left also depending on the length we need for the welding while holding the torch and then Installing the part by the screw ,

Dimension: length 75cm

Figure(3.7) part of the holder

Third part is connected to C-Clamp Dimensions: length 40cm

This type of clamp device typically used to hold the torch of the welding.

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Figure(3.8) part of the holder

Figure (3.9) c-clamp

3.1.5 Parts of the table section (a) Two parts of a sheet with dimension 200cmx2.5cm with thickness 2.5cm I used the two part of this sheet which welded on the table for the wheels bearing hub to move on it.

Figure (3.10) this part let the bearing hub wheel to move on it

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Figure (3.11) this part to prevent the bearing hub to move away (b)Wheel bearing hub There are eight wheels bearing hub, which attached to the upper part of the table to move on the table freely. Dimension: diameter 3cm

Figure (3.12) bearing hub wheel while moving

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Figure (3.13) eight bearing hub wheel

3.1.6 The motor with gearbox seating This shape were welded at the bottom of the table for motor with the gearbox and it is installed by 4 screws Dimensions of this Chassis: 35cmx20cmx80cm Dimensions of the seating of the motor with gearbox: 20cmx20cm.

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Figure (3.14) the motor with gearbox seating from the top view

Figure (3.15) the motor with gearbox seating from the side view

3.1.7 The shaft The Motor Shaft is primarily used as a mechanical component for torque transmission. This shaft is connected directly to motor. I took the dimension of the gears and pulley depends on it

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Figure (3.16) the motor shaft 3.1.8 Gears Gears have many uses in our lives. They are used to: - multiply or reduce speed and force, change the direction of motion, transmit a force over a distance. This type of gears is the pinion gears with Rack that are used to convert rotation (From the pinion) into linear motion (of the rack) Gears dimension: diameter 17cm

Figure (3.17) Gears connected to the shaft

Figure (3.18) Gears when it is

3.1.9 Rack

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Dimension: length 130cm it is attached down the upper part of the table and from the teeth side is directly connected to the gear

Figure (3.19) Rack

Figure (3.20) Rack with the gear

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3.1.10 Pulley

There is one pulley with a hole look like shape of key slot is directly connected to the shaft It’s Dimensions: diameter 6.5cm

Figure (3.21)Pulley with open key hole

And one pulley with a small hole connected to the shaft Dimensions: diameter 5cm

Figure (3.22)Pulley with small hole

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3.1.11 Safety electronic box


Holding a box in the table for putting the inverter inside it for more safe from the fumes of the welding and installed by 2 screws.

Figure (3.23) Safety inverter box with an open and close door

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3.2 Motor Power: 1HP Ampere: 8A Voltage: 380v Speed: 60rpm The motor was selected according to these specifications .The motor used in the project is three-phase induction motor, but three-phase motors are usually preferred for connecting it to the invertors. Various types of synchronous motors offer advantages in some situations, Motors that are designed for fixed-speed operation are often used. Certain enhancements to the standard motor designs offer higher reliability and better VFD performance. The motor has a 4 wires connected from the inverter, the red wire, yellow wire, and the green wire are connected to the motor and the black wire to the ground. Also the motor is connected to a gear box to reduce the speed.

Power= 1.732 x V x I x EFF x PF

Horse power= 1.732 x V x I x EFF x PF 746

Efficiency =

746 x HP 1.732 x V x I x PF

Power factor =

Input Watts 1.732 x V x I

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Current=

P 1.732 x V x EFF x PF

Where V= Voltage (volts)

I= Current (amps) HP= EFF= Efficiency Horsepower

P= Power (watts) F= Frequency (Hz)

Motor with gearbox

Gears

Output

Inverter

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Figure (3.24) Motor

3.3 Gear box The gear box is connected to the motor for two reasons: Because in the automatic welding operation, we need to take care in our speed, and the gearbox make that, it used to reduce the speed and increase the torque.

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Figure (3.25) Gear box side view

Figure (3.26) Gear box upper view

3.4 Inverter An inverter is a system for controlling the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. A variable frequency drive is a specific type of adjustable-speed drive. Variable-frequency drives are also known as adjustable frequency drives, variable-speed drives, AC drives, micro drives or inverter drives.

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Operation When a VFD starts a motor, it initially applies a low frequency and voltage to the motor. The starting frequency is typically 2 Hz or less. Thus starting at such a low frequency avoids the high inrush current that occurs when a motor is started by simply applying the utility (mains) voltage by turning on a switch. After the start of the VFD, the applied frequency and voltage are increased at a controlled rate or ramped up to accelerate the load without drawing excessive current. This starting method typically allows a motor to develop 150% of its rated torque while the VFD is drawing less than 50% of its rated current from the mains in the low speed range. A VFD can be adjusted to produce a steady 150% starting torque from standstill right up to full speed.

Figure (3.27) Inverter

3.5 Wire remote control

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This wire remote control is so simple, it contains only a black switch, red button, frequency silver switch. the black switch is used for moving the upper part forward or backward way or stop it, and another red button is the emergency which suddenly used to stop the motor if there is any problems, and other silver button which controls the speed (frequency) of the motor high or low depends on the type of the welding and the thickness for the material that will be welded. The wire remote control is connected to the inverter

Figure (3.28) Wire remote control

3.6 Assembly and Finishing

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Figure (3.29) first the design of the table

Figure (3.30) Grinding some parts and the edges of the table for finishing

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Figure (3.31) screws to attach some parts with others

Figure (3.32) Welding the small parts on the table to install the upper parts of table that will move

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Figure (3.33) the seating of the motor with the gearbox is done and ready to work

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Figure (3.34) Assembling and Installing all the system different parts altogether (motor, gearbox, control unit, gears, pulleys, wheels)

Figure (3.35) Holding the torch of the welding and can do the operation

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Testing and experiment results
3.7 Testing The objective of the experimental work is to find out that if the automatic welding table is better than the manual welding (workers). Destructive testing Testing the samples If the weld metal is stronger than the plate, failure occurs in the plate if the weld is weaker, failure occurs in the weld. After the weld section is machined to the specified dimensions, it is placed in the tensile testing machine and pulled apart. The tensile strength, in pounds per square inch is obtained by dividing the max load, required to brake the specimen, by the cross sectional area of the specimen at the middle. A=TTr2 or A=D2 .0.785 The test process involves placing the test specimen in the testing machine and applying tension to it until it fractures. During the application of tension, the elongation of the gauge section is recorded against the applied force. The data is manipulated so that it is not specific to the geometry of the test sample. The elongation measurement is used to calculate the engineering strain, ε, using the following equation:

Where ΔL is the change in gauge length, L0 is the initial gauge length, and L is the final length. The force measurement is used to calculate the engineering stress, σ, using the following equation:

Where F is the force and A is the cross-section of the gauge section. The machine does these calculations as the force increases, so that the data points can be graphed into a stress-strain curve

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Machine The most common testing machine used in tensile testing is the universal testing machine. This type of machine has two crossheads; one is adjusted for the length of the specimen and the other is driven to apply tension to the test specimen. There are two types: hydraulic powered and electromagnetically powered machines. The machine must have the proper capabilities for the test specimen being tested. There are three main parameters: force capacity, speed, and precision and accuracy. Force capacity refers to the fact that the machine must be able to generate enough force to fracture the specimen. The machine must be able to apply the force quickly or slowly enough to properly mimic the actual application. Finally, the machine must be able to accurately and precisely measure the gage length and forces applied; for instance, a large machine that is designed to measure long elongations may not work with a brittle material that experiences short elongations prior to fracturing.

Figure (3.36) Universal testing machine

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3.8 Experiment Results According to the experimental observations, there are four samples:


in case of the samples which are not welded

Test one of the two normal samples which are not welded.


In case of the two samples which are welded to each other:

Test the two samples which are welded to each other.

3.8.1 The tensile test.1

The normal sample which is without welding we will test it. Before testing

Figure (3.37) Normal sample before testing

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After testing

Figure (3.38) Normal sample after testing

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3.8.2 The tensile test.2 The two samples which are welded to each other, we will test it. Before testing

Figure (3.39) the two samples which are welded before testing

After testing

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Figure (3.40) the two samples which are welded after testing

Finally we found that the stress number of the samples which are welded to each other are larger than the stress number of the normal samples which are not welded and also the hardness of the samples which are welded by the automatic welding table is much more stronger than the normal sample.

Steps for preparing the sample: • • Cutting a very small strip from the sheet Mounting: by using the mounting machine where black phenolic powder is added to the strip then left for 7 min undress pressure, then cooling by quenching water for 3 min Grinding: by fixing the sample on the grinding machine and using a grinding paper grade 1200 silicon carbide at a speed of 350 rpm, the lubricant is water. Polishing: on the same machine but using polishing paper and the lubricant is diamond suspension solution. Etching: each material has its own etching solution.






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Chapter 4
Conclusion • Welding is used in the fabrication, maintenance, and repair of parts and structures. While there are many methods for joining metals, welding is one of the most convenient and rapid methods available. Products that are produced by the welding range from small objects, such as sunglasses and dental braces to larger structures such as building, ships and space shuttles. Welding improvers the hardness of the sheet and this was proved while testing the metal sheet samples. Welding improves the strength of the metal sheet and this was clear in the tensile test when the sample after welding has much higher stress than the sample before welding. Therefore Welding improves the mechanical properties of the sheet. Automatic welding is more better than the manual welding where welded structures have high rigidity






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