Several Types Of Welding Applications Engineering Essay

INTRODUCTION

Background of Study

Over the past decades, the importance of welding process especially in a wide range of industrial applications such as ships, railroad equipments, building construction, boilers, pipelines, nuclear power plants, aircraft and automobiles becomes more advance. Today, Flux Cored Arc Welding (FCAW) is one of the most popular welding methods, especially in industrial environments to join metals and alloys. FCAW was first introduced in the early 1950s as an alternative to Shielded Metal Arc Welding (SMAW). In 1965, it represented less than 5 percent of the total amount welding done by using FCAW. The rapid rise in the use of FCAW increasingly continued in 2005 when it passed 50 percent mark and still rising.

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Figure 1.1: Several types of welding applications.

Among the processes employed for welding such as Gas Metal Arc Welding (GMAW), Gas Tungsten Arc Welding (GTAW), Plasma Arc Welding (PAW) and Electroslag Welding (ESW), FCAW is more accepted in different industries to join metals and alloys [1] due to the following features.

High deposition rates.

More tolerant of rust and mill scale than GMAW.

Less operator skill required than GMAW.

High productivity than SMAW.

Good surface appearance.

Recently, automated robotic welding systems have received a great deal of attention, since they are highly appropriate both to increase production rate and quality as well as to decrease cost and production time [2, 3]. The process parameters for FCAW such as welding current, arc voltage and welding speed should be well recognized and categorized to enable automation and robotization of arc welding. The welding parameters are the most important factors affecting quality, productivity and cost of welding joint. Therefore, it is essential to properly select welding parameters for a given task to obtain the adequate bead geometry and shape relationship of a weldment based [4]. Furthermore, occurrence of various weld defects such as incomplete penetration, excess penetration, hollow bead and undercut are also affected by all of these parameters.

The relationship between welding process parameters and bead geometry began investigation in the mid 1900s and researchers were applied the regression analysis in 1987. Numerous attempts have been made by researchers using various types of software and analysis tools relating process variables and bead geometry to generate optimal welding output. Palani and Murugan [4] have built mathematical models using five level factorial technique to predict weld bead geometry for 317L flux cored stainless steel wire with IS:2062 structural steel as base plate. In addition, the performance of weld can be predicted by Genetic Algorithm method [5], Multiple Regression and Neural Network [6] and Taguchi and Particle Swarm Optimization [7].

The result from these researches show that the mathematical models derived can be used to predict bead geometry accurately. However, these analysis tools are costly and welding industries generally do not use them in production. Thus, the aim of this project is to develop the prediction calculator based on mathematical formulas that match the graphical profiles and represent the correlation between welding parameter and weld bead geometry.

Problem Statement

The bead geometry and welding parameter has to be given before welding start, but this input parameter cannot be easily guessed. Therefore, the quantitative relationship between welding parameter and bead geometry require reference to large number of experimental welding. Meanwhile, the selection of welding parameter for production based on trial and error is costly and time consuming. Hence, the cost of development of Welding Procedure Specification (WPS) will increase by many folds unless the welding parameter is optimal for welding.

Objective of Project

The main purpose of this project is to study the correlation between Flux Cored Arc Welding (FCAW) welding parameter and weld bead geometry in 2F position. Besides that, the aim of this study is to establish the limit of welding parameter that produces acceptable weld quality. In addition, the results from the experiment will be used to develop a calculator that can predict the welding parameter and weld bead geometry for FCAW in 2F position, then validate the accuracy of predicting calculator by experimental measurement.

Significance of Project

This project is intent to build a correlation between the FCAW welding parameter and weld bead geometry in 2F position based on experimental welded coupons. Hence, the result on this project can accurately predict the deposition profile using robotic FCAW process through a map which showing the range of welding parameter in 2G position that will produce good quality weld. As addition, the FCAW bead geometry in 4G position could be predicted based on selected welding parameter by using a validated calculator.

Scope of Project

The welding process is done by employing the robotic welder to perform the FCAW welding in 2F position. The material used is low carbon steel with a thickness of 9mm with T-fillet design. The quality of welding shall be evaluated based on the requirement of AWS D1.1 code of practice.

Project Methodology

In order to achieve the objectives and the scope of work that to get the good correlation between FCAW welding parameter and bead geometry in 2F position, several methods have been set:

To prepare fillet joint between two plate coupon on 9mm low carbon steel, in 2F position

To employ the robotic welder to weld by the FCAW process by varying one parameter at a time

To measure the weld bead geometry for all good quality bead geometry

To develop a mathematical formula that matches the correlation. Create the predicting calculator for FCAW welding in 2F position

To validate the accuracy and reliability of the calculator with measurements taken from an actual welded sample.

CHAPTER II

LITERATURE REVIEW

Introduction of Welding

Welding can be defined as a permanent joining process that produces coalescence of materials by heating them to the welding temperature, with or without the application of pressure or by the application of pressure alone, and with or without the use of filler metal [8]. Ibrahim [10] defined welding as a process of permanent joining two materials usually metals through localised coalescence resulting from suitable combination of temperature, pressure and metallurgical conditions. Most welding processes use heat to join parts together and the equipment used to generate the required varies, depending on the welding process.

Welding is used extensively for the manufacture and repair of farm equipment, construction of boilers, mining and refinery equipment, furnaces and railway cars. In addition, construction of bridges and ships also commonly requires welding. The application of welding process depends on the requirements of the weld, accessibility of the weld area, economic considerations and available welding equipment [9]. The strength and the integrity of a weld depend on the material properties of the metal being welded, as well as on a great many other factors. These factors include the shape of the weld, temperature of the heat sources, the amount of heat produced by the source and even the type of power source used.

Overview of Flux Cored Arc Welding (FCAW)

In recent years, pressure to increase productivity and reduce costs by the manufacturers has been the main driving force behind the adoption of flux cored wires. Productivity, quality and ease of use are the three main factors on which the increasing popularity of FCAW.

FCAW is an arc welding process that uses an arc between a continuous filler metal electrode and the weld pool [8]. The flux is used as a protection for molten metal from the atmosphere contaminations during welding operation. It will improve strength through chemical reactions and produce excellent weld shape. FCAW is very similar to GMAW in principle of operation and equipment used. In FCAW, weld metal is transferred as in GMAW globular or spray transfer. However, FCAW can achieve greater weld metal deposition and deeper penetration than GMAW short circuiting transfer [9]. The effects of electrode extension, nozzle angle, welding directions, welding speed and other welding manipulations are similar as GMAW.

The FCAW are welding process introduced in early 1950s with the development of an electrode that contained a core of flux material. However, an external shielding gas was required even with the flux cored electrode. After that, the flux cored electrode that did not require an external shielding gas was developed in 1959. Shielding gas is important in FCAW-G process for increased penetration and filler metal deposition [9]. FCAW can be applied automatically or semi-automatic. Most FCAW process is semi-automatic, which is the wire feeder continuously feeds the electrode wire and the welder must manually positions the torch into the weld. However, it can transform to fully automatically with a computer driven robot manipulating the torch along a preset path. FCAW is widely used for welding large sections and with materials of great thicknesses and lengths, especially in the flat position.

FCAW actually comprises two welding processes. The two variations for applying FCAW are self-shielded flux cored arc welding (FCAW-S) and gas-shielded flux cored arc welding (FCAW-G). The difference in the two is due to different fluxing agents in the consumables, which provide different benefits to the user. FCAW-S is a variation of FCAW in which the shielding gas is provided solely by the flux material within the electrode. The heat of the welding arc causes the flux to melt, creating a gaseous shield around the arc and weld pool. FCAW-S is also called Innershield and it is a flux cored arc welding process developed by Lincoln Electric Manufacturing Company [9]. On the other hand, shielding in FCAW-G is obtained from both the CO2 gas flowing from the gas nozzle and from the flux core of the electrode. FCAW-G is widely performed in flat and horizontal position. However, FCAW-G also can be performed for vertical and overhead position by using small diameter electrodes.

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Figure 2.1: Self-Shielded Flux Cored Arc Welding (FCAW-S). [11]

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Figure 2.2: Gas-Shielded Flux Cored Arc Welding (FCAW-G). [11]

FCAW requires more electrode extension than GMAW. It is because electrode extension will affect the vapour-forming ingredients to generate enough arc vapour for adequate shielding [11]. Inadequate arc vapour will cause porosity in the weld. Besides that, the deposition rates and current density in FCAW are also higher than GMAW. The increased current density occurs due flux cored electrodes are tubular rather than solid, and the flux core has less density and current-carrying capacity than metal [11]. FCAW has a wide range of applications in industry. FCAW combines the production efficiency of GMAW and the penetration and deposition rates of SMAW. FCAW also has the ability to weld metals as thin as that used in vehicle bodies and as thick as heavy structural members of high rise buildings. The most common application of FCAW is in structural fabrication. High deposition rates achieved in single pass make FCAW more popular in the railroad, shipbuilding and automotive industries.

Advantages of FCAW

FCAW has many advantages over the manual shielded metal arc welding. It is more flexible and acceptable in varies industry compared to other welding operation such as gas metal arc welding, submerged arc welding and oxyacetylene welding. These advantages of FCAW [9, 10] are as follows:

High quality weld metal deposit

Produces smooth and uniform beads with an excellent weld appearance

Produce less distortion than SMAW

Welds a variety of steels over a wide thickness range

High operating factor

High deposition rate with high current density

Economical engineering joint design

Limitations of FCAW

The limitations of FCAW regarding its applicability [12] are as follows:

Confined to ferrous metals which is primary steels

Removal of post weld slag requires another production step

Electrode wire is more expensive on a weight basis than solid electrode wires

Equipment is more expensive and complex than required for SMAW

Ventilation system need to be increased to handle added volume of smoke and fume

Robotic Welding Technology

Over the past decades, the importance of robot in a wide range of industrial and nonindustrial applications such as measurements, robotic manipulator and handling of hazardous materials becomes more advanced. These applications have to perform in high precision speed and accurate execution in order to achieve outstanding result. Nowadays, most of welding processes could be done in automated applications. With these automated applications, the welding process then called as robotic welding. Robot welding is the use of mechanized programmable tools, which completely automate a welding process by both performing the weld and handling the part. Figure 2.3 shows the comparison between robotic production setups that exhibit the best “cost per unit” performance if compared with manual work and hard automated setups [15].

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Figure 2.3: Industrial robotic zone. [15]

Robots can be defined as a programmable, self controlled device that perform task to move material, parts, tools or specialized devices through various programmed motions. The term ‘robot’ has the origination in the Czech dictionary word ‘robota’, meaning forced work or compulsory service [13]. The term of ‘robot’ has been created in Karel Capek’s play Rossum’s Universal Robots (R.U.R) in 1921 and also the term ‘robotics’ was first used within the short stories written by Isaac Asimov in the 1940s [14].

Robotic welding is one of the most successful applications of industrial robot manipulators. There are lot of products require welding operations in their assembly especially in automation industry. Robotic welding application in production can lead to cheaper products since productivity and quality can be increased, and costs and manpower can be decreased. However, the limitations of automatic welding is it ability to equilibrate for variations in welding joints in any but simplest welding design [8]. When a robot is added to a welding setup, the problems increase in number and in complexity. Robots are still difficult to use because it complexity and have limited remote facilities, program environments and software interfaces [15]. Nevertheless, there are a lot of advantages in robotic welding applications [8] include the following:

Increased productivity through higher operator factor and higher welding speeds

Good uniform quality that is predictable and consistent

Strict cost control through predictable weld time

Minimized operator skill and reduced training requirements

Better weld appearance, consistency of product and heavier-duty welding procedures can be done

FCAW robotic welding is widely used in industrial applications due to its numerous advantages. It can weld a variety of metals in a large range of thickness and effective in all position. It also can weld the material without having to stop frequently to change electrodes compared to other welding processes. In addition, high skill operator is not required because electrode wire is fed automatically and it can perpetuate the arc length approximately constant. However, this process is sensitive to the wind effects which can disperse the shielding gas [15]. In automatic welding, the welding device is programmed to provide the exact tough motion patterns and preset welding parameters. Inherent tolerance of welding process to accommodate minor variations will result good quality welds. An automatic or automated welding system consists of at least the following [8]:

Welding arc

It requires a welding power source and its control, an electrode wire feeder and its control, welding gun assembly and interfacing hardware.

Master controller

It acts as overall controller which controls all system functions. It can be robot controller or a separate controller.

Arc motion device

It can be the robot manipulator, a dedicated welding machine or a standardized welding machine which involve several axes.

Work motion device

It can be a standardized device such as tilt table positioner, a rotating turntable or dedicated fixture.

Work holding fixture

It must be customized or dedicated to accommodate the specific weldment to be produced which mounted on the work motion device.

Welding program

It requires the development of the welding procedure and the software to operate the master controller to produce weldment.

Welding Position

Welding must be done in the position in which the part will be used. In this project, the scope is to study and investigate the correlation between welding parameter and bead geometry in 2F position. 2F position indicates welding operation for fillet weld in horizontal position. According to the American Welding Society (AWS), horizontal fillet welding is the position in which welding is performed on the upper side of an approximately horizontal surface and against and approximately vertical surface [8].

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Figure 2.4: Schematic diagram of horizontal welding 2F position. [8]

The official AWS diagrams for welding positions are precise. They utilize the angle of the axis of the weld which is a line through the length of the weld perpendicular to the cross section at its center of gravity. Figure 2.4 shows the fillet weld and its limits of the various positions. It is necessary to consider the inclination of the axis of the weld as well as the rotation of the face of the fillet weld [8].

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Figure 2.5: Welding position for fillet welds. [20]

Table 2.1: Tabulation of position of fillet welds. [20]

TABULATION OF POSITIONS

OF FILLET WELDS

POSITION

DIAGRAM REFERENCE

INCLINATION OF AXIS

ROTATION OF FACE

FLAT

0O TO 15O

150O TO 210O

HORIZONTAL

0O TO 15O

125O TO 150O

210O TO 235O

OVERHEAD

0O TO 80O

0O TO 125O

235O TO 360O

VERTICAL

15O TO 80O

125O TO 235O

80O TO 90O

0O TO 360O

Welding parameter

Weld quality and weld deposition rate are influenced very much by the various welding parameters and joint geometry. Essentially a welded joint can be produced by various combinations of welding parameters as well as joint geometry. These parameters are the process variables which control the weld deposition rate and weld quality. Welding variables can be divided into three classifications which are primary adjustable variables, secondary adjustable variables and distinct level variables [8]. The primary adjustable variables are those most usually used to change the characteristics of the weld namely arc voltage, welding current and travel speed. These primary variables control formation of the weld by influencing the depth of penetration, bead width and bead height. They also affect deposition rate, arc stability and spatter level.

The secondary adjustable variables are consist of tip-to-work distance (stickout) and electrode or nozzle angle. Secondary adjustable variables do not directly affect bead formation and they are more difficult to measure and accurately control. The third class of variables also known as distinct level variables are include electrode size, electrode type, welding current type and its polarity, shielding gas composition and flux type. These variables are selected depends on the type and thickness of the material, joint design, welding position, deposition rate and appearance. In this research, the effects of various welding parameters by robotic FCAW were investigated. The welding current, arc voltage and welding speed were chosen as variable parameters.

Welding current

In welding process, welding current is the most influential variable in welding process because it many factors such as the electrode melting rate, deposition rate, the depth of fusion and geometry of the weldments. Among all welding parameters, welding current intensity has the greatest effect on melting capacity, weld seal’s size and geometry and depth of penetration [2]. It must be well determined especially for thin parts because excessive amount of welding current will cause high penetration depths. Otherwise, very low welding current causes insufficient penetration on base metal.

Karadeniz et. al [2] were investigated the effect of welding parameters on penetration in Erdemir 6842 steel having 2.5mm thickness welded by robotic gas metal arc welding. The result showed that the change in depth of penetration was increase with increasing welding currents. Shahfuan et. al [16] also proved in their research that the increasing welding current increases the penetrative power of the arc but reduce the leg size, face width and width of arc due to magnetic pinch. They also demonstrated that the throat size increases toward a maximum with welding current.

Welding voltage

The other most important parameter in welding process is welding voltage. Welding voltage can be defined as electrical potential difference between the surface of the molten weld pool and the tip of welding wire [17]. The primary function of voltage is to control the shape of the bead cross section and its outward appearance. Increasing the arc voltage will produce wider and less deeply penetrating welds than low welding voltages. The relationship between arc voltage and welding penetration is not a straight-line relationship [8]. The smoothest welding arc only can be obtained by certain voltage with constant welding current. Thus, the arc voltage is not suggested as a control for penetration.

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Figure 2.6: Effect of arc voltage variations on weld bead shape. [10]

The arc voltage depends on arc length and type of electrode. However, arc voltage is much easier to be controlled than arc length in order to obtain a quality welding. An increase in arc voltage tends to cause welding defects such as porosity, spatter and increase weld width [10]. In previous research, Shahfuan et.al [16] was investigated the correlation between welding arc voltage and fillet bead geometry. In this research, the values of arc voltage vary from 23V to 31V, while the current and welding speed are fixed at 250A and 7mm/s. The result shows that the leg size and face width increase with welding arc voltage after minimum at 24V. Besides that, increasing arc voltage increases the arc length but decreasing penetration power. They also concluded that the arc voltage only have small effect on welding bead geometry.

Welding speed

Welding speed is also particularly important variable because it control the actual time that directly effect on the production cost and also weld deposition rate and quality of weld. Welding speed also known as travel speed and can be defined as linear rate at which the arc moves along the weld joint. The relationship between travel speed and weld penetration is relatively straight line relationship [8]. Increasing travel speed will reduce the weld penetration. Welding speed is not recommended to be used as a major welding control if economical reason is emphasized because it is desired to weld at a maximum speed possible. Besides that, increasing the travel speed while maintaining constant arc voltage and welding current will reduce the bead width [17].

Figure 2.7: Effect of travel speed variation on weld bead size and the penetration. [9]

Travel speed is one of the most important parameters affecting weld quality such as penetration and bead size. High welding speeds will decrease weld penetration but increase tendencies for undercut, porosity and arc blow. Previous researches have shown that the weld penetration was increased by increasing the value of welding speed [1, 2, 3]. Besides that, the changes of welding speed will affect the weld bead geometry such as leg size, weld width and throat size. By increasing welding speed while maintaining constant value of welding current and arc voltage, the leg size, weld width and throat size will decrease on fillet weld [16].

Welding consumables and electrode requirements

The flux cored electrode wires also can be known as inside-outside electrodes because of the fluxing and alloying compounds are on the inside rather than on the on the outside as with a covered electrode [8]. The FCAW electrodes are consist of a metal outer sheath filled with a combination of mineral flux and metal powders which perform same function as the coating on covered electrode. Alternative configuration may be produced by lapping or folding the strip or the consumable may be made by filling a tube with flux followed by a drawing operation to reduce the diameter. Typical finishing wire diameter is range from 3.2 to 0.8 mm [18].

Figure 2.8: Alternative configuration for flux cored wires

(a) Outer Sheath, (b) Flux powder. [18]

Flux cored wires offer a lot of advantages in welding process. The deposition rate will be substantially higher than that normally achieved with Manual Metal Arc Welding (MMAW) and solid wire GMAW. This increase in deposition rate is attributable to the increased current density that carried by the sheath but it also depend on the thickness, polarity and electrode stickout [18]. Besides that, the solidification quality of the slag may be adjusted or designed to provide additional shielding than control the bead shape. The minimum slag generated by flux cored wires will make it possible to use narrower weld joints and fewer required weld passes especially in heavier base metals.

2.6.1 FCAW electrode wire classification

The system for identifying flux cored electrodes is complicated. The most common system is shown in Figure 2.9, which shows the numbering systems for electrodes for carbon steels. However, the electrode numbering system for low-alloy steels, corrosion-resisting steels and for welding cast iron are slightly different. For carbon steel electrode wires, the “E” indicates an electrode which is common for all specifications. The next digit is stands for the minimum tensile strength, as welded, in 10 ksi. The next digit is represents welding position which is “0” indicates flat or horizontal position welding while “1” indicates all position welding. After that, the “T” indicates a tubular or flux cored electrode and last digit following a dash designates the external shielding medium and welding power to be employed. There are four options which is “1” indicates use of CO2 gas as shielding and direct current with electrode positive (DCEP), “2” indicates use of argon plus 2% oxygen for shielding and DCEP, “3” indicates no external gas shielding and DCEP, and “G” indicates that the gas shielding and polarity are not specified.

Tubular or Flux Cored

Shielding medium and power

Welding position

Minimum tensile 10 ksi

Designates an electrode

E X X T- X

Figure 2.9: American Welding Society (AWS) designation for tubular electrode wire for carbon steel. [8]

2.6.2 Type of flux cored consumable

Flux cored wire have been developed by following group:

Plain carbon and alloy steel

Hardfacing and surfacing alloys

Stainless steel.

2.6.2.1 Plain carbon and alloy steel

In this group, there have several type of consumable such as

Rutile gas shielded

Basic gas shielded

Metal cored gas shielded

Self shielded

Rutile Gas Shielded

Rutile gas shielded wire have extremely good running performance, excellent positional welding capabilities, good slag removal and provide mechanical properties equivalent to or better than those obtained with a plain carbon steel solid wire [18]. Rutile which is a form of titanium dioxide became a popular base for stick electrode coatings in 1930s. It allowed the melting point and viscosity of the slag to be controlled. After that, the presence of sodium and potassium titanates in rutile wires was noticed with the new generation of E71T-1 all positional wires. The toughness of this electrode was good because of the residual impurities in the steel strip were getting lower all the time than improved the positional welding capability [19].

Basic Gas Shielded

Basic gas shielded wire give reasonable operating performance, excellent tolerance to operating parameters and very good mechanical properties. Alloyed formula for welding low alloy and high strength low alloy steels are available. The positional performance of these wires, particularly in the larger diameter, is not as good as that of the rutile consumables [18].

Metal Cored Gas Shielded

Metal cored wires contain very little mineral flux, the major core constituent is iron powder or a mixture of iron powder and ferrous alloys. These wires give very smooth spray transfer in argon/ CO2 gas mixture, particularly at currents around 300 A although they may also be used in the dip and pulse modes at low mean currents. They generate minimal slag and are suitable for mechanized applications [18].

Self Shielded

Self shielded wires are available for general purpose downhand welding and positional welding and a limited range of wires are available for applications which required higher toughness. As in the rutile wires, the higher toughness requirements are usually met by alloying with nickel [18].

2.6.2.2 Hardfacing and surfacing alloys

A wide range of hardfacing and surfacing alloys are produced in the form of flux-cored wire. These include plain carbon steel, austenitec stainless steels, alloying containing high chromium and tungsten carbide and nickel and cobalt based consumables. Many of these wires are self-shielded and intended primarily for site use [18].

2.6.2.3 Stainless steel

Stainless steels flux core wire have also been introduced and matching consumables are available for most the common corrosion resistant materials. Both gas shielded metal cored and rutile based formulation are available with the latter giving exceptionally good operating characteristics, wide process tolerance, low spatter and excellent surface finish [18].

Weld quality

The quality of welded joints is very important aspect especially in critical applications such as building construction, boilers and nuclear power plants where the failure will result into a catastrophe. Thus, the inspection methods should be carried out according to acceptance standards. Acceptance standards stand for the minimum weld quality and are based upon test of welded specimens containing some discontinuities [10]. There are many types of weld defects which have been classified namely undercuts, cracks, porosity, inclusions and overlap.

Visual inspection of fillet weld

The visual acceptable qualification for fillet weld shall meet the following requirements [20]:

Any crack shall be unacceptable, regardless of size.

All craters shall be filled to the full cross section of the weld.

The fillet weld leg sizes shall not be less than the required leg sizes.

Base metal undercut shall not exceed 1/32 inch (1 mm).

The weld profile shall meet the requirements of Figure 2.10.

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Figure 2.10: Acceptable and unacceptable fillet weld profiles. [20]

Macroetch examination

Macroetching examination differs from etching used for microstructural examination and requires the use of macroethants. Macroetchants are deep etchants to develop gross features such as weld solidification structures [9]. The main applications of macroetching are to study the weld structure, to measure joint penetration, to detect lack of fusion, to determine slag, flux, porosity or cracks are present in the weld. Specimens intended for use in macrocthing examination must undergo several processes which is removing a slice by flame cutting or sawing in the plane to be examined before grinding and polishing process. Macroetching is usually performed by gently daubing the sample with the macroetchant or by immersing smaller specimens in the macroetchant and gently swirling [9]. The surface must be preserved as quickly as possible after drying, once it has been determined that the amount of macroetching is sufficient.

For acceptable qualification, the weld specimens shall be provided with a finish suitable for macroetch examination and the test specimen when inspected visually shall conform to following requirements [20]:

Fillet welds shall have fusion to the root of the joint but not necessarily beyond.

Minimum leg size shall meet the specified fillet weld size.

Fillet welds and the corner macroetch test joint shall have:

No cracks.

Thorough fusion between adjacent layers of weld metals and between weld metal and base metal.

Weld profiles conforming to intended detail but with none of the variations prohibited.

No undercut exceeding 1/32 inch (1 mm).

For porosity 1/32 inch (1 mm) or larger, accumulated porosity not exceeding Â¼ inch (4 mm).

No accumulated slag, the sum of the greatest dimensions of which shall not exceed Â¼ inch (4 mm).

CHAPTER III

RESEARCH METHODOLOGY

Introduction

In this Chapter 3, it will cover the detail explanation about the process or methodology to complete this project. In order to ensure the project flow efficiently, project methodology had been drafted to assist and organizing the process of this project. There are several steps to achieve the objective for this project that will accomplish the perfect result.

Methodology

The main objective of this project is to study the correlation between FCAW welding parameter and weld bead geometry in order to develop a calculator that can predict the welding variables and their bead geometry. The project analysis is done through experimental study on fillet joint by using robotic welding. The flowchart of process flow in this project is depicted in figure 3.1.

Figure 3.1: Flowchart of the project.

Preparation of coupon, process and consumable

This project is focused on study the correlation between FCAW welding parameter and weld bead geometry in 2F position. The experimental study is includes welding process, visual inspection, analysis of bead geometry and development of predicting calculator. All welding process has done by employing the robotic welder to weld fillet joint by varying one parameter at a time. The sample was prepared before welding process is carried out and it involved several processes.

Figure 3.2: Method of welding process for this project.

Preparation of material and welding consumable

Preparation of sample before welding is consist of selection, inspection and preparation of welding process, material, joint design and consumable. In this case of study, the material used is low carbon steel with thickness of 9 mm and 25.4 mm in width. The low carbon steel is cut by using oxy acetylene cutter to 300 mm length with intent to be welded in six variation of welding parameter. After that, 2 pieces of low carbon steel is join to make T-joint by tack welding by GMAW between the plates.

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Figure 3.3: Dimension and arrangement of welding process applied for each specimen.

FCAW operations were performed by the OTC Almega AII-B4 series articulated robot welding. The welding consumables use for welding process is E71T-1 with 1.2 mm in diameter and 100% of CO2 was used as a shielding gas protected. Besides that, nozzle to work distance is 15 mm, the torch angle is 45o and only one pass on the weld plate.

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Figure 3.4: The OTC Almega AII-B4 articulated robot welding.

Welding parameter

The welding process was varying parameter with changes in welding voltage, welding current and welding speed. All of the parameters are shown in Table 3.1.

Table 3.1: Welding parameter for specimen Number 1 until 12.

No. of specimen

Current (C)

Voltage (V)

Speed (mm/sec)

100

Table 3.2: Welding parameter for specimen Number 13 until 48.

No. of specimen

Current (C)

Voltage (V)

Speed (mm/sec)

100

150

Table 3.3: Welding parameter for specimen Number 49 until 84.

No. of specimen

Current (C)

Voltage (V)

Speed (mm/sec)

200

250

Table 3.4: Welding parameter for specimen Number 85 until 120.

No. of specimen

Current (C)

Voltage (V)

Speed (mm/sec)

250

300

100

300

101

300

102

300

103

300

104

300

105

300

106

300

107

300

108

300

109

300

110

300

111

300

112

300

113

300

114

300

115

300

116

300

117

300

118

300

119

300

120

300

Safety practices in welding

Safety and health is extremely important in welding applications. Every year, thousands of welders suffer injuries because of accidents that occur when proper safety precautions are not taken seriously. Hazards can be avoided when necessary precautionary measures are followed. Safe workshop practice was applied throughout the project. The major hazards that relate to welding are fumes and gases, arc rays and spatter, noise, electrical shock and robotic arm movement.

Table 3.5: The major hazards and precautionary measures in welding process.

Type

Hazard

Precaution

Fumes and gases

Fumes and gases are produces from flames and combustion of the material contained in core of FCAW electrode wire. Chemical composition from fumes and gases are harmful and vey hazardous for health.

Do not breathe and keep head out the fumes. Use enough ventilation, exhaust system, or both to remove fumes from breathing zone and general area. Wear correct eye, ear and body protection.

Electrical shock

The shock hazard is related with electrical equipment includes power supply, extension lights, electrical hand tool and electrically powered machinery. Electrical shock can cause serious injuries or fatality.

Make sure all electrical connections are in good condition, tight, clean and dry. Do not overload cables and touch live electrical parts.

Arc rays and spatter

All welding processes will produce arc rays and spatter. Electric arc is very powerful source of light, ultraviolet and infrared. Electric arc and hot welding spatter can cause painful skin bums and permanent eye damage.

Cover all skin surfaces and wear safety equipment such as safety boot, insulated gloves and protective welding helmets. Protects people around from exposure to arc radiation by shielding the welding area with metal or heat resistant shields.

Noise

Flames, arcs and engine driven generator produce noise. Continued exposure to excessive noise will affect hearing capability.

Wear ear protection devices such as ear plugs or ear muffs.

Robotic arm

Movement of robotic arm during welding process will injure people around.

Creating distance while observing the welding process.

Inspection, testing and evaluation by code

After welding has finished, inspection and testing was applied on each samples to evaluate the welding quality. All samples are signified with specimen number according to the welding parameter and welding condition. Visual inspection was carried out on each samples to determine the weld bead can be acceptable or rejected. However, slag must be removed from the weld bead and the sample must be cleaned by using wire brush before the inspection.

After that, all acceptable samples were classified into four grades which is A, B, and C based on weld bead quality. Before proceed to the next weld bead analysis, every samples need to be sprayed coating with lacquer to avoid the corrosion before took the picture with ruler. The result and information from visual inspection is recorded to avoid confusion on further weld bead analysis.D:d0cuMenTs..!FYP IIpicsspecimen picsspecmn pics dslr104.JPG

Figure 3.5: Sample picture with ruler for specimen Number 104.

Bead geometry analysis

Preparation, measurement and analysis of bead geometry is consist of several processes and steps which are weld bead measurement, cutting, grinding, polishing, etching and weld bead analysis through stereo zoom microscope. The first step on bead geometry analysis is measurement of weld bead which is bead width and leg size. The measurement of bead geometry was carried out by using vernier calliper.

Figure 3.6: Flow chart of bead geometry analysis.

Cutting process

In order to perform macroetching examination, every specimen must be cut into acceptable small piece to obtain a representative metallographic specimen from the joint. Specimen orientation was first be determined and cut at respective number at 25 mm length by using abrasive cutter machine to make the surface of cutting become smoother and easier to be grinded.

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Figure 3.7: Abrasive cutter machine.

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Figure 3.8: Diagram of specimen cutting area.

Grinding process

The next step is grinding process. Every sample was grinded using Metaserve 200 grinding machine with five types of grit abrasive grinding paper. The sequential start with paper grit 240, 320, 400, 600 and finally 1200 for fine grinding. Grinding process is done to remove coarse material and features that gets from the cutting process. Besides that, the process was carried out in order to get the surface flatness and smoothness. Fine grinding is performed to prepare the specimen for polishing process.

Figure 3.9: Abrasive grinding paper used for grinding process.

Polishing process

Then, all samples are forwarded to the next step which is polishing process. Every samples was polished up using Metuser 200 grinder/polisher on the side section had been grinded. The polishing process was done by using Alpha Alumina Powder grade 9.5 Âµm, 5 Âµm, 3 Âµm and 1 Âµm. This process is conducted to remove the scratch on the sample surface and to get mirror finish.D:d0cuMenTs..!FYP IIpicspics samsungSAM_9803.JPG

Figure 3.10: Polishing process using Metaserve 2000 grinder/polisher.

Etching process

The final step of sample preparation for weld bead analysis before examination is etching process. The sided surface of sample was etched by dissolving the sided surface in Nital solution for 10 seconds to develop clearer view of weld defect, penetration and heat affected zone.

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Figure 3.11: Dipping specimen into Nital solution.

Weld bead analysis

The analysis of weld bead was carried out using stereo zoom microscope and IMAP Ver. 4.0 Professional Edition computer software. Surface of the specimen are measured to obtain the measurement of weld leg size, weld throat, weld penetration and heat affected zone. The specimen need to be examined as soon as possible after etched in order to avoid the surface features lose or become dark.D:d0cuMenTs..!FYP IIpicspics samsungSAM_9797.JPG

Figure 3.12: Analysis of weld bead using stereo zoom microscope.

Development and validation of predicting calculator

As a result of weld bead geometry analysis, a predicting calculator is developed to represent the correlation between welding parameter and weld bead geometry. Firstly, heat input should be calculated before plotting the graph between heat input and bead geometry and determine the trend line of leg, height, throat and penetration against the heat input. Then, formula is generated from the trend line to develop a predicting calculator of weld bead geometry and welding parameter. In order to ensure that the predicting calculator is accurate and can be used, the deviation from the actual welded sample is calculated. This calculator will make welding process become easier while it can cut more cost and time needed in production.

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